This invention discloses a rubber composition that is comprised of: (1) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of monomer units containing an amino group, and (2) from about 0.1 phr to about 25 phr of a 2:1 layered silicate clay, wherein the 2:1 layered silicate clay is an organophilic 2:1 layered silicate clay.

Tires are increasingly expected to provide higher and higher levels of performance characteristics. For instance, it is normally expected for tires to exhibit good traction characteristics on both dry and wet surfaces as well as low rolling resistance for good vehicle fuel economy. However, it has traditionally been very difficult to improve the traction characteristics of a tire without compromising its rolling resistance and treadwear. Low rolling resistance is important because good fuel economy is virtually always an important consideration. Reducing the weight of tires is also a goal of automobile and truck manufacturers because reduced weight results in improved fuel economy. Reducing the weight of tires is of particular importance in the case of aircraft tires. Good treadwear is also an important consideration because it is generally the most important factor in determining the life of the tire.
The traction, treadwear and rolling resistance of a tire is dependent to a large extent on the dynamic viscoelastic properties of the elastomers utilized in making the tire tread. In order to reduce the rolling resistance of a tire, rubbers having a high rebound have traditionally been utilized in making the tire""s tread. On the other hand, in order to increase the wet skid resistance of a tire, rubbers that undergo a large energy loss have generally been utilized in the tire tread. In order to balance these two viscoelastically inconsistent properties, mixtures of various types of synthetic and natural rubber are normally utilized in tire treads. For instance, various mixtures of styrene-butadiene rubber and polybutadiene rubber are commonly used as a rubber material for automobile tire treads. However, such blends are not totally satisfactory for all purposes.
Rubbers having intermediate glass transition temperatures (xe2x88x9270xc2x0 C. to xe2x88x9240xc2x0 C.) compromise rolling resistance and treadwear without significantly increasing traction characteristics. For this reason, blends of rubbers having low glass transition temperatures and rubbers having high glass transition temperatures are frequently utilized to attain improved traction characteristics without significantly compromising rolling resistance or treadwear. However, such blends of rubbers having low glass transition temperatures and rubbers having high glass transition temperatures exhibit poor processability. This major disadvantage associated with such blends has greatly hampered their utilization in making tire tread compounds.
U.S. Pat. No. 2,885,381 discloses a composition of matter comprising a copolymer of a conjugated diene and a heterocyclic nitrogen containing monomer having a sole CH2xe2x95x90CHxe2x80x94 substituent, such as 2-vinylpyridine, said copolymer having been compounded with 25-100 weight parts per 100 parts of said copolymer of a finely ground mineral pigment selected from the group consisting of silica and aluminum silicate as the sole reinforcing agent.
In recent years, there has been a trend to include silica as a filler in tire tread compounds to further improve traction characteristics. U.S. Pat. No. 5,036,133 discloses a vulcanizable rubber composition that is comprised of: (A) an uncured natural or synthetic isoprene rubber, or one or more uncured butadiene-based synthetic rubbers, or uncured blends thereof, said uncured rubbers being sulfur vulcanizable, (B) a silica filler, (C) sulfur, (D) an organic accelerator and (E) a vinylpyridine-butadiene interpolymer co-activator, said interpolymer co-activator (E) containing from about 20 percent to about 65 percent by weight of vinylpyridine units, the amount of said vinylpyridine-butadiene copolymer co-activator being from about 0.5 to 2 parts by weight per 100 parts by weight of said rubber.
Authors Wang et. al in the Journal of Applied Polymer Science, Vol. 78, 1879-1883 (2000) describe a process of making clay-rubber mixtures by mixing an SBR latex or a styrene-vinylpyridine-butadiene latex with the hydrophilic unmodified clay without quaternary ammonium salts. In the case of the styrene-vinylpyridene-butadiene latex and clay composite, the expansion of clay gallery in the case of styrene-vinylpyridine composite was reported to increase from 1.24 to 1.46 nm, which is not significant enough. The intercalation of the rubber was minimal and very limited exfoliation is evident from stacks of clay layers as shown in the TEM micrographs for the said composite. The limited extent of intercalation is not expected to provide substantial property enhancement in tire materials. The article does not suggest of achieving a light-weight rubber composition and a tire with improved rolling resistance. The intercalation achieved by using the organically modified modified clay with quaternary ammonium surfactant by mixing it in a solution of rubber is also described, that resulted in somewhat better intercalation or expansion of clay galleries. Nevertheless, the mixing time of 12 hours was used, which is rather long for an industrial process. The publication does not disclose a bulk thermomechanical mixing method of making rubber-clay nanocomposite with uniform dispersion and high degree of exfoliation that will result in a light weight composition and lower hysteresis.
European Patent Application EP1029823 A2 describes preparation of rubber composite materials. This European Patent Application discloses a composite clay rubber material comprising at least one material selected from the group consisting of a first composite clay material and a second composite clay material, and a rubber material; said first composite material comprising a clay mineral having interlayer section, an onium ion having 6 or more carbon atoms, bonding to said clay mineral via an ionic bond for expanding said interlayer section and rendering said interlayer section compatible with an organic molecule; a first guest molecule having a polar group therein being at least partially incorporated into said expanded interlayer section and bonded to said clay mineral through a hydrogen bonding between said clay mineral and said polar group; and a second guest molecule as said organic molecule without a polar group as said organic molecule being at least partially incorporated into said expanded interlayer section, said first guest molecule having a molecular length equal to or smaller than that of said onium ion, said second guest molecule having a molecular length equal to or larger than that of the said onium ion; said second composite clay material comprising a clay mineral having an interlayer section; an onium ion having 6 or more carbon atoms, bonding to said clay mineral via ionic bond for expanding said interlayer section and rendering said interlayer section compatible with an organic molecule; and a main guest molecule as said organic molecule having a polar group in a main chain and/or side chain thereof being at least partially incorporated into said expanded interlayer section and bonded to said clay mineral through a hydrogen bonding between said clay mineral and said polar group, said main guest molecule having a molecular length equal to or larger than that of the said organic onium ion-wherein said organic onium ion contained in at least one of said first composite clay material and said second composite clay material is crosslinked with at least one of said second guest molecule and said main guest molecule and a molecule of said rubber material.
European Patent 1029823A2 further describes that crosslinking be provided by using the onium ions with unsaturated groups for crosslinking with the guest molecule and rubber materials.
European Patent 1029823A2 also discloses the rubber materials as being selected from the group consisting of natural rubber, isoprene rubber, chloroprene rubber, styrene rubber, nitrile rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, butadiene rubber, styrene-butadiene rubber, butyl rubber, epichlorohydrin rubber, acrylic rubber, urethane rubber, fluoro rubber and silicone rubber. This European Patent also specifies the polar group of said first guest molecule and/or said main guest molecule is at least one selected from the group consisting of hydroxyl group, halogen group, carboxyl group, anhydrous carboxylic acid group, Thiokol group, epoxy group and amino group. The polar functional groups are present on the first or main guest molecules. However, this patent application does not require or suggest that the polar functional groups can be present on the xe2x80x9crubber material.xe2x80x9d
European Patent 1029823 A2 suggests the method of producing a composite clay rubber material. It calls for the onium ion containing unsaturated groups and be crosslinked with the unsaturated groups of the guest molecules and also the rubber material. One embodiment of European Patent 1029823 A2 calls for first incorporation of the clay with onium ion by contacting it with the first and second guest molecules. The process for incorporation or pre-dispersion of the clay in the guest molecules for preparing a clay-masterbatch required rather long mixing times for expanding or separating the clay layers and is considered herein somewhat industrially uneconomical. The masterbatch of the clay in the guest molecules was further kneaded with the rubber material to make the rubber-clay composite.
European Patent 1029823 A2 suggests the process for making a clay rubber material by blending with the rubber material. The first and second guest molecules were dissolved in a solvent when contacting the said rendered clay mineral. This additional step required long time for clay incorporation and furthermore, in such a process, all solvent was to be evaporated, which additionally requires considerable energy and extra care for handling solvents.
European Patent 1029823 A2 specifies the preferable main guest molecules as lauryl alcohol, stearyl aryl alcohol, oleyl alcohol, stearic acid, linolic acid, linolenic acid, sterayl chloride, or polyethylene, polypropylene or polyisoprene or polybutadiene with a polar group such as hydroxyl, carboxyl, epoxy or the like. This patent application mentions preparing a blend material of the composite clay material prepared with the guest molecule and synthetic resins such as polyethylene, polypropylene, polystyrene, polyisobutene, acrylic resin, polyurethane, and styrene-butadiene block copolymer. These resins have very limited use as rubber materials for use in tires and belts as many of these are not rubber-like materials. Resins like the styrene-butadiene block copolymers are not random copolymer rubbers that are generally used for specific performance achievement in tires and belts.
European Patent 1029823 A2 also specifies making the clay composite materials with two types of guest molecules, the first and the second. The first guest molecule had molecular length equal to or smaller than the onium ion and contained the polar group. The second guest molecule contained no polar group and had molecular weight exceed that of the onium ion. This process again required the use of two types of guest molecules for preparing the masterbatch. This patent application mentions the use of the second guest molecule with no polar groups as liquid polybutadiene, liquid polyisoprene, liquid butyl rubber or the like. Such liquid rubbers are known to plasticize the rubber materials and are known to generally improve processing of tire materials but at the same time, also increase the hysteresis or heat build-up or rolling resistance in a tire and are generally not used where low hysteresis and low rolling resistance are desired. This patent application also specifies making blend materials of the clay composite materials prepared with two types of guest molecules by blending with resins such as polyethylene, polypropylene, polybutylene, polyisoprene, polystyrene, acrylic resin, polyamide, polyester, or the like.
European Patent 1029823 A2 describes a composite clay rubber material obtained by kneading the composite clay materials prepared by blending the clay masterbatches of the guest molecules with the rubber like materials and crosslinking the guest molecule with rubber molecule. This European patent application also mentions that conventionally the rubber molecule cannot be uniformly dispersed in the clay mineral. European Patent 1029823 A2 has supposedly solved the problem of achieving a uniform dispersion of clay in a rubber material by masterbatching the clay mineral in the guest molecules and subsequently dispersing the masterbatch in a rubber material and crosslinking the guest molecules and rubber materials. Therefore, there is a need for obtaining the uniform dispersion of clay mineral in the rubber material without the need of pre-dispersion or masterbatching of the clay mineral in the guest molecules, firstly to eliminate the time consuming process of masterbatching, and secondly to eliminate the first and second guest molecules from the rubber materials, as they may deteriorate the properties due to plasticization or other undesirable effects in vulcanized articles of tire or belt rubber materials.
