JP6947540B2 - Polyvinyl acetal resin, manufacturing method of polyvinyl acetal resin and interlayer film for laminated glass - Google Patents

Description

The present invention relates to a polyvinyl acetal resin having excellent solubility in a solvent and capable of achieving excellent light resistance and transparency when formed into a molded product, and a method for producing the same. The present invention also relates to an interlayer film for laminated glass that has excellent light resistance, is resistant to discoloration, and can be reused.

Polyvinyl acetal resins are used in a wide range of applications such as interlayer films for laminated glass used for windshields of automobiles, adhesives, paints, and various binders.
However, if the surface of the base material is coated with polyvinyl acetal resin or the molded product molded into a sheet using a molding machine is placed in a high temperature environment or an environment exposed to ultraviolet rays, it will turn yellow. There was a problem.
Therefore, there is a problem that it is difficult to reuse a molded product such as an interlayer film for laminated glass because discoloration occurs.

In order to prevent such yellowing, antioxidants such as BHT (dibutylhydroxytoluene) and BHA (butylhydroxyanisole), and benzotriazole-based and hindered amine-based ultraviolet absorbers such as TINUVIN should be used as additives. However, there is a problem that sufficient effect is not obtained in a harsher environment.

Therefore, Patent Document 1 proposes a polyvinyl acetal sheet using polyvinyl acetal particles having a porosity of 60 to 85%. In such a sheet, since the porosity of the polyvinyl acetal particles is high, it is said that the transparency can be improved by improving the dispersibility of the additive in the sheet composed of a mixture such as the additive.
Further, Patent Document 2 proposes to suppress the coloring of polyvinyl butyral by using a specific phenol compound.

However, the proposals of Patent Documents 1 and 2 both maintain light resistance and transparency by using an additive, and have not been able to improve the physical characteristics of the polyvinyl acetal resin itself, and the polyvinyl acetal resin itself. It is required to improve physical properties and prevent discoloration.

International Publication No. 2008/050517 Japanese Unexamined Patent Publication No. 2012-12548

Therefore, the present inventors have studied suppressing the discoloration of the polyvinyl acetal resin by suppressing the discoloration of the polyvinyl alcohol resin as a raw material.
The polyvinyl alcohol resin, which is the raw material of the polyvinyl acetal resin, is obtained by saponifying the polyvinyl acetate resin, and in the saponification step, a catalyst such as sodium hydroxide is added to a solvent such as methanol or water. However, there is a problem that these polyvinyl alcohol resins are colored yellow or brown regardless of the degree of saponification, and the obtained polyvinyl acetal resin is also colored.

It is considered that such coloring of the polyvinyl alcohol resin is caused by foreign substances such as catalyst residue when polymerizing polyvinyl acetate, a polymerization inhibitor, and dust during drying. In addition, it is considered that the heat during drying modifies the low molecular weight compound generated during the production of polyvinyl acetate, and the obtained polyvinyl alcohol resin undergoes a dehydration reaction. Among the causes of these colorings, foreign substances such as catalyst residues, polymerization inhibitors, and dust can be removed relatively easily, but modified products of low molecular weight compounds and polyvinyl alcohol resins that have undergone a dehydration reaction should be removed. Is not easy, and in particular, it is necessary to eliminate the cause of such coloring.

In view of the above circumstances, the present invention provides a polyvinyl acetal resin having excellent solubility in a solvent and capable of achieving excellent light resistance and transparency when formed into a molded product, and a method for producing the same. The purpose. Another object of the present invention is to provide an interlayer film for laminated glass which is excellent in light resistance, hardly discolored, and can be reused.

The present invention is an acetal product of a polyvinyl alcohol resin having a light transmittance of 40% or more when irradiated with light having a wavelength of 330 nm, having an acetalization degree of 60 to 85 mol% and a hydroxyl group content of 15 to 40 mol%. A polyvinyl acetal resin.
The present invention will be described in detail below.

The polyvinyl acetal resin of the present invention is an acetal product of a polyvinyl alcohol resin.
The polyvinyl alcohol resin has a light transmittance of 40% or more when irradiated with light having a wavelength of 330 nm. By being an acetal product of the polyvinyl alcohol resin, the polyvinyl acetal resin of the present invention has excellent light resistance.
The light transmittance is determined by preparing an aqueous solution in which the polyvinyl alcohol resin is dissolved in 4% by weight and measuring an absorption band having a wavelength of 330 nm using an ultraviolet spectroscope (U-4000, manufactured by Hitachi, Ltd.). be able to.

