JP6302176B2 - Method for producing reduced polyvinyl alcohol resin and method for producing polyvinyl acetal resin - Google Patents

Description

The present invention relates to a method for producing a reduced polyvinyl alcohol resin that is unlikely to yellow due to thermal degradation and light degradation, and a method for producing a polyvinyl acetal resin.

Since polyvinyl alcohol resin is excellent in film forming property, transparency, strength and the like, it is widely used taking advantage of its properties. For example, it is used as a raw material for an interlayer film for laminated glass by forming it into a sheet. When used as an interlayer film for laminated glass, transparency is required. However, the polyvinyl alcohol resin and the polyvinyl acetal resin using the polyvinyl alcohol resin as a raw material have a problem of yellowing due to heat deterioration and light deterioration.

The polyvinyl alcohol resin can be obtained, for example, by polymerizing vinyl acetate to obtain a polyvinyl acetate resin and saponifying the polyvinyl acetate resin. One of the factors that cause the polyvinyl alcohol resin to yellow is that oxygen in the reaction system is taken in when vinyl acetate is polymerized, and a carbonyl group is formed in the main chain of the resulting polyvinyl acetate. Other factors include remaining polymerization catalyst, polymerization inhibitor, saponification catalyst, and the like.

In Patent Document 1, paying attention to the polymerization step, when polymerizing a carboxyl group-containing monomer and a vinyl ester-containing monomer, a polymerization catalyst having a half-life of 1 hour is 10 to 90 ° C., and the amount of residual catalyst It is described that a carboxyl group-containing polyvinyl alcohol resin having an excellent whiteness can be obtained by reducing the amount of. Further, it is described that the amount of the polymerization inhibitor can be reduced by using such a polymerization catalyst, and discoloration can be further suppressed.

However, in the method of Patent Document 1, a carbonyl group still exists in the main chain of the polyvinyl alcohol resin, and yellowing caused by the carbonyl group could not be suppressed.

JP 2008-143961 A

The present invention provides a method for producing a reduced polyvinyl alcohol resin that is unlikely to yellow due to thermal degradation and light degradation, and a method for producing a polyvinyl acetal resin.

The present invention relates to a method for producing a reduced polyvinyl alcohol resin in which the amount of carbonyl groups present in the main chain is 0.50 mmol / g or less, wherein the polyvinyl alcohol resin is produced by saponifying the polyvinyl acetate resin. And a reducing step of reducing the polyvinyl acetate resin or polyvinyl alcohol resin using a reducing agent, wherein the reducing agent is sodium borohydride, and in the reducing step, the polyvinyl acetate resin or polyvinyl alcohol It is a manufacturing method of the reduced polyvinyl alcohol resin which adds 4-22 weight% of reducing agents with respect to resin.

Conventionally, in a polymerization process of a polyvinyl acetate resin, as a method for preventing oxygen from being mixed into the reaction system, polymerization was performed in a nitrogen atmosphere. As a result, it was difficult to completely remove oxygen, and it was difficult to reduce the amount of carbonyl groups present in the main chain of the obtained polyvinyl acetate resin.

In contrast, the present inventors reduced the amount of carbonyl groups present in the main chain by reducing the polyvinyl acetate resin or polyvinyl alcohol resin with a predetermined amount of reducing agent, not at the time of polymerization of the polyvinyl acetate resin. In order to suppress the formation of double bonds between carbons in the main chain, the reduced polyvinyl alcohol resin that is difficult to yellow due to thermal deterioration and light deterioration can be obtained, and the present invention is completed. It came.

The present invention is a method for producing a reduced polyvinyl alcohol resin in which the amount of carbonyl groups present in the main chain is 0.50 mmol / g or less.
A carbonyl group present in the main chain forms a keto-enol tautomer with hydrogen bonded to an adjacent carbon atom by heating or light irradiation. The oxygen atom of the carbonyl group present in the main chain is hydrogenated to become an enol, and a double bond is formed between carbons of the main chain. The polyvinyl alcohol resin is yellowed by the occurrence of a double bond chain between the main chain carbons.
By setting the amount of carbonyl group present in the main chain to 0.50 mmol / g or less, yellowing of the polyvinyl alcohol resin due to such a carbonyl group can be effectively prevented.

