A multilayered packaging film having good antifog performance that is suitable for use in food packaging. The multilayered film comprises a nylon film having first and second surfaces; a sealant film positioned on the first surface of the nylon film, either directly on the first surface of the nylon film or via an intermediate adhesive; an antifog composition contained within at least part of the sealant film or coated on a surface of the sealant film opposite the nylon film; and a protective film applied onto the second surface of the nylon film.

1. Field of the Invention
The invention relates to packaging films. More particularly, the invention pertains case ready packaging films having good antifog performance that are suitable for use in meat packaging.
2. Description of the Related Art
Containers have long been used to store perishable foods, such as meats, fruits and vegetables, prior to sale in the marketplace to consumers. Maximizing the time in which the food remains preserved in the containers minimizes the amount of spoilage.
The environment around which the food is preserved is an important factor in the preservation process. It is important that the food is maintained at an adequate temperature, while also controlling the molecular and chemical content of the gases surrounding the food. By providing an appropriate gas content to the environment surrounding the food, the food can be better preserved when maintained at the proper temperature or even when it is exposed to variations in temperature. This gives the food producer some assurance that the food will be in an acceptable condition when it reaches the consumer. Preferred modified atmosphere packaging systems for foods, including raw meats, exposes these foods to extremely low levels of oxygen because it is well known that the freshness of meat can be preserved longer under anaerobic conditions than under aerobic conditions. Maintaining low levels of oxygen minimizes the growth and multiplication of aerobic bacteria. Additionally, modified atmosphere packaging can involve high levels of oxygen (80%) combined with nitrogen and/or carbon dioxide. The gases in these combinations do not favor bacterial growth but allow the raw meat to maintain a preferred red color that is acceptable to the consumer.
It is also important that the packaging exhibit good resistance to the formation of condensation inside the package on a surface of the film. This is known in the art as an antifog property. Multilayered films for modified atmosphere packaging having such antifog properties are well known and are commonly used when packaging food products having a high moisture content, such as fresh meats, and when it is important for the product to be clearly visible to the consumer. For example, U.S. Pat. No. 5,766,772 describes multi-layer heat-shrinkable films endowed with antifog properties having a different structure from this invention.
To produce a film exhibiting this antifog property, an antifog component is typically blended with or coated onto a sealant film such as a polyethylene film. This antifog-polyethylene component then forms a part of a multilayered packaging film, such as a nylon packaging film, that may also incorporate an oxygen barrier polymer layer such as ethylene vinyl alcohol. However, one significant problem associated with such known multilayered films having this antifog component is that the antifog component tends to be drawn toward polar materials, such as nylon, and away from the non-polar polyethylene. This is particularly a problem when the film is rolled up after manufacture such that the antifog layer or antifog containing polyethylene layer is brought into direct contact with an adjacent nylon layer. This causes the antifog component to migrate out of its existing polyethylene layer and into the nylon layer, compromising the performance of the nylon layer as well as degrading the antifog property of the film. Therefore, it would be desirable to have a multilayered packaging film having good antifog performance and having an antifog component which does not migrate into adjacent nylon layers when stored. The present invention provides such a solution to this need.
The invention provides a multilayered film comprising:
a) a nylon film having first and second surfaces;
b) a sealant film, positioned on the first surface of the nylon film, either directly on the first surface of the nylon film or via an intermediate adhesive;
c) an antifog composition contained within at least part of the sealant film or coated on a surface of the sealant film opposite the nylon film; and
d) a protective film applied onto the second surface of the nylon film.
The invention also provides a multilayered film comprising:
a) a first nylon layer having first and second surfaces;
b) an ethylene vinyl alcohol layer positioned on the first surface of the nylon layer;
c) a second nylon layer positioned on a surface of the ethylene vinyl alcohol layer opposite the first nylon layer;
d) a polyethylene sealant film, positioned on a surface of the second nylon layer which is opposite to the ethylene vinyl alcohol layer;
e) an antifog composition contained within the sealant film or coated on a surface of the sealant film which is opposite the second nylon layer; and
f) a polyurethane protective film applied on the second surface of the first nylon film.
The invention further provides a process for forming a multilayered film comprising:
a) positioning a sealant film onto a first surface of a nylon film, wherein the sealant film has an antifog composition which is either incorporated therein or coated on a surface of the sealant film opposite the nylon film; and
b) applying a protective film onto a second surface of the nylon film.
The invention still further provides a food package which comprises a container having an open portion and a multilayered film sealing the open portion, which multilayered film comprises:
a) a nylon film having first and second surfaces;
b) a sealant film, positioned on the first surface of the nylon film, either directly on the first surface of the nylon film or via an intermediate adhesive;
c) an antifog composition contained within at least part of the sealant film or coated on a surface of the sealant film opposite the nylon film; and
d) a protective film applied onto the second surface of the nylon film; the multilayered film being positioned such that the protective film is away from the open portion of the container.
The invention therefore provides a desirable multilayered packaging film having good antifog performance and having an antifog component which does not migrate into adjacent nylon layers when stored.
The invention provides a multilayered packaging film having good antifog properties wherein the antifog composition does not migrate into adjacent polar film layers. In the production of a multilayered film according to the invention, a nylon film having first and second surfaces is positioned on a surface of a sealant film, either directly on the first surface of the nylon film or via an intermediate adhesive layer. An antifog composition is contained within at least part of the sealant film or coated on a surface of the sealant film that is opposite to the nylon film, i.e. a surface different than the surface to which the nylon film is attached. A protective film is also applied onto the second surface of the nylon film opposite the sealant film. This film exhibits good, permanent antifog properties and avoids migration of the antifog composition out of the sealant film.
Nylons are conventionally used in the art of multilayered packaging films. Suitable nylons within the scope of the invention non-exclusively include homopolymers or copolymers selected from aliphatic polyamides and aliphatic/aromatic polyamides having a molecular weight of from about 10,000 to about 100,000. General procedures useful for the preparation of polyamides are well known to the art. Such include the reaction products of diacids with diamines. Useful diacids for making polyamides include dicarboxylic acids which are represented by the general formula
HOOCxe2x80x94Zxe2x80x94COOH
wherein Z is representative of a divalent aliphatic radical containing at least 2 carbon atoms, such as adipic acid, sebacic acid, octadecanedioic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid, and glutaric acid. The dicarboxylic acids may be aliphatic acids, or aromatic acids such as isophthalic acid and terephthalic acid. Suitable diamines for making polyamides include those having the formula
H2N(CH2)nNH2
wherein n has an integer value of 1-16, and includes such compounds as trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, hexadecamethylenediamine, aromatic diamines such as p-phenylenediamine, 4,4xe2x80x2-diaminodiphenyl ether, 4,4xe2x80x2-diaminodiphenyl sulfone, 4,4xe2x80x2-diaminodiphenylmethane, alkylated diamines such as 2,2-dimethylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4 trimethylpentamethylenediamine, as well as cycloaliphatic diamines, such as diaminodicyclohexylmethane, and other compounds. Other useful diamines include heptamethylenediamine, nonamethylenediamine, and the like.
Useful polyamide homopolymers include poly(4-aminobutyric acid) (nylon 4), poly(6-aminohexanoic acid) (nylon 6, also known as poly(caprolactam)), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-aminoundecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), nylon 4,6, poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(hexamethylene azelamide) (nylon 6,9), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(tetramethylenediamine-co-oxalic acid) (nylon 4,2), the polyamide of n-dodecanedioic acid and hexamethylenediamine (nylon 6,12), the polyamide of dodecamethylenediamine and n-dodecanedioic acid (nylon 12,12) and the like. Useful aliphatic polyamide copolymers include caprolactam/hexamethylene adipamide copolymer (nylon 6,6/6), hexamethylene adipamide/caprolactam copolymer (nylon 6/6,6), trimethylene adipamide/hexamethylene azelaiamide copolymer (nylon trimethyl 6,2/6,2), hexamethylene adipamide-hexamethylene-azelaiamide caprolactam copolymer (nylon 6,6/6,9/6) and the like. Also included are other nylons which are not particularly delineated here. Of these polyamides, preferred polyamides include nylon 6, nylon 6,6, nylon 6/6,6 as well as mixtures of the same.
Aliphatic polyamides used in the practice of this invention may be obtained from commercial sources or prepared in accordance with known preparatory techniques. For example, poly(caprolactam) can be obtained from Honeywell International Inc., Morristown, N.J. under the trademark CAPRON(copyright).
