A laminated multilayer film substrate for use in the production of banknotes having an oriented polypropylene core layer and at least one high density polyethylene layer on each side of the oriented polypropylene layer. The core layer may contain microcavities formed by the addition of a cavitating agent. The outer surfaces of the multilayer film substrate are coated with one or more epoxy layers, filed or unfilled, and one or more antistatic layers. The resultant films exhibit good embossability, dead-fold characteristics and other properties, making them highly suited for the production of bank notes and other security documents.

The present invention relates to a multilayer film for use in the production of paper-like products such as bank notes, security documents, including travelers and bank checks, and to a method for their production. More particularly, the present invention relates to a multilayer film having the characteristics of the high quality papers typically employed in the production of bank notes and security documents.
In the production of bank notes, security documents and the like, rag paper has been employed for more than 300 years. As is well known, rag paper has several properties which are highly desirable in such applications, including dead foldability, tear resistance, printablilty and embossability.
These highly desired properties may be characterized as follows: deadfold is the ability of a substrate to be creased or folded and to retain the fold without opening. Tear resistance is the ability of a substrate to resist both initiated and uninitiated tears and punctures. Printability is the ability of the substrate to adsorb and bond inks used during the lithographic printing process. Embossability is the ability of the substrate to deform under the pressures of the intaglio printing process to form a raised image on the resulting bank note or security document, with the intaglio ink remaining on the raised, deformed region resulting in a high degree of tactility or feel to the bank note or security document. As may be appreciated, these properties combine to give bank notes and the like their familiar feel and functionality.
With the advent of color copiers and computer graphic scanners, the counterfeiting of bank notes has markedly increased. While there are active programs underway by major currency paper producers to make their substrate more secure through the use of watermarks, metallized threads and optical variable devices (OVD""s), such as photochromics, holographics, and diffraction gratings, at this time, these efforts do not appear to hold much promise of thwarting counterfeiters.
Plastic substrates offer a major security feature if a clear xe2x80x9cwindowxe2x80x9d is incorporated into the bank note. This window would ensure that a scanner or color copier could not copy the note. Additionally, other security features can be incorporated into or onto the bank note, including reverse printing of the note to protect the security devices and the print.
Australian Pat. No. 488,652, discloses an approach to the production of security articles, particularly bank notes, and describes the serious problems which confront conventional bank notes with respect to forgery. The bank note disclosed therein comprises a substrate of opaque thermoplastic sheet material intimately bonded to a web of woven or unwoven thermoplastic fibers, the substrate being printed as desired and having bonded thereon one or more optically-variable security devices. The fibrous web was employed to impart durability, crumple-resistence resistance and tear-strength to the note. Where a security device, such as a Moire pattern, was employed which depended for its optically variable properties upon the transmission of light, it was necessary to punch out a hole in the substrate, insert the device and bond it in place with further layers of transparent plastic sheet material.
Although samples of bank notes formed according to the disclosure of Australian Pat. No. 488,652 were said to have performed most satisfactorily with respect to the durability and security of conventional notes, they were found to be rather complex in construction and relatively expensive to produce. Moreover, when transmission security devices were laminated between layers in the substrate, an area of weakness and high stress was created which reduced both durability and security.
Other disclosures relating to anti-counterfeiting techniques include U.S. Pat. Nos. 4,095,217 and 4,281,208, which relate to the use of a liquid crystal device driven by a photovoltaic element, such as a solar cell or an amorphous silicon material.
U.S. Pat. No. 4,472,627 relates to currency or other valuable documents containing a liquid crystal/ photovoltaic device which produces a coded display in response to artificial or ambient light. The device can function both as an anti-counterfeiting deterrent and also as a means for permitting a user to easily authenticate the validity of a document containing such a device.
U.S. Pat. No. 4,536,016 discloses a security token, such as a bank note or identity card, which comprised a sheet-like substrate made up from film of transparent biaxially oriented polymer coated with layers of opaque and heat activated adhesive material. The opaque layer is applied in such a way as to leave a transparent area for inspection of a security device, for example, a diffraction grating, incorporated in the polymer film. The substrate could bear printed or other identifying indicia and was protected with an intimately bonded layer of transparent polymeric material.
The substrate employed in U.S. Pat. No. 4,536,016 was based on the use of oriented polypropylene (OPP). After several commemorative bank note printings, while meeting many of the requirements for a bank note substrate, the plastic bank notes were found to fail in three major areas. First, the OPP substrate did not dead fold, causing problems in that the film retains either a flat or curved form, jamming cash registers and automatic handling equipment. Second, the OPP substrate has poor initiated tear resistance in the processing of currency, which quite frequently creates nicks on the edges of bills, resulting in catastrophic tears. Finally, the OPP product did not exhibit the tactility of paper currency, due to the fact that OPP does not emboss well during the intaglio process.
Oriented high density polyethylene films have been employed in the area of plastic packaging. Such films, biaxially oriented to a degree of greater than 6.5 times in both the machine direction (MD) and the transverse direction (TD) are described in British Patent 1,287,527. U.S. Pat. No. 4,680,207 relates to imbalance biaxially oriented films of linear low density polyethylene oriented up to six times in the machine direction, and up to three times in the transverse direction but less than in the machine direction.
U.S. Pat. No. 5,618,630 relates to a three-ply multilayer film structure for the production of banknotes.
While the aforementioned films have been shown to offer certain advantages over the prior art and generally meet the requirements for which they were designed, a need still exists for a film which provides the characteristics of a high quality, rag-type paper of the type typically employed in the production of bank notes and security products.
Therefore, it is an object of the present invention to provide a multilayer film having the characteristics of a high quality rag paper.
It is another object of the present invention to provide such a multilayer film which possesses the dead-fold characteristics of high quality papers while being easy to manufacture and reasonably durable.
It is a further object of the present invention to provide a multilayer film which possesses a high degree of tear resistance to both initiated and uninitiated tears and punctures in at least one direction.
It is yet another object of the present invention to provide a multilayer film which possesses the printability and embossability of a high quality paper.
It is still a further object of the present invention to provide a multilayer film which possesses a high degree of resistance to curling at higher temperatures, e.g., above 150xc2x0 F.
Still another object of the invention is to provide a multilayer film which is suitable for banknote production from which it is difficult to abrade inks resulting in banknotes of long service life. Such films can achieve high levels of durability without overlaying the inked surface with protective coatings such as lacquers or polyurethanes.
When money is circulated, it becomes soiled by contact with other materials, especially other money (coins and notes). If ink is rubbed into unprinted areas the results are undesirable. Likewise coins should not leave marks on the notes when the two are rubbed together. Therefore, a further object of the present invention is to provide inks and print surfaces that are abrasion resistant but cannot be overly abrasive.
Other objects and the several advantages of the present invention will become apparent to those skilled in the art upon a reading of the specification and the claims appended thereto.
The multilayer film of the present invention is a three-ply structure. In a preferred embodiment, at least one layer of oriented polypropylene (OPP) is surrounded by at least one layer of high density polyethylene (HDPE) on either side of the OPP layer. The multilayer film of the present invention comprises one or more epoxy layers to provide coating adhesion and opacity as well as provide a surface for receipt of an ink print image. The multilayer film of the present invention further comprises one or more antistatic layers to improve processability. The film substrate to be coated can be a clear or opaque structure.
The multilayer film of the present invention exhibits good performance in repetitive fold tests. The multilayer film structure of the present invention also has high tensile strength in both the oriented and unoriented direction. The multilayer clear structure of the present invention does not craze when crumpled in the print window.
In accordance with the present invention, there is provided a curl-resistant, cross-sectionally symmetrical, laminated multilayer film substrate for use in the production of banknotes, security papers and the like comprising:
(a) an imbalanced biaxially oriented first layer having inner and outer sides, comprising at least about 50 weight percent of a high density polyethylene having a density of at least about 0.94, said first layer being oriented in at least a first direction to a degree which is at least three times less than the degree of orientation present in a second direction substantially normal to the first direction wherein (a) further comprises a coextruded propylene copolymer skin on its inner side;
(b) a balanced biaxially oriented second layer having inner and outer sides, comprising at least about 90 wt. % polypropylene, said second layer being oriented in at least a first direction, at an orientation ratio of at least 4:1, and oriented in a second direction substantially normal to said first direction, at an orientation ratio of at least 6:1;
(c) an imbalanced biaxially oriented third layer having inner and outer sides, comprising at least about 50 weight percent of a high density polyethylene having a density of at least about 0.94, said third layer being oriented in at least a first direction to a degree which is at least three times less than the degree of orientation present in a second direction substantially normal to the first direction; and
(d) a laminating adhesive resin disposed between the inner sides of (a) and (c), said second layer being laminated to said first and third layers so that the first direction of orientation of said third layer is substantially aligned with the first direction of orientation of said first layer and wherein the outer sides of both (a) and (c) further comprise at least one epoxy layer and at least one antistatic layer.
