FI71776C - HARTSIMPREGNERAD FIBERSKIVA OCH FOERFARANDE FOER DESS FRAMSTAELLNING. - Google Patents

Description

1 71776

The present invention relates to resin-impregnated fibreboards.

Resin impregnated sheet materials such as fabrics, pile sheets, non-adhesive and filler-free sheets are all well known in the art. These resin-impregnated sheet materials are useful for a variety of purposes, including imitation leather formed by vinyls and the like, construction board materials such as conveyor belts, and the like.

In previous sheet impregnation methods, the porous material is impregnated or coated with a polymeric resin such as polyurethane, vinyl, or the like. Polyurethanes have become widely accepted as a coating or impregnation blend because of their highly variable chemical and physical properties, and in particular their flexibility and chemical resistance. Several methods are used to impregnate a porous sheet material with a polymeric resin. One such prior method uses a polymeric resin in an organic solvent system in which the sheet material is dipped in a solution and the solvent is removed therefrom. These solvent systems are not desirable because in many cases the solvent is toxic and must either be recovered for reuse or disposed of. These solvent systems are expensive and do not necessarily provide the desired product because the resin tends to migrate from the impregnated porous sheet material as the solvent evaporates, so that the porous sheet material becomes unevenly impregnated, resulting in 71776 resins abundant per sheet material surface and non-uniform impregnation.

To eliminate the problems associated with solvent systems, some aqueous polymeric systems have been proposed. When forming impregnated sheet materials by impregnation with aqueous polymers, the aqueous portion must be removed. Again, heat is required and the polymer is also transferred to the surfaces of the impregnated sheet material.

In one method in which polyurethane solutions are combined with porous substrates, the polymer is applied in an organic solvent to a substrate, such as a polyester sheet pierced with needles. The polymer substrate combination is then dipped in a mixture of an organic solvent of the polymer and a non-solvent of the polymer that is at least partially miscible with the solvent until the layer coagulates into a cellular structure formed by interconnected micropores. The solvent is removed from the coating layer together with the non-solvent to obtain a solvent-free microporous layer. Although this method gives the polyurethane impregnated fabric acceptable properties, it has the disadvantage of a partially organic solvent system when using high performance polyurethanes that require relatively toxic and high boiling solvents. An example of this method is disclosed in U.S. Patent 3,208,875.

In another method, polyurethane dispersions in organic solvents have been proposed and used to coat porous substrates, as disclosed in, e.g., U.S. Patent 3,100,721. In this system, the dispersion is applied to a support and coagulated by further adding a non-solvent.

Although this solution has been used with some success, it has two major limitations: (1) the solvent of the dispersion is mainly organic because relatively small amounts of non-solvent are required to form the dispersion.

71776 preferably water, (2) the usable range of the added non-solvent is narrow, so that reproducible results are difficult to obtain.

One particularly useful method of making a composite sheet material by impregnating a porous substrate is disclosed in U.S. Patent 4,171,391, which is incorporated herein by reference. In this system, the porous sheet material is impregnated with an aqueous ionic polyurethane dispersion, and the impregnating agent is coagulated therein. The combination is then dried to form a composite sheet material. The present invention is an improvement over this basic method and is broader in some respects.

Impregnated porous substrates and the like have been proposed as hardeners for leather, with the aim of producing a product with the same properties as natural leather.

Polyurethane polymers have long been known as fabric coating and impregnating agents. For example, polyurethanes can be made which are very resistant to solvents and abrasion and give coated fabrics dry cleanability and excellent durability. Thanks to the basic chemistry of polyurethanes, which involves reactions between isocyanate groups and molecules and several reactive hydrogen atoms, such as polyols and polyamines, the most diverse and variable final chemical and physical properties are possible through the choice of intermediates to achieve workability and end-use requirements.