Exemplary of aliphatic/aromatic polyamides include poly(tetramethylenediamine-co-isophthalic acid) (nylon 4,I), polyhexamethylene isophthalamide (nylon 6,I), hexamethylene adipamide/hexamethylene-isophthalamide (nylon 6,6/6I), hexamethylene adipamide/hexamethylene-terephthalamide (nylon 6,6/6T), poly (2,2,2-trimethyl hexamethylene terephthalamide), poly(m-xylylene adipamide) (MXD6), poly(p-xylylene adipamide), poly(hexamethylene terephthalamide), poly(dodecamethylene terephthalamide), polyamide 6T/6I, polyamide 6/MXDT/I, polyamide MXDI, and the like. Blends of two or more aliphatic/aromatic polyamides can also be used. Aliphatic/aromatic polyamides can be prepared by known preparative techniques or can be obtained from commercial sources. Other suitable polyamides are described in U.S. Pat. Nos. 4,826,955 and 5,541,267, which are incorporated herein by reference.
Positioned on a surface of the nylon film is a heat sealable sealant film which improves the ability of the multilayered film to be sealed onto a package. The sealant film is preferably comprised of polyethylene, and has an antifog composition that is either combined with the polyethylene or coated on a surface of the sealant film opposite the nylon film. Non-limiting examples of suitable polyethylenes are low density polyethylene (LDPE), linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), linear very-low density polyethylene (VLDPE), linear ultra-low density polyethylene (ULDPE), metallocene linear low density polyethylene (MLLDPE) high density polyethylene (HDPE). Of these, the most preferred is linear low density polyethylene.
The antifog composition prevents condensation on the film when used to package products such as fresh meats, vegetables, etc. Non-limiting examples of antifog compositions are glycerol monoesters of a saturated or unsaturated fatty acid having from about 8 to about 20 carbon atoms, glycerol diesters of a saturated or unsaturated fatty acid having from about 8 to about 20 carbon atoms and ionic surfactants having phosphate, sulfate or quaternary amine functional end groups. Also suitable as antifog compositions are surfactants including anionic, cationic, nonionic and amphoteric surfactants. Suitable ionic surfactants have phosphate, sulfate or quaternary amine functional end groups. Other antifog compositions include sorbitan esters of aliphatic carboxylic acids, glycerol esters of aliphatic carboxylic acids, esters of other polyhydric alcohols with aliphatic carboxylic acids, polyoxyethylene compounds, such as the polyoxyethylene sorbitan esters of aliphatic carboxylic acids and polyoxyethylene ethers of higher aliphatic alcohols. Preferred antifog compositions are glycerol monooleate, glycerol monostearate, sorbitan esters and blends thereof. When the antifog composition is incorporated into the sealant film, it is blended into the polyethylene composition preferably in an amount of from about 0.1 weight percent to about 5 weight percent. When the antifog composition is coated on the sealant film it is preferably applied at a coating weight of from about 0.2 to about 0.6 g/m2. Suitable antifog compositions are described, for example, in U.S. Pat. No. 5,766,772.
In an alternate embodiment of the invention, the sealant film may be comprised of a combination of various individual layers in addition to polyethylene. For example, the sealant film may comprise a structure comprising a heat sealable first polyethylene layer, an ethylene vinyl alcohol layer, a second polyethylene layer and an antifog layer (or an antifog composition containing second polyethylene layer). In yet another embodiment, the sealant film may comprise a structure comprising a polyolefin layer, a first polyethylene layer, an adhesive tie layer, an ethylene vinyl alcohol layer, another adhesive tie layer, a second polyethylene layer and an antifog composition containing third polyethylene layer. These structures may be formed either by lamination or by coextrusion of the individual layers.
In the latter embodiment, suitable polyolefins include polymers of alpha-olefin monomers having from about 2 to about 6 carbon atoms and includes homopolymers, copolymers (including graft copolymers), and terpolymers of alpha-olefins. Illustrative homopolymer examples include ultra low density (ULDPE), low density (LDPE), linear low density (LLDPE), medium density (MDPE), or high density polyethylene (HDPE); polypropylene; polybutylene; polybutene-1; poly-3-methylbutene-1; poly-pentene-1; poly-4-methylpentene-1; polyisobutylene; and polyhexene.
Polyolefins such as polyethylenes are commonly differentiated based on the density which results from their numbers of chain branches per 1,000 carbon atoms in the polyethylene main chain in the molecular structure. Branches typically are C3-C8 olefins, and which are preferably butene, hexene or octene. For example, HDPE has very low numbers of short chain branches (less than 20 per 1,000 carbon atoms), resulting in a relatively high density, i.e. density ranges from about 0.94 gm/cc to about 0.97 gm/cc. LLDPE has more short chain branches, in the range of 20 to 60 per 1,000 carbon atoms with a density of about 0.91 to about 0.93 gm/cc. LDPE with a density of about 0.91 to about 0.93 gm/cc has long chain branches (20-40 per 1,000 carbon atoms) instead of short chain branches in LLDPE and HDPE. ULDPE has a higher concentration of short chain branches than LLDPE and HDPE, i.e. in the range of about 80 to about 250 per 1,000 carbon atoms and has a density of from about 0.88 to about 0.91 gm/cc.
Illustrative copolymer and terpolymers include copolymers and terpolymers of alpha-olefins with other olefins such as ethylene-propylene copolymers; ethylene-butene copolymers; ethylene-pentene copolymers; ethylene-hexene copolymers; and ethylene-propylene-diene copolymers (EPDM). Preferred polyolefins are those prepared from alpha-olefins, and are most preferably ethylene polymers, copolymers, and terpolymers. The above polyolefins may be obtained by any known process. The polyolefin may have a weight average molecular weight of about 1,000 to about 1,000,000, and preferably about 10,000 to about 500,000. Preferred polyolefins are polyethylene, polypropylene, polybutylene and copolymers, and blends thereof. The most preferred polyolefin is polyethylene.
Suitable polyethylenes are those described above. This polyethylene layer may be attached to an ethylene vinyl alcohol layer, preferably via an intermediate adhesive tie layer. Suitable adhesive materials include polyurethanes, epoxies, polyesters, acrylics, anhydride modified polyolefin and blends thereof. Modified polyolefin compositions have at least one functional moiety preferably selected from the group consisting of unsaturated polycarboxylic acids and anhydrides thereof. Such unsaturated carboxylic acid and anhydrides include maleic acid and anhydride, fumaric acid and anhydride, crotonic acid and anhydride, citraconic acid and anhydride, itaconic acid an anhydride and the like. The adhesive layer may also optionally comprise a colorant, an ultraviolet light absorber or both. The adhesive layer may be applied either directly onto the nylon film or onto the polyethylene layer by any appropriate means in the art, such as by coating.
Ethylene vinyl alcohol compounds are well known in the art and readily commercially available. Copolymers of ethylene and vinyl alcohol suitable for use in the present invention can be prepared, for example, by the methods disclosed in U.S. Pat. Nos. 3,510,464; 3,560,461; 3,847,845; 3,595,740 and 3,585,177. The ethylene vinyl alcohol copolymer can be a hydrolyzed ethylene vinyl acetate copolymer. The degree of hydrolysis can range from about 85% to about 99.5%. The ethylene vinyl alcohol copolymer preferably contains from about 15 to about 65 mol percent ethylene and more preferably about 25 to about 50 mol percent ethylene. Copolymers of lower than 15 mol percent ethylene tend to be difficult to extrude while those above 65 mol percent ethylene have reduced oxygen barrier performance. The term xe2x80x9cethylene/vinyl alcohol copolymerxe2x80x9d or xe2x80x9cEVOHxe2x80x9d is intended to comprise also the hydrolyzed or saponified ethylene/vinyl acetate copolymers and refers to a vinyl alcohol copolymer having an ethylene comonomer, which may be obtained, for example, by the hydrolysis of an ethylene/vinyl acetate copolymer or by chemical reaction of ethylene monomers with vinyl alcohol.
Applied onto an opposite surface of the nylon film is a protective film. This protective film may comprise a material selected from the group consisting of polyurethane, polyvinylidene chloride (with or without a primer), acrylics, polyester polyols, and amine modified polyurethanes. Suitable primers include acrylics, urethanes, polyester polyols or amine modified polyurethanes.
These materials may be crosslinked with suitable crosslinking agents as is well known in the art. Suitable crosslinking agents include but are not limited to aromatic diisocyanates, such as toluene diisocyanate, aliphatic diisocyanates, such as hexamethylene diisocyanate, glycol adducts of isocyanates, prepolymers made from isocyanate monomers and butylated-melamine or methylated-melamine formaldehydes. In an additional embodiment of the invention, a layer of a polyvinylidene chloride may optionally be applied onto a surface of the protective film that is not adjacent to the nylon film.
In the preferred embodiment of the invention the protective film is coated onto the outer surface of the nylon film which is opposite the surface at which the sealant film is attached. Suitable coating methods include dip coating, meniscus coating, roller coating, doctor blade coating, and the like which are well known in the art.
Each of the nylon film, sealant film and protective film may optionally also include one or more conventional additives whose uses are well known to those skilled in the art. The use of such additives may be desirable in enhancing the processing of the compositions as well as improving the products or articles formed therefrom. Examples of such include: oxidative and thermal stabilizers, lubricants, release agents, flame-retarding agents, oxidation inhibitors, oxidation scavengers, dyes, pigments and other coloring agents, ultraviolet light absorbers and stabilizers, organic or inorganic fillers including particulate and fibrous fillers, reinforcing agents, nucleators, plasticizers, as well as other conventional additives known to the art. Such may be used in amounts, for example, of up to about 10% by weight of the overall composition. Representative ultraviolet light stabilizers include various substituted resorcinols, salicylates, benzotriazole, benzophenones, and the like. Suitable lubricants and release agents include stearic acid, stearyl alcohol, and stearamides. Exemplary flame-retardants include organic halogenated compounds, including decabromodiphenyl ether and the like as well as inorganic compounds. Suitable coloring agents including dyes and pigments include cadmium sulfide, cadmium selenide, titanium dioxide, phthalocyanines, ultramarine blue, nigrosine, carbon black and the like. Representative oxidative and thermal stabilizers include the Period Table of Element""s Group I metal halides, such as sodium halides, potassium halides, lithium halides; as well as cuprous halides; and further, chlorides, bromides, iodides. Also, hindered phenols, hydroquinones, aromatic amines as well as substituted members of those above mentioned groups and combinations thereof. Exemplary plasticizers include lactams such as caprolactam and lauryl lactam, sulfonamides such as o,p-toluenesulfonamide and N-ethyl, N-butyl benzylnesulfonamide, and combinations of any of the above, as well as other plasticizers known to the art.
Each of the layers may be joined together by coextrusion. In the coextrusion process, for example, the polymeric material for the individual layers are fed into infeed hoppers of a like number of extruders, each extruder handling the material for one or more of the layers. The melted and plasticated streams from the individual extruders are fed into a single manifold co-extrusion die. While in the die, the layers are juxtaposed and combined, then emerge from the die as a single multiple layer film of polymeric material. After exiting the die, the film is cast onto a first controlled temperature casting roll, passes around the first roll, and then onto a second controlled temperature roll, which is normally cooler than the first roll. The controlled temperature rolls largely control the rate of cooling of the film after it exits the die. Additional rolls may be employed. In another method, the film forming apparatus may be one which is referred to in the art as a blown film apparatus and includes a multi-manifold circular die head for bubble blown film through which the plasticized film composition is forced and formed into a film bubble which may ultimately be collapsed and formed into a film. Processes of coextrusion to form film and sheet laminates are generally known. Typical coextrusion techniques are described in U.S. Pat. Nos. 5,139,878 and 4,677,017.
Alternately the individual films may first be formed as separate layers and then laminated together under heat and pressure with or without intermediate adhesive layers. Lamination techniques are well known in the art. Typically, laminating is done by positioning the individual layers on one another under conditions of sufficient heat and pressure to cause the layers to combine into a unitary film. Typically the nylon film and the antifog composition containing sealant film will be positioned on one another, and the combination is passed through the nip of a pair of heated laminating rollers by techniques well known in the art. Lamination heating may be done at temperatures ranging from about 120xc2x0 C. to about 175xc2x0 C., preferably from about 150xc2x0 C. to about 175xc2x0 C., at pressures ranging from about 5 psig (0.034 MPa) to about 100 psig (0.69 MPa), for from about 5 seconds to about 5 minutes, preferably from about 30 seconds to about 1 minute. Further, when the sealant film comprises the multilayered structure described above, it is preferred that the individual layers are laminated together. However, it is most preferred that the nylon film be coextruded.
In one embodiment of the invention, the nylon film is oriented prior to being attached to the sealant film. For the purposes of the present invention the term draw ratio is an indication of the increase in the dimension in the direction of draw. Preferably, in the present invention the nylon film is drawn to a draw ratio of from 1.5:1 to 5:1 uniaxially in at least one direction, i.e. its longitudinal direction, its transverse direction or biaxially in each of its longitudinal and transverse directions. Preferably, the nylon film is simultaneously biaxially oriented, for example orienting a plasticized film in both the machine and transverse directions at the same. This results in dramatic improvements in clarity strength and toughness properties. Preferably, the nylon film is biaxially oriented and is not heat set so that it is shrinkable both in its transverse and longitudinal directions.
Although each layer of the multilayer film structure may have a different thickness, the thickness of the nylon film is preferably from about 1 xcexcm to about 25 xcexcm, more preferably from about 3 xcexcm to about 8 xcexcm, and most preferably from about 4 xcexcm to about 6 xcexcm. The thickness of the protective film is preferably from about 1 xcexcm to about 25 xcexcm, more preferably from about 2 xcexcm to about 8 xcexcm and most preferably from about 3 xcexcm to about 5 xcexcm. The thickness of the sealant film is preferably from about 1 xcexcm to about 50 xcexcm, more preferably from about 10 xcexcm to about 30 xcexcm, and most preferably from about 12 xcexcm to about 25 xcexcm. If a multicomponent sealant film is included rather than an individual antifog containing polyethylene layer, the thickness of that multicomponent sealant film is preferably within this range. While such thicknesses are preferred, it is to be understood that other film thicknesses may be produced to satisfy a particular need and yet fall within the scope of the present invention.
The oxygen transmission rate (OTR) of the multilayered film of the invention may be determined via the procedure of ASTM D-3985. In the preferred embodiment, the multilayered film according to this invention has an OTR of about 0.5 cc/100 in2/day or less, preferably from about 0.1 cc/100 in2/day or less and more preferably from about 0.05 cc/100 in2/day or less at 65% relative humidity at 20xc2x0 C.
The multilayered film of the invention is preferably heat shrinkable, generally by an amount of from about 2% to about 30%, more preferably from about 10% to about 20% in its length, or its width or each of its length and width. To provide a tightly adhering lid for a tray, for example, the film only need to exhibit shrinkage on the order of about 2 to about 3%. However, in order to have the film also form (unrestrained) about the side of the tray, higher shrinkage in the film is desirable. The multilayered film may further have printed indicia on the nylon film. Since such printing is on an internal surface of the structure, it will not rub off when the surface is contacted. Optionally, the multilayered film may be uniaxially or biaxially oriented in a manner and in an amount indicated above for the nylon film and is not heat set so that it is shrinkable both in its transverse and longitudinal directions. In this case the nylon film may or may not have been oriented already.
The film preferably has a puncture resistance of at least about 10 lbs. force as measured by ASTM F 1306, and preferably higher than 10 lbs. force. Preferably the film has a haze of about 4% or less and a clarity of about 92% or higher as measured by ASTM D1003.
The multilayered film may be formed into and stored as a roll. It has been found that the unique structure of this inventive film is particularly effective in preventing the migration of the antifog material from the polyethylene of the sealant film to the nylon film when in roll form.
The multilayered film is useful for forming a food package including a container, such as a tray, having an open portion and the multilayered film sealing the open portion. Such a structure is generally referred to a lidding or packaging film. Such containers are suitable for packaging a variety of raw meats such as beef, pork, poultry, and veal, among others. A packaged food may comprises the food package and a food product such as a meat in the food package.
The container may have enclosed side walls, a floor and an top opening defining a central cavity wherein the open top optionally has a substantially flat peripheral rim. The multilayered film surrounds the container and is heat shrunk and heat sealed to it such that the antifog composition is on the open portion (facing inward) and the protective film is facing away from the open portion of the container. The container may comprise a material such as cardboard, paperboard, boardstock, a plastic and combinations thereof. Preferred plastics include any one of several thermosetting or thermoplastic resins any of which are capable of sealing to the lidding material. Examples of materials include acrylonitrile, an acrylic polymer, polyethylene terephthalate (PET) or copolymers thereof, polyvinyl chloride, polycarbonate, polystyrene and polypropylene. In use the multilayered film is positioned around the open portion and is caused to shrink, e.g. by the application of heat, by a sufficient amount to seal the open portion of the container.
The invention further contemplates additional layers being attached to the multilayered film either before or after attaching the nylon film. For example, the nylon film of the invention may comprise a single nylon layer, or may also comprise additional layers. In particular, the nylon film may comprise a structure comprising a first nylon layer, an ethylene vinyl alcohol layer and a second nylon layer. In this embodiment, an ethylene vinyl alcohol layer is positioned onto a first surface of a first nylon layer, a second nylon layer is positioned on a surface of the ethylene vinyl alcohol layer opposite the first nylon layer, a sealant film is positioned on a surface of the second nylon layer opposite the ethylene vinyl alcohol layer, and a protective film is applied on a second surface of the first nylon film. Additionally, an antifog composition is preferably either contained within at least part of the sealant film or coated on a surface of the sealant film opposite the second nylon layer. In this embodiment, each of the layers are preferably attached by coextrusion, but may also be attached by lamination with or without an intermediate adhesive layer.
The following non-limiting examples serve to illustrate the invention.

