Non-woven web structures and method for making the same

Abstract

Improved method of preparing non-woven web structures which comprises adding, to an aqueous suspension of fibers, such as synthetic fibers, particles of a resin binder in the form of an aqueous suspension of a polymer having a glass transition temperature below 35.degree.C. (308.degree.K.), and then forming and drying said web. Non-woven web structures prepared by this method.

Parent Case Text

This is a continuation of application Ser. No. 247,686, filed Apr. 26, 1972 now abandoned.

Description

The present invention relates to non-woven web structures and to a method for making the same. More in particular, the invention relates to non-woven web structures prepared using an aqueous polymer suspension as a binding agent for such structures, and to the method of preparing the structures.

Ever since paper was first prepared in China for the first time nearly two thousand years ago from an aqueous pulp of fibers obtained by the crushing of mulberry bast, hemp, and rags, the process of preparing a planar structure, or web, from an aqueous suspension of fibers on a sieve, and the strengthening of this structure by pressing and drying, has taken on great significance in manifold variations. The preparation of paper in the modern age has itself undergone the most rapid development, according to which it is no longer unusual to achieve production rates of more than 1000 meters per minute and to produce paper in widths of several meters. The same basic process is also used for the preparation of other web structures, of which the most important are the non-woven fabrics, although in the preparation of such fabrics longer fibers must be employed in order to impart a textile-like hand to the finished structure. According to a proposal of the German Bureau of Standards, "Non-woven products" -- in accordance with the American definition -- would be defined as follows: "Non-woven products are flexible porous planar structures comprising textile fibers which, before strengthening by mechanical means (for example by stitching or the auxiliary use of other textile products), are bound to one another with the aid of a binding agent, by superficial solvation, by fusion, or by a combination of these processes."

Of the different methods for preparing non-woven fabrics, for example the mechanical, the pneumatic, the fiberspinning, and the wet process, the last-mentioned method can be outlined as follows, with a view to the invention later described herein.

As in the preparation of paper, fibers are suspended in water. However, the mixture of water and fibers, which is often characterized as "pulp", must be present in an extraordinarily high dilution in comparison with a paper pulp in order to avoid the entanglement of the fibers which arises when long fibers are used. The fiber concentrations are, for example, between 0.05 and 0.2 percent of the totoal weight of the suspension. The pulp is then fed to a webforming structure, for example an inclined sieve. Formation of the fabric follows by deposition of the fibers on the sieve, withdrawal of the water, ans subsequent strengthening of the web. Whereas in the preparation of paper the very finely ground cellulose fibers are brought into intimate contact and, with the formation of hydrogen bonds, reach a good initial wet strength, the longer fibers of non-woven fabrics must be additionally bound by the use of a binder system. The binder is either added to the aqueous fiber suspension or is applied to the web after web formation in a supplemental operation.

As raw materials for non-woven fabrics, synthetic fibers are preferably employed, in part also in admixture with cellulosics, said fibers having a staple length between 5 and 30 millimeters. Fibers of mineral or inorganic substances, such as mineral wool or glass are to be considered as technical equivalents of cellulose or textile fibers within the scope of the present invention as are also natural fibers, for example fibers obtained from scrap leather.

In the preparation of non-woven fabrics according to the wet method, the following strengthening techniques have heretofore been used to advantage: the addition of binding fibers which melt; the addition of binding fibers which swell in water; the addition of dispersions of synthetic resin which are precipitated in the fiber suspension; and, finally, the addition of priorly precipitated resin dispersions.

The strengthening of non-woven fabrics with the aid of binding agents of the type disclosed in the present invention on the one hand resembles the two last-mentioned methods to a certain degree. However, it is distinguished from these, on the other hand, in such a considerable degree that the materials used in the present invention must be viewed as forming a new class of binding agents for the preparation of planar, or web, structures from fibers, the use of which new agents entails a number of marked advantages.

In order to make these advantages clear, the following comments must be made concerning the prior art precipitation of resin dispersions on the fibers in suspension and the addition of pre-precipitated dispersions of binding agents. Latex particles cannot be quickly and completely deposited from a dispersion. This leads to a considerable loss of the binder and also to the appearance of so-called "vagabond binder", i.e. a balling together of the dispersion particles which do not adhere to the fibers to form large lumps. It is clear that the portions of binder which are not fixed in the structure leaad to water-disposal problems.

It must further be pointed out that the precipitation of a latex can only be controlled within wide limits with respect to a uniform size of the precipitated particles. An unavoidable fraction of small agglomerates do not form adhesive bonds, but only load the fibers with binder and thus detract from the textile-like hand of the material.

In order to precoagulate dispersions, particular apparatus modifications are necessary. However, these do not lead to a complete precipitation of all the latex particles so that in this case also a loss of binder and waste-water problems are involved. It should not unmentioned that the polymers useful as binders can also be precipitated from organic solutions. However, this process involves considerable disadvantages.

The advantage of using dispersions as binding agents in the preparation of non-woven fabrics, namely that by a choice of the monomers or monomer mixtures employed products which are "hard" or "soft" can be produced as desired and that corresponding non-woven fabrics can be prepared therefrom, is also inherent in the use of suspension polymers according to the present invention, as will be explained later herein.

The binding agents used according to the present invention are distinguished from the synthetic resin dispersions heretofore used in that they are aqueous suspensions, prepared according to a suspension polymerization process, of those resins which form "soft beads" or "soft pearls". Either the glass transition temperature, T.sub.g, of the polymer, or those values obtained with the aid of the torsion swign test (DIN 53445), can be employed as a measure of the softness or hardness of the suspension polymers according to the present invention.

As is known in the art, the glass transition temperature is obtained dilatometrically. This measuring technique has the disadvantage of considerably uncertainty in products having very low glass transition temperatures. However, since the suspension polymers suitable for use according to the present invention are characterized by a maximum value of the glass transition temperature (i.e. all suspension polymers whose glass transition temperature falls below a specified value are encompassed within the scope of the invention), the undependability described above in the method for determining T.sub.g is without practical significance in the present case. The characterization 10 suitable polymers by their glass transition temperature was principally chosen because the glass transition temperatures of numerous macromolecular compounds have already been determined and tabulated. For example, the "Polymer Handbook", by Brandrup and Immergut, Interscience Publishers, a division of John Wiley & Sons, New York (1966) lists the glass transition temperatures of a large number of homopolymers and copolymers in Chapter 3 entitled "Solid State Properties", pages 61-85. As well, the significance and the techniques for determining these values are explained.

Homopolymers and copolymers of the kind to be employed according to the present invention can thus be characterized as being prepared as suspension polymers, as already explained; as being employed in the form of an aqueous suspension; and finally as showing a glass transition temperature, T.sub.g, less than 35.degree.C (less than 308.degree.K.).

Data which are obtained from the torsion swing test mentioned earlier have in the recent past been increasingly used for the characterization of synthetic resins. Since the suspension polymers to be used according to the present invention can also be characterized by these test values, a short description of their determination follows.

In the torsion swing test, the temperature dependence of the dynamic shear modulus, G,(T), and of the torsion swing damping, .OMEGA. (T), are measured by means of free torsion swings.

The shear modulus is the quotient of the shear stress and the shear deformation. It is, thus, a measure of the stiffness of a polymer film.

For characterization of the softening region, use is made of a still further value determinable from the torsion swing test, namely the T.OMEGA..sub.max value. This value is the temperature at which the logarithmic decrement of the torsion swing damping goes through a maximum. The damping decrement is a measure of the inner friction of the material and is determined from the decrease in amplitude of a freely-damped torsional vibration.

The T.OMEGA..sub.max value which corresponds to the critical glass transition temperature, T.sub.g, of 35.degree. is about 60.degree.C. However, it should be repeated that in doubtful cases the glass transition temperature is to be taken as the decisive criterion of the suspension polymers in question.

The suspension or bead polymerization of polymerizable monomeric compounds can, as known in the art, be regarded as a well-cooled bulk polymerization in which a water-insoluble monomer is dispersed in the form of fine droplets by stirring in water in the presence of so-called suspension stabilizers or dispersing agents, for example gelatin, pectin, watersoluble starch, or synthetic high molecular weight materials, or in the presence of materials suspended in the water, such as talcum, magnesium carbonate, or aluminum hydroxide, and is then polymerized under the influence of an accelrator soluble in the monomer. In the polymerization, the droplets, which are liquid at first, become rubbery and, finally, solid. The goal of the suspension polymerization has until now in all cases been the preparation of solid products which can be separated from the aqueous phase in a simple way, for example by filtration, and which are bead-like particles which are "hard", i.e. which do not adhere to each other. The preparation of suspension polymers from "soft resins", i.e. the preparation of products which adhere together on separation of the aqueous phase, has appeared until now to be contrary to the desired end in suspension polymerizations, namely the easy separation and drying of the polymer. However, the use of just such bead polymers as binding agents for web structures comprising fibers is the object of the present invention.

It is not necessary to go into more detail concerning the technique of suspension polymerization to explain the present invention. It suffices to note that one skilled in the art can influence the size of the pearls, or beads, obtained by choice of the polymerization conditions, particularly by the intensity of stirring and by the kind and amount of the suspension stabilizer, and that by these measures he can prepare beads having a diameter from, for example, 0.01 mm to several millimeters.

In general, for purposes of the present invention average bead diameters between about 0.05 mm and 0.5 mm are preferred.

Although it is necessary to add the aforementioned suspension stabilizers or dispersing agents to the system in order to form defined monomer droplets and to hinder the adhesion, during the polymerization process, of the spherical polymer particles formed, it may be suitable additionally to stabilize the finished suspension to inhibit a precipitation of the solid particles (in case their density is greater than that of the aqueous phase), or to inhibit floating of the particles (when they have a lesser density than that of the aqueous phase). Also, possible adhesion which may occur on long storage is hindered.

Such a stabilization is achieved with beads whose density is greater than 1, for example by adding watersoluble salts such as sodium chloride, or other materials influencing the density of the aqueous phase.

Another possibility for stabilization lies in thickening the aqueous phase. For this purpose, high molecular weight natural pruducts (starch, alginate, pectin), modified forms of these materials (methyl cellulose, carboxylmethyl cellulose, etc.), or synthetic macromolecular products can be employed. Exemplary of the last-mentioned class of materials are copolymers containing carboxyl groups (or salts of the same) such as copolymers of acrylic acid or methacrylic acid, or polyvinyl pyrrolidone.

Monomers which can be used according to the present invention and which can be converted into bead polymers according to a suspension polymerization process include, principally, acrylic esters having 1-18 carbon atoms in the alcohol portion; methacrylic esters having from 4-18 carbon atoms in the alcohol portion; butadiene; vinylidene chloride; and vinyl acetate. These monomers can be copolymerized with one another or, also, with monomers producing hard homopolymers. In the latter case, the proportion in which those monomers forming hard homopolymers can be employed is limited by the requirement that the glass transition temperature of the resulting copolymer should not exceed the limiting value which is characteristic of the present invention. As monomers of this type forming hard homopolymers can be mentioned, for example, methyl and ethyl methacrylate, methacrylonitrile, acrylonitrile, acrylamide, methacrylamide, and styrene.

It should also be noted that the characteristic glass transition temperature, T.sub.g, for a suspension polymer to be used according to the present invention can be imparted by the use of so-called "external plasticizers", such as pthalic acid esters, even in those cases in which monomer or monomer mixture to be polymerized would give a polymer having a higher glass temperature in the absence of such a plasticizer.

