JPS6164735A - Production of porous sheet - Google Patents

Abstract

PURPOSE:To obtain easily the titled sheet having excellent surface smoothness with a miniaturized apparatus, by impregnating a cloth with a soln. of an elastomeric polymer, coagulating the surface layer of the cloth with a specified soln. and immersing it in a coagulating bath. CONSTITUTION:A cloth such as nonwoven fabric made of nylon/polystyrene blended yarn is impregnated with a soln. of an elastomeric polymer such as a soln. of a polyurethane elastomer composed of a chain extender such as polyethylene adipate glycol having an MW of 500-4,000 and a diisocyanate compd. such as tolylene diisocyanate dissolved in a solvent such as dimethylformamide. A coagulating soln. which is non-affinitive with said elastomeric polymer, but affinitive with said soln. of said polymer, such as water or an aq. soln. of not more than 50wt% dimethylformamide is sprayed on at least one side of the impregnated cloth in a spraying amount of 1-100l/m<2> of cloth to thereby coagulate the surface layer thereof. The cloth is then immersed in a coagulating bath such as an aq. soln. of 20-60wt% dimethylformamide at 20-70 deg.C to complete coagulation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a porous notebook with excellent surface smoothness.

BACKGROUND ART Conventionally, a method of impregnating a fabric with a solution of an elastic polymer and wet-coagulating it to obtain a porous sheet has been widely practiced in the fields of moisture-permeable waterproof notebooks and artificial leather. As a wet coagulation method, generally used is a method in which a fabric impregnated with an elastic polymer solution is immediately immersed in a coagulation bath and coagulated.

However, when this method is used, extreme irregularities occur on the surface of the normally obtained porous sheet. The cause of this unevenness is not necessarily clear, but it is caused by a combination of factors such as the flow and buoyancy of the coagulating liquid when immersed in the coagulating bath, and the contact of the surface with rolls, guides, etc. before solidifying in the coagulating bath. It is thought that this is the case. If there are irregularities on the surface of the resulting porous sheet, the surface must be ground to eliminate the irregularities, or a thick polymer layer must be laminated on the surface to hide the irregularities. However, the process is inevitably complicated.The present invention provides a porous material with extremely excellent surface smoothness, which eliminates the need to grind or provide a polymer layer to hide surface irregularities as in conventional methods. A sheet material is obtained by wet coagulation. That is, the present invention provides a method for manufacturing a porous sheet by impregnating a fabric with an elastomeric polymer solution and coagulating the elastomeric polymer by a wet coagulation method. After coagulating the surface layer of the fabric by flowing a liquid that has no affinity with the elastic polymer but with the solvent of the bath liquid on one side, the fabric is immersed in a coagulation bath to coagulate. This method of manufacturing porous sheet products is characterized by completing the following steps: This eliminates the need for extremely complicated processing as in conventional methods.

More specifically, in the present invention, before immersion in a coagulation bath, a coagulation liquid is poured onto the surface of a fabric soaked with an elastic polymer bath liquid to coagulate the surface layer. Suitable methods for applying the coagulating liquid include a shower method, a casting method, and a spray method. The amount applied is 1 to 10 per 1 rIl on one side of the sheet.
0j, but especially 10-50! is preferred.

As the coagulating liquid used to flow onto the light surface of the sheet, it is preferable to use a liquid with strong coagulating power.

When the elastic polymer solution is composed of a polymer mainly composed of polyurethane elastomer and a solvent mainly composed of dimethylformamide, water or an aqueous dimethylformamide solution having a # degree of 50% by weight or less is suitable. If the concentration of dimethylformamide exceeds 50 M%, coagulation will be delayed and the surface layer will often have to be immersed in the coagulation bath in a semi-solidified state, and there is a concern that an uneven surface will occur.

In addition, for the subsequent immersion coagulation treatment, concentration 2, which has relatively weak coagulation power, is used.
The purpose of the application is to form porosity inside the sheet using a dimethylformamide aqueous solution containing 0 to 60% by weight at a temperature of 20 to 70°C, which is the uniform porosity required for artificial leather, moisture-permeable waterproof sheets, etc. This is preferable in that a structure can be obtained.

As described above, by coagulating only the outermost surface of the sheet before immersing it in a coagulation bath, it is no longer necessary to perform slicing or puffing as in the conventional method.

Further additional advantages of the method of the invention include that the coagulation bath can be made smaller and the amount of liquid used for coagulation can be significantly reduced.

In other words, by applying a liquid with a strong coagulation effect to both sides of the sheet impregnated with an elastic polymer and solidifying only those surfaces, the next step of immersion coagulation treatment is performed using a large number of guides on the left and right sides or top and bottom of the tank. It becomes possible to use a compact tank equipment with rolls and compressed cloth, and the amount of liquid can be greatly reduced.

The fabrics used in the present invention include single spun fibers such as rayon, nylon, polyester, vinylon, and polyolefin, or knitted fabrics made of mixed spun fibers or composite spun fibers of nylon, polyester, polypropylene, etc., and polystyrene, polyethylene, etc. , woven fabric, or non-woven fabric.