In the present specification, the main chain refers to the longest molecular chain in the resin, and the carbonyl group present in the main chain refers to a carbonyl group in which an oxygen atom is double-bonded directly to a carbon atom of the main chain.
The polyvinyl alcohol resin, polyvinyl acetate resin and polyvinyl acetal resin, which will be described later, are partially modified by introducing a modified resin having an α-olefin introduced into the main chain, an amine group, a carboxyl group, etc. Also included are resin and the like.

When the amount of carbonyl groups present in the main chain of the reduced polyvinyl alcohol resin is 0.50 mmol / g or less, yellowing due to thermal deterioration and light deterioration can be suppressed. When the amount of the carbonyl group exceeds 0.50 mmol / g, a double bond chain occurs in the main chain due to the mechanism described above, the conjugation length of the main chain is extended, and the absorption wavelength of the reduced polyvinyl alcohol resin is in the visible region. When it reaches, it will turn yellow.
A preferred lower limit of the amount of carbonyl groups present in the main chain of the reduced polyvinyl alcohol resin is 0.01 mmol / g, and a preferred upper limit is 0.40 mmol / g.
According to Polymer Chemistry Vol. 11 (authors: Keizo Suzuki, Takahide Saito), No. 109, page 212 “Regarding the Carbonyl Group in Polyvinyl Alcohol”, when the amount of one unit of polyvinyl alcohol is 44, The content of carbonyl groups present in the polyvinyl alcohol main chain is generally about 0.68 mmol / g.

As a method for quantifying the carbonyl group present in the main chain, the “Chapter 10 Carbonyl Compound” described on page 360 of the organic compound confirmation method (author: Eiichi Funakubo, publisher: Yokendo Co., Ltd.) Quantitative method "and the like. Specifically, hydroxylamine sulfate is dissolved in a mixed solution of water and ethanol and recrystallized to prepare a 0.1 M hydroxylamine sulfate aqueous solution. The target resin is dissolved in a solvent such as butanol, mixed with a 0.1 M aqueous hydroxylamine sulfate solution, and reacted at room temperature for 4 hours. Next, bromophenol blue is added to the reaction solution as an indicator and titrated with a 0.1 M NaOH aqueous solution, whereby the amount of carbonyl groups present in the main chain can be determined. Separately, a blank test is performed using a solution that does not contain the target resin, and blank correction is performed.

The present invention includes a saponification step of saponifying a polyvinyl acetate resin to produce a polyvinyl alcohol resin.
By saponifying the polyvinyl acetate resin, the side chain acetyl groups are hydrolyzed. However, since saponification cannot be performed completely, acetyl groups remain in the obtained polyvinyl alcohol resin. The acetyl group is a functional group present in the side chain of the polyvinyl alcohol resin, and the carbonyl group constituting the acetyl group does not correspond to the above-mentioned “carbonyl group present in the main chain”.
The carbonyl group present in the main chain of polyvinyl acetate is not hydrolyzed by the saponification step.

The saponification method is not particularly limited. For example, an alkaline substance such as sodium hydroxide or potassium hydroxide is used as a saponification catalyst, and saponification is performed by mixing with a polyvinyl acetate resin in a solvent such as methanol or tetrahydrofuran. An alcohol resin can be obtained.

The minimum with the preferable saponification degree of the said polyvinyl alcohol resin is 70 mol%, and a preferable upper limit is 99 mol%.
If the degree of saponification of the polyvinyl alcohol resin is less than 70 mol%, the solubility in water decreases, and it becomes difficult to proceed the acetalization reaction uniformly in an aqueous solvent. Since the bond becomes too strong, the gel is not sufficiently dissolved when dissolved in water, and an aggregate gel is generated, leading to poor quality of the polyvinyl alcohol resin.

