US3551229A - Method for producing nonwoven fabrics from split fibers - Google Patents

Description

D 1970 MASAHIDE YAZAWA 3,551,229

METHQD FOR PRODUCING NON-WOVEN FABRICS FROM SPLTT FIBERS Filed Oct. 2, 1967 INVENTOR Mosh/'de Yozowo BY V Fwd ATTORNEY United States Patent 3,551,229 METHOD FOR PRODUCING NONWOVEN FABRICS FROM SPLIT FIBERS Masahide Yazawa, Tokyo, Japan, assignor to Polymer Processing Research Institute Ltd., Tokyo, Japan, a corporation of Japan Filed Oct. 2, 1967, Ser. No. 672,154 Int. Cl. B29j 1/00, 5/08 US. Cl. 156-622 11 Claims ABSTRACT OF THE DISCLOSURE A method for producing a web of substantially constant Width useful for non-woven fabrics from split fibers having dimensional instability inherent to their network structure which are made by splitting uniaxially-stretched films or tapes, the said method comprising feeding said split fibers into a duct through which a fluid is flowing at a velocity greater than the feeding velocity of said split fibers, blowing said split fibers against a screen whereby the fluid is allowed to pass through the screen and said split fibers are allowed to deposit on the screen in the state of their any desired width, thickness and distribution by the guiding and carding action of the fluid flowing through the duct. A method for producing non-woven fabrics from the web whose fiber distribution has been predetermined by the foregoing method, which comprises fixing the fiber distribution by mechanical quilting, needle punching or adhesion by way of a binder having a softening temperature lower than that of said split fibers, and a method for affording a pattern or holes upon said nonwoven fabrics to make them more flexible, less slippery, more air-permeable and more woven-like which comprises embossing said fabrics on heating at a temperature lower than the heat-resisting temperature thereof.

BACKGROUND OF THE INVENTION This invention relates to a method for producing nonwoven fabrics from split fibers having network structure of constituent fibers. More particularly, it relates to a method for producing non-woven fabrics from split fibers produced by any kind of splitting mechanism, such as by splitting of stretched films with a tap-like cutter, by fibrillation thereof during the slide-rubbing on the surface of a rotating file, by false-twisting via hard-twisting, by air jet method or the like. In contrast to the conventional nonwoven fabrics made of short fibers and connected only with conventional adhesive, the products of the present invention have the characteristics that the latter has much higher tenacity and is less fluffy than the former because of the fact that fibers of the latter are endless and connected in network structure with each other.

Persons skilled in the art who have noticed the abovementioned advantages of the split fibers of network structure have attempted to use them as a raw material of nonwoven fabrics. However, the split fibers having network structure cannot be applied to a conventional carding machine even when they are cut into small length on account of their net-work structure. Their attempts have failed on account of a problem how to make a web having substantially constant width and thickness. Anyhow, it is still an unsolved problem how to make the split fibers into non-woven fabrics of practical usage.

It is an object of the present invention to provide a method for producing a web of substantially constant width useful for non-woven fabrics from split fibers having dimensional instability inherent to their network structure.

It is another object of the present invention to pro- 3,551,229 Patented Dec. 29, 1970 "Ice vide a method for producing non-woven fabrics from the web obtained by the above-mentioned method.

It is a further object of the present invention to provide a method for affording said non-woven fabrics a wovenlike pattern or holes to make them more flexible, less slippery, air-permeable and more woven-like.

These objects and other advantages can be attained by the method of the present invention.

SUMMARY OF THE INVENTION According to the first embodiment of the present invention, a number of split fibers prepared from uniaxially stretched films or tapes are fed into a flat duct or a passageway through which a fluid is flowing at a velocity greater than the feeding velocity of said split fibers into the duct, blown against a screen by the flow of the fluid whereby the fluid passes through and comes out behind the screen and the split-fibers alone are left on it, the distribution of the fibers filtered on the screen is determined by the carding and guiding action of the flow of the fluid and the practically useful width and thickness of the split fibers, as a web of non-woven fabrics, are fixed.

