US3665157A

US3665157A - Method of producing a moisture permeable sheet material

Info

Publication number: US3665157A
Authority: US
Inventors: Kazuto Harada
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 1970-02-27
Filing date: 1971-02-19
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23
Also published as: FR2080813A1; CA927316A; DE2108785A1; DE2108785C3; GB1296942A; DE2108785B2; FR2080813B1

Abstract

A method of imparting moisture permeability to a sheet material having a porous base and a non-porous surface layer is provided comprising impregnating the pores within the porous base with an aqueous medium, subjecting the impregnated sheet material to electrical discharge, thereby forming a plurality of perforations in said non-porous surface layer, and recovering the sheet material exhibiting enhanced moisture permeability.

Description

United States Patent Harada [151 3,665,157 451 May 23, 1972 54,] METHOD OF PRODUCING A MOISTURE PERMEABLE SHEET MATERIAL [72] Inventor: Kazuto-l-larada, Kurashiki, Japan [73] Assignee: Kuraray Co., Ltd., Kurashiki Japan [22] Filed: Feb. 19, 1971 [21] App]. No.: 1 17,143

[30] Foreign Application Priority Data Feb. 17, 1970 Japan ..45/l748l June 12, 1970 Japan ..45/51403 [52] US. Cl ...2l9/384,83/l6, 219/284, 346/74 [51] Int. Cl. ..H05b 7/18 [58] Field of Search ..2l9/383, 384, 234, 284; 83/16, 83/169, 170; 346/74 [56] References Cited UNITED STATES PATENTS 853,755 5/1907 Belin ..219/383X 2,107,931 2/1938 2,481,048 9/ 1949 2,550,366 4/1951 3,164,716 1/1965 Schenker et a]. ..219/383 3,183,518 5/1965 Henry et a1. ..346/76 3,424,895 1/1969 Olson 2l9/ 384 Primary Examiner-Volodymyr Mayewsky Attorney-William Kaufman and Barry Kramer [57] ABSTRACT A method of imparting moisture permeability to a sheet material having a porous base and a non-porous surface layer 19 Claims, NO Drawings METHOD OF PRODUCING A MOISTURE PERMEABLE SHEET MATERIAL This invention relates to a method of producing sheet materials exhibiting excellent moisture permeability. More particularly, this invention relates to an improved method for electrically introducing perforations in a non-porous surface layer of sheet material to provide enhanced moisture permeability thereto.

Leather substitutes have heretofore been developed for use in the manufacture of shoes, boots, trunks, bags and the like. Generally, these leather substitutes comprise sheet materials .produced by forming a porous base material and covering said base material with a non-porous layer which can be colored or uncolored depending upon the desired effect to be obtained. The resulting sheet material is then embossed to impart a leather appearance thereto. When, however, the sheet materials are finished with sufficient thickness to provide a good appearance, it has inevitably been found that the moisture permeability of the sheet material is substantially impaired.

Methods have heretofore been developed for improving the moisture permeability of vinyl sheets and the like wherein electrical discharges such as corona discharges or pulse discharges have been employed to impart minute perforations or pores in the non-porous surface layer. Although this electrical discharge process can be employed to impartperforations to the non-porous surface layer of sheet materials comprising a porous base material and a non-porous surface layer, it has been found that the presence of the porous base material between the discharge electrodes necessitates the use of higher voltage to obtain the necessary degree of perforation. When using higher voltage, however, it is extremely difficult to obtain uniform perforation of the surface layer; moreover, the resulting perforations are larger than desired.

It is therefore an object of this invention to provide a method for imparting moisture permeability to sheet materials which overcomes the above-noted deficiencies.

It is another object of the present invention to provide a method for producing sheet materials exhibiting uniform and minute perforations as well as excellent moisture permeability by an electrical discharge process.

These as well as other objects are accomplished by the present invention which provides a method of imparting moisturepermeability to a sheet material having a porous base and non-porous surface layer comprising impregnating the pores within the porous base with an aqueous medium, subjecting the impregnated sheet material to electrical discharge, thereby forming a plurality of perforations in said non-porous surface layer, and recovering the sheet material exhibiting enhanced moisture permeability. The aqueous medium'employed in the present invention can be water or an aqueous electrolytic solution. if water is employed as the aqueous medium, the sheet material can be recovered by drying. if, however, an aqueous electrolytic solution is employed, the

treated sheet material can be first washed with water and then dried. in either case, sheet material exhibiting numerous minute pores therein and exhibiting excellent moisture permeability is obtained.

