US2832713A - Non-woven sheet material - Google Patents

Description

' April 29, 1958 w. A. RAGAN 2,832,713

NON-WOVEN SHEET MATERIAL Filed June 21, 1955 F G l Layers of non-woven mats of nylon fibers with atop STAGE A l4 AGE A layer of undrawn crystallizable Layup of the componv l, l4 fibers ents of one embodi i (\v/ I l rWMWl M t, 'r'

- I y 1 l STEP l. lmrnerse in solution of STEP I. Hot press and cool under binder l pressure. STAGE A STAGE B Uncompacted,

- Compacted, substantially impregnated, water vaporimpermenomwoven IO able sheet with (K fibrous mat.

"5822 g gz a 'gfi er STEP 2. Hot press and cool under STEP 3 (Optional) y pressure.

Apply additional binder polymer to upper and lower faces of sheet and hot press.

a; compacted sheet with additional binder polymer throughout sheet.

STEP 4 1 Stretch sheet in one or both directions to form contiguous channels. STAGE D Water vapor permeable sheet resistant to fuzzing.

. INVENTOR WILLIAM ANDREW RAGAN ATTORNEY United States Patent NON-WOVEN SHEET MATERIAL William Andrew Ragan, Williamsport, Ohio, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application June 21, 1955, Serial No. 516,954

2 Claims. (Cl. 154-46) This invention relates to leather replacement materials, and more particularly to non-woven sheet materials wherein, matted, structural fibers are bound together by an extensible, polymeric binder.

Leather replacement materials have had a long history dating from the days of pyroxylin-coated, fibrous materials to the vinyl-coated, woven fabrics available today. Recently, leather replacement materials have been developed which are not only cheaper than genuine leather and prior art synthetic leathers but can be tailored to various end uses by controlling their processes of manufacture.

These materials comprise matted, structural fibers bound together by a polymeric binder. They are generally prepared in three steps:

(1) A non-woven mat of interlaced fibers is formed from staple fibers by suitable means such as techniques used in Wool carding or paper making.

(2) The mat is impregnated with a thermoplastic binder polymer so that each individual fiber is completely surrounded by the binder.

(3) The impregnated mat is pressed, usually at an elevated temperature, to form a consolidated or integrated sheet structure.

The properties of the sheet material may be controlled by the particular binder and fibers used, the length and denier of the fibers and the location of special fibers in the original non-woven mat. Permeability to water vapor may be controlled by the degree of consolidation in the third step or by adding a fourth step which involves a chemical or physical treatment of the consolidated structure.

These leather replacement materials, despite improving on prior art materials in terms of properties and cost, suffer from an important shortcoming. They are not scuff-proof. An unsightly fuzz resulting from fibers being pulled from the structure by abrading or scufiing tends to form on the surface of the sheet material. Since there are many applications such as shoe uppers, gloves, etc., where this condition cannot be tolerated, these materials have failed to gain wide public acceptance.

It is an object of this invention to provide a new sheet material of the type in which matted, structural fibers are held together by an extensible, polymeric binder. Another object is to provide such a material having much greater scuff resistance than possessed by heretofore known sheet materials of this type. A further object is to provide a new sheet material having high scuff resistance as Well as softness, high tear strength, water repellency and, if desired, vapor-permeability. A still further object is to provide a process for preparing such materials. Other objects will appear hereinafter.

The above objects are accomplished by using undrawn crystallized thermoplastic fibers in the surface layer of a sheet material composed of a non-woven mat of structural fibers and an extensible polymeric binder. Preferably, the structure comprises a sheet material of 30% to 30% non-woven matted structural fibers and 70% to 2 20% of an extensible polymeric binder binding the fibers together, the sheet having a surface layer of undrawn crystallized fibers, and in the case of the permeable sheet, the sheet also having channels substantially contiguous with a major portion of the fibers throughout the thickness of the sheet.

The process for preparing the sheet material comprises plying a plurality of non-woven mats of fibers, a nonwoven mat of undrawn crystallized or undrawn crystallizable fibers being in the surface layer and non-woven mats of drawn structural fibers being in the sub-layers; impregnating the mats with an extensible polymeric binder; pressing at an elevated temperature the impregnated mats to form a compacted structure and, in the case of the crystallizable fibers, to crystallize the fibers in the surface layer of the compacted structure; and, to form a scuff-resistant, vapor-permeable sheet material, breaking a substantial portion of the fibers away from the binder to form channels substantially contiguous with a major portion of the fibers.

