EP0676496A2 - Nonwoven having superabsorbent particles adhesively fixed to its upper surface - Google Patents

Abstract

Bonded fibre fabric (I) consists of a raw fibre mat with a polymer dispersion as binder (II) and with particles of superabsorber (III) fixed to the surface with binder (II). Also claimed is bonded fibre fabric coated with (III), obtd. by treating the unbonded mat with aq. dispersion (II), coating the wt fabric with (III), removing excess water by suction, and opt. drying. Also claimed is the above process a such, and also textile materials, with super-absorbent properties made from (I).

Description

The invention relates to nonwovens based on a raw nonwoven and a polymer dispersion as a binder for the raw nonwoven, superabsorbent particles being fixed on the surface of the nonwoven by the binder for the raw nonwoven. Furthermore, the invention relates to a method for producing the nonwovens and their use for producing textile materials.

Flat textile materials with superabsorbent properties for absorbing liquids are becoming increasingly common. Typical areas of application are disposable diapers for babies, sanitary napkins or products for adult incontinence. These superabsorbent articles are usually constructed in such a way that they contain a more or less voluminous layer of cellulose (fluff), into which superabsorbent (SAP) particles are scattered. If a liquid gets into this layer, it is absorbed by the SAP particles, the liquid being conducted to the particles via the hydrophilic fluff fibers. The water absorption capacity can be many times higher than the weight of the material. The commonly used construction described here has the disadvantage that it leads to hygiene products which are several mm to cm thick and thus often only insufficiently meet the requirements for the greatest possible discretion when wearing these articles on the human body. This is especially true for adult incontinence.

There is therefore a need to produce a flat material with a high water absorption capacity, which is suitable for the construction of hygiene products, such as incontinence articles, disposable baby diapers or sanitary napkins, and which is significantly thinner than the usual products containing fluff.

JP-A 05077366 describes a thin, flat material with superabsorbent properties which is based on a nonwoven fabric which is mixed with an aqueous solution of monomeric Sodium acrylate is impregnated, from which the superabsorbent polyacrylate is then formed on the nonwoven.

US-A 4 888 238 describes fibers which are formed by immersion in an aqueous solution of an anionic polyelectrolyte, e.g. Polyacrylic acid and a polyvalent metal salt and subsequent drying can be coated with a superabsorbent material. Thin, textile fabrics can be produced from these fibers.

EP-A 357 474 describes a superabsorbent cellulosic nonwoven fabric which is produced in such a way that the nonwoven fabric is immersed in a solution of precursors to form a polymeric superabsorbent and the superabsorbent on the fibers is then obtained by polymerizing the precursors.

The object of the present invention was nonwovens with superabsorbent properties which can be obtained by a process which is as simple as possible and which are suitable for producing textile materials which are as thin as possible, in particular hygiene products such as diapers or sanitary napkins.

We have found that this object is achieved by the above-defined nonwovens, the process for their production and their use in the production of textile materials.

The nonwovens according to the invention are obtainable by applying an aqueous polymer dispersion as a binder to an unbound raw nonwoven, applying superabsorbent particles to the still wet nonwoven, suctioning off excess water and optionally subsequent drying.

All fibers customary for the production of nonwovens can be used as nonwoven fibers. In addition to synthetic fibers such as polyester, polypropylene or polyamide, fibers of natural origin such as viscose or cellulose can also be used. Fibers with a hydrophilic character such as viscose and cellulose are preferred.

In general, they are fibers with a diameter of 0.002 to 0.1 mm, preferably 0.01 to 0.05 mm.

The fibers are formed into raw nonwovens, the cohesion essentially being brought about by the inherent adhesion of the fibers. The raw nonwovens can be random fiber nonwovens or preferably directional nonwovens without or with mechanical pre-consolidation, for example by needling, swirling or sewing.

Suitable raw nonwovens preferably have a basis weight of 10 to 40 g / cm², particularly preferably 15 to 25 g / cm².

The raw fleeces are consolidated with an aqueous polymer dispersion as a binder. For this the polymer dispersion is e.g. applied to the raw fleece by means of customary processes such as immersion bath impregnation, spraying or foam application.

The weight ratio of fibers to polymer (solid) can e.g. from 15: 1 to 1:15, preferably from 15: 1 to 1: 1 and particularly preferably from 7: 1 to 3: 1.

Raw nonwoven webs are preferably passed through an immersion bath which contains the aqueous polymer dispersion.

The solids content of the polymer dispersion is generally 10 to 75% by weight, preferably 30 to 65% by weight.

The polymers are in particular those composed of monomers which can be polymerized by free radicals. Suitable polymers are preferably those which contain 40 to 100% by weight, particularly preferably 60 to 100% by weight, very particularly preferably 80 to 100% by weight, of so-called main monomers a), including monoethylenically unsaturated monomers such as olefins with up to 4 carbon atoms, for example ethylene, vinyl aromatic monomers with up to 10 carbon atoms such as styrene, α-methylstyrene, ortho-chlorostyrene or vinyltoluenes, vinyl and vinylidene halides, such as vinyl and vinylidene chloride, esters of vinyl alcohol and Monocarboxylic acids containing 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate, esters of α, β-monoethylenically unsaturated mono- and dicarboxylic acids, preferably having 3 to 6 carbon atoms, such as, in particular, acrylic acid, methacrylic acid, Maleic acid, fumaric acid and itaconic acid with alkanols generally having 1 to 12, preferably 1 to 8 and in particular 1 to 4 carbon atoms, such as in particular acrylic acid and methacrylic acid methyl, ethyl, n-butyl, isobutyl and -2-ethylhexyl ester, maleic acid dimethyl ester or maleic acid n-butyl ester, nitriles of said α, β-monoethylenically unsaturated carboxylic acids, such as acrylonitrile or methacrylonitrile and C₄ - C₈-conjugated dienes, such as 1,3-butadiene and isoprene, are to be understood. Mixtures of these monomers are preferably also suitable. In many cases it has proven to be advantageous if the proportion of nitriles is less than 15% by weight, preferably 0% by weight, of the total amount of the monomers used.

The monomers mentioned are essentially insoluble in an aqueous medium.

Crosslinking monomers b) can also be used in amounts of from 0 to 15% by weight, preferably from 0 to 10% by weight, in particular from 0 to 6% by weight, based on the total amount of the monomers used, which preferably undergo the crosslinking reaction during the drying of the polymer, the crosslinking reaction being able to be accelerated by tempering and, if appropriate, by adding catalysts, such as, for example, proton-releasing substances such as maleic acid, diammonium hydrogen phosphate or ammonium nitrate. If monomers b) are also used, a minimum amount of preferably 0.1, in particular 0.5,% by weight has proven to be suitable. Examples of such monomers are n-alkylolamides of 3 to 10 carbon atoms, α, β-monoethylenically unsaturated carboxylic acids, among which N-methylolacrylamide and N-methylolmethacrylamide are preferred. Particularly preferred as a crosslinking monomer is acrylamidoglycolic acid and methacrylamidoglycolic acid and their ethers, esters or ether esters with alcohols such as alkanols having up to 12 carbon atoms, for example methyl acrylamido methoxy acetic acid, methyl acrylamidohydroxyacetic acid, methacrylate methacrylate methacrylate, methacrylamide methacrylate methacrylate, methacrylamido methacrylate methacrylate, methacrylamide methacrylate methacrylate methacrylate , Butyl acrylamidobutoxyacetate and butyl methacrylamidobutoxyacetate. The ammonium salts of the (meth) acrylamido acids mentioned are also suitable. These crosslinking systems do not release formaldehyde that is toxicologically harmful during the crosslinking reaction.

The free (meth) acrylamidoglycolic acid is very particularly preferred.

Monomers c) which differ from the monomers mentioned and which, when polymerized, preferably give rise to water-soluble homopolymers, are normally only used as modifying monomers in amounts, based on the total amount of the monomers used, of 0 to 50% by weight, generally 0 to 30 wt .-%, preferably from 0 to 15 wt .-%, co-polymerized. Examples of such monomers are α, β-monoethylenically unsaturated mono- and dicarboxylic acids and their amides, such as e.g. Acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, furthermore vinylsulfonic acids and their water-soluble salts, vinylphosphonic acid, their salts and esters with alcohols with up to 4 C atoms as well as n-vinylpyrrolidone and 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate or dimethylaminoethyl .

• 70 bis 99,5 Gew.-% aus Estern der Acryl- und/oder Methacrylsäure mit 1 bis 12 C-Atome aufweisenden Alkanolen, Styrol, Butadien, Vinylacetat und/oder Vinylpropionat,
• 0,5 bis 15 Gew.-% vernetzender Monomerer b)und
• 0 bis 15 Gew.-% weiterer Monomerer c).

Particularly preferred polymers consist, for example, of

• 70 to 99.5% by weight of esters of acrylic and / or methacrylic acid with alkanols containing 1 to 12 carbon atoms, styrene, butadiene, vinyl acetate and / or vinyl propionate,
• 0.5 to 15% by weight of crosslinking monomers b) and
• 0 to 15% by weight of further monomers c).

Very particularly preferred polymers are e.g. from monomer mixtures of 90 to 99.5% by weight, preferably 94 to 99% by weight, of esters of acrylic and / or methacrylic acid with 1 to 12, in particular 1 to 8, C atoms and 0.5 to 10 % By weight, preferably 1 to 6% by weight, of acrylic acid, methacrylic acid and / or in particular acrylamidoglycolic acid, methacrylamidoglycolic acid and the above-mentioned derivatives of these acids, with acrylamidoglycolic acid and methacrylamidoglycolic acid being very particularly preferred.

The weight percentages in each case relate to the total amount of the ethylenically unsaturated monomers used.

The polymers used according to the invention preferably have a glass transition temperature below 60 ° C., in particular below 30 ° C. Particularly preferred glass transition temperatures are between -40 ° C and + 30 ° C. The glass transition temperature can be measured in a known manner according to ASTM 3418/82 (so-called "midpoint temperature").

The polymerization of the monomers mentioned takes place e.g. by solution polymerization and subsequent dispersion in water (secondary dispersion) or preferably by the process of free-radical aqueous emulsion polymerization.

The emulsion polymerization is usually carried out at temperatures between 20 ° C. and 95 ° C., preferably between 50 ° C. and 90 ° C.

Free radical polymerization initiators are all those which are capable of initiating a free radical aqueous emulsion polymerization. Both peroxides, e.g. Alkali metal peroxydisulfates, ammonium peroxydisulfate or H₂O₂, as well as azo compounds.

Combined systems composed of at least one organic reducing agent and at least one peroxide and / or hydroperoxide are also suitable, e.g. tert-butyl hydroperoxide and the sodium metal salt of hydroxymethanesulfinic acid or hydrogen peroxide and ascorbic acid.

In the polymerization e.g. Protective colloids or anionic, cationic or nonionic emulsifiers, preferably in amounts of 0 to 10% by weight, particularly preferably 0.1 to 5% by weight, based on the polymer, are used.

The polymer dispersion is used as a binder to consolidate the raw fleece. For this purpose, additives, for example crosslinking agents, which react with functional groups in the polymer, or usually thickeners or hydrophilizing agents or hydrophobizing agents, can also be added to the polymer dispersion.

The polymer dispersions should form sticky films so that the superabsorbent particles applied later are bound as firmly as possible to the nonwoven surface.

The film stickiness can be checked using a loop test. For this purpose, the polymer dispersion is spread on a smoothly calendered paper in 2 layers of 50 µm each. After application of each layer, the film is first dried at room temperature to film the dispersion. The dispersion film on the paper is then dried at 120 ° C. for 10 minutes at a time. In the case of dispersions with self-crosslinking molecular groups in the polymer, after application and drying of the second dispersion layer, heat is additionally given at 150 ° C. for 3 minutes in order to complete the crosslinking reaction in the dispersion film. Strips measuring 25 cm x 2 cm are cut out of the dispersion-coated paper produced in this way. In order to measure the film stickiness, a loop is formed from the strip and the ends of the loop are clamped in a commercially available tearing machine in such a way that the dispersion coating is on the outside of the loop. The loop is then slowly passed onto a steel metal plate, on the surface of which a strip with the same dispersion film is attached. This is done in such a way that there is contact between the dispersion films over 30 mm, so that the contact surface is 20 mm (strip width) x 30 mm. The force N (Newton) that must be applied in order to separate the coated loop from the coated paper on the metal base is then measured at a take-off speed of 300 mm / min. The measurement is carried out as a triple determination with three pairs of coated papers. The mean value is formed from the individual tear values obtained. This should preferably be greater than 1 N, particularly preferably greater than 3 N.

