JPS6236065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses acetic acid, sodium acetate and limited pka for polyvinyl alcohol-based polymers.
The present invention relates to a method for producing a polyvinyl alcohol-based polymer having good thermal stability by incorporating a partial alkali metal into an organic polybasic acid having the following. However, in the present invention, pka refers to the dissociation constant of an acid.
When ka, it is a value defined by pka=-logka. The polyvinyl alcohol-based polymer referred to in the present invention refers to saponified polyvinyl acetate (polyvinyl alcohol), saponified binary or multi-component copolymers of one or more olefins and vinyl acetate, or a saponified polyvinyl acetate (polyvinyl alcohol), a saponified binary or multi-component copolymer of vinyl acetate, or a polymer derived from these polymers. refers to derivatives that are In this case, examples of the olefin used in the copolymerization include ethylene and propylene. Examples of derivatives include various esterification products, etherification products, acetalization products, grafted products, molecular compounds, complex compounds, and chelate compounds. Note that the saponified product in the present invention includes both partially saponified products and completely saponified products. The polyvinyl alcohol polymer has poor thermal stability and cannot be melt-molded, or even if it can be melt-molded, it is extremely susceptible to coloring and thermal deterioration during melt-molding. In addition, not only during melt molding, but also during heat treatment, hot stretching, thermal bonding, drying, etc., in short, during heating,
It is easily colored, decomposed, or conversely exhibits crosslinking, changes in melt viscosity, and becomes insolubilized in solvents, resulting in poor thermal stability, which is a serious industrial problem. It is becoming. The present inventors have endeavored to overcome these drawbacks of polyvinyl alcohol polymers, and to develop a method for producing polyvinyl alcohol polymers that have fewer fissures, are less likely to be colored, are less likely to decompose or crosslink, and have good thermal stability. As a result of study, we have arrived at the present invention. That is, 0.005 to 0.1% by weight of sodium acetate and acetic acid are contained in the polyvinyl alcohol polymer in a manner that satisfies the following formula, α = content of acetic acid in the polyvinyl alcohol polymer (weight %)/polyvinyl alcohol The content (wt%) of sodium acetate in the system polymer, 1 < α < 10... Furthermore, the pka at 25°C is expressed by the formula: X = 1/2 (pk ₁ + pk ₂ ), 3.5 _< < pk ₂ ), in which the acid group corresponding to pk ₁ of the organic polybasic acid forms an alkali metal salt, and the acid group corresponding to pk ₂ is in a free state. One or two partial alkali metal salts of organic polybasic acids
By adding 0.001 to 0.5% by weight of seeds or more,
The present invention was completed based on the recognition that it is possible to obtain a polyvinyl alcohol-based polymer with good thermal stability, which has less fisheye, is less likely to be colored, is less likely to decompose or crosslink, and has good thermal stability. In the present invention _, pk ₁ and pk ₂ are defined as _{k 1} , _{k 2} , k ₃ . This is the value defined in ₂ . Examples of organic polybasic acids that satisfy the formula include phthalic acid, isophthalic acid, terephthalic acid, adipic acid, azelaic acid, citric acid, glutaconic acid, glutaric acid, succinic acid, suberic acid, pimelic acid,
Examples include, but are not limited to, organic acids such as fumaric acid, tartaric acid, maleic acid, malonic acid, and malic acid. In the present invention, acid groups corresponding to pk ₁ of these organic polybasic acids form an alkali metal salt,
Those in which acid groups corresponding to pk ₂ are in a free state are used. However, in the case of an organic polybasic acid of tribasic acid or higher, the acid dissociation constant of the organic polybasic acid is determined in order from the larger one.
