JPS5813573B2 - Manufacturing method for the standard - Google Patents

Description

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS The present invention relates to a method for producing a porous sheet that is free of bends, is strong, and has excellent flexibility.

Conventionally, one method for producing a flexible fiber-bonded sheet has been to provide a gap between the fibers and the binder in the sheet structure, thereby allowing the fibers themselves to move freely to a certain extent, thereby imparting flexibility. Numerous techniques have been proposed, for example, in Japanese Patent Publications 44-21835, 45-1943, 47-21275, and 48-28043.

That is, this is accomplished by pretreating the fibrous base material with a water-soluble polymer, followed by application of a binder, coagulation or drying, and then extraction of the water-soluble polymer.

In these conventional methods, the extractant is a water-soluble polymer such as polyvinyl alcohol, carboxymethyl cellulose, polyethylene oxide, or polyacrylamide, while the main binder is in most cases a water-miscible organic solvent solution of polyurethane, synthetic rubber, polyacrylate, or the like.

The reason for this is that the extracted substances are water-soluble, and if an aqueous binder is used, the water-soluble polymer that has already been attached during the impregnation process will easily dissolve due to the moisture in the binder liquid and disperse from the fiber surface into the binder liquid, which will not only increase the binder viscosity and cause problems during impregnation, but will also fail to achieve the desired objective.

Therefore, when using an aqueous binder, the extractable substances are:
This involves using a synthetic resin, such as polyvinyl acetate or polyvinyl chloride, which is insoluble in water but soluble in an organic solvent, and then extracting and removing the residue with an organic solvent, such as methanol or ethyl acetate, as a post-treatment.

However, these processes require organic solvents, which require special care in handling due to their toxicity, flammability, etc., and therefore have drawbacks in terms of workability and productivity.

On the other hand, in order to increase the pore-forming effect by such extraction, a fairly large amount of the extractant is required, and is usually attached in a weight of about 15% to 30% of the weight of the fibrous substrate. This is not only economically disadvantageous, but also causes a decrease in productivity because the substrate treated with a large amount of the extractant has a significantly impaired permeability in the subsequent binder impregnation process and the final extraction process requires a very long time.

Therefore, the present inventors have conducted extensive research into the extraction substances used in this technology, and as a result have discovered that an aqueous solution of a water-soluble alginate or carboxyalkylcellulose salt (hereinafter, these may be referred to as a gelling polymer) or the like instantly undergoes a cation exchange reaction with an electrolyte solution such as an acid or a polyvalent metal salt to produce a polymer jelly that is insoluble in water and almost all organic solvents, and that this insoluble polymer jelly and the product obtained by further drying this (hereinafter, this will be referred to as a polymer xerogel.

Moreover, the polymer jelly and polymer xerogel are sometimes collectively called insoluble polymers.

) can be converted back to the original water-soluble polymer by a cation exchange reaction. By making good use of this, all of the drawbacks of the above-mentioned prior art are resolved, and many other advantages are found.
The present invention provides a method for producing a flexible porous sheet that satisfies all of the requirements for productivity, workability, economy, etc.

That is, the present invention is characterized by comprising a first step of impregnating a fibrous substrate with a dilute aqueous solution of a water-soluble alginate or carboxyalkylcellulose salt, etc.; a second step of instantly converting the applied aqueous polymer solution into a water-insoluble polymer jelly, and if necessary, further drying this to convert it into an insoluble polymer xerogel; a third step of impregnating the substrate with a binder and fixing it; and a fourth step of converting the insoluble polymer back into a water-soluble form and extracting and removing it.

In the present invention, the soluble-insoluble reversible polymer jelly used as the extraction material is, for example, agar, gelatin, etc.
It is a solid that contains 9% water, in other words, it is a solid with an enormous volume even at an extremely low concentration.

Furthermore, the polymer xerogel obtained by drying this polymer jelly has a much larger volume than that obtained by simply drying a polymer aqueous solution without gelling it as in the past. This is also evident when one considers the original dried product of agar.

The insoluble polymer jelly used as the extraction material in the present invention can be produced, for example, as follows.

In other words, by subjecting a dilute aqueous solution of alginic acid soda or ammonium salt to a treatment such as immersion or spraying in an electrolyte solution such as a dilute aqueous acid solution of sulfuric acid or hydrochloric acid, or an aqueous solution of a polyvalent metal salt such as calcium chloride, zinc sulfate or aluminum sulfate, a polymer jelly that is insoluble in water and almost all organic solvents can be obtained instantly and easily.