In forming the multilayer film of the present invention at least one layer of the substrate comprises oriented polypropylene. The use of oriented polypropylene in the core results in high tensile properties and high performance in repetitive fold tests. In addition, there is no crazing in the print windows after hand crumpling when using the three-ply clear structure of the present invention.
It is preferred to use oriented polypropylene (OPP) in the core. However, other biaxially oriented polymers of a comparable tensile strength, such as linear low density polyethylene (LLDPE), nylons or polyester may also be used. It is preferred that the OPP core be free of any additives, for example, antistatic agents and silicone, which have an impact on adhesion to other layers.
The core layer of the present invention may also comprise a plurality of voids formed by cavitation about a solid cavitation agent, such as polybutylene terephthalate and/or calcium carbonate. Polybutylene terephthalate, e.g., 0.2 to 2 microns in diameter, as described in U.S. Pat. Nos. 5,288,548; 5,267,277; and 4,632,869, the contents of which are incorporated herein by reference, is a suitable cavitation agent. The spherical particles form microvoids on orientation, resulting in a white opaque product.
In forming the multilayer film substrates for use in the production of the bank notes and other security documents of the present invention, at least two layers of the substrate are to contain a major proportion of a high density polyethylene (HDPE) having a density of at least about 0.94, preferably at least about 0.945. These film layers may be composed exclusively of a single HDPE resin, a mixture of HDPE resins, or of HDPE containing a minor proportion of another polymeric material, such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene, ethylene vinyl alcohol (EVOH) copolymer, ethylene propylene (EP) copolymer, ethylene propylene butene-1 (EPB) copolymer, polyetser or nylon, although a single HDPE resin or a blend of HDPE resins is particularly preferred in the practice of the present invention. Films made with either a blend of HDPE resins or with microcrystalline wax have been found to reduce the splittiness of the film which manifests itself as the tendency of the film to break in the TD direction.
When blends of HDPE polymers are employed, such blends can comprise two or more polymers all of which preferably have densities of 0.94 or greater. Blends of HDPE polymers advantageously comprise a major proportion of HDPE having a melt index of 0.6 to 1.2 and one or more polymers having a different melt index.
Terblends may also be desirable. Suitable terblends generally comprise 50 to 98 weight percent, preferably 84 to 96 weight percent of HDPE having a density of 0.96 or higher and a melt index of greater than 0.5 to about 2.0; 1 to 25 weight percent, preferably 3 to 8 weight percent of HDPE having a density of 0.94 or greater and a melt index of 0.1 to 0.5; and 1 to 25 weight percent, preferably 3 to 8 weight percent, of HDPE having a density of 0.96 or higher and a melt index of greater than 2 to about 8. Preferably, the second and third HDPE polymers which are minor components are present in about equal amounts.
As is particularly preferred, the film substrate of the present invention includes a) a first layer comprising at least about 50 weight percent of a high density polyethylene having a density of at least about 0.94, the first layer oriented in at least a first direction, e.g., machine direction (MD), to a degree which is at least three times less than the degree of orientation present in a second direction substantially normal to the first direction, e.g., transverse direction (TD); (b) a second layer comprising at least about 90wt. % polypropylene, the second layer being oriented in at least a first direction e.g., machine direction (MD), at an orientation ratio of at least 3:1, and oriented in a second direction substantially normal to said first direction e.g., transverse direction (TD), at an orientation ratio of at least 6:1; and c) a third layer also comprising at least about 50 weight percent of a high density polyethylene having a density of at least about 0.95, the third layer also oriented in at least a first direction, e.g., MD, to a degree which is at least three times less than the degree of orientation present in a second direction, e.g., TD, substantially normal to the first direction, the third layer being laminated to the film substrate so that the first direction of orientation of the third layer is substantially parallel to (or aligned with) the first direction of orientation of the first layer.
A method of producing HDPE films with imbalanced biaxial orientation is disclosed in U.S. Pat. No. 4,870,122, the contents of which are incorporated by reference in their entirety.
As may be appreciated, to achieve the object of improved tear resistance in a multilayer film of the type describe herein, it has been discovered that imbalanced biaxially oriented HDPE films, laminated so that their primary directions of orientation are aligned substantially parallel to each other, can exhibit increased tear resistance where an orientable laminating resin, e.g., polyurethane, is disposed between the layers and subjected to orienting so that the primary direction of orientation in the oriented resin is substantially normal to the primary direction of orientation of the first and third HDPE film layers. In one embodiment, such orientation in the primary direction of orientation of the laminating adhesive resin is achieved during the laminating step itself, preferably in the machine direction (MD).
The degree of orientation of the HDPE film layers is an important aspect of this invention inasmuch as the proper degree of orientation provides desirable physical properties. Although higher density HDPE resin having a density of 0.957 or greater can be made directly into thin films by cast extrusion, problems of curling, uniformity and flatness exist. Accordingly, thin HDPE films of about 0.8 to 1.5 mils having the best balance of properties are obtained using imbalanced biaxially oriented films prepared from films having a cast gauge of 4 to 15 mils which are reduced to the desired gauge by stretching, i.e., orientation.
The films are produced and oriented in a conventional manner. The film is heated to its orientation temperature and first subjected to MD orientation between two sets of nip rolls, the second rotating at a greater speed than the first in an amount equal to the desired draw ratio. Then the film is TD oriented by heating and subjecting it to transverse stretching in a tenter frame. Typically MD orientation is conducted at 60 to 120xc2x0 C. and TD orientation at 110 to 145xc2x0 C.
While it is preferred that the degree of orientation in a first film direction be at least three times less than the degree of orientation present in a direction substantially normal to the first direction, it is more particularly preferred that each HDPE film layer be oriented to an extent of about 1.1 to about 2.0 times in the machine direction (MD) and about 6 to about 12 times in the transverse direction (TD). It has been found that the HDPE film layers can be produced with excellent quality at caster speeds of up to about 110 feet per minute (fpm) corresponding to line speeds of 140 fpm at 1.25 times MD orientation. In the alternative, the degree of orientation in a first film direction can be at least three times greater than the degree of orientation present in a direction substantially normal to the first direction. Even unoriented blown HDPE may be used as the first and third layers and still maintain some degree of deadfold in the multilayer film substrate of the present invention.
When employed, this degree of imbalanced orientation produces an interesting effect in the HDPE components of the structure. The effect is a visible rippled and striated appearance, with the ripples being parallel to the transverse orientation direction. Under low magnification, in each square centimeter of HDPE film there will be seen from about 5 to about 30 discontinuous undulating ripples and striations generally parallel to the direction of orientation. This effect gives the film a slight translucent appearance, which tends to slightly blur distant objects viewed through the film. This effect indicates that the layers have been oriented in an imbalanced manner. The high density polyethylenes contemplated for use in the practice of the present invention include those disclosed in U.S. Pat. No. 4,870,122.
In the oriented polypropylene layer the orientation is adjusted to give essentially balanced tensile properties in both directions.
To achieve the desired surface characteristics required of the paper-like products of the present invention, one or more skin layers can be applied, in any known manner, to the multilayer HDPE substrate material, for example by coating or coextrusion before orientation or by coating the HDPE after one or both of the orientation operations. The skin layer can be any of the conventional materials used for this purpose in conjunction with polyolefin films, particularly polyethylene films. For example, to achieve a press-ready surface, a polymeric resin could be blended with fillers, fibers, pigments or the like, as necessary.
Additionally, voided films, such as those disclosed in U.S. Pat. Nos. 4,377,616, 4,632,869, 4,758,462 and others, may be laminated to the multilayer HDPE substrate to impart the opacifying properties of those structures to the films of the present invention.
The HDPE-containing layers (a) and (c) as disclosed above can further comprise copolymer polypropylene skins, e.g., ethylene-propylene-butane 1 terpolymer, provided on at least one side thereof, preferably on both the inner and outer sides thereof. In one embodiment, the skins themselves can also comprise a component which is similar to components in the adhesive resin used to laminate layers (a), (b) and (c). For example, low density polyethylene (LDPE) can make up from 10 to 20 wt % of the skins, with the balance being a copolymer polypropylene.
A suitable adhesion-promoting primer which provides greater adhesion between the laminated surfaces, e.g., polymers selected from the group consisting of polyethyleneimide, epoxy, polyurethane, and acrylic, can be provided between the copolymer polypropylene skins (on the inner sides of (a) and (c)) and the laminating adhesive resin. Primer compositions are disclosed in U.S. Pat. Nos. 4,447,494 and 4,681,803, which are incorporated herein by reference.
The multilayer film of the present invention comprises one or more layers of epoxy coating. The outermost layer is an epoxy print cap. Underlying epoxy opacifying layers comprising fillers, such as titanium dioxide, are also included to provide coating durability and opacity. Additional functional coated layers on the multilayer film can be used, if desired, to improve the antistatic properties of the final structure, introduce additional security features, and/or enhance opacity.
The outer epoxy layer is for printing by lithography, intaglio and other types of printing methods. Hydrophobic filler, such as surface treated clays and hydrophobic titanium dioxide improve wet-scratch resistance. Hydrophobic clay fillers are preferred over coatings filled with calcium carbonate, titanium dioxide and/or epoxy based coatings without filler because they are less abrasive.
The epoxy print cap provides excellent wet-scratch resistance while at the same time affording good ink gloss, print image, and tack up times.
The epoxy coating (or epoxy binder) used to form the layers on the three-ply structure of the present invention is the reaction product of an epoxy resin and an acidified aminoethylated vinyl polymer, which is used as a hardener or curing agent. A description of such epoxy coatings is found in U.S. Pat. No. 4,214,039 to Steiner et al., which is herein incorporated by reference.
