JP2011241234A - Polyvinyl alcohol-based resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol-based resin (PVOH-based resin) composition little in coloration on melt-molding and high in the temporal stability of melt viscosity.SOLUTION: The PVOH-based resin composition includes a PVOH-based resin which has structural units represented by general formula (1) (wherein, R, R, R, R, Rand Rare each independently H or an organic group; X is a single bond or a bonding chain) and has an absorbance of 0.1 to 0.3 at 280 nm in the ultraviolet absorption spectrum in a 4 mass% aqueous solution, and at least one of carboxylic acids, alkali metal salts and alkaline earth metal salts, wherein the pH of an aqueous solution prepared so that the content of the PVOH-based resin is 4 mass% is 5.5 to 7 at 20°C.

Description

  The present invention relates to a polyvinyl alcohol-based resin composition, and more specifically, a melt-forming polyvinyl alcohol-based resin (hereinafter also referred to as a PVOH-based resin) composition that is less colored by melt molding and has a high melt viscosity temporal stability. Related to things.

  PVOH-based resins are excellent in water solubility, solvent resistance, gas barrier properties, strength, transparency, hydrophilicity, and the like, and are used for various purposes such as packaging for goods. Usually, PVOH-based resin has a melting point and a thermal decomposition temperature close to each other. When a molded product, particularly a film, is to be obtained by melt molding, it must be molded at a temperature near the decomposition temperature. There was a problem in the appearance of the molded product (contamination of foreign matter caused by scorching or thermal decomposition product) and long run moldability.

  As a PVOH-based resin that can be melt-molded, an ethylene / vinyl alcohol copolymer having a melting point lowered by ethylene modification is known, but it is not water-soluble and a gas barrier property is inevitably lowered. As another PVOH-based resin that can be melt-molded, a PVOH-based resin having a 1,2-diol component in the side chain has been proposed (Patent Document 1). This PVOH resin with a 1,2-diol component in the side chain has a low melting point while maintaining water solubility and gas barrier properties, and can be molded at low temperatures. Can be obtained, and a molded article having a good appearance can be obtained which is free from scorching, gel and fish eyes.

  However, although such a PVOH-based resin can be hot-melt molded, when molded at a high temperature of 200 ° C. or higher, particularly when molded, the molded product is likely to be colored, and the resin viscosity increases in the molten state over time. There were challenges and there was room for further improvement.

JP 2006-89538 A

  The present invention has been made in view of the above circumstances, and an object thereof is a PVOH-based resin composition that can be melt-molded. The PVOH-based resin composition is less colored by melt-molding and has a high melt viscosity stability over time. The object is to provide a resin composition.

In view of the above circumstances, the present inventors first conducted intensive research on the cause of coloring, and obtained the knowledge that the carbonyl group present in the PVOH-based resin had an effect. The reason why the carbonyl group affects the coloring is not clear, but in the PVOH resin having a carbonyl group, the hydroxyl group adjacent to the carbonyl group is easily dehydrated, and as a result, —CO— (CH It is considered that a conjugated double bond structure composed of = CH) _n -is formed.

  In addition, the present inventors have obtained the knowledge that the carbonyl group present in the PVOH-based resin has an influence on the temporal stability of the melt viscosity. The reason why the carbonyl group affects the aging stability of the melt viscosity is not clear, but for example, acetalization of the carbonyl group and the hydroxyl group of the PVOH resin promoted by an acid component or an alkali component in the PVOH resin. It is conceivable that the melt viscosity is increased by a crosslinking reaction such as ketalization or the like, or the melt viscosity is decreased due to decomposition by a reverse aldol reaction starting from a terminal carbonyl group.

  Therefore, the present inventors have defined the absorbance at 280 nm in the ultraviolet absorption spectrum as an index of the amount of carbonyl group incorporated into the PVOH resin in the aqueous solution, as well as carboxylic acid, alkali metal salt and alkaline earth metal salt. By using at least one of them, the pH of the aqueous solution is adjusted so as to be within a predetermined range. Although the reason why the melt viscosity is improved over time is not clear, by adjusting the pH of the aqueous solution using carboxylic acid and at least one of an alkali metal salt and an alkaline earth metal salt, It is considered that the change in the melt viscosity with time is reduced because a balance between the cutting of the PVOH molecules generated during the melt molding and the cross-linking reaction between the PVOH molecules is balanced and the change in the apparent molecular weight is reduced.