Similarly, carboxyalkylcellulose salts, e.g.,
In the case of soda salts of carboxymethyl cellulose, carboxyethyl cellulose, etc., it is advisable to use an aqueous solution of a trivalent metal salt, such as aluminum sulfate or aluminum nitrate, as the treatment electrolyte solution.

Both of these gelling reactions are so-called cation exchange reactions of metal ions of carboxyl groups, and it is believed that in the above-mentioned aqueous polymer solution, the polymer becomes three-dimensional when it comes into contact with hydrogen ions or polyvalent metal ions, and water is trapped within this three-dimensional network to become solid-phase water (jelly).

Therefore, it is completely different from the dehydration and coagulation of an aqueous polyvinyl alcohol solution or an aqueous viscose alkali solution with an aqueous sodium sulfate solution, or the coagulation of sodium polyacrylate as a trivalent salt, and the present invention would not be achieved at all if these were used as extraction substances.

On the other hand, when the insoluble polymer of the present invention is treated with an aqueous solution containing, for example, an alkali metal ion such as sodium or potassium ion or an ammonium ion, a cation exchange reaction or a complex ion formation reaction, which is the reverse of the previous gelling reaction, occurs instantly, so that the insoluble polymer can be restored to water-solubility again and can be easily extracted and removed by washing with water.

Specifically, for example, an insoluble polymer such as calcium alginate is treated with a 5 to 10% aqueous solution of sodium carbonate, and ion-exchange is carried out between calcium and soda, thereby changing it into a water-soluble polymer such as sodium alginate.

As described above, the present invention has many advantages since it utilizes a soluble/insoluble reversible polymer jelly or polymer xerogel as an extraction material, as follows:

First, the insoluble polymer that is the extract of the present invention is
Even though the solid content is very small, the volume is very large.
In the first step, the amount of the compound that needs to be attached to the fibrous base material is extremely small, which is economical.

Secondly, the polymer jelly, which is the extracted substance, is instantly and firmly fixed inside the fibrous base material in the second step, and the water in the jelly does not leak out at all. Therefore, no deformation occurs even when subjected to stress during subsequent steps such as squeezing and impregnation of the base material up to the fourth step, which contributes to improved workability and quality reproducibility.

Furthermore, when this is dried to form a polymer xerogel, it is clear that migration during drying cannot occur.

Thirdly, since the extracted substances, polymer jelly and polymer xerogel, are insoluble in water and almost all organic solvents, not only the conventionally used organic solvent-based binders but also water-based binders such as latex type and emulsion type, which have hardly been used until now, can be widely used as the fiber binder to be impregnated in the third step. This results in significant improvements in productivity, workability and economy, and at the same time makes it possible to manufacture a wide variety of distinctive products.

Fourth, the fibrous substrate with the polymer xerogel attached thereto obtained by drying in the second step has significantly improved liquid absorption properties due to the synergistic effect of the microporosity resulting from the three-dimensional mesh molecular structure of the polymer xerogel itself and the macroporosity resulting from the capillary structure that occurs between the polymer xerogel and the constituent fibers, and therefore the permeability of the binder and treatment liquid of the third step into the substrate is greatly increased.

In this case, the binder penetrates into the micropores of the polymer xerogel, and when the final product after extraction is observed, it is found that, compared to a product extracted as a polymer jelly, the binder is arranged in a fine mesh around the fibers, resulting in a porous sheet with very fine voids.

Fifth, and this is extremely important in the present invention, the polymer jelly which is the extraction substance contains a large amount of water, usually more than 95%, so if the binder solution applied in the third step uses water as a non-solvent, the binder impregnated in the fibrous base material will come into contact with the already attached polymer jelly and will be solidified near the surface of the polymer jelly by the moisture.

In this case, since the water in the polymer jelly cannot be discharged by mechanical stress, the binder solidifies over time after the binder is completely impregnated into the substrate.

That is, the binder never solidifies before penetrating into the substrate.

On the other hand, such polymer jellies and polymer xerogels contain polyvalent metals in their molecules as described above, and easily cause ion exchange reactions.

For example, if an anionic latex or emulsion containing an alkali metal ion such as sodium or potassium is used as a binder, after impregnation in the same manner as above, a cation exchange reaction occurs between the polyvalent metal of the already attached insoluble polymer and the alkali metal in the binder, and the polyvalent metal ion is liberated, causing the binder latex or emulsion to coagulate.

