US3317335A - Fibrous, non-woven sheet materials and the production thereof - Google Patents

Description

May 2, 1967 H. J. MARRINAN ETAL 3,317,335

FIBROUS, NON'WOVEN SHEET MATERALS AND THE PRODUCTION THEREOF Filed Feb. 24, 1964 MM ATTORNEYG United States Patent O 3,317,335 FIBRUS, NGN-WOVEN SHEET MATERIALS AND THE PRODUCTION THEREOF Henry .lames Marrinan and Eric Ivan Riseley, Harrogate, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Feb. 24, 1964, Ser. No. 347,038 Claims priority, application Great Britain, Mar. 4, 1963, 8,609/63; July 4, 1963, 26,530/63 11 Claims. (Cl. 117-11) The present invention relates to fibrous, non-woven sheet materials and the production thereof.

It is known to produce non-Woven sheet materials by laying fibres in the form of a thick batt or mat, partially consolidating by means such as needle punching and following With a shrinkage treatment to complete the consolidation process.

The non-woven batt is usually prepared on a carding machine. The majority of fibres in batts prepared in this way lie in planes parallel to the surface of the batt and exhibit a preferential fibre orientation in one direction which imparts to the batt a higher strength in this direction. In order to improve the strength in other directions, a plurality of layers in varying orientation are sometimes superimposed on the batt. The thickness of the batt may vary within wide limits.

An alternative method for lthe preparation of nonwoven batts comprises entraining the individual fibres in a. gas stream and then collecting them on a sieve or a perforated drum in the form of a batt having substantially random orientation and uniform strength in all directions.

A suitable method for the initial consolidation of these batts is to pass them through a needle-loom whereby they receive from 100 to 1,000 needle punches per sq. cm. The cohesion of the batts is thereby considerably increased since a minor proportion of the fibres is oriented through the thickness of the batt. The needle-punched batts are often impregnated with an elastomeric or resinous agent to confer greater strength. Many suitable agents are known such, for example, as natural latex emulsions, polyester-urethanes, polyether-urethanes, co-polymers of acrylonitrile with butadiene or certain =acrylate esters, neoprene rubbers, rubbery polymers and co-polymers derived from butadiene or isoprene, plasticised poly(vinyl chloride) and many others.

An initial consolidation by needle-loom punching and subsequent impregnation of the non-woven batt with a binder does not provide sufficient consolidation for some purposes, such, for example as the making of synthetic sheet materials which would be suitable as a satisfactory replacement for natural leather. It becomes necessary t provide further consolidation for example by a treatment which causes either fusing and/or shrinkage. To obtain the required shrinkage with batts made from synthetic fibres it is usual to incorporateV in the batt a major proportion of .shrinkable libres which have latent retractable properties, e.g. a high shrinkage when heated. In British Patent No. 787,900 is described a process for producing non-woven, felt-like material comprising forcing, as by needle punching, filaments of 4a batt or loose web comprising at least a major proportion of retractable, synthetic filaments, arranged in superimposed layers parallel to the faces of the batt or web, through or into the batt or web and thereafter, if desired, treating said batt or Web to retract said retract-able filaments.

British patent specification No. 908,613 discloses the use of 5 to 15% of polyolefine libres in the production of a fibrous fieece and a process in which the polyolefine libres are heated above their melting temperature to cause fusing of the fibres.

' process.

3,317,335 Patented May 2, 1967 In the shrinkage treatment, area shrinkages of 20 to 60% are usually required to give a product of the desired degree of consolidation. However, the synthetic libres heretofore proposed for these uses possess certain shortcomings. For example, if fibres of polyethylene terephthalate are used it is found that a high proportion of the libres comprising the batt must be in the incompletely drawn nor undrawn state in order that sufficient shrinkage will be obtained in the final stages of consolidation. These undrawn or incompletely drawn polyethylene terephthalate fibres tend to become brittle when subjected to heat, for example, in the shrinkage step or during manufacturing operations carried out on the product, particularly if the heat treatment exceeds about C. Such embrittlement greatly reduces the practical utility of the non-woven sheets by reducing their flexibility and exteni sibility and is therefore very undesirable.