Antifog/barrier laminate for use in meat packaging


Certain embodiments of the present invention provide a method for communicating inbound network data to provide QoS. The method includes receiving data over a network at a node, prioritizing the data at the node by assigning a priority to the data, and communicating the data to an application at the node based at least in part on the priority of the data. The data priority is based at least in part on message content. Certain embodiments of the present invention provide a system for communicating inbound networking data to provide QoS. The system includes a data prioritization component adapted to prioritize data by assigning a priority to the data and a data communications component adapted to receive the data over a network and to communicate the data to an application based at least in part on the priority of the data. The data priority is based at least in part on message content.

The present invention generally relates to communications networks. More particularly, the present invention relates to systems and methods for inbound content-based Quality of Service.
Communications networks are utilized in a variety of environments. Communications networks typically include two or more nodes connected by one or more links. Generally, a communications network is used to support communication between two or more participant nodes over the links and intermediate nodes in the communications network. There may be many kinds of nodes in the network. For example, a network may include nodes such as clients, servers, workstations, switches, and/or routers. Links may be, for example, based modem connections over phone lines, wires, Ethernet links, Asynchronous Transfer Mode (ATM) circuits, satellite links, and/or fiber optic cables.
A communications network may actually be composed of one or more smaller communications networks. For example, the Internet is often described as network of interconnected computer networks. Each network may utilize a different architecture and/or topology. For example, one network may be a switched Ethernet network with a star topology and another network may be a Fiber-Distributed Data Interface (FDDI) ring.
Communications networks may carry a wide variety of data. For example, a network may carry bulk file transfers alongside data for interactive real-time conversations. The data sent on a network is often sent in packets, cells, or frames. Alternatively, data may be sent as a stream. In some instances, a stream or flow of data may actually be a sequence of packets. Networks such as the Internet provide general purpose data paths between a range of nodes and carrying a vast array of data with different requirements.
Communication over a network typically involves multiple levels of communication protocols. A protocol stack, also referred to as a networking stack or protocol suite, refers to a collection of protocols used for communication. Each protocol may be focused on a particular type of capability or form of communication. For example, one protocol may be concerned with the electrical signals needed to communicate with devices connected by a copper wire. Other protocols may address ordering and reliable transmission between two nodes separated by many intermediate nodes, for example.
Protocols in a protocol stack typically exist in a hierarchy. Often, protocols are classified into layers. One reference model for protocol layers is the Open Systems Interconnection (OSI) model. The OSI reference model includes seven layers: a physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer. The physical layer is the "lowest" layer, while the application layer is the "highest" layer. Two well-known transport layer protocols are the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). A well known network layer protocol is the Internet Protocol (IP).
At the transmitting node, data to be transmitted is passed down the layers of the protocol stack, from highest to lowest. Conversely, at the receiving node, the data is passed up the layers, from lowest to highest. At each layer, the data may be manipulated by the protocol handling communication at that layer. For example, a transport layer protocol may add a header to the data that allows for ordering of packets upon arrival at a destination node. Depending on the application, some layers may not be used, or even present, and data may just be passed through.
One kind of communications network is a tactical data network. A tactical data network may also be referred to as a tactical communications network. A tactical data network may be utilized by units within an organization such as a military (e.g., army, navy, and/or air force). Nodes within a tactical data network may include, for example, individual soldiers, aircraft, command units, satellites, and/or radios. A tactical data network may be used for communicating data such as voice, position telemetry, sensor data, and/or real-time video.
An example of how a tactical data network may be employed is as follows. A logistics convoy may be in-route to provide supplies for a combat unit in the field. Both the convoy and the combat unit may be providing position telemetry to a command post over satellite radio links. An unmanned aerial vehicle (UAV) may be patrolling along the road the convoy is taking and transmitting real-time video data to the command post over a satellite radio link also. At the command post, an analyst may be examining the video data while a controller is tasking the UAV to provide video for a specific section of road. The analyst may then spot an improvised explosive device (IED) that the convoy is approaching and send out an order over a direct radio link to the convoy for it to halt and alerting the convoy to the presence of the IED.
The various networks that may exist within a tactical data network may have many different architectures and characteristics. For example, a network in a command unit may include a gigabit Ethernet local area network (LAN) along with radio links to satellites and field units that operate with much lower throughput and higher latency. Field units may communicate both via satellite and via direct path radio frequency (RF). Data may be sent point-to-point, multicast, or broadcast, depending on the nature of the data and/or the specific physical characteristics of the network. A network may include radios, for example, set up to relay data. In addition, a network may include a high frequency (HF) network which allows long rang communication. A microwave network may also be used, for example. Due to the diversity of the types of links and nodes, among other reasons, tactical networks often have overly complex network addressing schemes and routing tables. In addition, some networks, such as radio-based networks, may operate using bursts. That is, rather than continuously transmitting data, they send periodic bursts of data. This is useful because the radios are broadcasting on a particular channel that must be shared by all participants, and only one radio may transmit at a time.
Tactical data networks are generally bandwidth-constrained. That is, there is typically more data to be communicated than bandwidth available at any given point in time. These constraints may be due to either the demand for bandwidth exceeding the supply, and/or the available communications technology not supplying enough bandwidth to meet the user's needs, for example. For example, between some nodes, bandwidth may be on the order of kilobits/sec. In bandwidth-constrained tactical data networks, less important data can clog the network, preventing more important data from getting through in a timely fashion, or even arriving at a receiving node at all. In addition, portions of the networks may include internal buffering to compensate for unreliable links. This may cause additional delays. Further, when the buffers get full, data may be dropped.
In many instances the bandwidth available to a network cannot be increased. For example, the bandwidth available over a satellite communications link may be fixed and cannot effectively be increased without deploying another satellite. In these situations, bandwidth must be managed rather than simply expanded to handle demand. In large systems, network bandwidth is a critical resource. It is desirable for applications to utilize bandwidth as efficiently as possible. In addition, it is desirable that applications avoid "clogging the pipe," that is, overwhelming links with data, when bandwidth is limited. When bandwidth allocation changes, applications should preferably react. Bandwidth can change dynamically due to, for example, quality of service, jamming, signal obstruction, priority reallocation, and line-of-sight. Networks can be highly volatile and available bandwidth can change dramatically and without notice.
In addition to bandwidth constraints, tactical data networks may experience high latency. For example, a network involving communication over a satellite link may incur latency on the order of half a second or more. For some communications this may not be a problem, but for others, such as real-time, interactive communication (e.g., voice communications), it is highly desirable to minimize latency as much as possible.
Another characteristic common to many tactical data networks is data loss. Data may be lost due to a variety of reasons. For example, a node with data to send may be damaged or destroyed. As another example, a destination node may temporarily drop off of the network. This may occur because, for example, the node has moved out of range, the communication's link is obstructed, and/or the node is being jammed. Data may be lost because the destination node is not able to receive it and intermediate nodes lack sufficient capacity to buffer the data until the destination node becomes available. Additionally, intermediate nodes may not buffer the data at all, instead leaving it to the sending node to determine if the data ever actually arrived at the destination.
Often, applications in a tactical data network are unaware of and/or do not account for the particular characteristics of the network. For example, an application may simply assume it has as much bandwidth available to it as it needs. As another example, an application may assume that data will not be lost in the network. Applications which do not take into consideration the specific characteristics of the underlying communications network may behave in ways that actually exacerbate problems. For example, an application may continuously send a stream of data that could just as effectively be sent less frequently in larger bundles. The continuous stream may incur much greater overhead in, for example, a broadcast radio network that effectively starves other nodes from communicating, whereas less frequent bursts would allow the shared bandwidth to be used more effectively.
Certain protocols do not work well over tactical data networks. For example, a protocol such as TCP may not function well over a radio-based tactical network because of the high loss rates and latency such a network may encounter. TCP requires several forms of handshaking and acknowledgments to occur in order to send data. High latency and loss may result in TCP hitting time outs and not being able to send much, if any, meaningful data over such a network.
Information communicated with a tactical data network often has various levels of priority with respect to other data in the network. For example, threat warning receivers in an aircraft may have higher priority than position telemetry information for troops on the ground miles away. As another example, orders from headquarters regarding engagement may have higher priority than logistical communications behind friendly lines. The priority level may depend on the particular situation of the sender and/or receiver. For example, position telemetry data may be of much higher priority when a unit is actively engaged in combat as compared to when the unit is merely following a standard patrol route. Similarly, real-time video data from an UAV may have higher priority when it is over the target area as opposed to when it is merely in-route.
There are several approaches to delivering data over a network. One approach, used by many communications networks, is a "best effort" approach. That is, data being communicated will be handled as well as the network can, given other demands, with regard to capacity, latency, reliability, ordering, and errors. Thus, the network provides no guarantees that any given piece of data will reach its destination in a timely manner, or at all. Additionally, no guarantees are made that data will arrive in the order sent or even without transmission errors changing one or more bits in the data.
Another approach is Quality of Service (QoS). QoS refers to one or more capabilities of a network to provide various forms of guarantees with regard to data that is carried. For example, a network supporting QoS may guarantee a certain amount of bandwidth to a data stream. As another example, a network may guarantee that packets between two particular nodes have some maximum latency. Such a guarantee may be useful in the case of a voice communication where the two nodes are two people having a conversation over the network. Delays in data delivery in such a case may result in irritating gaps in communication and/or dead silence, for example.
QoS may be viewed as the capability of a network to provide better service to selected network traffic. The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. Another important goal is making sure that providing priority for one flow does not make other flows fail. That is, guarantees made for subsequent flows must not break the guarantees made to existing flows.
Current approaches to QoS often require every node in a network to support QoS, or, at the very least, for every node in the network involved in a particular communication to support QoS. For example, in current systems, in order to provide a latency guarantee between two nodes, every node carrying the traffic between those two nodes must be aware of and agree to honor, and be capable of honoring, the guarantee.
There are several approaches to providing QoS. One approach is Integrated Services, or "IntServ." IntServ provides a QoS system wherein every node in the network supports the services and those services are reserved when a connection is set up. IntServ does not scale well because of the large amount of state information that must be maintained at every node and the overhead associated with setting up such connections.
Another approach to providing QoS is Differentiated Services, or "DiffServ." DiffServ is a class of service model that enhances the best-effort services of a network such as the Internet. DiffServ differentiates traffic by user, service requirements, and other criteria. Then, DiffServ marks packets so that network nodes can provide different levels of service via priority queuing or bandwidth allocation, or by choosing dedicated routes for specific traffic flows. Typically, a node has a variety of queues for each class of service. The node then selects the next packet to send from those queues based on the class categories.
Existing QoS solutions are often network specific and each network type or architecture may require a different QoS configuration. Due to the mechanisms existing QoS solutions utilize, messages that look the same to current QoS systems may actually have different priorities based on message content. However, data consumers may require access to high-priority data without being flooded by lower-priority data. Existing QoS systems cannot provide QoS based on message content at the transport layer.
As mentioned, existing QoS solutions require at least the nodes involved in a particular communication to support QoS. However, the nodes at the "edge" of network may be adapted to provide some improvement in QoS, even if they are incapable of making total guarantees. Nodes are considered to be at the edge of the network if they are the participating nodes in a communication (i.e., the transmitting and/or receiving nodes) and/or if they are located at chokepoints in the network. A chokepoint is a section of the network where all traffic must pass to another portion. For example, a router or gateway from a LAN to a satellite link would be a choke point, since all traffic from the LAN to any nodes not on the LAN must pass through the gateway to the satellite link.
Thus, there is a need for systems and methods providing QoS in a tactical data network. There is a need for systems and methods for providing QoS on the edge of a tactical data network. Additionally, there is a need for adaptive, configurable QoS systems and methods in a tactical data network.