The degree of polymerization of the polyvinyl alcohol resin has a preferable lower limit of 200 and a preferable upper limit of 4000. When the degree of polymerization is at least the above preferable lower limit, the affinity for water can be optimized and the polyvinyl alcohol resin can be easily dried. When the degree of polymerization is not more than the above preferable upper limit, the handleability of the obtained polyvinyl acetal resin is improved. The degree of polymerization of the polyvinyl alcohol resin has a more preferable lower limit of 300 and a more preferable upper limit of 3000.

The saponification degree of the polyvinyl alcohol resin has a preferable lower limit of 75.0 mol% and a preferable upper limit of 99.9 mol%. When the saponification degree is not less than the above-mentioned preferable lower limit and not more than the above-mentioned preferable upper limit, the light resistance and transparency of the obtained polyvinyl acetal resin can be improved. The more preferable lower limit of the saponification degree is 83.0 mol%, and the more preferable upper limit is 98.0 mol%.

The viscosity of the aqueous solution of the polyvinyl alcohol resin having a resin solid content of 4% at 20 ° C. has a preferable lower limit of 2.5 mPa · s and a preferable upper limit of 200 mPa · s. When the viscosity is at least the above-mentioned preferable lower limit and at least the above-mentioned preferable upper limit, the light resistance and transparency of the obtained polyvinyl acetal resin can be improved. The viscosity of the polyvinyl alcohol resin has a more preferable lower limit of 2.7 mPa · s and a more preferable upper limit of 180 mPa · s.
The viscosity can be measured according to JIS K 6726.

The polyvinyl acetal resin of the present invention has a lower limit of 60 mol% and an upper limit of 85 mol% for the degree of acetalization. When the degree of acetalization is not less than the above lower limit and not more than the above upper limit, the solubility in a solvent is good when used as a binder, and the compatibility with a plasticizer is excellent when producing an interlayer film for laminated glass. A resin composition can be obtained. The preferred lower limit of the acetalization degree of the polyvinyl acetal resin is 63 mol%, and the preferable upper limit is 80 mol%.

The polyvinyl acetal resin of the present invention has a lower limit of 15 mol% and an upper limit of 40 mol% of the amount of hydroxyl groups. The polyvinyl acetal resin in which the amount of hydroxyl groups is at least the above lower limit can sufficiently improve the adhesion to the substrate and the cohesive force. When the amount of hydroxyl groups is not more than the above upper limit, a resin composition having excellent toughness and transparency can be obtained, and it can be preferably used as a material for producing a green sheet of a laminated ceramic capacitor or a film material for a laminated glass interlayer film. The preferable lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin is 20 mol%, and the preferable upper limit is 37 mol%.

The degree of polymerization of the polyvinyl acetal resin of the present invention has a preferable lower limit of 200 and a preferable upper limit of 4000. When the degree of polymerization is at least the above preferable lower limit, the strength of the coating film can be sufficiently improved. When the degree of polymerization is not more than the above-mentioned preferable upper limit, the heat-melt viscosity can be made suitable and the moldability can be improved. The degree of polymerization of the polyvinyl acetal resin has a more preferable lower limit of 220 and a more preferable upper limit of 3800.

The polyvinyl acetal resin of the present invention has a preferable lower limit of 0.001% and a preferable upper limit of 3% in the case of a 4% by weight ethanol and toluene mixed solution (ethanol: toluene = 50: 50). When the haze is equal to or greater than the above lower limit and equal to or less than the above upper limit, the transparency of the coating film becomes sufficient, and discoloration can be prevented even when the coating film is applied so that the coating film can be reused. can. The haze has a more preferable lower limit of 0.01% and a more preferable upper limit of 2.8%.

The conventional method for producing a polyvinyl acetal resin has a problem that a conjugated double bond is generated by a modified product due to heat of a low molecular weight compound or a dehydration reaction. It was not possible to produce a polyvinyl acetal resin that can be reused.
On the other hand, as a result of diligent studies, the present inventors conducted a cleaning step using a solvent having a boiling point of less than 64 ° C. and a vapor pressure of 20 ° C. of 100 mmHg or more, and stirring using a stirring blade having two or more shafts. It has been found that the polyvinyl acetal resin of the present invention can be produced by a method of acetalizing a polyvinyl alcohol resin obtained through a drying step of drying while.
Such a method for producing a polyvinyl acetal resin of the present invention is also one of the present inventions.