There are various methods known to those skilled in the art for applying polyurethane solutions or other post-curing liquid polymers to porous substrates. Article in "Journal of Coated Fabrics", Vol. 7 (July 1977), pages 43-47, describes some commercial coating 71776 systems, e.g., swivel roll coating, engraving, and the like. Lubrication and spraying can also be used to coat porous substrates with polyurethanes. After the porous substrate is impregnated or coated with these polyurethane solutions, the solutions are dried or cured by any method such as heated air, infrared radiation and the like. These methods are characterized by the deposition of a polymer and a film-like layer, which tends to produce a product that corrugates into unwanted sharp corrugations rather than leather-like fibrous corrugations. Other methods of combining polymeric solutions, and in particular polyurethane solutions, with porous substrates are described in U.S. Patents 3,208,875 and 3,100,721.

U.S. Patent 4,171,391 discloses an improved method of impregnating fabrics which includes certain steps necessary in the manufacture of a waste leather sheet material according to the invention.

According to the present invention, there is provided a method of impregnating porous sheet materials, and in particular needled sheets, to provide uniform impregnation in an aqueous system that forms products with high tear strength and integrity.

Furthermore, there is provided a impregnated fiberboard having a new and unusually usable structure suitable for use either as formed or subsequently machined, providing additional advantages.

The resin-impregnated fiberboard consists of a needled fiberboard and a polymeric resin distributed throughout the board. The density of the impregnated plate is uniform throughout, so that its total density is less than the nominal density of the plate, so that the plate is porous. The impregnated sheet contains filaments that are both coated with a polymeric resin and uncoated. The invention also relates to a method for forming an impregnated fiberboard.

5 71 776 "Total density" as used herein means the density of a substance, including airspace. "Nominal density" as used herein means the density of a substance without air space, i.e., specific gravity.

Useful pulp for the practice of the invention includes woven and knitted fabrics, felt and nonwovens, such as spunbonded sheets, needled fiberboard, and non-glued and filler-free sheets. Suitable substrate fibers and include natural fibers, especially cotton and wool, synthetic fibers such as polyester, nylon, acrylics, modacrylics and rayon. Most preferably, the pulp consists of needled fibreboards consisting of natural and man-made fibers. Preferably, the fibers have a denier of 1 to 5 and a length suitable for carding, which is typically 2.54 to 4.72 cm, and more preferably 3.8 to 7.62 cm.

Needled fiberboards can have either high, medium, or low density. High density sheets have a maximum density of 0.5 g / cm. These high density sheets are typically wool. When man-made fibers are used to form the sheets, the high-density sheets have a density 3 of not more than 0.25 g / cm. In the use of the invention, the fibreboards 3 preferably have a density of 0.08 to 0.5 g / cm. The thickness of the sheets may be at most 12.7 mm and preferably between 3.05 mm and 10.16 mm with a minimum thickness of 0.762 mm. In addition, the sheets are "saturating sheets" in nature, which have a high uniformity due to the needle punching step compared to weakly bonded sheets with only a few needle punches and little or no uniformity.

The polymeric resins useful in the practice of the invention are preferably polymeric resins capable of dissolving, dispersing and emulsifying in water and then coagulating from the aqueous system with an ionic coagulant.

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A preferred polymer system is one synthesized from acrylic monomers such as alkyl acrylates and methacrylates, acrylonitrile, methyl acrylonitrile and other known acrylic monomers. These acrylic monomers can be polymerized by emulsion polymerization to form a latex or other free radical polymerization mechanisms, after which they are dissolved or emulsified in water. The emulsification or dissolution system must be such that when the emulsion is contacted with a concentrated acid or base, the polymer coagulates from the aqueous system and becomes substantially insoluble.

Most preferably, emulsified or water-dispersed polyurethanes are used. U.S. Patent 2,968,575 discloses examples of emulsified polyurethanes prepared and dispersed in water with detergents under high shear forces. When these polyurethane emulsions are formed, the emulsifier must be ionic in nature so that the counterion can be added to the aqueous system to coagulate the polymer. Most preferably, the polyurethanes used in the practice of the invention are polyurethanes known in the art to be ionically water dispersible.

A preferred system for preparing ionic aqueous polyurethane dispersions is to prepare polymers having free acid groups, preferably carboxylic acid groups, covalently bonded to the polymer backbone. Neutralization of these carboxyl groups with an amine, preferably a water-soluble monoamine, results in water dilutability. The carboxyl group-containing compound must be carefully selected because isocyanates, which are essential components in any polyurethane system, generally react with carboxyl groups. However, as disclosed in U.S. Patent 3,412,054, which is incorporated herein by reference, 2,2-hydroxymethyl-substituted carboxylic acids can be reacted with organic polyisocyanates without significant reaction between the acid and isocyanate groups due to steric hindrance of adjacent alkyl groups.

