IL34982A - Compositions for non-woven textile fabrics - Google Patents

Description

Π'ΐηκ-κ V Dopo **a menu nww NOVEL COMPOSITIONS FOR NON-WOVEN TEXTILE FABRICS The present invention relates to compositions useful in the production, by a wet process, of sheets of non-woven fibre fabrics, and to the sheets so produced,, These compositions comprise essentially textile fibres and a binder to bind them together into a coherent mass. The composition of the invention can be used to produce non-woven sheets of high strength which possess such desired properties as flexibility, smooth feel, and high absorption properties.

It is well known that sheets of non-woven fibre fabrics could be manufactured using various fibrous materials, blended or unblended for example, cellulose fibres, artificial fibres and/or synthetic fibres, by binding them together by different processes. Such sheets are normally made either by textile machinery operating in the dry using air deposition, or by carding (see, for example, United States Patent Nos. 3,329,556 and 3,117,055), or using paper-making machinery, the fibres being dispersed in water and deposited on the conveyor belt of the machine. Whatever technique is used for manufacturing the sheets, the fibres which comprise the sheets have to be bound together to ensure their cohesion and to impart to the non-woven fabric the mechanical properties necessary for their use. Thus, in the manufacture of such fabrics by the dry process, the use of needle felting has been widely describedj this is a mechanical process involving joining together the fibres throughout the depth of the fabric, and making use of a resin chosen for the purpose when bonding by impregnation. In the wet process, the use of a binding agent such as a latex, or impregnation of the fabric after the liquid has been drained off and the fabric dried, has been recommended and made use of. Thus United States Patent No.- 3,098,786 describes a process for making paper from an aqueous suspension of acrylic fibres dispersed with the aid of araya gum and British Speci ication No. 1,064,094 describes a process for making artificial leather from at least two types of synthetic fibres, the fibres being bound at their points of contact by dissolution of part of one of the fibre materials. Also, British Specification No. 1,084,777 describes the production of a non-woven mat produced from continuous fibre, the fibres being bound by a thermal treatment causing the thermoplastic fibres to melt. Again, United States Patent Nos. 3,329,556 and 3,533,725 disclose the treatment of cellulosic fibres such as cotton so as to cross-link them. Another known method of binding together the fibres making up the fabric is to introduce into the fabric materials such as fibrils, (synthetic fibres with a low melting point) , which will join the fibres together when a suitable heat treatment is applied.

All these methods of bonding result in the production of non-woven fabrics which have properties that are not entirely suited to certain applications, in particular, applications requiring a high mechanical strength in a dry or humid atmosphere, improved resistance to tearing, and to splitting, and high flexibility, etc.

A principal difference between the wet and the dry processes is that the former produces much more ^ entanglement of the fibres than the latter. As a result products produced by the dry process have only a poor resistance to rupture in the transverse direction, in contrast to those produced by the wet process.

It has now been found that the above-mentioned disadvantages can be overcome if the sheet is prepared from a composition comprising fibres of more than one type which are bonded with acrylic fibrils which ensure the cohesion of the fabric thus manuf ctured.

According to the present invention there is provided a composition particularly suitable for the manufacture of disposable sheets having a high wet and dry strength and improved resistance to tearing by a wet process, comprising a mixture including, for each 100 parts, at least 45 parts of viscose staple fibre, 15 to 20 parts of bleached non-refined wood pulp, 1 to 10 parts of refined polynosic fibres, 5 to 15 parts of polyamide fibres and 15 to 25 parts of acrylic fibrils, the parts being parts by weight.

The compositions according to the invention derive their advantage from the judicious blending of the artificial fibres and the natural and synthetic fibres.

Introducing the artificial fibres, namely the viscose staple fibre and polynosic fibres and the natural cellulose fibres, namely the paper pulp, which can be blended with the synthetic fibres, namely the polyamide fibres, into the body of the fabric gives this fabric the desired properties of improved mechanical strength, and flexibility, and gives the feel of a textile material.

The binding agent introduced into the body of the fabric for making the fibres cohere together is of great importance. It is, in fact, known that in the wet process of bonding the fabric by impregnation, all the fibres adhere together by stopping up the interstices; this process gives the fabric a rough feel, and results in a lack of flexibility, which has frequently to be compensated for by subsequently subjecting the fabric to mechanical treatment, such as creping. This sometimes results in a considerable deterioration in the mechanical properties of the fabric. It is known furthermore, that by other bonding procedures, certain essential characteristics of the fabric and the desired appearance thereof are not achieved,, We have found that the use of acrylic fibrils as binder has special advantages in the manufacture of non-woven textile fabrics obtained by the wet process,, One of the immediate advantages is that the fibrils, which are incorporated to consolidate the structure of the fabric, do not cover the fibres constituting this fabric, as is the case when impregnation takes place with a liquid binder, but are placed preferably at the intersections of the fibres and bind them together during the subsequent heat treatment process. For this reason, the fibrous fabric retains the actual textile properties of the fibre form from which it is made, such as the feel, appearance, flexibility, and high absorption capacity towards liquids, all of which are highly desirable properties for articles made of non-woven fabrics. In addition, the mechanical properties of the fabric are greatly improved, in particular when used in a humid atmosphere. Finally, being very flexible, the said fabrics which are made of pulp that has been well blended, are suitable for imprinting coloured designs on them covering ail or part of the surface, so enhancing the appearance. The use of well blended pulp also improves the mechanical properties of the product.

