JPS6235514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for uniformly applying an emulsion to the inner layer of a sheet-like article (emulsion herein includes liquid-liquid, liquid-solid and intermediate systems).

In recent years, various resins have been added to sheet materials,
Its use as a composite material has become very widespread. A typical example is so-called artificial leather. In these cases, the resin applied is often a viscoelastic substance such as polyurethane. These resins may be applied in the form of a solution or in the form of an emulsion. In the case of a solution,
A desolvation step is inevitably required. However, polymer solvents are often highly flammable or highly toxic substances. Therefore, in order to prevent fire and toxicity hazards, great care must be taken when recovering the solvent, resulting in very high costs. Due to these various problems, various studies have been carried out to shift from solution-based to emulsion-based systems, but in the case of emulsion-based systems, it is difficult for the emulsion to adhere uniformly to the sheet.
There was a big drawback. That is, when a sheet material was impregnated with an emulsion and dried, a phenomenon was observed in which particles dispersed in the medium migrated during drying and adhered intensively to the surface of the sheet.

If the emulsion cannot be uniformly applied to the inner layer of the sheet, it will not only have a significant negative impact on the physical properties (e.g. strength, elongation, flexibility, etc.), texture, quality, etc. of the sheet, but also the processability of the sheet. may also cause serious problems. For example, when making suede-like artificial leather by brushing sheets,
If a large amount of emulsion adheres to the surface, the naps may become uneven in length or become tangled, making it impossible to obtain a nap of good quality. In order to uniformly apply the emulsion to the inner layer of the sheet-like material, a substance called a migration inhibitor is used. However, the current situation is that this has little effect and is not a fundamental solution. A method of rapidly freezing the emulsion-applied sheet and then drying it is also known, but freeze-drying is extremely expensive, which is too great a disadvantage for industrialization.

On the other hand, a method in which a sheet material impregnated with emulsion up to its inner layer is directly coagulated in a liquid bath is not generally employed. The reason for this is that a large amount of emulsion falls off during coagulation, making it impossible to avoid contamination of the coagulation bath.

In other words, in the case of emulsion-based materials, it has not been easy to industrially apply the emulsion uniformly to the inner layer of the sheet-like material.

The inventors of the present invention have made extensive studies to solve this problem, and have arrived at the following invention. That is,
The present invention has the following configuration.

``A method for uniformly applying an emulsion to the inner layer of a sheet-like object, which is characterized by impregnating the inside of the sheet-like object with the emulsion, then evaporating a part of the emulsion medium by dry processing, and then performing wet coagulation.''

Typical effects of the present invention are as shown below.

(1) Emulsion can be uniformly applied to the inner layer of a sheet-like object in an extremely simple and efficient manner. No emulsion sheds into the coagulation bath, but very little.

(2) Since the emulsion can be uniformly applied to the inner layer of the sheet-like product, the physical properties of the product have been improved. Also, the uniformity of the product has improved. This allowed us to greatly expand the range of product uses.

(3) In many cases, it is possible to change from an organic solution system to an aqueous emulsion system. In this case, safety and costs for solvents, etc., were significantly reduced.

(4) Because it is extremely easy to operate, running costs can be significantly reduced.

(5) When used as a base fabric for suede-like artificial leather, it was found that it has the potential to be made into a leather with very good naps (it was found to be a very effective base fabric for suede-like artificial leather).

This will be explained in more detail below.

The effects of the present invention can be exerted on, for example, any sheet-like material having porosity. Fabrics made of nylon, polyester, acrylic, cotton, glass, etc., or porous composites containing them, are particularly widely applied.

Although the effect of uniform application can be achieved using an organic liquid emulsion, it is preferable to use an aqueous emulsion from the viewpoint of stability and low toxicity. Regarding the type of emulsion, the effects of the present invention can be achieved regardless of the type of emulsion, such as solid or liquid, organic or inorganic, low-molecular or high-molecular. Particularly widely applied are viscoelastic substances such as polyurethane, natural rubber, polyvinyl chloride (copolymers), polyamides (copolymers), polyamino acids, ethylene-vinyl acetate copolymers, polyacrylic acid copolymers. Polyacrylic acid ester, NBR, etc., or a composition containing them.

In addition, various stabilizers such as weathering agents are added to the emulsion.
Also, there is no problem even if a migration inhibitor or the like is included.

The concentration of the emulsion varies greatly depending on the degree of porosity of the sheet, the viscosity of the emulsion, etc., and cannot be determined unconditionally. However, it is necessary to have a viscosity that does not easily fall off the sheet.