We have now found that the effectiveness of shrinkable libres depends on their ability to shrink under restraint. Surprisingly the property of shrinkage under restraint, hereinafter referred to as shrinkage force, is not proportional to free shrinkage. Using libres of high shrinkage force, -consolidated batts can be effectively produced using smaller proportions of shrinkable fibres or even using fibres of high shrinkage force which have a relatively low free shrinkage.

Certain isotactic polypropylene fibres have a very high shrinkage force and because of this they provide excellent consolidation when incorporated into fibrous batts, even in a minor proportion with other fibres and Without fusing the libres or heating them above their melting temperature.

According to the present invention a process for the production of fibrous, non-woven sheet materials by forming a batt of fibres and submitting said batt to a shrinkage treatment, is characterised in that the batt comprises at least 20% and less than 50% by weight of shrinkable synthetic organic fibres which are capable of shrinking by at least 10% of their original length when under a load of 0.005 gr-am per denier at C.

Preferably, the batt comprises `at least 20% and less than 50% by weight of shrinkable synthetic organic fibres which are capable of shrinking by fat least 20% of their original length when under a load of 0.01 gram per denier at 150 C.

The present invention further provides a batt wherein the .shrinkable synthetic organic libres comprising the batt have an extension at break of at least 20% iafter heat treatment under zero load at a temperature above 90 C. and at least 5 C. below the melting point of the fibres.

The first stage of consolidation may be effected by known means, such `as needle-punching by passing the batt through a needle loom. This serves to orient a proportion of fibres in the batt through the thickness of the batt in contrast to the majority of fibres in the batt which take up positions in planes parallel to the surfaces of the batt. The second stage of consolidation by shrinkage may be effected by heat treatment of the partially consolidated batt, preferably at a temperature below the melting point of the constituent fibres.

Fibres of high shrinkage force are exemplified by polypropylene fibres which are at least partially drawn, and which exhibit a shrinkage force many times, even as much as 30 times, greater than the maximum shrinkage force developed by the high shrinkage polyethylene Iterephthalate fibres previously used for batt consolidation.

The invention will be further understood from the following detailed discussion in conjunction with the drawing which is a flow sheet illustrating the steps in the The high shrinkage force measured for polypropylene fibres is shown in the following tables:

TABLE 1 Fibre shrinkage, percent linear retraction Polyethylene teroephthalate,

Isotaetie polypropyl- Temp., D C.

ene, Temp.,

Applied load, grams per denier:

Composition l were heated to various temperatures |between 80 and 152 C. As a result of this heating it was found that at temperatures above 90 C. the fibres in the batts became brittle. At temperatures below 90 C. i.e. at 80 C. no embrittlement of batts II to VIII occurred, but the batt area shrinkage waslow compared with batt I, which moreover was heated at a relatively high temperature of 150 C., without causing any embrittle-ment.

Even though the drawn polypropylene iibres in batt I and the undrawn polyethylene terephthalate in batts II to VIII have approximately the same shrinkage in the free state, the drawn polypropylene in batt I, because of its much greater shrinkage force is much more effective in consolidating the batt, i.e. the batt area shrinkage, which is the criterion of batt consolidation, is considerably greater in batt I containing the high shrinkage force polypropylene fibres. Thus it is apparent that for good batt consolidation fibres with a` high shrinkage force are required.

TABLE 2 Percent Retraetion of B Shrinkable att area Iibres in free shrinkage State percent Shrinkage,

Property of Temp., C. Batt 58% drawn polyethy terephthalate 1%/1 42% drawn polypropylene 42% undrawn polyethylene terephthalate 1%'73 d.p.f.

le e V2 d.p.f.

150 44 46 Not brittle.

Not brittle.

1 The shrinkage fibres in batt I are the dravigi polypropylene bers, and in batt .II to VIII are the undrawn polyethylene terephthalate fibres. The drawn polyethylene terephthalate fibre in batts I to VIII have a shrinkage in the free state of less than 6%.

Table l shows that lhigh shrinkage polyethylene terephthalate fibers have a much lower shrinkage force than high shrinkage polypropylene fibers. Under a load of 0.005 gnam per denier, polyethylene terephthalate ibres cease to contract altogether, whereas the polypropylene fibres still contract 10% at 130 C. and as much as 28% at 150 C.