European Patent 1029823 A2 does not teach that a light weight tire composition can be obtained. The said application does not teach that a low rolling resistance tire material can be developed. Furthermore, there is a need for a light-weight and low rolling resistance rubber material that can be prepared without the need for masterbatching of the clay in the guest molecules, for better production economies and better performance.
This invention relates to a rubber composition that can be used to reduce the weight of rubber articles, such as tires and power transmission belts, without compromising performance characteristics. For instance, the rubber composition of this invention can be utilized in manufacturing tires having reduced weight without compromising the rolling resistance or traction characteristics of the tire. This invention also relates to improving the strength, modulus and elongation of carbon black and silica filled compounds by addition of 2:1 layered silicate clays thereto without modifying the level of carbon black or silica. Such compounds have increased flexibility for tire side-wall applications with enhanced tensile strength. The rubber compositions of this invention are a blend of (1) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of a monomer containing an amino group, (2) from about 0.1 phr to about 25 phr of a 2:1 layered silicate clay, preferably an organophilic 2:1 layered silicate clay, and optionally (3) a silica coupling agent. The rubber compositions of this invention will also typically contain from about 5 phr to about 100 phr of carbon black and optionally silica.
This invention more specifically discloses a rubber composition that is comprised of: (1) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of a monomer containing an amino group, and (2) from about 0.1 phr to about 25 phr of a 2:1 layered silicate clay.
The present invention further discloses a tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads; wherein said tread is adapted to be ground-contacting; wherein the tread is comprised of: (1) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of a monomer containing an amino group, (2) from about 0.1 phr to about 25 phr of a 2:1 layered silicate clay, and optionally (3) a silica coupling agent.
In this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d are used interchangeably. With the term rubber, it is generally referred to as a flexible polymer with a low glass transition temperature Tg preferably less than about 0xc2x0 C., more preferably below xe2x88x9220xc2x0 C., and most preferably below xe2x88x9225xc2x0 C., as measured in a differential scanning calorimeter at 10xc2x0 C./minute heating rate.
In this invention, the terms crosslinking, curing and vulcanization are also used interchangeably.
The light weight rubber compositions of this invention comprised of: (1) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of a monomer containing an amino group, (2) from about 0.1 phr to about 20 phr a 2:1 layered silicate clay, and (3) optionally, a silica coupling agent. The 2:1 layered silicate clay will preferably be an organophilic 2:1 layered silicate clay.
This invention more specifically claims a process for making a vulcanized rubber article comprising the steps of (1) kneading (a) an amino group containing rubbery polymer, wherein said amino group containing rubbery polymer contains from about 0.1 weight percent to about 20 weight percent of a monomer containing an amino group, and (b) from 0.1 to about 25 phr of a 2:1 layered silicate clay which is an organophilic 2:1 layered silicate clay; and (c) conventional rubber compounding ingredients selected at least from the group of curing agents, cure accelerators, cure activators, processing aids, reinforcing fillers, oils, cure retarders, resins, and antidegradants at a temperature within the range of about 70xc2x0 C. to about 190xc2x0 C. in a bulk thermomechanical mixer to produce a mixed compound; (2) discharging the said mixed compound from the bulk thermomechanical mixer; (3) forming the mixed compound into an article; and (4) vulcanizing the article.
The amino group containing monomer will typically also contain a vinyl group (CH2xe2x95x90CH2xe2x80x94). Some representative examples of the amino group-containing vinyl monomers include polymerizable monomers having at least one amino group selected from the group consisting of primary, secondary and tertiary amino groups in their molecules. Of these, tertiary amino group-containing vinyl monomers are particularly preferred. These amino group-containing vinyl monomers may be used either singly or in any combination thereof. It is highly preferred that the amino group containing monomers are incorporated as a block or multiple blocks in the said rubber The rubbery polymer is preferably comprised of at least one olefinic unsaturated monomers selected at least from the group of isoprene or butadiene, and optionally, another monomer selected from styrene or alpha-methyl styrene and at least one block of amine functional group containing monomers anchored to the said rubbery polymer.
Examples of the primary amino group-containing vinyl monomers include acrylamide, methacrylamide, p-aminostyrene, aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, aminopropyl (meth)acrylate and aminobutyl (meth)acrylate.
Examples of secondary amino group-containing vinyl monomers include anilinostyrenes; anilinophenylbutadienes; and N-monosubstituted (meth)acrylamides, such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-methylolacrylamide and N-(4-anilinophenyl) methacrylamide.
Examples of tertiary amino group-containing vinyl monomers include N,N-disubstituted aminoalkyl acrylates, N,N-disubstituted aminoalkyl acrylamides, N,N-disubstituted amino-aromatic vinyl compounds and vinyl compounds having a pyridyl group.
Examples of the N,N-disubstituted amino alkyl acrylates include esters of acrylic acid or methacrylic acid, such as N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, N,N-diethylaminobutyl (meth)acrylate, N-methyl-N-ethylaminoethyl (meth)acrylate, N,N-dipropylaminoethyl (meth)acrylate, N,N-dibutylaminoethyl (meth)acrylate, N,N-dibutylaminopropyl (meth)acrylate, N,N-dibutylaminobutyl (meth)acrylate, N,N-dihexylaminoethyl (meth)acrylate, N,N-dioctylaminoethyl (meth)acrylate and acryloylmorpholine. Of these, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dipropylaminoethyl (meth)acrylate, N,N-dioctylaminoethyl (meth)acrylate and N-methyl-N-ethylaminoethyl(meth)acrylate.
Examples of the N,N-disubstituted aminoalkyl acrylamides include acrylamide compounds or methacrylamide compounds such as N,N-dimethylaminomethyl (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, N,N-dimethylaminobutyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, N,N-diethylaminobutyl (meth)acrylamide, N-methyl-N-ethylaminoethyl (meth)acrylamide, N,N-dipropylaminoethyl (meth)acrylamide, N,N-dibutylaminoethyl (meth)acrylamide, N,N-dibutylaminopropyl (meth)acrylamide, N,N-dibutylaminobutyl (meth)acrylamide, N,N-dihexylaminoethyl (meth)acrylamide, N,N-dihexylaminopropyl (meth)acrylamide and N,N-dioctylaminopropyl (meth)acrylamide. Of these, N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide and N,N-dioctylaminopropyl (meth)acrylamide are preferred.
Example of the N,N-disubstituted amino-aromatic vinyl compounds include styrene derivatives such as N,N-dimethylaminoethylstyrene, N,N-diethylaminoethylstyrene, N,N-dipropylaminoethylstyrene and N,N-dioctylaminoethylstyrene.
Examples of the pyridyl group-containing vinyl compounds include 2-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine and 5-ethyl-2-vinylpyridine. Of these pyridyl group-containing vinyl monomers, 2-vinylpyridine which has the structural formula:
and 4-vinyl pyridine which has the structural formula:
are preferred. The most preferred pyridyl group-containing monomer is 2-vinylpyridine. Amino group containing monomers that contain more that one amino group can be used. Some representative examples of such monomers include 2-vinyl pyrimidine which has the structural formula:
and 2-vinyl 1,3,5-triazine which has the structural formula:
Heterocyclic amines having the structural formula:
wherein A represents a xe2x80x94CHxe2x80x94 group or a xe2x80x94CH2xe2x80x94 group and wherein the heterocyclic amine is aromatic or aliphatic and derivatives thereof are in general a preferred class of amino group containing monomers. The amino group containing monomer can be an N-vinyl substituted pyrrole, an N-vinyl substituted 3-pyrroline, an N-vinyl substituted 4-(1-pyrrolidinyl) piperidine, an N-vinyl substituted imidazole, an N-vinyl substituted 1-(2-pyridyl)piperazine, or an N-vinyl substituted 1-(2-pyrimidyl) piperazine. For instance, the amino group containing monomer can be of the structural formula:
The amino group containing monomer can also contain more that one aromatic ring, such as vinyl substituted quinazoline, vinyl substituted quinaldine, or vinyl substituted quinoline. For instance, vinyl substituted quinazoline of the structural formula:
can be utilized as the amino group containing monomer. Vinyl group containing bicyclo amines can also be employed as the amino group containing monomer. For instance, the amino group containing monomer can be a vinyl substituted 1,4-diazocycloheptane or a vinyl substituted 1,5-diazacyclooctane.
For economic reasons N-vinyl 2-pyrrolidone and N-vinyl caprolactam are desirable amino group containing monomers. N-vinyl 2-pyrrolidone has the structural formula:
and N-vinyl caprolactam has the structural formula:
N-vinyl dialkyl amines are another class of amino group containing monomer that can be used. The N-vinyl dialkyl amines that can be used are typically of the structural formula:
wherein R and Rxe2x80x2 represent alkyl groups that can be the same or different. R and Rxe2x80x2 will typically represent alkyl groups that contain from 1 to about 10 carbon atoms. For instance the alkyl groups can be methyl groups, ethyl groups, n-propyl groups, iso-propyl groups, n-butyl groups, iso-butyl groups, or t-butyl groups. N-vinyl diisopropyl amine and N-vinyl diethylamine are representative examples of such amino group containing monomers. The alkyl groups will preferably contain from 1 to 4 carbon atoms.
The amino group containing monomer can also be a conjugated diolefin that is substituted with amino and/or cyano groups. Monomers of this type can be polymerized into the backbone of the amino group containing rubbery polymer. Some representative examples of such monomers include the following:
wherein R and Rxe2x80x2 can be the same or different and represent alkyl groups that contain from 1 to about 10 carbon atoms. It is typically preferred for R and Rxe2x80x2 to represent alkyl groups that contain from 1 to about 4 carbon atoms.
The amino group containing rubber will typically contain from about 0.1 weight percent to about 20 weight percent of the amino group containing monomer. In other words, repeat units in the amino group containing rubber are derived from the amino group containing monomer. Generally, the repeat units derived from the amino group containing monomer differ from the amino group containing monomer in that double bonds are consumed as a result of the polymerization. In any case, it is normally preferred for the amino group containing rubber to contain from about 0.5 weight percent to about 10 weight percent of the amino group containing monomer. It is typically more preferred for the amino group containing rubber to contain from about 1 weight percent to about 4 weight percent of the amino group containing monomer.
In synthesizing the amino group containing rubber one or more conjugated diolefin monomers are copolymerized with the amino group containing monomer. The conjugated diolefin monomers which can be utilized in the synthesis of rubbery polymers generally contain from 4 to 12 carbon atoms. Those containing from 4 to 8 carbon atoms are generally preferred for commercial purposes. For similar reasons, 1,3-butadiene and isoprene are the most commonly utilized conjugated diolefin monomers. Some additional conjugated diolefin monomers that can be utilized include 2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and the like, alone or in admixture.