This gives the desired carboxyl-containing polymer, the carboxyl groups being neutralized with a tertiary monoamine so as to obtain an internal quaternary ammonium salt and thus water solubility.

Suitable carboxylic acids and preferably sterically hindered carboxylic acids are known and readily available.

For example, they can be prepared from an aldehyde containing at least two hydrogen atoms in the alpha position, which are reacted with two equivalents of formaldehyde in the presence of a base to form 2,2-hydroxymethylaldehyde. The aldehyde is then oxidized to the acid by methods known to those skilled in the art. Such acids are represented by the structural formula

CH-OH

i *

R - CH - COOH

CH 2 OH

wherein R represents hydrogen or alkyl of up to 20 carbon atoms and preferably up to 8 carbon atoms. The preferred acid is 2,2-di- (hydroxymethyl) propionic acid. Polymers containing dependent carboxyl groups are called anionic polyurethane polymers.

Furthermore, dilutability with water according to the invention can alternatively be achieved by using a cationic polyurethane having dependent amino groups. Such cationic polyurethanes are disclosed in U.S. Patent 4,066,591, which is incorporated herein by reference, and in particular in Example XVII. In the context of the present invention, it is preferred to use anionic polyurethane.

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The polyurethanes used in the practice of the invention involve the reaction of di- or polyisocyanates and compounds with a number of reactive hydrogen compounds suitable for the preparation of polyurethanes. Such diisocyanates and reactive hydrogen compounds are described in more detail in U.S. Patents 3,412,034 and 4,046,729. In addition, methods for preparing such polyurethanes are disclosed in the aforementioned patents. According to the present invention, aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used to form the polymer. Examples of such diisocyanates are tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, meta-phenylene diisocyanate, biphenylene 4,4'-diisocyanate, methylene bis (4-phenyl isocyanate), 4-chloro-1,3-phenylenediisocyanate, naphthylene 1,5-diisocyanate, tetramethylene 1,4-diisocyanate, hexamethylene-1,6-diisocyanate, decamethylene 1,10-diisocyanate, cyclohexylene-1,4-diisocyanate, methylene bis (4-cyclohexyl isocyanate), tetrahydronaphthylene diisocyanate, isopropylene diisocyanate and the like. Arylene and cycloaliphatic diisocyanates are most preferably used in the practice of the invention.

Typically, arylene diisocyanates are those in which the isocyanate group is attached to the aromatic ring. The most preferred isocyanates are the 2,4- and 2,6-isomers of tolylene diisocyanate and mixtures thereof due to their easy availability and reactivity. Furthermore, the most preferred cycloaliphatic diisocyanates used in the practice of the invention are 4,4'-methylene bis (cyclohexyl isocyanate) and isophorone diisocyanate.

The end use of a given substance determines the choice of aromatic or aliphatic diisocyanates. As is well known to those skilled in the art, aromatic isocyanates can be used when the final product is not overexposed to ultraviolet radiation, which tends to be yellow in such polymeric compositions. Aliphatic diisocyanates 71776, on the other hand, can be used more advantageously in external applications and have a lower tendency to turn yellow under ultraviolet radiation. Although these principles provide a general basis for the choice of isocyanate to be used in each case, aromatic diisocyanates can be further stabilized with known ultraviolet stabilizers to improve the final properties of the polyurethane impregnated sheet material. In addition, antioxidants may be added in amounts accepted in the art to improve the properties of the final product. Typical antioxidants include thioethers and phenolic antioxidants such as 4,4'-butylidine-bis-meta-cresol and 2,6-di-tert-butyl-para-cresol.

The isocyanate is reacted with a number of reactive hydrogen compounds such as diols, diamines or triols. When diols or triols are used, they are typically either polyalkylene ether or polyester polyols. Polyalkylene ether polyol is the preferred active hydrogen-containing hydrogen compound for polyurethane formation. The most useful polyglycols have a molecular weight of 50 to 10,000 and most preferably 400 to 7,000 in the context of the present invention. Polyether polyols further improve flexibility with increasing molecular weights.