It should |be noted that the fibres suggested hitherto were supposed toV have a high shrinkage with a minimum of retraction, which was considered to be the requirement for batt consolidation suitable for leather-like sheet materials.

Because of the high shrinkage force of our fibres made from e.g. isotactic polypropylene, the linear retraction or shrinkage of the bres can be much less than that previously employed. As a result `when preparing batts from our high shrinkage force bre, a relatively smaller retraction is suicient to give adequate batt consolidation; this is due to the greater force with which the fibres are pulling the batt together. 'Ii-able 2 illustrates the improved consolidation given with batts of libres of high shrinkage force compared with similar batts of high shrinkage fibres having a low shrinkage force. In Table 2, batt I is made from a minor proportion of high shrinkage polypropylene fibres Ipossessing a high shrinkage force whereas batts II to VIII are made from a similar proportion of high shrinkage undrawn libres of polyethylene terephthalate. Batts II to VII had the same composition and Table 3 gives the results of a number of experiments that have been carried out to compare high shrinkage undrawn polyethylene terephthalate iibres with our isotactic polypropylene fibres havin-g a high shrinkage force.

The undrawn polyethylene terephthalate libres referred to in Table 3 and in batts II to VIII of Table 2 were melt spun from a dried polymer with an I V. (intrinsic viscosity) of 0.67 to give :fibres with a birefringence of approximately 8.0 l03.

The drawn polyethylene terephthalate bres used in all the batts referred to in Table 2 were made as above but the undrawn fibres were subsequently drawn to a draw ratio of 3.2:1.

These drawn fibres have a tenacity of approximately 5.0 g.p.d. The drawn polypropylene fibres referred to in Table 3 and used in batt I of Table` 3 were melt spun from a polymer with an I.V. of 1.5 dL/gm. to give fibres with a birefringence of approximately 3 l103 and these were subsequently drawn to a draw ratio of 4.5:1. The tenacity of these drawn fibres were approximately 5.5 g.p.d.

Table 3 shows clearly that high shrinkage undrawn polyethylene terephthalate bres when treated at ter`nperatures of C. and above generally have a low breaking load and low extensions, i.e. they are brittle, whereas high shrinkage polypropylene iibres even after being subjected to temperatures as high as C. have a high extension at break and a lhigh breaking load, i.e.

they do not embrittle when subject to the temperatures employed for example in the shrinkage treatment or in shoe manufacture.

noni-woven material may often be subjected to high temperatures. For example, in the bonding of synthetic leather shoe uppers to moulded rubber soles the edges TABLE 3 Load on v Temp., nbre Percent Breaking Percent Fibre Type C. during shrinkage Load Ext. at Comments shrinkage (g.p.d.) break (and) Hlgh Shrinkage Drawn poly- 130 0.0001 22 3. 68 69. 5 Not brittle propylene. 0. 001 13. 3 4. 34 44. 5 Do. 0.002 11. 5 4.47 46. 0 Do. 0. 005 10. 3 4. 54 46. 5 Do. 0. 01 9. 5 4. 54 42. 5 D0. 150 0.0001 41 3. G8 131 Do. 0.001 36 4.15 113 Do. 0. 002 32 4, 21 96 Do. 0. 005 28 4. 3 85. 5 Do. o. 01 24 4. 44 7s. 5 Do. High shrinkage Undrawn 90 0 56 0. 56 380 Do. Polyethylene terephthalate. 0. 002 7. 5 0. 42 6 Brittle. 0. 003 35 '.0. 32 6 Do. 100 0 57 0.53 10 Do. 0. 0005 46 0. 84 6 D0. 0. 001 31 0.73 2 Do. 0. 0015 0. 59 4 D0 0. 002 0.39 4 130 0. 0005 40 0. 63 5 Do.

Embrittlement consequent upon heat treatment is most 30 of the non-woven sheet are often subjected to temperaeasily detected by measuring the extension at break of a specimen of fibres before Vand after lthe heat treatment. A brittle yarn will have an extension at break of less than say 20% compared with about 10% before heat treatment. We have found, for example, that if at least partially drawn polypropylene fibres are used to form the shrinkable portion of the batt, no embrittlement occurs in the shrinkage step of the consolidation process or in subsequent heat treatments, even if such treatments expose tures up to 150 C. If the batts contain partially drawn polyethylene terephthalate, serious embrittlement results from such treatment -but when, :for example, isotactic polypropylene fibres, having the properties hereinbefore defined, are used to prepare the batts, no embrittlement results up to a temperature of 155 C. which is about 5 C. below the melting point of isotactic polypropylene.