Other ethylenically unsaturated monomers, in addition to the amino group containing monomer, can also be copolymerized into the rubber. Some representative examples of additional ethylenically unsaturated monomers that can potentially be synthesized into the rubbery polymer include alkyl acrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and the like; vinylidene monomers having one or more terminal CH2xe2x95x90CHxe2x80x94 groups; vinyl aromatics, such as styrene, xcex1-methylstyrene, t-butylstyrene, bromostyrene, chlorostyrene, fluorostyrene, and the like; xcex1-olefins such as ethylene, propylene, 1-butene, and the like; vinyl halides, such as vinylbromide, chloroethane (vinylchloride), vinylfluoride, vinyliodide, 1,2-dibromoethene, 1,1-dichloroethene (vinylidene chloride), 1,2-dichloroethene, and the like; vinyl esters, such as vinyl acetate; xcex1,xcex2-olefinically unsaturated nitriles, such as acrylonitrile and methacrylonitrile; xcex1,xcex2-olefinically unsaturated amides, such as acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamide, and the like.
Rubbery polymers which are copolymers of one or more diene monomers with one or more other ethylenically unsaturated monomers will normally contain from about 50 weight percent to about 99 weight percent conjugated diolefin monomers and from about 1 weight percent to about 50 weight percent of the other ethylenically unsaturated monomers in addition to the conjugated diolefin monomers. For example, copolymers of conjugated diolefin monomers with vinylaromatic monomers, such as styrene-butadiene rubbers which contain from 50 to 95 weight percent conjugated diolefin monomers and from 5 to 50 weight percent vinylaromatic monomers, are useful in many applications. In such cases, the rubber will, of course, also contain from 0.1 weight percent to 10 weight percent of the amino group containing monomer.
Vinyl aromatic monomers are probably the most important group of ethylenically unsaturated monomers which are commonly incorporated into polydiene rubbers. Such vinyl aromatic monomers are, of course, selected so as to be copolymerizable with the conjugated diolefin monomers being utilized. Generally, any vinyl aromatic monomer which is known to polymerize with organolithium initiators can be used. Such vinyl aromatic monomers typically contain from 8 to 20 carbon atoms. Usually, the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. The most widely used vinyl aromatic monomer is styrene. Some examples of vinyl aromatic monomers that can be utilized include styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, xcex1-methylstyrene, 4-phenylstyrene, 3-methylstyrene, t-butylstyrene, and the like.
The amino group containing rubber can be synthesized by emulsion polymerization, solution polymerization, vapor phase polymerization or bulk polymerization. The polymerization process can be conducted as a batch, semi-continuous, or continuous process. However, in solution polymerizations the amino group containing monomer will be added after substantially all of the other monomers have been incorporated into the rubbery polymer.
In many cases, it is preferred for the vinylpyridine containing rubbery polymer to be a vinylpyridine-styrene-butadiene terpolymer rubber. Such vinylpyridine-styrene-butadiene terpolymer rubbers will typically contain from about 0.5 weight percent to about 10 weight percent vinylpyridine, 0.5 weight percent to about 50 weight percent styrene and from about 50 weight percent to about 99 weight percent 1,3-butadiene. It is more preferred for the vinylpyridine-styrene-butadiene terpolymer rubbers to contain from about 1 weight percent to about 5 weight percent vinylpyridine, 5 weight percent to about 33 weight percent styrene and from about 66 weight percent to about 94 weight percent 1,3-butadiene. It is generally most preferred for the vinylpyridine-styrene-butadiene terpolymer rubbers to contain from about 1 weight percent to about 4 weight percent vinylpyridine, 10 weight percent to about 30 weight percent styrene and from about 82 weight percent to about 89 weight percent 1,3-butadiene.
The rubber compositions of this invention also contain from 0.1 phr (parts by weight per 100 parts by weight of rubber) to about 25 phr of an organophilic clay. It is typically preferred for the rubber compositions of this invention to contain from about 1 phr to about 10 phr of an organophilic clay. It is generally more preferred for the rubber compositions of this invention to contain from about 1 phr to about 7 phr of an organophilic clay. It is normally most preferred for the rubber compositions of this invention to contain from about 3 phr to about 6 phr of an organophilic clay.
The clays used in the practice of this invention are 2:1 layered silicate clays of the smectite, vermiculite and mica families. The 2:1 layered silicate clay can be synthetic or from a natural source. However, it should be understood that the 2:1 layered silicate clays used in the practice of this invention do not include clays that do not have any appreciable swelling potential, such as talc. The general clay terminoogy for the 2:1 layered silicates is described in the book Developments in Sedimentology 31, xe2x80x9cElectron Micrographs of Clay Mineralsxe2x80x9d, Elsevier Scientific Publishing Company, 1981, and is incorporated herein as a reference. The 2:1 layered silicate clays that are typically preferred include montmorillonite, bentonite, hectorite, saponite, nontronite, beidellite, fluorohectorite, stevensite, volkonskoite, sauconite laponite, related analogs thereof and their physical blends. Clays that have been chemically modified to make them compatible with organic materials are preferred and are generally referred to as xe2x80x9corganophilicxe2x80x9d clays or xe2x80x9corgano-claysxe2x80x9d. The basic starting material used to make organophilic clay is an exchangeable clay of the smectite group and can include montmorillonite (commonly known and mined as bentonite), hectorite, saponite, attapulgite and sepolite. These clays include exchangeable cationic species such as sodium, potassium or calcium ions on their surface and between clay galleries or layers. In the course of manufacturing an organophilic clay, at least a portion of these exchangeable cationic species are substituted by an organic cation such as a quaternary amine, an organophosphorus ion, any other ion of the type known in the art as an oniumion, or the like. Some representative examples of surfactants that can be used include methyl tallow bis-2 hydroxy ethyl ammonium salt, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium salt, dimethyl benzyl hydrogenated-tallow ammonium salt, dimethyl dihydrogenated tallow ammonium salt, N-tallow alkyltrimethylenediamine, hydrogenated tallow amine, octadecylamine, octadecylamine and gamma-aminopropyltriethoxy silane, polyoxyethylene decycloxypropylamine, n-dodecylpyrrolidone, or their combinations and analogs. Quarternary ammonium surfactants, such as methyl tallow bis-2-hydroxyethyl ammonium chloride, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium methyl sulfate, and dimethyl dehydrogenated-tallow ammonium chloride, are typically preferred. The addition of the organic group modifies the clay, making it compatible with organic compositions and in general allowing it to provide rheological modification in select organic fluids. The clay will typically be modified with up to about 70 parts by weight of the organic surfactant. The clay will more typically be modified with up to about 60 parts by weight of the surfactant and will preferably be modified with up to about 40 parts by weight of the surfactant.
The organophilic 2:1 layered silicate clay may be modified with up to about 70 part by weight of a quaternary ammonium salt surfactant selected from the group consisting of methyl tallow bis-2-hydroxyethyl ammonium halides, methyl tallow bis-2-hydroxyethyl ammonium alkyl sulfates, methyl tallow bis-2-hydroxyethyl ammonium nitrate, methyl tallow bis-2-hydroxyethyl ammonium hydroxide, methyl tallow bis-2-hydroxyethyl ammonium acetate, methyl tallow bis-2-hydroxyethyl ammonium phosphate, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium halides, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium alkyl sulfates, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium nitrate, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium hydroxide, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium acetate, dimethyl hydrogenated-tallow (2-ethylhexyl) ammonium phosphate, dimethyl dehydrogenated-tallow ammonium halides, dimethyl dehydrogenated-tallow ammonium alkyl sulfates, dimethyl dehydrogenated-tallow ammonium nitrate, dimethyl dehydrogenated-tallow ammonium hydroxide, dimethyl dehydrogenated-tallow ammonium acetate, and dimethyl dehydrogenated-tallow ammonium phosphate.
It is not necessary for the quaternary ammonium surfactant to possess unsaturation for providing improved physical properties.
There is a large body of prior art relating to the manufacture of organophilic clays. For example, U.S. Pat. No. 2,531,427 and U.S. Pat. No. 2,531,440 both disclose general processes for the manufacture of organically substituted clays. U.S. Pat. No. 5,110,501 discloses a process for preparing organophilic clay in which the starting materials are reacted in a slurry under high shear. U.S. Pat. No. 5,334,241, discloses a low moisture, direct addition process for the fabrication of organophilic clays. U.S. Pat. No. 4,569,923 discloses yet another process for manufacturing organo-clays in which the clay is subjected to high energy pugmilling before reaction with the cation. The teachings of U.S. Pat. No. 2,531,427, U.S. Pat. No. 2,531,440, U.S. Pat. No. 5,110,501, and U.S. Pat. No. 5,334,241 are incorporated herein by reference in their entirety. In addition to processing parameters, the properties of an organophilic clay will depend upon the nature of the organic cation used for modification, as well as upon the amount of the cation incorporated into the clay. Specific modifiers are utilized for particular mixtures.
It has been found that the amount of organic cationic material that is incorporated into the clay will depend upon the particular technique used for its incorporation. The clays of interest have a generally lamellar structure, and the structure must be opened to some degree in order to permit the cation exchange reaction to take place. At the same time, care must be taken to avoid destroying the lamellar microstructure of the clay. One group of substitution techniques involves processing the clay in a slurry form, in which instance, salvation relaxes the clay""s structure in order to permit penetration of the organic cations. While such techniques are effective, and widely employed, it is desirable to avoid such highly dilute reaction conditions since forming the slurry involves a time and space-consuming step. Furthermore, dewatering of the finished product is energy-intensive. For this reason, low moisture, direct addition techniques as described in U.S. Pat. No. 5,334,241, the disclosure of which is incorporated herein by reference in its entirety, are advantageously employed in the preparation of modified clays.
U.S. Pat. No. 5,616,286 discloses a method for manufacturing an organophilic clay comprising the steps of: (1) providing a substantially non-slurried volume of a clay having an exchangeable cationic species; (2) providing a volume of a cationic organic material; (3) subjecting said non-slurried clay and said cationic material to a first stage reaction process wherein said clay and said cationic material are subjected to a confining pressure of at least 3,000 psi (2.07xc3x97107 Pa) while being mixed so that at least some of the exchangeable cationic species in the clay are substituted by said cationic material so as to provide a non-slurried first stage reaction mixture, which comprises an organically substituted clay which has some residual, exchangeable cationic species therein and some residual cationic material in a free form; and (4) subjecting said non-slurried first stage reaction mixture to a second stage reaction process wherein said mixture is subjected to a confining pressure of at least 8,000 psi (5.52xc3x97107 Pa) while being mixed so that at least some of the residual, exchangeable cationic species in the clay are substituted by said residual, cationic material. The teachings of U.S. Pat. No. 5,616,286 are hereby incorporated herein by reference in their entirety.
The rubber compositions of this invention can optionally further contain about 0.5 phr to about 15 phr of a silica coupling agent. The rubber compositions of this invention will typically contain about 1 phr to about 5 phr of a silica coupling agent. The rubber compositions of this invention will preferably contain 2 phr to 4 phr of a silica coupling agent. The weight ratio of the silica coupling agent to the clay will typically be within the range of 0.1:1 to 1.5:1. The weight ratio of the silica coupling agent to the clay will preferably be within the range of 0.2:1 to 1.1:1. The weight ratio of the silica coupling agent to the clay will more preferably be within the range of 0.4:1 to 0.7:1.
The silica coupling agent is generally a sulfur containing organosilicon compound Examples of suitable sulfur-containing organosilicon compounds are of the formula:
Z-Alk-Sn-Alk-Zxe2x80x83xe2x80x83(I)
in which Z is selected from the group consisting of
where R1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; wherein R2 is alkoxy of 1 to 8 carbon atoms or cycloalkoxy of 5 to 8 carbon atoms; and wherein Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8.