Method and system for inbound content-based QoS


A catalyst for olefin polymerization of the formula:

The invention relates to a metallocene catalyst useful in preparing syndiotactic/atactic block polyolefins and to the polymers so obtained. The catalyst comprises a bridged monocyclopentadienyl metallocene in which the cyclopentadienyl is part of a fluorene ligand which is substituted symmetrically with respect to the active coordination position and is 3,6 substituted. The invention further includes a process of preparing syndiotactic/actactic block polyolefins that comprises the use of the present catalyst.
The present invention also provides a process for polymerising olefins having three or more carbon atoms to produce polymers with syndiotactic/atactic stereochemical configurations. The catalyst and process of the invention are particularly useful in polymerising propylene to form a syndiotactic/atactic block polypropylene.
As known in the art, syndiotactic polymers have a unique stereochemical structure in which monomeric units having enantiomorphic configuration of the asymmetrical carbon atoms follow each other alternately and regularly in the macromolecular main chain. Syndiotactic polypropylene was first disclosed by Natta et al. in U.S. Pat. No. 3,258,455. The Natta group obtained syndiotactic polypropylene by using a catalyst prepared from titanium trichloride and dietyl aluminium monochloride. A later patent to Natta et al., U.S. Pat. No. 3,305,538, discloses the use of vanadium triacetylacetonate or halogenated vanadium compounds in combination with organic aluminium compounds for producing syndiotactic polypropylene.
U.S. Pat. No. 3,364,190 to Emrick discloses a catalyst system composed of finely divided titanium or vanadium trichloride, aluminium chloride, a trialkyl aluminium and a phosphorus-containing Lewis base as producing syndiotactic polypropylene. U.S. Pat. No. 4,892,851 discloses a metallocene catalyst for producing highly crystalline syndiotactic polyolefins.
As disclosed in these patent references and as known in the art, the structure and properties of syndiotactic polypropylene differ significantly from those of isotactic polypropylene. The isotactic structure is typically described as having the methyl groups attached to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the main chain of the polymer, e.g., the methyl groups are all above or below the plane. Using the Fischer projection formula, the sterochemical sequence of isotactic polypropylene is described as follows:
Another way of describing the structure is through the use of NMR. Bovey""s NMR nomenclature of an isotactic pentad is . . . mmmm . . . with each xe2x80x9cmxe2x80x9d representing a xe2x80x9cmesoxe2x80x9d dyad or successive methyl groups on the same side in the plane. As known in the art, any deviation or inversion in the structure of the chain lowers the degree of isotacticity and crystallinity of the polymer.
In contrast to the isotactic structures, syndiotactic polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the chain lie on alternate sides of the plane of the polymer. Using the Fischer projection formula, the structure of a syndiotactic polymer is designated as:
In NMR nomenclature, this pentad is described as . . . rrrr . . . in which each xe2x80x9crxe2x80x9d represents a xe2x80x9cracemicxe2x80x9d, i.e., successive methyl groups on alternate sides of the plane.
The percentage of r dyads in the chain determines the degree of syndiotacticity of the polymer. Syndiotactic polymers are crystalline and, like the isotactic polymers, are insoluble in xylene.
This crystallinity distinguishes both syndiotactic and isotactic polymers from an atactic polymer that is soluble in xylene. Atactic polymer exhibits no regular order of repeating unit configurations in the polymer chain and forms an essentially waxy product. While it is possible for a catalyst to produce all three types of polymer, it is desirable for a catalyst to produce predominantly syndiotactic or isotactic polymer with some atactic block fractions.
WO 98/02469 discloses use of metallocene catalysts in the formation of syndiotactic/atactic block homopolyolefins. The catalyst is a monocyclopentadienyl type catalyst. The cyclopentadienyl may be part of a fluorene ligand which is symmetrically substituted. The document is specifically concerned with 2,7 substituted fluorene ligands. However, the polymers produced using these catalysts do not have a melt temperature and are thus very sticky. This greatly reduces the utility of these polymers.
EP-A-0,931,814 discloses production of syndiotactic/atactic block polypropylene. The catalyst used in the production of the syndiotactic/atactic block polypropylene is a monocyclopentadienyl type catalyst. The cyclopentadienyl may be part of a fluorene ligand which is symmetrically substituted. The application is specifically concerned with 2,7 substituted fluorene ligands.
WO 96/00734 relates to group IV metal diene complexes and addition polymerisation catalysts produced therefrom. The document is particularly concerned with metallocenes having a cyclopentadienyl ligand and additionally a chelating alkenyl ligand.
Shiomura et al. disclose, in Macromol. Rapid Commun., 17, 9-14, (1996), inversion of stereoregularity in a metallocene catalyst. This document relates to an inversion of stereoselectivity of a particular metallocene from syndiospecific into isospecific by changing the cocatalyst. In particular, the document relates to an unsubstituted fluorene-containing metallocene.
EP-A-0,628,577 relates to fluorenyl-containing silyl bridged metallocenes, processes of using such metallocene to polymerise olefins and the syndiotactic polypropylene so produced. This document refers specifically to a 2,7-substituted fluorenyl type catalyst.
WO 93/19103 relates to a process and a metallocene catalyst system for the production of stereoregular polyolefins. The process permits improved control over tacticity, molecular weight and molecular weight distribution. In one example, the document relates to a polymerisation process employing a catalyst comprising an unsubstituted fluorene type ligand.
It is an object of the present invention to overcome the above and other problems associated with the prior art catalysts. Accordingly, the present invention provides a catalyst for the polymerisation of olefins of general formula:
Rxe2x80x3(C4Rxe2x80x2mC5C4Rxe2x80x2n)XMeQ
wherein X is an hetero-atom ligand with one or two lone pair electrons selected from the elements of Group VA or VIA which can be substituted or non-substituted; (C4Rmxe2x80x2C5C4Rnxe2x80x2) is a symmetrically substituted, 3,6-substituted fluorenyl; Rxe2x80x2 is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an alkylamino or alkylsilylo radical, each Rxe2x80x2 may be the same or different and m and n independently are 1, 2 3 or 4, with the proviso that the bilateral symmetry is maintained; Rxe2x80x3 is a structural bridge between X and the (C4Rxe2x80x2mC5C4Rxe2x80x2n) ring to impart stereorigidity; Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; and Me can be in any of its theoretically possible oxidation states.
The present invention further provides a process for preparing syndiotactic/atactic block polyolefins, and more particularly syndiotactic/actactic block polypropylene using the above catalyst. The catalyst and process can each be adapted to produce a polymer with differing syndio-/atactic block ratios.
The invention also provides syndiotactic/atactic block homopolyolefins and particularly a syndiotactic/atactic block homopolypropylene, obtainable using the present catalysts.
One advantage of the present catalysts is that they are capable of producing syndiotactic/actactic block homopolyolefins which are not sticky and which exhibit a melt temperature, unlike polymers produced using prior art catalysts. In addition, the present catalysts show good activity as compared with prior art catalysts.
The catalyst comprises a metallocene, i.e., a metal derivative of a cyclopentadiene, and an ionising agent. The metallocene compound contains only one substituted cyclopendadienyl ring and is of the general formula:
Rxe2x80x3(C4Rxe2x80x2mC5C4Rxe2x80x2n)XMeQ
wherein X is an hetero-atom ligand with one or two lone pair electrons and selected from the elements of Group VA or VIA and is preferably nitrogen, phosphorus, oxygen or sulfur, which can be substituted or non-substituted; (C4Rmxe2x80x2C5C4Rnxe2x80x2) is a symmetrically substituted fluorenyl which is 3,6-substituted hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylamino or alkylsilylo radical, each Rxe2x80x2 may be the same or different and m and n independently are 0, 1, 2, 3 or 4, with the proviso that the bilateral symmetry is maintained; Rxe2x80x2 is a structural bridge between the X and (C4Rmxe2x80x2C5C4Rnxe2x80x2) ring to impart stereorigidity and, preferably is a silyl or hydrocarbyl biradical having at least one silicon or carbon atom to form the bridge; Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Peridic Table of Elements; Me can be in any of its theoretically possible oxidation states. Preferred metals for the catalyst of the invention are Zr, Ti, and Hf.
It is particularly preferred that the fluorenyl group is 3,6 substituted and not substituted at any other position.
The term xe2x80x9csymmetricallyxe2x80x9d shall mean that the local bilateral symmetry of the active polymerisation sites is essentially maintained.
The present invention further provides a process for producing syndiotactic/atactic block polyolefins, particularly syndiotactic/atactic polypropylene. The process comprises utilising at least one of the catalysts described by the above formula and introducing the catalyst into a polymerisation reaction zone containing an olefin monomer. In addition, a co-catalyst such as alumoxane may be introduced into the reaction zone. Further, the catalyst may also be pre-polymerised prior to introducing it into the reaction zone and/or prior to the stabilisation of reaction condition in the reactor.
Metallocene catalysts are single site catalysts which, generally, produce polymers having a narrow molecular weight distribution.
While the present invention is mainly directed to xcex1-olefin homopolymerisation, co-polymerisation with other olefins can be carried out.
The present invention also provides for a new polymer comprising alternating blocks of syndiotactic and atactic sequences, preferably long syndiotactic and short atactic sequences, most preferably comprising a fraction of syndiotactic triads (rr) of at least 70%.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily understood by reference to the following detailed description.
The present invention provides a polymer comprising alternating blocks of syndiotactic and atactic sequences. The polymer of the invention possesses particularly long sequences of syndiotactic species and short sequences of atactic species. The syndio-/atactic ratio can easily be modified by changing the polymerisation conditions and/or the catalyst structure within the invention. For example, as shown below, increasing the polymerisation temperature for a given catalyst decreases the syndio-/atactic ratio. As also evidenced below, replacing a dimethylsilyl bridge by a diphenylsilyl bridge also decreases the syndio-/atactic ratio for identical polymerisation conditions.
In the specific case of polypropylene, it ahs been noted that the polymer has elastomeric properties. Without being bound by the theory, it may be considered that these properties are deriving from the combination of the crystalline syndiotactic part and the amorphous atactic part.
