JPH08260236A - Preparation of polyvinyl alcohol-based spinning dope - Google Patents

Abstract

PURPOSE: To readily and efficiently obtain a PVA-based spinning dope having a high saponification degree effective for improving hot water resistance by using a polyvinyl alcohol (PVA) having a saponification degree of commercially available grade. CONSTITUTION: In preparing a spinning dope by dissolving PVA in a solvent, the preparation is performed to satisfy following four conditions. (A) A solution of an alkaline component is added to a solvent and/or PVA and dissolved, (B) the concentration of the added alkaline solution is made to 0.05-10 normal, (C) the amount of the added alkaline component is made to 0.1-3.0 equivalent of the residual acetyl group amount in PVA and (D) in adding the alkaline component and preparing the spinning dope, the temperature at the contact of the PVA with the alkaline component is controlled to 10-80 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a spinning dope for obtaining polyvinyl alcohol (hereinafter abbreviated as PVA) fibers, and more specifically, it has a degree of saponification that is commercially available. The present invention relates to a method for easily and efficiently obtaining a PVA spinning stock solution having a high degree of saponification, which is effective for improving hot water resistance, from PVA.

[0002]

2. Description of the Related Art The relationship between the hot water resistance of PVA-based fibers and the saponification degree of the raw material PVA has been studied in the past, and it is known that the hot water resistance decreases when the saponification degree is low. on the other hand,
The applications of PVA-based fibers are mainly in the field of industrial materials, and fibers in this field are generally required to have excellent hot water resistance.

PVA is usually produced commercially by polymerizing vinyl acetate in a methanol solvent to give a solution of polyvinyl acetate in methanol, which is then saponified with an acid or an alkali as a catalyst to give PVA. There is. However, since this saponification reaction is a transesterification reaction,
When the saponification degree exceeds 99 mol%, the rates of the forward reaction and the reverse reaction become equal, and the saponification degree does not increase. Therefore, the saponification degree of commercially available PVA is about 99 mol%, and if a higher saponification degree is desired, it is necessary to perform re-saponification treatment by the method described later.

PVA-based fibers have been conventionally produced as vinylon, but since the coagulating bath containing a high concentration of alkaline components is used in the process for producing vinylon, the saponification degree of the raw material PVA is not so high. The saponification reaction proceeds in the coagulation bath, and the degree of saponification of the final product becomes 99.9 mol% or more. Therefore, in the conventional production of PVA-based fibers, no special attention is paid to the saponification degree of the raw material PVA, and the saponification degree of a commercially available degree, for example, about 99 mol% is used. If it is above, there is no particular problem.

On the other hand, recently, various attempts have been made to increase the strength and elastic modulus of PVA fibers. For example, JP-A-59-140314 discloses a method of spinning a glycerol solvent of PVA having a weight average molecular weight of 500,000 or more in a methanol bath, and JP-A-60-126311 discloses a method of dimethyl sulfoxide of PVA. A method of spinning a solution in a methanol bath is disclosed. In these spinning methods, since all spinning steps from the preparation of the spinning dope to coagulation and washing are carried out using an organic solvent, the saponification reaction does not proceed in the steps like vinylon described above. Absent.

Therefore, in order to obtain a fiber made of PVA having a high degree of saponification for the purpose of improving hot water resistance, PVA is required.
It is necessary to increase the degree of saponification from the raw material stage. Raw material PV
As a method for increasing the saponification degree of A, several methods have been conventionally known. For example, powdery or granular P
A method in which VA is dispersed in water to form a suspension, and an alkaline component in excess of the amount required for the saponification reaction is added to this suspension, and if necessary, a slight amount of heating is performed to carry out the saponification reaction is there. A method of performing the same operation using alcohol is also known.

However, although these methods can increase the degree of saponification, there is a problem that the operation and the subsequent handling of the polymer are complicated. That is, PVA is typically obtained commercially as a dry polymer. Therefore, first, it is necessary to suspend this polymer in water or alcohol. Further, an excess amount of alkaline component is added thereto to carry out the saponification reaction, and thereafter,
Excess alkali must be neutralized with acid. Next, a step of separating the liquid and the polymer by a method such as dehydration and further washing is necessary, and after the washing step, a drying step is required to restore the original dry polymer.

