JPH0235044B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyvinyl alcohol synthetic fibers that are ultrafine, have high strength, and have excellent water resistance. Synthetic leather is a typical use for ultrafine fibers. The main manufacturing method is to obtain sea-island-shaped fibers by melt-mixing and spinning two types of heat-melting polymer chips that are not compatible with each other.
After creating a dimensional processed product, the sea component in the fiber is extracted and removed to create an ultrafine fiber molded product that contains only the island component. Although this manufacturing method is suitable for fields where it is difficult to directly manufacture two-dimensional molded products from ultrafine fibers, the ultrafine fibers obtained by this method have low strength, so it is not suitable for synthetic leather. In terms of performance, it is unsuitable for use as an industrial material, and since it requires processes such as extracting and removing sea components, ultrafine fibers that are obtained with a lot of waste in terms of raw materials and operations have to be extremely expensive. I don't get it. On the other hand, attempts have been made to produce ultrafine fibers using polyvinyl alcohol (hereinafter abbreviated as PVA) fibers. For example, Japanese Patent Publication No. 47-31376 discloses that fully saponified PVA and low saponified PVA are mixed and spun using a conventional method, and the fibers of normal denier obtained by drawing and heat treatment are beaten to form ultrafine fibrils for use in paper making. A method for obtaining fibers is described. Since this method uses partially saponified PVA with large side chains, the mixed spun fibers are difficult to draw and crystallization is significantly inhibited. Therefore, even before beating, the strength and water resistance are low, but mechanical beating also disturbs the orientation of molecules and crystals in the amorphous material and destroys the crystals, resulting in low strength of the fibers. And low water resistance will be further promoted. Furthermore, Japanese Patent Application Laid-open No. 77720/1983 also discloses a method for producing PVA-based ultrafine fibers. This is also highly saponified
This is a method of spinning a mixture of PVA and low saponification PVA, and its feature is that the low saponification PVA is dissolved and removed from the obtained normal denier fibers by washing with water. The difference between this manufacturing method and the former manufacturing method is that the method used to make denier into ultra-fine denier is
The former uses the mechanical power of beating to reduce saponification.
In contrast to the method in which PVA is eluted and fibrillated, the latter method significantly swells and washes out the low-saponification PVA by washing with water, and the ultrafine fibers obtained by either method have low strength and water resistance. There is no difference in the fact that it is low. In addition, the method described in Japanese Patent Publication No. 58-38526 is a method similar to the method described in the above-mentioned patent publication, and is a technology that simply uses low polymerization degree PVA as partially saponified PVA, and The fibers also have low tenacity and low water resistance as in the above method. For example, the examples of this patent exemplify PVA-based ultrafine fibrils, but even normal denier fibers before washing are described as having only 3.4 g/denier, which is extremely low strength. Furthermore, in Japanese Patent Application Laid-open No. 54-30930, low saponification
A method using an amorphous water-soluble polymer instead of PVA has been described, but it is basically the same as the above method. In any case, the known method involves spinning a mixture of crystalline PVA, which is a strength component, and a low-crystalline, easily water-soluble polymer, resulting in a normal denier.
Easily soluble components are eluted and removed from PVA fibers to make them ultra-fine.The fibers obtained by these methods all have low strength and water pressure resistance, as well as the process of dissolving and removing them. It is unavoidably expensive because of the necessity and the loss of components to be dissolved and removed. In recent years, there has been a growing need for inexpensive PVA fibers that are ultra-fine, have high strength, and have excellent water resistance. For example, this applies to the field of reinforcing brittle materials such as hardened cement and low-strength plastic materials such as plastics. For reinforcement, it is basically important that the fibers are strong, but in addition, the adhesive strength with the matrix is also a major factor. Making the fibers thinner will significantly increase the contact area with the matrix, thus greatly improving the adhesion and reinforcing effect. Furthermore, process passability during molding is significantly improved. Water resistance is particularly important when the matrix is a hydraulic material. That is, since it will be exposed to relatively high temperature water during molding and solidification, it must not swell or lose strength under such conditions. Also, regular PVA fibers are used mainly as industrial materials due to their high strength. Since this fiber also has a very high Young's modulus, yarns, cords, ropes, nets, fabrics, etc. made from this fiber are characterized by being rigid, but this may be a drawback depending on the application. In such cases, it is effective to reduce the single fiber denier. In addition, by making the size smaller, the strength utilization rate increases, which increases the strength of the product, which is a win-win situation. Furthermore, in recent years, sterile and dust-free rooms have become necessary in hospitals and the electronics industry, and there is a strong demand for high-performance filters. Nonwoven fabrics made of ultrafine fibers are effective for this purpose. As mentioned above, it has high strength and excellent water resistance.
