DE69103534T2 - COVER FOR HYDROPHILE PENETRATE NETWORKS. - Google Patents

Description

initial situation 1. Field of the invention

The present invention relates to transparent materials capable of absorbing liquids, and in particular to materials that can be used as ink-receiving layers for transparent imaging materials.

2. State of the art

Transparent materials that can absorb substantial amounts of liquid while retaining a degree of durability and transparency are useful in contact lenses, primer coats for coatings applied from aqueous solutions, fog-resistant coatings, and transparent imaging materials for use with mechanized ink deposition devices such as pen plotters and ink jet printers. Transparent imaging materials are used as overlay films in engineering drawings and as transparencies for daylight projection. It is desirable that the surface of liquid-absorbing materials for use in transparent graphic applications be tack-free when touch dry even after absorbing substantial amounts of ink.

During normal use of pen plotters and ink jet printers, the inks used in such machines are exposed to the open air for long periods of time before the image is produced. After such exposure to air, the ink must still function acceptably without loss of solvent. To meet this requirement, ink formulations typically use solvents with very low volatility, such as water, ethylene glycol, propylene glycol, etc. Inks containing water or water-miscible solvents are generally preferred to aqueous inks, and the solvents of these inks are generally referred to as aqueous liquids.

Due to the low volatility of aqueous liquids, drying of an image by evaporation is very limited. In the case of imaging on a sheet of paper, which has a fibrous texture, a substantial amount of the liquid diffuses into the sheet and the surface appears dust-dry (also called "touch-dry") within a very short time. In the case of imaging on a polymeric film, some means of absorbing aqueous liquids is required if satisfactory drying of the image is to take place.

Compositions useful as transparent, liquid-absorbent materials have been formed by compounding a liquid-insoluble polymeric material with a liquid-soluble polymeric material. The liquid-insoluble material is believed to form a matrix which receives the liquid-soluble material. Examples of such blends are the transparent, water-absorbent polymeric materials disclosed in U.S. Patent Nos. 4,300,820 and 4,369,229 and in EP-A-0 233 703.

A common problem in the preparation of polymer blends is the incompatibility of the polymers to be compounded. When attempting to compound polymers that are incompatible, phase separation occurs and results in turbidity, lack of transparency and other forms of inhomogeneity.

The compatibility between two or more polymers in a blend can often be improved by that monomer units which have a certain affinity for the liquid-soluble polymer are incorporated into the liquid-insoluble, matrix-forming polymer chains. Polymer materials which still have a small proportion of acid functionality are more likely to show compatibility with polyvinyllactams. Normally, the compatibility of polymers to be compounded is improved if the polymers can form hydrogen bonds with one another.

A second form of incompatibility found when using blends of liquid-absorbing polymers is the incompatibility of the matrix forming insoluble polymer with the liquid to be absorbed. For example, if the liquid to be absorbed is water and if the water-insoluble polymers are hydrophobic, some inhibition of water absorbency is to be expected. One method of overcoming this difficulty is to use hydrophilic matrix polymers which are water-insoluble at the temperatures at which they are to be used, although they may be water-soluble at another temperature. U.S. Patent No. 4,503,111 discloses dye-receiving layers comprising either polyvinyl alcohol or gelatin compounded with polyvinyl pyrrolidone. Both polyvinyl alcohol and gelatin, which are water-insoluble at room temperature, can act as matrix-forming polymers for the coatings, whereby the coatings are highly receptive to aqueous printing inks. However, the coatings have a tendency to become sticky either due to image formation or due to high humidity.

It is clear that although blends of soluble and insoluble polymers may be useful as liquid-absorbent compositions, they face major limitations in terms of liquid absorbency and durability.

Summary

The present invention provides a coatable composition capable of forming hydrophilic, liquid-absorbing semi-interpenetrating networks, hereinafter referred to as SIPN. The SIPN of the present invention are formed from polymer blends comprising (a) at least one crosslinkable polymer, (b) at least one liquid-absorbing polymer comprising a water-absorbing polymer, and (c) optionally a crosslinking agent. Substantially all of the crosslinking of the crosslinkable polymer occurs after the composition is applied to a substrate and allowed to dry. These SIPN are continuous networks in which the crosslinked polymer forms a continuous matrix throughout the volume of the material and through which the liquid-absorbing polymer is entangled in such a manner that a macroscopically homogeneous composition is formed. The SIPNs of the present invention can absorb substantial amounts of liquids that are solvents or swelling agents of the non-crosslinked portion of the SIPN without loss of spatial coherence and without dissolution or other forms of phase separation. In cases where the SIPNs are initially transparent, they remain transparent even after absorbing substantial amounts of liquids.