The porous base material of the sheet material of the present invention exhibits a high breakdown voltage. When impregnated with an aqueous medium, it exhibits a higher electrical conductivity than when it is not so impregnated. Thus, the electrical discharge process is facilitated enabling a great number of uniform and minute perforations to be obtained in the non-porous surface layer of the sheet material. Additionally, because of the higher electrical conductivity obtained in accordance with the present invention, the initial discharge voltage of the electrical discharge can be decreased thereby enabling finer and more uniform perforations to be obtained.

It .is considered preferable to employ an aqueous electrolytic solution in accordance with the present invention 'since the electrical conductivity of said solution is far higher than that obtained by simply impregnating the porous base layer with water. However, it has been found quite convenient to employ plain water. Even ordinary tap water can be employed successfully to impart excellent moisture penneability to the sheet material. In the absence of impregnation with an aqueous medium in accordance with the present invention, electrical discharge of sheet material of the type disclosed herein. fails to impart numerous and uniform perforations to the non-porous surface layer.

The sheet material of the present invention may be impregnated by any convenient method such as immersion, spraying, padding or the like with an aqueous medium. If desired, the sheet material can be impregnated by a combination of immersion and pressing. If desired the impregnation treatment can be affectively expedited by employing a higher temperature for the aqueous medium and/or employing a penetrating agent such as a surfactant.

The aqueous medium employed from impregnation of the base material can be ordinary tap water or water to which an electrolytic material has been added. Suitable electrolytic materials are acids such as hydrochloric acid, sulfuric acid, formic acid, trichloroacetic acid, acetic acid, and other acids; bases such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like, as well as salts such as sodium chloride, sodium sulfate, sodium carbonate, calcium chloride and the like. Preferably the salts which are employed exert no adverse hydrolytic effects on the polymers employed in the sheet material. The concentration of the electrolyte in the solution depends upon the electrolytic material employed. Generally, however, it is considered desirable that the concentration of the electrolytic material be at least about 1 percent by weight and can range up to the solubility limit of the particular electrolyte at the temperature at which the aqueous medium is employed, however, the concentration should be below that which would cause hydrolytic attack on the polymers employed in the sheet material. Since dilute electrolytic solutions are effective in the present invention and most economical, they are preferred. it is considered preferable that the prous base material be impregnated with the aqueous medium to the extent of at least about percent by weight.

In operation, the porous base layer of the sheet material is impregnated with an aqueous medium and placed on the grounded electrode of an electrode pair. The other electrode is employed to effect an electrical discharge through the nonporous surface of the sheet material. This latter electrode, i.e., the non-grounded electrode, can be of any convenient shape but is desirably in the form of a needle. The waveform of the voltage applied to the electrode pair can be selected as desired to give rise to a spark discharge. Preferably, the waveform is a rectangular or semi-rectangular waveform giving rise to a pulse spark discharge. The voltage, frequency and duration of discharge will vary depending upon the material being treated. By suitably selecting the voltage, frequency and pulse width with respect to a given material, the number, diameter and depth of the perforations imparted to the non-porous surface layer and the appearance thereof can be altered.

The porous base layer of the sheet material of the present invention comprises fibrous materials such as paper, woven fabric, non-woven cloth, knitted fabric and other similar fibrous materials. Also, the porous base layer can comprise said fibrous materials impregnated with a polymer to provide a porous and bulky base material. Further, the porous base material can consist of two layers namely a porous polymer layer obtained by impregnation of a fibrous material layer and a second fibrous material layer. Both of said layers can be additionally impregnated with a polymer to provide a porous and bulky structure. The porous base material exhibits a substantial degree of porosity and thus a high breakdown voltage. By

filling these pores with an aqueous medium in accordance with the present invention, the effective discharge distance to the non-porous surface layer is decreased thereby facilitating the electrical discharge. Moreover, the discharge is further facilitated by the enhanced electrical conduction afforded by the presence of the impregnated aqueous medium.