The minimum with a preferable polymerization degree of the said polyvinyl acetate resin or polyvinyl alcohol resin is 300, and a preferable upper limit is 3000.
When the polymerization degree of the polyvinyl acetate resin or polyvinyl alcohol resin is less than 300, when used as an interlayer film for laminated glass, the penetration resistance may decrease. When the polymerization degree exceeds 3000, the melt viscosity is Since it does not flow high, extrusion failure may occur when forming an interlayer film for laminated glass.

As for the average molecular weight of the said polyvinyl acetate resin, a preferable minimum is 25800 and a preferable upper limit is 258000. Moreover, as for the average molecular weight of the said polyvinyl alcohol resin, a preferable minimum is 13200 and a preferable upper limit is 132000.

The present invention includes a reduction step of reducing the polyvinyl acetate resin or polyvinyl alcohol resin using a reducing agent.
By reducing using a reducing agent, the carbonyl group present in the main chain of the polyvinyl acetate resin or the polyvinyl alcohol resin can be selectively reduced. When the carbonyl group present in the main chain is reduced, yellowing can be suppressed because a double bond chain between carbons of the main chain does not occur.
In addition, since a reducing agent does not act with respect to the carbonyl group which comprises an acetyl group, the amount of acetyl groups of a polyvinyl acetate resin or a polyvinyl alcohol resin does not change before and after a reduction process.

The reducing agent is preferably a compound that generates hydride ions by hydration or solvation.
The hydride ion reduces a carbonyl group present in the main chain of the polyvinyl acetate resin or polyvinyl alcohol resin to an alcohol. As a nucleophile, the hydride ion nucleophilically attacks the carbonyl carbon of the carbonyl group present in the main chain, and then hydrolyzes it to reduce it to an alcohol. Therefore, it is possible to prevent the double bond of the main chain from keto enol.
Examples of the compound that generates hydride ions by hydration or solvation include metal hydrides. Examples of the metal hydride include lithium aluminum hydroxide (LiAlH ₄ ) and a hydride containing boron.
Examples of the hydride containing boron include sodium borohydride (NaBH ₄ ), lithium triethylborohydride (LiBH (C ₂ H ₅ ) ₃ ), lithium borohydride (LiBH ₄ ), sodium cyanoborohydride (NaBH). ₃ CN) and the like, among which sodium borohydride is particularly preferable.
Lithium aluminum hydroxide (LiAlH ₄ ) is a carbonyl group present in the main chain of the polyvinyl acetate resin or polyvinyl alcohol resin, and a carbonyl group constituting the acetyl group of the side chain of the polyvinyl acetate resin or polyvinyl alcohol resin. From the viewpoint of more selectively reducing the carbonyl group present in the main chain, it is more preferable to use a hydride containing boron.
Although it is possible to reduce the double bond existing in the main chain directly by hydrogenation reaction using Raney nickel or palladium carbon as a catalyst, it is environmentally unfavorable due to the use of heavy metals, and in the resin In this case, heavy metal remains in a small amount, which makes it difficult to develop electronic materials.

As the reduction step, a step of reducing the polyvinyl acetate resin using a reducing agent and a step of reducing the polyvinyl alcohol resin using a reducing agent can be performed.
When performing the process of reducing the said polyvinyl acetate resin using a reducing agent, a polyvinyl acetate resin can be reduced, and the reduced polyvinyl acetate resin can be saponified after that, and a reduced polyvinyl alcohol resin can be produced.
When the step of reducing the polyvinyl alcohol resin using a reducing agent is performed, the polyvinyl acetate resin is saponified to produce the polyvinyl alcohol resin, and then the polyvinyl alcohol resin is reduced to produce the reduced polyvinyl alcohol resin. it can.
Industrially, from the viewpoint of handleability, the step of reducing a polyvinyl acetate resin using a reducing agent is preferable to the step of reducing the polyvinyl alcohol resin using a reducing agent.

When performing the process of reducing the said polyvinyl acetate resin using a reducing agent, 0.1 to 35 weight% of reducing agents are added with respect to a polyvinyl acetate resin.
When the amount of the reducing agent added to the polyvinyl acetate resin is less than 0.1% by weight, the carbonyl group to be reduced is small and yellowing cannot be sufficiently suppressed. The environmental impact of draining waste liquid is large. Further, when a reducing agent containing boron is used, the remaining boron and the hydroxyl group of the polyvinyl acetate resin are cross-linked and gelled, so that the handleability of the obtained polyvinyl acetate resin is lowered.
The minimum with the preferable addition amount with respect to the polyvinyl acetate resin of the said reducing agent is 1.0 weight%, and a preferable upper limit is 25 weight%.

When performing the process of reduce | restoring the said polyvinyl alcohol resin using a reducing agent, 0.1-35 weight% of reducing agents are added with respect to polyvinyl alcohol resin.
When the amount of the reducing agent added to the polyvinyl alcohol resin is less than 0.1% by weight, the carbonyl group to be reduced is small and yellowing cannot be sufficiently suppressed, and when it exceeds 35% by weight, boron is contained. When the reducing agent to be used is used, the remaining boron and the hydroxyl group of the polyvinyl alcohol resin are cross-linked and gelled, so that the handleability of the obtained polyvinyl alcohol resin is lowered.
The minimum with the preferable addition amount with respect to the polyvinyl alcohol resin of the said reducing agent is 1.0 weight%, and a preferable upper limit is 25 weight%.

Before the reduction step, a step of dissolving a polyvinyl acetate resin or a polyvinyl alcohol resin in a solvent so as to be 0.1 to 50% by weight may be performed.
If the amount of the polyvinyl acetate resin or polyvinyl alcohol resin dissolved in the solvent is less than 0.1% by weight, the running cost during industrialization may increase, and if it exceeds 50% by weight, the viscosity increases. Since the reduction reaction is not uniform, the composition of the reduced polyvinyl acetate resin or polyvinyl alcohol resin may vary.
A more preferable lower limit of the amount of the polyvinyl acetate resin or polyvinyl alcohol resin dissolved in the solvent is 3% by weight, and a more preferable upper limit is 10% by weight.

The solvent is preferably water or an alcohol solvent. Examples of the alcohol solvent include methanol, ethanol, isopropanol, butanol and the like. Among these, methanol is preferable.
The said solvent may be used independently and the mixed solvent which mixed two or more types of solvents can also be used.

Examples of the method for adding the reducing agent include a method in which a polyvinyl acetate resin or a polyvinyl alcohol resin is dissolved in the solvent, and the reducing agent is added separately while stirring. As another method, a polyvinyl acetate resin or a polyvinyl alcohol resin is dissolved to prepare a resin solution, and separately, a reducing agent solution in which a reducing agent is dissolved in a solvent is prepared, and the reducing agent solution is dropped into the resin solution. And the like.

It is preferable to perform the said reduction | restoration process at 10-80 degreeC.

The manufacturing method of the polyvinyl acetal resin which has the process of acetalizing the reduced polyvinyl alcohol resin obtained by the manufacturing method of the reduced polyvinyl alcohol resin of this invention and obtaining a polyvinyl acetal resin is also one of this invention.
By having a reduction step before acetalization, boron and counter cations remaining in the reduction step can be washed in the neutralization step after the acetalization reaction, so that residual boron and counter cations in the obtained polyvinyl acetal resin are reduced. be able to.
In the reduction process, it is preferable to completely dissolve the resin. However, if the reduction process is performed after acetalization, a separate process for re-dissolving the resin in an organic solvent or the like and further purification is required. It becomes complicated.

The method for acetalizing the reduced polyvinyl alcohol resin is not limited. For example, in the presence of an acid catalyst, the reduced polyvinyl alcohol resin in an aqueous solution, an alcohol solution, a mixed solution of water and alcohol, or a dimethyl sulfoxide (DMSO) solution. A conventionally known method such as a method of adding aldehyde can be used.

The aldehyde used for acetalization of the reduced polyvinyl alcohol resin is, for example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, glyoxal, glutaraldehyde, Examples include furfural, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde, and other phenyl-substituted alkyl aldehydes. These aldehydes may be used alone or in combination of two or more.

The preferred lower limit of the amount of carbonyl groups present in the main chain of the polyvinyl acetal resin is 0.01 mmol / g, the preferred upper limit is 0.50 mmol / g, the more preferred lower limit is 0.05 mmol / g, and more A preferable upper limit is 0.4 mmol / g.

The acetalization is preferably performed in a high-temperature high-pressure fluid having a temperature of 100 to 400 ° C. and a pressure of 0.5 to 100 MPa.
By acetalizing in a high-temperature and high-pressure fluid at a temperature of 100 to 400 ° C. and a pressure of 0.5 to 100 MPa, acetalization can be performed uniformly in a short time, and a polyvinyl acetal resin having a high degree of acetalization can be obtained. .

If the temperature of the high-temperature and high-pressure fluid is less than 100 ° C., acetalization does not proceed sufficiently, and the degree of acetalization of the resulting polyvinyl acetal resin may be insufficient. May decompose. The temperature of the high-temperature and high-pressure fluid exceeds 100 ° C., preferably 400 ° C. or less, more preferably 350 ° C. or less, and further preferably 300 ° C. or less.
Further, when the pressure of the high-temperature and high-pressure fluid is less than 0.5 MPa, acetalization does not proceed sufficiently, and the degree of acetalization of the obtained polyvinyl acetal resin may be insufficient. The cost required increases and is not economical. A preferable upper limit of the pressure of the high-temperature high-pressure fluid is 40 MPa, and a more preferable upper limit is 10 MPa.

The high temperature and high pressure fluid is not particularly limited, and examples thereof include water, alcohol, air, carbon dioxide, nitrogen, helium, and argon. These may be used singly or in combination of two or more as a mixed fluid. Among these, water, alcohol, or a mixed fluid of water and alcohol is preferable. In addition, from the viewpoint of preventing deterioration due to oxidation by oxygen in the atmosphere, carbon dioxide and nitrogen are preferable to the atmosphere. The alcohol is not particularly limited, and examples thereof include methanol, ethanol, propanol, butanol, pentanol, and hexanol.

In the polyvinyl acetal resin obtained by the method for producing a polyvinyl acetal resin of the present invention, the preferable lower limit of the degree of acetalization is 40 mol%, and the preferable upper limit is 90 mol%.
When the degree of acetalization of the polyvinyl acetal resin is less than 40 mol%, the compatibility with the plasticizer may be reduced. When the degree of acetalization exceeds 90 mol%, the breaking strength is reduced when used as an interlayer film for laminated glass. There are things to do.
The minimum with a more preferable acetalization degree of the said polyvinyl acetal resin is 50 mol%, and a more preferable upper limit is 85 mol%.
In the present specification, the degree of acetalization refers to the ratio of the number of hydroxyl groups acetalized with aldehydes among the number of hydroxyl groups of polyvinyl alcohol.

The minimum with the preferable amount of hydroxyl groups of the said polyvinyl acetal resin is 10 mol%, and a preferable upper limit is 60 mol%.
When the amount of hydroxyl groups in the polyvinyl acetal resin is less than 10 mol%, the breaking strength may decrease when used as an interlayer film for laminated glass, and when it exceeds 60 mol%, the compatibility with the plasticizer decreases. Sometimes.
The more preferable lower limit of the hydroxyl group content of the polyvinyl acetal resin is 50 mol%, and the more preferable upper limit is 25 mol%.

Although the polymerization degree of the said polyvinyl acetal resin is not specifically limited, A preferable minimum is 300 and a preferable upper limit is 3000. When the degree of polymerization of the polyvinyl acetal resin is less than 300, when used as an interlayer film for laminated glass, the penetration resistance may decrease. When the degree of polymerization exceeds 3000, the melt viscosity is increased when forming the interlayer film for laminated glass. May rise and cause poor extrusion.

The reduced polyvinyl alcohol resin obtained by the method for producing the reduced polyvinyl alcohol resin of the present invention may be formed into a sheet shape to form a polyvinyl alcohol resin sheet. Moreover, the polyvinyl acetal resin obtained by the method for producing a polyvinyl acetal resin of the present invention may be formed into a sheet shape to form a polyvinyl acetal resin sheet.

The preferable lower limit of the thickness of the polyvinyl alcohol resin sheet and the polyvinyl acetal resin sheet is 3 mm, and the preferable upper limit is 150 mm.

The polyvinyl alcohol resin sheet or the polyvinyl acetal resin sheet may be laminated between a pair of glass plates to form a laminated glass.

The said glass plate can use the transparent plate glass generally used. Examples thereof include inorganic glass such as float plate glass, polished plate glass, template glass, netted glass, wire-containing plate glass, colored plate glass, heat ray absorbing glass, heat ray reflecting glass, and green glass. Further, an ultraviolet shielding glass having an ultraviolet shielding coating layer formed on the glass surface can also be used. Furthermore, organic plastics plates such as polyethylene terephthalate, polycarbonate, and polyacrylate can also be used.
Two or more types of glass plates may be used as the glass plate. For example, a transparent float plate glass and a colored glass plate such as green glass may be used. Moreover, you may use the glass plate from which 2 or more types of thickness differs as said glass plate.

The reduced polyvinyl alcohol resin obtained by the method for producing the reduced polyvinyl alcohol resin of the present invention and the polyvinyl acetal resin obtained by the method for producing the polyvinyl acetal resin of the present invention are a metal-treated wash primer, various paints, an adhesive, It can be used for various purposes, such as a resin processing agent and a ceramic binder, and can also be used for electronic materials.

By the method for producing a reduced polyvinyl alcohol resin of the present invention, a reduced polyvinyl alcohol resin in which the amount of carbonyl groups present in the main chain is 0.50 mmol / g or less is obtained.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reduced polyvinyl alcohol resin which is hard to yellow by heat deterioration and light deterioration, and the manufacturing method of polyvinyl acetal resin can be provided.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

Example 1
(Production of reduced polyvinyl alcohol resin)
Reaction vessel containing 5 g of polyvinyl acetate resin (PVAc resin) having a carbonyl group content of 0.93 mmol / g in the main chain, 0.55 g of sodium borohydride (NaBH ₄ ) as a reducing agent, and 100 g of methanol as a solvent In addition, the reaction was carried out at 25 ° C. for 60 minutes for reduction. The reduced polyvinyl acetate resin was extracted and washed with ethyl acetate and water respectively, further washed with brine, then dried over magnesium sulfate and filtered to obtain a polyvinyl acetate resin powder.
The resulting polyvinyl acetate resin was saponified by adding 100 parts by weight of methanol and 5 parts by weight of 0.5M sodium hydroxide methanol solution, so that the amount of carbonyl groups present in the main chain was 0.08 mmol / g. Reduced polyvinyl alcohol resin (PVA resin) was obtained.
The amount of carbonyl group present in the main chain was determined by the following method. First, hydroxylamine sulfate was dissolved in a mixed solution of water and ethanol and recrystallized to prepare a 0.1 M hydroxylamine sulfate aqueous solution. 20 ml of butanol solution containing 0.5 g of polyvinyl acetate resin or reduced polyvinyl alcohol resin and 25 ml of 0.1 M hydroxylamine sulfate aqueous solution were mixed and reacted at room temperature for 4 hours. Next, bromophenol blue was added to the reaction solution as an indicator and titrated with a 0.1 M NaOH aqueous solution to determine the amount of carbonyl groups present in the main chain. Separately, a blank test was performed using 20 ml of butanol not containing polyvinyl acetate resin or reduced polyvinyl alcohol resin, and blank correction was performed.