As described above, in order to increase the degree of saponification of PVA at the stage of the raw material polymer, it is necessary to perform several treatments, which naturally leads to an increase in the raw material cost. For this reason, the PV method is
A method for preparing a spinning dope having a high degree of saponification from PVA having a degree of saponification that is commercially available has been desired in the production of A fiber.

In order to meet this demand, the present inventors proposed in Japanese Patent Application No. 5-353146 a method of increasing the saponification degree by adding an alkaline component when preparing a spinning solution for PVA. However, in this method, since the concentration and temperature of the alkaline component added to PVA are not taken into consideration, the spinning dope may be colored or the degree of polymerization of PVA may decrease, so that a spinning dope with a high degree of saponification is prepared. A more practical method of doing so has been desired.

[0010]

The present invention solves the above problems and has a high degree of saponification effective for improving hot water resistance from PVA having a degree of saponification that is commercially available. Moreover, it is a technical subject to provide a method for practically, easily, and efficiently obtaining an uncolored PVA-based spinning stock solution.

[0011]

The present inventors have reached the present invention as a result of extensive studies to solve the above problems. That is, in the present invention, when PVA is dissolved in a solvent to prepare a spinning dope, (A) a solution of an alkaline component is added to the solvent or / and PVA and then dissolved.
(B) The concentration of the alkaline solution to be added is 0.05 N or more,
10% or less, (C) the amount of the alkaline component to be added is 0.1 equivalent or more and 3.0 equivalents or less with respect to the residual acetyl group amount of PVA, (D) the alkaline component is added, A method for preparing a PVA-based spinning dope is characterized in that a temperature at which PVA and an alkaline component come into contact with each other is 10 ° C. or more and 80 ° C. or less when a spinning dope is prepared.

The present invention will be described in detail below.

In the present invention, ethylene glycol, dimethyl sulfoxide (hereinafter abbreviated as DMSO), glycerin, or a mixture thereof may be used as a solvent when dissolving PVA to prepare a spinning dope. However, DMSO is particularly preferable.

The PVA concentration in preparing the spinning dope is preferably 3 to 35% by weight in order to obtain fibers having good physical properties. If it is less than 3% by weight, the spinnability during spinning tends to deteriorate and the spinnability tends to deteriorate. If it exceeds 35% by weight, the viscosity tends to be too high and the drawability of the resulting fiber tends to decrease. .

In the present invention, when PVA is dissolved in a solvent to prepare a spinning dope, a solution of an alkaline component is added to either the solvent or PVA, or the solvent and P are mixed.
It is important to add to both of the VAs to dissolve the PVA. In this case, as a solution of the alkaline component to be added,
Use an alkaline component dissolved in water, alcohol, or a mixture thereof with a concentration of 0.05 normal or more and 10 normal or less, and adjust the amount of the alkaline component added to PVA.
0.1 equivalent or more with respect to the amount of residual acetyl groups of PVA, 3.0
It is important that the amount is not more than the equivalent amount, and further, that the PVA and the alkaline component are brought into contact with each other at a temperature of 10 ° C. or higher and 80 ° C. or lower when mixing, and as described later, even if any of these requirements is lacking The object of the present invention cannot be achieved.

As described above, the solution of the alkaline component is added to the solvent or / and PVA to saponify the residual acetyl groups of PVA, and this mixture is dissolved by heating to obtain a spinning dope.

As described above, the hot water resistance of PVA fibers is greatly affected by the degree of saponification of the final fiber product, and the degree of saponification is low. Specifically, below 99.4 mol%, it dissolves in boiling water at 100 ° C. To do. However, according to the present invention, the alkaline component and PVA are brought into contact with each other prior to the dissolution of PVA, so that the saponification reaction proceeds due to this alkaline component and the saponification degree is increased.
It is possible to raise it to 99.8 mol% or more.