The non-porous surface layer to which improved moisture permeability is imparted in accordance with the electrical discharge process of the present invention adheres to the surface of the porous base material. This surface layer comprises a non-porous polymeric film generally having a thickness of from about 0.001 to about 0.05 centimeters. The non-porous surface layer is applied to the surface of the porous base material by spraying or coating a solution or dispersion of the polymer thereon or by bonding a preformed polymeric film thereto. The non-porous surface layer can also be prepared by partial dissolution and drying or partial melting and cooling of the surface of the porous polymer layer. The non-porous surface layer imparts an excellent surface appearance to the sheet material and also imparts excellent anti-scratch resistance thereto. Additionally, the resultant sheet material exhibits a good hand or feel due to interaction between the porous base material and non-porous surface layer.

The polymers of the porous base layer and the non-porous surface layer may be polyurethane elastomers, polyamides, polyesters, polyamino acid resins, polymethacrylates, polyvinyl chlorides, polyvinyl acetates, polyisoprenes, copolymers of butadiene and acrylonitrile. They may be used alone or in admixture with each other.

The electrical discharge process of the present invention imparts numerous uniform fine pores having diameters ranging from about 1 to about 100 microns to the non-porous surface layer of the sheet material. These fine pores are directly connected to the porous base material thereby improving the moisture permeability of the sheet material without deteriorating the appearance of the sheet material or its physical properties.

The sheet material of the present invention can be employed for many purposes wherein the excellent physical properties, appearance, touch, moisture permeability and the like can be used to advantage. For example, the sheet material of the present invention can be employed in the manufacture of shoes, boots, clothes, gloves, headgear and like wearing apparel, trunks, bags, furniture covering, interior decoration and the like. i

The following examples further define, describe and compare methods of preparing the improved sheet material of the present invention. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 An unwoven cloth of nylon fibers was impregnated with a polyurethane elastomer solution. The same polyurethane elastomer solution was further spread upon the impregnated cloth and the resulting cloth was then coagulated into a porous structure in a coagulation bath. After the coagulating liquid was 'washed out and the cloth dried, the surface of the resultant porous sheet base material was coated with a finishing solution consisting of the polyurethane elastomer to a thickness of microns and was then pressed by passage through rollers heated at 160 C. By applying a coating of the finishing solution and partially melting the porous polyurethane elastomer layer due to the pressing operation a operation, non-porous surface layer was formed about microns thick and was firmly bonded to the porous base. The resulting sheet material exhibited an improved appearance and enhanced physical properties; however, its moisture permeability dropped from 1,560 gm./m /day to 390 gm./m /day.

The above sheet material was then dipped in hot water at 80 C. and pressed and the dipping operation and pressing were repeated until the porous base material was thoroughly impregnated with water. The impregnated sheet material was placed on a grounded electrode plate. Rectangular wave pulses 2,100 volts, 1,000 Hz, 5 microseconds wide were applied to an electrode situated above the sheet material causing pulsating electrical discharges to be impressed upon the nonporous layer of the sheet material resulting in the formation of pores in said surface layer having an average diameter of about 35 microns and a pore density of about 104 pores per square centimeter. After the electrical discharge treatment, the sheet material was dried. The moisture permeability of the resultant product was raised to 930 gmJm lday without deteriorating the appearance or physical properties of the product.

For purposes of comparison, an identical sheet material which was not impregnated with water as described above failed to give rise to electrical discharge and perforation of the non-porous surface layer under the identical conditions described above.

EXAMPLE 2 A porous base material comprising a first layer of an unwoven cloth of nylon fibers impregnated with a polyurethane elastomer and a second layer bonded to said first layer comprising a porous polyurethane elastomer structure, was coated with a non-porous film consisting of polyurethane elastomer having a thickness of 14 microns forming a sheet material exhibiting excellent appearance, physical properties and touch.