Monomers effecting a cross-linking can be employed in the preparation of the suspension polymers to be used according to the present invention. However, they must be used with the proviso that cross-linking of the suspended particles may only occur to such an extent that the thermoplastic "welding" of the web fibers by fusion of the binder resin on heating of the deposited web is not impaired. The use of methylol compounds or methylol ether compounds of acrylamide or methacrylamide, or the use of monomers having at least two carbon-carbon double bonds in the molecule as comonomers is exemplary of such a cross-linking mechanism. Also, a cross-linking of macromolecular compounds can be brought about by graft copolymerization reactions.

In special cases it can be advantageous to combine the binders according to the present invention with resin dispersions known in the prior art, for example in order to increase the film-forming properties of the resin. Also, the use of mixtures of different resin suspensions which are differentiated according to composition, particle size, or molecular weight, can be advantageous.

Resin suspensions according to the present invention can be advantageously prepered with a solids content of from 50-70 percent by weight. The materials can be stored and shipped in this form, optionally after taking the stabilizing measures discussed earlier herein. The resin suspensions can be added to fiber suspensions in this concentrated form, particularly if good stirring is provided, or can be diluted before addition if this is more convenient.

The amount of the suspension polymer to be added to the web-forming fiber suspension can vary between wide limits according to the nature of the fiber web to be prepared. In general, an amount of suspension is employed which contains resin solids which are from 10 to 100 percent by weight of the suspended fibers.

A better understanding of the present invention will be had by referring to the following specific examples, given by way of illustration.

Measures available to one skilled in the art, such as the addition of dyes, pigments, and the like, the selection of synthetic, natural, or inorganic fibers which are not described herein in greater detail, and the use of homopolymers and copolymers which are not specifically described -- providing these can be obtained as suspension polymers and have a glass transition temperature below the characteristic limiting value described herein -- expand the scope of specific embodiments of the binders according to the present invention without taking them outside the scope of the invention. It should particularly be mentioned that by appropriate choice of the suspension polymer and of its average particle size, products which are substantially "made to order" for a particular use can be prepared. It is common to all of these products that they can be stored for a long period of time, optionally using supplemental stabilizing measures; that they deposit on fibers even at extraordinarily low concentrations, calculated on the water phase; and, in the drying process, lead to a uniform punctiform, adhesion of the fibers on which they are deposited. When the resin suspensions described above are employed, the disadvantage of "vagabond" binder portions involved with the use of dispersions of the prior art is not encountered, whereby losses of the binder as well as waste-water problems are avoided.

EXAMPLES

I. Preparation of Resin Suspensions Suitable for Use According to the Invention

The bead polymers listed in Table 1 are prepared either in a two-liter round glass vessel having a triangular stirrer or in a 100-liter kettle with an impeller-type stirrer and wave breaker. Heating in the first case is with a water bath: in the second case a heating mantle having circulating water is employed. The apparatus in each case is equipped with temperature sensors, a reflux condenser, and an arrangement for flushing with inert gas. The speed of stirring is variable by a gear arrangement. For the polymerization of monomers which are gaseous at the polymerization temperature (for example, vinylidene chloride), the 100-liter kettle is sealed pressuretight.

The polymerization is carried out in the following manner.

The suspending agent (suspension stabilizer) is dissolved or suspended in an already-present total amount of de-ionized water while stirring, introducing inert gas (e.g. nitrogen or carbon dioxide), and heating to polymerization temperature (65.degree. -80.degree.C.). As is evident from Table 1, a partially-hydrolyzed polyvinyl acetate (commercially available under the tradename "Mowiol N 70- 88") or the sodium salt of a copolymer of methacrylic acid and one of its higher alkyl esters (more than four carbon atoms in the alcohol portion), characterized in Table 1 as PMAA copolymer, are used as water-soluble suspending agents. For the preparation of a water-insoluble suspending agent, aluminum hydroxide is precipitated from a solution of aluminum sulfate with a soda solution. To improve the suspending effect, 5 percent, by weight of the aluminum hydroxide, of a C.sub.14 -C.sub.16 alkyl sulfonate sodium salt (commercially available under the tradename "Statexan K 1") is added.