The epoxy resin can be defined as glycidyl ethers of polyhydroxy compounds. Polyhydroxy compounds that can be used include, but are not limited to, bisphenol A (common name for 4,4xe2x80x2-isopropylidene bisphenol), ring substituted bisphenol A, resorcinol, hydroquinone, phenol-formaldehyde novolac resins, aliphatic diols, such as ethylene glycol, propylene glycol, 1,4xe2x80x2-butanediol, 1,6 hexanediol glycerol, poly(oxyethylene)glycol, poly(oxypropylene)glycol, and the like. A preferred class of epoxy resins includes derivatives of bisphenol A.
The epoxy resins to be used are commonly classified by their epoxy equivalent weight (E.E.W.), which is defined as the gram weight of resin that contains one gram equivalent of epoxy groups. Resins with an E.E.W. ranging from 170 to 280 can be used with the present invention, with resins having an E.E.W. of 180 to 210 being preferred.
Other types of epoxy resins based on aliphatic diols and having E. E.W.""s ranging from about 150 to about 380 can also be used in mixtures with bisphenol A resins where increased flexibility of the resulting layer is desired.
Although the specific structure of the epoxy resin is not critical to the epoxy coating, considerations in the selection of the epoxy resin revolve around its physical state. For example, the resin should be a liquid and capable of being readily dispersed or dissolved with the acidified aminoethylated vinyl polymer (i.e., hardener), which is as described below. If the epoxy resin is of low viscosity, it can be stirred directly into the hardener.
Preferably, the epoxy resin is dispersed in an aqueous emulsion for ease of handling. A commercially available emulsified epoxy resin is Daubond(copyright)42X6311 from Daubert Chemical Company, Inc., in Chicago, Ill.
An alternative to emulsifiers is to substitute a hydantoin compound for bisphenol A. For example, 1,1-dimethyl hydantoin can be employed as a low molecular weight epoxy resin since resins based on this material are completely water soluble thereby eliminating the necessity for emulsification.
The liquid epoxy resin can be dispersed in a solution of hardener by rapid stirring. The resultant dispersion can be diluted with water and/or alcohol to the desired solids concentration for use as the coating or binder. When a completely water soluble epoxy resin is employed, simple mixing of aqueous solutions of the resin and the hardener is sufficient to produce a clear, infinitely dilutable, coating solution. The solids content of the coating solution prior to the addition of mineral fillers or other opacifying agents, such as titanium dioxide or clays, in the emulsion, can range from about 2 up to about 35% solids, with 15 to about 30% solids more preferred. Although it is difficult to obtain a stable dispersion at low concentrations since the epoxy resin tends to separate in large globules rather than remain in minute emulsified droplets, it has been found that usable products may be produced using this system.
A solid epoxy resin can be emulsified in water employing a non-ionic emulsifying agent. A stable, fine particle size emulsion containing about 50% epoxy resin may be readily prepared utilizing known prior art techniques. Opacifying agents can be added to the emulsion to make a grind paste. The opacifying agents may be ground using conventional methods including a Cowles mixer, ball mill, or other well-known dispersion methods. To facilitate the dispersion of the opacifying agents, water, alcohol or other suitable dispersion aids may be added. This dispersion may be subsequently stirred into the solution of the previously described hardener, either before or after dilution to the desired solids concentration.
The second component of the epoxy coating is the water soluble, acidified aminoethylated vinyl polymer, which is used as the hardener or primary curing agent. The preferred material is described in U.S. Pat. No. 3,719,629, which is incorporated herein by reference, and may be generically described as an acidified aminoethylated vinyl polymer having pendant amino alkylate groups of the general formula:
wherein R1 and R2 are hydrogen or lower alkyl radicals and the average value of n is in the range of about 1.0-2.5.
As described U.S. Pat. No. 3,719,629, the hardener is produced by polymerizing acrylate, methacrylate, styrene or other suitable monomers with sufficient methacrylic or acrylic acid to give axe2x80x94COOH content of about 7.5 to about 12.5%. Solvent polymerization techniques are preferred. The polymer is thereafter reacted with an ethylene imine monomer and acidified with hydrochloric acid to render the polymer water soluble. A commercially available epoxy hardener is NSK7000, manufactured by Nippon Shokubai Co., Ltd., in Tokyo, Japan. The hardener contains approximately 50% resin in an ether/water solvent system. The resin has an amine hydrogen equivalent weight of between 350 and 450. This clear viscous solution is capable of being diluted infinitely with water.
When mixing the epoxy resin with the hardener, it is generally preferred to use a stoichiometric equivalent balance of epoxy and amine groups. However, the stoichiometric ratio can be varied over a wide range, from about 1 epoxy to about 3 amine through 3 epoxy to 1 amine, with about 1 epoxy to 2 amine through about 2 epoxy to 1 amine being more preferred. The actual stoichiometric ratio does not seriously affect the product""s usefulness.
The epoxy binder can also contain various wetting aids and secondary curing agents. For example, the solution or dispersion of epoxy resin and hardener when applied to the substrate may not xe2x80x9cwet-outxe2x80x9d uniformly, especially when such materials are applied in very thin layers. As a result, the dry but as yet uncured liquid mixture may retract into droplets or xe2x80x9cislands.xe2x80x9d
To improve the xe2x80x9cwet-outxe2x80x9d of the coating, small amounts of high boiling (above 100xc2x0 C.) wetting aids, from 0.5 up to about 10% by weight of the total solids, can be used. Any conventional non-ionic wetting agents can be employed. However, optimum results are obtained utilizing partially water-soluble organic compounds having hydrophilic groups attached to hydrophobic groups. Examples of such compounds include, but are not limited to, the hexyl or benzyl ether of ethylene glycol, the hexyl ether of diethyl glycol, butyl alcohol, hexyl alcohol, octyl alcohol, diacetone alcohol, and the like. One such preferred wetting aid is the hexyl ether of diethyl glycol also known as Hexyl Cellosolve, which is commercially available from Union Carbide. Larger amounts of low boiling (less than 100xc2x0 C.) wetting aids, from more than about 5% by weight of the total solids, can be used with, or in the alternative of high-boiling wetting aids. Preferred low-boiling wetting aids include n-propyl alcohol and isopropyl alcohol.
A secondary curing agent can also be added to the binder in a ratio of 0.5 to 15 parts per 100 parts of dry epoxy resin to enhance the rate of cure. Such curing agents can include, but are not limited to, propylene diamine, hexamethylene diamine, diethylene triamine, triethylamine, tetraethylene pentamine and the like. In addition, aliphatic polymeric amines can be employed such as poly(ethyleneimine) and poly(propyleneimine). Aromatic amines including tri(dimethyl aminomethyl) phenol can also be employed. Likewise, mixtures of the secondary curing agents can also be used.
A preferred secondary curing agent is poly(ethyleneimine). One such poly(ethyleneimine) resin commercially available is EPOMIN(trademark)P-1050 available from Nippon Shokubia Co., Ltd., located in Tokyo, Japan. The EPOMIN(trademark) resins contain a semi-linear polymer having branched chains of primary, secondary and tertiary amines. The P-1050 grade resin is a clear viscous liquid containing 50wt. % resin
Opacifying agents (fillers) in the epoxy print cap are added per 100 parts binder, at minimum level of about 50 parts per hundred resin (phr), with about 75 phr being preferred, and about 90 phr being more preferred. Maximum levels of filler material per 100 parts binder should not exceed more than about 300 phr, with no more than about 250 phr being preferred and no more than about 160 phr being more preferred.
Epoxy opacifying coatings for underlying layers can be formed with the same methods used to make the print cap. However, fillers in the epoxy opacifying layers are added per 100 parts alcohol or solvent based binder, at minimum level of about 100 phr, with about 150 phr being preferred, and about 200 phr being more preferred. Maximum levels of filler material per 100 parts binder should not exceed more than about 350 phr, with no more than about 300 phr being preferred and no more than about 250 phr being more preferred. Titanium dioxide is the preferred filler for the opacifying coating.
In general, opacifying agents for the print cap or opacifying coatings can be any conventional filler material used in printing applications. Examples of such materials include, but are not limited to, silica, clays, zinc oxide, tin oxide, talc, Tospearl(trademark), surface modified clays, for example hydrophobic clay, surface-modified silicas, titanium dioxide (TiO2), surface-modified TiO2 and calcium carbonate. The filler materials are classified into two functional groups: hydrophilic fillers and hydrophobic fillers.
The hydrophilic fillers include silicas, clays, zinc oxide, tin oxide and talc. They are referred to as hydrophilic due to the ability to absorb water, which is measured by pore volume or porosity. The hydrophilic filler materials preferably have a low porosity or are non-porous. In the context of the present invention, low porosity means a porosity less than 3 milliliters/gram (ml/g), with less than 1.5 mug being preferred and less than 0.5 ml/g being more preferred. Low porosity and non-porous fillers have been found to provide the coated substrate with better overall properties than their more porous counterparts. A preferred low porosity filler is silica since it can be obtained in various grades of porosity and particle size. Examples of commercially available low porosity silicas are silica gels manufactured by Fuji Silysia Chemical Company, under the tradename Sylysia(trademark) and silica gels manufactured by Grace-Davison, under the tradenames Sylojet(trademark), Syloid(trademark).
The hydrophobic fillers include the surface-modified clays, surface-modified silicas, TiO2 and surface-modified TiO2, which have been rendered non-porous to water due to their surface modification with an organic moiety. Examples of surface-modified clays include surface-modified kaolinite clays sold under the tradename Kalophile-2(trademark) by Dry Branch Kaolin and Lithoperse(trademark)7015HS and 7005CS by Huber Engineered Minerals, and Kaopolite SFO from Kaopolite, inc., which is no longer in production. A surface modified silica is AeroSil RX50 manufactured by Aerosil Nippon, located in Japan. Examples of surface-modified titanium dioxide are Tipure R104, manufactured by Dupont and Tioxide RXL, manufactured by Tioxide Americas.
In accordance with the present invention, hydrophobic fillers are preferred since they allow for excellent wet-scratch resistance while providing excellent ink gloss and graphics. Combinations of the hydrophobic and hydrophilic can also be used The epoxy binder is prepared by admixing the required amount of the emulsified epoxy resin and opacifying agents to the hardener, which has been diluted with water and/or alcohol to the desired concentration. Optional components such as secondary curing agents and wetting aids can also be added. The total solids concentration for the binder is generally dependent upon the coating application technique. In general, total solids concentrations of at least 5% up to about 50% are desirable, with 20% to 45% being more preferred.
The epoxy coating, filled or unfilled, and functional layers can be applied utilizing a standard coating technique to one or both sides of the film substrate. An example of a coating process is gravure coating which allows patterned application of the opacifying coatings to create a security window. The filler type and thickness of the epoxy coating is dictated by the targeted opacity, surface appearance, surface texture, and economics. Generally, the epoxy coating is applied to the film substrate after orientation at a dry coating weight of at least 0.1 grams/1000 in2 (g/msi) per layer and normally not more than 4 g/msi per layer. The total epoxy coating weight, including filler, for opaque laminates is generally 0.3 to 5.0 g/msi per side and 4 to 8 g/msi per side for clear laminates. Generally, the total epoxy coating weight is about the same on each side of the laminate.
The coated substrate is subsequently passed through a hot air oven to remove the water and solvent present. Residence times from 1 to about 10 seconds in the oven between 140xc2x0-250xc2x0 F. (60-120xc2x0 C.) are usually sufficient.
Functional layers, such as antistatic layers, that provide antistatic properties, promote adhesion, contain security features, and/or provide additional opaciity can be applied to the film substrate before, in between and/or after coating with one or more epoxy dispersions. The antistatic layers can also be the epoxy layers. Examples of the primer for thermoplastic materials include poly(ethyleneimine), which can be coextruded with or coated on the plastic substrate, and the epoxy coating at a low coating weight following the teaching of U.S. Pat. No. 4,214,409, to Steiner et al. Corona, plasma or flame treating can also be used with or instead of the primer. PD95849MO1, manufactured by Adhesion Systems, Inc., is an example of an antistatic opacifying polyurethane that can be applied over, under, and/or between layers of epoxy coatings described in this invention.
It is also envisioned that the coated substrate can be embossed, dyed, printed, texturized or otherwise treated before or after lamination; this being done on the internal or external surfaces of the laminated layers, so as to provide, for example, visual and/or tactile identification of the nature of a banknote, its significance or value. Printing processes include, but are not limited to, lithography, UV-screen, flexography, gravure and intaglio printing processes. Any flexo or gravure printable ink, either colors or machine readable ink, such as lithographic, IR, UV, magnetic and intaglio inks, can be used. Printing on the core is also a security feature as well.
The laminating techniques which can be employed to effect the present invention are known in the art and include: adhesive-bonding or cementing, e.g., with laminating adhesive resins, preferably with a transparent agent; solvent-bonding, where a mist of solvent is sprayed over the surfaces to be bonded together; thermal lamination by heat-bonding where thermoplastic sheets are subject to a hot rolling or pressing operation; cast-lamination where one layer is cast onto the second and the second forms a substrate; or, extrusion or draw-lamination as in calendering operations known in the art.
The use of solventless or 100% solids adhesive resins, such as a two-part polyurethane resin, WD4110, available from H.B. Fuller Co., is particularly preferred. 100% solids laminating adhesives are an effective alternative to solvent-based adhesives. 100% solids laminating adhesives impart excellent clarity, enhancement of printing, high bond strength and heat sealing resistance to the multilayer film laminated structure of the present invention.
When discrete security devices are incorporated within the substrate, e.g., optically-variable devices (OVD""s), they can be enclosed in pouches affixed to the substrate. On the other hand, the optically-variable devices themselves may be incorporated in one (or both) layers of the laminated substrate or between the layers, it not being necessary to incorporate a physically discrete device within a clearly defined pouch formed between the layers.
Any suitable security device can be employed in the present invention such as one selected from the group consisting of optically variable devices (OVDs), magnetic devices, electronic devices, and rare earth element-containing devices, with OVDs particularly preferred.
As employed in the present specification, the term xe2x80x9coptically-variablexe2x80x9d is used to denote any device which can readily be made to change appearance in a reversible, predictable and reproducible manner. The appearance of such devices may be altered, for example, by the application of body-heat or manual pressure, the variation of the angle of viewing and, the lighting conditions under which viewing takes place. The type of devices envisioned by the present invention are: diffraction gratings, liquid crystals, moire patterns and similar patterns produced by cross-gratings with or without superimposed, refractive, lenticular and transparent grids, such as Fresnel lenses, spaced partially-reflective, and partially transparent, coatings yielding variable interference patterns or the like, bi-refringent or polarizing layers, zone-plates and the like.
Generally, optically-active devices of this nature are readily recognized by unskilled persons and are yet extremely difficult to reproduce by photographic and printing techniques. Moreover the production of any one such device in a reproducible fashion and the incorporation of such a device in a plastic laminate as described by the present invention is likely to be beyond the resources of the great majority of would-be forgers. Where a flexible paper-like product such as a bank-note is sought, it is of course preferable that the optically-variable devices should, themselves, be sheet-like, flexible and thin; it is also preferable for such devices to be compatible with the plastic material employed for the laminae to facilitate bonding and mitigate against reactive changes occurring with time.
According to the present invention, one preferred form of optically variable device may be a reflecting diffraction grating consisting of a metallized thermoplastic film embossed with a diffraction pattern. To prevent access to the embossed pattern for the purpose of illicit replication, it is preferable according to the present invention to employ a layer of thermoplastic material on each side of the metallized film which has similar solubility characteristics to that of the metal layer so that separation by preferential etching will be rendered extremely difficult. Another preferred device is a moire pattern formed by photographically reproducing fine line or dot patterns on each side of a thin film. The spacings of the dots and lines can be readily made too fine to be reproduced by printing techniques and yet the moire pattern can be displayed upon a much larger scale. Unique diffraction and moire patterns will often be preferred for use in bank notes and techniques are available for producing those by computer and photo-reduction methods.
In the production of low denomination bank notes, a suitable level of security against counterfeiting may be obtained by merely providing a clear xe2x80x9cwindowxe2x80x9d through the bank note. As indicated above, such a window would ensure that a scanner or color copier could not copy the note. Additionally, other security features can be incorporated into or onto the bank note, including reverse printing of the note to protect the security devices and the print.
It has been found that films similar to those of the present invention but which are xe2x80x9ccross-oriented,xe2x80x9d can be susceptible to curling at temperatures above 150xc2x0 F. Such cross-oriented films are similar to those of the present invention except that the second layer is laminated to the film substrate so that the first (primary) direction of orientation of the second layer is substantially normal to the first (primary) direction of orientation of the first layer. It is believed that such curling can result from differences in shrinkage at high temperatures in the machine direction and transverse direction of each layer. Additional curling susceptibility can result where coatings or skins of the layers have different coefficients of contraction from the HDPE component of the layers. Such imbalanced contraction and its attendant curling can be avoided by counterbalancing the overall shrinkage properties of one layer by laminating thereto a second layer identical to the first layer which is provided as a mirror image of the first layer. In other words, one half of the layered film structure is a mirror image of the other, with the plane of symmetry being along the horizontal midline of the layered film structure cross-section. This provides a cross-sectionally symmetrical layered film structure. Examples of such films include those of ABA, ABBA, ABCCBA, ABCDCBA, etc. construction where each letter represents a film layer, skin, coating, or adhesive layer. Such a cross-sectionally symmetrical layered film structure is necessarily a xe2x80x9cparallel-orientedxe2x80x9d structure, i.e., the primary direction of orientation of the first layer is parallel to the primary direction of orientation of the second layer in order to meet the mirror image requirement. Such a construction provides a symmetrical structure wherein the opposing shrinkage forces counteract each other to a significant degree. However, such a two layer parallel construction can be susceptible to poor tear properties in one direction, e.g., TD where two TD oriented films are employed.
It has now been found that using a low density polyethylene (LDPE) and/or a linear low density polyethylene (LLDPE) laminating resin oriented in the primary direction of orientation which is substantially perpendicular to the primary direction of orientation of the layers which it ties, evinces reduced susceptibility to tearing. The laminating resin can itself be subjected to orienting to some extent during lamination, preferably after the resin has at least partially or completely solidified, and preferably in the machine direction. Such orienting can be from 1.5 to 10 times, preferably from 4 to 6 times, corresponding to a total drawdown of the laminating adhesive resin of greater than 10%, preferably greater than 20%, say, 75%.
It has also been found that by using a 100% solids resin as the laminating adhesive resin employed, orientation effects resulting from the lamination procedure are improved, resulting in a multilayer film exhibiting curl resistance and improved chemical resistance.
One or both of the HDPE containing layers may be weakened in terms of tear resistance in one direction to a point where they are significantly weaker than the laminating adhesive resin and the OPP containing core layer. When attempting to delaminate the structure for counterfeiting purposes, only small strips of the outer printed HDPE containing layers would be removed. The entire HDPE containing layers would not be removable.
The HDPE containing layer can be tear weakened using process conditions during manufacture. Microperforating with laser technology and/or nicking will also cause the HDPE containing layers to weaken. The microperforations are either diagonal or unidirectional, e.g. in the range of from about 50 to about 300 dots per inch (dpi).
The HDPE layers can also be tear weakened through the addition of incompatible additives that would cause the layer to fibrilate or fracture during orientation. Suitable incompatible polymer additives which effect crystallization include polyester (PET), polybutylene terephthalate (PBT), polystyrene or a mixture thereof. Generally, from about 1 to about 10 wt. %, preferably from about 4 to about 8 wt. % of incompatible additive is added to the HDPE layer(s). Fibrillation results in regions of oriented HDPE surrounding long, planar regions of the incompatible polymer resulting in low tear regions.
The OPP core layer is not weakened and essentially provides the tensile properties and tear resistance of the structure as a whole.

Epoxy coated multilayer structure for use in the production of security documents


The carboxylic acid ester compound of the invention is represented by the following formula [I]: ##STR1## wherein R is an alkyl group of 3-20 carbon atoms; n is 0 or 1; at least one of A.sup.1, A.sup.2 and A.sup.3 is a group having tetralin structure, and the residual groups of A.sup.1, A.sup.2 and A.sup.3 are each independently a group having specific aromatic cyclic structure such as a phenylene group and a biphenyl group; Y.sup.1 and Y.sup.2 are each independently a group selected from the group consisting of --COO--, --CH.sub.2 CH.sub.2 -- and --CH.sub.2 O--; Q.sup.1 is a group selected from the group consisting of --CH.sub.3, --CF.sub.3, --C.sub.2 H.sub.5 and --C.sub.2 F.sub.5 ; and q is an integer of 4 to 12.. This carboxylic acid ester compound may be used as an antiferroelectric liquid crystal material, and also be used as a liquid crystal composition by using other liquid crystal material in combination. A liquid crystal element which is formed by filling the carboxylic acid ester compound in a gap between two substrates opposite to each other shows excellent properties required for antiferroelectric liquid crystal elements, for example, high speed switching.

Display devices using liquid crystal compounds, which are used widely at present, are driven in a TN (twisted nematic) mode.
Such driving display devices, however, have problems that since the position of the molecule of the liquid crystal compound present in the element must be changed in order to change displayed images, the driving time necessary therefor is prolonged, and also a voltage necessary for changing the position of the molecule of the liquid crystal compound becomes higher and electric power consumption becomes larger.
Differing from switching elements utilizing the TN mode or a STN mode, switching elements comprising ferroelectric liquid crystal compounds are able to function as switching elements only by changing the direction of molecular orientation of the liquid crystal compounds, and hence the switching time required for operating the switching elements is prominently shortened. Further, because a Ps.times.E value obtained from a spontaneous polarization (Ps) of the ferroelectric liquid crystal compound and an intensity of the electric field (E) applied thereto is an effective energy output for changing the direction of molecular orientation of the liquid crystal compound, the electric power consumption required therefor can also be extremely reduced. Such ferroelectric liquid crystal compounds are suitable particularly for use in display devices for moving picture, because they have two stable states depending upon the direction of the applied electric field, namely, bi-stability, and also have very favorable switching threshold value characteristics.
When such ferroelectric liquid crystal compounds are used in optical switching elements or the like, these compounds are required to have various characteristics such that an operating temperature is in the vicinity of or below ordinary temperature, an operating temperature range is broad, a switching speed is high (fast), and a switching threshold value voltage is within an appropriate range. In particular, of these characteristics, the operating temperature range is especially important when the ferroelectric crystal compounds are put into practical use.
However, in ferroelectric liquid crystal compounds known hitherto, the operating temperature range is generally narrow, and even in the case of ferroelectric liquid crystal compounds having a wide operating temperature range, the operating temperature range is in a high temperature region out of room temperature, as described, for example, in a paper by R. B. Meyer et al., "J. de Phys.", Vol. 36, p. L-69 (1975) or in a paper by M. Taguchi and T. Harada, "Proceedings of Eleventh Conference on Liquid Crystal," p. 168 (1985). Thus, no ferroelectric liquid crystal compounds satisfactory from the standpoint of practical use are obtainable yet.

Carboxylic acid ester compound, liquid crystal material, liquid crystal composition and liquid crystal element


An improved technique more accurately determines pore pressure of sedimentary rock penetrated by a borehole from the earth's surface. Formation overburden is directly measured at one or more locations in the borehole, and a log of formation overburden is generated using the measured overburden pressures and conventional geophysical data. A linear relationship has been determined between the logarithm of effective stress for a specific mineral and the logarithm of solidity, which allows the maximum effective stress and the compaction exponent for that mineral to be determined. This linear relationship enables the effective stress and compaction exponent for rock comprising a combination of minerals to be precisely determined at multiple borehole intervals. The effective stress and overburden calculated according to the techniques to the present invention are particularly useful to geologist and well planners in the oil and gas industry.