For some purposes it may be desirable to make both surfaces of the sheet material scuff resistant. It is understood that the sheet material of this invention can have undrawn crystallized fibers in both surface layers.

crystallized fibers as used in this specification refer to polymeric fibers that are obtainable in crystalline form upon quenching freshly formed molten fibers and polymeric fibers that are converted from amorphous form to crystalline form upon being heated to temperatures above the second order transition temperature. In undrawn condition, such fibers are brittle and tend to break off under normal abrading action, e. g., the flexing action received by shoe-upper leather during wear. Examples of useful polymeric fibers obtainable in the crystalline state upon quenching the molten fibers include polymerized hydroxyacetic acid and polymerized vinylidene chloride. Examples of useful polymeric fibers that can be converted to crystalline form by heating above their second order transition temperatures include polyethylene terephthalate and ethylene terephthalate-ethylene isophthalate copolymers.

By compolymers of ethylene terephthalate and ethylene isophthalate is meant the reaction products formed by reacting together a glycol of the series HO(CH ),,OH, where n is an integer from 2-10 inclusive, with from 5% to 35% by weight based on the total weight of acid components, of an acid component from the group consisting of isophthalic acid and the lower alkyl esters of isophthalic acid, and from 95% to 65% by weight of an acid component from the group consisting of terephthalic acid and the lower alkyl esters of terephthalic acid.

Second order transition temperature is defined in U. S. Patent 2,578,899 to Pace as the temperature at which a discontinuity occurs in the curve of a first derivative thermodynamic quantity plotted versus temperature. it is correlated with the yield temperature and the polymer fluidity and can be observed from a plot of density, specific volume, specific heat, sonic modulus or index of refraction versus temperature.

Besides being crystallized, the fibers must be undrawn or unoriented. Stretching or rolling or similar methods for molecularly orienting the fibers increases their tensile strength, modulus, flex strength and impact strength. Abrading action would merely pull such fibers from the surface of the sheet instead of breaking them olf cleanly. Such fibers, which would accumulate upon the surface as a fuzz, would be totally unacceptable for use in the surface stratum.

The term contiguous channels as applied to the vaporpermeable sheet material, refers to channels or pores adjacent to portions of fibers throughout the structure,

The channels are not necessarily completely annular. In some cases, the channel may spiral around part of the length of the fiber or may take the form of a hairline crack substantially parallel to or immediately adjacent to the fiber. They are formed by breaking away fibers from the binder, particularly at points where fibers cross or otherwise contacteach other.

Three processes for forming contiguous channels are described in more detail in three copending applications. In U. S. Serial No. 318,732, filed November 4, 1952, by V. L. Simril, now U. S. Patent 2,757,100, a process is described wherein non-extensible structural fibers are used with a relatively extensible binder. Stretching the structure in one or two directions results in contiguous channels. in U. S. Serial No. 325,689,. filed December 12, 1952, by J. C. Richards, now aban cloned, contiguous channels are formed by first swelling the fibers followed by deswelling (or shrinking) to break the fibers away from the binder. In U. S. Serial No. 430,550 filed ltiay 18, 1954,. by H. R. Mighton, now U. S. Patent 2,802,767, the previous alternativemethods are combined into a single method for forming contiguous channels.

Figure l is a flow diagram of a representative process for preparing the preferred sheet material.

Figure 2 is an enlarged cross section of the final sheet material.

Stage A in Figure 1 represents a layup or composite of the essential components of one embodiment of the sheet material. About four layers of non-woven mats of drawn or oriented nylon (polyhexamethylene adiparnide) fibers 10 are placed in crossgrain fashion, one over the other so that the grain of each mat is substantially perpendicular to the grain of adjacent mats. A top layer of a non-woven mat of undrawn polyethylene terephthalate fibers 14 is placed over the layers of nylon fibers. Non-woven mats can be prepared by the techniques known to paper making or wool carding or they may be prepared by deposition from an air stream on a screen. Homogeneous films or sheets of cast polyethylene-polyisobutylene (5050 by weight) 12, the binder, are placed between each layer of mats.