PVA-based ultrafine fibers are desired. An object of the present invention is to provide a method for manufacturing ultrafine PVA fibers with high strength and excellent water resistance at low cost. The present invention is completely different from expensive methods such as known dissolution and removal methods, and is an extremely inexpensive and economical method that simply uses an ordinary spinning device and employs specific conditions. That is, the present invention comprises polyvinyl alcohol with an average degree of polymerization of 1200 to 3000, boric acid or a boric acid salt in an amount of 0.5 to 5% by weight based on the polyvinyl alcohol,
Dissolve an acid that will make the PH of the spinning stock solution 5 or less after dissolution in water and make polyvinyl alcohol with a concentration of 8 to 8.
A 14% by weight aqueous solution is prepared, and this aqueous solution is used as a spinning stock solution.It is a highly concentrated aqueous solution containing alkali and having dehydrating ability within the range of 10 to -60% bath draft from a spinneret having an average diameter of 0.02 to 0.04 mm. This is a method for producing ultrafine PVA fibers, which is characterized by discharging the fibers into a bath and then stretching the fibers by a factor of 10 times or more. The PVA used in the present invention has an average degree of polymerization of 1200
~3000, and the degree of saponification is 96% or more (a degree of saponification that is almost completely saponified in the alkaline coagulation bath described below). PVA like this,
A PVA concentration of 8-14% is obtained by dissolving in water using a conventional method with 0.5-5% by weight of boric acid or boric acid salt based on PVA and an amount of acid such that the pH of the spinning stock solution after dissolution is 5 or less. An aqueous solution is prepared, and this solution is used as a spinning dope. If the PVA concentration is less than 8%, poor coagulation will occur, and if it exceeds 14%, the spinning condition will deteriorate significantly. More preferably, it is 10 to 13% by weight. Borax is a representative example of borates. If the amount of boric acid or borate is less than 0.5% by weight or exceeds 5% by weight, high strength fibers cannot be obtained. Examples of the acid added to make the spinning stock solution pH5 or less include organic acids such as acetic acid, tartaric acid, and oxalic acid, and mineral acids such as nitric acid, but organic acids are preferred. It is extremely important to maintain the pH of the spinning dope at 5 or less in order to maintain the spinning condition. The spinning dope is discharged from a single-pore diameter mouthpiece with a diameter of 0.02 to 0.04 mm into a bath consisting of a highly concentrated salt aqueous solution containing an alkali and having a dehydrating ability within a bath draft range of 10 to -60% to form a leaky yarn. do. The bus draft referred to in the present invention is defined by the following equation. Bath draft % = bath separation speed - discharge speed / discharge speed x 100 Note that the bath separation speed mentioned above refers to the first roller speed. The pore diameter of a wet spinning nozzle is generally smaller than that for melt spinning and dry spinning, but in the case of wet spinning of PVA fibers, the conventional wisdom was that the minimum diameter was 0.05 mm. The reason for this is that below this, the spinning condition becomes extremely unstable. The present inventors believed that it was necessary to further reduce the diameter of the spindle hole in order to obtain ultrafine fibers, and conducted various studies on methods that could stably spin even with such a small spindle hole diameter. As a result, it is necessary to thoroughly filtrate the stock solution to eliminate foreign matter, but more than that, it is necessary to keep the bath draft at 10 to -60%, more preferably 0 to -50%, in order to maintain a stable spinning condition. We found that this is extremely important in ensuring that In normal wet spinning, a bath draft of -60% or less is generally adopted, and compared to such conditions, the bath draft used in the present invention can be said to be beyond common sense. A method for producing PVA fibers similar to the method of the present invention has already been filed by the applicant and is well known. For example, in Japanese Patent Publication No. 47-50330, PVA
A spinning stock solution obtained by adding boric acid to an aqueous solution of
It is described that PVA-based fibers can be obtained. However, the method described in this publication is intended only to obtain PVA fibers of normal denier, and is not intended to obtain ultrafine fibers as the purpose of the present invention. Furthermore, the bath draft conditions and spindle diameter conditions of the present invention, which are significantly different from conventional spinning conditions, are extremely fine.