(Manufacture of polyvinyl acetal resin)
Acetalization is performed by adding 5 g of the obtained reduced polyvinyl alcohol resin, 100 g of water, 3.5 ml of n-butyraldehyde, and 3 g of 25% hydrochloric acid as a catalyst to another reaction vessel and reacting at 50 ° C. and 1 MPa for 180 minutes. A polyvinyl acetal resin solution was obtained.
After drying the polyvinyl acetal resin, it was dissolved in dimethyl sulfoxide and precipitated in water three times. Thereafter, the polyvinyl acetal resin was sufficiently dried, redissolved in deuterated dimethyl sulfoxide, and the degree of acetalization, the amount of hydroxyl groups, and the amount of acetyl groups were measured by ¹ H-NMR measurement.
The amount of carbonyl groups present in the main chain of the polyvinyl acetal resin was measured by the same method as described above.

(Manufacture of resin sheets)
The obtained polyvinyl acetal resin was press-pressed to obtain a resin sheet. The thickness of the resin sheet was 5 mm.

(Manufacture of laminated glass)
The obtained resin sheet was laminated | stacked between a pair of glass plate (thickness 10mm) of length 300mm x width 300mm, and the laminated body was obtained. The obtained laminate was vacuum-pressed while being held at 90 ° C. for 30 minutes with a vacuum laminator to be pressure-bonded. After the pressure bonding, pressure bonding was performed for 20 minutes using an autoclave under conditions of 140 ° C. and 14 MPa to obtain a laminated glass.

(Example 2)
A polyvinyl acetate resin was reduced in the same manner as in Example 1 except that the formulation described in Table 1 was used, and then the polyvinyl alcohol resin was saponified to obtain a reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 3)
A polyvinyl acetate resin was reduced in the same manner as in Example 1 except that the formulation described in Table 1 was used, and then the polyvinyl alcohol resin was saponified to obtain a reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 except that the reaction conditions described in Table 1 were used to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

Example 4
A reduced polyvinyl alcohol resin was obtained by reducing in the same manner as in Example 1 except that a polyvinyl acetate resin having a carbonyl group content in the main chain of 1.03 mmol / g was used. Using the obtained reduced polyvinyl alcohol resin, carbon dioxide was injected into the reaction vessel, the temperature inside the vessel was adjusted to 130 ° C., the pressure inside the vessel was adjusted to 3.0 MPa using a pressure regulating valve, and stirring was performed for 60 minutes. An acetalization reaction was performed. Then, the reaction part was cooled to room temperature and the liquid mixture containing a polyvinyl acetal resin was obtained. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 5)
5 g of polyvinyl alcohol resin obtained by saponifying polyvinyl acetate (the amount of carbonyl groups present in the main chain is 0.97 mmol / g), 0.55 g of sodium borohydride (NaBH ₄ ) as a reducing agent, and 100 g of water as a solvent was placed in a reaction vessel and reacted at 25 ° C. for 60 minutes for reduction. The reduced polyvinyl alcohol resin was washed with cold water three times and dried to obtain a reduced polyvinyl alcohol resin powder.
The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 6)
A polyvinyl alcohol resin was reduced in the same manner as in Example 5 except that the composition described in Table 1 was used, to obtain a reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Examples 7 and 8)
A polyvinyl alcohol resin was reduced in the same manner as in Example 5 except that the formulation and reaction conditions described in Table 1 were used, to obtain a reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 except that the reaction conditions described in Table 1 were used to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