Also, the size of the emulsion varies greatly depending on the emulsion type, etc., and cannot be generalized.
Larger types are preferable. In the case of an aqueous emulsion of a high-molecular viscoelastic substance such as polyurethane, a particle size of 0.08 μm or more is desirable from the viewpoint of uniform application of the emulsion product.

Next, the emulsion is applied to the sheet by conventional impregnation. If the emulsion is insufficiently impregnated into the sheet, the effects of the present invention will not be achieved at all, so it is necessary to impregnate the sheet sufficiently. In this case, in order to prevent uneven application to the sheet, it is desirable to consider the type of sheet (thickness, density, porosity, etc.), the viscosity of the emulsion, etc., and select the appropriate amount.

Impregnation using a mangle is very effective in applying emulsions of polyurethane, various rubbers, etc. to materials made of relatively flexible and high-density fibrous materials, such as the base fabric of artificial leather. Further, the amount of emulsion applied can be set to any value depending on the purpose.

For example, when manufacturing suede type synthetic leather, if the base fabric is non-woven fabric, the
When the base fabric is a knitted fabric, it is preferably 1 to 150 parts based on the knitted fabric.

After this, the sheet is exposed to a temperature 20° C. or more higher than the temperature of the liquid to be impregnated, and the sheet is dry-treated for a short time to evaporate a portion of the emulsion medium on the surface of the sheet.

The amount of evaporation is required to be such that the emulsion on the surface of the sheet is sufficiently concentrated so that no shedding occurs in the coagulation bath, or the amount of shedding is very small. The amount varies depending on the sheet structure, thickness, emulsion concentration, properties, etc., but is usually between 0.8 and 0.8 of the emulsion medium.
It is in the range of 40%, particularly preferably from 1.5 to 30%.

There are various specific methods for dry processing, but a typical method is heat processing. The heat treatment includes hot air heating, infrared heating, high frequency heating, steam treatment, etc., or a combination thereof.

Heating time and temperature vary widely depending on sheet type, emulsion concentration, and viscosity. The heating time varies greatly depending on the heating method, but if the emulsion has a high viscosity or concentration, even a very short time is effective. The heating temperature is at least 20° C. higher than the liquid to be impregnated (the emulsion liquid applied to the sheet material). If the temperature is below 20°C, there will be little effect. More preferably, the temperature is 50°C or higher. On the other hand, it is sufficient to set the maximum heating temperature (atmospheric temperature in the case of a hot air method, etc.) as high as 200°C.
However, in such cases, it is necessary to reduce the processing time to a very short time.

The sheet that has been dry-treated in this way is then wet-coagulated. Solidification is performed in a liquid phase at 20°C or higher. That is, the sheet is introduced into a liquid that is compatible with the emulsion medium and destroys the dispersion of the emulsion, thereby extracting the emulsion medium and causing the emulsion to coagulate within the sheet. Most use water or an aqueous salt solution. In addition, physical means such as heating and vibration (ultrasonic waves) may be used in combination.

Although the coagulating liquid may be aqueous or organic solvent based, it is preferable to use an aqueous coagulating liquid because it facilitates the recovery process.
In the case of an aqueous system, the water temperature is preferably higher, particularly preferably 60°C or higher. It is also a particularly preferred method to add various coagulation accelerators and the like to the aqueous liquid. This wet coagulation time is preferably sufficient to coagulate the emulsion applied inside the sheet. After that, it is dried and the emulsion is fixed. During this time, it is also an effective method to add sheet sets as appropriate.

As described above, the present invention achieves uniform emulsion coagulation by performing two stages of coagulation, completely overturning the conventional concept that emulsion coagulation is performed in one stage.

Now, the details of why the effects of the present invention appear are unknown, but it is thought to be as follows.
In other words, it is considered that the dispersed particles did not migrate sufficiently because the dry treatment was carried out for a short time. Furthermore, as mentioned above, it is thought that during the wet solidification process, the migration structure that may or may not have occurred during the dry process is alleviated.

One of the major fields of application of the present invention is the field of suede-like artificial leather. Conventionally, in the production of suede-like artificial leather, a method has been adopted in which almost 100% of the viscoelastic substance is applied as a solution. This is because when emulsion is applied using the conventional conventional method, migration occurs and it adheres only to the sheet surface, and almost no emulsion is applied to the inner layer of the sheet, and no naps occur even after buffing. Ta. However, this problem could also be solved by the invention of this method.