The bath draft conditions of the present invention are necessary for the first time when obtaining PVA fibers, and the method of the above-mentioned publication, which is not aimed at obtaining ultrafine fibers, does not bring about any merit when obtaining normal denier fibers. and cap hole diameter conditions are not normally adopted. In the present invention, when the diameter of the spinneret hole was less than 0.02 mm, the spinning condition was somewhat unstable regardless of the bath draft. The discharge amount is adjusted so that the denier is 0.05 to 0.5 denier. If the discharge rate is small and the resulting fibers are thinner than 0.05 denier, the fibers will be too thin and break in the spinning cylinder, making the condition unstable and making stable production impossible.
For example, when considering cement, plastic reinforcement, and paper manufacturing, it is necessary to cut the material to 1 mm or less due to dispersion problems, but cutting it to such short lengths is industrially impossible and meaningless. Further, if the denier exceeds 0.5, the expected effect of fine denier will not be sufficient. As the coagulation bath, a highly concentrated aqueous salt solution containing an alkali and having dehydrating ability is used. Typical examples of salts having dehydration ability include Glauber's salt and ammonium sulfate. The concentration of the salt having dehydration ability in the aqueous solution is 200 g/~saturation amount. Representative examples of alkalis include sodium hydroxide and potassium hydroxide, and their concentrations range from 1 to
100g/. After such spinning, the fibers are first subjected to stretching in a wet state, neutralization, and washing with water. Specifically, after roller stretching, neutralization, followed by water washing to remove residual boric acid, and wet heat stretching in a sodium sulfate bath, or roller stretching, neutralization, wet heat stretching, and then water washing to remove residual boric acid. A typical example is a method of removing it. As a result, the amount of boric acid remaining in the fiber is 0.1 to 0.6% by weight/PVA. Residual boric acid: 0.6% by weight/PVA
If the amount is larger than that, the stretchability will be significantly impaired, making it impossible to obtain the desired strength and water resistance. Also 0.1
In order to reduce the weight to less than %/PVA, severe washing conditions must be used, resulting in significant swelling of the fibers and deterioration of quality. The total stretching ratio in the wet area (that is, in the above case, the product of the stretching ratio in roller stretching and the stretching ratio in wet heat stretching) is preferably at least 3 times, particularly 4 times or more. After that, drying is carried out, and the total stretching ratio is 10.
Dry heat stretching to more than double the size. Furthermore, if necessary, heat shrinkage and heat treatment are performed to lower the underwater softening point to 105.
℃ or higher. 9.0g/ unless stretched more than 10 times
Strength greater than denier cannot be obtained. tensile strength
If it is less than 9.0 g/denier, the effect as a reinforcing fiber will not be sufficient, and it will also lack suitability as a general industrial material. In addition, the underwater softening point is particularly important when used for reinforcing hydraulic materials such as cement; if it is lower than 105°C, swelling will occur during the molding process, reducing the original strength and significantly reducing the reinforcing effect. This will result in a decline. In addition, even in general applications, post-processing is often done in aqueous systems, which causes problems such as fibers swelling and strength loss due to drying after processing at a temperature of 105°C, and parts of the surface dissolving and sticking. result in causing. To increase the underwater softening point,
The stretching ratio may be increased or the heat treatment conditions may be increased. Note that the underwater softening point referred to in the present invention is determined by the following measurement method. Softening point in water: Take out the fiber bundle arbitrarily so that the denier is about 1000 dr, align it, attach a weight of 1/500g of the fiber bundle denier to one end, and fix it on the scale plate 10 cm from the weight. This is placed vertically over a pressurizable glass tube filled with water and immersed in water. The temperature at which the fiber bundle shrinks or melts by 10% when the temperature rises from room temperature at a rate of 1°C per minute. The PVA fiber thus obtained has a denier of
0.05~0.5 dr, strength 9.0 g/d or more, underwater softening point 105