The monomer phase, which contains the initiator and optional molecular weight regulators, as well as other additives such as plasticizers, dyestuffs, and the like in dissolved form, is introduced into this solution or suspension of the suspending agent and is dispersed in the form of fine droplets by the shearing action of the stirring. The form and the speed of rotation of the stirrer are variable over wide limits. What is necessary is that the stirring system bring about such a strong vertical circulation of the kettle contents that, in addition to the dispersion of the monomer as droplets of the desired size, any rising or sinking of the monomer droplets brought about by density differences between the water phase and the monomer phase is hindered. As monomers suitable for bead polymerization, water-insoluble compounds or compounds difficulty soluble in water are principally employed. Nevertheless, water-soluble monomers such as acrylic acid or methacrylic acid and their amides or, optionally, their substituted amides, can be employed in minor amounts. It is decisive for the success of such a bead polymerization that the equilibrium distribution of these monomers between the water phase and the monomer phase makes polymerization in the monomer droplets possible. The ratio between the water phase and the monomer phase is variable between 4:1 and 1.5:1 (by weight). At the ratio of 3:1 generally used, the following batch sizes are involved: 2 liter round flask: 900 g water; 300 g monomer; 100 liter kettle: 45 kg water; 15 kg monomer.

In the choice of auxiliary polymerization agents (initiator, chain transfer agent), the only limitations observed for the preparation of soft beads are the same as those which are generally observed for bead polymerization, for example with respect to solubility properites of these agents with respect to water and the monomers.

The compositions of the bead polymers prepared are set forth in Table 1.

During the polymerization, the exterior temperature (water bath or circulating heating) is held constant. The inner temperature increases because of the heat of polymerization which is released and reaches a maximum which is about 10.degree. - 20.degree.C. above the starting temperature after about 30- 120 minutes.

The temperature reached is held constant for about 2 hours by regulation of the heating, after which the batch is cooled to about 25.degree.C. and introduced into a storage container.

By subsequent separation of a portion of the water phase, the solids content of the bead suspension is adjusted to 50 percent. Since there are as a rule density differences between the bead polymer and the water phase, the polymer either settles or rises. However, the dispersing agent added before the polymerization generally suffices to hinder adhesion of the beads under these conditions, even on long storage.

The average particle size of the polymer beads is, to the extend that the data is given in the Table, determined microscopically. The average bead size in suspensions O - X is between 0.1 and 0.2 mm.

To characterize the molecular size, the .eta. .sub.sp/c value [Makromolekulare Chemie 7, 294 (1952)] is given, measured at 20.degree.C. in chloroform. The molecular weights of the polymers are in excess of 5000.

In the following Table, all parts given are parts by weight.