( Reference Example 9)
A polyvinyl acetate resin was reduced in the same manner as in Example 1 except that the reducing agent was lithium borohydride (LiBH ₄ ), and then the polyvinyl alcohol resin was saponified to obtain a reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 1)
Using polyvinyl alcohol (PVA) having a carbonyl group content of 0.83 mmol / g in the main chain, acetalization was carried out in the same manner as in Example 1 without reducing polyvinyl alcohol to obtain a polyvinyl acetal resin. It was. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Examples 2 to 4)
Acetalization was carried out in the same manner as in Example 1 except that the reaction conditions shown in Table 1 were used without reducing polyvinyl alcohol to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 5)
Except having changed the addition amount of a reducing agent as shown in Table 1, it reduced similarly to Example 1, and saponified after that, and obtained the reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 6)
Except having changed the addition amount of a reducing agent as shown in Table 1, it reduced similarly to Example 1, and saponified after that, and obtained the reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. Part of the obtained polyvinyl acetal resin was gelled, and the amount of carbonyl groups could not be measured. In Comparative Example 6, the handleability of the obtained reduced polyvinyl acetal resin was poor, and the resin sheet and the laminated glass could not be produced.

(Comparative Example 7)
Except having changed the addition amount of a reducing agent as shown in Table 1, it reduced the polyvinyl alcohol resin like Example 5, and obtained the reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. A resin sheet and a laminated glass were produced in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 8)
Except having changed the addition amount of a reducing agent as shown in Table 1, it reduced the polyvinyl alcohol resin like Example 5, and obtained the reduced polyvinyl alcohol resin. The obtained reduced polyvinyl alcohol resin was gelled and the amount of carbonyl groups could not be measured. The obtained reduced polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin. In Comparative Example 8, the handleability of the obtained reduced polyvinyl acetal resin was poor, and the resin sheet and the laminated glass could not be produced.

<Evaluation>
About the laminated glass obtained by the Example and the comparative example, it evaluated by the following method. The results are shown in Table 1.

(Heat resistance test)
About the laminated glass obtained by the Example and the comparative example, it tested by the method based on 7.4 "heat resistance test" of JIS R3205: 2005 "laminated glass", observed visually, and evaluated on the following references | standards. .
○: Coloring is not observed Δ: Colored slightly yellow ×: Colored yellow

(Light resistance test)
About the laminated glass obtained by the Example and the comparative example, it tested by the method based on 7.3 "light resistance test" of JIS R3205: 2005 "Laminated glass", observed visually, and evaluated on the following references | standards. .
○: Coloring is not observed Δ: Colored slightly yellow ×: Colored yellow

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reduced polyvinyl alcohol resin which is hard to yellow by heat deterioration and light deterioration, and the manufacturing method of polyvinyl acetal resin can be provided.

Claims (3)

A method for producing a reduced polyvinyl alcohol resin in which the amount of carbonyl groups present in the main chain is 0.50 mmol / g or less,
A saponification step of producing a polyvinyl alcohol resin by saponifying a polyvinyl acetate resin, and
A reduction step of reducing the polyvinyl acetate resin or polyvinyl alcohol resin using a reducing agent;
The reducing agent is sodium borohydride;
In the said reduction process, 4-22 weight% of reducing agents are added with respect to polyvinyl acetate resin or polyvinyl alcohol resin, The manufacturing method of reduced polyvinyl alcohol resin characterized by the above-mentioned. A method for producing a polyvinyl acetal resin comprising a step of acetalizing a reduced polyvinyl alcohol resin obtained by the method for producing a reduced polyvinyl alcohol resin according to claim 1 to obtain a polyvinyl acetal resin. The method for producing a polyvinyl acetal resin according to claim 2, wherein the acetalization is performed in a high-temperature high-pressure fluid at a temperature of 100 to 400 ° C and a pressure of 0.5 to 100 MPa.