When k ₁ , k ₂ , k ₃ , ......kn _-1 , kn, kn ₊₁ ......, if the acid group below kn _-1 has already been replaced with another substituent, for example, salt or an ester, the formula X=1/2 (pkn + pkn ₊₁ ) satisfies the formula for kn and kn ₊₁ , and the acid corresponding to pkn Partial alkali metal salts of organic polybasic acids in which the groups form an alkali metal salt and the acid salt corresponding to pkn ₊₁ is in the free state are included in the present invention. Examples of such partial alkali metal salts of organic polybasic acids include:
Ethylenediaminetetraacetic acid (pk ₁ = 2.0, pk ₂ = 2.7,
pk ₃ = 6.2, pk ₄ = 10.3 (25℃)) and citric acid (pk ₁
= 3.13, pk ₂ = 4.76, pk ₃ = 6.40 (at 25°C)), such as disodium salts and dipotassium salts. However, for citric acid, even if we focus on pk ₁ and pk ₂ , the above-mentioned X value satisfies the formula, so
Monoalkali metal salts of citric acid are also examples of those that can be used in the present invention. Incidentally, the alkali metal as used in the present invention refers to lithium, sodium, potassium, cesium, etc. among the Group 1 elements of the periodic table. Now, in order to fully obtain the effects of the present invention, it is necessary to satisfy all of the various conditions constituting the present invention described above, and if even one of these conditions is not satisfied, the effects of the present invention may not be fully obtained. can't get it. For example, even when using an organic polybasic acid that satisfies the formula, all of the acid groups of the organic polybasic acid may be in a free state, or all of the acid groups may form metal salts. or when a partial alkali metal salt of an organic polybasic acid that does not satisfy the formula is used, there is almost no thermal stabilizing effect on the polyvinyl alcohol polymer; rather, when heated, the polyvinyl alcohol polymer There is even a tendency to actively promote coloration, decomposition, or insolubilization of the polymer. In addition, if the content of the partial alkali metal salt of the organic polybasic acid according to the present invention is so high as to exceed 0.5% by weight, the polyvinyl alcohol polymer will rather become colored and insolubilized, and conversely,
The content of the partial alkali metal salt of the organic polybasic acid is
When the amount is less than 0.001% by weight, the effect of the partial alkali metal salt of the organic polybasic acid becomes small, so that thermal deterioration of the polyvinyl alcohol polymer cannot be sufficiently prevented. On the other hand, if the content of sodium acetate in the polyvinyl alcohol polymer exceeds 0.1% by weight, it tends to promote coloring and decomposition of the polyvinyl alcohol polymer. When the amount is less than 0.005% by weight, the effect of the present invention becomes extremely small, and in this case also, thermal deterioration of the polyvinyl alcohol polymer cannot be prevented. Furthermore, if the sodium acetate content is less than 0.005% by weight, there will be significant restrictions on the acetic acid content in the polyvinyl alcohol polymer, and the effective range of the acetic acid content for preventing thermal deterioration of the polyvinyl alcohol polymer will be limited. This is not preferable because it is extremely narrow compared to Eq. In addition, if the acetic acid content in the polyvinyl alcohol polymer deviates from the formula and is high, the polyvinyl alcohol polymer exhibits a yellowish brown color.
It becomes easily insolubilized, and if the acetic acid content is deviating from the formula and is low, the polyvinyl alcohol polymer becomes yellow and tends to be easily decomposed. That is, 0.005 to 0.1% by weight of sodium acetate and acetic acid are contained in the polyvinyl alcohol-based polymer so as to satisfy the above formula,
Furthermore, very good results can be obtained by adding 0.001 to 0.5% by weight of a partial alkali metal salt of an organic polybasic acid that satisfies the above formula. Particularly noteworthy is that when acetic acid and sodium acetate are used in combination with the partial alkali metal salt of the organic polybasic acid, a synergistic effect is observed, the yellowness during heating is extremely low, and white clay is even better, and moreover, it can withstand severe heating. It is possible to obtain a polyvinyl alcohol-based polymer that can maintain thermal stability under various conditions. Such a synergistic effect was not anticipated by the inventors and was a truly unexpected phenomenon. In other words, if a polyvinyl alcohol-based polymer contains only acetic acid or only sodium acetate, the thermal stability of the polyvinyl alcohol-based polymer will be poor; When sodium is used in combination, a significant thermal stabilizing effect is observed under weak heating conditions, for example, when heating at a relatively low temperature or for a relatively short time, or when melting and molding is performed only once. However, under severe heating conditions, such as heating at a relatively high temperature or for a relatively long time, or when melt molding is repeated, almost no effect is observed.