The polymer obtained has a molecular weight ranging from 50,000 to more than 1,000,000 depending on the polymerisation conditions and on the catalyst used in the process. For example, as shown below, replacing a dimethylsilyl bridge by a diphenylsilyl bridge results in increased molecular weight under identical polymerisation conditions.
The present invention provides a catalyst and process for the production of syndiotactic/atactic block polyolefins, particularly polypropylene. The catalysts of the present invention produce a polymer with a syndiotactic/atactic block microstructure.
The applicants have now unexpectedly found that the catalyst of the invention can be used for the production of high molecular weight polyalphaolefin with stereoregular/stereoirregular block micro-structure.
When propylene or other alpha-olefins are polymerised using a catalyst consisting of a transition metal compound, the polymer product typically comprises a random mixture (reactor blend) of amorphous atactic and crystalline xylene insoluble fractions. The crystalline fraction may contain either isotactic or syndiotactic polymer or a mixture of both. The catalysts of the present invention have syndio-/atactic specificity and produce polymeric chains with differing syndio-/atactic block ratios.
The metallocene catalysts of the present invention may be described by the formula:
Rxe2x80x3(C4Rxe2x80x2mC5C4Rxe2x80x2n)XMeQ
wherein X is an hetero atom ligand with one or two lone pair electrons and selected from the elements of Group VA or VIA and is preferably nitrogen, phosphorus, oxygen or sulfur which can be substituted or not.
(C4Rxe2x80x2mC5C4Rxe2x80x2n) is a fluorenyl ring, substituted symmetrically and substituted at the 3 and 6 positions each Rxe2x80x2 is hydrogen or hydrocarbyl radical having form 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylamino or alkylsilylo radical, each Rxe2x80x2 may be the same or different, m and n independently are 0, 1, 2, 3 or 4, and with the proviso that the bilateral symmetry is maintained; Rxe2x80x3 is a structural bridge between the hetero atom X and (C4Rxe2x80x2mC5C4Rxe2x80x2n) ring to impart stereorigidity, and preferably is a silyl or hydrocarbyl biradical having at least one silicon or carbon atom to form the bridge; Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen: Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; the transion metal can adopt any of the possible oxidation states. Preferred metals for the catalysts of the invention are Ti, Zr, and Hf. A particularly suitable metal is Ti. (C4Rxe2x80x2mC5C4Rxe2x80x24) comprises hydrocarbyl biradicals bonded to two adjacent carbon atoms in a cyclopentadienyl ring to form a fused ring.
In order to obtain syndiospecificity the cyclopentadienyl or fluorenyl rings in the metallocene catalysts must be substituted in an essentially symmetric manner with respect to the active coordination positions so that the metallocene exhibits bilateral symmetry at least around the active coordination site. It has been unexpectedly noted that if in the original syndiospecific catalysts described in U.S. Pat. No. 4,892,851 the non-substituted cyclopentadienyl is replaced by a heteroatom ligand with one or two lone pair electrons and selected from elements of Group VA or VI A, the stereospecificity of catalyst will be periodically changed from syndiospecificity to aspecificity during the polymerisation giving rise to the formation of atactic blocks within the predominantly syndiotactic chain.
Bilateral symmetry is defined as the condition in which there is no substituent or one or more substituents on one side and no substituent or one or more substituents on the other side in the same relative position such that a mirror image is formed from one side to another. One preferred example of such a compound is 3,6-di-tert-butyl-9-fluorenyl-dimethylsilyl-tert-butylamido titanium dichloride.
An illustration of the ligands of this compound is shown in the diagrams presented in Tables 1 and 2.
Bilateral symmetry is illustrated by a plane bisecting the fluorenyl and the bridge resulting the right side of each ligand being a mirror image of its left side. The numerical positions of the fluorenyl ring represent the position of possible substituents on the fluorenyl ring, 9 being the position of the bridge.
Whilst not wishing to be bound by a theory and without intending to limit the scope of the present invention as indicated by the claims, it is believed that during the polymerisation reaction the growing polymer chain migrates from one coordination position to the other after each monomer insertion as the catalyst simultaneously isomerises and enchains sequences of polymer of the syndiotactic structure; occasionally this mechanism is disturbed by a haptocity change of the fluorenyl-transition metal bonding or through inversion of the chiral nitrogen center, leading to the loss of steric control and formation of short sequences of atactic blocks within a predominantly syndiotactic polymer chain. This mechanism differs from that put forward for syndiospecific catalysts such as the active species formed from isopropylidene [cyclopentadienyl-9-fluorenyl] zirconium dichloride as disclosed in U.S. Pat. No. 4,892,851 wherein the fluorenyl ring exhibits mainly pentahapto bonding, i.e. all five carbon atoms of the fluorenyl rings are coordinated with the zirconium atom.
It is believed that the catalysts of the present invention demonstrate a reversible transformation of syndiospecific sites to atactic specific sites through a haptocity change related stereoregulation/stereoderegulation mechanism.
In theory, the steric condition for a preferred orientation of the growing chain, adoption of one of the two possible conformations, intermittently disappears and the coordination and insertion of either of the propylene prochiral faces at both lateral coordination positions becomes accidental. This mechanism enchains atactic sequences in a predominantly syndiotactic polymer chain by a spontaneous change in haptocity of the bonding between the fluorenyl and the transition metal from pentahapto to tri- and possibly mono-hapto bonding which results in the loss of stereoregulating property of the sites.
This electro-dynamic behaviour of the active species provides in effect a temporary transformation of enantiotopic, equivalent sites to non-enantiotopic, non-equivalent environment at the lateral coordination positions, atactic sequences being formed whenever this occurs. Theoretically, only when both events, i.e. periodic loss of stereoregularity and the stereospecific character of the catalyst occur simultaneously, is a syndiotactic/atactic block homopolymer formed.
When catalysts of the present invention are used in polymerisation of olefins, the polymer which results is of a syndio-/atactic microstructure as illustrated below:
In a preferred embodiment of the catalyst of the present invention (C4Rxe2x80x2mC5C4Rxe2x80x2n) is preferably a substituted fluorenyl ring with bulky substituents in 3 and 6 positions such as tert-butyl and trimethylsilyl; Me is preferably titanium, zirconium or hafnium, more preferably; zirconium or titanium and most preferably titanium; Q is preferably a halogen and is most preferably chlorine; and Rxe2x80x3 is preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon atom which is coordinated with the heteroatom ligand and with (C4Rxe2x80x2mC5C4Rxe2x80x24), most preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon atom being connected with heteroatom ligand and the (C4Rxe2x80x2mC5C4Rxe2x80x2Rn) moiety.
Exemplary hydrocarbyl biradicals for the structural bridge include ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and the likes. Other hydrocarbyl radicals useful as the structural bridge in the present catalysts include linear alkyl radicals of 1-10 carbon atoms or branched alkyl radicals of 1-20 carbon atoms, preferably one carbon atom, which may be substituted or unsubstituted, preferably substituted.
Exemplary silyl biradicals for a structural bridge include dimethylsilyl (which is preferred), diphenylsilyl of the general formula R2Sixe2x95x90, with each R independently being any C1-C20 hydrocarbyl or C1-C20 mono-, di- or trialkyl silyl radicals.
The catalyst may be prepared by any method known in the art. Generally, the preparation of the catalyst complex consists of forming and isolating the substituted cyclopentadienyl or fluorenyl ligands which are then reacted with a halogenated metal to form the complex. The preferred method is that disclosed in U.S. Pat. No. 4,892,851. The catalyst may further be supported on an organic or inorganic carrier. The synthesis process generally comprises the steps of (1) preparing the halogenated or alkylated metal compound, (2) preparing the ligand, (3) synthesizing the complex, and (4) purifying the complex.
The metalocene catalysts of the present invention are useful in many of the polymerisation processes (solution, slurry or gas phase) known in the art including many of those disclosed for the preparation of crystalline or amorphous polypropylene. When the catalysts of the present invention are used in these types of processes, the processes produce syndiotactic/atactic block polymers.
Further examples of polymerisation processes useful in the practice of the present invention include those disclosed in U.S. Pat. No. 4,767,735 and European Patent Application 310,734, the disclosure of which are hereby incorporated herein by reference. Those preferred polymerisation procedures include the step of prepolymerising the catalyst and/or precontacting the catalyst with a cocatalyst and an olefin monomer prior to introducing the catalyst into a reaction zone.
The ionising agent is an alumoxane, an aluminium alkyl, other Lewis acid or a combination thereof which will ionise a neutral metallocene compound to form a cationic metallocene catalyst. Examples of such ionising agents are methyl alumoxane (MAO), triethyl aluminium (TEA1) and tris (pentafluorophenyl)boron. Other ionising agents are disclosed in European Patents 277003 and 277004 which are hereby incorporated by reference.
The syndio-/atactic-specific catalysts of the present invention are particularly useful in combination with an aluminium alkyl cocatalyst or with an alumoxane, preferably with the latter.
In addition, a complex may be isolated between a metallocene catalyst as described herein and an aluminium cocatalyst in accordance with teachings of European Patent 226,463. As disclosed therein, a metallocene is reacted with an excess of alumoxane in the presence of a suitable solvent. A complex of the metallocene and alumoxane may be isolated and used as a catalyst in the present invention.
The Alumoxanes useful in combination with the catalysts of the present invention, either in the polymerisation reaction or in forming the complex disclosed above, may be represented by the general formula (Rxe2x80x94A1xe2x80x94Oxe2x80x94)n in the cyclic form and R(Rxe2x80x94A1xe2x80x94Oxe2x80x94)nAlR2 in the linear form, wherein R is an alkyl group with one to five carbon atoms and n is an integer from 1 to 20. Most preferably, R is a methyl group and the preferred alumoxane is methylalumoxane (MAO). The alumoxanes can be represented structurally as follows:
The alumoxanes can be prepared by various methods known in the art. Preferably, they are prepared by contacting water with a solution of trialkyl aluminium, such as trimethyl aluminium, in a suitable solvent such as benzene. Another preferred method includes the preparation of alumoxane in the presence of a hydrated copper sulfate as described in U.S. Pat. No. 4,404,344 the disclosure of which is hereby incorporated by reference. This method comprises treating a dilute solution of trimethyl aluminium in toluene with copper sulfate. The preparation of other aluminium cocatalysts useful in the present invention may be prepared by methods known to those skilled in the art.