Hereinafter, the effects of the invention will be described in more detail with reference to Examples.

Example 1 Needle-punched nonwoven fabric made of 2-denier 51 mm polyester (fabric weight 515 g/m ² , thickness 3.7 mm)
The inner layer of the 30% colored polyurethane emulsion sheet was fully impregnated with the emulsion (the emulsion solution was colored by adding a metal-containing dye to the solution). Wet pickup was 450%. The temperature of this impregnation liquid was 23°C. This nonwoven fabric was treated in a hot air dryer at 110°C for 3 minutes. It was observed that the viscosity of the surface of the nonwoven fabric increased compared to immediately after applying the emulsion. Thereafter, it was poured into a 3% saline solution at 70°C and left for 15 minutes. During this period, the emulsion dropped into the saline solution only slightly. Then 80
It was dried with hot air at 120°C for 40 minutes, and then heat set at 120°C. The thickness was 3.5mm. When a cross section of this test product was cut and observed under a stereomicroscope, it was found that urethane was evenly adhered to the entire cross section. Furthermore, buff this product from one side,
When I ground it down to 0.4mm, there was no particularly rough surface until the end.

Comparative Example 1 A nonwoven fabric coated with the same emulsion as in Example 1 was dried in a hot air dryer at 110° C. until the weight became constant (drying time: 30 minutes).

Thereafter, it was heat set at 120°C. When the thickness was measured, it was 3.6 mm. When a cross section of this test product was cut and observed in the same manner as in Example 1, it was found that a large amount of polyurethane was applied to the surface of the sheet, but almost no polyurethane was applied to the inside.
When this product was buffed from one side to a thickness of 0.4 mm, it was extremely difficult to buff and had poor fluffing properties.
When I buffed it by more than 0.4 mm, it suddenly started to fluff, but the length of the naps was uneven, and it was tangled, which was not of good quality.

Example 2 A polymer array fiber (island ratio 55% by weight, number of islands 16, 3.5 denier, 51 mm) whose island component is polyethylene terephthalate and sea component is polystyrene is passed through a card cross wrapper to form a web.
Further, 3000 needles/ ^cm2 were punched to obtain felt. The felt weight was 510 g/m ² and the thickness was 2.83 mm. This felt was treated in hot water at 90°C for about 5 minutes. The shrinkage rate was 32.5% in area shrinkage rate.
After drying, completely saponified polyvinyl alcohol (PVA manufactured by Nippon Gohsei, Gohsenol NL-
The shrink treated felt was impregnated with a 14% aqueous solution of 05) and dried at 130°C. PVA when observed in cross section
was observed to migrate to the surface layer. The amount of PVA applied was 29.8% to the fiber. Next, this felt was soaked in trichlorene and passed through a mangle 15 times to remove the polystyrene component. Removal rate is 98.7
It was %. Next, a 15% solution of emulsion polyurethane (emulsion polyurethane manufactured by Sanyo Kasei Co., Ltd.) was passed through the sea-removal felt through a mangle three times to fully apply the emulsion to the inside of the sheet-like material. At this time, the emulsion liquid temperature was 18.5℃, and the ambient temperature was 17℃.
It was warm at ℃. Next, dry it in a hot air dryer at 110℃ for 5 minutes, and then put it in 3% saline solution at 70℃.
Wet treatment was performed. At this time, almost no emulsion was observed to fall into the water. Next, dry it in a hot air dryer at 90℃ until it reaches a constant weight, and then dry it at 150℃.
After heat setting for 10 minutes, the mangle was passed through hot water at 90°C 15 times to remove PVA. As a result, it was found that the amount of urethane applied was 60 parts based on the fiber. When this was further sliced and buffed from both sides, beautiful naps were observed on the non-sliced side. When this piece dyeing process was performed, a good suede-like artificial leather was obtained.

Comparative Example 2 The emulsion was applied in the same manner as in Example 2, and after application, it was directly dried with hot air at 90°C until it reached a constant weight. Thereafter, heat setting, removal of PVA, slicing, and buffing were performed under the same conditions as in Example 2.
As a result, some naps came out, but they were short and tangled. Even after the dyeing process, it was still short, tangled, and ugly.

Claims (1)

[Claims] 1. A method for uniformly applying an emulsion to the inner layer of a sheet-like material, which comprises impregnating the inside of the sheet-like material with the emulsion, then evaporating a part of the emulsion medium by dry processing, and then performing wet coagulation.