In the first step, the composite as illustrated in stage A is placed between two layers of non-heat-sealing cellophane (not shown) and hot pressed at a temperature suflicient to cause the binder polymer 12 to flow and to crystallize the undrawn polyethylene terephthalate fibers 14 in the surface layer but not sufiicient to fuse or transpose the nylon fibers 10 to any appreciable extent. The resulting compacted structure, as represented by stage B, is a water vapor-impermeable binder polymer sheet reinforced with nylon structural fibers having undrawn crystallized polyethylene terephthalate fibers in the surface layer.

Stage B may also be reached by the alternative procedure shown in stages A and A Stage A represents layers of non-woven mats of oriented nylon fibers l plied in cross-grain fashion with a top layer of undrawn polyethylene terephthalate fibers as previously described. In the first step the mats are impregnated with the binder polymer by immersing them in a solution of polyethylene-polyisobutylene in a volatile solvent such as toluene, and solidifying the polyethylene-polyisobntylene binder. Alternatively, the mats of stage A; may be conducted through a dispersion of polyethylenepolyisobutylene in a non-solvent medium. Stage A; represents the uncornpacted, impregnated, non-woven fibrous mat. in the next step, the second step, the com posite undergoes the hot pressing treatment previously described to form stage B, the compacted structure of a binder polymer sheet reinforced with nylon structural fibers and having undrawn crystallized polyethylene terephthalate fibers in the surface layer.

The next step, step 3, is an optional step and involves applying additional binder polymer, polyethylene-polyisobutyleue, to the upper and lower faces of the sheet followed by hot pressing. This step is an effort to distribute binder around all the fibers in the sheet by filling any voids that might exist after the second step. In effect, this step increases the binder/fiber ratio. The additional binder polymer may be applied by spraying or immersion or as thin sheets followed by pressing. The result shown in stage C is substantially the same sheet as that of stage B with additional binder polymer throughout the sheet. This sheet may be used in applications where water vapor-permeability is not desired. Such uses include: draperies, shower curtains, book bindings, brief cases, luggage, table covers, etc.

However, to form synthetic leathers permeable to water vapor, the next step, step 4, is applied to the sheet of stage C. This step broadly involves breaking a substantial portion of the nylon and polyethylene terephthalate fibers away from the binder to form contiguous channels along a major portion of a substantial number of the fibers. Specifically, the sheet shown in stage C is stretched from to 50% in one or two directions. The fibers, being less extensible compared to the relatively extensible binder polymer, break away from the binder polymer leaving the contiguous channels. As an alternative procedure the sheet may be dipped in water at a temperature above the softening temperature of the binder to swell the fibers. By then drying the sheet at a temperature below the softening temperature of the binder, the fibers shrink and tend to break away from the binder leaving the contiguous channels. These two alternative methods for forming contiguous channels may also be combined in a single method for the most effective results, i. e., stretching, followed by swellingdeswelling. In any case the resulting sheet shown in stage D, or the enlarged cross section shown in Figure 2, is formed. The sheet is composed of non-woven structural fibers 10 throughout a polymeric binder 12 with undrawn crystallized polyethylene 'terephthalate fibers 14 in the surface of the sheet. The-interconnecting channels 16 contiguous with the fibers provide water vapor-permeability in the sheet material yet do not destroy its liquid repellency.

The leather replacement sheets may range in thickness from mils to mils with the surface stratum varying anywhere from 2% to 33% of the total thickness of: the sheet. The outstanding result achieved in the pre pared sheet is the failure of the sheet to produce surface fuzz after 100,000 scuffing strokes compared to prior art products without the described surface layer which produce fuzz after about 25 scufling strokes.

Other specific embodiments of the invention are illustrated in the examples which follow. In these examples all percentages are by weight unless otherwise stated. The following tests were used to determine the properties of the products:

(1)-Eccentric wheel scuff tesr.Scutf resistance was determined in a test instrument composed of two wheels. One was a non-rotatable wheel, 6 inches in diameter and 1 inch wide. The second wheel was a 4 inch diameter, 1 inch thick felt disk mounted so as to rotate about an offcenter axis. The smaller wheel was so arranged that at its maximum displacement, it abraded strongly against the larger non-rotatable wheel. The sample to be tested was placed on the periphery of the non-rotatable wheel. A single rotation of the off-center wheel was referred to as a scuff.