According to the second embodiment of the present invention, the distribution of the fibers of the resultant web of the material obtained by multiplying thereof, is fixed (1) by subjecting them to needle-punching or local sewing (quilting) or (2) by adding, mixing or laminating an adhesive binder in various forms having a softening temperature lower than the heat-resisting temperature of the split fibers to the web.(or webs) and then pressure-adhering the entire material at a temperature lower than the heat-resisting temperature of the split fibers to cause mutual adhesion.

According to the third embodiment of the present invention, resultant non-woven fabrics are subjected to embossing at a temperature lower than the heat-resisting temperature of the split fibers to produce various pattern or air-permeable holes thereupon, to strengthen the local adhesion between each fiber, to aiford slip-preventive unevenness on their surface, to increase their flexibility, or to improve their appearance as non-woven fabrics.

DESCRIPTION OF THE FIGURE Reference is now made to an appended drawing in order to give a clear understanding of the nature and the process of the present invention to those skilled in the art.

The figure is a schematic drawing showing the process in which split fibers having network structure, warped and arranged in parallel to each other are sucked and fed into a flat duct through its side slit-opening where their fiber distribution is determined by the carding and guiding action of a fluid, then they are blown against a travelling screen, the fluid is discharged through a suction box behind the screen, they are deposited on the screen to form a layer of evenly spread warp fibers which moves forward together with the screen, on which split fibers of narrower width blown, through another flat duct of narrower width, traversing from side to side, are piled up zigzag as weft fibers on the layer of the warp fibers while allowing the fluid to be discharged through another suction box, and as a result, a Web of split fibers, composed of their warps and wefts, is formed; then an adhesive binder which is explained later, a binder of network shape, for example, is applied on the lower or upper surface of the said web, if necessary, and the entire material is pressure-adhered together on heating at a temperature lower than the heat resistant temperature of split fibers by passing over a heated roller, if necessary heated rollers covered with a backing canvas and thereafter held between the belts of metal nets so that it may be embossed with a network pattern, thereby forming a non-woven fabric.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS First of all, a more detailed description is given to a method for producing the webs of split fibers for nonwoven fabrics having a desired width, a desired thickness, and a desired fiber distribution.

Non-twisted split fibers which are obtained by splitting of uniaxially streached tapes or films are arranged in parallel to each other by warping from wound bobbins or immediately after splitting process. They are fed into a duct through which a fluid flows at a greater velocity than the feeding velocity of split fibers, their distribution is determined by the carding and guiding action of the fluid in the duct, the shape, length and sectional form of which are selected suitably, the fibers are then blown through the duct against a travelling screen beind which suction boxes are installed to suck and discharge the blown fluid behind the screen, the duct is in a fixed state or moving traversely back and forth or from side to side, and the fibers are deposited on the screen, forming warps and wefts which are slackened in random directions by their over-feeding so that they may be piled on each other or not slackened, thereby producing split-fiber webs for a non-woven fabric.

As shown in the drawing, a screen 1 travels horizontally along revolving rollers 2 and 2', warped split fibers 4 having network structure, supplied by rollers 3 and 3 are sucked into a duct 5 through its slit-like side opening 6, compressed air is supplied to the duct 5 through a tube 25, carding the fibers in the duct and after the distribution of the fibers is determined according to the crosssectional shape of the duct, they are blown against on the screen through the end 8 of the duct. If the layer of fibers is thin, blown air is passed through easily behind the screen, depositing the fibers on it, but if it is thick, a suction box 7 is installed behind the screen thereby depositing the fibers on it without their being disturbed by the turbulent fiow of the air. If the sectional area of the duct is even laterally, then the fiber distribution carded by air flow is even laterally but if the section has a shape of uneven thickness laterally, the web deposited on the screen is distributed in stripes different laterally in the density of fibers or if the section of the duct widens gradually like a fish tail, the fibers are spread more widely, then the distribution of fibers becomes thinner than feeding state. If the feeding velocity of fibers is equal to the travelling velocity of the screen, the web of which the fibers are not slackened in a longitudinal direction is obtained on the screen but if the relative velocity of it is lower, the blown fibers are piled on each other at random and as a result, the web of the fibers distributed at random is obtained. If two ducts, before and behind, are installed, though not illustrated in the appended drawing, each being fed with half amount of split fibers which are picked up alternately from the split fibers running side by side and as a result, each split-fiber being able to spread twice as wide laterally as in case of one duct and thus arranged split fibers are blown out zigzag through each of the ducts, the fibers thus fed exessively are piled on each other laterally, thereby producing the web of fibers with random distribution and good entanglement. If a guide rod 9 is swung from side to side at the inlet side of the duct, split fibers are placed in a wave-like shape on the screen and if the duct is traversed back and forth, they are piled on each other in a longitudinal direction.