It has excellent physical properties above ℃. In addition, according to the present invention, it can be manufactured using conventional wet manufacturing equipment and processes, and the spinning condition is very good, resulting in high productivity, and ultrafine fibers can be produced at the same cost as normal denier PVA fibers. It has the great advantage of being able to The present invention will be explained below with reference to Examples. Examples 1-2, Comparative Examples 1-2 PVA with a degree of polymerization of 1750 and a degree of saponification of 99.0 mol%,
Boric acid and acetic acid were added and dissolved together in amounts of 1.5 and 0.3% by weight based on PVA, respectively, to obtain a PVA concentration of 13% by weight,
It was made into an aqueous solution with a pH of 4.5 and used as a spinning stock solution. This spinning stock solution was discharged from a nozzle with a hole diameter of 0.03 mm and a number of holes of 10,000 into a coagulation bath consisting of an aqueous solution containing 50 g of caustic soda and 300 g of mirabilite to form a thread. By changing the discharge amount at this time, the bath draft is -10% (Example 1), -40% (Example 2), +
20% (Comparative Example 1) and -70% (Comparative Example 2). At a bath separation speed of 10 m/min, it was stretched 2.5 times between rollers, and after neutralization, it was subjected to wet heat stretching 1.8 times, washed with water so that the residual boric acid was 0.3% by weight/PVA, and then subjected to a focusing treatment. Dry. Thereafter, dry heat stretching was carried out by 2.8 times to make the total stretching ratio 12.6 times, and heat shrinkage was performed by 2%. The spinning condition was determined by continuous spinning for 8 hours with 10 spindles. Table 1 includes the quality measurement results.

[Table] The spinning condition of the example was very good compared to the comparative example, and the quality was also excellent.
There is.
Example 3, Comparative Examples 3 to 4 PVA with a polymerization degree of 1650 and a saponification degree of 99.9 mol%,
Boric acid and acetic acid were added to PVA in amounts of 2.0 and 0.3% by weight, respectively, and dissolved together, resulting in concentrations of 11% by weight (Example 3), 7% by weight (Comparative Example 3), and 16% by weight (Comparative Example 4). ) were prepared and used as spinning stock solutions. The stock solution is pore diameter 0.03mm, the number of pores
Using a 10000 nozzle, 20g of caustic soda, Glauber's salt
It was discharged into a coagulation bath consisting of an aqueous solution containing 350 g/ml to form a thread. Bass draft is -40%
The bathing speed was 10 m/min. The spun fibers were stretched twice with a roller, neutralized, washed with water to reduce the remaining boric acid to 0.4% by weight/PVA, treated with a Glauber's salt bath, and subjected to wet heat stretching to a stretching ratio of 4.5 times. After drying, dry heat stretching is performed to increase the total stretching ratio.
It was set to 12.5 times. However, for those that cannot be stretched 12.5 times, the cutting stretching ratio was determined and the stretching ratio was set to 80%.
Subsequently, it was subjected to 2% heat shrinkage, oiled, dried, and then its quality was measured. The results are shown in Table-2.

[Table] Compared to the comparative examples, the examples have better spinnability and higher quality.
Examples 4 to 5, Comparative Example 5 The stock solution concentration was 13.0% (PH4.5) and the total stretching ratio was 13.5 times (Example 4), 10.5 times (Example 5), 8.5 times (Comparative Example 5) The conditions were the same as in Example 3 except for the following. The results are summarized in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. Polyvinyl alcohol with an average degree of polymerization of 1200 to 3000 and 0.5 to 0.5 to that polyvinyl alcohol.
An aqueous solution with a polyvinyl alcohol concentration of 8 to 14% by weight is prepared by dissolving 5% by weight of boric acid or a boric acid salt and an acid such that the pH of the spinning stock solution after dissolution is 5 or less, and this aqueous solution is used for spinning. Average diameter as stock solution
Discharged from a mouthpiece with a hole diameter of 0.02 to 0.04 mm into a bath consisting of a highly concentrated salt aqueous solution having a dehydrating ability and containing an alkali within a bath draft range of 10 to -60%,
A method for producing ultrafine polyvinyl alcohol fibers, which comprises then stretching 10 times or more to obtain fibers with a thickness of 0.05 to 0.5 denier. 2. The method according to claim 1, wherein the PVA concentration in the spinning dope is 10 to 13% by weight. 3. The method according to claim 1, wherein the bath draft is 0 to -50%.