The crosslinking used in forming the matrix component of the SIPN is such that it provides durability in the presence of the liquids encountered in use and compatibility with the liquid absorbing component. The crosslinked matrix component and the liquid absorbing component are miscible, exhibit little or no phase separation, and produce little or no haze upon coating. The nature of the crosslinking should not cause phase separation or other inhomogeneity in the SIPN or gelation of the coating solutions prior to application or application.

The present invention further provides transparent compositions that can provide improved absorption and durability while maintaining transparency and are amenable to the processing methods commonly used in the manufacture of transparent graphic materials.

Detailed description

The cross-linked part of the SIPN is hereinafter referred to as the matrix component and the liquid-absorbing part as the absorbent component.

The term "hydrophilic" as used herein is used to describe a material that is normally water absorbent either in the sense that its surface is wettable by water or in the sense that the volume of the material is capable of absorbing substantial amounts of water. In particular, materials that exhibit surface wettability with respect to water are said to have hydrophilic surfaces, while materials with surfaces that are not wettable by water are said to have hydrophobic surfaces. The term "hydrophilic, liquid-absorbent materials" as used herein describes materials that can absorb substantial amounts of water, mixtures of water and other liquids, including those materials that are water-soluble. In discussing molecular structures, monomer units are referred to as hydrophilic units if they have a water sorption capacity of at least one mole of water per mole of monomer unit. The sorption capacity of different monomer units is given, for example, by DW Van Krevelin in collaboration with PJ Hoftyzer, in "Properties of Polymers: Correlations With Chemical Structure", Elsevier Publishing Company (Amsterdam, London, New York: 1972) pp. 294 ... 296. Monomer units are said to be hydrophobic if they form water-insoluble polymers that can only absorb small amounts of water when polymerized with themselves.

The matrix component of the SIPN of the invention comprises crosslinkable polymers which are either hydrophobic or hydrophilic and can be derived from the copolymerization of acrylic or other hydrophobic or hydrophilic ethylenically unsaturated monomer units with monomers which have acid groups or when ester pendant groups are already present in these acrylic or ethylenically unsaturated monomer units by means of hydrolysis.

Hydrophobic monomer units suitable for producing crosslinkable matrix components are preferably selected from:

(1) Acrylates and methacrylates with the structure:

wherein R¹ is hydrogen or -CH₃ and R² is an alkyl group having up to 10 carbon atoms, preferably up to 4 carbon atoms and more preferably 1 to 2 carbon atoms, a cycloaliphatic group having up to 9 carbon atoms, a substituted or unsubstituted aryl group having up to 14 carbon atoms and an oxygen-containing heterocyclic group having up to 10 carbon atoms;

(2) Acrylonitrile or methacrylonitrile;

(3) Styrene or α-methylstyrene having the structure:

wherein X and Y are independently hydrogen or alkyl groups having up to 4 carbon atoms, preferably 1 or 2 carbon atoms, a halogen atom, alkyl halide group or ORm, wherein Rm is hydrogen or an alkyl group having up to 4 carbon atoms, preferably 1 or 2 carbon atoms and Z is hydrogen or methyl; and

(4) Vinyl acetate.

Hydrophilic monomer units suitable for the preparation of crosslinkable polymers are preferably selected from: (1) Vinyllactams having the basic structure:

where n represents the integer 2 or 3; (2) acrylamide or methacrylamide having the structure:

wherein R¹ is as defined above, R³ represents hydrogen or an alkyl group having up to 10 carbon atoms, preferably from 1 to 4 carbon atoms, and R⁴ represents hydrogen or an alkyl group having up to 10 carbon atoms, preferably from 1 to 4 carbon atoms, or a hydroxyalkyl group or a Alkoxyalkyl group having the structure -(CH₂)p-OR³, wherein p represents an integer from 1 to 3, inclusive;

(3) tert-aminoalkyl acrylates or tert-aminoalkyl methacrylates having the structure:

wherein m represents the integer 1 or 2, R¹ and R³ are as defined above and R⁵ represents hydrogen or an alkyl group having up to 10 carbon atoms, preferably from 1 to 4 carbon atoms;

(4) Hydroxyalkyl acrylates, alkoxyalkyl acrylates, hydroxyalkyl methacrylates or alkoxyalkyl methacrylates having the structure:

wherein R¹ and R⁴ are as defined above, q represents an integer from 1 to 4, inclusive, preferably 2 to 3, and

(5) Alkoxyacrylates or alkoxymethacrylates having the structure:

wherein r represents an integer from 5 to 25, inclusive, and R¹ is as defined above.