In the Table 4 the effect of the heat treatment of partially drawn polyethylene terephthalate is shown and the fibres to `temperatures Within about 5 C, of the melt- 40 compared with partially drawn isotactic polypropylene.

TABLE 4 Extension at break, percent Fibre Draw Shrinkage,

Ratio Temp. C. Before After After further shrinkage shrinkage treatment at Polyethylene terephthalate 2.0 80 130 150 i 18 D0 2.5 80 90 125 10 Do- 2. 0 100 130 7. 5 D0--- 2.5 100 90 10.0 Isotactic polypropylene 4. 5 150 30 105 105 ing points of the fibers. Thus the products of the present invention are very useful as non-woven sheet materials, generally and in particular in the preparation of leatherlike; non-woven products, especially where these products are subjected -to temperatures of 130 C. yor more either in use or at some processing stage of further manufacturing operations. For the production of leatherlike products various operations subsequent to the final consolidation are necessary, as for example, impregnation with an elastomeric filling agent which may subsequently be subjected to -a modifying treatment, such as coagulation and/or curing. Impregnation may be carried out bef-ore the shrinkage step, and a single treatment may serve both to shrink the fibres and to modify the resinous or elastomeric filling agent. The sheet may be provided with a finish coating -on one or both sides, and this may be smooth or may be patterned to resemble the grain of natural leather or the sheet may be treated to simulate suede. n n

In these and subsequent fabricatlon operations the From Table 4 it is clear that these two types of fibres behave very differently on heat treatment and that above C. the partially drawn polyethylene terephthalate libres are greatly embrittled. i

As already stated, the needle punching or other first stage of sonsolidation serves t-o produce further entangement of the fibresV comprising the batt. This entanglement leads to resistance to shrinkage of the fibre in the shrinking step of the consolidation process. Unless the inherent shrinkage propensity of the -shrinkable fibres is sufiicient to overcome this resistance, little consolidation (measured for example by area shrinkage) 'will result from the shrinkage treatment. We have found that for adequate `consolidation to ta-ke place the shrinkable fibres should have a high shrinkage force of at least 0.005 g./ denier for 10% shrinkage at 150 C. and preferably 0.01 g./denier at 20% shrinkage. The shrinkage force is simply measured by treating successive hanks of the filaments at the shrinkage temperature, each being loaded with successively increasing weights, and determining the 7 length retraction. From a plot of the length shrinkage against load in g./denier, the shrinkage force at any value of shrinkage may be read.

A comparison of the effectiveness (as measured by area shrinkage) in producing an adequately consolidated batt of fibres having the high shrinkage force according to the present invention `'and fibres having an inadequate shrinkage force (and consequently giving inadequate batt area shrinkage) is given in Table wherein batts IX and X comprised: Batt IX 42% by weight of partially drawn isotactic polypropylene fibres (draw ratio 4:5, shrinkage force 0.04 g. per denier for 10% shrinkage at 150 C.) and 58% drawn polyethylene terephthalate fibres.

In the process of this invention 20-50% by weight of the shrinkable synthetic libres are used together with 50-80% by weight of other fibres which shrink, if at all, by a very small amount compared with the shrinkable synthetic fibres. Such other fibres may be natural fibres or polyester, polyamide or other synthetic fibres possess- 'ing little shrinkage at the treatment temperature.

