DK160259B - Water-soluble, flexible, strongly water-absorbing polymer film based on acrylic acid and a (meth)acrylate comonomer - Google Patents

Description

DK 160259 B

The present invention relates to a water-insoluble, flexible, highly water-absorbing polymeric film having a thickness of up to 0.64 mm.

Many different hydrophilic polymers useful in the production of water-absorbent films and fibers have been previously described. U.S. Patent No. 3,915,921 discloses copolymers of unsaturated carboxylic acid monomers with alkyl acrylate esters, wherein the alkyl group contains 10 to 30 carbon atoms. However, due to the high glass temperature Tg of these polymeric materials 10, it is difficult to extrude them in fiber or foil form. In addition, the films pressed from the powders require high temperatures, the films are brittle and fragile and have a reduced initial water absorption rate.

U.S. Patent No. 4,062,817 discloses polymers of unsaturated copolymerizable carboxylic acids, at least one alkyl acrylate or methacrylate wherein the alkyl group has 10-30 carbon atoms and another alkyl acrylate or methacrylate wherein the alkyl group has 1-8 carbon atoms. This material 20 addresses many of the shortcomings of the prior art materials. Further improvements in the hydrophilic properties are achieved by the materials disclosed in U.S. Patent No. 4,066,583.

This patent discloses a material comprising (1) a copolymer of the type described in U.S. Patent No. 4,062,817, except that after copolymerization, 30 to 90 percent of the carboxyl groups are neutralized with an alkali metal or ammonia, and ( 2) an aliphatic glycol, a plasticizer which is important to facilitate extrusion of the polymer.

More recently, U.S. Patent No. 4,167,464 discloses more water-absorbing polymer obtained by photopolymerization of an alkali metal salt of acrylic acid, a long chain alkyl acrylate or methacrylate and a short chain alkyl acrylate or methacrylate in the presence of a photoinitiator.

35 The polymer film of the above-mentioned type is characterized in that it is made by photopo-2.

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polymerization of a monomer mixture consisting of (a) 65 to 95% by weight acrylic acid, wherein 70 to 100% of the carboxyl groups in the acrylic acid are neutralized with an alkali metal hydroxide or ammonia prior to polymerization, (b) 5 to 35% by weight of a comonomer selected from the group consisting of 2-hydroxyethyl methacrylate and dialkyl aminoalkyl acrylate or methacrylate, each alkyl group of the dialkyl substituent having 1-8 carbon atoms and the other 10 alkyl group having 2-6 carbon atoms, and (c) 0 to 5 weight percent based on the weight of the monomers of a crosslinking agent containing two or more ethylenically unsaturated bonds in the presence of from 0.01 to 5% by weight of a photoinitiator, based on the total weight of the monomers.

In the preparation, the monomer mixture can either be spread to the desired thickness or spun into a fiber and then photopolymerized by exposure to a UV light or other radiation source.

20 Examples of dialkylaminoalkyl acrylates and methacrylates for use as component (b) in the polymeric film herein are preferred, dimethylaminoethyl acrylate, dimethylaminobutyl acrylate, dimethylamino acrylate, diethylaminobutyl acrylate, diethylaminobutylacrylate, diethylaminobutylacrylate, diethylaminobutylacrylate. dibutylaminohexyl acrylate, di-n-hexylaminoethyl acrylate, di-n-octylaminoethyl acrylate, di-n-octylaminobutylacrylate, dimethylaminoethyl methacrylate, dimethylaminobutylmethylacetyl, dimethylaminoethylmethylacrylate, diethyl

The above monomers (a) and (b) are copolymerized by exposing the monomer mixture to UV light. If a foil is desired, the monomer may be spread on a surface to the desired thickness, e.g. 0.02 mm to 0.64 mm and then exposed to UV light for a short period of time, e.g. l sec. to several 3

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minutes. The actual irradiation length will depend on a number of factors such as the thickness of the monomer film, the distance from and the intensity of the radiation source, the specific monomers used, and the relationship between such monomers and the nature and amount of the photoinitiator used. The type of photoinitiator used will depend, at least in part, on the type of UV radiation used (especially its wavelength), as different photoinitiators can be degraded by UV light of different wavelengths. If it is desired that the material be in the form of fibers, the monomer mixture can be made denser and then spun into fibers which are polymerized by exposure to UV light.