Some of the above structures of both the hydrophobic and hydrophilic monomer units contain ester pendant groups which can be readily made crosslinkable by hydrolysis. For the others, monomer units containing acid groups must be incorporated into the polymer structure to make it crosslinkable. Polymerization of these monomers can be carried out by the typical methods of free radical, solution, emulsion or suspension polymerization. Suitable monomer units containing acid groups include acrylic or methacrylic acid, other copolymerizable carboxylic acids and ammonium salts.

The crosslinking agent is preferably selected from the group of polyfunctional aziridines containing at least two crosslinking sites per molecule, such as trimethylolpropane tris-(β-(N-aziridinyl)propionate)

Pentaerythritol tris-(β-(N-aziridinyl)propionate)

Trimethylolpropane tris-(β-(N-methylaziridinyl)propionate)

Crosslinking can also be carried out with the aid of metal ions, such as those provided by salts with polyvalent metal ions, provided that the composition containing the crosslinkable polymer is prepared from 80 to 99 parts by weight of monomer and from 1 to 20 parts by weight of a chelating compound.

The metal ions can be selected from ions of the following metals: cobalt, calcium, magnesium, chromium, aluminium, tin, zirconium, zinc, nickel, etc., with the preferred compounds being selected from aluminium acetate, aluminium ammonium sulphate dodecahydrate, alum, aluminium chloride, chromium(III) acetate, chromium(III) chloride hexahydrate, cobalt acetate, cobalt(II) chloride hexahydrate, Cobalt(II) acetate tetrahydrate, cobalt sulfate hydrate, copper sulfate pentahydrate, copper acetate hydrate, copper chloride dihydrate, iron(III) chloride hexahydrate, iron(III) ammonium sulfate dodecahydrate, iron(II) chloride tetrahydrate, magnesium acetate tetrahydrate, magnesium chloride hexahydrate, magnesium nitrate hexahydrate, manganese acetate tetrahydrate, manganese chloride tetrahydrate, nickel chloride hexahydrate, nickel nitrate hexahydrate, tin(II) chloride dihydrate, tin(II) chloride, tin(II) acetate, tin(IV) acetate, strontium chloride hexahydrate, strontium nitrate, zinc acetate dihydrate, zinc chloride, zinc nitrate, zirconium(IV) chloride, zirconium acetate, zirconium oxychloride, zirconium hydroxychloride, ammonium zirconium carbonate, etc.

The preferred chelating compounds can be selected from:

(1) Alkali metal salts of acrylic or methacrylic acid having the structure:

wherein R¹ is as described above and M represents Li, Na, K, Rb, Cs or NH₄, preferably NH₄, Na or K;

(2) N-substituted acrylamido or methacrylamido monomers containing ionic groups and having the following structure:

wherein R¹ is as described above, R⁶ represents hydrogen or an alkyl group having up to 4 carbon atoms, preferably hydrogen, R⁷ represents COOM or -SO₃M, wherein M is as described above;

(3) alkali metal salts of p-styrenesulfonic acid;

(4) Sodium salt of 2-sulfoethyl acrylate and sodium salt of 2-sulfoethyl methacrylate;

(5) 2-vinylpyridine and 4-vinylpyridine;

(6) vinylimidazole;

(7) N-(3-aminopropyl)methacrylamide hydrochloride; and

(8) 2-Acetoacetoxyethyl acrylate and 2-acetoacetoxyethyl methacrylate.

Other crosslinkable polymers suitable for the matrix component of the hydrophilic SIPN of the invention are polymers having crosslinkable tert-amino groups, where the groups can either be provided as part of the monomer units as used in forming the polymer or graft polymerized onto the polymer after formation of the polymer backbone. These have the general structure:

wherein R⁸ represents a member selected from the group consisting of substituted and unsubstituted alkyl groups, substituted and unsubstituted amide groups and substituted and unsubstituted ester groups, the aforementioned groups preferably having no more than 10 carbon atoms, more preferably no more than 5 carbon atoms, substituted and unsubstituted aryl groups, preferably having no more than 14 carbon atoms; R⁹ and R¹⁰ independently represent a member selected is selected from the group consisting of substituted and unsubstituted alkyl groups, preferably having no more than 10 carbon atoms, more preferably having no more than 5 carbon atoms, and substituted and unsubstituted aryl groups, preferably having no more than 14 carbon atoms. In addition, R⁹⁰ and R¹⁰ may be linked to form the substituted or unsubstituted cyclic structure -R⁹⁰-R¹⁰-. The symbol /\/\/\/ represents a plurality of unsubstituted or substituted or -CH₂- groups linked together to form the backbone of the chain.

Where water or other aqueous liquids are to be absorbed, it is preferred that R⁸ is selected as -(C=O)NH(R¹¹)-, wherein R¹¹ represents a substituted or unsubstituted divalent alkyl group, preferably having no more than 10 carbon atoms, and more preferably no more than 5 carbon atoms. Preferred substituents for R¹¹ are those capable of bonding hydrogen, including -COOH, -CN and -NO₂. In addition, R¹¹ may comprise in its structure hydrogen bonding groups such as, for example,

Crosslinkable polymers suitable for the matrix component, in which R⁸ is - (C=O)NH(R¹¹) -, can be prepared by treating polymers or copolymers containing maleic anhydride with an amine of the following structure: wherein R⁹, R¹⁰ and R¹¹ are as described above.

A particularly useful example of a crosslinkable matrix component is a copolymer of polymethylvinylether and maleic anhydride, wherein these two monomer units are present in approximately equimolar amounts. This copolymer can be formed in the following manner:

wherein R9, R10 and R11 are as described above, while s is preferably a number from about 100 to about 600. This reaction can be readily prepared by dissolving the polymethylvinylether/maleic anhydride copolymer, i.e., reactant (a), in methyl ethyl ketone; by dissolving the amine, i.e., reactant (b), in an alcohol such as methanol or ethanol, and by mixing the two solutions. This reaction proceeds rapidly at room temperature with stirring. The product of this reaction may begin to form a cloudy suspension which becomes clear again by adding water to the solution.

Crosslinking agents suitable for this type of polymer are multifunctional alkylating agents, each functional group of which forms a bond with a polymer chain via a tert-amino group by quaternization of the trivalent nitrogen of the tert-amino group. Difunctional alkylating agents are suitable for this purpose. In the case where the tert-amino group is a side group on the backbone of the polymer, the crosslinking reaction can be represented as follows:

wherein R⁸, R⁹⁰, R¹⁰ and s are as described above, R¹² may be R⁸, R⁹⁰ or R¹⁰ and Q may be a halide, an alkylsulfonate, preferably having no more than 5 carbon atoms, or any arylsulfonate, preferably having no more than 14 carbon atoms.

Other crosslinkable polymers suitable for forming the matrix component of the SIPN of the invention include polymers containing silanol groups, where the silanol groups can either be part of the monomer units used in forming the polymer or are grafted onto the polymer after the polymer backbone has been formed. If grafting is preferred, the polymer backbones normally contain Monomer units of maleic anhydride that can be converted to graft-polymerizable sites by reaction with compounds containing primary amino groups. Silanol pendant groups can be grafted onto these sites by heating a solution containing the backbone polymer with an aminoalkoxysilane. The alkoxysilane can then be hydrolyzed by adding water. The reaction scheme can be represented as follows: Page group

wherein A represents a monomer unit, preferably selected from the group consisting of acrylonitrile, allyl acetate, ethylene, methyl acrylate, methyl methacrylate, methyl vinyl ether, stilbene, isostilbene, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, vinylpyrrolidone, divinyl ether, norbornene and chloroethyl vinyl ether;

R¹³ represents a divalent alkyl group, preferably having up to 10 carbon atoms, more preferably having no more than 5 carbon atoms; R¹⁴, R¹⁵ and R¹⁶ independently represent alkoxy groups having up to about 5 carbon atoms, more preferably having no more than about 3 carbon atoms; and

R¹⁷ represents a member selected from the group consisting of substituted or unsubstituted alkyl groups, preferably having up to 10 carbon atoms, more preferably not more than 5 carbon atoms, and substituted or unsubstituted aryl groups, preferably having up to 14 carbon atoms.

Suitable substituents for R¹⁷ include alkoxy, -OH, -COOH, -COOR, halide and -NR², where R represents an alkyl group, preferably having up to 5 carbon atoms, more preferably having no more than 3 carbon atoms.