(2)Leather permeability measuremerzL-This test was carried out substantially as described by Kanagy and Vickers in Journal of American Leather Chemists Association 45, 211-242 (April 19, 1950). Briefly, a 3 inch diameter crystallizing dish was filled with 12 mesh calcium chloride and covered with a membrane of the sub stance under test. The dish was inverted and suspended in an atmosphere of relative humidity and a temperature of 23 C. and weighed at intervals. The increase in weight was a measure of the moisture vaporpermeability of the substance under test.

Example I 2 /2 inches long and 3 denier/filament, and reinforced with alternate layers of cast polyethylene-polyisobutylene (50-50 by weight) film.

The cast film was prepared by dissolving the polyisobutylene in-hot toluene, adding the polyethylene, and casting the hot dope in the form of a film onto a piece of plate glass. Webs of carded nylon fibers were pressed lightly into the cast dope before it began to skin over. These webs acted as backing sheets for the film. Alternate layers of webs and film were then cross-lapped on the thus formed bottom layer to form a sheet consisting of layers of nylon fibrous webs and layers of the polyethylenepolyisobutylene binder with a top layer of a mat of undrawn polyethylene terephthalate fibers blended with cellulose acetate fibers. The weight of the sheet of fiber and binder totaled 22.7 grams. The weight of the nylon Web totaled 11.47 grams. The binder thus comprised 23% by weight of the structure.

The composite sheet was then cured under a pressure of 500 lbs. per sq. inch in a Carver press for 3 minutes at 140 C. The pressure was maintained until the temperature fell to 90 C. The compacted, substantially impermeable sheet was then placed in boiling water to allow the liquid-swellable nylon structural fibers to swell. The sheet was then withdrawn from the water and dried in air. The pore-forming cellulose acetate fibers were then extracted by placing the composite sheet in a cold acetone bath.

The sheet was air dried leaving a water vapor-permeable non-woven sheet composed of (1) a bottom stratum having contiguous channels running therethrough by reason of the swell-deswell operation wherein the nylon fibers were broken away from the binder, and (2) a top stratum having uniformly distributed undrawn crystallized polyethylene terephthalate fibers, embrittled and weakened by the successive steps of hot pressing and extraction with solvent. Interspersed throughout the top stratum were pores formed by the removal of the soluble cellulose acetate fibers.

The surface of the sheet was subjected to a scufiing action on a felt wheel abrading apparatus, as described previously, in order to remove any remaining surface fuzz. A smooth-surfaced composite sheet having excellent resistance to further fuzzing or scufiing was obtained after 3,000 scuffs. Further scufiing on the felt wheel abrading apparatus up to 100,000 scufis failed to produce further surface fuzz. The leather permeability value (LPV) of the finished sheet was above 3,000 grams/ 100 square meters/hr.

Example 11 Undrawn polyvinylidene chloride fibers, 1%. inches long and 3 denier/ filament, were carded to form a non-woven mat or web according to the wool carding technique. This web was placed over 4 layers of carded webs of crimped staple fibers of nylon (polyhexamethylene adipamide), 2 /2 inches long and 3 denier/filament. The 5 layers of mats were plied in cross-grain fashion to form a composite structure. The composite was placed between screens and immersed in an aqueous solution of wetting agents, the solution comprising 2% octyl sodium sulfosuccinate and 2% of a sodium salt of an alkyl benzene sulfonate. The structure was squeezed through a tworoll wringer and permitted to dry.

to the structure.

6 The composite was then impregnated with 60% by weight of the binder polymer by immersing in an aqueous dispersion of plasticized vinyl chloride polymer. The dispersion contained the following ingredients:

500 parts of a dispersion containing about 50% vinyl chloride polymer 300 parts of a dispersion containing about 50% dioctyl pthalate 50 parts of a dispersion containing about 50% black pigment 275 parts of water The total percent solids was, therefore, 34.5% and the percent plasticizer was 35.2% of the total solids. About 0.3% of sodium alginate was used in the dispersion to prevent loss of polymer during subsequent dipping for gelling the polymer.

After immersion, the composite structure was allowed to drain and again was squeezed through the two-roll wringer. The binder polymer was then gelled by dipping the impregnated composite structure in a solution containing 50% acetic acid in methanol. Acid and salt were removed by washing with water and excess Water was pressed out of the structure.

The structure was dried at a temperature below C.; placed between sheets of cellophane and Bristol board; and pressed at 500 pounds per square inch and at a temperature of about 150 C.

The resulting compacted structure was then stretched about 25% in two directions to impart vapor-permeability The leather permeability value for the structure was well above 3,000 grams/ square meters/hour. The surface of the sheet was subjected to a scuffing action on a felt wheel apparatus in order to remove any remaining surface fuzz. composite sheet having excellent resistance to further scuffing or fuzzing was obtained after 3,000 sculfs. Further scufling on the felt wheel abrading apparatus failed to produce further surface fuzz.

Example III A composite structure of 4 layers of mats was pre pared from nylon fibers substantially in the manner described for Example I. Polyhyd-roxyacetic acid fibers, prepared in accordance with U. S. Patent 2,585,427 to Beck, 1 /2 inches long and 3 denier/filament, were carded to form a web and placed on top of the composite structure of nylon fibers. The structure was impregnated with about 40% of its weight of a polymericbinder by immersing in an aqueous dispersion of plasticized neoprene. The dispersion contained the following ingredients:

500 parts of a dispersion containing about 50% neoprene 300 parts of a dispersion containing about 50% polyethylene glycol di-Z-ethyl hexoate 20 parts of a dispersion containing about 50% zinc oxide 12 parts of a dispersion containing a polyoxyethylated fatty alcohol as a stabilizer 32 parts of a dispersion containing 50% of a curing agent for neoprene 50 parts of a dispersion containing 50% black pigment 385 parts of water The structure was dried at a temperature below 95 C.

to prevent the neoprene binder from curing. Thereafter,

the composite structure was placed between sheets of cellophane and Bristol board and, pressed at 1,000 to A smooth-surfaced 1,500 pounds per square inch and a temperature of about 150 C. and held for sufiicient time to cure the neoprene binder. The consolidated fiber/binderstructure was permitted to cool under pressure.

The compacted structure was then stretched from to in two directions. The resulting leather permeability value for the structure was well above 2,000 grams/ 100 square meters/hour while the fuzz characteristics were substantially as obtained in. Examples I and II.

Example IV Crimped staple fibers of nylon, 2% inches long and 3 denier/filament, and rayon, 1 /2 inches long and 1.5 denier/filament (SO/ by weight), were carded into four non-woven mats or Webs in a manner previously described. Undrawn fibers, 2 inches long and 6.75 denier/filament, of a copolymer of ethylene isophthalate and ethylene terephthalate, prepared in accordance with the process defined in U. S. application Serial No. 486,290,

filed February 4, 1955, to Berr and Izard, were cut in half and carded into a non-woven mat or web. This mat was placed on top of the four nylon-rayon mats. The structure was then impregnated with about neoprene and formed into a composite structure as described in Example III. The composite structure was abraded on the felt wheel abrading apparatus to remove any remaining surface fuzz. This was accomplished after 2,750 scuifs. Further scufiing on the felt wheel apparatus failed to produce any further surface fuzzing after 100,000 scuffs.

It is understood that the preceding examples are merely illustrative of specific preferred embodiments. The invention broadly resides in using undrawn crystallized fibers in the surface layer of a sheet material composed of matted structural fibers bound together by an extensible p-olymetric binder. The same crystallizable fibers may be used throughout the structure with undrawn fibers being limited to the surface layer. An alternative structure is suggested by the examples wherein undrawn crystallized fibers are used for the surface layer and different structural fibers are used throughout the remaining portion of the structure. This latter structure is preferred. Mixtures or blends of fibers may also be used for certain puproses. Thus, when a swel-ling-deswelling treatment is used for imparting permeability, it may be advantageous to use rayon blended with nylon as the structural fibers while retaining undrawn polyethylene terephthalate fibers in the surface layer. Permeability is more easily attained since rayon reacts to a milder swelling-deswelling treatrment than nylon. It also may be advantageous to incorporate pore-forming fibers in the structure to enhance permeability. Thus, cellulose acetate fibers which are soluble in acetone may be distributed throughout the structure.

The preferred fibers for use as undrawn, crystallized fibers include, as mentioned previously, two varieties: (1) those undrawn fibers that are crystalline as formed upon quenching from the molten state and (2) those undrawn fibers that can be converted from amorphous form to crystalline form upon being heated at a temperature above the second order transition temperature.