Specific examples of sulfur-containing organosilicon compounds which may be used in accordance with the present invention include: 3,3xe2x80x2-bis(trimethoxysilylpropyl) disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) octasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(triethoxysilylethyl) tetrasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl) trisulfide, 3,3xe2x80x2-bis(tributoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl) hexasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)octasulfide, 3,3xe2x80x2-bis(trioctoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(trihexoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(tri-2xe2x80x2-ethylhexoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triisooctoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(tri-t-butoxysilylpropyl)disulfide, 2,2xe2x80x2-bis(methoxy diethoxy silyl ethyl)tetrasulfide, 2,2xe2x80x2-bis(tripropoxysilylethyl)pentasulfide, 3,3xe2x80x2-bis(tricyclonexoxysilylpropyl) tetrasulfide, 3,3xe2x80x2-bis(tricyclopentoxysilylpropyl)trisulfide, 2,2xe2x80x2-bis(tri-2xe2x80x2-methylcyclohexoxysilylethyl)tetrasulfide, bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl 3xe2x80x2-diethoxybutoxy-silylpropyltetrasulfide, 2,2xe2x80x2-bis(dimethyl methoxysilylethyl) disulfide, 2,2xe2x80x2-bis(dimethyl sec:butoxysilylethyl) trisulfide, 3,3xe2x80x2-bis(methyl butylethoxysilyipropyl)tetrasulfide, 3,3xe2x80x2-bis(di t-butylmethoxysilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(phenyl methyl methoxysilylethyl) trisulfide, 3,3xe2x80x2-bis(diphenyl isopropoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(diphenyl cyclohexoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(dimethyl ethylmercaptosilylpropyl) tetrasulfide, 2,2xe2x80x2-bis(methyl dimethoxysilylethyl)trisulfide, 2,2xe2x80x2-bis(methyl ethoxypropoxysilylethyl)tetrasulfide, 3,3xe2x80x2-bis(diethyl methoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(ethyl di-sec. butoxysilyipropyl)disulfide, 3,3xe2x80x2-bis(propyl diethoxysilyipropyl) disulfide, 3,3xe2x80x2-bis(butyl dimethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(phenyl dimethoxysilylpropyl)tetrasulfide, 3-phenyl ethoxybutoxysilyl 3xe2x80x2-trimethoxysilylpropyl tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilylbutyl) tetrasulfide, 6,6xe2x80x2-bis(triethoxysilylhexyl) tetrasulfide, 12,12xe2x80x2-bis(triisopropoxysilyl dodecyl) disulfide, 18,18xe2x80x2-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18xe2x80x2-bis(tripropoxysilyloctadecenyl) tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilyl-buten-2-yl) tetrasulfide, 4,4xe2x80x2-bis(trimethoxysilylcyclohexylene) tetrasulfide, 5,5xe2x80x2-bis(dimethoxymethylsilylpentyl) trisulfide, 3,3xe2x80x2-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide, 3,3xe2x80x2-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.
The preferred sulfur-containing organosilicon compounds are the 3,3xe2x80x2-bis(trimethoxy or triethoxy silylpropyl)sulfides. The most preferred compound is 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to Formula I, preferably Z is
where R2 is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularly preferred; Alk is a divalent hydrocarbon of 2 to 4 carbon atoms with 3 carbon atoms being particularly preferred; and n is an integer of from 3 to 5 with 4 being particularly preferred.
The rubber compositions of this invention will typically also contain carbon black as a filler. The carbon black will normally be utilized at a level of about 5 phr to about 100 phr. It is generally preferred for the carbon black to be employed at a level of about 25 phr to about 75 phr. It is desirable to substitute as much of the organophilic clay for carbon black as possible to reduce the weight (specific gravity) of the rubber composition to the greatest possible extent. In some cases, it will be beneficial to utilize a combination of silica and carbon black as the filler. It is to be appreciated that the silica coupler may be used in conjunction with a carbon black (namely, pre-mixed with a carbon black prior to addition to the rubber composition) and such carbon black is to be included in the aforesaid amount of carbon black for the rubber composition. Talc can also be included as a portion of the filler to reduce cost.
The commonly employed siliceous pigments used in rubber compounding applications can be used as the silica, including pyrogenic and precipitated siliceous pigments (silica), although precipitated silicas are preferred. The siliceous pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.
Such silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, page 304 (1930).
The silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, and more usually about 150 to about 300. The silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.
Various commercially available silicas may be considered for use in this invention such as, only for example herein, and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc: silicas available from Rhone-Poulenc, with, for example, designations of Z 1165 MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3.
The rubbery compositions of this invention can be compounded utilizing conventional ingredients and standard techniques. For instance, the amino group containing rubbery polymer will typically be mixed with the silica coupling agent, the organophilic clay, optionally additional fillers, sulfur, accelerators, oils, waxes, scorch inhibiting agents and processing aids. The rubber compositions of this invention can also be blended with conventional rubbers, such as polybutadiene rubber, synthetic polyisoprene rubber, natural rubber, styrene-butadiene rubber (SBR), xcex1-methylstyrene-butadiene rubber, xcex1-methylstyrene-isoprene rubber, styrene-isoprene-butadiene rubber (SIBR), styrene-isoprene rubber (SIR), isoprene-butadiene rubber (IBR), xcex1-methylstyrene-isoprene-butadiene rubber, and xcex1-methylstyrene-styrene-isoprene-butadiene rubber. In most cases, the rubbery polymer will be compounded with sulfur and/or a sulfur-containing compound, at least one accelerator, at least one antidegradant, at least one processing oil, zinc oxide, optionally a tackifier resin, optionally a reinforcing resin, optionally one or more fatty acids, optionally a peptizer and optionally one or more scorch inhibiting agents. Such blends will normally contain from about 0.5 to 5 phr (parts per hundred parts of rubber by weight) of sulfur and/or a sulfur-containing compound with 1 phr to 2.5 phr being preferred. It may be desirable to utilize insoluble sulfur in cases where bloom is a problem.
The rubber compounds of this invention will also normally include from 0.1 phr to 2.5 phr of at least one accelerator with 0.2 phr to 1.5 phr being preferred. Antidegradants, such as antioxidants and antiozonants, will generally be included in the rubber blend in amounts ranging from 0.25 phr to 10 phr with amounts in the range of 1 phr to 5 phr being preferred. Processing oils will generally be included in the blend in amounts ranging from 2 phr to 100 phr with amounts ranging from 5 phr to 50 phr being preferred. The rubber compounds of this invention will also normally contain from 0.5 phr to 10 phr of zinc oxide with 1 phr to 5 phr being preferred. These blends can optionally contain from 0 phr to 10 phr of tackifier resins, 0 phr to 10 phr of reinforcing resins, 1 phr to 10 phr of fatty acids, 0 phr to 2.5 phr of peptizers and 0 phr to 1 phr of scorch inhibiting agents.
The silica and the organosilicon compound (silica coupling agent) will typically be mixed into the rubber blend utilizing a thermomechanical mixing technique. The mixing of the rubber formulation can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients are typically mixed in at least two stages; namely, at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the xe2x80x9cproductivexe2x80x9d mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The rubber, silica and sulfur-containing organosilicon, and carbon black, if used, are mixed in one or more non-productive mix stages. The method of mixing the rubber formulation and the 2:1 layered silicates includes a bulk thermomechanical mixing technique. The method of mixing the rubber formulation and the 2:1 layered silicate does not include mixing the 2:1 layered silicates in an aqueous dispersion or latex of the rubber. The bulk thermomechanical mixing technique provides tremendous flexibility in achieving desired physical properties and performance on an industrial scale. The bulk thermomechanical mixing technique eliminates the need for a process for pre-intercalation or pre-dispersion or incorporation of the 2:1 layered silicates in the rubber that contains amino groups. This method of making the rubber and silicate blends has an advantage over the prior art in the sense that pre-intercalation of the 2:1 layered silicate in the guest molecules or dispersing medium requires long times, sometimes several hours. The pre-intercalation or dispersion of the 2:1 layered silicates aided with solvents requires additional energy for removal of the solvents, which is furthermore uneconomical. The bulk-thermomechanical method of preparing the rubber blends eliminates such a long process and provides additional flexibility of additions of required quantities of 2:1 layered silicates and other rubber compounding ingredients. In this invention, it was generally determined that sufficient exfoliation of the 2:1 layered silicate that was required for good balance of physical properties, was achieved in the thermomechanical bulk mixing process in about and upto 6 minutes of mixing time of the 2:1 layered silicate and the said rubber with amino groups. 2:1 layered silicate clay will preferably be an organophilic 2:1 layered silicate clay.
It is preferred for the rubber to be of high enough molecular weight so that the Mooney viscosity of the said rubber is in the range of 20 to about 120 ML 1+4@100xc2x0 C., and when crosslinked, it can be used as a useful tire material.
The terms xe2x80x9cnon-productivexe2x80x9d and xe2x80x9cproductivexe2x80x9d mix stages are well known to those having skill in the rubber mixing art. Sulfur-vulcanizable rubber composition containing a sulfur-containing organosilicon compound, a vulcanizable rubber and silica are normally subjected to a thermomechanical mixing step. This thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140xc2x0 C. and 190xc2x0 C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions and the volume and nature of the components. For example, conventional thermomechanical working is typically carried out for a duration of time which is within the range of about 2 minutes to about 20 minutes. It is normally preferred for the rubber blend to reach a temperature which is within the range of about 145xc2x0 C. to about 180xc2x0 C. and to be maintained at said temperature for a period of time which is within the range of about 4 minutes to about 12 minutes. In practicing this invention the need for prolonged mixing at elevated temperatures is eliminated. However, the rubber compounds of this invention will be mechanically worked until a temperature within the range of 140xc2x0 C. to 190xc2x0 C. is attained. It is normally preferred for the mixing to be carried out until a temperature within the range of about 145xc2x0 C. to 180xc2x0 C. and most preferable within the range of about 155xc2x0 C. to 170xc2x0 C. is attained. The weight ratio of the silica coupling agent to silica will typically be within the range of about 0.05:1 to about 0.3:1. The weight ratio of the silica coupling agent to silica will preferably be within the range of about 0.1:1 to about 0.25:1. The weight ratio of the silica coupling agent to silica will more preferable be within the range of about 0.12:1 to about 0.2:1.
The rubbery polymers of this invention can be used in tire treads in conjunction with ordinary tire manufacturing techniques. Tires are built utilizing standard procedures with the rubber compositions of this invention simply being substituted for the rubber compounds, such as standard styrene-butadiene rubber, typically used in the tread rubber. After the tire has been built with the rubber composition of this invention, it can be vulcanized using a normal tire cure cycle. Tires made in accordance with this invention can be cured over a wide temperature range. However, it is generally preferred for the tires of this invention to be cured at a temperature ranging from about 132xc2x0 C. (270xc2x0 F.) to about 166xc2x0 C. (330xc2x0 F.). It is more typical for the tires of this invention to be cured at a temperature ranging from about 143xc2x0 C. (290xc2x0 F.) to about 154xc2x0 C. (310xc2x0 F.). It is generally preferred for the cure cycle used to vulcanize the tire to have a duration of about 10 minutes to about 20 minutes with a cure cycle of about 12 minutes to about 18 minutes being most preferred.
This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Light weight rubber composition containing clay