The relative proportions of the two types of side groups in polymer (d) are determined by the relative amounts of compounds (b) and (c) used in the grafting solutions. The molar ratio of compound (c) and compound (b) in the reaction is in the range of about 3 to about 6, preferably about 4 to about 5.

A discussion of the copolymerization of these monomer units with maleic anhydride and the properties of the resulting copolymers can be found in Brownell, G. L., "Acids, Maleic and Fumaric" in Encyclopedia of Polymer Science and Technology, Vol. 1, John Wiley & Sons, Inc., (New York: 1964), pp. 67...95.

Once the silanol groups have been formed by hydrolysis, the resulting polymer can be crosslinked by removing water and other solvents from the system without the addition of further crosslinking agents according to the reaction:

In addition, cross-linking can occur at more than one of the -OH groups bonded to the silicon atom.

While the primary function of the matrix component of the SIPN is to provide spatial coherence and durability to the SIPN without compromising the overall liquid absorption capacity of the SIPN, the primary function of the liquid absorbing component is to promote the absorption of liquids. If aqueous liquids are to be absorbed, as is the case with most printing inks, the liquid absorbing component must be capable of absorbing water and preferably be water soluble. The liquid absorbing component can be selected from polymers formed from the following monomers:

(1) Vinyllactams with the basic structure:

where n is as described above;

(2) Alkyl tert-aminoalkyl acrylates and alkyl tert-aminoalkyl methacrylates having the structure:

wherein, R¹ and R³ are as described above;

(3) Alkyl quaternary aminoalkyl acrylates or alkyl quaternary aminoalkyl methacrylates having the structure:

wherein p represents the integer 1 or 2, R¹ is as described above, R¹⁸, R¹⁹9, R²⁰ independently represent hydrogen or an alkyl group having up to 10 carbon atoms, preferably having 1 to 6 carbon atoms, and Q represents a halide, R¹⁸SO₄, R¹⁹9SO₄ or R²⁰SO₄.

The polymerization of these monomers can, as already mentioned, be carried out using conventional radical polymerization methods.

Optionally, the liquid-absorbing component can be selected from commercially available water-soluble or water-swellable polymers such as polyvinyl alcohol, polyvinyl alcohol/poly(vinyl acetate) copolymer, poly(vinyl formal) or poly(vinyl butyral), gelatin, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethyl starch, polyethyloxazoline, polyethylene oxide, polyethylene glycol, polypropylene oxide, etc. The preferred polymers are polyvinyllactams, particularly polyvinylpyrrolidone and polyvinyl alcohol.

The SIPNs of the present invention to be used to form ink-receiving layers typically comprise from about 0.5% to 6.0% by weight of crosslinking agent, preferably from about 1.0% to 4.5% by weight, if crosslinking agent is required. The crosslinkable polymer may comprise from about 25% to about 99% by weight, preferably from about 30% to about 60% by weight, of the total SIPN. The liquid-absorbing component may comprise from about 1% to about 75% by weight, preferably from about 40% to about 70% by weight, of the total SIPN.

Such ink-receiving layers are normally supported on a substrate, such as transparent polymer films. To form an ink-receiving layer, a composition for producing such a layer is simply applied to the substrate using a coating solution, which is then dried to form a solid layer. A coatable liquid composition can be prepared by dissolving polymers of the matrix component and the liquid-absorbing component in a conventional solvent, which may be water or water-miscible solvents, in appropriate proportions depending on the solubility of the components. The appropriate cross-linking agent, if used, is then added and mixed until a uniform solution is obtained.

Common solvents can be selected by making use of the Hansen parameters, which are are numerical values characterizing the individual contributions to the cohesive energy density that come from intermolecular dispersion forces, dipole forces, and hydrogen bonding forces of a particular compound. Soluble solid materials tend to be more readily dissolved by liquids with Hansen parameters within a given range, called solubility zones, and less likely to be dissolved by liquids with Hansen parameters outside the solubility zone. Because of this tendency, the Hansen parameters can be used as a basis in selecting individual solvents or in formulating solvent mixtures capable of dissolving a particular solid material or combination of solid materials.

Experimentally determined Hansen parameters and solubility zones for a variety of solid materials, together with the Hansen parameters for many commonly used solvents, as well as formulas for the mathematical determination of Hansen parameters for materials not listed, can be found in Barton, A.F.M. CRC Handbook of Solubility Parameters and Other Cohesion Parameters, CRC Press, Inc., (Boca Raton: 1983), which is hereby incorporated by reference.