Of course, it is well known to use fibrils as the binding agent in the production of non-woven fabrics. The essence of the present invention is the realisation that by using a specified combination of fibres with a particular type of fibril in carefully defined proportions it is possible to prepare a fabric having particularly valuable properties.

There are certain prior art disclosures which relate principally to the preparation of new types of fibrils. Thus Belgian Specification No. 564,206 describes in great detail the production of fibrides derived from a large number of different polymers , including polyacrylonitrile although there is little exemplification of fibrides of polyacrylonitrile. Furthermore there is no disclosure of a composition containing a combination of natural, synthetic and artificial fibres together with the fibrides, let alone of the specific combination of fibres or of the specific proportions used in the present invention. United States Patent No, 3,259,539 describes the use of such fibrides but, again, there is no exemplification of a composition which even closely resembles the compositions of this invention. British Specification No. 1,169,167 relates to a process for preparing special fibres based on an acrylic ester which may be combined with a variety of other types of fibre; the fibres are produced by extrusion and it is only subsequently, after they have been combined with other fibres, that they may be converted into fibrils; no proportions for the various fibres are specified. British Specification No. 1,116,824 also relates to special fibres, based on a polymer derived from 80% or more of acrylonitrile, which can be fibrillated by agitation (in contrast to the preferred method of precipitation using a coagulating liquid used for the acrylic fibrils of the present invention). Further at least 80% of the paper produced therefrom is derived from the fibrils (in contrast to 15 to 25% in the compositions of this invention) and there is no suggestion of the use of synthetic and natural fibres. Again, British Specification Nos. 982,114 and 952,703 describe the preparation of fibrils, for example of an acrylic polymer, from a continuous filament with cutting up of the filament followed by mechanical agitation in an aqueous bath. The resulting fibrils can then be mixed with other fibres to produce a non-woven material. It will be appreciated that such a procedure is very different from that used in the present invention; fundamentally, however, there is no disclosure of the relative proportions of the various ingredients as specified for the compositions of this invention.

French Specification No. 1,468,649 describes the preparation of a non-woven fabric which uses fibrils of an acrylic polymer or copolymer as binder. However there are significant differences between the compositions described and those of the present invention. In particular, although there is a suggestion that the amount of binder can be from 15 to 50%, only 30% is exemplified, in contrast to 15 to 25% used in the compositions of this invention. Furthermore there is no disclosure of the use of natural or polynosic fibres. Perhaps the most relevant disclosure is of a composition comprising 62% of regenerated cellulose, 8% of copolyamide and 30% of acrylic fibrils. Apart from the differences noted above, if in the composition of the present invention the minimum amounts of binder, polynosic fibres and wood pulp are 2^ used, the maximum amount of viscose fibres which can be present is only 61%, the preferred range being 50 to 55%. Finally, British Specification No. 959,977 describes the preparation of a paper from copolyacrylonitrile fibres and modified cellulose fibres which are fibrillated by agitatio: and then formed into a matt. The composition specifically mentioned, however, contains 75 to 95% of acrylic fibres and 5 to 25% of cellulose fibres. Clearly, regardless of the degree of fibrillation this composition is entirely different from the compositions of this invention.

It can thus be seen that in spite of the very large number of disclosures relating to the preparation of non-woven fabrics using fibrils as binder material there is no disclosure of the compositions of this invention; this fact alone must strongly suggest that the compositions are inventive. Further, however, as mentioned below, the compositions of this invention produce papers having a very special combination of desirable properties.

The fibrous compositions of the present invention have particular utility in the production of disposable articles, for example disposable sheets. Non-woven fibre fabric made by the wet method from the compositions, is particularly suited for this purpose having a smooth feel, an agreeable appearance, adequate wet and dry mechanical strength, and improved resistance to tearing and splitting, particularly when wet; the economics for the manufacture of such disposable articles is particularly favourable.

The acrylic fibril binder used in tie present invention is preferably obtained by precipitating an acrylic latex in a liquid coagulant, e.g. an aqueous coagulating bath. This is a known technique, and is described in French Patent Specification No. 1,516,178.

The latex can be a homopolymer of acrylic acid, a homopolymer of an acrylic ester such as methyl acrylate, ethyl acrylate, butyl acrylate or copolymers of these acrylates with one another or, if desired, with another copolymerisable ethylenic monomer, for example, vinyl 'acetate, butyl maleate, etc. Advantageously, mixtures of these polymers and/or copolymers can be used.

In practice, the compositions are prepared by blending the various fibres and the binding agent in variable proportions according to the use to which the products will be put.

Some specific compositions for particular applications are mentioned below by way of illustration.

In the case of disposable sheets, the proportions of each of the constituents of the composition may be varied advantageously between the following limits: (for 100 parts of the total composition, part by weight) Viscose staple fibre: at least 45 parts and preferably 50 to 55 parts Bleached pulp, refined or unrefined, (resinous or deciduous): 15 to 20 parts Refined polynosic fibre: 1 to 10 parts Polyamide fibre: 5 to 15 parts Acrylic fibrils: 15 to 25 parts The non-woven fabrics of the present invention can be subjected to various heat treatments and/or mechanical treatments such as shrinkage according to known processes.

It has been found however, that by using an acrylic fibril binder and incorporating into the compositions the synthetic fibres with a high shrinkability, it is possible to omit the conventional stages of drying and impregnation and to proceed directly to "textilisation" by thermal treatment, to obtain craped materials of high flexibility and a smooth textile feel.

The characteristics and advantages of the invention will appear more clearly from the following Example, which is given to illustrate the invention further.

The various physical characteristics given in the different examples have been evaluated by the standards AFNOR N.F. Q 03 004 for wet and dry breaking length and A.S.T. . D 2261-64 T for the tearing strength.

EXAMPLE A non-woven fibre sheet, to be used as a disposable sheet was made from natural, artificial and synthetic fibres and acrylic fibril binder and using, in the head tank of a paper-making machine, a dispersion containing 10 g/1 of the following mixture: Viscose staple fibre 1.5 den/10 mm 25 parts (by weight) Viscose staple fibre 3 den/10 mm 25 parts " M Nylon fibre 6 den/32 mm 10 parts " " Bleached resinous unrefined pulp 15 parts " " Viscose polynosic type BX staple fibre refined to 83° Schopper 5 parts " " Acrylic fibrils (binder) 20 parts " " The fibrils were obtained according to the method of French Patent Specification No. 1,516,178 using a latex comprising a mixture of homopolymers of methyl acrylate, ethyl acrylate, and acrylic acid and a butyl maleate -vinyl acetate- butyl acrylate terpolymer. 0.6%, with regard to the fibrous mass, of an aqueous solution of a cationic polyamide of the Kyraene 557 type (Ste. Hercules-Powder) was also added.

Therea ter a sheet was produced on the paper-making machine which was drained, dried, etc.

A non-woven fibre sheet was obtained with the following characteristics s Weight 20 g/m2 Dry breaking length 1800 m Wet breaking length 700 m Tearing strength D/G 10 The results given above correspond to the average values measured along the direction of travel and the crosswise direction of the sheete In order to demonstrate the superior physical characteristics of the sheet according to the invention, a sheet of non-woven fibre sheet was made under the same 2 conditions and with the same weight (20 g/m ), the composition of this latter sheet being of the same type as that of the above-mentioned sheet except that the fibrils and Kymene 557 were absent.

The characteristics evaluated by the same analytical methods as mentioned above are as follows: Dry breaking length 800 - 1000 m Wet breaking length not measurable Tearing strength not measurable

Claims (6)

1. 34982/2 WE CLAIM; A composition particularly suitable for the manufacture of disposable sheets having a high wet and dry strength and improved resistance to tearing by a wet process, comprising a mixture including, for each 100 parts, at least 45 parts of viscose staple fibre, 15 to 20 parts of bleached non-refined wood pulp, 1 to 10 parts of refined polynosic fibres, 5 to 15 parts of polyamide fibres and 15 to 25 parts of acrylic fibrils, the parts being parts by weight.

2. A composition according to claim 1 wherein the fibrils of acrylic polymer are obtained by precipitation of an acrylic latex in a coagulating bath, and comprise a homopolymer or copolymer, or mixture thereof, of acrylic acid, or an acrylic ester and, if desired, another copolymerisable ethylenic monomer.

3. A composition according to claim 1 or 2 wherein the viscose staple fibre has been modified by treatment with a polymerisable ethylenic monomer, such as acrylic acid or acrylonitrile, in the presence of ionising radiation.

4. A composition according to any one of claims 1 to 3 which includes 50 to 55 parts of viscose staple fibre.

5. A composition according to claim 1 substantially as hereinbefore described.

6. A non-woven disposable sheet obtained from a composition according to any one of the preceding claims.