An embodiment of the invention directed to a method is associated with data content, comprising discrete data portions including first data and second data portions separated from each other in the data content. A copy operation is implemented on data portions so that at least some of the data portions are each copied to a buffer, which include the first and second data portions. A paste operation is carried out to present each of the copied data portions as an input for an output data selection task. Prespecified criteria is used in the output data selection task to select a number of the copied data portions to be selected data for a given purpose, the selected number of copied data portions being less than data portions presented by the paste operation, and the selected copied data portions including the first and second data portions.

1. Field
The invention disclosed and claimed herein generally pertains to a smart copy clipboard. More particularly, the invention pertains to a computer clipboard provided with intelligent capabilities, for selecting portions of specified data content, including data content portions which are non-contiguous or disjointed portions in relation to each other.
2. Description of the Related Art
As is known by those of skill in the art, a computing clipboard is a software facility that can be used for short term data storage and/or data transfer between documents or applications, via copy and paste operations. It is usually implemented as an anonymous, temporary data buffer that can be accessed from most or all programs within an environment, via defined programming interfaces. Frequently, it would be desirable to use a clipboard function for a purpose such as summarizing a conversation that the user was having with another user, by means of a messenger such as a Sametime platform or the like. It might also be desirable to extract out certain portions of such a conversation, and paste them to someone else. However, currently used clipboard techniques are generally not adaptable for these purposes.
Moreover, current clipboard techniques generally do not allow two data portions which are disjointed, or are separated or not located contiguous to each other in a body of data content, to be copied in a single operation. Rather, only a portion of text that can be shadowed in "one pass" is able to be copied and pasted.
In addition, users may want to chat or communicate through different messenger services during a conversation between them. This could happen if users start from a messenger platform such as Sametime, then move to another messenger such as gtalk to discuss some private matters, and then move to Skype to see each other via a webcam. It would be desirable to provide a single intelligent capability that could acquire, filter and process data pertaining to these interactions across different messengers. Yet another need is to provide an intelligent copy and paste operation to acquire and process data across different media, such as audio, text and video.