In order to effect rapid and efficient polymerization under UV light, 0.01 to 5% by weight of a photoinitiator, preferably 0.1 to 5% by weight and especially 0.3 to 1.0% by weight, must be incorporated into the monomer mixture. Any compound dissociated in free radicals when exposed to UV radiation can be used. There are many known photoinitiators or photosensitizers, e.g. acetopheone, propiophenone, benzophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3- or 4-methylacetophenone, 3- or 4-pentylacetophenone, 3- or 4-methoxyacetophenone, 3- or 4 -bromoacetophenone, 3- or 4-allylacetophenone, p-diacetylbenzene, 3- or 4-methoxybenzophenone, 3- or 4-methylbenzophenone, 3- or 4-chlorobenzophenone, 4,4-dimethoxybenzophenone, 4-chloro-4 ' -benzylbenzophenone, 3-chloroxanthone, 3,9-dichloroxanthone, 3-chloro-8-nonyl-xanthone, 3-methoxyxanthone, 3-iodo-7-methoxyxanone, 2,2-dimethoxyacetophenone, 2,2-dimethoxy-2 -phenylacetophenone, 2,2-diethoxyacetophenone, 2,2-dibutoxyacetophenone, 2,2-dihexoxyacetophenone, 2,2-di- (2-ethylhexoxy) -acetophenone, 2.2-diphenoxyacetophenone, benzoin, methylbenzoinether, ethylbenzoin ether, ethylbenzoin ether butyl benzoin ether, isobutyl benzoin ether, benzoin acetate, benzoin phenylcarbamate, α, α-diethoxyacetophenone, α, α-diethoxy-α-phenylacetophenone, α, α, dimethoxy-α-phenylacetophenone , 4,4'-dicarboethoxybenz-4

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zoinethyl ether, α-chloroacetophenone, α-bromoacetophenone, benzoin phenyl ether, α-methylbenzoin ethyl ether, benzoin acrylate, α-methylbenzoin methyl ether, α, α, α, -trichloroacetophenone, o-bromoacetophenone, 4- (benzoylphenyl) 1-methylbenzene, cymene hydroperoxide, benzoyl peroxide, dicumyl peroxide, tert.butyl perbenzoate, α, α-azobisisobutyronitrile, phenyl disulfide, chiormethyl-benzanthrone, chloromethylanthraquinone, chloromethyl naphthalene, bromomethyl naphthalene, bromomethyl naphthalene,

The monomer mixtures are prepared as aqueous dispersions, eliminating the need for organic solvents. Thus, the pollution problems caused by the removal of organic solvents and the costs associated with the removal of the impurities are avoided. In order to obtain a stable homogeneous dispersion of the monomers, it is preferred that the aqueous dispersions contain 0.01 to 5%, and preferably 0.1 to 1% of a surfactant such as a% anionic, amphoteric or nonionic dispersant 20. or a mixture of dispersants. Useful anionic dispersants include alkali metal or ammonium salts of sulfates of alcohols having 8-18 carbon atoms, such as sodium lauryl sulfate; ethanolamine lauryl sulfate, ethylamine lauryl sulfate; alkali metal and ammonium salts of sulfonated earth and paraffin oils; sodium salts of aromatic sulfonic acids such as dodecane-1-sulfonic acid and octadecane-1-sulfonic acid; aralkyl sulfonates such as sodium isopropylbenzenesulfonate, sodium dodecylbenzenesulfonate and sodium isobutylnaphthalenesulfonate; alkali metal and ammonium salts of sulfonated dicarboxylic acid esters, e.g. sodium dioctyl sulfosuccinate, disodium n-octadecyl sulfosuccinate; alkali metal or ammonium salts of the free acid of complex organic mono- and diphosphate esters, sulfuric acid derivatives ("AEROSOL" dispersants) and organic phosphate esters ("GAFAC" -35 dispersants). Nonionic dispersants, such as octyl or nonylphenyl polyethoxyethanol, and "PLU-5

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RONIC® "and" TRITON® "dispersants may also be used. Amphoteric dispersants such as dicarboxyl coconut derivatives (" MIRANOL® ") are also useful. Additional examples of useful dispersants are described on page 102 of J. Van Alphen's "Rubber Chemicals," Elsevier Publishing Co., 1956.