TABLE 1 __________________________________________________________________________ Composition of the Polymerization Batch Polymer- Stir- Sus- Chain- ization ring Bead pen- Appa- Transfer Temp. Rate Size .eta..sub.sp T.sub.g sion ratus Dispersant Monomers Initiator Agent Additive (.degree.C.) (rpm) (mm) (l/g) (.degree.C) __________________________________________________________________________ A Kettle 0.4 Al(OH).sub.3 80 Butylacrylate/ 0.3 Lauroyl- 0.2 Dodecyl- -- 75 170 0.05 0.080 -25 20 Acrylonitrile Peroxide mercaptan B " " " " " -- " 110 0.10 0.078 -25 C " " " " " -- " 90 0.15 0.079 -25 D " " " " " -- " 75 0.20 0.077 -25 E " " " " " -- " 65 0.25 0.080 -25 F " " " " 0.5 Ethyl- -- 75 110 0.050 -25 hexylthio- glycolate G " " " " 0.1 Dodecyl- -- 75 110 0.13 -25 mercaptan H Flask 0.4 Al(OH).sub.3 80 Butylacrylate 0.2 AIBN* 0.2 " 0.1 Blue 75 710 0.10 0.083 -23 20 Methylmeth- Dye** acrylate I " " " " " " " 610 0.15 0.086 -23 K " " " " " " " 470 0.20 0.087 -23 L " " " " " " " 390 0.25 0.084 -23 M Flask 0.4 Al(OH).sub.3 60 Butylacrylate/ 0.2 AIBN* 0.2 Dodecyl- -- 75 610 0.1-0.2 0.085 +8 40 Methylmeth- mercaptan acrylate N " " 45 Butylacrylate/ " " -- 75 610 " 0.088 +33 55 Methylmeth- acrylate O " 0.1 PMAA 75 Butylacrylate/ 0.5 Lauroyl- 0.4 Ethyl- -- 75 610 " 0.10 -15 Copolymer 20 Acrylonitrile/ Peroxide hexylthio- 5 Methacrylamide glycolate P " 0.4 Al(OH).sub.3 95 Ethylacrylate/ 0.2 Lauroyl- 0.2 Dodecyl- not 3 Methylolmeth- Peroxide mercaptan -- 75 610 " mea- -20 acrylamide/ 2 surable Methacrylamide Q Pres- 65 Vinylidene- 0.3 " -- -- 80 110 " 0.078 +15 sure 0.4 Al(OH).sub.3 chloride/ 35 Kettle Ethylacrylate R Flask 1.0 poly- 75 Ethylacrylate/ 0.3 AIBN* 0.2 Thioglycol -- 75 610 " not +20 vinyl ace- 15 methylmeth- mea- tate acrylate/ 10 meth- surable acrylic acid S " 0.4 Al(OH).sub.3 80 Butylacrylate/ 0.5 Lauroyl- 0.2 Dodecyl- -- 75 610 " 0.13 <-30 20 Vinylacetate Peroxide mercaptan T " " 100 C.sub.12.sub.-18 -Alkyl- 0.5 " 0.2 " -- 75 610 " 0.031 " methacrylate U " " 100 C.sub.12.sub.-18 -Alkyl- 0.5 " 0.2 " 75 610 " 0.048 " acrylate V Flask 0.4 Al(OH).sub.3 100 2-Ethylhexyl- 0.5 Lauroyl- 0.2 Dodecyl- acrylate Peroxide mercaptan 75 610 " 0.062 <-30 W " 0.1 PMAA- 70 Methylmeth- 0.2 t-Butyl- 0.1 " 30 Dibu- Copolymer acrylate perpivalate tyl- phthalate 65 610 " 0.075 +30 X " " 50 Methylmeth- 0.2 " 0.1 " 50 " 65 610 " 0.053 -13 acrylate __________________________________________________________________________ *Azo-isobutyronitrile **Commercially available as "Makrolex-blau R

II. Preparation of Web Structures from Fibrous Materials Using Resin Suspensions According to I as a Binder

The following process is generally employed.

The binder is added in the form of an aqueous 50 percent suspension of bead-like resin particles to a 0.1 percent aqueous fiber suspension. (In those cases where a different fiber concentration is employed, this is specifically noted.) The amount employed depends on the desired binder deposit. After thorough mixing, the suspension is deposited in web form on an inclined sieve (sieve mesh number 0.16; DIN 4188 ), and water is removed. The surface weight of the web is determined by the rate of web formation. In all cases investigated, a clear waste water was obtained.

The web formed is then subjected to a heat treatment, for example on heated cylinders, in order to evaporate the remaining water and to adhere the resin particles to the fibers. In this step, the temperatures employed are determined by the hardness or softness of the resin employed as a binder, and may vary from about 80.degree.C. to about 180.degree.C.