In fact, there is even a tendency to accelerate thermal deterioration of the polyvinyl alcohol polymer. On the other hand, when a polyvinyl alcohol-based polymer is made to contain only the partial alkali metal salt of the organic polybasic acid according to the present invention, the polyvinyl alcohol-based polymer does not decompose or become insolubilized even under severe heating conditions. Although it can be prevented relatively well, the whiteness during heating is not necessarily sufficient. That is, when acetic acid and sodium acetate are used together with the partial alkali metal salt of the organic polybasic acid, a synergistic effect is observed, and even under severe heating conditions,
Extremely low yellowness, excellent whiteness, and
This makes it possible to obtain a polyvinyl alcohol polymer that has fewer eyes and is less susceptible to thermal deterioration. The method of incorporating the acetic acid and sodium acetate according to the present invention into the polyvinyl alcohol polymer and adding the partial alkali metal salt of the organic polybasic acid is a method of directly adhering it to the powder or pellet of the polyvinyl alcohol polymer. , or a method of treating the polyvinyl alcohol polymer with a mixed aqueous solution or alcohol solution or water-alcohol solution of acetic acid and sodium acetate and a partial alkali metal salt of the organic polybasic acid, or a solution of the polyvinyl alcohol polymer,
Any method such as adding acetic acid, sodium acetate, and a partial alkali metal salt of the organic polybasic acid can be used, but the method is not necessarily limited to these, and an appropriate method can be used in consideration of various circumstances. All you have to do is choose. The present invention particularly exhibits its effect particularly when the polyvinyl alcohol-based polymer is heat-molded, but it also exhibits its effect during heat treatment, hot stretching, heat adhesion, drying, etc., in short, during heating. It is something. Furthermore, the present invention provides that when the polyvinyl alcohol-based polymer is heated in a solution state,
Alternatively, even when heated in an emulsion state, the effect is exhibited. The polyvinyl alcohol polymer produced according to the present invention can be molded into molded products, films, fibers, etc. by melt molding, wet molding, dry molding, etc., and can also be made into emulsion or solution and used as a paint. It can be used in various processing agents such as adhesives, fiber processing agents, and paper processing agents. Furthermore, the present invention is sufficiently effective even when additives such as plasticizers, colorants, stabilizers, and lubricants that are normally added to plastic products are added. Next, the present invention will be explained in detail with reference to Examples. Example 1 40 parts (by weight) of ethylene-vinyl acetate copolymer (ethylene component content 33 mol%, vinyl acetate component content 67 mol%, degree of polymerization 2150) was dissolved in 60 parts of methanol, and 10 parts of caustic soda was dissolved in this. 20 parts of a wt% methanol solution was added and saponified at 60°C for 3 hours. The saponified stock solution was poured into 500 parts of water to precipitate the polymer. After removing the liquid, the precipitated polymer was extracted with water at 50°C using a large Soxhlet extractor.