In the present invention, the method of adding the alkaline component to the solvent or PVA is not particularly limited,
A method of preparing a solution of an alkaline component and adding it to a solvent, a method of impregnating the solution of the alkaline component into powdery or granular PVA and adding it, or a method combining these can be adopted. Among them, a method of making a solution of alkaline components and adding this to a solvent,
The method of impregnating PVA and adding it is preferable because the operation is simple.

As mentioned above, prior to the dissolution of PVA,
In order to raise the saponification degree to 99.8 mol% or more by contacting the alkaline component with PVA, the addition amount of the alkaline component should be P
It is preferably 0.1 equivalent or more and 3.0 equivalents or less, particularly preferably 0.3 equivalent or more and 2.0 equivalents or less with respect to the residual acetyl group amount of VA. If the amount of the alkaline component added is less than 0.1 equivalent, the degree of saponification is unlikely to increase, and if it exceeds 3.0 equivalent, the alkali concentration in the mixture becomes too high and the degree of polymerization of PVA decreases,
This is not preferable because the formation of heterogeneous bonds and the coloration are likely to occur.

When the alkaline component is added as a solution to the solvent or PVA, the solvent for preparing this solution may be any solvent having a high solubility of the alkaline component used,
It is convenient and preferable to use water, alcohol, or a mixture thereof. In this case, it is necessary to use an alkaline solution with a concentration of 0.05 normal or more and 10 normal or less so that the alkaline component can uniformly contact PVA. If the concentration of the alkaline solution is lower than 0.05 N, the ratio of the solvent of the alkaline component to the solvent of PVA becomes too high, and gelation occurs, making it difficult to uniformly discharge the spinning dope from the spinneret. On the other hand, when the concentration is higher than 10 N, this alkaline solution is used as a solvent for PVA or PV.
When added to the A solution, an alkaline component is precipitated or P
It is not preferable because it lowers the degree of polymerization of VA.

When further mixing, the temperature at which the PVA and the alkaline component come into contact is also important, and is 10 ° C or higher, 80 ° C or higher.
Must be: If this temperature is lower than 10 ° C, the saponification reaction rate becomes slow and the reaction time becomes long. Again 80
If the temperature is higher than ° C, the saponification reaction rapidly occurs and the decomposition reaction of PVA is promoted, which is not preferable.

The alkaline component which can be used in the present invention is not particularly limited as long as it can promote the saponification reaction, but monoacids such as sodium hydroxide, potassium hydroxide and lithium hydroxide can be used. Inexpensive and easily available bases are preferable, and these are used alone or in combination.

In the present invention, various heat-resistant agents, cross-linking agents, pigments and other additives may be added to the spinning dope in the above-mentioned manner, as long as the saponification reaction is not impaired.

According to the present invention, P having a higher degree of saponification
A spinning dope containing VA is obtained, which can be confirmed by measuring the saponification degree of the undrawn yarn obtained by spinning the spinning dope.

The spinning method of the spinning dope prepared by the present invention is a dry-wet spinning method in which an organic solvent is used as a solvent of the spinning dope and the solvent is coagulated from the organic solvent or discharged through an inert atmosphere layer in a cooling bath. It is applicable to the above-mentioned wet spinning method in which the spinning dope is directly discharged into the coagulation bath, or the dry spinning method in which it is discharged into the heated gas, but the dry-wet spinning method is preferable.

[0026]

In the present invention, a spinning stock solution having a high degree of saponification and not being colored can be obtained by using PVA having a saponification degree which is commercially available. At this time, it is considered that the residual acetyl group of PVA reacts with the alkaline component at the same time as the dissolution or at the stage before spinning by adding the solution of the alkaline component to the solvent or / and PVA.