In the drawing, in case of piling weft split-fibers on a already warped web, if split fibers 10 are sucked into a duct.12 through its side opening 13 by pinch rolls 11, the duct 12 is traversed by the width of the warp and the blown air is sucked and discharged into a suction box 14 behind the screen, the resultant fibers can be combined as the weft web 15 with the warp web. If the weft web is placed at a narrower width in this case, it can be combined with the warp more nearly at a rectangular angle, but if the width is too narrow, there will be a disadvantage of slow-down of web-making speed. When the non-woven fabric is not required to be so strong, the guide rod 9 is swung from side to side in one-stage blowing so that split fibers may be blown out in the state of being swung from side to side in the duct and deposited in a wave-like pattern on the screen. In this case, if the fibers are overfed so as to be piled on each other and the travelling velocity of the screen is made suitably slower than their feeding velocity, the web of split fibers distributed at random and having any desired thickness can be obtained by one blowing only. Of course, air is usually used as the fluid in the duct but water or an aqueous emulsion of an adhesive binder may be used. In this case, drying is carried out before the subsequent process.

If on the web of split fibers of the present invention, or between two such webs, a conventional web produced by carding or screening of short fibers is placed and the entire material is quilted, that is, sewed locally, or punched with a needle puncher by which greater entanglement of fibers is attained in the thickness direction and the fiber distribution is fixed in that state, thus obtained nonwoven fabric is different from the conventional one, i.e., it is composed of split fibers having a network structure in which fibers are connected together here and there to form endless state in length and so, their fibers scarcely fall out from the fabric and further, it is superior in strength and practical value to fabrics made of the conventional staple fibers alone. If crimped split fibers are used, a more bulky product can be obtained. Though it is not illustrated in the appended drawing, films, threads, or tapes of a polymer having a softening temperature lower than the heat resistant temperature of the split fiber applied, can be used as adhesive binder.

Film or perforated film as an adhesive binder is placed on both surfaces of a web, or between its warp and weft, or thread-, bristle-, or tape-shaped adhesive binder is placed in a waveor stripe-like pattern on both surfaces of a web or between its warp and weft, or a network or lattice-shaped binder product is placed on it and when the entire material is introduced on a heating roller 16 where the web is prevented from collapsing and its cooling with a backing canvas 17, and pressure-adhered with a pressure roller 18 on heating at a lower temperature than the heat-resistant temperature of split fibers, the parts of the fibers where the adhesive binder penetrates in a binders pattern are pressure-adhered to each other firmly, thereby producing the non-woven fabric 19. Next, it is held between the two travelling metal nets, upper and lower, 20 and 20', preheated between the guide rollers 21 and 21' and the pressure rubber rollers 22 and 22', though not illustrated in the appended drawing, embossed by the pressure loaded On the roller 22 and 22', cooled before reaching the guide rollers 23 and 23', though not illustrated in the appended drawing, at the outlet, and Separated from the metal nets, and then, the resultant product 24, embossed with a network pattern, looks like a conventional woven fabric. If it is embossed under a great pressure such as kg./cm. the projected parts of the nets make regular small holes through it, even in the case of using a film as an adhesive binder, giving a perforated product of good air or gas permeability. In general, a paper-like product is obtained if smooth rollers are used for compression. If it is embossed with a network pattern, its flexibility increases and it feels in touch like woven fabric, though its pressure-adhered parts are somewhat hard. If softening-process is applied to it after pressure-adhered, the parts of it which are not adhered sufficiently are detached and it becomes a softer product.