The method for producing a polyvinyl acetal resin of the present invention includes a step for producing a polyvinyl alcohol resin and an acetalization step for acetalizing the polyvinyl alcohol resin.
The polyvinyl alcohol resin manufacturing step includes a washing step of washing with a solvent having a boiling point of less than 64 ° C. and a vapor pressure of 20 ° C. of 100 mmHg or more, and drying of drying while stirring using a stirring blade having two or more shafts. Has a process. By having the above-mentioned production step of the polyvinyl alcohol resin, it is possible to obtain a polyvinyl alcohol resin having a light transmittance of 40% or more when irradiated with light having a wavelength of 330 nm.

The polyvinyl alcohol resin can be obtained by saponifying a polyvinyl ester in an organic solvent in the presence of a catalyst.
Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate and the like, and vinyl acetate is preferably used.
Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, ethylene glycol, propylene glycol, glycerin and diethylene glycol, and among them, methanol is preferably used.
Examples of the catalyst used in the saponification include alkaline catalysts such as sodium hydroxide, potassium hydroxide, sodium alcoholate and sodium carbonate, and acid catalysts such as sulfuric acid, phosphoric acid and hydrochloric acid. Of these, an alkaline catalyst is preferable, and sodium hydroxide is more preferable because the saponification rate can be increased and the productivity can be improved.

The method for saponifying the polyvinyl ester is not particularly limited. For example, a method of mixing a solution containing a vinyl ester polymer and an organic solvent with a catalyst using a kneader and then saponifying using a tower-type saponification reactor, or a method of saponifying a vinyl ester polymer and an organic solvent. A method of mixing the solution containing the ester and the catalyst with a mixer and then saponifying the mixture in a reactor equipped with a planetary stirrer can be mentioned.

The temperature at which the polyvinyl ester is saponified is not particularly limited, but the preferred lower limit is 35 ° C and the preferred upper limit is 60 ° C. When the reaction temperature is equal to or higher than the preferable lower limit, the reaction reaction can sufficiently proceed.

In the present invention, the step of producing a polyvinyl alcohol resin includes a washing step of saponifying the polyvinyl ester and then washing with a solvent.
The boiling point of the solvent is less than 64 ° C. If the boiling point of the solvent is 64 ° C. or higher, the detergency becomes insufficient. The boiling point of the solvent is preferably 30 ° C. or higher, more preferably 34 ° C. or higher, preferably lower than 64 ° C., and more preferably lower than 62 ° C.
The solvent has a vapor pressure of 100 mmHg or more at 20 ° C. When the vapor pressure is 100 mmHg or more, acetic acid or the like as a by-product in the saponification reaction can be removed. The vapor pressure is preferably 100 mmHg or more, more preferably 150 mmHg or more, more preferably 600 mmHg or less, and even more preferably 400 mmHg or less.
Usually, in the production of a polyvinyl alcohol resin which is a raw material of a polyvinyl acetal resin, a step of saponifying the polyvinyl ester and then removing the catalyst such as sodium hydroxide remaining in the system by washing with methanol is performed. In such a washing step, it is necessary to remove the methanol used for washing by drying. However, since methanol is very compatible with polyvinyl alcohol resin, when a slurry of methanol and polyvinyl alcohol resin is put into a drying furnace, heat treatment at high temperature for a long time is required, which is the cause of such heat treatment. Then, the dehydration reaction of the polyvinyl alcohol resin proceeds to form a conjugated double bond. It is known that the presence of a conjugated system in a molecule has a color, and polyvinyl alcohol resin and polyvinyl acetal resin are no exception.
In the present invention, by using the above-mentioned solvent, it is possible to suppress the formation of a conjugated double bond in the polyvinyl alcohol resin by the heat treatment during drying, and to suppress the discoloration of the obtained polyvinyl alcohol resin. Can be done. Therefore, the polyvinyl acetal resin of the present invention obtained by using the above-mentioned polyvinyl alcohol resin has excellent light resistance and transparency.

Examples of the solvent include methyl acetate (boiling point 57.8 ° C., vapor pressure 200 mmHg), acetone (boiling point 56.12 ° C., vapor pressure 200 mmHg), diethyl ether (boiling point 34.6 ° C., vapor pressure 200 mmHg), dichloromethane (boiling point 34). .6 ° C., vapor pressure 356 mmHg), chloroform (boiling point 55 ° C., vapor pressure 159 mmHg), methyl-t-butyl ether (boiling point 55 ° C., vapor pressure 203 mmHg) and other petroleum ethers. Of these, methyl acetate and acetone are preferably used because the modified product of the low polymerization degree composition generated by heating can be washed and removed at the same time.
The above solvent may be used alone or in combination of two or more.
Further, a solvent other than the above solvent can be used in combination as long as the boiling point of the mixed solvent with the above solvent can be less than 64 ° C. Examples of such other solvents include tetrahydrofuran and the like.