Clipboard for processing received data content

International Business Machines Corporation


A vacuum cleaner system having an intake nozzle integrally formed with a concave lower portion of a main vacuum canister of a vacuum cleaner system. The intake nozzle protrudes downwardly and communicates with an opening in a convex upper surface of a liquid pan removably attached to the concave lower portion of the main vacuum canister. In an alternative preferred embodiment, an intake member is included which is secured to the concave lower portion of the main vacuum canister. The intake member includes a downwardly protruding tubular member which protrudes outwardly of the lower surface of the main vacuum canister. The tubular member has a first opening which forms an intake port on the side surface of the main vacuum canister and a second opening forming an exhaust port at a lowermost end portion thereof. The intake member further includes a downwardly depending shroud for enabling the main vacuum canister to be more securely supported on a floor. In one preferred embodiment the liquid pan includes a pivotally foldable handle portion for facilitating handling of the liquid pan and a pivotally, removably disposed comb for filtering said debris from a liquid filtering agent when the filtering agent is emptied from the pan. In other preferred embodiments, the liquid pan assembly integrally includes vertically disposed ribs which serve to filter the liquid filtering agent of solid debris, and spherical protrusions and recesses on a movable handle which help to stabilize the liquid pan when the pan is carried while full.

1. Technical Field
This invention relates to liquid bath vacuum cleaner systems and, more particularly, to a liquid pan assembly including integrally formed filtering means for use with a liquid bath vacuum cleaner.
2. Discussion
Liquid bath vacuum cleaners are used in a wide variety of residential and industrial applications. These vacuum cleaners typically include a main vacuum canister with a removably attached liquid pan. An intake nozzle of the pan matingly engages with an opening in the canister when the pan is attached to the canister to allow dust and dirt entrained air to be ingested by a vacuum force through the intake nozzle into the area defined by the liquid pan. The pan is removed periodically from the main vacuum canister and flushed out with water or another cleaning solution as it is articulated into various positions.
Although liquid pan and canister combinations as described above operate well to receive and trap dust and dirt particles entrained in ingested air, the attached intake nozzle tends to impede cleaning by trapping dirt when flushing out the pan. In addition, the shape of many heretofore designed liquid pans usually requires that the pan be held and manipulated with both hands as the liquid cleaning agent is emptied therefrom. Accordingly, since two hands are often required to handle the liquid pan, it can at times be difficult for an individual to catch unwanted debris such as cloth, hair, carpet fibers, etc., from being drained from the liquid pan as the liquid filtering agent is emptied from the pan.
In a co-pending U.S. application Ser. No. 713,059, a liquid pan assembly was disclosed which represented a significant step forward in alleviating the problems of prior art liquid pan assemblies. The above-mentioned liquid pan assembly includes a handle portion and a comb. The handle, which is pivotally secured to a portion of the pan, serves to make the liquid pan more easy to handle and manipulate as the contents of the pan are emptied. The comb enables the liquid contents of the pan to be filtered from debris intermixed therewith as the liquid contents are emptied from the pan.
While the above-mentioned invention has proved to be a significant advance in the art, it would be even further desirable to provide a one-piece liquid pan assembly with which the liquid contents of the liquid pan assembly can be filtered of solid debris such as pieces of cloth, hair, carpet strands and the like, as it is emptied from the assembly.
Accordingly, it is an object of the present invention to provide a liquid pan for a liquid bath vacuum cleaner which may be more easily cleaned than conventional pans for liquid bath vacuum cleaners.
It is a further object of the present invention to provide a main vacuum canister having an attached intake nozzle operable to receive dust and dirt entrained air ingested by the vacuum cleaner and to direct the ingested air towards a removably attached liquid pan.
It is yet a further object of the present invention to provide a removable liquid pan having an opening operable to communicate with an intake nozzle of a main vacuum canister to thereby allow airflow through the nozzle and the opening into an interior area of the liquid pan.
It is another object of the present invention to provide an intake means for a main vacuum canister of a vacuum cleaner, which intake means includes an integrally formed tubular intake port, and where the intake means may be removed from the lower surface of the main vacuum canister.
It is yet another object of the present invention to provide an intake means which may be coupled to a lower surface of a main vacuum canister, which intake means includes a tubular intake port protruding outwardly of the lower surface of the main vacuum canister, and which intake means further includes a downwardly depending shroud extending outwardly of the lower surface of the main vacuum canister a distance at least equal to a distance at which the tubular intake port extends outwardly of the lower surface, to thereby rest on a floor in a level manner and support a main vacuum canister secured thereto in a level, stabilized manner.
It is yet another object of the present invention to provide a removable liquid pan for a liquid bath-type vacuum cleaner, where the liquid pan incorporates a handle portion which is pivotally secured to a portion of the liquid pan and foldably positionable to enable it to be stowed away when the liquid pan is coupled to a main vacuum canister of the vacuum cleaner system.
It is still another object of the present invention to provide a liquid pan for a liquid bath-type vacuum cleaner system, where the liquid pan incorporates a pivotally, removably disposed comb, and where the comb operates to filter unwanted debris such as pieces of cloth, hair, carpet strands and the like from a liquid filtering agent contained within the pan as the filtering agent is emptied from the pan.
It is still a further object of the present invention to provide a liquid pan for a liquid bath-type vacuum cleaner system where the liquid filtering agent can be quickly emptied from the pan.
It is still another object of the present invention to provide a liquid pan for a liquid bath-type vacuum cleaner system where solid debris and the liquid filtering agent can be separately disposed without having to physically handle any of the debris or employ any separate filtering implements.
It is yet another object of the present invention to provide a liquid pan for a liquid bath-type vacuum cleaner system where the liquid pan provides an integrally formed filtering means to filter unwanted debris from a liquid filtering agent contained within the pan as the filtering agent is emptied from the pan.
It is yet another object of the present invention to provide a liquid pan for a liquid bath-type vacuum cleaner system where the liquid pan includes a plurality of molded-in ribs disposed vertically on a spout portion of the liquid pan to more completely filter unwanted debris from a liquid filtering agent contained within the pan as the filtering agent is emptied from the pan.
It is still yet another object of the present invention to provide a handle assembly for a liquid pan for a liquid bath-type vacuum cleaner system where the liquid pan includes a handle assembly which, when extended, is held rigid with respect to the pan, and is pivotally disposed such that it can be foldably stored below the uppermost portion of the liquid pan.

Filtering means for a liquid pan assembly for a liquid bath vacuum cleaner


A semiconductor structure includes a varactor and a field effect transistor. The varactor includes a body region that includes a semiconductor material and a first gate structure over the body region. The body region is doped to have a first conductivity type. The first gate structure includes a first gate insulation layer and a first work function adjustment metal layer. The field effect transistor includes a source region, a channel region, a drain region and a second gate structure over the channel region. The source region and the drain region are doped to have a second conductivity type that is opposite to the first conductivity type. The second gate structure includes a second gate insulation layer and a second work function adjustment metal layer. The first work function adjustment metal layer and the second work function adjustment metal layer include substantially the same metal.

1. Field of the Disclosure
Generally, the present disclosure relates to integrated circuits and methods for the formation thereof, and, more particularly, to integrated circuits including capacitors whose capacitance can be adjusted by applying a voltage thereto.
2. Description of the Related Art
Integrated circuits typically include a large number of circuit elements, in particular field effect transistors. In a field effect transistor, a gate electrode is provided. The gate electrode may be separated from a channel region of the field effect transistor by a gate insulation layer that provides electrical insulation between the gate electrode and the channel region. Adjacent the channel region, a source region and a drain region that are doped to have a different conductivity type than the channel region are provided. Depending on an electric voltage applied to the gate electrode, the field effect transistor may be switched between an ON-state and an OFF-state, wherein an electrical conductivity of the channel region in the ON-state is greater than an electrical conductivity of the channel region in the OFF-state.
In addition to field effect transistors, other circuit elements, such as inductivities, resistors, diodes and capacitors, may be provided in an integrated circuit. Types of capacitors that may be provided in integrated circuits include metal oxide semiconductor capacitors (MOS capacitors). A MOS capacitor may have a configuration similar to that of a field effect transistor, wherein, however, no transitions between regions having a different conductivity type, such as those provided in a field effect transistor between the channel region and the source and drain regions, are provided. The MOS capacitor may include a body region that is provided below a gate electrode of the MOS capacitor and separated therefrom by a gate insulation layer. Adjacent the body region, highly doped semiconductor regions may be provided which are doped to have a same conductivity type as the body region and have a higher dopant concentration than the body region. A first capacitor electrode of the MOS capacitor is provided by the gate electrode, and a second capacitor electrode of the MOS capacitor is provided by the body region. The highly doped semiconductor regions adjacent the body region may be used for providing an electrical connection to the body region by means of contact holes that are formed in an interlayer dielectric above the highly doped semiconductor regions and are filled with an electrically conductive material. An additional contact hole filled with an electrically conductive material may be provided over the gate electrode for providing an electrical connection to the gate electrode.
Types of MOS capacitors include NMOS capacitors, wherein the body region is N-doped, and PMOS capacitors, wherein the body region is P-doped.
A capacitance of a MOS capacitor may be adjusted by varying a gate voltage that is applied between the gate electrode and the body region of the MOS capacitor. The application of the gate voltage may create an electric field in the body region, which may have an influence on the distribution of charge carriers in the body region. Depending on the polarity of the gate voltage, an accumulation or a depletion of majority charge carriers may be obtained in a portion of the body region adjacent the gate insulation layer. In an NMOS capacitor, an accumulation of electrons may be obtained by applying a positive voltage to the gate electrode, and depletion of electrons may be obtained by applying a negative voltage to the gate electrode. In a PMOS capacitor, an accumulation of holes may be obtained by applying a negative voltage to the gate electrode, and a depletion of holes may be obtained by applying a positive voltage to the gate electrode. An accumulation of majority charge carriers may increase the capacity of the MOS capacitor, and a depletion of majority charge carriers may reduce the capacity of the MOS capacitor. Hence, the MOS capacitor may provide a voltage dependent capacitance, thus being a varactor. Herein, the term "varactor" will be used to denote a capacitor whose capacitance can be varied by applying a voltage thereto.
As described above, for using the full tuning range of the capacitance of the MOS varactor, it may be necessary to use both positive and negative gate voltages. For some applications, this may be disadvantageous, and it may be useful to have a device that provides a high tunability of its capacitance by using only one polarity of the gate voltage, which is denoted as "zero referenced tunability." For this purpose, it has been proposed to form the gate electrode of a MOS varactor from doped polysilicon, wherein the doping of the gate electrode is opposite to the doping of the body region. Accordingly, a P-doped gate electrode may be used in NMOS capacitors, and an N-doped gate electrode may be used in PMOS capacitors. The doping of the gate electrode may have an influence on the Fermi energy of electrons in the gate electrode, which may lead to a bending of the valance band and the conduction band of the semiconductor material of the body region in the vicinity of the gate electrode. The bending of energy bands may have an influence on the distribution of charge carriers in the body region, which may have an influence on the voltage dependency of the capacity of the MOS capacitor similar to that of a bias of the gate voltage. Thus, a zero referenced tunability of the MOS capacitor may be improved.
However, this approach may have some issues associated therewith. For doping the gate electrode of the MOS capacitor differently than the highly doped semiconductor regions adjacent the body region, masks, such as photoresist masks, may be required for blocking dopant ions in ion implantation processes that are used for doping the highly doped semiconductor regions and the gate electrode. In particular, a mask may be formed over the gate electrode when ions of a dopant of a first conductivity type, for example, ions of an N-type dopant in the case of an NMOS capacitor, are implanted into the highly doped semiconductor regions adjacent the gate electrode, and a mask may be formed over the highly doped semiconductors when ions of a dopant of a second conductivity type, for example, ions of a P-type dopant in the case of a PMOS capacitor, are implanted into the gate electrode. In order to avoid an inadvertent doping of the highly doped semiconductor regions and/or the gate electrode with dopants of the wrong conductivity type, it has been proposed to form shallow trench isolations below the sidewalls of the gate electrode. Thus, a relatively complex manufacturing process may be required for forming a MOS capacitor having a relatively high zero referenced tunability.
In view of the situation described above, the present disclosure provides semiconductor structures and varactors that may help to substantially avoid or at least reduce the above-mentioned problems, and methods for the formation of such semiconductor structures and varactors.