In one case a thin film is used as an adhesive binder on both surfaces of the web, in another case a shaped product like fiber, thread, bristle, tape or network is laminated on it, and in a further case a powder or emulsion binder can be used. I

When the temperature of pressure-adhesion is nearly as high as the heat-resistant temperature of the split fibers, if the web is embossed with metal nets, the parts of it which are held between the convex parts of the metal nets undergo a high pressure so that the fibers of the said parts are pressure-adhered to each other even if an adhesive binder is not present, and in this case the fibers are bonded together to form a reversed replica of network of the metal net and as a result, the web looks as if it had been woven. However, adhesion by this pressure-adhesion is weak against detaching stress, so the resultant product is separated easily by crumpling. Adhesion to this extent may be suitable for the intermediate product of non-woven fabrics for some purposes.

If an adhesive binder is a networkor lattice-shaped material and its meshes are large, split fibers distributed at random can be expanded considerably freely in the direction of their thickness. If such non-woven fabric is impregnated with a foaming polyurethane compound and then foamed between two pieces of polypropylene film (as a releasing film), the foamed urethane sheet mixed with split fiber layer which is stable in dimensions and expands and contracts elastically only in the direction of its thickness, can be obtained.

In the present invention, split fibers, whether crimped or not, can be used. When the split fibers capable of generating crimps by heating are used, they can be crimped as follows: a fluid duct is installed in a heating chamber in which hot air is circulated for use, the fibers alone are introduced into the heating chamber from outside and the split fibers which are deposited slackeningly on the screen TABLE characterized to be so strong as if it were made by way of welding. When low density polyethylene, for example, is combined with split-fiber of high density polyethylene, or polypropylene of low crystallinity or ethylene-propylene copolymer or polypropylene derivative with highly crystalline polypropylene split-fiber, they are adhered well to each other.

When the product obtained by the method of the present invention is held between metal net belts for embossing on it a network, a texture or some other desired unevenness, the surface of the pressure roller is preferably elastic like rubber but a pair of metal rollers are used when it is embossed with a texture, using a cloth belt. Of course, a metal embossing roller with a suitable unevenness can be used instead of belts.

For a clear understanding of the present invention, the following specific examples are given. These examples are intended to be merely illustrative of the present invention and not in limitation thereof.

EXAMPLE 1 In this example, film was used as the adhesive binder for comparing in strength the non-Woven fabric obtained using an adhesive binder of the polymer or copolymer belonging to the same kind or group as the split fibers, with that obtained using a binder of polymer different from that of the split fiber, the latter binder being inferior in adhesion to the former.

1.IENACITY AND ELONGATION OF STRETCHED TAPE AND SPLIT FIBER TAPE THEREOF Polymer Polyentylene (P.E.) Polypropylene (P.P.)

are crimped. The bulky webs obtained by crimping are piled up and quilted, by which a product suitable for a quilt can be made.

The present invention lies in a method for producing the non-woven fabrics of split fibers but on working the above-mentioned methods, webs of carded short fibers obtained by the conventional methods or paper webs can be used as the intermediate layer between split fibers of network structure, or yarns or tows can be mixed with split fibers. Further the split fibers of different kinds can be mixed together.

As the adhesive binder, vinyl compounds having COOH CONH OAc, OH, C1 or F radical in their side chains are used and besides, there are used the poly- The above-mentioned split fibers, spread at a rate of 7 g./m. and warped without slackening, are pressureadhered to each other on heating using film binder of 18 g./m. and the resultant sheets were piled at right angle on each other as weft and warp, and then the entire material was pressure-adhered again on heating to form a non-woven fabric. Therefore, the non-woven fabric containing 36 g./m. of film and 14 g./m. of fiber, that is, 28% of fiber, was used as the specimen. The results of testing its tenacity and elongation are shown in Table 2, in which the tenacity is calculated by dividing the strength of a piece of the fabric, 50 mm. wide, by the Weight of split fibers contained only in the direction of its Weft or warp per 9,000 m. length and 50 mm. width (expressed in g./d.). The tenacity of film, PE. or R1. used was 0.8 g./d.

