JP2015196753A - polyvinyl acetal resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl acetal resin that prevents the occurrence of residual stress in molding and can reduce birefringence, and an optical member made using the polyvinyl acetal resin, and a method of producing the polyvinyl acetal resin.SOLUTION: This invention relates to a polyvinyl acetal resin that is obtained by the acetalization of polyvinyl alcohol using aromatic aldehyde and alkyl aldehyde, wherein when differential scanning calorimetry is performed, the polyvinyl acetal resin has a melting peak in the range of 120-250°C.

Description

The present invention relates to a polyvinyl acetal resin that hardly causes residual stress during molding and can reduce birefringence, an optical member using the polyvinyl acetal resin, and a method for producing the polyvinyl acetal resin.

Conventionally, polymethylmethacrylate resins have good transparency and low birefringence characteristics, and are therefore used in large numbers as optical members such as lenses and light guide plates.
However, in recent years, polymethylmethacrylate resin has not been able to be said to have sufficient heat resistance amid increasing demand for higher heat resistance to resins from the viewpoint of higher density and safety of electronic devices. .

On the other hand, polycarbonate resins obtained by reacting bisphenol A with a carbonate precursor are excellent in transparency, heat resistance, mechanical properties, and dimensional stability, and thus are used in various applications including optical members.
However, polycarbonate resin has a large birefringence caused by the orientation of molecular chains and has a residual stress at the time of molding for the characteristics required for optical members such as lenses, prisms, light guide plates and optical waveguides that require optical accuracy Due to the large optical distortion caused by the above, it has been difficult to develop the optical element.

In contrast, attempts have been made to use polyvinyl acetal resins having excellent transparency, weather resistance, and the like for optical members.
For example, Patent Document 1 discloses a technique for reducing the occurrence of birefringence by using a polyvinyl acetal resin as an optical member and further increasing the glass transition temperature.

However, even when a polyvinyl acetal resin is used, as in the case of a polycarbonate resin, the problem that optical distortion occurs due to heating during molding and birefringence occurs in the optical member has not been solved.

JP 2008-69235 A

An object of the present invention is to provide a polyvinyl acetal resin that hardly causes residual stress during molding and can reduce birefringence, an optical member using the polyvinyl acetal resin, and a method for producing the polyvinyl acetal resin. To do.

The present invention is a polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol using an aromatic aldehyde and an alkyl aldehyde, and has a melting peak in the range of 120 to 250 ° C. when differential scanning calorimetry is performed. It has a polyvinyl acetal resin.
The present invention is described in detail below.

As a result of intensive studies, the present inventors obtained an acetalization of polyvinyl alcohol using an aromatic aldehyde and an alkyl aldehyde, and within the range of 120 to 250 ° C. when differential scanning calorimetry was performed. The polyvinyl acetal resin having a melting peak at the bottom is less likely to cause residual stress during molding and can reduce birefringence, so that it can be particularly suitably used as a material for optical members, and the present invention is completed. It came.

The polyvinyl acetal resin of the present invention has a melting peak in the range of 120 to 250 ° C. when differential scanning calorimetry is performed. If the melting peak temperature (peak top temperature) is less than 120 ° C., the elastic modulus decreases. When it exceeds 250 ° C., the transparency is lowered. The preferable lower limit of the melting peak temperature is 170 ° C., and the preferable upper limit is 220 ° C.
In the present invention, differential scanning calorimetry (DSC) is a method of measuring a difference in energy input as a function of temperature while changing the temperature of a substance and a reference substance according to a program.

When the polyvinyl acetal resin of the present invention is subjected to differential scanning calorimetry, the preferred lower limit of the heat of fusion is 5 mJ / mg, and the preferred upper limit is 100 mJ / mg. If the heat of fusion is less than 5 mJ / mg, the equilibrium elastic modulus may be reduced, and if it exceeds 100 mJ / mg, the transparency may be reduced.
A more preferable lower limit of the heat of fusion is 10 mJ / mg, and a more preferable upper limit is 70 mJ / mg.