Next, as the elastic polymer used for impregnation, any polymer that can be wet-coagulated can be used, but polyurethane elastomer is used for -e. Examples of the polyurethane elastomer include polyethylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyethylene adipate glycol, polybutylene adipate glycol, polyhexamethylene adipate glycol, polycaprolactone glycol, etc., and ethylene glycol with a molecular weight of 500 to 4000. Chain extenders such as butanediol, hexanediol, ethanolamine, hydrazine, 4,4'-methylenebis-2-chloroaniline and diphenylmethane-4,
4'-diisocyanate, tolylene diisocyanate,
A typical example is one consisting of a diisocyanate compound such as hexamethylene diinocyanate. Furthermore, other polymers compatible with these polyurethane elastomers in a solution state can also be used in combination.

Note that fillers, pigments, softeners, coagulation regulators, stabilizers, and the like may be added to the elastic polymer liquid.

Any liquid with good solubility can be used as the solvent for the elastic polymer. For example, when the elastic polymer is a polyurethane elastomer, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dioxane, or a mixed solvent thereof is used.

In addition, the liquid that has a coagulating effect on the elastic polymer solution is a liquid that is a low or poor bath for the elastic polymer and is easily soluble in the solvent of the elastic polymer. All can be used. For example, in the case of polyurethane elastomer, water, alcohol, acetone, etc. are used, but mixtures of these with dimethylformamide etc. can also be used. In the method of the present invention, the operation of flowing a coagulating liquid onto the surface of the sheet to solidify the cinnabar layer may be performed on one line of the sheet or on both sides.

The present invention will be specifically explained below using Examples.

Example 1 Nitrogen content based on polyethylene acylate glycol, ethylene glycol and diiso/anate made of diphenylmethane-4,4'-diincyanate is 4.0
% by weight of polyurethane distomer was made. Next, a nonwoven fabric made of nylon-polystyrene mixed spun fibers was impregnated with 20% by weight of the polyurethane elastomer-dimethylformamide solution containing a small amount of a coagulation regulator at a weight ratio of 4:1. After impregnation, excess impregnating liquid adhering to the surface of the sheet was removed by draining with a draining rod to obtain a smooth surface. Next, shower water only on the back side of the sheet for 10 minutes.
The impregnated polyurethane disstomer liquid on this surface was coagulated by spraying at a ratio of J/♂. Thereafter, the sheet was slowly solidified in a coagulation bath with a small number of guide rolls in which the sheet moved horizontally.

The concentration of the coagulation bath at this time was 401! L quantity, temperature 38℃
The residence time of the sheet was 10 minutes. The sheet is further entered into a second stage coagulation bath to complete coagulation, and then washed with hot water to remove dimethylformamide, extracting and removing polystyrene from the nylon-polystyrene mixed spun fibers, and forming a porous layer with good surface smoothness. A quality sheet material was obtained.

The back surface of this sorted material had no irregularities and could be used as a commercial product as it was, so slicing or puffing to smooth the back surface was unnecessary.

Comparative Example 1 A porous sheet material was prepared in the same manner as in Example 1, but without water shower treatment, but the resulting material had severe irregularities on both sides, especially on the back side. Since it is not commercially viable in this state, we performed a slicing process to remove the uneven surface.

Example 2 A nonwoven fabric was impregnated with a polyurethane disstomer liquid in the same manner as in Example 1, and the excess impregnating liquid applied to the back surface was drained off using a draining rod to form a smooth surface.

Next, a dimethylformamide aqueous solution having a degree of σ of 40: mm % was sprayed onto the back surface of the sheet at a rate of 30 t/♂ to solidify the impregnated polyurethane elastomer liquid on this surface. After that, the sheet is guided to a neat roller, and a 15% polyurethane elastomer coating of the same composition is cast on the surface on a coat roller, and the sheet is placed in a coagulation bath as it is, peeled off from the coat roller in the bath, and further coagulated. The coagulation bath conditions were the same as in Example 1. Subsequently, the processes after solidification were carried out under the same conditions as in Example 1 to obtain a porous sheet material having a coating layer on the surface and a smooth back surface.

Comparative Example 2 A porous sheet material was produced using the same method as in Example 2, except for shower treatment with an aqueous dimethylformamide solution without rLX Ilm, but the back surface was extremely uneven.

Example 3 A porous sorted material was left in the same manner as in Example 1, but the water spray treatment applied each IAl to both the front and back sides of the sheet.
d to coagulate only the outermost surface of each sheet.Then, the sheet was guided into a coagulation bath which had a large number of guide rolls on the left and right sides of the tank and had a compact blood vessel, and was slowly coagulated. Note that the coagulation bath conditions are the same as in Example 1. Subsequently, the treatments after solidification were carried out under the same conditions as in Example 1 to obtain a porous sheet material with good surface smoothness similar to that in Example 1.

Patent applicant RiRashi Co., Ltd. Acting Patent Attorney Ken Honda

Claims (1)

[Claims] When producing a porous sheet by impregnating a fabric with an elastic polymer solution and coagulating the elastic polymer by a wet coagulation method, at least one side of the fabric impregnated with the elastic polymer solution,
After coagulating the surface layer of the fabric by flowing a liquid that has no affinity with the elastic polymer but has an affinity with the solvent of the solution, the fabric is immersed in a coagulation bath to complete coagulation. A method for producing a porous sheet product characterized by: