US3228786A - Process for impregnating fibrous sheets - Google Patents

Description

PROCESS FOR IMPREGNATING FIBROUS SHEETS Filed July 13, 1962 NEEDLE PUNCHED NON-WOVEN WEB 0F SHRIIIIIABLE FIBERS IIIPIIEGNATING WITH AQUEOUS DISPERSION 0F POLYMER IIIPREGNATED WEB COAGULATING INPREGIIATED WEB WITH COAGULATED IMPREGIIAIIT HEATIIIB SIIRUNIIEN IMPREGNATED WEB INVENTORS EMERSON B. FITZGERALD FRANCIS E. JENKINS BY 5 m 8 GM ATTORNEY United States Patent OfiFice Patented Jan. 11, 1966 3,228,786 PRUCES FOR IMPREGNATING FIBRGUS SHEETS Emerson l3. FitzGerald and Francis E. Jenkins, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed July 13, W62, Ser. No. 209,791 4 Claims. (Cl. 117-62) This invention relates to a method of impregnating shrinkable fibrous webs.

It has been proposed to make shoe upper material by preparing a non-woven web of heat shrinkable fibers, such as, 'e.g., polyethylene terephthalate fibers, needle looming the web, shrinking the needled web, impregnating the nonwoven needled and shrunken web, finally applying a microporous surface coating.

One of the problems encountered during the lasting operation when forming shoes from material prepared as described above, is the development of roughness in those areas which requires some stretching over the last such as in the toe and quarter areas of the shoe. This roughening has been associated with the pattern that results from the needling of the non-woven web prior to impregnation.

It is an object of this invention to provide a process of preparing shoe upper material which involves impregnating and coating a non-woven web having a pattern on its surface prior to impregnating and coating which is obscured by the impregnant and surface coating, and is not visually apparent when the impregnated and coated web is stretched as in the case of toe and quarter lasting during shoe making.

The objective of this invention is accomplished by impregnating a heat shrinkable non-woven web capable of shrinking 2080% of its planar area and having a pattern on its surface with an aqueous dispersion of a polymeric material, coagulating the dispersion in situ, heat shrinking the impregnated web 2070% of its planar area before the impregnant has been allowed to dry and drying the impregnant. The more specific objects of this invention are accomplished by surface coating the impregnated web referred to above wherein the pattern on the surface of. the non-woven web is not discernible when the coated fabric is stretched as in shoe lasting.

The drawing illustrates a flow sheet of the process.

The degree of roughening or absence of roughening encountered in the toe and quarter area of the shoes made with an impregnated and coated shrunk non-woven web, having a pattern on its surface prior to impregnating and coating, is dependent upon the amount of impregnant introduced into the Web prior to the shrinking of the web. The amount of impregnant also affects the degree of shrinking as does the temperature and method of heat shrinking. As the amount of the non-volatile components of the impregnant introduced into the web increases the amount of heat shrinking of the non-woven web decreases. The amount of non-volatile impregnant introduced into the web is controlled primarily by the concentration of the solids (non-volatile components) in the dispersion. The maximum amount of area shrinkage of a web capable of 90% area shrinkage is reduced to about 60% area shrinkage when it is saturated with an aqueous dispersion having a concentration of non-volatile components of about 30%. Non-woven webs impregnated with dispersions having lower solids concentrations will permit greater amount of area shrinkage with the same heat shrinkable webs.

The amount of impregnant which is introduced into the web is determined to a large extent by the end use of the product. For shoe uppers, the preferred amount of dry impregnant, based on the weight of the fibers, is about 100 to 400% and the particularly preferred range is about 200 to 300%, same weight basis. If the amount of dry impregnant in the web is less than about based on the weight of the fibers, roughening is encountered when the impregnated and coated web is subjected to about 35% stretching in the direction of width and/or length. The upper limit of the amount of dry impregnant is controlled by the concentration of the non-volatile components in the impregnating compositions. Concentrations greater than that required to introduce about 400% dry impregnant, based on the weight of the fibers, do not result in uniform impregnation.

Impregnating the heat shrinkable non-woven webs with an aqueous dispersion prior to heat shrinking has other advantages besides reducing the roughening encountered when the impregnated and coated sheets are stretched as encountered in shoe lasting operations. Impregnation is more uniform and faster with the aqueous dispersions prior to heat shrinking due to the rapid wicking of the less dense web. It is also possible to achieve a higher ratio of impregnant to fiber by impregnating prior to shrinking due to the more open structure of the web.

The use of an aqueous dispersion as the impregnant has still further advantages over solutions of polymer in organic solvents in that it is possible to use much higher solids concentration of aqueous dispersions at lower viscosity to achieve thorough and uniform impregnation of the web; no solvent recovery or toxicity problems are en countered with the aqueous dispersions; water does not destroy the shrinkability of the shrinkable fibers as do most organic liquids; and it is much easier to impregnate fragile non-woven webs with low viscosity dispersions than with high viscosity solutions of the same polymer.

The aqueous dispersion impregnants can be coagulated within the web by a variety of techniques including freeze coagulating, immersing the web in an aqueous solution of an electrolyte, heating the impregnated web, and in the case of non-coalescible dispersions allowing the impregnating composition to dry at room temperature.

In making moisture permeable shoe upper material by impregnating a heat shrinkable non-woven web with an aqueous dispersion, the freeze coagulation is particularly preferred in that the coagulum is deposited uniformly throughout the web in a highly porous form thus aiding the permeability of the final product. There is also very little, if any, migration of the impregnant, during the freeze coagulation, drying, and heat shrinking of the nonwoven web.

The aqueous dispersions which have been found to be particularly useful in practicing this invention are the aqueous dispersions of rubbery low-modulus elastomers, such as neoprene (polychloroprene), butyl rubber, Hycar (copolymer of butadiene and acrylonitrile), Buna S (copolymer of butadiene and styrene), natural rubber, aqueous dispersions of thermoplastic polymers and copolymers, such as, e.g., Geon 351 (plasticized polyvinyl chloride), oil modified alkyd resin, acrylic resins and methacrylic resins, as well as various mixtures of the aforementioned dispersions.

The particularly preferred heat shrinkable fiber for forming the non-woven web is composed of polyethylene terephthalate. Other useful heat shrinkable fibers include those composed of cellulose acetate, nylon, 40/60 copolymer of acrylonitrile and vinyl chloride, polyethylene, polypropylene, polystyrene and polytetrafluoroethylene. Blends of the foregoing heat shrinkable fibers are also useful for forming the non-woven web. It is also possible to blend heat shrinkable fibers with nonshrinkable fibers in which the shrinkable fibers represent at least 50% of the fibers in the non-woven web. EX- amples of non-shrinkable fibers are any of the foregoing shrinkable fibers which have been shrunk prior to forming the non-woven web, as well as natural fibers, including cotton, jute, flax, wool, etc.

Example I A fluffy, loosely bound, non-woven web weighing 14.9 ounces per square yard and composed of polyethylene terephthalate fibers of 1.25 denier, formed on a card and crosslapper, was passed through a needle loom six times. The density of the needle punches was about 1536 per square inch. The needle punched web weighed 11.9 ounces per square yard and possessed a very pronounced needle pattern having a herringbone-like appearance.

The needled web was immersed in an aqueous latex of neoprene containing 30% non-volatile ingredients, including polychloroprene, antioxidants, curing agents, accelerators, etc., as described in Example 1 of French Patent 1,289,754. The web was saturated and uniformly impregnated throughout with the aqueous latex. The impregnated web was removed from the impregnating bath and the excess latex was allowed to drain from the web. Before the impregnant was allowed to dry, the impregnated Web was exposed to a temperature of 40 F. until the impregnant was frozen and coagulated throughout the web. After the impregnant was freeze coagulated and thawed, the excess water was allowed to drain therefrom. Before the impregnant was allowed to dry completely, the impregnated Web was immersed in a water bath heated to 65 C. for about 5 minutes during which time it was shrunk 63% of its planar area. The shrunken impregnated web was thoroughly washed with water to remove any water soluble ingredients deposited in the web from the latex, such as dispersants. The washed web was dried in an oven for 1 hour at 100 C. and then heated for 30 minutes at 140 C. to cure the neoprene impregnant. The dry impregnant was deposited throughout the web in a porous condition with both micro and macro pores being present.