Abstract: wherein X is an hetero atom ligand with one or two lone pair electrons selected from the elements of Group VA or VIA which is substituted or non-substituted: (C4Rmxe2x80x2C5C4Rnxe2x80x2) is a 3,6-substituted fluorenyl; Rxe2x80x2 is hydrogen or hydrocarbyl radical having 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an alkylamino or alkylsilyo radical, each Rxe2x80x2 being the same or different and m and n independently are 1, 2, 3 or 4, with bilateral symmetry maintained; Rxe2x80x3 is a structural bridge between S and (C4Rxe2x80x2mC5C4Rxe2x80x2n) to impart stereorigidity; Q is a hydrocarbyl radical having 1-20 carbon atoms or a halogen; Me is a Group IIIB, IVB, VB, or VIB metal having any of its theoretically possible oxidation states. Olefin monomers polymerised using these catalysts to form syndiotactic/atactic block polymers of high molecular weight and comprising at least 70% of syndiotactic triads.


Novel binder compositions have been discovered that offer an alternative to Portland Cement and reduced carbon dioxide footprint. The compositions typically include the reaction product of a mixture of fly ash, calcium oxide, nanosilica, water, and an effective amount of an activator. The 7, 14, and/or 28 day compressive strength may be at least about 15 MPa or more in some embodiments.

Despite the myriad of research efforts on exploiting fly ash as an alternative binder, its current role in industry is largely restricted to the supplementary use, which enables only partial replacement of conventional portland cement. Herein, we propose an unprecedented binder composite with the promising early-age strength, which is cost-effective and reduces the CO2 footprint compared with portland cement. The major constituent is fly ash occupying 76.4%-80.3% by the total mass of the constituents, while calcium oxide, nanosilica, and the minimum amounts of sodium-based activators are added to induce the early-age strength development. Optimization of the composition via the Taguchi design of experiments produced the early (7-day) compressive strength of 16.18 MPa. This value is encouraging considering that it is comparable to that of conventional portland cement and that a cementless composition with the minimum amounts of sodium-based activators was employed. The extensive materials analysis demonstrates that the starting Ca/Na molar ratio and the amount of nanosilica play instrumental roles in strength development by influencing the formation of key reaction products, which include the sodium-substituted AFm phase (the U-phase), katoite and portlandite. Overall, the promising strength coupled with the significantly decreased amount of sodium-based chemicals and the reduced CO2 footprint will lay a foundation for development of low-cost, environmentally friendly binder in diverse industries.

Synthesis of cementless fly ash based binders and applications thereof


A dispenser comprising at least two parallel, hollow cylinders for supplying different mutually reactive components to a mixing device located downstream of the cylinders. The dispenser comprises a respective first piston moveable in each of the cylinders and displaceable by a piston rod connected to the respective piston. A component for actuating the pistons rods to perform a forward stroke of the pistons in their respective cylinders for dispensing an amount of the reactive components to the mixing device comprises at least one rotatable member biased in a rotational direction by a torsion spring, and at least one flexible string attached to the rotatable member and to an element connected to the piston rods. A manually operable brake member is arranged to normally act on the rotatable member to hold it still, but, when deactivated, adapted to release the rotatable member thereby causing the pistons to dispense the reactive components to the mixing device.

The present invention relates in general to a dispenser comprising at least two parallel, hollow cylinders for supplying different mutually reactive components to a mixing device located downstream of said cylinders; a respective first piston moveable in each of the cylinders and displaceable by a piston rod connected to the respective piston; said pistons rods being interconnected for simultaneous dispensing of the components contained in the cylinders, when the piston rods and pistons are displaced in the cylinders towards a respective outlet therein; and a means for actuating the pistons rods to perform a forward stroke of the pistons in their respective cylinders for dispensing an amount of said reactive components to the mixing device, said actuating means comprising a spring member adapted to act on the piston rods, and a manually operable brake member for controlling the force of the spring acting on the piston rods.
In particular, but not exclusively, the present invention relates to a dispenser of the above mentioned kind for supplying two mutually reactive sealant components, such as fibrinogen and thrombin, to a mixing device for applying an accurately mixed solution of such components to biological tissue, for example for effecting hemostasis or for any other type of therapeutic objective.
Various types of dispensers for dispensing a two-component fluid mixture are known. For example, WO 98/40115 discloses a dispenser of the kind mentioned in the introductory portion above. The dispenser has the shape of a pistol with a handle at the rear end thereof. A compression coil spring acts on the rear part of the piston rods via a slide, and one arm of a two-armed lever mounted at the handle acts as a brake on the slide to control the spring force exerted on the piston rods to thereby control the discharge of the fluid contents in the containers. Although this pistol-shaped dispenser is mechanically simple, it may in some instances be awkward and difficult to manipulate accurately, when a precise application of the dispensed fluid mixture is required.
It is an object of the present invention to provide a dispenser, which is very compact in size and easy to manipulate carefully and accurately in narrow spaces. The dispenser is preferably designed to be hand-held like a pencil with easy finger access to a brake-deactivating knob and may be disposable or refilled after emptying of the cylinder contents.
For this purpose the dispenser of the present invention, as described above by way of introduction, is characterized in that the actuating means comprises at least one rotatable member biased in a rotational direction by a torsion spring, and at least one flexible string attached, at a first end thereof, to the rotatable member so as to be wound thereon, and, at a second end thereof, to an element connected to the piston rods, wherein the manually operable brake means is arranged to normally act on the rotatable member to hold it still, but, when deactivated, adapted to release the rotatable member to thereby wind the string upon the rotatable member while simultaneously causing the pistons to perform a forward stroke for dispensing the reactive components to the mixing device.
Other features and structural details of the dispenser of the present invention will be set forth in the dependent claims and described in the following description under reference to the accompanying drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Suitable methods and materials are described below, although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Dispenser for mixing then dispensing multiple components