Examples of polyether polyols include, but are not limited to, polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol, polydecamethylene ether glycol, polydodecamethylene thereof. Polyglycols containing several different radicals in the molecular chain can also be used, such as HO (CH 2 O 2 H 2 O), where n is an integer greater than one.

The polyol may also be a polyester terminated by hydroxy or containing hydroxy and may be used in place of or in combination with polyalkylene ether glycols. Such polyesters are formed by reacting acids, esters or acid halides with glycols. Suitable glycols include polymethylene glycols such as ethylene, propylene, tetramethylene or decamethylene glycols, substituted methylene glycols such as 2,2-dimethyl-1,3-propanediol, cyclic glycols such as cyclohexanediol and aromatic glycols. Aliphatic glycols are generally preferred when flexibility is desired.

These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester-forming derivatives to give polymers of relatively low molecular weight, preferably having a melting point of less than about 70 ° C and a molecular weight equal to that of polyalkylene. is mentioned. Acids used in the preparation of such polyesters include, for example, phthalic, maleic, succinic, adipic, cork, sebacic, terephthalic and hexahydrophthalic acids and alkyl and halogen substituted derivatives of these acids. In addition, polycaprolactone having hydroxyl groups as end groups can be used.

As used herein, "ionic dispersant" means an ionizable acid or base capable of forming a salt with a solubilizing agent. These "ionic dispersants" include amines and preferably water-soluble amines such as triethylamine, tripropylamine, N-ethylpiperidine and the like, as well as acids and preferably water-soluble acids such as acetone, propionic, lactic acid and the like. Of course, the acid or amine is selected according to the polymer chain-dependent solubilizing group.

The desired elastomeric behavior would generally require about 25-80% by weight of the long chain polyol (i.e., 700-2000 equivalent weight) in the polymer. The degree of elongation and elasticity can vary greatly from product to product depending on the desired properties of the final product.

71776

In the formation of polyurethanes useful in the practice of the invention, a molar excess of polyol and diisocyanate is reacted to give a polymer having an isocyanate end group. Although suitable reaction conditions and reaction times and temperatures may be varied depending on the isocyanate and polyol used in the art, those variations are well known to those skilled in the art.

It will be appreciated by those skilled in the art that the reactivity of the ingredients used requires a balance of reaction rate with undesired secondary reactions leading to deterioration of color and molecular weight. Typically, the reaction is carried out with stirring at about 50 to about 120 ° C for 1 to 4 hours. To obtain pendant carboxyl groups, the isocyanate-terminated polymer is reacted with a molar subset of dihydroxy acid for 1-4 hours at 50-120 ° C to give an isocyanate-terminated polymer. The acid is preferably added as a solution, for example in N-methyl-1,2-pyrrolidone or N-N-dimethylformamide. The amount of acid solvent is typically up to 5% of the total charge to minimize the concentration of organic solvent in the polyurethane composition. After the dihydroxy acid is reacted with the polymer chain, the dependent carboxyl groups are neutralized with an amine at about 58-75 ° C for about 20 minutes, and chain extension and dispersion are accomplished by the addition of water with stirring. The water-soluble diamine can be added to water as an additional chain extender. Chain extension involves the reaction of the remaining isocyanate groups with water to form urea groups, and the polymeric material is further polymerized, with all isocyanate groups reacting with the addition of a large stoichiometric excess of water. It should be noted that the polyurethanes of the invention are thermoplastic in nature, i.e. they do not harden much more after formation unless an external curing agent is added. Preferably, such a curing agent is not added to form the composite sheet material.

Water is used sufficiently to disperse the polyurethane at a concentration of about 10-40% by weight solids with a viscosity of 10-1000 centipoise. The viscosity can be adjusted according to the desired impregnation properties and the respective dispersion mixture, all of which are determined by the properties of the final product. It should be noted that neither emulsifiers nor thickeners are required for the stability of the dispersions.

Modes by which the primary polyurethane dispersions are modified according to the uses of the final product are known to the person skilled in the art, for example by adding colorants, suitable vinyl polymer dispersions, ultraviolet filtration mixtures, anti-oxidant stabilizers and the like.