FIG. 1 shows an example of the DSC curve when the differential scanning calorimetry is performed at 10 to 250 ° C. for the polyvinyl acetal resin of the present invention. The upper curve is the DDSC curve, and the lower curve is the DSC curve. In the DSC curve shown in FIG. 1, a peak having a peak top near 192.9 ° C. is a melting peak, and the temperature is a so-called melting point. In the present invention, the heat of fusion is defined as the area of the portion surrounded by the straight line connecting the inflection points from the inflection points of the melting peaks and the lines constituting the melting peaks. The differential scanning calorimetry can be performed using, for example, a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Co., Ltd., DSC 6220).

As DSC measurement conditions, for example, the temperature is raised from room temperature to 250 ° C. at 10 ° C./min as a first cycle under nitrogen flow conditions, held for 5 minutes, and then lowered to 10 ° C. at 10 ° C./min. Subsequently, as a second cycle, the temperature can be raised to 250 ° C. at 5 ° C./min, and the heat of fusion and the melting point can be evaluated using the DSC curve shown in the second cycle. The glass transition temperature (Tg) is the intersection of the original baseline and the tangent at the inflection point.

In the polyvinyl acetal resin of the present invention, the preferable lower limit of the meso / racemo ratio of the acetal ring structure is 60, and the preferable upper limit is 95. When the meso / rasemo ratio of the acetal ring structure is less than 60, the syndiotactic hydroxyl group relatively increases, which may increase the molding viscosity and cause molding failure. The meso / rasemo ratio is 95. If it exceeds, the isotactic hydroxyl group relatively increases, whereby the temperature of the melting peak is lowered and the elastic modulus may be lowered. A more preferred lower limit is 80, and a more preferred upper limit is 90.
In the present invention, the “meso / racemo ratio of the acetal ring structure” means the amount of acetal group having an acetal ring structure (racemore acetal ring) formed from a hydroxyl group having a syndiotactic structure in the three-dimensional structure of the acetal ring. Is the ratio of the amount of acetal groups having an acetal ring structure (mesoacetal ring) formed from a hydroxyl group having an isotactic structure. For example, a polyvinyl acetal resin is dissolved in a solvent such as dimethyl sulfoxide. The proton NMR was measured at a measurement temperature of 150 ° C., and the integrated value of the peak derived from the mesoacetal ring structure appearing near 4.5 ppm and the peak derived from the racemoacetal ring structure appearing near 4.2 ppm was compared, Measure carbon NMR and appear around 100ppm A peak derived from the meso acetal ring structure can be measured by comparing the integral value of peaks derived from Rasemoasetaru ring structure appearing near 94 ppm.

The polyvinyl acetal resin of the present invention preferably has a syndiotactic hydroxyl ratio of 28 to 65 mol%. Birefringence may occur when the syndiotactic hydroxyl group ratio is outside the above range. The syndiotactic hydroxyl group ratio is more preferably 36 to 50 mol%.
The said syndiotactic hydroxyl group ratio shows the three-dimensional state of the hydroxyl group of polyvinyl acetal resin, and can be represented by the ratio of the syndiotactic hydroxyl group with respect to all the hydroxyl groups in polyvinyl acetal resin. In addition, the total amount of hydroxyl groups (mol%) and the amount of syndiotactic hydroxyl groups (mol%) in the polyvinyl acetal resin can be evaluated by ¹³ C-NMR.
Specifically, the amount of syndiotactic hydroxyl groups is determined from an integration ratio of 63.5 to 64.5 ppm on a ¹³ C-NMR chart, and the value is A, and the total amount of hydroxyl groups in the polyvinyl acetal resin is 62. Obtained as 5-69.0 ppm, and the value is B. The syndiotactic hydroxyl group ratio is represented by A / B × 100 (mol%).

The total degree of acetalization of the polyvinyl acetal resin of the present invention is preferably 5 to 50 mol%. When the total degree of acetalization is less than 5 mol%, the transparency may be lowered when used for an interlayer film for laminated glass. When the total degree of acetalization exceeds 50 mol%, the amount of hydroxyl groups is relatively decreased, and the crystallinity may be lowered. The more preferable lower limit of the degree of total acetalization is 10 mol%, and the more preferable upper limit is 40 mol%. The degree of total acetalization is a value indicating the mole fraction obtained by dividing the amount of ethylene groups to which acetal groups are bonded by the total amount of ethylene groups in the main chain as a percentage. The amount of ethylene group to which an acetal group is bonded can be measured using, for example, JIS K 6728 “Testing method for polyvinyl butyral”.
In the present specification, the total degree of acetalization indicates the content of all acetal groups. When the acetal group is an acetoacetal group, the degree of acetoacetalization, when the acetal group is a butyral group, Also called the degree of butyral.