In the present invention, the polyvinyl alcohol resin can be obtained by washing the polyvinyl ester with the solvent and then performing a drying step of drying while stirring using a stirring blade having two or more shafts.
Since the polyvinyl alcohol resin has a very high compatibility with water, it is necessary to efficiently replace the dry surface with the resin inside containing water at the time of drying. At this time, if the drying temperature becomes high or the drying time becomes long, a conjugated double bond is formed in the polyvinyl alcohol resin by the dehydration reaction, which causes discoloration.

Various drying methods are used for drying the polyvinyl alcohol resin, and examples thereof include a stirring rotary blade type drying device, a rotary type drying device, a continuous shelf type drying device, and a fluid type drying device.
The stirring rotary blade type drying device is a device in which a crank shaft-shaped stirring blade installed on the central axis of a tubular dryer dries the slurry while stirring, and the side surface of the dryer is heated by steam or the like. Then, the resin in contact with the side surface is dried by heat. In such a drying device, it is necessary to set the dryer to a very high temperature, and a dehydration reaction is likely to occur, which causes coloring.
The rotary type drying device is a device that heats the side surface of the cylindrical drying device with steam to dry it, but it is less efficient than the stirring rotary blade type drying device and is exposed to heat for a longer time. It causes.
The continuous shelf-stage drying device has a rotating shelf-shaped blade installed inside the dryer, and is kneaded by the rotating blade in the drying gas, and gradually falls while being scraped out to collect the dried product. Although it has, it easily stays in the furnace or adheres to the blades, which causes discoloration of the resin.
In the flow type drying device, a gas rectifying plate is installed in a chamber in which drying gas is blown from the bottom, the resin put on the rectifying plate is dried, and the dried resin that has blown up is carried to the collection port. It will be dried. In such a drying device, particles are likely to coalesce and it takes a long time to dry, which causes coloring.

In the present invention, in the manufacturing process for producing the polyvinyl alcohol resin, by performing the drying step of drying while stirring using a stirring blade having two or more shafts, the dehydration reaction of the polyvinyl alcohol resin is less likely to occur, and the resin is discolored. It can be suppressed.
In the present invention, the apparatus for drying the polyvinyl alcohol resin is not particularly limited, and examples thereof include a multi-paddle dryer such as a double paddle dryer.
The double paddle dryer has a mechanism in which a biaxial wedge-shaped heat transfer blade sends out the resin to be dried while grinding it, which makes it easy to seal the inside of the device and introduce an inert drying gas. It has become. In addition, the amount of resin that stays in the apparatus is small, and the progress of the dehydration reaction due to the staying resin being exposed to heat for a long time can be suppressed.

The drying temperature at the time of performing the above drying is preferably 110 ° C. or higher and lower than 127 ° C. When the drying temperature is 110 ° C. or higher, the drying property can be sufficiently enhanced and the productivity can be improved. By setting the drying temperature to less than 127 ° C., the transmitted light intensity of the obtained polyvinyl alcohol resin at 330 nm can be in a suitable range. The drying temperature is more preferably 110 ° C. or higher and lower than 125 ° C.

The method for producing a polyvinyl acetal resin of the present invention includes an acetalization step for acetalizing the polyvinyl alcohol resin. For acetalization of the polyvinyl alcohol resin, a conventionally known method such as reacting the polyvinyl alcohol resin with aldehyde in the presence of an acidic catalyst can be used.

The aldehyde is not particularly limited, and examples thereof include linear, branched, cyclically saturated, cyclically unsaturated, and aromatic aldehydes having 1 to 19 carbon atoms. Specifically, for example, formaldehyde, acetaldehyde, propionyl aldehyde, n-butyl aldehyde, isobutyl aldehyde, tert-butyl aldehyde, amyl aldehyde, hexyl aldehyde, heptyl aldehyde, 2-ethylhexyl aldehyde, cyclohexyl aldehyde, furfural, glioxal, glutaaldehyde, Examples thereof include benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxyaldehyde, m-hydroxyaldehyde, phenylacetaldehyde, phenylpropionaldehyde and the like. Of these, acetaldehyde and butyraldehyde are preferably used. The above aldehyde may be used alone or in combination of two or more.

The acidic catalyst is not particularly limited, and either an organic acid or an inorganic acid can be used, and examples thereof include acetic acid, paratoluenesulfonic acid, nitric acid, sulfuric acid, and hydrochloric acid.

In the method for producing a polyvinyl acetal resin of the present invention, after performing the acetalization step, neutralization, washing with water, and drying may be further performed.

Examples of the alkali used in the above neutralization include sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium hydrogencarbonate, potassium carbonate and the like.

In the drying of the polyvinyl acetal resin, the drying temperature is not particularly limited, but since the polyvinyl acetal resin has a lower glass transition temperature than the polyvinyl alcohol resin, blocking may occur when the polyvinyl alcohol resin is dried at a high temperature. Therefore, the polyvinyl alcohol resin is dried. It is preferable to dry at a temperature lower than the drying temperature at which the above-mentioned product is obtained.
The drying method is not particularly limited, but a double paddle dryer may be used or a fluidized drying furnace may be used as in the case of the polyvinyl alcohol resin. Further, it is preferable to dry at a low temperature by introducing a large amount of drying gas or reducing the pressure in the drying furnace in order to dry more efficiently.

According to the method for producing a polyvinyl acetal resin of the present invention, polyvinyl alcohol obtained by suppressing the dehydration reaction of the polyvinyl alcohol resin that causes coloring and acetalizing the polyvinyl alcohol resin having excellent light resistance and transparency is obtained. The acetal resin is difficult to color and has excellent transparency.

Since the polyvinyl acetal resin of the present invention is excellent in light resistance and transparency, it can be suitably used as a silver salt film, a reflective sheet substrate, various inks, and a coating material, and it is also excellent in solvent solubility. It can also be suitably used as a green sheet for ceramic products, an electrode paste, an adhesive and the like. In particular, the polyvinyl acetal resin of the present invention does not easily discolor even when it is used as a coating film, and it is possible to reuse scraps and defective molded products during molding. It is preferably used for the purpose of use.
An interlayer film for laminated glass containing the polyvinyl acetal resin of the present invention is also one of the present inventions.

It is preferable to use a plasticizer for the interlayer film for laminated glass of the present invention.
As the plasticizer, for example, a monobasic organic acid ester-based plasticizer, a polybasic organic acid ester-based plasticizer, an organic phosphoric acid-based plasticizer, or the like can be used.

Examples of the monobasic organic acid ester-based plasticizer include glycols such as triethylene glycol, tetraethylene glycol and tripropylene glycol, and butyric acid, isobutyric acid, caproic acid, 2-ethylbutyric acid, heptyl acid and n-octyl. Examples thereof include glycol-based esters obtained by reacting with a monobasic organic acid such as an acid, 2-ethylhexic acid, pelargonic acid (n-nonyl acid) or decyl acid. Among them, triethylene glycol-di-caproic acid ester, triethylene glycol-di-2-ethylbutyric acid ester, triethylene glycol-di-n-octylate ester, triethylene glycol-di-2-ethylhexyl acid ester, tri Monobasic organic acid esters of triethylene glycol such as ethylene glycol-di-2-ethylbutyrate and triethylene glycol-di-2-ethylhexanoate are preferably used.

The polybasic organic acid ester-based plasticizer is not particularly limited, and is, for example, a multibasic organic acid such as adipic acid, sebacic acid or azelaic acid, and a linear or branched alcohol having 4 to 8 carbon atoms. Esters and the like can be mentioned. Of these, dibutyl sebacic acid ester (for example, triethylene glycol-di-butyl sebacate, etc.), dioctyl azelaic acid ester, dibutyl carbitol adipate, and the like are preferably used.

The organic phosphoric acid-based plasticizer is not particularly limited, and examples thereof include tributoxyethyl phosphate, isodecylphenyl phosphate, and triisopropyl phosphate.

The content of the plasticizer is preferably 20 to 60 parts by weight, more preferably 30 to 50 parts by weight, based on 100 parts by weight of the polyvinyl acetal resin. If the content of the plasticizer is less than 20 parts by weight, the obtained interlayer film for laminated glass and the impact absorption of the laminated glass using the interlayer film for laminated glass may be insufficient. When the content of the above-mentioned thermoplastic agent exceeds 60 parts by weight, the optical distortion of the laminated glass interlayer film or laminated glass obtained by bleeding out of the thermoplastic agent becomes large, or the transparency or the glass and the laminated glass interlayer film becomes large. Adhesion to and the like may be impaired.