The measurement of second order transition temperature may be accomplished by observing the rate of change of the specific heat of the polymer with the temperature. If a polymer is heated at a constant rate beginning at a temperature below its second order transition temperature, the temperature will increase at a constant rate until the transition temperature is reached. At this point a break in the curve will occur. The determination may be made by placing the insoluble polymer with either normal heptane or toluene at a temperature of about 6 C. in calorimeter. A constant rate of heating is applied by using an electrical heater connected to a source of voltage which may be varied as desired. The powdered polymer is kept suspended by a stirrer turning at constant speed. The temperature is measured by means of a copper-constantan thermocouple with an ice water reference. Current is applied :so that the temperature will rise about 1 C. per minute. When the temperature rises to at least 20 C. below the transition temperature, the lapse of time is read using a stop watch to the nearest th of a minute for every degree rise in temperature. The inflection point, as read from the data is the second order transition temperature.

For undrawn polyethylene terephthalate, the second order transition temperature is about 69 C. Since hot pressing in the present process is conducted at a temperature from C. to 200 C. under pressure of 50 p. s. i. to 2,000 p. s. i., the temperature is more than enough to crystallize the undrawn polyethylene tereph tbalate fibers making them brittle.

The denier and length of the staple fibers are not critical to the invention. The length mayvary from .01 inch up to 8 inches or greater and the denier may vary from 1 to 16 denier per filament. The longer fibers, 0.5 to 4 inches long, are preferred since they provide improved tensile strength and improved extensibility in the finished sheet material. The heavier deniers are also preferred since they make the sheet material tougher and more durable. The denier may also afiect the efficiency of the treatment for imparting permeability. In general, as denier increases, the rate of penetration of any liquid used for treatment will decrease.

Crystallizing undrawn polymeric materials involves changing their molecular structure so that the material becomes drastically embrittled. The tensile strength of the resulting fibers is no more than 75%, usually 50% or less of the strength of the original fibers. The desired depth of the surface layer or layers, which is the depth of the undrawn crystallized fibers may vary from 2% to 33% of the total thickness of the sheet and will depend on the particular end use. For instance, materials used for shoe uppers require a deeper layer than those used as drapery materials because of the harsher scutfing treatment received by shoe uppers in use. In all cases, the depth should be kept to the minimum necessary for the particular use. Otherwise, the structure may be weakened and its leather permeability value reduced. The depth can be determined by experiment and will vary with the fibers used, the binder used, the degree of consolidation achieved during pressing and the time, temperature and pressure of the pressing treatment.

For sufiicient fiber reinforcement in the final sheet material, it has been found necessary that the structure contain from about 30% to 30% structural fibers.

The heating treatment to crystallize undrawn, crystallizable fibers may be accomplished in any suitable manner. 'The simplest method is to use the hot-pressing treatment, which is essential to this process to provide a water vapor-impermeable sheet, to crystallize the fibers. Of course, the surface layer may be heated prior to presing to crystallize the undrawn fibers. This latter case would then resemble the case where the fibers can only be obtained as undrawn crystallized fibers and the process begins with the hot-pressing treatment.

The embrittled fibers may be chipped from the surface layers at any time following the formation of the compacted structure. In the case of the vaporpermeable sheet this is most conveniently accomplished by abrading the sheet after forming the contiguous channels.

The critical factor in selecting the polymeric binder is that it should be chemically different from the structural fibers. A convenient rule is that the binder be incompatible in the melt with the structural fibers. Otherwise, the structures are usually deficient in drape, hand, flex life and tear strength. Furthermore, the

merizable ethylenic unsaturation, groups wherein the terminal carbon is a methylene carbinder should flow at a temperature at least 50 below the deformation temperature of the structural fiber and, as a film, exhibit a tensile strength of at least 500 pounds/square inch, an elongation of at least 100% and a tensile modulus no greater than 25,000 pounds/ square inch. A binder fulfilling these requirements may be described as tough, pliable and initially thermoplastic.

A number of thermoplastic materials useful as binder materials are classified as elastomers and are disclosed by H. L. Fisher in Industrial and Engineering Chemistry, August 1939, page 942. In the most preferred sheet materials of this invention, the polymeric binder will be a linear addition polymer. Because of their availability and particularly their low cost and desirable polymer properties, the most outstanding are the vinylidene polymers and copolymers including both the monoene and diene types. This class of polymers is characterized by having in each polymerizable monomer as the only polytermin-al ethylenic dene polymers, e. g., chlorinated polyethylene, and chlorinated polyvinyl chloride; the various vinylidene polymers wherein one or both of the indicated free valences of the 2-carbon of the vinylidene group are bonded directly to carboxyl groups or groups hydrolyzable to carboxyl groups either directly to the acyl carbon or to the oxy oxygen thereof, such as polymers of various vinylidene esters, including vinyl acetate and ethylidene diacetate; vinylidene carboxylic acids and their derivatives such as acrylic acid, acrylonitrile, and methacrylamide.

Also included in this more preferred group are the various copolymers of such vinylidene monomers, including specifically the various monoene and diene copolymers of this class such as 2,3-dichlorobutadiene-1,3/2- chlorobutadiene-l,3 copolymers; the various monoene/ vinylidene copolymers such as the commercially important vinyl and vinylidene chloride copolymers, e. g., vinyl chloride/ vinyl acetate, vinyl chloride/vinylidene chloride, and vinyl chloride/vinyl acetate/acrylonitrile copolymers;

the various vinylidene hydrocarbon negatively substituted vinylidene copolymers, e. g., ethylene/vinyl acetate and the hydrolyzed products therefrom; ethylene/vinyl chloride, and butadiene/acrylonitrile copolymers.

In the case of those binder components containing in combined form appreciable proportions of diene monomers, particularly the vinylidene diene monomers, it is frequently desirable to have present in the solution, dispersion, or bulk treating material, whichever is used, suitable amounts of chemical agents for effecting under controlled conditions, after the fiber has been impregnated with the binder and the whole mat suitably compacted, the cross-linking of the diene copolymer component. The agents for effecting such controllable cross-linking are well known in the rubber art. In the case of the diene hydrocarbon polymers and copolymers, the presence of mercaptans and/or sulfur in the diene polymer composition provides cross-linking by disulfide formation. In the case of negatively substituted diene polymers and copolymers such as the 2-chlorobutadiene-l,3 (chloroprene) polymers, the presence of metallic oxides such as zinc or magnesium oxides provides cross-linking by removal of halogen.

Various polyesters containing terephthalic acid or derivatives thereof as essential components are also useful as binder polymers, these including polyethylene terephthalate and copolyesters made from ethylene glycol, terephthalic acid and sebacic'acid of the general type described and claimed in United States Patents Nos.

tainable by reacting (a) one'or more polyhydric alcohols with (b) one or more polycarboxylic acids (either in the presence or absence of oneor more monocarboxylic acids). Specified products of this type are described and claimed in United States Patent No. 2,333,639 to R. E. Christ and W. E. Hanford. Other types of elastomeric polymers which may be used as binders include reaction products of polyalkylene ether glycols and organic diisocyanates.

In many instances, it is desirable to. have appreciable proportions of plasticizers for the binder polymers in the binder composition. This is particularly important in the case of the vinylidene resins. Plasticizers provide high pliability and desirable drape in products that might otherwise be too stifi. This is particularly true of the higher molecular weight, negatively substituted vinylidene polymers and copolymers, such as the vinyl chloride/ vinylidene chloride and vinyl chloride/vinyl acetate copolymers. Suitable examples of plasticizers include the higher molecular weight monoor dicarboxylic acid/alcohol or/polyolesters such as glycerol mono-oleate, glycerol sebacate, dioctyl phthalate, and ethylene octanoate; or the lower molecular weight polyesters and polyesters such as the polyalkylene oxides and their esters, e. g., polyethylene oxide, methoxypolyethylene glycol; and the lower molecular weight condensation polyesters such as polyethyleneglycol adipate.

The binder polymer employed in the surface stratum may be different from the binder in the internal strata of the sheet. This might be desirable to obtain a flexible structure with a hard top layer. To obtain an integral structure, the binder polymer in the top layer must be compatible with and chemically similar to the binder employed in the lower layers of the composite. A typical lay-up might consist of alternate layers of films of polyisobutylene and non-woven fibrous mats with polyethylene in the top layer.

Another method of obtaining a flexible structure with a hard top stratum would be to use the same binder polymer throughout but with different contents of plasticizer in the various strata. For example, the top stratum may be composed of a binder Without plasticizer and the lower strata may contain varying amounts of a plasticizer. Such a structure will have a relatively hard surface stratum, but with high flexibility due to the plasticized internal strata.