In order to achieve a good transmission of liquid to the superabsorbent particles on the nonwoven, the film made from the polymer dispersion should preferably have a hydrophilic character. The hydrophilicity of the dispersion film can be determined, for example, on a test nonwoven that has been consolidated with the dispersion. Viscose fibers can be used as the test fleece. The production of nonwovens can the generally known methods by bath impregnation, foam impregnation or spraying the nonwoven fabric with the dispersion. The treatment with the dispersion can be followed by drying and tempering of the nonwoven obtained, crosslinking constituents which may be present in the polymer reacting with one another and / or with other functional groups in the polymer and / or with functional groups of the nonwoven fibers. The drying conditions depend on the type of dryer used, usually the drying temperature is between 100 ° C and 230 ° C, and the drying or tempering is carried out between a few seconds and several minutes.

The quantity ratio fiber / binder (solid / solid) is set to 2.5: 1 for the determination of the nonwoven fabric hydrophilicity.

The nonwoven fabric hydrophilicity is determined according to the so-called runoff test:

Test equipment:

Drainage distance of 9 * 28 cm with an angle of 10 °. Bottle of 2000 ml for test solution, 50 ml burette for holding the test solution, scales, funnel with an outlet speed of 3.75s + -0.15s / 25 ml of the test solution, drip pan.

Preparation for the exam:

• a. Basic solution
  Weigh 2.5 + -0.01 g of Triton X-100 (ethoxylated octylphenol from Rohm and Haas) on a balance into a 100 ml flask, make up to the calibration mark with distilled water and stir well with a magnetic dust.
• b. Test solution
  Weigh 20 + -0.01 g of table salt in a 2 l flask on a weighing machine, add 4 + -0.01 g of the basic solution and make up to 2 l with distilled water. The surface tension, which must have a value of 30 + -3 mN / m, is then determined using a tensiometer.

Sampling:

• 1. Fleece: 28 cm in the preferred fiber direction and 9 cm wide
• 2. Underlay to hold the continuous test solution: cellulose pulp (Lohmann GmbH, order no .: 16000) in layers, 28 cm lengthways, 9 cm across, weight approx. 40 to 42 g / edition.
• 3.Number of samples: 3

Carrying out the test:

The drain plate, covered with a 0.025 mm thick polyethylene film, rests on a flat surface so that the drip pan for the test solution can be pushed under the edge of the drain section. Then you put on 40 to 42 g of bandage pulp. The nonwoven fabric to be tested is now placed in such a way that the lower edge of the nonwoven fabric extends 1 to 2 cm beyond the cellulose, thereby preventing the test solution from flowing back into the cellulose.

The test distance from the impact of the test solution on the nonwoven to the drain edge is 23 cm.

The distance between the funnel and the nonwoven is 2.5 cm.

In order to prevent the test solution from flowing off to the side, a small channel is created in the middle of the sample using a rod by applying slight pressure to the nonwoven and the base. Depending on the nature of the nonwoven, the test solution runs off or through the nonwoven into the underlay.

When 25 cm³ of the test solution has expired, the amount collected in the drip pan is weighed out.

Evaluation:

Angegeben wird die abgelaufene Menge in %. Aus 3 Einzelwerten wird ein Mittelwert gebildet.

The expired quantity is given in%. An average is formed from 3 individual values.

The polymer dispersions which are used to produce the nonwovens according to the invention should yield viscose nonwovens, of which less than 80% by weight of water preferably runs off in the run-off test.

In the production of the nonwoven fabric according to the invention, after the aqueous polymer dispersion has been applied to the raw nonwoven, superabsorbent particles are applied to the still wet nonwoven.

The still wet nonwoven preferably has a residual water content of more than 1% by weight, particularly preferably more than 5% by weight, based on the wet, polymer-coated nonwoven.

After the polymer dispersion has been applied, the superabsorbent particles are preferably sprinkled onto the wet fleece without further intermediate treatments of the fleece.

Superabsorbent particles are known as such. For example, Superabsorbent particles made from (meth) acrylic acid or copolymers in a proportion of at least 30% by weight, preferably at least 50% by weight (meth) acrylic acid.