The properties of the dispersions prepared according to the invention are determined by measuring the content, particle size, viscosity and stress-strain properties of the non-volatile substances on cast film strips.

The concentration ranges useful in the practice of the invention are controlled by the desired percentage addition of polymer to the needle.

The dispersion viscosity is usually 10-1000 centipoise. The low viscosity relative to the viscosity of identical polymers at the same solids concentrations in organic solvent polymer solutions helps the rapid and complete permeation of the aqueous dispersion and the subsequent permeability of the coagulant. Useful polyurethane solutions, on the other hand, generally have a viscosity of several thousand centipoise, up to 50,000 centipoise at concentrations of 20-30%.

The polymers should be impregnated into the fiberboard at a level of at least 70% by weight based on the weight of the fiberboard and no more than about 400% by weight. Preferably, the polymeric resin is impregnated at a level of about 200-300% by weight based on the weight of the sheet.

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Coagulation is accomplished by contacting a saturated substrate with an aqueous solution of an ionic medium intended to ionically replace a solubilizing ion. In the case of an anionically soluble polymer, the amine which neutralizes the carboxyl-containing polyurethane is theoretically replaced, although the invention is not limited to such a theory, by a hydrogen ion which restores the anionic carboxyl ion and thus restores the polymer to its original "undiluted" state.

This causes the polymer to coagulate in the substrate structure.

In the case of an anionic polymer, aqueous acetic acid solutions in concentrations of 0.5 to about 75% are a suitable ionic coagulant for anionic dispersions and are preferred over more concentrated acids because of their relatively easy handling, low corrosivity and disposability.

"Salting" to coagulate the dispersion by adding neutral salt is possible, but not recommended due to the large amounts of salt required, which are about 10 times the acid concentration, resulting in product contamination problems.

When the needled sheet is impregnated with a polymeric resin according to the invention, the sheet is immersed in an aqueous ion emulsion or dispersion at a concentration level sufficient to give an increase of at least 70% by weight. Once immersed in an aqueous emulsion or dispersion, the plate can be compressed to remove air so that the emulsion or dispersion completely saturates the plate. The sheet, which is completely impregnated with the aqueous dispersion or emulsion, is then passed through sweeping rollers or the like to remove excess dispersion or emulsion from the surface of the impregnated sheet. The sheet is then immersed in a counterion-containing bath so that coagulation is effected by the counterion-containing substance penetrating through the sheet by diffusion and the resin coagulates within the fibrous structure. After coagulation, the plate is compressed to remove excess water, and the plate is dried to form a saturated plate.

In the manufacture of certain products, this method is an improvement over the method described in U.S. Patent 4,171,391. The difference between the reference patent and the present method is that the sheet is completely impregnated, i.e. there is no air space left, whereby the aqueous dispersion or emulsion gives an addition of at least 70% by weight of polymeric resin based on the weight of the sheet. Due to these differences, a new structure is obtained in which the plate has a uniform density throughout and the overall density of the plate is lower than its nominal density.

The structures of the impregnated sheet are shown more clearly in the accompanying drawings, which are photomicrographs of cross-sections of an impregnated sheet and a simulated leather sheet material made in accordance with the invention.

In the accompanying drawings, Fig. 1 is a plan view of a resin impregnated sheet prepared according to Example 1, Fig. 2 is a photomicrograph taken through the thickness of the sheet of Fig. 1 through line II-II, Fig. 3 is a 100-fold photomicrograph of Part III of Fig. 2; fold photomicrograph of Part IV of Figure 2, Fig. 5 is a 100-fold photomicrograph of Part V of Fig. 2, Fig. 6 is a 100-fold photomicrograph of a resin impregnated sheet prepared according to Example I, split.

Figures 1-5, in which the same reference numerals refer to the same parts, show a resin impregnated sheet 10 made according to Example 1. More specifically, Figures 2-5 show a cross-section through the thickness of the sheet 10. The sheet 10 consists of a top surface 12 and a bottom surface 14. The sheet 10 has a substantial number of uncoated fibers 16, n 15 71 776 resin concentrations 20, voids 18 and resin coated fibers 22 throughout. The structure and thus its overall density is substantially uniform throughout the thickness of the material. although the structure at the microscopic scale is inhomogeneous.