Color can be imparted to the sheet material of this invention by incorporating dyes or pigments in the polymeric hinder or, preferably, by dyeing the structural fibers prior to forming the initial composite with the binder. Another method is to apply a special color coat, about 2 to 4 mils thick, which contains a pigment, a polymeric binder and a plasticizer. The binder may be difierent from that used in the basic sheet material. A typical color coating may comprise 100 parts of polymeric binder, 70 parts of plasticizer and 40 parts of the pigment. When using a color coat, it may also be desirable to apply a depth coat about 0.5 mil thick. The depth coat usually contains binder and plasticizer wherein the plasticizer content is lower than in the color coat and in the remaining structure. A top coating called a fgloss coat, about .Olto 2 mils thick, may he applied over the color and depth coats. This coating is normally transparent, :a typical formulation comprising 1.0.0 parts of tbinder -polymer, .33 parts of polymethylrnethacrylate, .6.6 parts of silica and 1.4 'parts of .stearic acid. These .three coats may be made permeable if desired by suitable means heretofore known in the art.

The advantage of .the product .lies in the high scuff resistance attainable without sacrificing tear strength, tensile strength, -flex life or extensibility. The process is relatively easy .to control and can be modified to tailor the product for particular end uses. The process is also easily adapted for continuous operation. Most important, the product is economical .to produce and the process requires relatively little time.

The product, Manor-permeable orimpermeable, can be substituted in substantially all leather applications: the impermeable material in handbags, shoe soles, book bindings, luggage, brief cases, table: covers, ,etc. .the vapor-permeable material in gloves, shoe uppers etc.

As many different embodiments of .this invention may be made without departing from the spirit and .scope thereof, it is understood that the invention is not limited except as defined in the appended claims.

The invention claimed is:

1. A Water vapor permeable sheet material comprisinga plurality, of layers of non-woven mats of polymeric fibers, the fibers in the mats and the mats being bound together with an extensible polymeric hinder, the fibers in the surface layer only being undrawnand crystallized, said undrawn and crystallized fibers having up to 75% of their original tensile strength prior to crystallization, said surface layer being 2% to 33% of the total thickness of said sheet material, the fibers in other than the surface layer of said sheet material :being drawn, and said sheet material having channels substantially .contiguous with a major portion of the fibers throughout the thickness of said sheet material.

2. The product of claim 1 in which the :undrawn and crystallized fibers in the surface layer are selected from the group consisting of polyethylene terephthalate, co-

' polymer of ethylene terephthalate and .ethylene' isoph thalate, polyvinylidene chloride, and polymerized hydroxyacetic acid.

References Cited in the file of this patent UNlTED STATES "PATENTS 1,520,510 Respess Dec. ,23, 1924 2,306,781 Francis Dec. 29, 1.942 2,357,392 Francis Sept. 5, .1944 2,373,033 Kopplin Apr. 3, 1945 2,673,823 Biefeld et a1. Mar. 30, 1954 2,676,128 Piccard Apr. 20, .1954

Claims (1)

1. A WATER VAPOR PERMEABLE SHEET MATERIAL COMPRISING A PLURALITY OF LAYERS OF NON-WOVEN MATS OF POLYMERIC FIBERS, THE FIBERS IN THE MATS AND THE MATS BEING BOUND TOGETHER WITH AN EXTENSIBLE POLYMERIC BINDER, THE FIBERS IN THE SURFACE LAYER ONLY BEING UNDRAWN AND CRYSTALLIZED, SAID UNDRAWN AND CRYSTALLIZED FIBERS HAVING UP TO 75% OF THEIR ORIGINAL TENSILE STRENGTH PRIOR TO CRYSTALLIZATION, SAID SURFACE LAYER BEING 2% TO 33% OF THE TOTAL THICKNESS OF SAID SHEET MATERIAL, THE FIBERS IN OTHER THAN THE SURFACE LAYER OF SAID SHEET MATERIAL BEING DRAWN, AND SAID SHEET MATERIAL HAVING CHANNELS SUBSTANTIALLY CONTIGUOUS WITH A MAJOR PORTION OF THE FIBERS THROUGHOUT THE THICKNESS OF SAID SHEET MATERIAL.

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