In a preferred embodiment of the invention, a batt was prepared by blending together 41% by weight of polypropylene fibres (l1/2" staple length, 3 denier per filament drawn with a draw ratio of 4.511 and exhibiting a shrinkage force of 0.04 g./ denier when shrunk by 10% at 150 C.) and 59% by 4weight of fully drawn polyethylene terephthalate fibres (l1/2 staple length, 1.5 denier per filament), carding and making the batt of three superposed layers of the carded web, the inner layer being arranged at right angles to the outer layers. First stage consolidation was then carried out by 23 passes through a needle loom such that the batt was subjected to a total of 410 punches per square centimetre. Final consolidation was carried out by treatment of the batt in an oven with high pressure steam (60 p.s.i.g., 152 C.) for five minutes, after which the batt was dried. Area shrinkage of the batt during the heat treatment was 42%. The batt prepared in this manner was used to prepare a synthetic leather sheet by first immersing in a aqueous emulsion of butadiene-acrylonitrile copolymer, squeezing to remove excess of this elastomeric filling agent, followed by drying in air at room temperature for about 12 hours when 30.6% by weight of the copolymer was left dispersed throughout the batt. The thus-bonded batt, having a thickness of 1.5 mm. at 140 C. for 5 minutes after which it was coated with a polyurethane resin which formed a surface coating 0.1 mm. thick after drying and curing. The finished sheet material had the following properties:

Density, g. per cm. 0.3 Tensile strength, kg. per sq. cm. 116.5 Elongation at break, percent 71 Bending modulus, kg. per sq. cm 63 The above process is illustrated in general terms in the drawing. If it is desired to produce a suede-like finish on the product, either the impregnated batt or the coated batt may 4be treated. As previously indicated, it is preferred to treat the impregnated batt.

Because of the use of cheap polypropylene fibres this product is cheaper to make than if made from high shrinkage polyester fibres; and in addition, because of the lower density of the polypropylene fibres which is between 0.89 and 0.92, the product of this invention is lighter in weight and easier to handle in bulk.

What we claim is:

1. A method of manufacturing a high density, nonwoven, fibrous sheet material, comprising forming a batt of fibres of which at least 20% and less than 50% by weight are partially drawn polypropylene fibres capable of shrinking by at least 20% of their original length when under a load of at least 0.01 gram per denier at 150 C. and the remainder of the fibres having low shrinkability relative to said polypropylene fibres, initially consolidating the batt by needlepunching, and finally consolidating the batt by subjecting it to a heat shrinkage treatment.

2. A process according to claim 1 wherein the shrinkable polypropylene fibres comprising the batt have an extension at break of at least 20%, after heat treatment under zero load at a temperature above C. and at least 5 C. below the melting point of the fibres.

3. A process according to claim 1, comprising the further step of impregnating the batt with a resinous filling agent.

4. A process according to claim 3, wherein the batt is impregnated with the resinous filling agent before it is submitted to the shrinkage treatment.

5. A fibrous, non-woven sheet material produced by a process according to claim 1.

6. A process according to claim 1 comprising the further step of impregnating the batt with an elastomeric filling agent.

,7. A process according to claim 6 wherein the batt is impregnated with the elastomeric filling agent before it is submitted to the shrinkage treatment.

8. A process according to claim 1 comprising the further step of applying a finish coating on at least one side of the batt.

9. A non-woven sheet material produced by the process of claim 8.

10. A process according to claim 1 comprising the step of treating the sheet material to resemble suede.

11. A non-woven sheet material produced by the process of claim 10.

References Cited by the Examiner UNITED STATES PATENTS 2,978,785 4/1961 Wenzell et al. 117-140 3,067,482 12/1962 HolloWell 117-140 3,067,483 12/1962 Hollowell 117--140 3,188,233 6/1965 Powers et al 117-140 3,199,167 10/1965 Charlton et al. 117-140 FOREIGN PATENTS 909,213 10/ 1962 Great Britain.

MURRAY KATZ, Primary Examiner.

Claims (2)

1. A METHOD OF MANUFACTURING A HIGH DENSITY, NONWOVEN, FIBROUS SHEET MATERIAL, COMPRISING FORMING A BATT OF FIBRES OF WHICH AT LEAST 20% AND LESS THAN 50% BY WEIGHT ARE PARTIALLY DRAWN POLYPROPYLENE FIBRES CAPABLE OF SHRINKING BY AT LEAST 20% OF THEIR ORIGINAL LENGTH WHEN UNDER A LOAD OF AT LEAST 0.01 GRAM PER DENIER AT 150*C. AND THE REMAINDER OF THE FIBRES HAVING LOW SHRINKABILITY RELATIVE TO SAID POLYPROPYLENE FIBRES, INI-

10. A PROCESS ACCORDING TO CLAIM 1 COMPRISING THE STEP OF TREATING THE SHEET MATERIAL TO RESEMBLE SUEDE.

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