The monomer mixture is not polymerized without the carboxyl groups first being neutralized to an extent of 70-100%, as polymers obtained from free radical polymerizations generally do not achieve their maximum properties until they are converted to a partial alkali metal, ammonium or amine salt. The neutralizing agent is preferably a monovalent alkali such as sodium, potassium, lithium or ammonium hydroxide or carbonates and bicarbonates thereof, or mixtures thereof and amine bases having no more than one primary or secondary amino group. Such amines include e.g. triethanolamine, ethanolamine, isopropanolamine, triethylamine and trimethylamine.

Although crosslinking agents are not required to obtain the high absorbency materials of the present invention, it may be desirable to incorporate a crosslinking agent, as films made from materials containing a crosslinking agent tend to have greater gel strength and an improved ability for the copolymers. to 25 to swell under a limiting pressure. Crosslinking agents can be used at a concentration of up to approx. 5% by weight, based on the weight of the monomers.

Useful crosslinking monomers are polyalkenyl polyethers having more than one alkenyl ether groups per molecule 30 or monomers containing two to six ethylenically unsaturated groups such as allyl, acrylate or vinyl groups. The most useful are in the possession of alkenyl groups in which an olefinic double bond is attached to a terminated methylene group, CH 2 = C <. Other crosslinking monomers include e.g. diallyl esters or ethers, allyl or methyl acrylates and acrylamides, diacrylates and dimethacrylates, 6

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divinyl compounds and the like. Illustrative examples of polyfunctional cross-linking agents are polyethyleneglycol diacrylate and dimethacrylate, ethylene glycol dimethacrylate, tetraethylene glycol, 1,3-butylene glycol dimethacrylate, diethylene glycol divinyl ether 5, trimethylolpropane diallyl ether, divinylbenzene, trimethylolpropane triacrylate, trimethylolpro-pantrimethacrylat, triallylcyanuarat, pentaerythritol tri-acrylate, diallyl itaconate, methylene bis (acrylamide ), allyl pentaerythritol, allyls sucrose, 1,6-hexanediol diacrylate, tetramethylene glycol diacrylate and dimethacrylate, ethylene glycoldiacrylate and dimethacrylate, triethylene glycol dimethacrylate, triallyl cyanurate, triallylisocyanurate, triallylisocyanurate, triallylisocyanurate

As indicated above, the polymer sheets 15 are made by photopolymerization. By using photopolymerization or radiation polymerization methods, the polymer films herein can be obtained in the form of a film or a fiber. The resulting foil or fiber is a% elastic, flexible material which has a substantial strength.

If a fine, flake-like shape is desired, the film can be converted to such a form by drying it and then pulverizing or grinding it in standard equipment.

As water-absorbing materials, these polymers find many uses in films, fibers, textiles and the like. They are particularly useful in the industry in nonwoven disposable materials where there is a need for polymers that will absorb and retain water and ionic physiological fluids. An important feature of these polymers is their increased thickening property even in the presence of a salt.

30 Specific uses include disposable diapers, medical-surgical supplies, and personal hygiene products. Such applications require a polymer to absorb the liquid to be absorbed quickly and to be a non-dissolving polymer. In addition, the liquid must be immobilized or solidified in some way to be withheld. The materials can also be used as appropriate additives.

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is widely used to enhance the absorbent properties of conventional absorbents such as cotton, wood pulp and other absorbent cellulose materials used for such products as handkerchiefs, surgical tampons, sanitary napkins and tampons, and the like. In a particular application, e.g. a disposable diaper, there is an inner layer of a soft absorbent nonwoven material which absorbs and directs urine to an inner layer of a downy, fibrous absorbent material wherein agglomerates or fibers of the polymers herein are incorporated during and a further impervious plastic layer such as polyethylene. A film of the copolymers herein can be used between the outer plastic layer and the inner downy absorbent layer. Use of the polymers herein may result in reduction of the total size of nonwoven disposable materials.