Systematic methods for applying Hansen parameters to the calculation of solvent mixture formulations capable of dissolving specific combinations of solid materials in more complicated systems can be found in Teas, J.P., "Solubility Parameters", Treatise on Coatings, R.R. Myers and J.S. Long, Eds., Vol. 2, Part 11, Marcel Dekker (New York: 1976), pp. 413 ... 448, which is hereby incorporated by reference. Since such methods of calculation often lead to more than one possible solvent formulation, additional experimental evaluations may be necessary to arrive at an optimal formulation.

Additional constraints on the choice of solvents may arise from practical requirements, such as coating, drying, toxicity or other considerations.

In solution, little or no cross-linking of the matrix polymer occurs prior to coating. The components remain uniformly dissolved in solution, retain good coating properties without gelling, have a reasonable pot life to enable coating on a transparent substrate such as a polymer film and then dry to form a continuous layer. The amount of heat required to achieve drying in a reasonable time is usually sufficient to cause cross-linking of the matrix component. In this way, problems of handling volatile monomers, some of which may be toxic, and unreacted monomers resulting from incomplete reaction are eliminated.

SIPN solutions of the present invention may contain additional modifying ingredients such as coupling agents, particles, surfactants, viscosity improvers and similar materials, provided that such additives do not adversely affect the liquid absorption capability of the invention.

Coating may be done by any suitable means such as knife coating, rotogravure, reverse roll coating or other conventional means. Drying may be done by heated air. If preferred, an adhesion promoting primer layer may be applied to the substrate prior to coating. Such primer layers may include primer coatings, surface treatments such as corona treatment or other suitable treatment. The adhesion of the SIPN layer may also be improved by providing a gelatin undercoat of the type used in photographic film supports between the primer layer and the SIPN layer. Film supports having both a primer layer and a gelatin undercoat are commercially available and are often referred to as primer-undercoat film supports.

When the SIPNs of the present invention are to be used to form the ink-receiving layer of a film for use with an ink-jet printer, it is preferred that the support of the film have a thickness in the range of about 50...125 micrometers. Films with thicknesses below about 50 micrometers tend to be too brittle for graphics-capable films, while films with thicknesses above about 125 micrometers tend to be too stiff for easy passage through many of the imaging devices currently in use. Materials suitable for supports of graphics-capable films include polyesters, e.g., polyethylene terephthalate, cellulose acetates, polycarbonates, poly(vinyl chlorides), polystyrenes, and polysulfones.

When the SIPN of the present invention is to be used to form the ink-receiving layer of a film for use with ink-jet printers, the SIPN layer may be additionally coated with an ink-permeable overcoat, tack-free protective layer, such as a layer of polyvinyl alcohol having starch particles dispersed therein, or a semi-interpenetrating polymeric network in which polyvinyl alcohol is the absorbent component. Such overcoats may provide surface properties that assist in properly controlling the spread of ink droplets and thereby optimizing image quality.

In addition to the polymeric materials comprising the SIPN, other modifying ingredients, such as surfactants, particles, or the like, may be added to the topcoat formulation to improve ink flow, dot spread, or other aspects of ink receptivity to improve the appearance of the image.

To better illustrate the various embodiments of the present invention, the following non-limiting examples are given.

example 1

A polymeric material suitable for the matrix of a SIPN was prepared by combining in a 1-liter brown bottle: N-vinyl-2-pyrrolidone (75 parts by weight), N,N-dimethylacrylamide (2 parts by weight), the ammonium salt of acrylic acid (5 parts by weight), azo-bisisobutyronitrile (0.14 parts by weight, "Vazo", available from E. I. DuPont de Nemours and Company) and deionized water (566 parts by weight). The mixture was purged with anhydrous nitrogen gas for 5 minutes; polymerization was then effected by immersing the bottle for a period of between 18 and 24 hours in a bath maintained at a constant temperature of 60 °C. The resulting polymerized mixture was then diluted with deionized water to give a 10% aqueous solution. The resulting solution is hereinafter referred to as "Solution A".

Solution A (8 g of a 10% aqueous solution) was mixed with surfactant (0.2 g of a 2% aqueous solution of "Triton X100", Rohm and Haas Co.), polyvinyl alcohol (8 g of a 5% aqueous solution of "Vinol 540", Air Products and Chemicals, Inc.) and polyfunctional aziridine crosslinking agent (0.5 g of a 10% aqueous solution, XAMA-7, Sanncor Ind. Inc.) in a separate vessel.