[0027]

EXAMPLES Next, the present invention will be specifically described by way of examples. The saponification degree in the present invention is measured by the PVA test method described in JIS-K6726. The hot water resistance was evaluated by the hot water temperature measured by the following method. Apparatus: Perkin-Elmer DSC-2C type differential scanning calorimeter Temperature rising rate: 10 ° C / min Sample cell: High pressure (50 atm) cell Sample preparation method: Fiber sample 5 mg cut to about 5 mm in length 10 mg water Together with it, it is enclosed in a sample cell. Heat resistant water temperature: The peak temperature of the melting (dissolution) curve obtained by the above method is defined as the heat resistant water temperature.

Examples 1-2, Comparative Examples 1-2 Polymerization degree 4000, saponification degree 99.45 mol% (amount of residual acetyl groups
0.55 mol% of PVA was dissolved in DMSO to a concentration of 15% by weight to prepare a spinning dope, and 1.5 equivalent of sodium hydroxide was first added to the residual acetyl group concentration to give a concentration of 0.5%. A solution dissolved in water to 1N was added to DMSO. Next, PVA was added to this DMSO and stirred, saponified and dissolved to prepare a spinning dope. The contact temperature (solution temperature) between PVA and DMSO at this time was 20 ° C.
Met. Further, in Example 2, a spinning dope was prepared in the same manner as in Example 1 except that potassium hydroxide was used instead of sodium hydroxide.

[0029] These spinning dope solutions were prepared with a pore diameter of 0.4 mm and a pore number of 1
From the spinneret of 72, by dry-wet spinning method, it was discharged into a methanol coagulation bath at room temperature at 100 ° C, and while collecting the coagulated yarn, it was further washed with methanol to remove DMSO of the yarn, and then an oil agent was applied. And dried to obtain an undrawn yarn.

For comparison, the amount of residual acetyl groups was 0.
A spinning stock solution (Comparative Example 1) prepared by adding an aqueous solution of 05 equivalent of sodium hydroxide adjusted to a concentration of 0.1 N and 8.0 equivalent of sodium hydroxide with respect to the amount of residual acetyl groups Was added to an aqueous solution adjusted to have a concentration of 0.1 N, and dry spinning was performed in the same manner as in Example 1 using both of the prepared spinning dope (Comparative Example 2) to produce an undrawn yarn. .

The surface temperatures of these undrawn yarns are
Supply roll and take-off roll set at 80 ℃ and 170 ℃,
And a 17.5-fold hot drawing using a hot air oven with a yarn inlet temperature of 160 ° C and an outlet temperature of 220 ° C arranged between these PV
A fiber was obtained.

Table 1 shows the measurement results of the saponification degree and the polymerization degree of the undrawn yarn and the heat-resistant water temperature of the drawn yarn.

[0033]

[Table 1]

As is clear from Table 1, in both Examples 1 and 2, the unstretched yarn had a saponification degree of 99.95 mol% and a polymerization degree of 4000, and the saponification degree was sufficiently high. In addition, the heat-resistant water temperature of the PVA fiber after stretching is 135 ° C in all cases.
It was excellent in hot water resistance.

On the other hand, the undrawn yarn of Comparative Example 1 had a saponification degree of 99.45 mol% and a polymerization degree of 3990, and the saponification degree of 3990 remained low. The undrawn yarn of Comparative Example 2 was
At 99.97 mol%, 3560, the degree of saponification was high, but the degree of polymerization was greatly reduced, and the undrawn yarn was colored dark brown. The heat-resistant water temperature of the stretched PVA fiber obtained in Comparative Example 1 was as low as 109 ° C, and the fiber of Comparative Example 2 had excellent hot-water resistance of 136 ° C, but was not colored. It was not very preferable.

Example 3, Comparative Examples 3 to 4 Polymerization degree 4000, saponification degree 99.45 mol% (amount of residual acetyl groups
0.55 mol% PVA so that the concentration becomes 15% by weight D
When preparing a spinning dope by dissolving in MSO, 1.0 equivalent of potassium hydroxide with respect to the amount of residual acetyl groups was dissolved in water in a PVA solution dissolved in DMSO so that the concentration became 1.0 N. After the ingredients were added, they were stirred and dissolved to prepare a spinning dope (Example 3). In addition, PVA and DMS at this time
The contact temperature with O was 20 ° C. Using this spinning dope, an undrawn yarn was prepared in the same manner as in Example 1 and then drawn in the same manner as in Example 1.