Semiconductor structure including a varactor


A phantom assembly includes a plurality of cylindrical shaped phantoms connectable to each other and/or a plurality of column-shaped phantoms connectable to each other with fitting portions. An x-ray radiation measuring device for measuring an x-ray radiation from an x-ray CT device is inserted in a through-hole of the phantom.

1. Field of the Invention
The present invention relates to a phantom and a phantom assembly (phantom unit) used as a dummy for a human body in assessing CT dosage of x-ray radiation, and is based on Japanese Patent Application No. 2003-427312, filed on Dec. 12, 2003, the disclosure of which is incorporated herein by reference.
2. Description of Related Arts
In a conventional assessment of CT dose, phantoms according to IEC (International Electrotechnical Commission) have been used (For example, see International Electrotechnical Commission, "Evaluation and routine testing in medical imaging departments constancy tests-x-ray equipment for computed tomography," pub. IEC, 1223-2-6 (1994); T. B. Shope, R. M. Gane, and G. C. Johnson, "A method for describing the doses delivered by transmission x-ray computed tomography," Med. Phys. 8, 448-495 (1981); and W. Leitz, B. Axelsson, and G. Szendro, "Computed tomography does assessment-A practical Approach." Radiat. Prot. Dosim., 57, 377-380 (1995)). In this case, for example, two phantoms, one for body portion, and another for head, are ready and each made of an acrylic resin and formed into a cylinder having a diameter of 320 mm and 160 mm, respectively, and a length of 150 mm. Cavities of 10 mm diameter were located parallel to the central axis of the cylinders, and the centers of the holes were located at the cylinder center and also 10 mm below the cylinder surface at 90 degree intervals (detailed in IEC document), and evaluation of x-ray irradiated onto a human body has been made by inserting a device for measuring dose.
In the conventional assessment of CT dose as described above, if conical beam having a large beam width of x-ray, what is called, cone beam is assessed by utilizing the phantoms, the phantoms should be form in a shape where the length of the shaft direction is large to meet the shape of the cone beam. In this case, weight and the size of the phantom are increased, inconvenient for carrying the phantom and for storing it. As a result, only an x-ray having a narrow beam width can be assessed by the conventional phantom.
When an x-ray is irradiated on such a phantom, the x-ray induces scattered radiation within the phantom, which is scattered distributed at random. Accordingly, when the assessment of the x-ray radiation (patient dose) including the scattered radiation will be made, the weight and the size of the phantom will be much more increased, leading to inconvenience in terms of portability and storage of the phantom. (For dose assessment for the cone-beam, although the weight of the phantom will be increased, the phantom length should be longer than the conventional one, because the scattered radiation is distributed wider than that in the narrow beam width.)
In order to overcome the inadequacy just mentioned, it can be considered that edges portion of phantoms are lined up in a face-to-face manner whereby the length of the phantoms in the shaft direction is set to be large as a whole. However, lining up of the phantoms has problems that fixation of the phantoms is incomplete and that x-ray radiation is passed through from gaps between the edge portions of the phantoms and, thus, no accurate assessment can be made. In order to make a long phantom from a practical point of view, we joined unit phantoms together to provide phantoms of the necessary length.
An object of the present invention is to provide a phantom and a phantom assembly which can easily be carried, in which the length of the phantom can be freely set to meet the shape of an x-ray beam, in which phantoms can be tightly connected, and which can assess CT dose of x-ray radiation in an accurate manner without passing the radial from phantoms. By inserting acrylic sticks through these holes, the cylinders were more tightly fixed to each other. Moreover, the connection portion of the phantoms was step-shaped so as not to allow direct passage of x-rays through any gaps.

National Institute of Radiological Sciences


Embodiments of the present application disclose a capacitor and a method for producing a capacitor. The capacitor includes: an electrode layer including a first electrode and a second electrode separated from each other; a laminated structure including n dielectric layer(s) and n+1 conductive layers, where the n dielectric layer(s) and the n+1 conductive layers form a structure that a conductive layer and a dielectric layer are adjacent to each other, and the laminated structure forms at least two columnar structures, and n is a positive integer; and an interconnection structure configured to electrically connect an odd-numbered conductive layer in the n+1 conductive layers to the first electrode and electrically connect an even-numbered conductive layer in the n+1 conductive layers to the second electrode. According to the technical solution of the embodiments of the present application, capacitance density of the capacitor could be improved.

A capacitor is an important electronic component. With the continuous development of modern electronic system towards multi-function, high integration, low power consumption and miniaturization, an existing capacitor manufacturing technology has been unable to meet diversified needs of various high-end applications.
A wafer-level three-dimensional (3D) capacitor is a new type of capacitor manufactured on a silicon wafer by utilizing a semiconductor processing technology in recent years. Compared with a commonly used multilayer ceramic capacitor, the wafer-level three-dimensional capacitor has significant advantages in terms of minimum thickness, frequency response, and temperature coefficient of a chip. The wafer-level 3D capacitor has a wide range of applications in consumer electronics that require an extremely small size of a device, or in medical, vehicle-mounted devices, aerospace electronics fields that require strict device performance and reliability.
However, at present, capacitance density of the wafer-level 3D capacitor is still limited, and how to improve the capacitance density of the capacitor has become an urgent technical problem to be resolved.

Capacitor and method for producing capacitor


A rotation quantity measuring method and system measures a rotation quantity of an object body. The rotation quantity is measured by irradiating a light from a light source on a grating pattern which is formed on a peripheral surface of a cylindrical body which rotates integrally with the object body, and detecting a shadow picture pattern which is generated by a reflected light received from the grating pattern based on a diffraction caused by the grating pattern. Then, the rotation quantity of the object body is measured based on a movement of the shadow picture pattern as the object body rotates.

The present invention generally relates to rotation quantity measuring methods and systems, and more particularly to a rotation quantity measuring method and system for measuring a rotation quantity of an arbitrary rotary body which is applicable to various rotary encoders.
As a method of measuring a rotation quantity of an object body, there is a conventional method which forms a grating pattern on a peripheral portion of a disc shaped rotary body as an encoder pattern and fixes the rotary body on the object body so that the rotary body rotates integrally with the object body. According to this conventional method, the rotation quantity of the object body is measured by optically detecting a movement of the encoder pattern. For example, "The Use of Optical Parts and Consideration to be Given", Optronics Company, 1985 proposes this conventional method.
However, the above described conventional method suffers from the following problems. First, a measuring apparatus which employs the conventional method becomes bulky because the rotary body which is fixed on the object body has a disc shape. Second, the patterning of the grating pattern on the rotary body is formed by a photolithography, but it is troublesome to carry out a large number of patterning steps which are required to form the grating pattern. Third, when setting a pitch of gratings of the grating pattern to one micron or less so as to obtain a high resolution, for example, the patterning must be carried out over a large area thereby making it difficult to improve the accuracy of the measurement.
Therefore, there is a demand to realize a rotation quantity measuring method which does not require a bulky measuring apparatus and which is capable of making a highly accurate measurement.

Rotation quantity measuring method and system


A packaging material used for wrapping foodstuffs and for inhibiting the growth of micro-organisms in foodstuffs, the packaging material having a metal-ion sequestering agent capable of removing designated metals ions from the surfaces of the foodstuffs and from liquid extrudates of foodstuffs.