EXAMPLE 1

Using cellulose fibers (1.7 dtex; length: 6 mm; and binders A - G, webs having a weight of 50 g/m.sup.2 and a binder deposit of 30 percent are prepared and dried. Subsequently, they are calendered at a pressure of 1 metric ton/cm.sup.2 at 20.degree.C. and then treated on a flat-iron press for about 1 minute at 170.degree.C. under a pressure of 13 gf/cm.sup.2. All the non-woven products show a pleasant soft and textile-like hand. Their resistance to tear is determined on samples which are 5 cm in width according to DIN 53857. The values obtained are collected in the following Table.

TABLE 2 ______________________________________ Sus- Average particle Average Load pen- Size of the Resin .eta..sub.sp /c (l/g) on Tearing sion Particles (mm) (kgf) ______________________________________ A 0.05 1.0 B 0.10 1.1 C 0.15 ca. 0.08 2.1 D 0.20 1.4 E 0.25 0.7 F 0.10 0.05 1.0 B 0.10 0.08 1.1 G 0.10 0.13 1.3 ______________________________________

EXAMPLE 2

Example 1 is repeated using binder C, with the difference that differing amounts of deposited binder are employed. In this case also, the strength properties of the material are determined according to DIN 53857.

TABLE 3 ______________________________________ Binder Deposit Load on Tearing Extension on Tearing (%) (kgf) (%) ______________________________________ 20 1.2 20 25 1.4 25 30 2.1 30 35 2.8 45 40 3.3 55 ______________________________________

EXAMPLE 3

Example 1 is repeated with the difference that nonwoven products having a surface weight of 100 g/m.sup.2 are prepared from cellulose fibers or from mixtures of cellulose fibers with polyamide or polyester fibers using binder C at a binder deposit of 80 percent. The density of solids in the solid suspension in this case is 0.3 percent. The strength values determined according to DIN 53857 are given in following Table 4.

TABLE 4 ______________________________________ Mix Load Extension Ratio on on (Parts by Tearing Tearing Fiber or Fiber Mixture Weight) (kgf) (%) ______________________________________ Cellulose Fiber (1.7 dtex; length = 6mm) 100 17.3 65 Cellulose fiber (1.7 dtex; length = 6mm)/poly- 70/30 13.5 60 amide (6 dtex; length = 3mm) Cellulose fiber (1.7 dtex; length = 6mm)/polyester 70/30 19.7 68 (1.7 dtex; length = 6mm) ______________________________________

EXAMPLE 4

Example 1 is repeated with the difference that colored binders H - L are employed. In the finished web, the colored resin particles clearly make evident the uniform dispersion of the punctiform adhesion sites.

TABLE 5 ______________________________________ Suspension Average Particle Size of the Resin Particles Load on Tearing (mm) in (kgf) ______________________________________ H 0.10 0.2 I 0.15 0.7 K 0.20 0.2 L 0.25 0.3 ______________________________________

EXAMPLE 5

Example 1 is repeated with the difference that fabrics having the binding agents I, M, and N are prepared. It is clearly evident from manual handling of the finished nonwoven product that an increasing fraction of methylmethacrylate produces a harder hand.

EXAMPLE 6

Example 1 is repeated with the difference that binders C, O, and P are employed as binding agents. The weight of the non-woven product was 50 g/m.sup.2 and the binder fraction was 50 percent. The finished non-woven products are subjected to laundering according to DIN 54014 (30 minutes at 40.degree.C. with 5 g of soap per liter of wash water in the ABK-Lavatest) and to drycleaning according to DIN 54024 (30 minutes at 30.degree.C. in perchloroethylene with the addition of 3 grams of cleaning intensifier per liter of bath in ABK-Lavatest). After laundering, the web adhesion is maintained in all the non-woven products.