TABLE 2.COMPARISON OF TENACITY AND ELONGATION OF NON- WOVEN FABRICS WITH BINDER POLYMERS OF THE SAME AS AND DIFFERENT FROM THAT OF SPLIT FIBER Increasing 1 1 Increasing rate of strength (percent) tenacity of N.W.F.tenacity of 8.13. not twisted where tenacity of S.F. not twisted N.W.F. indicates non-woven fabric, $.13. indicates split fiber, tenacity is shown in g./d.

mers of the same groups of the polymer (for instance,

As it is evident in Tables 1 and 2, it can be seen that homopolymers, copolymers or their derivatives as) that of when adhesion between film and split fibers is great, the

the split fiber, the softening temperatures of which are lower than that of the split fibers because of the nonstretched polymer or copolymers or derivatives thereof. When the polymer of such group as above mentioned is tenacity of the non-woven fabric is as great as the tenacity of stretched tape before splitting, owing to the sizing effect of adhesion plus the strength of film but when P.E. film and RP. split fibers are combined, the tenacity used as the adhesive binder, adhesion thus attained is of the resultant non-woven fabric does not increase, above the ordinary effect of sizing and they both are stripped apart from each other under loading.

As it is clear according to Tables 1 and 2, when the film of the polymer or copolymer of the same kind or group as the fiber is used as an adhesive binder, it is possible to save the consumption of the split fiber to make a strong non-woven fabric.

Similarly to the above, to the split fibers of various polymers the adhesive binders or their shaped products, lower in the softening temperature, can be easily selected such as the film binder of the copolymer of 60% vinyl chloride and 40% acrylonitrile to the split fibers of polyacrylonitrile (more than 85% of acrylonitrile), that of polyvinyl chloride to those of the copolymer of 60% vinyl chloride and 40% acrylonitrile, that of intermolecularly plasticized polyvinyl chloride to those of polyvinyl chloride and that of low softening temperature polyester to those of ordinary polyester.

EXAMPLE 2 Two sheets of polypropylene film, 60 microns thick and 1 m. wide, produced by the fiat-die system, were cut into 100 tapes, of mm. width each. The tapes were fed at a velocity of 10 m./minute and stretched by 6 times in hot water at 100 C. in the state of being not piled on each other, thereafter the tapes stretched in the primary stretching were arranged side by side within a width of l m. without being piled on each other, and dried and stretched further by 9 times their original length while they were travelling on rollers installed in a dry hot chamber maintained at 125C. Next, these 100 stretched tapes were split by slide-rubbing under tension on a round bar-file mm. in diameter and 1 m. in working length), revolving at a surface velocity 3 times as fast as the velocity of the tapes. Those split fibers thus obtained were passed through the guide rod 9 (comb) moving by 100 mm. from side to side at 150 times per minute, introduced into the side slit opening 6 of the fiat duct 5 (1100 mm. wide) the end of which 8 was swung by 300 mm. back and forth at 60 times per minute, guided by compressed air blown at an air source pressure of 0.15 atm., blown against the screen travelling at in. per minute and deposited on it. Thus obtained web was composed of split fibers having random distribution and their good entanglement of weft and warp and the amount of fibers contained in the web was 32-35 g./m.

In this example, the production of the web of split fibers for the non-woven fabric was connected directly with the process for splitting the stretched film but it may be preferred to wind up the split fibers and then afterward produce their webs, in any desired width, fiber density and velocity of web making, by a separate process.

The web of split fibers thus obtained was tucked up at its selvages to give a width of l m. and two sheets of 2 mesh net-shaped binders made of non-stretched polypropylene bristles or tapes of about 1,500 d., were placed on both surfaces of it, and the entire material was pressure-adhered to each other on heating at 140145 C. and further, held between metal nets of 15 meshes, to be embossed at the same temperature and a pressure of kg./cm. between rubber rollers. As a result, when em bossed with a network (woven texture), a product looking like woven fabric, was obtained, of which the parts permeated with the binder were adhered to each other very firmly but other parts without the binder were adhered slightly to each other under the heavy pressure of the projected parts of the metal net, and the fibers were rearranged like a network. The product thus obtained was very flexible and of great practical usefulness as material for packaging fertilizers or polymer powders.

