US3536639A - Method for producing vapor permeable polyurethane fibers - Google Patents

Description

27, 1970 T. SCHACHOWSKOY 3,536,639

METHOD FOR PRODUCING VAPOR PERMEABLE POLYURETHANE FIBERS Filed April 21, 1966 IO 0 70 OM50 90 I00 9'0 THF IN VENTOR THEODOR SCHACHOWSKOY AT TORNEYS.

United States Patent C) F Int. Cl. B29d 7/20, 27/ 4; C08g 22/10, 53/ 08; D0611 3/08 US. Cl. 260-25 6 Claims ABSTRACT OF THE DISCLOSURE Production of air and water-vapor-permeable films of polyurethane by coagulating polyurethane from a mixture of dimethylsulfoxide and tetrahydrofuran, dioxane, acetone or methyl-ethyl ketone.

This invention relates to the production of sheet or film-form materials having a relatively high degree of air and water vapor permeability. It more particularly refers to the production of an air and water vapor permeable coating on a substrate.

Luggage, upholstery material or other non-apparel goods have been made from plastic materials which have the appearance and hand of leather for many years. The production of artificial leather for these uses is a recognized art which is relatively highly developed and which has been relatively successful.

Attempts have been made for many years to produce artificial leather for apparel use with only limited success at best. The primary problem facing the art is producing artificial or synthetic leather for apparel use is and has been the difficulty of producing a self-supporting sheet or film-form material which not only has the look and hand of leather, but also has the breathing qualities of leather, i.e., the ability to pass water vapor and air and yet be relatively impervious to liquid water. Additionally, particularly in the case of shoe upper material, the synthetic leather product must be relatively soft and supple such that it is resistant to creasing and paper break as a result of flexing over an extended period of time. Another quality which must be present in such artificial leather shoe upper material is abrasion resistance sufficient to be resistant to the relatively minor sending and scraping to which shoes are so often subjected.

In recent years much attention has been given to solving these problems and the art pertaining thereto has been advanced. The best type of system found to date has been one which utilizes a fabric substrate having a surface coating thereon. Thus, both the substrate and the coating must be air and water vapor permeable to a degree sufiicient to simulate leather, and the substrate and the coating thereon must be supple and crease-resistant in their composite form to a degree suflicient to simulate or surpass the properties of natural leather. Additionally, the surface coating must be sculfand abrasion-resistant both in the wet and in the dry state. One additionally optional requirement for the surface coating is that,

where the coating is to have a highly glossy appearance, it should not have large pores on the surface thereof.

It has generally been found that suitable substrates for synthetic leather type materials can be produced from a batt or fleece of non-woven fibrous fabric or from a woven fibrous fabric. The fleece or batt approach has appeared to take predominance in this area because its properties seem to be better suited to this application. Such battings are generally needled in order to impart resistance to planar delamination thereto and impregnated with a suitable material to render the batt relatively dimensionally stable and self-supporting.

It has been proposed to produce porous film-form materials by the so-called coagulation method. In this method, the material from which the film will be produced is dissolved in a suitable solvent and then coagulated from the solvent by the admixture of the solution with a suitable coagulant. For example, French Pat. 822,742 shows the solution of nitrocellulose in an acetone-alcohol mixture and coagulation of the nitrocellulose into a film-form material by the use of water as a coagulant. In particular, this patent shows the production .of a film by deposition of the above-described solution on a glass plate and immersion of the solution-coated glass plate into a water bath. After a suitable immersion time, e.g., about 350 seconds, a coagulated film of nitrocellulose could be lifted from the glass plate. The patent states that coagulation of the film can be accelerated by use of aqueous solutions of organic acids as the coagulation agent.

It can be appreciated that it is possible to apply a preformed film-form material referred to above to a suitably prepared fibrous or other form substrates so as to produce a composite structure having more desirable physical strength properties than those possessed by the coating film alone. This has been found to be a less than totally satisfactory solution to the problem in that additional costs are incurred in joining the preformed surface coating to the substrate, and in addition, it has been found that the permeability properties of the composite material are less advantageous with respect to the instant application use than are the properties of either the coating or the substrate alone.

It has also been proposed to spray a solution of an elastomeric coating material directly onto a suitable substrate (cf. US. Pat. 3,109,750). Elastomeric materials which have been suggested for application as top coatings in this manner are exemplified by polychloroprene, butadiene-styrene, chlorosulfonated polyethylene copolymer, butadiene-acrylonitrile copolymer and vinylidenefluoridehexafluoropropene copolymer. The solvent for the selected elastomer is suitably a mixture of materials wherein the elastomer is soluble in the mixture, but is insoluble in either of the components thereof. For example, mixtures of an alkane and a lower ketone will readily dissolve the elastomer, but the elastomer is substantially insoluble in either the alkane or the lower ketone chosen.

In this immediately above-referred to process, the solvent components are so selected that these have respective vapor pressures, under the same conditions of temperature and pressure, which are markedly different. The temperature and pressure conditions obtaining during spraying constitute the most critical conditions at which to determine the vapor pressure differential of the individual components of the solvents.

When the elastomer solution is sprayed onto the substrate, the solvent component with the higher vapor pressure preferentially evaporates thereby leaving a mixture of the elastomer and one of the components of the solvent (the remaining component being substantially a nonsolvent for the elastomer), wherefrom the elastomer precipitates and coagulates upon the substrate, whereby a microporous coating is said to be produced. For example, an elastorneric polymer is dissolved in a solvent mixture of acetone and n-hexane (neither acetone nor n-hexane being individually a solvent for the chosen elastomer) and the solution sprayed onto a suitable porous supporting material. When the solution is coated on the support, one of the components of the solvent (probably acetone, since it has the lower atmospheric pressure boiling point of the two) preferentially evaporates and the elastomer coagulates.

It has been sought to take advantage of the same principle, of preferential evaporation of one component of a solvent mixture, in applying a suitable coating to a substrate by means other than spraying; e.g., brushed on or rolled on coatings. For other purposes it has been suggested that solutions of cellulose derivatives or vinyl polymers in acetone could be prepared and a precipitant such as toluene for such polymers added to such solution in an amount less than that which would be sufficient to cause polymer precipitation. Upon coating of the solution upon a substrate, the solvent preferentially evaporates, whereby the concentration of the precipitant increases to a level sufficient to cause coagulation of the dissolved polymer. This technique is supposed to result in a porous coating, but tests carried out to confirm this have shown that the resulting coating is a substantially opaque film of individually coagulated or precipitated polymer particles, where the coating has a thickness great enough to be desirable for synthetic leather applications.

It was even attempted to produce usable permeable coatings by utilizing elastorneric polymers, such as polychloroprene, butadiene copolymers, acrylic ester polymers and copolymers, polyurethane, in the coating solution, but it was found not possible to produce permeable coating from even these polymers, according to this technique, in thickness greater than about 0.1 to 0.15 millimeters. Thus, it is apparent that these prior art processes do not adequately solve the problem of producing an artificial leather material which has sufficient air and water vapor permeability to be completely acceptable.

In German Pat. 888,706, a process is described by means of which permeable coatings are said to be provided on various substrates including paper, leather and non-woven battings. According to this process, solutions of a polyurethane polymer in a suitable solvent, e.g., dimethylformamide, are applied to the surface of or impregnated into a suitable substrate. The substrate having the suitably applied polymer solution is dipped into water to coagulate the polymer and thus provide a coating on or an impregnant in, as the case may be, the substrate. The solvent is said to be removed by action of the water coagulant.

Further, it has been shown that the water vapor and air permeability of film-form or sheeting materials produced by coagulation of solutions of appropriate polymers, utilizing dimethyl formamide or dimethyl sulfoxide solvent, can be improved if there are admixed with the polymer solutions emulsifiers, particularly about 0.3 to percent by weight based upon the weight of the entire solution of emulsifier.

Despite the fact that air and water vapor permeable films and coatings have been produced according to many, if not all, of the prior art processes, it is still desirable to produce such film-forming or sheeting materials either in self-supporting form or applied as a coating or impregnant for a suitable substrate.

It is therefore an object of this invention to provide a polyurethane film having an outstanding airand water vapor permeability.

It is another object to provide a novel process of producing such improved film-form material.

Other and additional objects of this invention will become apparent from a consideration of this entire specification including the claims appended hereto.

In accord with and fulfilling these objects, this invention comprises, in one of its broad aspects, the production of polyurethane film having superior air and water vapor permeability characteristics. This film-form material is produced by coagulation thereof from a solvent which is a mixture of dimethyl sulfoxide and either tetrahydrofuran, acetone, 1,4-dioxane, methyl ethyl ketone or mixtures thereof.