The interlayer film for laminated glass of the present invention preferably contains an adhesive force adjusting agent. In particular, when producing laminated glass, it is preferable to contain the above-mentioned adhesive force adjusting agent.
As the adhesive force regulator, for example, an alkali metal salt, an alkaline earth metal salt, a modified silicone oil, or the like is preferably used. Examples of the adhesive strength adjusting agent include salts of potassium, sodium, magnesium and the like.
Examples of the acid constituting the salt include organic acids of carboxylic acids such as octyl acid, hexic acid, 2-ethylbutyric acid, butyric acid, acetic acid and formic acid, and inorganic acids such as hydrochloric acid and nitric acid. Since the adhesive force between the glass and the interlayer film for laminated glass can be easily adjusted when the laminated glass is manufactured, it is preferable to use a magnesium salt as the adhesive force adjusting agent.

The content of the adhesive force adjusting agent is preferably 0.01 part by weight and a preferable upper limit is 0.1 part by weight with respect to 100 parts by weight of the polyvinyl acetal resin. When the content of the adhesive force adjusting agent is not more than the above lower limit, an interlayer film for laminated glass having more excellent penetration resistance can be obtained. When the content of the adhesive force adjusting agent is not more than the above upper limit, the transparency of the interlayer film for laminated glass is further improved.

The interlayer film for laminated glass of the present invention is an ultraviolet absorber such as a malonic acid ester compound, a oxalic acid anilide compound, a benzotriazole compound, a benzophenone compound, a triazine compound, a benzoate compound, and a hindered amine compound; Agents; light stabilizers; surfactants; flame retardants; antistatic agents; moisture resistant agents; heat ray reflecting agents; heat ray absorbers; chelating agents; weather resistant agents and other conventionally known additives may be contained.

According to the present invention, it is possible to provide a polyvinyl acetal resin having excellent solubility in a solvent and capable of realizing excellent light resistance and transparency when formed into a molded product, and a method for producing the same. The present invention also relates to an interlayer film for laminated glass that has excellent light resistance, is resistant to discoloration, and can be reused.

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

(Example 1)
(Preparation of polyvinyl acetate resin)
100 parts by weight of vinyl acetate and 30 parts by weight of methanol as an organic solvent were put into a reaction vessel equipped with a stirrer, a cooler, a thermometer, a hot water bath and a nitrogen gas inlet and mixed to obtain a monomer solution.
The obtained monomer solution was bubbling with nitrogen gas for 20 minutes to remove dissolved oxygen, and then the inside of the reaction vessel was replaced with nitrogen gas and the temperature was raised while stirring until the hot water bath boiled. Then, a solution obtained by diluting the polymerization initiator (Perbutyl, manufactured by NOF CORPORATION) with methyl acetate was added. In addition, a methyl acetate solution containing a polymerization initiator was added several times during the polymerization.
After 10 hours from the start of the polymerization, the reaction solution was cooled to room temperature to complete the polymerization, and a methanol solution of a polyvinyl acetate resin was obtained. The obtained polyvinyl acetate resin was analyzed by gel permeation chromatography using LF-804 (manufactured by SHOKO) as a column, and the number average molecular weight in terms of polystyrene was as shown in Table 1.

(Preparation of polyvinyl alcohol resin)
The obtained polyvinyl acetate resin in methanol is transferred to a reactor equipped with a planetary stirrer, 10 parts by weight of sodium hydroxide is added to 100 parts by weight of the polyvinyl acetate resin, and the mixture is stirred for 5 hours while heating to 40 ° C. And saponified to obtain a polymer. The obtained polymer was washed with methanol and further washed with methyl acetate. Then, the amount of water and methanol contained in the polymer was reduced, the content of sodium acetate was reduced to 0.1 mol per 1 mol of polyvinyl acetate, and the obtained slurry was centrifuged by a decanter type. Solid-liquid separation was performed with a container to obtain a polyvinyl alcohol slurry composition having a resin solid content of 45% by weight.

Further, the polyvinyl alcohol slurry composition was passed through a double paddle dryer at a set drying temperature of 124 ° C. and dried to a volatile content of 4% by weight to obtain a polyvinyl alcohol resin. As a result of measurement based on JIS K6726, the saponification degree, the average degree of polymerization, and the viscosity of the aqueous solution having a resin solid content of 4% at 20 ° C. were as shown in Table 1.
Further, the obtained polyvinyl alcohol resin was dissolved in water at a concentration of 4% by weight, and the transmittance of the absorption band at 330 nm was measured using an ultraviolet spectroscope (U-4000, manufactured by Hitachi, Ltd.). The results are shown in Table 1.