In recent years people have become very concerned about exposure to the hazards of microbe contamination. For example, exposure to certain strains of Escherichia coli through the ingestion of under-cooked beef can have fatal consequences. Exposure to Salmonella enteritidis through contact with unwashed poultry can cause severe nausea. Mold and yeast (Candida albicans) may cause skin infections. In some instances, biocontamination alters the taste of the food or drink or makes the food unappetizing. With the increased concern by consumers, manufacturers have started to produce products having antimicrobial properties. A wide variety of antimicrobial materials have been developed which are able to slow or even stop microbial growth; such materials when applied to consumer items may decrease the risk of infection by micro-organisms.
Noble metal-ions such as silver and gold ions are known for their antimicrobial properties and have been used in medical care for many years to prevent and treat infection. In recent years, this technology has been applied to consumer products to prevent the transmission of infectious disease and to kill harmful bacteria such as Staphylococcus aureus and Salmonella. In common practice, noble metals, metal-ions, metal salts or compounds containing metal-ions having antimicrobial properties may be applied to surfaces to impart an antimicrobial property to the surface. If, or when, the surface is inoculated with harmful microbes, the antimicrobial metal-ions or metal complexes, if present in effective concentrations, will slow or even prevent altogether the growth of those microbes. Antimicrobial activity is not limited to noble metals but is also observed in organic materials such as chlorophenol compounds (Triclosan™), isothiazolone (Kathon™), antibiotics, and some polymeric materials.
In order for an antimicrobial article to be effective against harmful micro-organisms, the antimicrobial compound must come in direct contact with micro-organisms present in the surrounding environment, such as food, liquid nutrient or biological fluid. This creates a problem in that the surrounding environment may become contaminated with the antimicrobial compounds, which may potentially alter the color or taste of items such as beverages and foodstuffs, and in the worst case may be harmful to the persons using or consuming those items. The wide spread use of antimicrobial materials may cause further problems in that disposal of the items containing these materials cannot be accomplished without impacting the biological health of the landfill or other site of disposal; and further the antimicrobial compounds may leach into surrounding rivers, lakes and water supplies. The wide spread use of antimicrobial materials may cause yet further problems in that micro-organisms may develop resistance to these materials and new infectious microbes and new diseases may develop. It has been recognized that small concentrations of metal-ions may play an important role in biological processes. For example, Mn, Fe, Ca, Zn, Cu and Al are essential bio-metals, and are required for most, if not all, living systems. Metal-ions play a crucial role in oxygen transport in living systems, and regulate the function of genes and replication in many cellular systems. Calcium is an important structural element in the formation of bones and other hard tissues. Mn, Cu and Fe are involved in metabolism and enzymatic processes. At high concentrations, metals may become toxic to living systems and the organism may experience disease or illness if the level cannot be controlled. As a result, the availability and concentrations of metal-ions in aqueous and biological environments is a major factor in determining the abundance, growth-rate and health of plant, animal and micro-organism populations.
It has been recognized that iron is an essential biological element, and that all living organisms require iron for survival and replication. Although the occurrence and concentration of iron is relatively high on the earth's surface, the availability of "free" iron is severely limited by the extreme insolubility of iron in aqueous environments. As a result, many organisms have developed complex methods of procuring "free" iron for survival and replication; and depend directly upon these mechanisms for their survival.
Articles, such as packaging materials, are needed that are able to provide for the general safety and health of the public in a safe and efficient manner. Articles, such as packaging materials, are needed that are able to improve the quality and safety of food supplies for the general public. Food and consumer packaging materials are needed that are able to improve food quality, to increase shelf-life, to protect from microbial contamination, and to do so in a manner that is safe for the user of such items and that is environmentally clean. Materials and methods are needed to prepare articles having antimicrobial properties that are less, or not, susceptible to microbial resistance. Methods are needed that are able to target and remove specific, biologically important, metal-ions while leaving intact the concentrations of beneficial metal-ions.

Packaging material for inhibiting microbial growth


A method for producing a membrane device includes: forming an insulating film as a first film on a Si substrate; forming a Si film as a second film on the entire surface or a part of the first film; forming an insulating film as a third film on the second film; forming an aperture so as to pass through a part of the third film positioned on the second film and not to pass through the second film; etching a part of the substrate on one side of the first film with a solution that does not etch the first film; and etching a part or all of the second film on the other side of the first film with a gas or a solution that does not etch the first film and has an etching rate for the third film lower than an etching rate for the second film.

As an approach for realizing a more advanced generation DNA sequencer, techniques using nanopores have been studied. That is, an aperture (nanopore) having a size similar to DNA are provided in a thin film membrane, an upper and lower chambers of the thin film membrane are filled with an aqueous solution, electrodes are provided in the two chambers so as to be in contact with the aqueous solution, DNA to be measured is put in one of the chambers, a potential difference is caused between the electrodes provided in the two chambers to subject the DNA to electrophoresis to allow the DNA to pass through the nanopore, and during this time, the temporal change in the ionic current flowing between the two electrodes is measured, thereby determining a structural feature or the basic sequence of the DNA. The above technique is useful for acquiring a structural feature of not only DNA but also various biological molecules.
For producing the nanopore device, methods using a semiconductor substrate, a semiconductor material, or a semiconductor process, which has a high mechanical strength or other characteristics, are attracting attentions. For example, a thin film membrane can be formed with a silicon nitride film (SiN film). Voltage stress is applied to a membrane in an ionic aqueous solution to cause dielectric breakdown, whereby fine pinholes can be bored to form a nanopore in the membrane (NPL 1). In an alternative method, a nanopore can be formed by subjecting a membrane to etching by a focused electron ray.
One of important factors for determining accuracy in DNA reading by a nanopore sequencer is a film thickness of the membrane. Specifically, a smaller thickness of the membrane is more preferred. The reason is that the interval between adjacent two of four kinds of bases arranged in a DNA strand is approximately 0.34 nm, and the larger the thickness of the membrane is as compared to the interval, the larger number of bases are simultaneously placed in one nanopore. In this situation, a signal obtained by measuring a current is a signal generated by multiple bases, resulting in reduction of the accuracy of base sequence determination and leading to a complicated signal analysis. Also when acquisition of structural features is intended for various biological molecules other than DNA, a larger thickness of the membrane results in reduction of space resolution. Accordingly, for enhancement of accuracy in structure determination of a substance to be measured, it is highly important to make the thickness of the membrane having a nanopore as small as possible.
In order to reduce the thickness of a membrane, it is obviously preferred that the membrane area is as small as possible. The smaller the membrane area, the lower the possibility of presence of unavoidable defects (weak spots or pinholes due to bonding failure between atoms) generated during forming the membrane in the membrane. In addition, when the membrane is formed, it is important to avoid a process involving the possibility of scratching and breaking the membrane as much as possible.
Hereinunder, attempts of reduction in thickness of a membrane will be described with explanation of some examples of a conventional representative method for forming a membrane using a semiconductor material.
In the simplest method of forming a membrane, a film of a material for the membrane (e.g., SiN) is formed on a Si substrate, a film of SiN is formed on the back surface, a part of the SiN film on the back surface is etched so as to expose the Si substrate, and then the Si substrate is etched with an aqueous solution of KOH or TMAH from the part of the back surface where the Si is exposed, toward the front surface, whereby a membrane supported on the Si substrate can be formed. In this method, it is difficult to make the area of the membrane small. Although the etching of the Si substrate with the KOH aqueous solution or TMAH aqueous solution is a crystal anisotropy etching in which only the (100) face is preferentially etched, etchings in other directions than the (100) face proceeds in certain degrees and variation in etching shape is also large. In particular, etching proceeds also in an unexpected direction with a crystal defect present in Si as the starting point, and therefore the variation in shape increases. In addition, the thickness of the Si substrate to be etched is generally large and at least 100 um or more (for example, 725 um in the case of a Si wafer of 8 inches). The thickness of the substrate varies in one wafer or among wafers, and generally, there is a variation of 1 um or more. Thus, a membrane having a size greatly deviated from the membrane size expected from the shape of a mask of the SiN film on the back surface is formed. For the above reason, according to the result of our previous study, it has been difficult to stably form a membrane having an area of 50 um×50 um square or smaller size by this production method. However, in order to aim at forming a thin film membrane, it is required to make the area of the membrane further smaller.
In another production method, as described in NPL 1, a SiN film is formed on a Si substrate, then a SiO2 film is formed on the SiN film, then SiN films are formed on the SiO2 and the back surface of the Si substrate, then a part of the uppermost SiN film on the front surface side of the wafer is patterned by dry-etching to expose the SiO2 film under the SiN film, then a part of the SiN film on the back surface is etched so as to expose the Si substrate, the Si substrate is etched from the back surface with a TMAH aqueous solution, then remove the SiO2 film on the SiN film with an HF aqueous solution, whereby a SiN membrane can be formed. According to this method, if a hole pattern of, for example, 100 nm square or smaller is formed by using a latest lithography technique and dry etching in the patterning of the SiN on the SiO2, after the subsequent SiO2 etching with the HF aqueous solution, the thinnest area of the membrane (an area with a single layer of the SiN membrane) can be made into a size of approximately 100 to 500 nm square inclusive of the variation. In this respect, the method is advantageous in reduction of the membrane thickness.
However, an HF aqueous solution etches a SiN film although the etching rate is lower as compared with the case of a SiO2 film. For this reason, the contact of the HF aqueous solution with the SiN membrane of the thin film part causes breaking of the membrane. In the results of our experiments, the lower limit of the thickness of the membrane in the thinnest part is 7 nm in the above method.
In another method, as described in NPL 2, a thick SiN membrane is formed, and the thickness is reduced by dry etching in a partial area thereof. According to this method, since the thickness of the membrane can be reduced only in an area of a limited part by a latest lithography technique and dry etching, it is possible to achieve the surface area reduction in a thin film membrane part. However, variation in the dry etching rate among different batches is large, and the variation in the etching rate in one wafer surface is also large. Furthermore, since the SiN film before etching has a large thickness, variation in the initial film thickness is also large. For this reason, the thickness of the obtained membrane has large variations among different batches and different samples, relative to the target thickness. In dry etching, ions with a high energy collide with the membrane and therefore damage the membrane. In an ultrathin film area, therefore, there is a possibility of breaking the membrane, and hence the method is unsuitable to reduction of the membrane thickness. According to the description in NPL 2, the thickness of the SiN film is 5 to 8 nm.
Incidentally, a material that is used most widely as a membrane material is SiN. SiN has a high density, is hydrophilic, and is highly excellent in chemical stability. These give a great advantage for a nonopore sensor used in an aqueous solution. In fact, there are many studies in which a nanopore was formed in a SiN membrane and DNA passing through the nanopore was confirmed, other than NPL 1 and NPL 2, and a highly stable passing of DNA through a nanopore was confirmed. Thus, SiN is one of materials that are currently used most frequently as a membrane material for a nanopore sensor. In addition, SiN is excellent in mechanical strength and the membrane is difficult to break. SiN is one of the most general materials that are used in a semiconductor process, and is advantageous also in a very high compatibility with a conventional semiconductor process (for example, CMOS process). That is, a membrane of SiN can be produced in most semiconductor lines in the world. For this reason, a sensor (nanopore sensor) with a SiN membrane is expected to be spread to the industry without any large barrier. Even in the case where an MOS transistor circuit for measurement is installed on the same circuit board with a nanopore sensor, the membrane made of a SiN material is not a large barrier. For the above reasons, SiN is being greatly expected as a material of a nanopore membrane having a very small thickness.

Membrane device and method for manufacturing same