The instant invention will be better understood from a consideration of the following fiow diagram:

Solvent Solvent- Polyurethane Coagulant Solvent Film Removal Mixing dz Formation Permeability data presented herein were obtained by practicing the Mitton test method which appears in Physikalische Messmethoden fiir Leder, JUP l5, Measurement of Water Vapor Permeability.

It is preferred in the practice of this invention to use a solvent mixture containing about 30 to 90 percent by weight dimethyl sulfoxide and about 10 to percent by weight of the other solvent used. While it is within the contemplation of the practice of this invention to use as the other solvent, mixtures of the above-named sol vents, it is preferred to utilize a single other solvent in admixture with dimethyl sulfoxide, and it is most particularly preferred to use a solvent mixture composed of dimethyl sulfoxide and tetrahydrofuran.

The polymer solute (and ultimately, the film-form material) is a polyurethane. It has been found that no remarkable improvements in the airand water-vapor permeability are obtained if one works with other polymers.

The coagulating agent can be any of the known materials which alone and in suitably proportional admixture with the solvent composition of this invention cause the solute polymer material to coagulate from the solution. Water is the preferred coagulant. Also useful coagulants are lower alcohols, n-hexane and toluene. Mixtures of these coagulants may be used.

It will, of course, be understood that a judicious selection of the system to be used in this invention must be made taking advantage of the combination of properties of the selected other solvent, coagulant and polymer. Thus, the chosen other solvent must, in combination with dimethyl sulfoxide, be a solvent for the particular polymer chosen. Similarly, the coagulant chosen must be related to both the solvent system and to the chosen polymer, since it must have the capacity, in admixture with the chosen solvent system, to cause the polymer to coagulate. Data sufficient to make this choice a matter of routine are known to those skilled in the art or are straight forwardly determinable by such workers as a routine matter.

Film-form and sheet materials may be prepared according to this invention either in self-supporting form or as coatings upon a suitable substrate. Production of selfsupporting films may be accomplished by coating of a smooth surface with a polymer solution according to this invention; coagulating the polymer into a film; and then lifting the film off the surface. Coatings may be applied to supporting substrate which is itself porous and to which the coated polymer will adhere so as to thus form a composite article comprising the substrate and the coating thereon by applying to the substrate surface a polymer solution according to this invention; and suitably coagulating the polymer from solution onto the substrate as an adherent layer thereon.

A suitable substrate onto which a polymeric coating according to this invention may be applied is a fibrous fabric. This fabric may be woven, knitted or a non-woven fleece or batting. The fabric may be composed of natural or synthetic organic or inorganic fibers as desired which are exemplified by cellulosics, polyamides, polyesters, wool, silk, linen, acrylics, etc.

By applying the polyurethane to a suitably chosen substrate from a solution, the solvent of which is a mixture of dimethyl sulfoxide and at least an other solvent, selected from the group consisting of tetrahydrofuran, 1,4- dioxane, acetone and methyl ethyl ketone, it has been surprisingly found that the polyurethane film produced by coagulation from this solution are significantly more air and water vapor permeable than are similarly coagulated polymer films derived from the same polyurethane in solution in either dimethyl sulfoxide or in the second solvent alone. This is particularly true in the case of coagulation from the other solvent alone from which solutions polymeric film-form materials have been coagulated having less than 0.5 mg./cm. /hr. water vapor permeability.

Where a polyurethane film has been produced by coagulation of a polyester-polyurethane polymer from a solution thereof in dimethyl sulfoxide alone, the film had a water vapor permeability of about 2 mg./cm. /hr.; whereas the same polymer coagulated in the same manner into a film of the same thickness from a solution of the polymer in 80 parts by weight of dimethyl sulfoxide and 20 parts by weight of tetrahydrofuran had a water vapor permeability of 4 mg./ cm. hr.

It is surprising that an increase in the water vapor permeability of polyurethane films can be realized from coagulation thereof from a solvent mixture according to this invention, which increase is with respect to the water vapor permeability of film form materials obtained by production of such films by coagulation thereof from either of the solvent components alone.

It is even more surprising that a corresponding increase in the water vapor permeability of film-form materials coagulated from dimethyl formamide containing combination solvents does not take place. In fact, the water vapor permeability of such films is not in any way improved over that obtained by coagulation production of materials from solution in dimethyl formamide alone.

The film-form materials produced by the practice of this invention can be post-treated, and/or the polymers from which they are produced pro-treated, in the conventional manner. Thus, dyes or pigments can be incorporated according to the usual processes. The product filmform material can be physically treated and worked in the conventional manner, such as, for example, by applying suitable finishes thereto if desired, roughened with abrasives or smoothed by polishing or by applying a suitable top coating thereon, as is known in the art.

The solutions for use in this invention may be prepared in a conventional manner, that is, the solvent mixture can first be made with or without emulsifier therein and the suitably selected polymer dissolved therein. In the alternative, the polymer can be dissolved in either component and the second component then added thereto.

In either case, or regardless of the solution preparation means, it is desirable that the solution contain no air bubbles trapped therein at the time of use. In order to insure this condition, the solution is suitably deaerated either by applying a low vacuum over said solution or by merely permitting the solution to stand for a relatively long time between preparation and use thereof.

The term film-form material as used herein is intended to encompass both material coated upon a suitable substrate as well as self-supporting material, as the case may be.

The following examples are given by way of illustration of this invention and are in no Way limiting upon the scope thereof. All parts and percentages are by weight, unless expressly stated to be to the contrary.

EXAMPLE I A ZO-percent solution of a soluble polyester-polyurethane (Estane X7 of Goodrich) was prepared by dissolving such polymer in a mixture of parts dimethyl sulfoxide and 20 parts tetrahydrofuran. The solution was applied in one coat to a batting of polyamide fibers containing butadiene-acrylonitrile copolymer as binding agent (the batting having a thickness of about 1.2 mm. and a specific gravity of about 0.5).

The solution was applied in a thickness of about 1.2 mm. (space between rollers). The batting thus coated was immediately placed in water for coagulation, freed of solvent by rinsing with water (rinsing time about 2 hours) and then dried.

After drying, an opaque, white coating was obtained. The water vapor permeability of the sample thus obtained was about 4 mg./cm. /hr. The coating remained undamaged after 200,000 flexings on the Bally Flexometer.

EXAMPLE II A solution of the same polymer as in Example I was prepared in a mixture of 70 parts dimethyl sulfoxide and 30 parts acetone. This solution was utilized to produce a coated batting by the same process as described in Example I, and a coated batting was obtained which had a water vapor permeability of about 4 mg./cm. /hr.

EXAMPLE III A solution of a soluble polyester-polyurethane (Goodrich Estane X7) was prepared in a mixture of 60 parts dimethyl sulfoxide and 40 parts 1,4-dioxane as the solvent composition in the same manner as in Example I.

A coating on a batting was provided by coagulation of the polymer thereon from said solution, as described in Example I. The coating thus obtained in this manner showed a water vapor permeability of about 5.5 to 6 mg./cm. /hr.

EXAMPLE IV A solution of polyurethane was prepared in the same manner as described in Example I, using a mixture of 40 parts dimethyl sulfoxide and 60 parts of methyl ethyl ketone as the solvent. The procedure continued as described in Example I. The film-forming material thus obtained had a water vapor permeability between 6.5 and 7 mg./cm. /hr.

Data taken from various tests performed on a variety of coated substrates prepared according to this invention are shown graphically in the drawing. The film-form material tested was the same as described in Example I, as was the substrate to which it was applied. The curve in the attached drawing shows data taken from tests conducted on mixed solvent coagulation produced materials.

What is claimed is:

1. A process for the production of air and water vapor permeable polyurethane films which comprises dissolving a polyurethane in a solvent composed of a mixture of dimethyl sulfoxide and at least one member selected from the group consisting of up to 40% tetrahydrofuran, 1,4- dioxane, methyl ethyl ketone and acetone; adding a coagulant; coagulating said polyurethane in film-form from said solution; and removing the solvent from contact with said film-form material.

2. A process as claimed in claim 1, wherein said coagulant is selected from the group consisting of lower alcohols, n-hexane, toluene, water and mixtures thereof.

3. A process as claimed in claim 1, wherein said filmform material is deposited upon a substrate and forms a coating thereon.

4. A process as claimed in claim 1, wherein said filmform material is self-supporting.

5. A process as claimed in claim 1 wherein said solvent is a mixture of dimethyl sulfoxide and 1,4 dioxane.

6. The product produced by the process of claim 1.

2,884,336 4/1959 Loshaek et al. 3,190,765 6/1965 Yuan 26449 XR 3,100,721 8/1963 Holden. 3,348,963 10/1967 Fukushima et al. 3,388,100 6/1968 Thoma et al.

FOREIGN PATENTS 639,553 4/1962 Canada.

1,296,758 5/1962 France.

PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

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