In this way, since the binder can be solidified by solvent-non-solvent replacement in the former case, and by an ion exchange reaction in the latter case, a binder solidification step is not necessarily required in the third step, and no migration of the binder will occur even if the mixture is dried as is.

Furthermore, the solidification of the binder weakens the adhesive force between the binder and the insoluble polymer or the constituent fibers, improving the extractability of the insoluble polymer in the fourth step and at the same time giving the resulting fibrous sheet excellent flexibility.

Next, each step of the present invention will be described.

In the first step, the fibrous base material which is the raw material layer is made of woven fabric, knitted fabric, felt, or nonwoven fleece produced by carding or air laying, etc., made of natural fibers, synthetic fibers or a mixture of these fibers.

First, a dilute aqueous solution of a gelling polymer such as sodium alginate or carboxymethyl cellulose is impregnated or sprayed in liquid or foam form onto a fibrous substrate. The form in which the gelling polymer aqueous solution is applied is as follows:
The fibers may be distributed uniformly within the fibrous base material or may have a density gradient with more fibers being distributed on one or both sides of the base material.

In the former case, the resulting porous sheet will have a uniform distribution of binder throughout, whereas in the latter case, the binder will be more highly distributed on one side or within the substrate, resulting in a wider variety of porous sheet products.

The aqueous solution of the gelling polymer is usually used at a concentration of 0.5% to 5%, but this can be adjusted appropriately depending on the viscosity of the solution and the amount of adhesion.

In addition, the amount of the adhesive to be applied to the fibrous substrate has conventionally been required to be as large as 15% to 40% in terms of solid fraction, but in the present invention, 0.2% to 15% is sufficient, and preferably 1.
A range of 10% to 15% is preferable.

In the second step, the aqueous solution of the gelling polymer previously applied to the fibrous substrate is gelled. This is done by adding 1% to 10% of the electrolytes such as dilute acids and polyvalent metal salts as described above.
% aqueous solution or by spraying it thereon, it is instantly transformed into an insoluble jelly, and the excess electrolyte solution is squeezed out, followed by washing with water if necessary.

The gelling treatment time can be effective even for a few seconds, but taking into consideration the stabilization of quality, productivity, etc., a time of about 10 to 50 seconds is appropriate.

If necessary, this can be further dried to obtain a fibrous base material having a polymeric permeable gel attached thereto, which is more preferable since the permeability of the binder in the third step is improved.

Next, in the first step of the third process, the fibrous base material is impregnated with a binder, which acts as the main binder for binding the material. As long as the binder itself is not extremely hard, most binders normally used for nonwoven fabrics can be used.

For example, solvent solution types of natural rubber, chloroprene, NBR, SBR, ethylene-vinyl acetate copolymer, polyacrylate, plasticized polyvinyl chloride, polyamide, polyurethane, etc., or aqueous dispersion types of these latexes, dispersions, etc. may be used.

Now, the required amount of the binder is applied to the fibrous base material that has been subjected to the second step by a conventionally known method such as impregnation, spraying or coating, and then the binder is fixed. The fixing method can be a method of drying the material as it is, or a method of first solidifying the binder.

Methods for solidifying the binder include well-known heat-sensitive solidification methods and wet solidification methods, and can be appropriately selected depending on the type of binder.

As mentioned above, if the binder solidifies due to the insoluble polymer that is the extract, the quality will be quite satisfactory even if you dry it as is. If not, however, it is better to go through a post-treatment process to solidify the binder.
A flexible sheet is obtained.

Now, in the final fourth step, the fibrous base material to which the insoluble polymeric substance and binder have been fixed is treated with a solubilizing liquid which is inactive to the constituent fibers and binder but which makes the insoluble polymer soluble in water, and then the base material is squeezed and washed with water or hot water to extract and remove the insoluble polymer from the base material, with the aim of creating many voids inside the base material.

For the solubilization treatment, for example, a 5% to 10% aqueous solution of table salt, sodium carbonate, sodium citrate, ammonia, or the like is suitable, and the solubilization treatment is accomplished by impregnating or spraying the substrate with such a solubilizing solution.

The treatment time is approximately the same as the gelling time in the second step, but is preferably from 15 seconds to 1 minute.

As an advantageous method, when a binder coagulation step is carried out in the third step, it is preferable to mix the above-mentioned solubilizing liquid into a binder coagulation bath, and simultaneously carry out binder coagulation and solubilization of the insoluble polymer.