The dry impregnated web was buffed on each side to remove the skin surface of the impregnant. The web at this stage, about 150 mils thick, was skived into three layers, each about 50 mils thick.

A control sample was made in the same manner and with the same ingredients as described above except the impregnating step was carried out after the web shrinking step and the temperature of the water during the shrinking step was 63 C. instead of 65 C. in order to obtain a comparable amount of shrinkage. The amount of planar shrinkage of the unimpregnated web for the control sample was 50%.

The product produced in accordance with Example I and the control for Example I had the following physical properties:

Example I Control for Example I Density, g./cc 0. 764 0. 43 Thickne mils"- 50 50 Permeability Value 6, 900 8, 700 Elongation at Break:

Machine Direction, percent 240 150 Cross Machine Direction, percent- 230 140 Strength at Break:

Machine Direction, p.s.i 1, 600 1, 000 Cross Machine Direction, p.s.i 950 1, 100 Initial Modulus:

Machine Direction, p.s.i 2, 800 1, 900 Cross Machine Direction, p.s.i 1, 700 1, 900 Tonguer'lear (Pounds per Inch T ckness) Machine Direction 128 98 Cross Machine Direction 180 105 The permeability values were carried out by filling a three inch diameter crystallizing dish with 12 mesh calcium chloride, covering the dish with membrane of the substance to be tested and placing the covered dish in an atmosphere of high humidity (23 C. and 90% relative humidity). The assemblage is weighed at intervals and the equilibrium rate of sorption is recorded as grams of water per 100 sq. meters of surface per hour which is the leather permeability value. This is a modification of a test developed by the Bureau of Standards, Kanagy & Vickers, J. Res. Nat. Bureau of Standards, 44, 347-62, 1950 (April).

The impregnated product as described above, before and after the skin on the surface is removed, as well as after skiving, is an article of commerce and has a variety of uses such as gaskets, diaphragms, bearing seals, paulins, etc. The buffed and skived product is particularly useful as a substrate for surface coatings in the making of shoe upper materials as described more fully hereinafter.

The 50 mil thick impregnated substrate produced in accordance with Example I and the 50 mil thick control materials were each coated on one side with a surface coating composition described below. Sufiicient composition was applied to deposit a dry surface film about 10 mils thick. The surface coating composition consisted of about 10.5% of a polyurethane elastomer, 5.7 parts of polyvinyl chloride and 83.8 parts of N,N-dimethyl formamide (referred to hereinafter as dimethyl formamide). The coating composition was prepared by mixing 52.5 parts of a 20% solution of the polyurethane elastomer dissolved in dimethyl formamide with 47.5 parts of a 12% solution of polyvinyl chloride dissolved in dimethyl formamide. Suffiicent non-solvent for the polymers, such as an /20 mixture of dimethyl formamide and water, was added to the mixture of solution to form an incipient gel.

The 20% solution of polyurethane elastomer was prepared by first mixing 3343 parts of polytetramethylene ether glycol of about 1000 molecular weight with 291 parts of tolylene-2,4-diisocyanate and heating the mixture for 3 hours at C. Then 2485 parts of the resulting lhydroxyl terminated dimer were mixed with 570 parts of methylene-bis-(4-phenyl isocyanate). This mixture was heated for one hour at 80 C., yielding a prepolymer with isocyanate groups. The prepolymer was dissolved in 10,000 parts of dimethyl formamide and the resulting solution was added slowly toa solution consisting of 50 parts of a polymer chain extender dissolved in 1710 parts of dimethyl formamide. The chain extender consisted of N-methyl-bis-amino propyla-mine and hydrazine hydrate in a molar ratio of 40:60. The re sulting reaction mixture was stirred at 40 C. for 30 minutes to form a polyurethane solution having a viscosity of about 115 poises and a polymer content of about 20%.

Immediately after the surface coating composition was applied to the substrate and before any appreciable amount of dimethyl formamide was allowed to evaporate therefrom the coated substrate was immersed in water at room temperature for 2 hours. During this water immersion step, the coating solution was coagulated and converted into a gelatinous polymeric layer having a cellular structure of interconnecting micropores and substantially all of the dimethyl formamide was extracted from the solution coating.