The structure shown in Figures 2-5 is thought to be due to the fact that the needled sheet is completely impregnated with an aqueous emulsion or dispersion, after which the polymer is coagulated when the sheet is fully impregnated with an aqueous resin system.

Figure 6, which is a 100-fold photomicrograph, shows a split impregnated needled sheet 24 having a uniform density throughout, as shown in Figures 1-5. The impregnated sheet 24 has a substantial amount of uncoated fibers, polymer masses 28, coated fibers 32, and voids 30. It is found that although the impregnated sheet is inhomogeneous on a microscopic scale, it has a uniform overall density throughout.

The following examples illustrate the products prepared according to the invention.

Example I

The heat-cured needle sheet, having a density of 1200 g / m 2 and consisting of polyester, polypropylene and rayon fibers and a thickness of 7.62 mm with a total density of 0.16 g / cm, was embedded in a polyurethane made of U.S. Pat. according to Example III of U.S. Patent 4,554,308. The total solids content of the polymer dispersion was 22%, resulting in an increase of 120% based on the weight of the plate. The plate was immersed in the polyurethane dispersion for 10 minutes at room temperature until all air had escaped from the inside of the plate and the plate was completely saturated. The surface of the plate was wiped with a straight blade on both sides to remove excess water dispersion, and the plate was immersed in a 10% acetic acid bath for 10 minutes at room temperature. Immersion in acid completely coagulates the polyurethane within the fibrous structure.

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Excess acetic acid was washed off the plate and the resin-saturated plate was pressed to remove excess water. The resin impregnated plate was split into four slices through its thickness, and each slice was dried at 149-177 ° C in a convection oven to form four resin impregnated plates with a total density of 0.41 g / cm. The photomicrograph of the final product was as shown in the drawings.

Example II

Example I was repeated except that a 100% polyester sheet 3 having a density of 0.13 g / cm and a thickness of 5.08 mm was impregnated with the 22% solids dispersion of Example I. The obtained impregnated plate had a uniform density throughout, a high integrity and a total density of 0.38 g / cm.

Example III

Example I was repeated except that a 100% needled polyester sheet having a thickness of 5.59 mm and a density of 0.23 g / cm was impregnated with a 32% solids dispersion to give a needled impregnated resin fiber sheet having a total density of 0.56 g. / cm ^. The product of Example III was used as a polishing pad.

It was tough, had good tear strength and flexibility, and recovered completely after compression.

Thus, the method and product of the present invention result in a impregnated fiberboard having a high integrity, which is useful in itself as a product, as well as useful in the manufacture of other products. In addition, the impregnated fiberboard can be ground to provide the desired finish.

Although the invention has been described with reference to certain materials and certain methods, the invention is limited only within the scope of the appended claims.

Claims (13)

1. Resin impregnated fiber board, characterized in that it consists of a sewn fiber board and a polymer resin distributed throughout the board, whereby a resin impregnated fiber board is formed; that the density of the impregnated fiber board is the same throughout; that the bulk density of the sheet is less than its actual density whereby the sheet is porous and that the impregnated sheet has filaments which are both coated and uncoated with polymer resin and various concentrations thereof. Resin impregnated fiber board according to claim 1, characterized in that the bulk density of the nailed fiber board is less than 0.5 g / cm or less than 0.25 g / cm, preferably 0.12-0.4 g / cm 2. Resin impregnated fiber board according to claim 1, characterized in that the thickness of the nested fiber board is at least 0.7617 mm. Resin impregnated fiber board according to claim 1, characterized in that the nested fiber board consists of substantially indigestible fibers. 5. Resin impregnated fiber board according to claim 1, characterized in that the polymer resin is polyurethane. 6. Resin impregnated fiber board according to claim 5, characterized in that the polyurethane is water-dispersible polyurethane. 7. Resin impregnated fiber board according to claim 5, characterized in that the polyurethane is a cross-linked polyurethane. 1 Resin impregnated fiber board according to claim 1, characterized in that the polymer resin is polyacrylate.