In this case, the third step and the beginning of the fourth step are carried out simultaneously in one step.

The fibrous sheet obtained through the above-mentioned processes has almost no direct bonding between the fibers and the binder and has numerous voids inside the sheet, so that it has a very flexible, strong porous structure that is breathable, hygroscopic, etc., and is ideal as a base fabric for cloths such as wiping cloths and tablecloths, or as a base fabric for artificial leather and synthetic leather for shoes, bags, furniture, etc.

The present invention will be described in more detail below with reference to examples.

Example 1 A random fleece made of 3 denier nylon stable fiber having a length of 51 mm was subjected to two-dollar punching at a needle density of 200 needles/cm to obtain a two-dollar felt having a weight of 200 g/d.

Next, sodium alginate (Datsuk algin NSPH2
The above-mentioned Nidol felt was uniformly impregnated with a 1% aqueous solution of 1% cellulose acetate (manufactured by Kamogawa Chemical Industry Co., Ltd.) to give a solid content of 3% to the Nidol felt.

This impregnated substrate was immersed in a 5% aqueous solution of calcium chloride for 30 seconds, whereby the adhering aqueous solution of sodium alginate was immediately converted into calcium alginate jelly, which was then fixed to the fibers.

After washing with water and squeezing, the fabric was immediately impregnated with a heat-sensitive compounded composition of NBR latex without drying, and the fiber/binder ratio was adjusted to 60/40 in terms of solid content.

This was placed in a 150°C oven for 1 minute to heat-solidify the binder, and then immersed in an 8% aqueous solution of sodium carbonate for 1 minute to replace the calcium alginate components in the base material with sodium alginate, and then this was squeezed with 50°C hot water to completely extract and remove it.

The nonwoven fabric sheet thus obtained had a porous structure with good air permeability and with almost no substantial bonding between the fibers and the binder, and had a very soft feel.

Example 2: A 21-dollar felt of the same composition as in Example 1 (weight 150 g) was used.
A zinc alginate jelly was fixed to the inside of a Nidol felt by uniformly impregnating the same with a 1% aqueous solution of sodium alginate and then spraying a 5% aqueous solution of sodium nitrate.

After washing with water and drying, it was found that 8% of the needle felt had adhering lead alginate.

Next, the fibers were impregnated with a binder latex compound liquid having the following composition so that the fiber/binder ratio was 55/45.

This was immediately dried at 150°C for 5 minutes, and then the alginic acid was extracted and removed in the same manner as in Example 1.The resulting nonwoven fabric sheet was a uniformly colored, flexible, porous sheet with adhesive and welding properties, and showed no binder migration phenomenon, despite the binder latex having been dried at high temperature.

Example 3 60% 1.5 denier 51 mm long nylon fiber and 3
A fiber fleece consisting of 40% polyester fiber having a denier of 64 mm was subjected to needle-driving at a needle density of 180 needles/crA to obtain a needle felt having a weight of 180 g/m2.

To this, carboxymethylcellulose (Cellogen PR,
A 2% aqueous solution of aluminum nitrate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was applied to one side of the above-mentioned 21-dollar felt so that one side was impregnated with more aluminum nitrate, and then both sides were sprayed with a 3% aqueous solution of aluminum carboxymethyl cellulose, which immediately transformed the felt into a jelly made of aluminum carboxymethyl cellulose.

Next, after squeezing the fiber, the fiber was impregnated with a 12% dimethylformamide solution of one-liquid polyurethane (Crisbon 7667EL, manufactured by Dainippon Ink Co., Ltd.) as a binder, so that the fiber/binder ratio was 65/35.

This was then immersed in a 10% aqueous solution of sodium carbonate to simultaneously coagulate the polyurethane binder and solubilize the extractable substances, and then thoroughly washed with water to completely extract and remove DMF and the extractable substances.

After drying, the surface on which the extract was more adhered in the first step was buffed to obtain a soft and strong napped porous sheet.

Claims (1)

[Claims] 1. A process for impregnating a fibrous substrate with an aqueous solution of a water-soluble polymer that becomes jelly-like when insolubilized, and a process for converting the applied aqueous polymer solution into a water-insoluble polymer jelly.
A method for producing a flexible porous sheet, comprising the steps of: impregnating a sheet with a binder and fixing the binder; converting the water-insoluble polymer back into a water-soluble polymer; and extracting and removing the water-soluble polymer.