The resulting sheet material was subjected to repeated pressing in water containing 1 weight percent of a nonionic surfactant at 50 C. for thorough impregnation. The thus treated material was placed on a grounded electrode plate. Electrical pulses 1,500 volts, 1,000 Hz, 50 microseconds wide were applied to an electrode situated above the sheet material thereby subjecting the surface layer thereof to pulse discharges giving rise to the formation of perforations in said surface layer. Thereafter the sheet material was washed and dried. Numerous uniform pores having an average diameter of about 25 microns were formed in the surface layer at a pore density of about 842 pores per square centimeter. The moisture permeability of the sheet material was increased from 410 gm./m /day prior to treatment to 1,850 gm./m /day after treatment without in any way impairing the appearance, touch, or other physical properties of the sheet material.

For purposes of comparison, the identical sheet material was not impregnated with water and was found not to undergo electrical discharge or the generation of perforations in the surface layers thereof under the identical conditions.

EXAMPLE 3 A sheet of unwoven cloth of nylon fibers was impregnated with a polyurethane elastomer solution and was then overcoated with the polyurethane elastomer solution and coagulated in a coagulation bath to form a porous structure. After removing the coagulating liquid and drying, a porous base material was obtained. The resultant base material was coated with a finishing solution of polyurethane elastomer to a thickness of 5 microns and the resultant sheet material was pressed by being passed through heated rolls maintained at C. Through application of the finishing solution and partial melting of the surface of the porous polyurethane elastomer layer, a beautiful non-porous surface layer about 20 microns thick was obtained exhibiting improved appearance and physical properties. The moisture permeability of the product however decreased from 1560 gm./m /day to 390 gm./m /day.

The resulting sheet material was immersed in a 5 percent by weight aqueous solution of sodium chloride at 70 C. and was repeatedly pressed therein to thoroughly impregnate the porous base layer of the sheet material with said solution. Thereafter the impregnated sheet material was placed on a grounded electrode plate and rectangular wave pulses 2,000 volts, 1,000 Hz, 10 microseconds wide were impressed upon an electrode situated above the sheet material giving rise to an electrical discharge through the surface layer resulting in formation of numerous perforations in said surface layer. Thereafter the sheet material was washed with water and dried. The resulting product exhibited numerous uniform perforations in the surface layer thereof having an average diameter of about 10 microns, and an average pore density of about 1,420 perforations per square centimeter. The moisture permeability of the resulting product was found to be 1,190 gm./m /day as compared to 390 gm./m /day for the untreated material. The appearance and other physical properties of the sheet material were not impaired by the electrical discharge treatment.

For purposes of comparison, sheet material of the type described above was impregnated with water and subjected to electrical discharge under the same conditions as described hereinabove. The moisture permeability of the resulting product was increased to 730 gm./m /day.

EXAMPLE 4 A porous base material comprising a first layer of unwoven cloth of nylon fibers impregnated with a polyurethane elastomer and a second layer bonded thereto comprising a porous polyurethane elastomer structure was surface coated with a non-porous film of polyurethane elastomer 4 microns thick to produce a sheet material exhibiting an excellent appearance, physical properties and touch.

This sheet material was thoroughly immersed in a 5 percent weight aqueous solution of sodium sulfate at 70 C. with repeated pressing.

The impregnated sheet material was placed on a grounded electrode plate and rectangular wave pulses, 2,000 volts, 1,000 Hz, 7 microseconds wide were applied to an electrode situated above the sheet material giving rise to electrical discharges through the surface layer of the sheet material. The resultant material was washed and dried and found to exhibit numerous minute perforations in the surface layer thereof having an average diameter of 34 microns and an average pore density of about 312 pores per square centimeter. The moisture permeability of the resultant product was increased from 410 gm./m /day before treatment to 1,390 gmJm lday after treatment without impairing the appearance, touch and other physical properties of the sheet material.

What is claimed is:

1. Method of imparting moisture permeability to a sheet material having a porous base exhibiting a high breakdown voltage and a non-porous surface layer comprising impregnating the pores within the porous base with an aqueous medium to increase the electrical conductivity of said porous base, placing the impregnated sheet material between an electrode pair, subjecting the impregnated sheet material to electrical discharge between said electrode pair, thereby forming a plurality of perforations in said non-porous surface layer, and recovering the sheet material exhibiting enhanced moisture permeability.