Next the coated fabric was subjected to steam for about 15 minutes then dried at C. in dry heat zone. When dry, the surface coating had a White milky appearance and was highly permeable to water vapor.

The dry coated fabric was next immersed for 30 minutes in a boiling aqueous dye bath containing 5% of chromed monoazo black dye identified as C1-15711 (Colour Index number) in Colour Index, Second Edition, vol. 3, 1957, American Association of Textile Chemists and Colorants.

The dyed coated fabric is next scoured for 15 minutes in a boiling aqueous scouring bath containing 0.3% of a non-ionic detergent based on the weight of the water. The detergent was the condensation product obtained by reacting 20 moles of ethylenic oxide with one mol of a C-l8 aliphatic monohydroxy alcohol.

The dried and scoured impregnated and coated fabric had a deep black color. It Was highly permeable to moisture vapor, tough, abrasion resistant and eminently suited for use as mens and womens shoe uppers.

Both coated substrates, i.e., the Example I and its control, were fabricated into mens dress shoes by the usual shoe making techniques which involved stretching the coated substrates over a last and holding the material in the stretched condition during the shoe making operation.

In the case of the control, the needle pattern in the non-woven web which had been obscured by the impregnating and surface coating compositions was caused to reappear in the surface coating upon stretching during lasting of the shoes and remained in the areas of greatest stretch, such as, the toe and quarter portions of the shoe after the shoe was separated from the last and the stress removed.

In the case of the Example I material, the needle pattern in the non-woven web was likewise obscured by the impregnant and surface coating. The pattern was not discernible in the surface coating during or after the shoe lasting operations.

On an evenly graduated scale where zero represents complete absence of needle pattern in the surface coating when subjected to stress during shoe making operation and 6 represents severe roughening, i.e., appearance of needle pattern, the Example I impregnated and coated substrate had a rating of 1 and the control for Example 1 had a rating of 6.

Example 11 Example I was repeated except a fluffy, loosely bound non-woven web weighing 13.3 ounces per square yard of polyethylene terephthalate fibers of 1.25 denier, formed on a card and cross-lapper, was passed through a needle loom nine times. The density of the needle punch was 2750 per square inch. The weight of the web after needle punching was 10.3 ounces per square yard and possessed a very pronounced needle pattern having a herringbonelike appearance.

A further variation in the procedure of this Example II from that described in Example I was that the temperature of the hot water bath employed for the shrinking of the impregnated web was 70 C. instead of 65 C. The impregnated web of Example II shrunk 63% of its planar area as compared to 53% for the impregnated web of Example I.

A control for Example II was prepared in the same manner and with the same ingredients as employed for Example 11, the only difference being the shrinking step was carried out before the impregnating step.

The product produced in accordance with Example II and the control for Example II had the following physi- The impregnated webs of Example II and the control for Example 11 were coated with the same composition and same manner as described above for Example I and then formed into mens shoes by the usual lasting processes. The needle pattern which had been obscured by the impregnating and surface coating composition in the 6 case of the Example II material was hardly discernible in that area of the shoe upper which had been stretched during lasting, i.e., the toe and quarter areas and had a rating of 1 on the scale mentioned above, whereas the control material had a rating of 6.

Example III A non-woven web of polyethylene terephthalate fibers composed of 0.8 denier crimped staple was formed on a card and cross-lapper. The Web Weighed 9.0 ounces per square yard. It was passed through a needle loom to orient some of the fibers perpendicular to the plane of the web to give it reinforcement.

The Web was immersed in the following impregnating composition until it was completely saturated:

Parts by weight Neoprene latex (Example IFrench Patent 1,289,754) 180.0 Water 157.0

Calco A-2246 (33% aqueous dispersion of 2,2-

methylene bis (6 tertiary butyl paracresol) 5.4 Zinc oxide aqueous solution) 9.0 Aquarex SMO (33% aqueous dispersion sodium salt of sulfated methyl oleate) 8.1 Tepidone (50% aqueous solution sodium dibutyl dithiocarbamate) 1.8 Thiocarbanalide (33% aqueous dispersion) 2.7 Geon Latex 351 vinyl chloride polymer (57% aqueous dispersion) 10.0 Water 13.4

The impregnated web was freeze-thaw coagulated in the same manner described above in Example I. Before the thawed impregnant was allowed to dry, the impregnated Web was immersed in water, heated to 70 C. and allowed to remain therein for 15 minutes after which it was removed and dried. The impregnated web shrunk of its original planar area during the exposure to the hot water. The impregnant was cured at 120 C. for minutes. The fiber to hinder ratio was to 274.

The cured impregnated web was sanded on both sides to remove the skin of the excess impregnant. The impregnated product was microporous, smooth and free of macro voids. The product was flexible and on 35% transverse and on 35% longitudinal stretching, no roughening was observed, i.e., it had a roughening value of zero on the scale described above. The stretched sample returned to its original dimension after the stress was removed.

The impregnated web was ideally suited as a substrate for surface coating in the manufacture of shoe upper material.

Good results as to non-roughening, i.e., absence of needle pattern on the surface of the impregnated and coated non-woven Webs produced in accordance with this invention when formed into shoes by the standard shoe making techniques are obtained when the aqueous dispersions contain about 20-60% solids. Dispersions containing 25-40% solids are preferred and best results are obtained with about 30% solids. If higher concentrations are used, the area shrinkage of the impregnated webs is reduced and there is also a reduction in roughening of the coating during the lasting operation when the coated Web is formed into shoes, although other valuable properties are decreased, such as unsightly appearance in the vamp area of the shoe when flexed, which is referred to as poor leather break.

At lower concentrations of the latex impregnant, there is less impregnant introduced into the web, and there is an increase in the shrinkage of the impregnated nonwoven web accompanied by an increase in roughening (i.e., appearance of needle pattern) during and after the lasting operation of shoe manufacture.

A coated Web having a roughening value greater than 2 is not considered commercially acceptable for high grade shoe uppers.

It Will be understood, however, that the products made in accordance with this invention having a roughening value greater than 2 are useful for other end uses where the roughening on stretching is not detrimental, such as e.g., gaskets, fuel pumps, upholstery, pocketbooks, mens and ladies jackets, paulins, etc.

We claim:

1. A process Which comprises:

(a) preparing a non-Woven web of fibers, said Web being capable of shrinking 2080% of its planar area and having a needle pattern on its surface,

(b) impregnating said Web 'with an aqueous dispersion of a polymeric material,

(c) coagulating said aqueous dispersion impregnant,

and

(d) subjecting said impregnated Web to an elevated temperature Which causes it to shrink 2070% of its planar area before the impregnant dries.

2. The method of claim 1 in which step (d) is carried out by immersing the impregnated web in Water at a temperature of 63 C. to 90 C.

3. The method of claim 1 in which the coagulation step is carried out by freezing the aqueous suspending medium for the dispersant.

4. The method of claim 1 which involves an additional step of applying a surface coating to the impregnated Web.

References Cited by the Examiner UNITED STATES PATENTS 2,444,124 6/1948 Wedler 117-62 2,723,935 11/1955 Rodman 161- 166 2,910,763 11/1959 Lauterbach 161189 X 2,930,106 3/1960 Wrotnowski et a1. 117-440 2,973,284 2/1961 Semegen l17-l40 XR 3,067,482 12/ 1961 Hollowell 17763 XR 3,100,721 8/1963 Holden 117135.5

FOREIGN PATENTS 931,374 7/1963 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

Claims (1)

1. A PROCESS WHICH COMPRISES: (A) PREPARING A NON-WOVEN WEB OF FIBERS SAID WEB BEING CAPABLE OF SHRINKING 20-80% OF ITS PLANAR AREA AND HAVING A NEEDLE PATTERN ON ITS SURFACE, (B) IMPREGNATING SAID WEB WITH AN AQUEOUS DISPERSION OF A POLYMERIC KMATERIAL, (C) COAGULATING SAID AQUEOUS DISPERSION IMPREGRANT, AND (D) SUBJECTING SAID IMPREGNATED WEB TO AN ELEVATED TEMPERATURE WHICH CAUSES IT TO SHRINK 20-70% OF ITS PLANAR AREA BEFORE THE IMPREGNANT DRIES.

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