(Preparation of polyvinyl acetal resin)
250 parts by weight of the obtained polyvinyl alcohol resin was added to 2000 parts by weight of pure water, and the mixture was stirred and dissolved at 90 ° C. for 2 hours. This solution is cooled to 40 ° C., 170 parts by weight of hydrochloric acid having a concentration of 35% by weight and 150 parts by weight of n-butyraldehyde are added, the liquid temperature is lowered to 20 ° C., and the acetalization reaction is carried out while maintaining the temperature. The product was precipitated. Then, the liquid temperature was kept at 40 ° C. for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried by a conventional method to obtain a white powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in _{DMSO-d 6} (dimethyl sulfoxide), and the degree of acetalization and the amount of hydroxyl groups were measured using ^{13 C-NMR (nuclear magnetic resonance spectrum).} The results are shown in Table 1.

(Example 2)
In (Preparation of polyvinyl acetate resin), 100 parts by weight of vinyl acetate and 300 parts by weight of methanol were mixed to prepare a monomer solution, and in (Preparation of polyvinyl acetal resin), the amount of n-butylaldehyde added was 160 parts by weight. A polyvinyl acetal resin was obtained in the same manner as in Example 1 except that the resin was changed to.

(Example 3)
In (Preparation of polyvinyl acetate resin), a polyvinyl alcohol resin was prepared in the same manner as in Example 1 except that the resin was saponified by stirring for 2 hours.
220 parts by weight of the obtained polyvinyl alcohol resin was added to 2000 parts by weight of pure water, and the mixture was stirred and dissolved at 90 ° C. for 2 hours. This solution is cooled to 40 ° C., 35 parts by weight of hydrochloric acid having a concentration of 35% by weight and 220 parts by weight of n-butyraldehyde are added, the liquid temperature is lowered to 15 ° C., and the acetalization reaction is carried out while maintaining the temperature. The product was precipitated. Then, the liquid temperature was kept at 40 ° C. for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried by a conventional method to obtain a white powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in _{DMSO-d 6} ^{(dimethyl sulfoxide), and the degree of acetalization was measured using 13} C-NMR (nuclear magnetic resonance spectrum). The results are shown in Table 1.

(Example 4)
In (Preparation of polyvinyl acetate resin), 100 parts by weight of vinyl acetate and 300 parts by weight of methanol were mixed to prepare a monomer solution, and in (Preparation of polyvinyl acetal resin), the amount of hydrochloric acid added was 32 parts by weight, n-. A polyvinyl acetal resin was obtained in the same manner as in Example 1 except that the amount of butyl aldehyde added was changed to 210 parts by weight.

(Example 5)
In (Preparation of polyvinyl alcohol resin), a polyvinyl acetal resin was obtained in the same manner as in Example 1 except that acetone was used instead of methyl acetate.

(Example 6)
In (Preparation of polyvinyl alcohol resin), a polyvinyl acetal resin was obtained in the same manner as in Example 2 except that diethyl ether was used instead of methyl acetate.

(Example 7)
A polyvinyl acetal resin was obtained in the same manner as in Example 3 except that methyl-t-butyl ether was used instead of methyl acetate in (Preparation of polyvinyl alcohol resin).

(Example 8)
A polyvinyl acetal resin was obtained in the same manner as in Example 4 except that a mixed solvent of tetrahydrofuran and acetone (weight ratio 1: 1) was used instead of methyl acetate in (Preparation of polyvinyl alcohol resin).

(Comparative Example 1)
In (Preparation of polyvinyl alcohol resin), the obtained polyvinyl alcohol slurry composition was washed with ethyl acetate (boiling point 77 ° C., 75 mmHg), and used in a fluid drying furnace to dry at a set drying temperature of 132 ° C. A polyvinyl alcohol resin was prepared in the same manner as in Example 1 except that the resin was dried to%.
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin.

(Comparative Example 2)
In (Preparation of polyvinyl alcohol resin), the obtained polyvinyl alcohol slurry composition was washed with ethyl acetate using the polyvinyl acetate obtained in the same manner as in Example 2, and the rotary aeration type drying furnace (rotary) was used. A polyvinyl alcohol resin was prepared in the same manner as in Example 1 except that it was dried to a volatile fraction of 4% by weight at a set drying temperature of 132 ° C. using a mold).
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin.

(Comparative Example 3)
In (Preparation of polyvinyl alcohol resin), the obtained polyvinyl alcohol slurry composition was washed with ethyl acetate, and a cylindrical stirring / drying furnace (stirring rotary blade type) was used to dry at a set temperature of 132 ° C. and a volatile content of 4 weights. A polyvinyl alcohol resin was prepared in the same manner as in Example 3 except that the resin was dried to%.
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin.