In the polyvinyl acetal resin of the present invention, the content of the portion acetalized by the aromatic aldehyde (the degree of acetalization by the aromatic aldehyde) is preferably 3 mol% and the preferable upper limit is 50 mol%. If the degree of acetalization with an aromatic aldehyde is less than 3 mol%, the solvent solubility may decrease, and if the degree of acetalization with an aromatic aldehyde exceeds 50 mol%, the melting point decreases and the elastic modulus decreases. There are things to do.

The preferable lower limit of the degree of acetalization of the polyvinyl acetal resin with an alkyl aldehyde is 5 mol%, and the preferable upper limit is 40 mol%. If the degree of acetalization with an alkyl aldehyde is less than 5 mol%, solvent solubility may decrease, and if the degree of acetalization with an alkyl aldehyde exceeds 40 mol%, the melting point decreases and the elastic modulus May decrease.

The minimum with the preferable amount of hydroxyl groups of the polyvinyl acetal resin of this invention is 50 mol%, and a preferable upper limit is 95 mol%. When the amount of the hydroxyl group is less than 50 mol%, the melting point may disappear. When the amount of the hydroxyl group exceeds 95 mol%, the transparency may be lowered. The more preferable lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin is 60 mol%, and the more preferable upper limit is 90 mol%.
The amount of hydroxyl groups in the polyvinyl acetal resin is a value obtained by dividing the amount of ethylene groups to which hydroxyl groups are bonded by the total amount of ethylene groups in the main chain, as a percentage. The amount of ethylene groups to which hydroxyl groups are bonded can be determined, for example, by measuring the amount of ethylene groups to which hydroxyl groups of polyvinyl alcohol as a raw material are bonded using JIS K 6726 “Testing methods for polyvinyl alcohol”.

The preferable lower limit of the amount of acetyl groups in the polyvinyl acetal resin of the present invention is 1 mol%, and the preferable upper limit is 25 mol%. When the amount of the acetyl group exceeds 25 mol%, the melting point disappears and desired physical properties may not be obtained.
The amount of acetyl groups means the value obtained by subtracting the amount of ethylene groups to which acetal groups are bonded and the amount of ethylene groups to which hydroxyl groups are bonded from the total amount of ethylene groups in the main chain. This is a value obtained by dividing the mole fraction obtained by dividing by the base amount as a percentage.

The preferred lower limit of the average degree of polymerization of the polyvinyl acetal resin of the present invention is 1000, and the preferred upper limit is 3000. If the average degree of polymerization is less than 1000, it may flow during molding and cause molding defects. A more preferable lower limit of the average degree of polymerization is 1500, and a more preferable upper limit is 2500.
In addition, the average polymerization degree of the said polyvinyl acetal resin can be calculated | required by the average polymerization degree of polyvinyl alcohol used as a raw material.

The polyvinyl acetal resin of the present invention can be produced by acetalizing polyvinyl alcohol using an aromatic aldehyde and an alkyl aldehyde. Thereby, aromatic stacking can be used, and molecular chains are regularly oriented. As a result, ordering is also generated in the amorphous part of the resin, and it becomes a tough material together with the crystal part.

Examples of the aromatic aldehyde include benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, other alkyl-substituted benzaldehydes, chlorbenzaldehyde, and other halogen-substituted benzaldehydes. Moreover, you may use a polycyclic aromatic aldehyde as said aromatic aldehyde.
Examples of the polycyclic aromatic aldehyde include naphthyl aldehyde.
Furthermore, an aromatic aldehyde having a substituent such as a hydroxy group, an alkoxy group, an amino group, or a cyano group on the aromatic ring may be used. Of these, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, and 4-methylbenzaldehyde are preferable.

As said alkyl aldehyde, the C1-C19 linear alkyl and the aldehyde which has branched alkyl are preferable. Specific examples include acetaldehyde, propionyl aldehyde, n-butyraldehyde, isobutyraldehyde, tert-butyraldehyde and the like.