The resulting solution was coated onto a support of polyethylene terephthalate film of 100 micrometers thickness, primed with polyvinylidene chloride and over which had been coated a gelatin undercoat of the type used in photographic films to improve the adhesion of gelatin ("Scotchpar" Type PH, primer-undercoated film, available from Minnesota Mining and Manufacturing Company). The coating was applied using a doctor blade Coating equipment to a wet thickness of 200 microns. The coating was then dried by exposure to circulating heated air at a temperature of 90 ºC for 5 minutes to form a clear SIPN layer.

Printing was carried out with an inkjet printer and a pen using ink containing "Direct Blue 99" dye (3% solution in water). After 6 minutes, the imaged film was immersed in water without removing dye from the image. The SIPN layer remained intact.

Example 2

A solution of the matrix component of the present invention was prepared by first dissolving 1.3 g of a copolymer of methyl vinyl ether and maleic anhydride ("Gantrez" AN-169, available from GAF Chemicals Corporation) in 24.6 g of methyl ethyl ketone. In a separate container, 1.3 g of aminopropylmorpholine (available from Aldrich Chemical Company, Inc.) was dissolved in 11.6 g of methanol. The previously prepared solution of the copolymer was then added dropwise to the aminopropylmorpholine/methanol solution, after which 36.6 g of distilled water was added to the resulting combined solution. The resulting solution is hereinafter referred to as "Matrix Component Solution B".

In another vessel, 2.5 g of polyvinylpyrrolidone (K90, available from GAF Chemicals Corporation) was dissolved in 22.1 g of distilled water. This solution was then added to the matrix component solution B and stirred until a uniform solution was obtained. The resulting solution, hereinafter referred to as "Blend Solution B," was then divided into 5 samples of 20.0 g each.

The dihalogen compound 3,3-bis-(iodomethyl)-oxetane was prepared according to the procedure described in Sorenson, WR and Campell, TW, "Preparative Methods of Polymer Chemistry", 2nd edition, New York, Interscience Publishers, Inc., 1968, p. 376. process, which is hereby incorporated by reference. A solution of 10 parts by weight of this compound to 90 parts by weight of dimethylformamide (DMF) was prepared for use as an alkylating agent to crosslink the matrix component.

Crosslinkable solutions according to the present invention were prepared by adding 0.35 g of the 3,3-bis(iodomethyl)oxetane/DMF solution to one of the 20.0 g samples of Blend Solution B, 0.70 g of the 3,3-bis(iodomethyl)oxetane/DMF solution to a second 20.0 g sample of Blend Solution B, and 1.4 g of 3,3-bis(iodomethyl)oxetane/DMF solution to a third 20.0 g sample of Blend Solution B.

These solutions were each coated on a support of 100 micrometers thick polyethylene terephthalate film primed with polyvinylidene chloride and over which had been coated a gelatin undercoat of the type used in photographic films to improve the adhesion of gelatin ("Scotchpar" Type PH primer and undercoat film, available from Minnesota Mining Manufacturing Company). Coating was carried out using a doctor blade coater with a wet thickness of solution applied to the film of 75 micrometers. Drying was carried out by exposure to circulating heated air at a temperature of 90°C for 5 minutes.

After drying, all three solutions resulted in clear SIPN layers that maintained their spatial integrity when washed under a moving stream of water at room temperature. Exposure to water in selected areas resulted in detectable water absorption, as documented by swelling of the SIPN layer. Swelling of the SIPN layer was detected by the protrusion that can be felt by running a finger across the surface of the coated film in such a way that one goes from the part of the layer not exposed to water to the part exposed to water. Since the amount of water used crosslinking agent could be varied over a wide range without crosslinking failure and without loss of hydrophilicity, it was concluded that this type of crosslinking is sufficiently tolerant of variability to be useful in a manufacturing process.

Example 3

The polymeric material for the matrix of the SIPN was prepared by combining in a 1-liter brown bottle: N-vinyl-2-pyrrolidone (28 parts by weight), N,N-dimethylacrylamide (20 parts by weight), 2-acrylamido-2-methylpropanesulfonic acid (2 parts by weight of the ammonium salt), azo-bis-isobutyronitrile (0.07 parts by weight, "Vazo", available from E. I. du Pont de Nemours and Company), and deionized water (280 parts by weight). After the mixture was purged with dry nitrogen gas for 5 minutes, polymerization was carried out by immersing the bottle in a bath maintained at a constant temperature of 60 ºC for 8 hours to give a very viscous clear solution (97.8% conversion). The resulting polymerized mixture was then diluted with deionized water to yield a 10% solution in water, hereinafter referred to as "Solution C".