1. Field of Invention
The present invention relates to an improved method for calculating the pressure of fluid contained in a sedimentary rock which has been naturally compacted under the influence of gravity. A more accurate calculated pore pressure profile at various depth ranges produced according to the method of this invention produces valuable geological information useful in the hydrocarbon recovery industry.
2. Background
Pore fluid pressure is the major factor affecting the planning and drilling of an oil well. The borehole fluid hydrostatic pressure must be greater than the formation pore fluid pressure if one is to avoid the possibly catastrophic risk of blowout. Likewise, the borehole fluid circulating pressure must be less than fracture propagation pressure if one is to avoid the risk of lost circulation. Several expensive casing strings are usually required so that an oil well can be drilled within these two pore fluid pressure and fracture propagation pressure limits. The present invention thus enhances the safety of oil or gas well drilling operations, and also reduces the overall cost of hydrocarbon recovery by providing more reliable information to a drilling operator and thus avoiding complicated correction operations.
Because of its critical relationship to drilling operations, there are numerous techniques for calculating pore fluid pressure. All known petrophysical prior art methods calculate pore fluid pressure indirectly based upon measured rock properties, e.g., rock density or drilling rate of penetration. Most of these methods follow a calibration procedure which is not based on mechanical or physical information. Instead, these calibration procedures are generally based upon an observed empirical relationship between a measured physical parameter and a "normal" or hydrostatic compaction trend. The "normal" trend line is the average value of the measured parameter which changes as a function of depth. The change in the measured parameter according to these prior art techniques is thus related to a change in compaction of the sedimentary rock.
Sedimentary rocks are compacted by the stress applied to their grain matrix framework, which is not solely function of depth. When fluid pressure is approximately hydrostatic and the overburden is gradually increasing, both depth and stress are increasing. Under these conditions, depth behaves as a pseudo-stress variable. However, when pore pressure is elevated, effective stress and overburden gradients can be either increasing or decreasing and depth is not a pseudo-stress variable. Most of the prior art methods for determining pore fluid pressure use depth as a pseudo-stress variable in both "normal" and "excess" pressured intervals which results in significant pore pressure calculation errors.
Another significant failing of prior art pore pressure calculation techniques is attributable to their basic formulation. According to prior art techniques, pore pressure (P) is calculated as a sum of "normal" hydrostatic fluid pressure (Pn) which is inferred from compaction-depth trend, plus a differential or "excess" fluid pressure (.DELTA.P) which is related to a measured difference from the "normal" trend. The equation expressing this relationship is: EQU P=Pn+.DELTA.P (1)
Equation 1 is a physically incorrect mathematical formulation. In fact, Pascal's Principle requires that all of the fluids in a given local pore space or container be at the same pressure. Since the "excess" pressure term (.DELTA.P) does not exist in nature, there is no way it can be physically related to a measured parameter. Calibrating a measured physical parameter to a quantity which does not exist (.DELTA.P) is not reasonably sound.
The "normal compaction" vs depth trend line methods give the drilling operator a false sense of confidence based entirely upon the hydrostatic (Pn) calibration interval, wherein depth is a pseudo-stress variable. Pascal's Principle is not violated in the upper hydrostatic (Pn) interval because .DELTA.P=0 and P=Pn. Unfortunately, this sense of confidence gained in the (Pn) calibration interval is then transferred to the associated empirical "excess" pressured (.DELTA.P) calibration where two entirely different conditions apply.
In the "excess pressured" interval, depth is not a pseudo-stress variable. Also, the change in the measured physical parameter, such as density, resistivity, or rate of penetration, is related according to this prior art technique to the positive (.DELTA.P) term of Equation 1, which violates Pascal's Principle. Apparent success of pore pressure predictions derived from these methods below the base of the hydrostatically compacted interval may be due to a coincidence between pressure and depth which is peculiar to a given area or depth range. Any correspondence between calculated and observed pore pressures cannot be attributed to a physical relationship between the measured parameter and the excess fluid pressure, however, because such a relationship does not physically exist.
Lacking a physical cause-effect relationship, these prior art methods have been judged on a raw observed pressure vs. hydrostatic fluid pressure (Pn) trend basis. The (.DELTA.P) calibration correlates the difference between the observed measurement and the projected (Pn) normal compaction trend. There is no data to support the (Pn) projection below the top of the overpressured (.DELTA.P) zone because known pressure (P) is above (Pn). Consequently, all these methods include depth below the base of (Pn) as a contributing calibration factor. To make these "calibrations" work, similar depth-pore pressure profiles are taken within a given study area. What is presumed to be pore pressure prediction accuracy using these methods is actually a raw vs an averaged form of the same pressure data within a given area. The scatter of data about its own average trend is more commonly known as measurement precision. A narrow scatter within a given study area, such as reported in a 1965 article by Hottman et al., actually also means that depth-pore pressure profiles are similar within the area. In that case, the only measurement that is needed to successfully predict pore pressure is the measured depth to the top of the overpressured zone. A paper published that same year by Matthews et al shows both positively and negatively curving correlations of (.DELTA.P) to resistivity in different study areas and depth ranges. If there was a direct correlation between resistivity and pore pressure, one would expect one relationship or the other, but not both. The dozens of pore pressure methods in practice today which follow the P=Pn+.DELTA.P formulation violate a law of physics in their fluid pressure calibration and are flawed since they are not based on valid theories.
U.S. Pat. No. 4,833,914 to Rasmus is an example of a P=Pn+.DELTA.P method which violates Pascal's Principle. Rasmus volumetrically subdivides total rock porosity into overpressured porosity, effective porosity, and water porosity. A response equation solver then uses these terms to solve for pore pressure. As all fluid molecules are free to exchange position with each other through Brownian movement, there is no boundary between these artificially calculated pore volumes and no natural way to define them. The overpressured pore volume used by Rasmus is also a (.DELTA.P) term which exists in the same total pore space as "normally pressured" pore volume, which further violates Pascal's Principle. The method uses complicated statistics to converge on these artificially calculated, physically non-existent pore volume terms. This patent discloses pressure results being calculated in shales only from the "overpressured porosity" term. Although this calibration technique is performed statistically with a computer, it has the same physical shortcomings of the methods described in the previous paragraph.
U.S. Pat. No. 5,081,612 to Scott et al discloses a method for determining formation pore pressure from remotely sensed seismic data. This particular method and the prior art methods cited in this patent depend upon a hydrostatically compacted reference velocity profile. Referring back to Equation 1, this profile is essentially an observed or inferred curved (Pn) velocity gradient. The Scott et al pore pressure gradient technique applies to only one lithology, which is common to most of the prior art methods using a P=Pn+.DELTA.P formulation. Pore pressures are calculated with respect to the reference velocity gradient, which again is a violation of Pascal's Principle.
A 1990 article by Haas presented a seismic data pore pressure method which accounts for the difference in formation velocity which is a function of lithology and not pore pressure. These lithologic changes are "normalized" out by either addition or subtraction to make a smooth (Pn) velocity trend. After normalization, a velocity overlay is developed which empirically relates P=Pn+.DELTA.P by using lithology normalized velocity as the measured parameter. To operate properly, this Haas method would require all lithologies to compact in the same manner after normalization. Different lithologies did not compact similarly before their transit time offset normalization, and there is no logical basis to presume that they would compact similarly after offset normalization. The Haas procedure does not make rock compactional sense, and results derived therefrom should be suspect.
There are at least three prior art methods for determining pore fluid pressure from petrophysical measurements which are based upon the effective stress law, which was first elucidated by Terzaghi in 1923 through compactional studies of marine sediments: EQU P=S-.sigma..sub.v ( 2)
This relationship states that the fluid pressure in the pore space (P) can be calculated as the difference between the total overburden load (S) and the load borne by the sediment grain-grain contacts (.sigma..sub.v). In the science of rock and soil mechanics, this .sigma..sub.v term is known as the effective stress. Effective stress law is not widely used today for pore pressure prediction for various reasons, including the absence of an effective .sigma..sub.v calibration technique.
Effective stress was ignored by most geologic compaction studies, which instead evaluated geologic compaction as depth - porosity functions. Overburden gradients which differ considerably from place to place were assumed to be equal or uniformly varying. Although pore pressure was mentioned as a possible explanation for porosity differences, it was not subtracted from the total overburden load (S) to calculate effective stress. The mechanical effective stress explanation for the differences in porosity vs depth trends were thus ignored by geologists. The differences between porosity vs depth compaction curves were instead attributed to geologic factors such as geologic age and temperature. Articles by Maxwell published in 1964, and by Schmoker et al in 1988 and 1989, evidence this explanation.
A 1972 article by Baldwin et al unified the compaction of shales worldwide through use of a power law solidity vs depth relationship. These researchers re-cast the then-standard shale porosity vs depth curves, noting that each of the compaction curves from 14 worldwide basins fell within 2% of the Baldwin et al worldwide average power law solidity vs depth relationship. These researchers then substituted effective stress (.sigma..sub.v) for depth in a power law equation of the same form: EQU .sigma..sub.v =.sigma..sub.max (Solidity).sup..alpha.+1 ( 3)
In this equation, the .sigma..sub.max term is the power law intercept of the compaction curve with the 100% solidity axis. .sigma..sub.max is the effective stress that will cause complete compaction of the sedimentary particle mixture. .alpha.+1 is the slope of the power law compaction function for that granular material. This seemingly simple mathematical substitution transformed the Baldwin et al unified depth (pseudo-stress) empirical compaction function into a mechanically sound stress-strain relationship. The critical difference between this and all other compaction functions is that effective stress is the load applied to the sedimentary rock grain matrix framework. Solidity is a linear function of the compactional strain experienced by that rock grain matrix framework. Calibration using this equation represents a sound cause-effect relationship based on valid mechanical theories. However, Baldwin et al made no attempt to calculate pore pressure using this approach. The accompanying discussion of sandstone compaction curves in the Baldwin et al article indicated that sandstone compaction was apparently not governed by power law functions. The observed wide variance between sandstone compaction curves between different basins apparently suggested to them that no unified sandstone compaction function was possible.
A 1987 article by Holbrook et al and U.S. Pat. No. 4,981,037 applied the effective stress law for pore pressure prediction using a power law effective stress compaction function. The initial .sigma..sub.max and, .alpha.+1 constants used were expressed in the Baldwin et al article. The method was highly successful at predicting pore pressures in mid-shelf and off-shelf Gulf Coast sandstone-shale sequences. However, very deep highly sand prone wells forced a change of the effective stress constants .sigma..sub.max and .alpha. to higher values than suggested by Baldwin et al. The revised constants include the effects of pore pressure and are based upon calculated stress rather than pseudo-stress. The revised constants are more accurate and cover a broader depth and stress range than the Baldwin et al constants.
1989 and 1992 articles by Alixant also disclose the use of the effective stress law for pore pressure prediction. However, Alixant used a single laboratory derived compaction function, which he applied to shales only. In field testing, the compaction constant could not accurately cover the range of shale solidities. This method requires considerable changes in unrelated non-physical constants to match observed pore pressure data within a given local area. It is known, however, that strain hardening changes the compaction function of a rock. A constant laboratory compaction function can calculate stress from strain accurately only where the constant coincidentally matches the changing compaction function.
Another 1989 article by Bryant also disclosed an attempt to use the effective stress law for pore pressure prediction. Bryant used an average exponential function to calculate overburden as a function of depth rather than data from the well. His results were inaccurate partially because of this average exponential function, and partially because he used the same compaction function for sandstones and shales. Bryant's methods in not in common use today, possibly due to these large inaccuracies.
Holbrook extended the effective stress concept to the prediction of vertical fracture propagation pressure in a 1989 article. This approach was at least 4 times more accurate than prior art fracture pressure methods. Leakoff tests calibrated using this effective stress method all fell at or below the calculated overburden for that depth. Kehle noted in a 1964 article that all his observed onshore leakoff tests fell below the calculated overburden. However, neither the Kehle nor Holbrook articles used this observation as a feedback mechanism to improve the calculation of formation pore fluid pressure.
The disadvantages of the prior art are overcome by the present invention, and improved and techniques are hereinafter disclosed for more accurately calculating pore pressure of sedimentary rock which has been naturally compacted under the influence of gravity. The techniques of the present invention provide more meaningful pore pressure profiles which are useful in the hydrocarbon recovery industry.