For comparison, 1.0 equivalent of potassium hydroxide was added to the PVA solution at a concentration of 0.01 with respect to the amount of residual acetyl groups.
What was melt | dissolved in water was added so that it might become regulation, and the spinning dope was produced (Comparative Example 3). Further, 1.0 equivalent of potassium hydroxide aqueous solution was adjusted to have a concentration of 15 N and added to prepare an undrawn yarn (Comparative Example 4). Then, these undrawn yarns were drawn in the same manner as in Example 1.

Table 2 shows the measurement results of the saponification degree and the polymerization degree of the undrawn yarn, and the heat-resistant water temperature of the drawn yarn.

[0039]

[Table 2]

As is clear from Table 2, the unstretched yarn obtained in Example 3 had a saponification degree and a polymerization degree of 99.94 mol% and 3990, respectively, and the PVA fiber after stretching had a heat-resistant water temperature. It had 135 ° C and excellent hot water resistance.

On the other hand, the saponification degree and the polymerization degree of the undrawn yarn of Comparative Example 3 were 99.56 mol% and a low saponification degree of 3980, and the heat resistant water temperature of the drawn PVA fiber was as low as 110 ° C. Indicated.

Further, the saponification degree and the polymerization degree of the undrawn yarn of Comparative Example 4 were 99.90 mol% and 3400, which showed a high saponification degree, and the heat-resistant water temperature of the drawn PVA fiber was 135 ° C. Although it was good, the degree of polymerization was significantly reduced.

Comparative Examples 5-6 Polymerization degree 4000, saponification degree 99.45 mol% (amount of residual acetyl groups
0.55 mol%) of PVA was dissolved in DMSO to a concentration of 15% by weight to prepare a spinning dope, and 2.0 equivalent of sodium hydroxide was added to the amount of residual acetyl groups at a concentration of 1.
It was dissolved in water so as to be 0 N and added to DMSO.
The contact temperature between PVA and DMSO at this time was 2 ° C. in Comparative Example 5 and 90 ° C. in Comparative Example 6. Using this spinning dope, an undrawn yarn was prepared in the same manner as in Example 1,
It was then stretched.

Table 3 shows the measurement results of the saponification degree and the polymerization degree of the undrawn yarn and the heat-resistant water temperature of the drawn yarn.

[0045]

[Table 3]

As is apparent from Table 3, the unstretched yarn obtained in Comparative Example 5 had a saponification degree and a polymerization degree of 99.45 mol% and 4000
The saponification degree was low, and the heat resistant water temperature of the PVA fiber after stretching was as low as 108 ° C. The saponification degree and the polymerization degree of the undrawn yarn obtained in Comparative Example 5 were 99.90 mol% and 3500
The saponification degree showed a high value, and the heat-resistant water temperature of the drawn PVA fiber was good at 135 ° C, but the degree of polymerization was remarkably reduced.

[0047]

According to the present invention, a commercially available PVA having a saponification degree is used to obtain a PVA fiber having a high saponification degree, good hot water resistance, and no coloration. A spinning stock solution can be obtained easily and efficiently, and its usefulness is extremely high.

Front page continued (72) Inventor Keisuke Murai 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd. Central Research Laboratory

Claims (1)

[Claims] 1. When preparing a spinning dope by dissolving polyvinyl alcohol in a solvent, (A) adding a solution of an alkaline component to the solvent and / or polyvinyl alcohol and then dissolving, (B) adding an alkaline solution The concentration of 0.05 normal or more and 10 normal or less, (C) the amount of the alkaline component added is 0.1 equivalent or more and 3.0 equivalent or less with respect to the residual acetyl group amount of polyvinyl alcohol, ( D) A method for preparing a polyvinyl alcohol-based spinning stock solution, characterized in that, when a spinning stock solution is prepared by adding an alkaline component, the temperature at which the polyvinyl alcohol and the alkaline component come into contact with each other is 10 ° C to 80 ° C. .