EXAMPLE 3 Two sheets of high density polyethylene film, 120 microns thick and 1 m. wide, were cut into 20 tapes, of

mm. width each. The tapes were stretched by 9 times on heating and split; The split fibers thus obtained, moving in parallel to each other, were introduced into the fiat duct 5, and while traversing the duct 5 back and forth and the guide rod 9 from side to side, they were blown against the screen to form a web of 90-100 g./m. and 1 in. width, fibers of which were distributed at random. Immediately before the web entered the roller which was covered with a backing canvas and heated to C. with steam, low density polyethylene film, of 1520 microns in thickness and 1 m. in width, was placed each on both surfaces of it like a sandwich. The entire material was pressure-adhered together, held between metal nets of 15 meshes, to be embossed at 115 C. under a pressure of 100 kg./cm. between rubber rollers, and separated from the metal nets after it had cooled. As a result, nonwoven fabrics, embosed with network pattern and having small holes regularly so as to be of good air permeability, were obtained. The product was usable as material for heavy duty packaging bags. If film is adhered to its surfaces, the resultant product is not mapped during its use.

EXAMPLE 4 Three kinds of split fibers of polypropylene colored in brown, green and yellow, respectively, having latent crimping ability, and warped in alternative sequence of the above-mentioned three colours, were divided equally in three new groups and each group thus divided was fed into three ducts arranged in parallel over a travelling screen in the same way as the duct 5 shown in the drawing, respectively and deposited as one layer of the fibers over another on the screen according to the method as shown in Example 2 and the feeding speed of the mixed colored split-fibers and the travelling speed of the screen were so controlled that the weight of the web thus obtained per square meter became 1 kg.

This web was piled up on the non-woven fabric obtained in Example 3 and the fiber distribution of the entire material was fixed by needle punching and its back surface was coated with an adhesive and the product was heated up to C. in an oven so as to create crimps in the split fibers used, whereby the whole surface of the split fibers became bulky and soft in touch and showed a beautiful appearance of mixed colors. This product served nicely as a carpet of cheaper cost than conventional one.

What I claim is:

1. A method for producing a non-woven fabric from split fibers having net-work structure which comprises: feeding the warped and mutually paralleled split fibers produced by splitting uniaxially stretched films or tapes into a duct where a fluid is flowing rapidly, blowing said fibers against a screen while determining the distribution of fibers by the guiding and carding action of the fluid and by using an appropriate shape of the duct, depositing the split fibers upon the screen so as to form a web of substantially constant width, separating the web from the screen, and fixing one or more webs piled up to any desired thickness into a non-woven fabric having a desired distribution of s lit fibers.

2. A method of claim 1 wherein said split fibers are fed in the form being warped and arranged in parallel to each other, immediately after splitting.

3. A method of claim 1 wherein said split fibers are fed in the form being warped and arranged in parallel relationship to each other from take-up bobbins of split fibers after undergoing the step of splitting and winding.

4. A method of claim 1 wherein depositing of split fibers upon the screen is carried out by using a screen having a suction box behind it in order to separate the fluid easily.

5. A method of claim 1 wherein depositing of split fibers upon the screen is carried out by affording slacking by overfeeding and depositing fibers randomly in every directions.

6. A method of claim 1 wherein fixing of one or more webs into a non-woven fabric having a fixed distribution of fibers is carried out by needle-punching.

7. A method of claim 1 wherein fixing of one or more webs into a non-woven fabric having a fixed distribution of fibers is carried out by quilting.

8. A method of claim 1 wherein fixing of fiber distribution of one or more piled webs into a non-woven fabric is carried out by applying to said web an adhesive binder having a softening temperature lower than the heat-resisting temperature of the split fibers, and pressure-adhering the entire material on heating at a temperature lower than the heat-resisting temperature of the split fibers.

9. A method of claim 8 wherein an adhesive binder is used in a form of film.

10. A method of claim 8 wherein an adhesive binder is used in a form of shaped articles of network structure.

10 11. A method of claim 8 wherein an adhesive binders are non-oriented shaped articles of the same kind of polymer as that of the split fibers selected from the group consisting of homo-polymers, co-polymers and derivatives thereof which affords stronger binding.

References Cited UNITED STATES PATENTS 2,886,877 5/1959 Frickert et al. l5662.4X 3,049,466 8/1962 Erlixch l56334 3,169,899 2/1965 Steuber 15662.2X 3,368,934 2/1968 Vosburgh l56-62.4X

LELAND A. SEBASTIAN, Primary Examiner U.S. Cl. X.R.

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