The web prepared using binder C is completely destroyed on drycleaning. The web containing biner O still shows a certain maintenance of the web adhesion. The non-woven product prepared with binding agent P, typifying a self-cross-linking acrylic resin, is resistant to the rigors of drycleaning according to DIN 54024.

EXAMPLE 7

Non-woven fabrics are prepared as in Example 1, using binding agent Q at increasing concentrations of the binder. At a binder deposit of 30 percent, a flame-inhibiting effect is observed [DIN-Standard: Determination of Burning and Smoldering Properties of Inflammable Textiles (Arc Tester); presently in draft].

EXAMPLE 8

A non-woven fabric is prepared as in Example 1 using binder R. The finished article is tested for resistance to water according to H. Joerder, Textil-Industrie 71, 302 (1969). The test show that a time of only 60 seconds is necessary for destruction of the web prepared using this carboxy group-containing copolymer as a binder. Such limited resistance to water is of significance for many hygienic articles.

EXAMPLE 9

Example 1 is repeated using binders S - V. The resultant webs (binder deposit = 50 percent) are carefully dried at 80.degree. - 100.degree.C. They have a tacky hand and can be adhered to one another by calendering under pressure.

EXAMPLE 10

Non-woven products are prepared as in Example 9 using binders W and X. The binder deposit is 50 percent. Both non-woven fabrics can be heat sealed, i.e., they can be adhered under pressure at temperatures of 140.degree.C. to cotton fabric. It can clearly be seen that better adhesion is obtained with binder X than with binder W.

Claims

What is claimed is:

1. In a process for the preparation of non-woven fabric by adding particles of a resin binder to an aqueous suspension of fibers, forming a web by depositing said fibers on a sieve, removing water from said web, and drying said web, the improvement wherein said particles of resin binder are added as an aqeous suspension of a suspension polymer in an amount such that the resin solids added are from 10 - 100 percent by weight of the suspended fibers, said suspension polymer particles having an average diameter between about 0.05 mm and 0.5 mm and said polymer having a glass transition temperature below 35.degree.C. and being a homopolymer or copolymer comprising a member selected from the group consisting of acrylic acid esters having 1 - 18 carbon atoms in the alcohol portion thereof, methacrylic acid esters having from 4 - 18 carbon atoms in the alcohol portion thereof, butadiene, vinylidene chloride, vinyl acetate, methyl methacrylate, ethyl methacrylate, methacrylonitrile, acrylonitrile, acrylamide, methacrylamide, and sytrene.

2. A process as in claim 1 wherein said suspension polymer comprises an alkyl acrylate having from 1 - 18 carbon atoms in the alcohol portion thereof.

3. A process as in claim 1 wherein said web is dried by heating at a temperature between about 80.degree. and about 180.degree.C.

4. A process as in claim 1 wherein the aqueous phase of said aqueous suspension of resin binder comprises a thickening agent increasing the viscosity of the aqueous phase, whereby the particles of the suspended polymer phase do not float or sink.

5. A process as in claim 1 wherein the aqueous phase of said aqueous suspension of resin binder comprises water-soluble additives rendering the density of the aqueous phase substantially equal to the density of the suspended polymer phase.

6. A flexible porous planar non-woven fabric consisting essentially of fibers bound to one another by fused particles of a suspension polymer, said suspension polymer particles having an average diameter between about 0.05 mm and 0.5 mm and said polymer having a glass transition temperature below 35.degree.C. and being a homopolymer or copolymer comprising a member selected from the group consisting of acrylic acid esters having 1 - 18 carbon atoms in the alcohol portion thereof, methacrylic acid esters having from 4 - 18 carbon atoms in the alcohol portion, butadiene, vinylidene chloride, vinyl acetate, methyl methacrylate, ethyl methacrylate, methacrylonitrile, acrylonitrile, acrylamide, methacrylamide, and styrene.