When performing the acetalization, in addition to the aromatic aldehyde and the aldehyde, for example, an aldehyde such as cyclic saturation having 1 to 19 carbon atoms may be added.
Specific examples of aldehydes other than the aromatic aldehyde and alkyl aldehyde include formaldehyde and cyclohexyl aldehyde. The aldehyde may be one obtained by substituting one or more hydrogen atoms with halogen or the like except formaldehyde. These may be used alone or in combination of two or more.

As for the compounding quantity of the said aromatic aldehyde with respect to the said polyvinyl alcohol, a preferable minimum is the same as mass ratio, and a preferable upper limit is 30 times of mass ratio. If the blending amount of the aromatic aldehyde is less than 1 times the mass ratio, acetalization may not proceed sufficiently, and the degree of acetalization of the resulting polyvinyl acetal resin may be insufficient. Even if the blending amount of the aromatic aldehyde exceeds 30 times the mass ratio, it may not contribute to the improvement of the degree of acetalization, leading to an increase in cost, and may cause a side reaction other than acetalization. A more preferable upper limit of the blending amount of the aromatic aldehyde is 12 times the mass ratio, and a more preferable upper limit is 3 times the mass ratio.

The polyvinyl acetal resin of the present invention is obtained by, for example, reacting polyvinyl alcohol with an aromatic aldehyde and an alkyl aldehyde 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 in the presence of an acid catalyst. It can manufacture by performing the process of acetalizing. By using such a method, the amorphous part is preferentially acetalized by the aromatic aldehyde, the intermolecular interaction is small, and the residual stress can be reduced. As a result, a polyvinyl acetal resin having a small birefringence is obtained.
On the other hand, in a general acetalization reaction under normal temperature and pressure, when the reaction proceeds uniformly, intermolecular interaction occurs in the micro and residual stress increases, resulting in residual birefringence. Will be.

As said polyvinyl alcohol, conventionally well-known polyvinyl alcohols, such as resin manufactured by saponifying polyvinyl acetate with an alkali, an acid, ammonia water, etc., can be used, for example. The polyvinyl alcohol may be completely saponified, but it needs to be completely saponified if at least one unit having a double hydroxyl group with respect to the meso or racemic position is present at least in one position of the main chain. Alternatively, partially saponified polyvinyl alcohol may be used.
Moreover, as said polyvinyl alcohol, the copolymer of the monomer and vinyl alcohol which can be copolymerized with vinyl alcohol, such as an ethylene-vinyl alcohol copolymer and a partly saponified ethylene-vinyl alcohol copolymer, can also be used.

The polyvinyl alcohol may have a carbonyl group.
In general, as a cause of coloring polyvinyl alcohol, it has been reported that a small amount of carbonyl group is involved in polyvinyl alcohol (polymer papers, vol. 37, No. 8, p. 521-525), in the method for producing a polyvinyl acetal resin of the present invention, by using an acid catalyst as described later, even when there is a large amount of carbonyl groups contained in a trace amount, the resulting polyvinyl acetal resin is colored. Can be reduced.

As the aromatic aldehyde, alkyl aldehyde, and other aldehydes, those similar to those described above can be used.

The acid catalyst preferably has a pKa value of 0 to 5 and a molecular weight of 60 or more. By using such an acid catalyst, coloring of the obtained polyvinyl acetal resin can be reduced, and a transesterification reaction as a side reaction can be suppressed.
When the pKa value of the acid catalyst is less than 0, the acid chain of the acid catalyst has a high acid strength, so that the main chain deteriorates and the resulting polyvinyl acetal resin may be colored. When the pKa value of the acid catalyst exceeds 5, the acid strength of the acid catalyst is low, so that the reaction rate of acetalization is slow and the reaction time may be long. From the viewpoint of such a balance between coloring and reaction time, a more preferable lower limit of the pKa value of the acid catalyst is 3, and a more preferable upper limit is 4.5.
In the present specification, the pKa value means a common logarithm of the acid dissociation constant Ka measured in water at 25 ° C. It means that it is a weak acid, so that the said pKa value is large.

When the molecular weight of the acid catalyst is less than 60, the acid catalyst itself reacts with the hydroxyl group of the polyvinyl alcohol, and the transesterification proceeds as a side reaction, so that a polyvinyl acetal resin having a desired composition cannot be obtained. Sometimes. The more preferable lower limit of the molecular weight of the acid catalyst is 80, the still more preferable lower limit is 120, and the particularly preferable lower limit is 190.
In addition, the upper limit of the molecular weight of the acid catalyst is not particularly limited.

The acid catalyst is not particularly limited as long as the acid has a pKa value and a molecular weight within the above range. For example, trichloroacetic acid, dichloroacetic acid, chloroacetic acid, benzoic acid, squaric acid, picric acid, trifluoroacetic acid, citric acid, Examples include malic acid, succinic acid, gluconic acid, ascorbic acid, lactic acid, oxalic acid, acetic acid, glyoxylic acid and the like. These may be used alone or in combination of two or more. Among them, from the viewpoint of productivity, handling properties, etc., carboxyls such as trichloroacetic acid, dichloroacetic acid, chloroacetic acid, benzoic acid, trifluoroacetic acid, citric acid, malic acid, succinic acid, gluconic acid, lactic acid, oxalic acid, acetic acid, etc. An acid having a group is preferred, citric acid or benzoic acid is more preferred, and citric acid is still more preferred. Table 1 shows pKa values and molecular weights of typical acids generally used as acid catalysts.

As for the addition amount of the said acid catalyst, a preferable minimum is 1 mass% and a preferable upper limit is 100 mass% with respect to 100 mass% of the said polyvinyl alcohol. If the amount of the acid catalyst added is less than 1% by mass, acetalization may not proceed sufficiently, and the degree of acetalization of the resulting polyvinyl acetal resin may be insufficient. Even if the addition amount of the acid catalyst exceeds 100% by mass, it may not contribute to the improvement of the degree of acetalization, leading to an increase in cost, and may cause a side reaction other than the acetalization. A more preferable lower limit of the addition amount of the acid catalyst is 5% by mass, and a more preferable upper limit is 25% by mass.

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.

The high-temperature and high-pressure fluid preferably has a temperature of 100 to 400 ° C. and a pressure of 0.5 to 100 MPa. By reacting the polyvinyl alcohol and the aromatic aldehyde in the high-temperature and high-pressure fluid, it is possible to uniformly acetalize in a short time and obtain a polyvinyl acetal resin having a high degree of acetalization. Further, since the acetalization reaction proceeds selectively in the amorphous part of the hydroxyl group, the remaining hydroxyl group can increase the crystal part.
In the acetalization reaction between the polyvinyl alcohol and the aromatic aldehyde, the resin may be insolubilized or inhomogeneously precipitated as the reaction proceeds. In the resin thus deposited, since the hydroxyl group to be acetalized is confined in the resin, the progress of the acetalization reaction is inhibited, and the atmospheric pressure reaction can only achieve an acetalization degree of about 40 mol%. In the method for producing a polyvinyl acetal resin of the present invention, the aromatic aldehyde can penetrate into the precipitated resin by reacting the polyvinyl alcohol and the aromatic aldehyde in the high-temperature and high-pressure fluid. A high degree of acetalization that could not be achieved by pressure reaction can be achieved. Further, the remaining hydroxyl groups are easy to form a crystal structure.

When the temperature of the high-temperature and high-pressure fluid is less than 100 ° C., acetalization does not proceed sufficiently, the degree of acetalization of the obtained polyvinyl acetal resin becomes insufficient, or coloring occurs in the obtained polyvinyl acetal resin. There is. When the temperature of the high-temperature and high-pressure fluid exceeds 400 ° C., the main chain of the polyvinyl alcohol is deteriorated, and the resulting polyvinyl acetal resin may be colored. The temperature of the high-temperature and high-pressure fluid is more than 200 ° C. and preferably 400 ° C. or less, more preferably 350 ° C. or less, and particularly preferably 300 ° C. or less.

If 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 resulting polyvinyl acetal resin may be insufficient. If the pressure of the high-temperature and high-pressure fluid exceeds 100 MPa, the cost required for the reaction apparatus increases, which may not be economical. A more 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 method of reacting the polyvinyl alcohol and the aromatic aldehyde in the high-temperature and high-pressure fluid in the presence of the acid catalyst is not particularly limited, but contains the polyvinyl alcohol, the aromatic aldehyde, and the acid catalyst. After preparing the liquid mixture (henceforth a raw material liquid mixture) to perform, the method of inject | pouring the said high temperature / high pressure fluid in a reactor and adjusting temperature and pressure is preferable.
The raw material mixture may be a solution or suspension containing a solvent such as water. In addition, in order for the said acid catalyst to exhibit a catalytic action, it is necessary to melt | dissolve in the solvent to be used. In the method for producing the polyvinyl acetal resin of the present invention, the dielectric constant of the solvent is increased by making the raw material mixture under high temperature and high pressure, and such increase in dielectric constant contributes to the dissolution of the acid catalyst in the solvent. The reaction rate of acetalization can be increased.

The above reaction apparatus is not particularly limited. For example, when a continuous reaction apparatus using a flow system, a batch reaction apparatus that performs a reaction using raw materials in one reaction container, and a reaction container is connected in series, the reaction rate proceeds to a certain rate. Examples include a semi-flow type reaction apparatus that is sequentially sent to the next reaction vessel.

The reactor preferably has a mechanism for stirring the raw material mixture and the high-temperature high-pressure fluid.
As described above, in the acetalization reaction between the polyvinyl alcohol and the aromatic aldehyde, as the reaction proceeds, the resin may be insolubilized or inhomogeneously precipitated. If the resin thus deposited becomes clogged in the reaction part or line, the production is interrupted. Further, the precipitation of the resin is more likely to occur as the concentration of the raw material is increased, and the production efficiency is lowered. Since the reaction apparatus has a mechanism for stirring the raw material mixture and the high-temperature high-pressure fluid, the precipitated resin can be atomized, and the precipitated resin is prevented from clogging in the reaction part or line. Can do.

The mechanism for stirring the raw material mixture and the high-temperature high-pressure fluid is not particularly limited as long as it is a component that can be disposed in the reaction section and can stir the fluid. And the like, a static stirring mechanism such as a static mixer, and a stirring mechanism that causes convection by applying a temperature gradient.

An optical member is obtained by performing molding or the like using the polyvinyl acetal resin of the present invention. Such an optical member is also one aspect of the present invention. The optical member of the present invention preferably has a birefringence value of 0.01 or less at 130 ° C.

Examples of the optical member of the present invention include optical members for use in optical semiconductor elements such as lenses, transparent substrates, optical waveguides, light emitting diodes (LEDs), phototransistors, photodiodes, and solid-state imaging devices.

According to the present invention, it is possible to provide a polyvinyl acetal resin that hardly causes residual stress during molding and can reduce birefringence, an optical member using the polyvinyl acetal resin, and a method for producing the polyvinyl acetal resin.

It is an example of the DSC curve at the time of performing differential scanning calorimetry about the polyvinyl acetal resin of this invention. It is a schematic diagram which shows the apparatus used in the residual stress and birefringence measurement.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
(Synthesis of polyvinyl butyral resin)
In a reaction vessel, 5.5 g of water was added to 0.5 g of powdery polyvinyl alcohol (saponification degree 99%, polymerization degree 1800), and the mixture was heated and stirred to obtain an aqueous polyvinyl alcohol solution. 0.1 g of hydrochloric acid was added to 6.0 g of the obtained aqueous polyvinyl alcohol solution, and 0.1 g of benzaldehyde and 0.1 g of butyraldehyde shown in Table 2 were added.
Carbon dioxide was injected into the reaction vessel, the temperature inside the vessel was adjusted to 130 ° C., and the pressure inside the vessel was adjusted to 2.0 MPa using a pressure regulating valve. After performing the reaction with stirring at 130 ° C. for 5 hours, the reaction part was cooled to room temperature to obtain a mixed solution containing a polyvinyl butyral resin.
The mixed solution was re-precipitated in methanol, solid-liquid separation was performed, and the obtained solid was washed three times with pure water to obtain a white resin.

(Production of optical film)
A solution obtained by dissolving the obtained resin in DMSO was prepared, and an optical film having a thickness of 40 μm was produced by a casting method using a bar coater.

(Examples 2-3, Comparative Examples 1-3)
A polyvinyl butyral resin was obtained in the same manner as in Example 1 except that the formulation and reaction conditions described in Table 2 were used.

<Evaluation>
The following evaluation was performed about the polyvinyl acetal resin obtained by the Example and the comparative example, the intermediate film for laminated glasses, and a laminated glass.
[Evaluation of resin]
(1) Melting peak temperature (melting point)
About the obtained polyvinyl acetal resin, DSC measurement was performed using the differential scanning calorimeter (Hitachi High-Tech Science company make, DSC6220). As a temperature program, the temperature was increased from 10 ° C. to 250 ° C. at 10 ° C./min as the first cycle, and the temperature was decreased from 250 ° C. to 10 ° C. at 10 ° C./min. The temperature was raised from 10 ° C. to 250 ° C. at 5 ° C./min as the second cycle, and the melting point was read from the DSC curve in the second cycle. This measurement was performed in a nitrogen atmosphere, and the holding time was 5 minutes. The glass transition temperature was also measured.
When no peak was observed, the melting point was “−”.

(2) Meso / racemo ratio The obtained polyvinyl acetal resin was dissolved in dimethyl sulfoxide, proton NMR was measured at a measurement temperature of 150 ° C., and a peak derived from a mesoacetal ring structure appearing in the vicinity of 4.5 ppm; The meso / racemo ratio was determined by comparing the integrated values of the peaks derived from the racemoacetal ring structure appearing in the vicinity of .2 ppm.

[Evaluation of optical film]
(3) Residual stress and birefringence measurement Basically, NIHON REOROJI GAKKAISI vol. 27, no. Evaluation was performed in the same manner as the measurement of stress birefringence relaxation behavior described in 1, 43 to 48 (1999). As the apparatus, a measuring apparatus capable of simultaneously measuring residual stress and birefringence shown in FIG. 2 was used.
The measuring device consists of two parts, a stress measuring device and a birefringence measuring device.
Specifically, a tensile test apparatus (manufactured by Far-East Manufacturing Inc.), 632.8 nm He-Ne laser (05LHP151, Melles Griot Inc.) was used, and data processing was performed using LabVIEW (manufactured by National Instruments). It was.
A strip-shaped sample (area 5 cm × 7 mm, thickness 150 to 250 μm) is fixed to a chuck in a thermostat set to a predetermined temperature (130 ° C.). The sample was subjected to high-speed uniaxial stretching (90 mm / s) in the vertical direction using a pulse motor, and the stress relaxation (E) after applying a constant strain ε was measured.
In order to perform simultaneous measurement of stress relaxation and birefringence relaxation with high accuracy, a He-Ne laser beam (wavelength 632.8 nm) is modulated by a Glan-Thompson prism (polarizer) and a photoelastic modulator, The sample in the stress measuring device was irradiated with light having a retardation modulated with a period. Incidentally, about 0.5% in the following _{T g,} the _{T g} or more by applying a strain of about 1.0%, was determined divided by strain e and Dn as the birefringent value (Dn / e).
The values of residual stress and birefringence were values at 130 ° C. (Log (E), Log | Δn / ε |) as evaluation indices.
(Residual stress)
○: Residual stress (Log (E)) is 8.0 or more ×: Residual stress (Log (E)) is less than 8.0 (birefringence)
○: Birefringence (Log | Δn / ε |) is −2.5 or more ×: Birefringence (Log | Δn / ε |) is less than −2.5

According to the present invention, it is possible to provide a polyvinyl acetal resin that hardly causes residual stress during molding and can reduce birefringence, an optical member using the polyvinyl acetal resin, and a method for producing the polyvinyl acetal resin.

Claims (5)

It is a polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol using an aromatic aldehyde and an alkyl aldehyde, and has a melting peak in the range of 120 to 250 ° C. when differential scanning calorimetry is performed. A polyvinyl acetal resin. The polyvinyl acetal resin according to claim 1, wherein the degree of acetalization by an aromatic aldehyde is 3 to 50 mol%. The polyvinyl acetal resin according to claim 1 or 2, wherein the syndiotactic hydroxyl group ratio is 28 to 65 mol%. An optical member comprising the polyvinyl acetal resin according to claim 1, wherein the birefringence value at 130 ° C. is 0.01 or less. A method for producing the polyvinyl acetal resin according to claim 1, 2 or 3,
A polyvinyl acetal comprising a step of acetalizing a polyvinyl alcohol and an aromatic aldehyde by reacting them 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 in the presence of an acid catalyst. Manufacturing method of resin.

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