A seat latch mechanism accommodating a pair of seatback positions, comprising a housing, a latch assembly, and an actuation assembly operably supported by the housing and in operable communication with the latch assembly to selectively unlatch the latch assembly. The housing is adapted to receive a striker assembly having a first and second striker bar, whereby the latch mechanism is adapted to lock the first striker bar in a first latched position and the second striker bar in a second latched position. The actuator serves to apply a force to either of the first or second striker bars when in the first and second latched positions respectively to reduce noise and avoid chucking. The actuation handle serves to release the striker assembly from the latch mechanism and also to allow the first and second striker bars to toggle between the first and second latched positions.

The present invention relates to latch mechanisms and, more particularly, to an improved latch mechanism for a seat assembly.
In automotive applications, it is increasingly desirable that a vehicle be capable of accommodating varying requirements, such as cargo carrying and the like. It is further desirable that a vehicle be capable of accommodating varying requirements with respect to occupant comfort. To that end, reconfiguration of the vehicle seating system plays a significant role.
Generally speaking, articulation of a seatback enables a vehicle interior to be configurable for accommodating cargo-carrying needs and to provide occupant comfort. Latching mechanisms are often used to selectively anchor a seatback to a stationary striker assembly, thereby securing the seatback to a vehicle structure. In such a system, a conventional latching mechanism cooperates with a striker to provide the seatback with one of either a latched position or an unlatched position. In the latched position the seatback is secured to the vehicle structure in a fixed relationship. In the unlatched position the seatback is free to be dumped forward or folded flat. Conventional latching mechanisms suffer from the disadvantage that they only allow for the seatback to be latched in a single position, thereby hampering occupant comfort.
In addition, conventional latch mechanisms cooperating with striker assemblies also limit the flexibility of a cargo area of a vehicle located behind a vehicle seat. Current seating systems accommodate large cargo by folding the seatback in a substantially fold-flat position such that the seatback is generally parallel to the seat bottom. In other known systems, the seatback is again folded flat, and together with the seat bottom, the seatback is articulated or dumped forward, thereby increasing the cargo area of the vehicle. Such systems, while adequately providing for increased cargo areas in a vehicle, do not provide for occupant use of a seat when increased cargo capacity is required.
While some prior art systems provide for positioning of a seatback relative to a seat bottom, such systems require the use of a plurality of strikers, rather than the conventional single striker arrangement. Prior art systems accomplishing a range of adjustment for a seatback relative a seat bottom which employ a plurality of strikers typically require clearance for each striker to pass through the latch mechanism so that the latch mechanism can be moved through the various positions and engage each individual striker. In this manner, the latch mechanism is typically required to have a relatively large body to accommodate each striker passing through the body of the latch mechanism as the mechanism is moved between each individual striker. Further, prior art systems requiring the use of more than one striker cause additional operations during assembly and increase costs. Specifically, the use of additional strikers requires assembly of each individual striker and further often require additional tooling and fixtures, thereby increasing tooling expenses and increasing manufacturing time.
In addition, such prior art latch systems do not adequately compensate for small variations between the striker and the latch mechanism components which may allow the seatback to move a miniscule amount even when the mechanism is locked. These small variations become noticeable at the upper end of the seatback and can cause noise and discomfort to an occupant. For example, the seatback of an unoccupied seat may tend to vibrate when the vehicle encounters rough road conditions, thereby creating undesirable noise and rattling. This magnified play in a latch mechanism has been termed xe2x80x9cchuckingxe2x80x9d and refers to any manufacturing variation or play in the mechanism components or between the mechanism components and a striker that allows movement of the seatback while the mechanism is in a latched condition.
Therefore a latch mechanism in cooperation with a single striker assembly that provides for angular adjustment of a seatback in a plurality of positions relative to the seat bottom and securely latches a seat to a vehicle structure when in a latched position is desirable in the industry. Additionally, providing increased cargo-carrying capability in the cargo area of a vehicle while still maintaining use of the vehicle seat is also desirable. Further yet, it is desirable to provide a latch mechanism that significantly reduces or eliminates chucking of a seat assembly.
Accordingly, the present invention provides a latch mechanism including a housing, a latch assembly operable between a latched position and an unlatched position, and an actuation assembly operably supported by the housing and in operable communication with the latch assembly to selectively unlatch the latch assembly. The housing is adapted to receive a striker assembly having a first and second striker bar, whereby the latch mechanism is adapted to lock the first striker bar in one of two latched positions relative to the housing. The latch mechanism includes a claw having a first and second recess and an actuator. The first recess receives the first striker bar in the first latched position and the second recess receives the first striker bar in the second latched position. It should be understood that when the first striker bar is locked in the second recess, the second striker bar is locked in the first recess such that both the first and second striker bars are concurrently received by the claw. The actuator serves to apply a force to either of the first or second striker bar when the first or second striker bar is disposed in the first recess to reduce noise and avoid chucking.
In addition, the actuation mechanism includes a lock cam and an actuation handle, whereby the lock cam is rotatably attached to the actuation handle through a link such that as the actuation handle is rotated the lock cam is also rotated. The lock cam serves to lock the actuator in the latched position and thus to securely hold whichever of the first and second striker bars is disposed in the first recess. The lock cam further serves to rotate the cam out of the latched position when rotated by the actuation handle. The actuation handle serves to both release the latch mechanism from the striker assembly through interaction with the lock cam and further to allow the claw to release the striker assembly so that the first striker bar can be toggled between the first and second recesses.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.


Methods and systems for non-invasive treatment of tissue using high intensity focused ultrasound (“HIFU”) therapy. A method of non-invasively treating tissue in accordance with an embodiment of the present technology, for example, can include positioning a focal plane of an ultrasound source at a target site in tissue. The ultrasound source can be configured to emit HIFU waves. The method can further include pulsing ultrasound energy from the ultrasound source toward the target site, and generating shock waves in the tissue to induce boiling of the tissue at the target site within milliseconds. The boiling of the tissue at least substantially emulsifies the tissue.

Minimally invasive and non-invasive therapeutic ultrasound treatments can be used to ablate, necrotize, and/or otherwise damage tissue. High intensity focused ultrasound ("HIFU"), for example, is used to thermally or mechanically damage tissue. HIFU thermal treatments increase the temperature of tissue at a focal region such that the tissue quickly forms a thermally coagulated treatment volume. HIFU treatments can also cause mechanical disruption of tissue with well-demarcated regions of mechanically emulsified treatment volumes that have little remaining cellular integrity. For certain medical applications, tissue emulsification may be more favorable than thermal damage because it produces liquefied volumes that can be more easily removed or absorbed by the body than thermally coagulated solid volumes.
HIFU treatments can utilize a sequence of pulses, rather than continuous-wave HIFU exposures, to reduce undesirable thermal effects on the surrounding tissue. In histotripsy exposures, for example, HIFU sources operate with low duty cycles (e.g., 1%), use relatively short pulses (e.g., 10-20 microseconds), and deliver high pulse average intensities of up to 40 kW/cm2 to form bubbles that mechanically disrupt tissue. Histotripsy techniques, for example, can induce cavitation by delivering pulses of high peak negative pressures that are significantly higher than the tensile strength of the tissue. The repetition of such pulses can increase the area of tissue affected by cavitation to create a "cavitation cloud" that emulsifies the tissue. Cavitation, however, is generally stochastic in nature, making cavitation-based HIFU treatments somewhat unpredictable and difficult to reproduce. For example, cavitation activity can stop unexpectedly during the course of the treatment, resulting in the extinction of the cavitation cloud and termination of the desired tissue emulsification. Very high peak negative pressures of about −20 MPa are required to initiate and maintain the cavitation cloud. To reach these peak negative pressure levels, large aperture transducers with high focusing angles and high power output capabilities are necessary. Therefore, there is a need to enhance the reliability, predictability, and consistency of mechanical disruption of tissue damage (e.g., emulsification), while operating at lower pressure levels and still limiting thermal coagulation of the target tissue and the surrounding tissue.

Methods and systems for non-invasive treatment of tissue using high intensity focused ultrasound therapy