The present copolymers can also be used as flocculants in water treatment, in metallurgical processes, in quality improvement and flotation of ore, they can be used in agriculture, such as in soil treatment or seed coating 20 or for all applications where the inherent properties of the polymer are desirable such as its thickening ability in an aqueous medium.

To prepare the cured copolymers of the present invention, the monomers, a dispersant and a photoinitiator, if used, are mixed in a container. Then either a film or fibers are provided from the monomer mixture, which, upon exposure to UV light or radiation, is rapidly polymerized. The various steps in the process are described in detail below.

3 ° Preparation of monomer mixture: The monomer mixture can be prepared by one of the following two simple methods.

One method is to dissolve a previously prepared and dried alkali metal or ammonium salt of acrylic acid in water, to which is added a dispersant. To the aqueous solution 35 is then added an acrylate or methacrylate ester, which already contains a photoinitiator, if used. Another δ

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o Method is to prepare the acrylic acid salt in situ by adding acrylic acid to the correct amount of cold aqueous base (i.e.

KOH, NaOH or NH4 OH) under cooling. To the aqueous solution is then added a mixture of the acrylate or methacrylate ester, to which, if necessary, a photoinitiator has been added. The dispersant is finally added.

Foil Preparation: The aqueous monomer dispersion is spread to a desired thickness (for example, using an adjustable Boston-Bradley blade, by spraying methods or other known methods) on a suitable support (eg "Mylaj® f polyethylene, paper, etc.) The liquid film is then exposed to a UV or radiation source which polymerizes the monomer mixture into a soft, flexible film. If desired, this film can be dried in an oven at about 50 ° C for 1-15 minutes. the foil 15 may still retain some flexibility or become brittle and flaky, depending on the length of the drying time.

Fiber Preparation: The aqueous monomer dispersion is thickened to the desired degree with a non-reactive thickener such as a cellulose derivative, e.g. hydroxypropyl cellulose, high molecular weight polyvinylpyrolidone and the like? natural gums such as guar gum, locust bean gum, tragacanth gum agar, naturally occurring hydrocolloids such as alginates and the like. Fibers are then spun regularly from a spin devort and are immediately exposed to a UV or radiation source.

The following examples serve to illustrate the present invention in greater detail. The copolymers and films are prepared according to the above methods. The copolymers of Examples 1 to 9 set forth in Table I have been photopolymerized using "QC 1202 Processor" manufactured by Radiation Polymer Co. (with a tape speed of 0 to 304.8 m / min at 78.7 W / linear cm. The distance from the lamps to the foil is 15 cm and the exposure time is 20 seconds at a belt speed of 6 m / min.

35

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Comonomers used in the Examples and identified in Table I by uppercase letters A through I are identified below: 5 A - methyl methacrylate B - 2-hydroxyethyl methacrylate C - lauryl methacrylate D - stearyl methacrylate E - phenoxyethyl acrylate 10 F - dimethylaminoethyl acrylate G - mixture of 17.0 g DMAEA +1.9 g trimethylol propane triacrylate H - phenyl acrylate I - n-hexyl methacrylate 15 20 25 30 35 10

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DK 160259B

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Copolymers having practically the same properties are obtained when some of the above compounds are used potassium hydroxide instead of sodium or axtmonium hydroxide, 2,2-diethoxyacetophenone instead of "IRGACURE ^ d51" and an oligomeric surfactant "POLYWET KX -3 "(from Uniroyal) or" TRITONEN-111 "(monophenoxypolyethoxyethanol) instead of" AEROSOL A102 ".

A number of tests are available to determine the absorbency of a material. The following are descriptions of two test methods used in assessing the absorbency of the interpolymers herein.