Method for calculating sedimentary rock pore pressure


The apparatus includes a wet electrostatic precipitator (ESP) field disposed along a combusted fossil-fuel flue gas stream path downstream of a dry ESP field. The wet ESP field includes a chamber having a flue gas inlet and a flue gas outlet, and at least one collection plate positioned within the chamber. The chamber also includes one or more wash nozzle positioned adjacent the collection plate, and a wet hopper positioned substantially under the collection plate. The apparatus preferably further includes one or more cooling nozzles positioned near the flue gas inlet. The cooling and wash nozzles are fluidly coupled to a water source, while the wet hopper is fluidly coupled to either a pH adjustment module or a treatment processor. A method of removing contaminants from a flue gas stream using the above apparatus is also disclosed.

This invention relates generally to the control of pollutants emitted from a combustion process. More particularly, this invention relates to an apparatus and method for decreasing the concentration of contaminants present in a flue gas stream emitted by a fossil-fuel fired boiler by using a hybrid electrostatic precipitator.
The 1990 amendments to the United States Clean Air Act require major producers of air emissions, such as electrical power plants, to limit the discharge of airborne contaminants emitted from combustion processes. In most steam power plants in operation today, fossil fuels (such as petroleum or coal) are burned in a boiler to heat water into steam. The steam drives electrical turbines, which generate electricity. These fossil-fuel fired boilers, however, emit highly polluting flue gas streams into the atmosphere. These flue gas streams typically contain noxious gaseous chemical compounds, such as carbon dioxide, chlorine, fluorine, NOx and SOx, as well as particulates, such as fly ash that is a largely incombustible residue that remains after incineration of the fossil-fuel.
To date, many devices have been used to reduce the concentration of contaminants emitted by fossil-fuel fired boilers. One of the most effective devices is the electrostatic precipitator or ESP. An ESP is a device with evenly spaced static conductors, typically plates, which are electrostatically charged. When flue gases are passed between the conductors, particulates in the flue gas become charged and are attracted to the conductors. Typically, twenty to sixty conductors are arranged parallel to one another, and the flue gas stream is passed through gas passages formed between the conductors. The particulate layer formed on the conductors limits the strength of the electrostatic field and reduces the performance of the ESP. To maintain performance, the conductors are periodically cleaned to remove the collected particulates.
There are two types of ESPs, dry and wet ESPs. A dry ESP removes particulates from the conductors, by shaking or rapping the conductors and collecting the removed particulates in a dry hopper. A wet ESP removes the particulates by washing the particulates off the conductors and collecting the removed particulates in a wet hopper.
Dry ESPs, however, have a number of shortfalls. First, when the conductors are rapped, some of the particulates are re-entrained in the flue gas stream. If the flue gas is vented to atmosphere after such a dry ESP field, any re-entrained particulates will vent into the atmosphere. Therefore, although dry ESPs are highly efficient, a certain amount of contaminants cannot be removed by the dry ESP. It has been shown through experimentation, that each field of a dry ESP can remove approximately 70% of the particulates entrained in a flue gas stream. Therefore, a number of dry ESP fields are typically arranged in series until a desired concentration of particulates is attained. An example of a dry ESP can be found in U.S. Pat. No. 5,547,496, which is incorporated herein by reference.
To date, wet ESPs have not been used in electric power stations. However, existing systems for removing particulates using a series of wet ESP fields are well known in the industrial sector. An example of a wet ESP is disclosed in U.S. Pat. Nos. 3,958,960 and 3,958,960, which are incorporated herein by reference. A problem with these systems is that the introduction of too much moisture into the flue gas leads to moisture saturation of the flue gas. This tends not to be a problem in industrial plants, as there is little or no gaseous chemical compounds present in the flue gas stream that can dissolve in the moisture to form acidic solutions. However, in combusted fossil-fuel flue gas, the saturated flue gas condenses and combines with the gaseous chemical compounds present in the flue gas to form highly corrosive acid solutions. To limit corrosion of the system by these acids, the system must be lined with acid inhibitors and include induced draft fans.
A system for removing particulates using a series of dry ESP fields and a wet ESP field is disclosed in U.S. Pat. No. 3,444,668, which is also incorporated herein by reference. This system removes particulates from a cement manufacturing process. This process does not address problems specific to fossil-fuel fired boiler emissions, such as removing contaminant gaseous chemical compounds present in a combusted fossil-fuel flue gas stream.
Furthermore, systems that position a wet ESP field upstream of a dry ESP field, such as that disclosed in U.S. Pat. No. 2,874,802, which is also incorporated herein by reference, do not sufficiently remove contaminants from a gas stream or address the above described problems.
In view of the foregoing, it would be highly desirable to provide an efficient system for decreasing the concentration of contaminants within a flue gas stream emitted by a fossil-fuel fired boiler, while addressing the above described shortfalls of prior art systems.
According to the invention there is provided an apparatus for decreasing the concentration of contaminants within a flue gas stream emitted by a fossil-fuel fired boiler. The apparatus includes a wet electrostatic precipitator (ESP) field disposed along a combusted fossil-fuel flue gas stream path downstream of a dry ESP field. The wet ESP field includes a chamber having a flue gas inlet and a flue gas outlet, and at least one collection plate positioned within the chamber. The chamber also includes one or more wash nozzle positioned adjacent to the collection plate and a wet hopper positioned substantially under the collection plate. The apparatus preferably further comprises one or more cooling nozzles positioned near the flue gas inlet. The cooling and wash nozzles are fluidly coupled to a water source, while the wet hopper is fluidly coupled to either a pH adjustment module or a treatment processor.
Further according to the invention there is provided a method of decreasing the concentration of contaminants within a flue gas stream emitted by a fossil-fuel fired boiler. Contaminants are electrostatically collected from a combusted fossil-fuel flue gas stream on dry and wet electrostatic precipitator (ESP) conductors, where the wet ESP conductor is disposed downstream of the first ESP conductor. The dry ESP conductor is then shaken to remove contaminants collected thereon, while the wet ESP conductor is washed to remove contaminants collected thereon. The wet ESP conductor is washed either continuously or intermittently, however, a continuous wash is preferred for ease of control.
To improve performance, water is preferably sprayed into the wet ESP inlet flue gas stream to lower the flue gas temperature. In one embodiment, the water sprayed into the flue gas stream to lower the temperature and used to wash the collection plates is acquired from an untreated water source. In another embodiment, the sprayed water is recirculated in a closed loop.