Usual superabsorbent particles have an average particle size of 10 to 2000 μm (sieve analysis).

After the superabsorbent particles have been applied, a large part of the water can be sucked out of the fleece, for example by passing the fleece through a slot in which there is a vacuum generated by a pump. During this suction process, the superabsorbent particles are pre-fixed on the nonwoven surface. The fleece, which is still moist after vacuuming, can then be dried at elevated temperature in order to complete the adhesive bonding of the fleece to the nonwoven and to fix the superabsorbent particles to the nonwoven surface as permanently as possible. Drying can be done in a hot air dryer. The drying conditions depend on the type of dryer used, usually the drying temperature is between 100 ° C and 230 ° C, and the drying or tempering is carried out between a few seconds and several minutes. A conveyor belt is recommended for rapid transport of the fleece or raw fleece from the treatment with the polymer dispersion to the suction to the dryer.

The nonwovens according to the invention are outstandingly suitable for the production of articles with superabsorbent properties, such as e.g. Baby diapers, incontinence products, sanitary napkins and cosmetic or medical wipes. The superabsorbent nonwovens are characterized by their low thickness and high water absorption capacity. This enables the construction of particularly thin articles that meet the highest demands for the discreet wearing of such products.

example

A raw fleece of viscose fibers with a basis weight of 35 g / m² was in an immersion bath with an aqueous polymer dispersion of a copolymer of ethyl acrylate and acrylamidoglycolic acid with a solids content of 50 wt .-%, a glass transition temperature of -10 ° C, a film tack of 3 N im Loop test and a hydrophilicity on the viscose test fleece of 0% amount of water in the drain test, impregnated.

Immediately afterwards, superabsorbent particles (polyacrylic acid with a water content of 10 to 15% by weight) were sprinkled on the wet fleece. These SAP particles were a product of Ultrasorb Chemicals GmbH, a joint venture of BASF AG and Nippon Shokubai with the name Aqualic CA W3. Excess water was suctioned off and the fleece was then dried at 150 ° C.

The viscose nonwoven fabric obtained had a fiber / polymer (solid) weight ratio of 2.5: 1. Seven times the nonwoven weight of superabsorbent particles was firmly fixed on the nonwoven, ie almost no particles trickled down from the nonwoven surface.

The superabsorbent nonwoven had a thickness of approximately 0.8 mm. Its water absorption capacity was determined by placing the nonwoven fabric in a 0.9% saline solution for 10 minutes, then hanging it up for 10 minutes to dry and then weighing it. The water absorption capacity of the material results from the difference in weight before and after immersion in the aqueous saline solution. In the present example it was 1,500%.

Claims (10)

Nonwovens based on a raw nonwoven and a polymer dispersion as a binder for the raw nonwoven, superabsorbent particles being fixed on the surface of the nonwoven by the binder for the raw nonwoven. Nonwovens coated with superabsorbent particles, obtainable by applying an aqueous polymer dispersion as a binder to an unbound raw fleece, applying superabsorbent particles to the still wet nonwoven, suctioning off excess water and, if appropriate, subsequent drying. Nonwovens according to claim 1 or 2, wherein the polymer present in dispersion has a glass transition temperature less than 30 ° C. Nonwovens according to one of claims 1 to 3, wherein the weight ratio of raw nonwoven to the polymer (solid) is 15: 1 to 1: 1. Nonwovens according to one of claims 1 to 4, wherein the superabsorbent particles have a diameter of 10 to 2000 µm. Nonwovens according to one of claims 1 to 5, wherein the superabsorbent particles are poly (meth) acrylic acid or poly (meth) acrylic acid copolymers with a content of at least 50% by weight (meth) acrylic acid. Nonwovens according to one of claims 1 to 6, wherein the raw nonwoven is viscose or cellulose. Process for the production of nonwovens coated with superabsorbent particles, characterized in that an aqueous polymer dispersion is applied as a binder to a raw nonwoven, superabsorbent particles are applied to the still wet nonwoven, excess water is suctioned off and then optionally dried. Use of nonwovens according to one of claims 1 to 7 for the production of textile materials with superabsorbent properties. Textile materials with superabsorbent properties, obtainable using nonwovens according to one of claims 1 to 7.