Static test (ST) - A weighed foil sample is immersed in a test liquid for 10 minutes. It is then removed from the liquid, the excess liquid is discharged for a few seconds, and then lightly shaken 15 several times. The swollen sample is weighed again to determine the weight of the liquid absorbed by the polymer. Required Humidity Test (DWT) - A test diaper is prepared from a pad that is 10.16 cm in diameter using materials from a commercially available diaper. A film 20 made from a polymer to be tested for absorbency is placed in the middle of the test diaper between two layers of down (wood pulp). A diaper without the polymer film is used as a blank test. The required humidity apparatus is a burette filled with the test fluid and firmly plugged in the top, with an air outlet 25 on the side and a drain opening on the bottom connected by a flexible tube to the sample holder. The sample holder has a center opening which is connected to the flexible tube leading to the drain opening on the cage. The sample holder is level with the air outlet opening in the burette. With this closed system, the liquid in the flexible tube which reaches the opening in the sample holder is at zero pressure. When the test diaper is placed on the sample holder above the opening, it will absorb the liquid by its own force through the action of the tissue. The absorbent ability of the sample will determine the velocity and amount of liquid discharged from the burette. The amount of drained liquid at any given time can be read easily from the burette calibration. A further feature is that the absorbency can be measured against a pressure 0

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13 range which can be obtained by placing different weights on top of the test diaper. Such pressures are intended to simulate the pressures applied to a diaper when used in practice.

This experiment is described in more detail by Lichstein, 5 "Demand Wettability, a New Method for Measuring Absorbency Characteristics of Fabrics", Symposium Papers-INDA Technical Symposium, 1974, pages 129-142.

Compression Trial (CT) - This trial is a trial that follows up the DWT trial. After the sample has absorbed the liquid against a low pressure in a DWT test, it is removed from the DWT apparatus and placed on top of a porous filter funnel. The sample is then subjected to a pressure of 0.105 kg / cm for one minute and the amount of liquid pressed from the sample is measured. This pressure corresponds to the maximum pressure exerted on parts of a diaper when a baby is picked up or held. This pressure is 10 to 15 times greater than the pressure that the diaper would normally be exposed to. The sample is then weighed to determine the amount of liquid in grams retained per gram. grams of polymer.

Table II below provides data comparing the absorbent properties of the copolymer of this invention with two other polymers. The polymer number in the table corresponds to the example describing the preparation of the specific polymer.

Table II

ST DWT CT

polymer (g / g) (ml / g) (g / g) 1 26 30 2 26 - - 3 - 56 40 4 - 36 30 5 - 33 29 6 - 27 22 35 7 - 37 31 8 - 5.5 9 - 13

Claims (4)

A water-insoluble, flexible, highly water-absorbing polymeric film having a thickness of up to 0.64 mm, characterized in that it is prepared by photopolymerization of a monomer mixture consisting of (a) 65 to 95% by weight acrylic acid, wherein 70 to 100 percent of the carboxyl groups in the acrylic acid are neutralized with an alkali metal hydroxide or ammonia prior to polymerization, 10 (b) 5 to 35 weight percent of a comonomer selected from the group consisting of 2-hydroxyethyl methacrylate and dialkyl aminoalkyl acrylate or methacrylate, 8 carbon atoms and the other alkyl group has 2-6 carbon atoms and 15 (c) 0 to 5% by weight based on the weight of monomers of a crosslinking agent containing two or more ethylenically unsaturated bonds in the presence of from 0.01 to 5 weight percent of a photoinitiator, based on the total weight of the monomers. Polymer film according to claim 1, characterized in that the photoinitiator is used in an amount of 0.1 to 5.0% by weight. Polymer film according to claim 1, characterized in that it contains from 0.1 to 5.0% by weight of a crosslinking agent selected from the group consisting of 1,3-butylene glycol dimethacrylate, polyethylene glycol diacrylate and dimethacrylate, ethylene glycol dimethacrylate, diethylene glycoldivinyl ether, tetraethylene glycol diacrylate, trimethylolpropentrimethacrylate, triallylisocyanurate, diallylitaconate, allyl pentaerythritol and methylene bis acrylamide. Polymer film according to claim 1, characterized in that the photoinitiator is selected from the group consisting of 2,2-dimethoxy-2-phenylacetophenone, benzophenone, a benzoin ether and a mixture thereof.