Apparatus and method for decreasing contaminants present in a flue gas stream


Provided herein are methods, compositions, devices, and systems for the 3D printing of biomedical implants. In particular, methods and systems are provided for 3D printing of biomedical devices (e.g., endovascular stents) using photo-curable biomaterial inks (e.g., or methacrylated poly(diol citrate)).

Biodegradable stents (BDSs"), both metallic and polymeric, offer promising alternatives to conventional bare metal stents (BMSs) and drug-eluting stents (DES s) in providing temporary drug release for vessel patency, resisting late stent thrombosis due to uncovered struts, and potential reduction in the usage of antiplatelet drugs (refs. 4, 9; incorporated by reference in their entireties). Moreover, disappearance of BDS over time allows for eventual recurrence of natural vasomotion.


A device for fixing the screen of a ceiling light fixture to the base of the ceiling light fixture, wherein a seat is formed in the peripheral region of the base and is adapted to receive and retain an end of an elastic hook-shaped element, the opposite end whereof is adapted to engage, with a snap action, an undercut formed in the peripheral region of the screen, so as to clamp the rim of the screen against the rim of the base.

The present invention relates to an improved device for fixing the screen to the base of a ceiling light fixture.
In current wall-mounted, ceiling-mounted and suspended light fixtures the screen is conventionallly detachably coupled to the base by means of devices consisting of a sort of lever that is articulated to the base and is provided with means adapted to engage the screen so that by actuating the lever the screen is retained against the base.
However, conventional devices have the drawback that they protrude from the ceiling light fixture and are therefore aesthetically unpleasant. Furthermore, their application requires relatively troublesome assembly operations.

Ceiling light fixture with improved device for fixing the screen to the base


The present invention relates to novel fabric care compositions water containing dispersible or water-soluble copolymers which contain at least one UV-absorbing monomer and one hydrophilic monomer component.

1. Field of the Invention
The subject invention relates to fabric care compositions comprising novel water-dispersible or water-soluble copolymers which contain at least one UV-absorbing monomer and one hydrophilic monomer component. The copolymers used in these compositions may optionally contain a hydrophobic monomer component (i.e., if you have a water-soluble UV absorber, then you need hydrophobic groups to ensure it adsorbs). The compositions of the invention provide anti-fading and soil release benefits. Because of their UV absorbancy, the copolymers used in the composition of the invention could also be used in sunscreen compositions. The copolymers may also be used in other compositions such as may be recognized by those skilled in the art.
2. Prior Art
UV light induced fading of fabric is a major concern to those residing in areas of high solar intensity. A fabric care composition comprising an agent which could provide protection from solar ultraviolet radiation and thereby retard the rate of garment fading would therefore prove most useful to consumers living in tropical and sub-tropical climates.
To the applicants' knowledge, compositions comprising a UV absorbing monomer in combination with a hydrophilic monomer (which both delivers the copolymer into an aqueous system and also provides soil-release effect) are unknown.
More particularly, it is known, for example, that poly(ethylene terephthalate/poly(ethylene glycol) copolymers absorb onto hydrophobic surfaces to confer soil release properties (U.S. Pat. Nos. 4,702,857 to Procter & Gamble; 4,569,772 to Colgate Palmolive, and 3,959,230 to Procter & Gamble). These materials are believed to function by hydrophilicly modifying a hydrophobic surface such as oily soil on fabric or polyester fabric itself, deterring deposition of hydrophobic soils including body sebum. The poly(ethylene terephthalate) unit is believed to seek and adhere to the hydrophobic surface; the poly(ethylene glycol) portion is felt to give hydrophilic character to the fabric surface as well as aid the polymer in transfer through the aqueous medium.
In addition, it is also well known that UV-absorbing agents such as p-aminobenzoic acid (PABA) and its derivatives have been used for nearly half a century as UV screening agents (N. A. Shaath in "Sunscreens: Development, Evaluation, and Regulatory Aspects," N. J. Lowe and N. A. Shaath, Eds., Marcel Dekker, Inc., New York, 1990 ).
UV sunscreen agents such as PABA, however, are generally water-insoluble and there appears to be no teaching of combining such agents in carriers such that they may be used in fabric cleaning compositions.
U.S. Pat. No. 4,153,744 to K. H. Remley teaches the use of a tetrakis(hydroxymethyl)phosphonium salt to impart resistance to UV light-induced shade change to vat-dyed cellulosic textile materials. These compounds are unrelated to the copolymers used in the compositions of the invention. Further the process for delivering the compound is time-consuming and requires ammoniation of fabric followed by treatment with glacial acetic acid/hydrogen peroxide.
U.S. Pat. No. 4,788,054 to R. J. Bernhardt, et al. teaches the use of N-phenylphthalisimides as ultraviolet radiation [check] absorbers for cotton, wool, polyester, and rayon fabric. Again, these compounds are unrelated to the copolymers used in the compositions of the invention. Further, an aqueous sulfuric acid vehicle is required for deposition.
In P. C. Crews et al., Text. Chem Color, 19 (11): 21 (1987), the use of 2-hydroxy-4-dodecyloxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, and 2-hydroxy-4-methoxybenzophenone as UV absorbers for museum textiles is taught. These compounds differ from those used in the compositions of the invention. Here, potentially carcinogenic perchloroethylene is required as the vehicle. Water-soluble 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid was also shown to reduce dye fading of museum textiles, but with significant yellowing of fabric.
B. Milligan et al., Polym. Degrad. Stab., 10(4):335(1985), teach the use of 2,2'-dihydroxy-4-4'-bis-sulphobutyloxybenzophenone as a water-soluble ultraviolet light absorber for retarding the photo degradation of wool, but its synthesis requires the use of butanesultone, a suspected carcinogen.
None of the above-identified references make mention of soil release potential or teach materials that can be delivered in home laundry care.
U.S. Pat. Nos. 3,888,965, to S. L. Kwolek; 3,699,085 to T. A. Johnson; and 3,600,350 to S. L. Kwolek teach the synthesis of poly (.rho.-benzamide) via homopolymerization of 4-aminobenzoylchloride hydrochloride, and German Patents Get. Offen. 2,351,892 and 2,538,143 teach the synthesis of poly (.rho.-benzamide) via homopolymerization of 4-aminobenzoic acid in the presence of phosphates. In each of these references, the resulting poly PABA is insoluble in water, dilute acid, dilute base, and most organic solvents, rendering its application as a UV-absorbing polymer for fabric or skin care useless.
Japanese Patent Jpn. Kokai Tokkyo Koho 80,137,217 (Unitika Ltd.) teaches the synthesis of poly(ethylene terephthalate)/poly(.rho.-benzamide) copolymers for high modulus automobile tire cords. I. F. Osipenko, et al., Vesti Akad. Navuk BSSR, Ser. Khim. Navuk; 1:105 (1980), teach the synthesis of poly(ethylene terephthalate)/poly(.rho.-benzamide) copolymers and that the incorporation of .rho.-aminobenzoic acid into poly(ethylene terephthalate) improves fiber-forming properties and dye ability. Neither of these patents or publications mention the use of the poly(.rho.-benzamide)-based materials as UV absorbing agents or soil-release agents, nor do these disclosures mention that the poly( .rho.-benzamide)-based materials are water-soluble or water dispersible.
In each of the above-identified references, the compound used differs from the copolymer used in the compositions of the invention, there is no teaching that a UV absorbing monomer can be delivered in an aqueous (e.g., fabric care) system, and there is no teaching or suggestion that the UV absorbing monomer can be used in a copolymer which imparts fade-resistance or soil-release properties.
As such, there is a need in the art for compositions comprising copolymers containing a UV-absorbing monomer copolymerized with a hydrophilic monomer which allows the UV-absorbing polymer to be delivered in an aqueous system and simultaneously provides soil release benefits.

Fabric care composition comprising water soluble or water-dispersible copolymer containing UV-absorbing monomer

Lever Brothers Company, Division of Conopco, Inc.