(Comparative Example 4)
In (Preparation of polyvinyl alcohol resin), the obtained polyvinyl alcohol slurry composition was washed with ethyl acetate, and volatilized at a set drying temperature of 132 ° C. using a continuous shelf-stage drying furnace (shelf-type box-shaped drying furnace). A polyvinyl alcohol resin was prepared in the same manner as in Example 4 except that it was dried to a fraction of 4% by weight.
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 4 to obtain a polyvinyl acetal resin.

(Comparative Example 5)
In (Preparation of polyvinyl alcohol resin), the obtained polyvinyl alcohol slurry composition was washed with ethanol (boiling point 78 ° C., 44.1 mmHg), and the volatile content ratio was 4 at a drying set temperature of 132 ° C. using a fluid drying furnace. A polyvinyl alcohol resin was prepared in the same manner as in Example 1 except that it was dried to% by weight.
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin.

(Comparative Example 6)
In (Preparation of polyvinyl alcohol resin), except that the obtained polyvinyl alcohol slurry composition was washed with ethyl acetate and dried to a volatile content of 4% by weight at a set drying temperature of 132 ° C. using a double paddle dryer. A polyvinyl alcohol resin was produced in the same manner as in Example 3.
Further, the obtained polyvinyl alcohol resin was acetalized in the same manner as in Example 1 to obtain a polyvinyl acetal resin.

(evaluation)
The polyvinyl acetal resins obtained in Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1.

(1) Transparency The polyvinyl acetal resins obtained in each Example and Comparative Example were subjected to an ethanol / toluene solution (ethanol) having a resin content of 4% by weight using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory). : Toluene = 50: 50) The haze at 20 ° C. was measured.

(2) Solubility The polyvinyl acetal resin obtained in each Example and Comparative Example was diluted with an ethanol / toluene (weight ratio 1: 1) solution so as to have a concentration of 2% by weight, and in 10 ml of the obtained diluted solution. The particle size distribution was measured using a particle counter (KL-11A, manufactured by Rion Co., Ltd.), and the number of particles having a diameter of 2 μm or more per 1 ml was confirmed and evaluated according to the following criteria.
◯: It was less than 30,000.
X: The number was 30,000 or more.

(3) Light resistance (colorimeter YI)
To the ethanol / toluene solution of the polyvinyl acetal resin obtained in each Example and Comparative Example, 30% by weight of triethylene glycol bis (2-ethylhexanoate) as a plasticizer was added to the resin as an antioxidant. The resin solution was applied onto the substrate to a thickness of 500 μm and dried in a vacuum oven at 60 ° C. for 12 hours to prepare a resin film. Laminated glass was produced using the obtained resin film. The laminated glass was photodegraded using an ultraviolet irradiation device (“HLS-2S” manufactured by Suga Test Instruments Co., Ltd.), and the yellowness of the deteriorated resin was evaluated by a spectrocolorimeter manufactured by Konica Minolta.
◯: YI was less than 3 after 200 hours of irradiation.
X: YI was 3 or more after 200 hours of irradiation.

According to the present invention, it is possible to provide a polyvinyl acetal resin having excellent solubility in a solvent and capable of realizing excellent light resistance and transparency when formed into a molded product, and a method for producing the same. Further, according to the present invention, it is possible to provide an interlayer film for laminated glass which is excellent in light resistance, hardly discolored, and can be reused.

Claims (5)

It is an acetal product of a polyvinyl alcohol resin having a light transmittance of 40% or more when irradiated with light having a wavelength of 330 nm.
A polyvinyl acetal resin characterized by having a degree of acetalization of 60 to 85 mol% and a hydroxyl group content of 15 to 40 mol%. The polyvinyl acetal resin according to claim 1, wherein the haze is 0.001 to 3% when a 4% by weight mixed solution of ethanol and toluene is used. The polyvinyl acetal resin according to claim 1 or 2, wherein the polyvinyl alcohol resin has a saponification degree of 75.0 to 99.9 mol%. An interlayer film for laminated glass, which contains the polyvinyl acetal resin according to claim 1, 2 or 3. The method for producing a polyvinyl acetal resin according to claim 1, 2 or 3.
It has a step of manufacturing a polyvinyl alcohol resin and a step of acetalizing the polyvinyl alcohol resin.
The steps for producing the polyvinyl alcohol resin include a washing step of saponifying the polyvinyl ester and then washing with a solvent having a boiling point of less than 64 ° C. and a vapor pressure of 20 ° C. of 100 mmHg or more, and a washing step of washing the polyvinyl ester with the solvent. A method for producing a polyvinyl acetal resin, which comprises a drying step of drying while stirring using a stirring blade having two or more shafts.