2. Method as defined in claim 1 wherein the aqueous medium is water.

Method as defined in claim 2 wherein said water additionally contains a surfactant.

4. Method as defined in claim 1 wherein the aqueous medium is an aqueous electrolytic solution.

5. Method as defined in claim 4 wherein the electrolytic solution contains an electrolyte in the amount of at least about 1 weight percent up to about the solubility limit of the electrolyte in water at the temperature of impregnation.

6. Method as defined in claim 1 wherein the sheet material is impregnated by immersion in said aqueous medium and pressing of said sheet material thereby thoroughly impregnating the porous base of such sheet material with said aqueous medium.

7. Method as defined in claim 6 wherein the sheet material is immersed in the aqueous medium and pressed until the porous base has been impregnated with at least about weight percent of the aqueous medium.

8. Method as defined in claim 1 wherein a rectangular wave form electrical pulse is applied to one of the electrodes of said electrode pair.

9. Method as defined in claim 1 wherein the electrical discharge is a pulse spark discharge.

10. Method as defined in claim 1 wherein the porous base material is a fibrous material impre nated with a polymer.

11. Method as defined in claim 0 wherein the polymer is a polyurethane elastomer.

12. Method as defined in claim 1 wherein the non-porous surface layer is of a thickness ranging from about 0.001 to about 0.05 centimeters.

13. Method as defined in claim 1 wherein the perforations formed in the non-porous surface layer after electrical discharge range in diameter from about 1 to about microns.

14. Method as defined in claim 2 wherein the treated sheet is recovered by drying.

15. Method as defined in claim 4 wherein the treated sheet material is recovered by washing the subsequent drying.

16. Method as defined in claim 1 wherein the porous base material comprises a first layer of a fibrous material impregnated with a polymer and a second layer of fibrous material.

17. Method as defined in claim 16 wherein the polymer is a polyurethane elastomer.

18. Method as defined in claim 16 wherein said first and second layers are additionally impregnated with a polymer.

19. Method as defined in claim 18 wherein the polymer is a polyurethane elastomer.

Claims

2. Method as defined in claim 1 wherein the aqueous medium is water. Method as defined in claim 2 wherein said water additionally contains a surfactant.
4. Method as defined in claim 1 wherein the aqueous medium is an aqueous electrolytic solution.
5. Method as defined in claim 4 wherein the electrolytic solution contains an electrolyte in the amount of at least about 1 weight percent up to about the solubility limit of the electrolyte in water at the temperature of impregnation.
6. Method as defined in claim 1 wherein the sheet material is impregnated by immersion in said aqueous medium and pressing of said sheet material thereby thoroughly impregnating the porous base of such sheet material with said aqueous medium.
7. Method as defined in claim 6 wherein the sheet material is immersed in the aqueous medium and pressed until the porous base has been impregnated with at least about 80 weight percent of the aqueous medium.
8. Method as defined in claim 1 wherein a rectangular wave form electrical pulse is applied to one of the electrodes of said electrode pair.
9. Method as defined in claim 1 wherein the electrical discharge is a pulse spark discharge.
10. Method as defined in claim 1 wherein the porous base material is a fibrous material impregnated with a polymer.
11. Method as defined in claim 10 wherein the polymer is a polyurethane elastomer.
12. Method as defined in claim 1 wherein the non-porous surface layer is of a thickness ranging from about 0.001 to about 0.05 centimeters.
13. Method as defined in claim 1 wherein the perforations formed in the non-porous surface layer after electrical discharge range in diameter from about 1 to about 100 microns.
14. Method as defined in claim 2 wherein the treated sheet is recovered by drying.
15. Method as defined in claim 4 wherein the treated sheet material is recovered by washing the subsequent drying.
16. Method as defined in claim 1 wherein the porous base material comprises a first layer of a fibrous material impregnated with a polymer and a second layer of fibrous material.
17. Method as defined in claim 16 wherein the polymer is a polyurethane elastomer.
18. Method as defined in claim 16 wherein said first and second layers are additionally impregnated with a polymer.
19. Method as defined in claim 18 wherein the polymer is a polyurethane elastomer.