Solution C (21.94 g of a 10% aqueous solution) was thoroughly mixed with polyvinyl alcohol ("Vinol 540", available from Air Products and Chemical, Inc., 28.6 g of a 5% aqueous solution) and chromium chloride crosslinking agent (0.29 g of a 10% aqueous solution) in a separate container. The resulting solution was coated onto a support of polyethylene terephthalate film 100 microns thick which had been primed with polyvinylidene chloride and over which was coated a gelatin undercoat of the type used in photographic films to improve the adhesion of gelatin ("Scotchpar" Type PH, primer and undercoat film, available from Minnesota Mining and Manufacturing Company). Coating was carried out using a doctor blade coater. with a wet thickness of 200 microns. The coating was then dried by exposure to circulating heated air at a temperature of 90 ºC for 5 minutes. After drying, a clear SIPN layer was formed.

Printing was carried out with an inkjet printer and a pen plotter using a dye-containing ink (3 ... 5% solution in water). After one minute, the imaged film was dust-dry. The SIPN layer remained intact.

Example 4

The purpose of this example is to illustrate the use of a SIPN according to the invention as a single-layer, hydrophilic coating capable of absorbing aqueous ink.

A solution of the graft material was prepared by first dissolving 0.07 g of 3-aminopropyltriethoxysilane (Aldrich Chemical Co., Inc.) and 0.22 g of 2-methoxyethylamine (Aldrich Chemical Co., Inc.) in 7.9 g of methanol. In a separate vessel, a solution of the backbone polymer was prepared by dissolving 0.5 g of a copolymer of methyl vinyl ether and maleic anhydride ("Gantrez AN-169", GAF Chemicals Corporation) in 9.5 g of methyl ethyl ketone. The solutions of the graft material and the backbone polymer were then combined and stirred to give a clear, viscous liquid. A solution of the absorbent component was prepared in a separate vessel by adding 1.5 g of polyvinylpyrrolidone (K-90, GAF Chemicals Corporation) to 13.5 g of deionized water and stirring the resulting mixture until a clear solution was formed. To the previously prepared combined solutions of graft material and backbone polymer, the solution of the absorbent component was added along with 15.0 g of water and the resulting mixture was stirred at room temperature until a clear solution was obtained.

A dye-receiving layer was formed by coating the solution thus prepared onto a sheet of 100 micron thick polyethylene terephthalate film ("Scotchpar" Type PH primer and undercoat film available from Minnesota Mining and Manufacturing Company) with polyvinylidene chloride primer and gelatin undercoat using a doctor blade coater set to apply a liquid layer having a wet thickness of 125 microns. The liquid layer was dried in a drying oven at a temperature of 90°C for 5 minutes.

The ink uptake in the dried coating was tested by writing on it with a pen using an aqueous ink (“Expresso” brand pen, Sanford Corp. Bellwood, IL). The ink image dried sufficiently in 10 seconds to be smudge-proof when lightly rubbed with a finger. The SIPN layer tended to become tacky at relative humidities of about 90% or higher.

Numerous modifications and variations of the present invention will become apparent to those skilled in the art without departing from the scope of the claims, it being understood that the present invention is not unduly limited to the illustrative embodiments contained herein.

Claims (4)

1. An article comprising a substrate containing on at least one of its major surfaces a hydrophilic, liquid-absorbing, semi-interpenetrating network comprising: (a) at least one cross-linked polymer; and (b) at least one liquid-absorbing polymer, comprising a water-absorbing polymer, wherein the cross-linked polymer is derived from a cross-linkable polymer that has been cross-linked after its application to the substrate. 2. A method for producing the article according to claim 1, comprising the steps: (1) compounding the at least one crosslinkable polymer with the at least one liquid-absorbing polymer in a liquid medium to form a solution; (2) applying the solution to the substrate and (3) drying the solution, thereby crosslinking the crosslinkable polymer. 3. The article of claim 1, further comprising a crosslinking agent. 4. A method of manufacturing the article according to claim 3, comprising the steps: (1) compounding the at least one crosslinkable polymer with the at least one liquid-absorbing polymer and a crosslinking agent in a liquid medium to form a solution; (2) Applying the solution to the substrate and (3) Drying the solution, thereby crosslinking the crosslinkable polymer.