It was continuously extracted and washed for a week. 100 parts of the extracted and washed saponified ethylene-vinyl acetate copolymer (degree of saponification 99.5 mol%) was dissolved in 400 parts of a methanol-water mixture (70% by weight of methanol + 30% by weight of water) at 60°C. The solution contains 0.04 part of sodium acetate, 0.15 part of acetic acid, and the monosodium salt (sodium hydrogen succinate) of succinic acid (pk ₁ = 4.21, pk ₂ = 5.64, X value 4.93) whose pka at 25°C satisfies the above formula. )
0.05 part was added and sufficiently stirred at 60°C to dissolve. The composition was cooled to room temperature to form a gel, which was pulverized with a mixer, air dried for 20 hours, and further dried by heating at 100° C. for 16 hours in a hot air circulation dryer. The sodium acetate content in the saponified copolymer thus obtained was 0.0364% by weight, and the acetic acid content was
The content of sodium hydrogen succinate was 0.1231% by weight (α value 3.38) and 0.0486% by weight. 3 g of the saponified copolymer was sandwiched between hot plates (Shindo tabletop test press YS-5) heated to 230°C, and the gap between the hot plates was maintained at 5 m/m.
The sample was heated for 10 minutes and 30 minutes (thermal coloring test), and the yellowness (YI, model ND-K5 manufactured by Nippon Denshoku Industries) of the sample after the heat coloring test was measured. On the other hand, in order to examine the thermal deterioration characteristics of the melt viscosity, the melt index of the saponified copolymer was measured under a 190°C load according to ASTM D1238(E).
Measured at 2160g (Takara Kogyo melt indexer)
MX-101-A type orifice outer diameter 9.5 m/m, orifice inner diameter 2.095 m/m, length 8.0 m/m). However, the saponified copolymer must be placed in a melt indexer and heated at 190°C for 30 minutes without applying any load.
After preheating, a load was applied and measurements were taken. The measurement results are shown in Table-1. On the other hand, as a control example, when only acetic acid and sodium acetate were added to the saponified copolymer (Control Example 1), and when only sodium hydrogen succinate was added (Control Example 2), acetic acid, For the case where neither sodium acetate nor sodium hydrogen succinate was added (Control Example 3), a sample was prepared in the same manner as in Example 1 and evaluated in the same manner. The evaluation results are shown in Table-1.

[Table] In the case of Example 1 containing acetic acid, sodium acetate, and sodium hydrogen succinate, the coloring during heating was extremely small, and the melt index, which is a measure of melting characteristics, was normal, and melt molding was possible. The value applied to processing is shown. On the other hand, in the case of Control Example 1, in which only acetic acid and sodium acetate were added, and sodium hydrogen succinate was not added, the heating conditions were severe (heating at 230°C for 30 minutes).
The coloration was significant, the melt index value was also large, and there was a slight tendency to decompose. In addition, in the case of Control Example 2 in which only sodium hydrogen succinate was added without adding acetic acid or sodium acetate, the melt index value was almost normal, but the coloration during heating was unsatisfactory. . Furthermore, in the case of Control Example 3 in which neither acetic acid, sodium acetate nor sodium hydrogen succinate was added, both the coloration upon heating and the melting properties were poor. Next, the sample prepared in Example 1 was subjected to melt extrusion film formation (using a P-115 extruder manufactured by Japan Steel Works, cylinder temperature 230°C, die temperature 210°C) to create a 17 μ film. The number of particles was extremely small, and a beautiful film with no coloring was obtained. Further, the film was compressed and cut into chips (using Mitsubishi Heavy Industries' NCP-3 model crimpel unit), and the chips were again run in the same extruder under the same conditions.
A 17μ film was formed and melt extrusion film formation was repeated. When the film was formed by melt extrusion 10 times in this manner, the number of film eyes hardly increased and a beautiful film without coloration was obtained. Table 2 also shows the results obtained when the samples prepared in Comparative Examples 1 to 3 were melt-extruded into films in the same manner.

[Table] In the case of Control Examples 1 and 2, no major problems were observed in both coloring and film formability when melt extrusion film formation was performed only once, but when melt extrusion film formation was repeated,
Increase in fish eye, coloration, change in melt viscosity,
Phenomena such as poor film formation were observed. In addition, in the case of Control Example 3, the film was significantly colored yellow during the first melt extrusion film formation, and there were many fish eyes on the entire surface of the film.Also, the back pressure of the extruder was low due to the decrease in melt viscosity, and the film There are many holes in the film, and the die lip often cuts the film.
It was difficult to unroll. Examples 2 to 3 and Control Example 4 Ethylene-propylene-vinyl acetate copolymer (ethylene component content 31 mol%, propylene component content 2 mol%, vinyl acetate component content 67 mol%, degree of polymerization 1700) 40 parts (by weight) was dissolved in 60 parts of methanol, and 40 parts of a 5% by weight methanol solution of caustic soda was added thereto, followed by saponification at 60°C for 3 hours. The saponified stock solution was poured into 500 parts of water to precipitate the saponified copolymer, and the saponified copolymer was washed under running water for 5 hours. 40 parts of the washed saponified ethylene-propylene-vinyl acetate copolymer (degree of saponification 98.5 mol%) was mixed with acetic acid, sodium acetate and pka at 25°C.
Citric acid (pk ₁ =
3.13, pk ₂ = 4.76, pk ₃ = 6.40, 1.5g
300 parts (dissolved) for 2 hours. After deliquing, dry in a hot air circulation dryer for 80
Dry at ℃ for 16 hours. The acetic acid content in the saponified copolymer thus obtained was 0.1257% by weight, and the sodium acetate content was 0.1257% by weight.
The content of sodium dihydrogen citrate was 0.0298% by weight (α value 4.22) and 0.0721% by weight. Further, the sodium dihydrogen citrate in Example 2 was replaced with disodium hydrogen citrate (X value 5.58), and samples shown in Table 3 (Example 3) were prepared. On the other hand, as a control example, sodium dihydrogen citrate in Example 2 was treated with salicylic acid whose pka at 25°C did not satisfy the above formula (pk ₁ = 2.8, pk ₂
Table for the case of replacing monosodium salt (sodium salicylate) with = 12.4,
A sample shown in No. 3 (Comparative Example 4) was prepared and evaluated in the same manner. The results are also shown in Table 3. In the case of Examples 2 and 3, both the coloration upon heating and the melt index are almost good, but in the case of Control Example 4, the coloration upon heating is remarkable, and the value of the melt index is large, and there is a slight tendency for decomposition. showed that.

[Table] Example 4 and Comparative Examples 5 to 6 Composition of saponified ethylene-vinyl acetate copolymer prepared in the same manner as in Example 1 except that potassium succinate was used in place of the sodium hydrogen succinate used in Example 1. I made things. The sodium acetate content in the saponified copolymer is 0.0362% by weight, and the acetic acid content is 0.1227% by weight.
(α value 3.39), potassium hydrogen succinate content is
It was 0.0484% by weight. Table 4 shows the results of evaluation in the same manner as in Example 1. Table 4 also shows the results of similar evaluations when only acetic acid and potassium hydrogen succinate were added (Control Example 5) and when only sodium acetate and potassium hydrogen succinate were added (Control Example 6). show. Example 4 that satisfies all the structural conditions of the present invention
Although good results almost equivalent to those of Example 1 were obtained, Control Examples 5 to 5 did not satisfy the constitutional conditions of the present invention.
6 gave unsatisfactory results.

【table】

Claims (1)

[Claims] 1. For polyvinyl alcohol polymer,
0.005 to 0.1% by weight of sodium acetate and acetic acid using the formula α = content of acetic acid in polyvinyl alcohol polymer (% by weight) / content of sodium acetate in polyvinyl alcohol polymer (% by weight), 1 < α < 10 … and further at 25°C.
An organic polybasic acid whose pka satisfies _{the formula: X = 1/2 (pk 1 + pk 2 ) , 3.5 <} One or two partial alkali metal salts of organic polybasic acids in which the corresponding acid groups form an alkali metal salt and the acid groups corresponding to pk ₂ are in a free state.
A method for producing a polyvinyl alcohol-based polymer with excellent thermal stability, characterized by adding 0.001 to 0.5% by weight of a polyvinyl alcohol-based polymer.