  That is, the PVOH-based resin composition of the present invention has a structural unit represented by the following general formula (1) and has an absorbance at 280 nm in an ultraviolet absorption spectrum of 0.1 to 0. 3, an aqueous solution containing a polyvinyl alcohol-based resin, a carboxylic acid, and at least one of an alkali metal salt and an alkaline earth metal salt, and the content of the polyvinyl alcohol-based resin is 4% by mass. The pH at 20 ° C. is 5.5-7. In the following, the alkali metal salt and the alkaline earth metal salt may be collectively referred to as an alkali (earth) metal salt.

[Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom. Or an organic group is shown. ]

  Furthermore, the present inventors have found that the carbonyl group present in the PVOH-based resin undergoes chain transfer at the terminal of the polymerization chain of the vinyl ester to the aldehyde compound present in the system during the polymerization of vinyl ester such as vinyl acetate. It was found that hydroxyl groups were oxidized during polymerization at high temperature or drying. As such aldehyde compounds, for example, acetaldehyde derived from vinyl alcohol produced by transesterification reaction between vinyl acetate and methanol as a polymerization solvent, and polymerization that is widely used for polymerization of vinyl acetate and has a long half-life and high activity. Formaldehyde produced by oxidation of methanol as a polymerization solvent by an initiator (AIBN [half-life 32 hours], acetyl peroxide [half-life 32 hours], benzoyl peroxide [half-life 60 hours], etc.) The

  Therefore, the present inventors have shown that the polyvinyl alcohol resin having the structural unit represented by the general formula (1) in the PVOH resin composition of the present invention is represented by the vinyl ester monomer and the following general formula (2). Saponification of a copolymer obtained by copolymerizing a compound having a 1,2-diol structure or a derivative thereof with an organic peroxide having a half-life of 10 to 300 minutes at 60 ° C. as a polymerization initiator It has been found that it is more preferable that it is obtained.

[Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom. Or an organic group is shown. ]

  In addition, as described above, the PVOH-based resin composition of the present invention has a specific non-coloring property and stability over time of melt viscosity as compared with the conventional one, and is specified as follows. You can also That is, the PVOH-based resin composition of the present invention has an YI (Yellow Index) value of an extrudate obtained by using an extruder at a resin temperature of 210 ° C. and a residence time of 3 minutes. The ratio of the torque 60 minutes after the start of kneading to the torque 10 minutes after the start of kneading when melt kneading at a resin temperature of 230 ° C. is 3 or less.

  Since the PVOH-based resin composition of the present invention is less colored by melt molding and has a high melt viscosity stability over time, it can be suitably used for melt molding.

The present invention is described in detail below.
The PVOH-based resin composition of the present invention has a structural unit represented by the following general formula (1) and has an absorbance at 280 nm of 0.1 to 0.3 in an ultraviolet absorption spectrum when a 4% by mass aqueous solution is obtained. It contains a certain polyvinyl alcohol resin, carboxylic acid, and at least one of alkali metal salt and alkaline earth metal salt. First, the PVOH resin used in the present invention will be described.

The PVOH resin used in the present invention has a 1,2-diol structural unit represented by the following general formula (1), and R ¹ , R ² and R ³ in the general formula (1) are each independently hydrogen. An atom or an organic group is represented, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represents a hydrogen atom or an organic group.

R ^{1 to} R ³ and R ^{4 to} R ⁶ in the structural unit represented by the general formula (1) are preferably all hydrogen atoms, and have a structural unit represented by the following general formula (1 ′). Resins are preferably used.

R ^{1 to} R ³ and R ^{4 to} R ⁶ in the structural unit represented by the general formula (1) may be organic groups as long as the resin properties are not significantly impaired. Although it does not specifically limit as group, For example, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, an isopropyl group, n-butyl group, an isobutyl group, a tert- butyl group, are preferable and needed Accordingly, these alkyl groups may have a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group.

Further, X in the structural unit represented by the general formula (1) is most preferably a single bond from the viewpoint of thermal stability and structural stability under high temperature / acid conditions. A binding chain may be used as long as the effect is not inhibited. Such a bond chain is not particularly limited, but other than hydrocarbon groups such as alkylene, alkenylene, alkynylene, phenylene, naphthylene (these hydrocarbon groups may have halogen such as fluorine, chlorine, bromine, etc.) , —O—, — (CH ₂ O) _m —, — (OCH ₂ ) _m —, — (CH ₂ O) _m CH ₂ —, —CO—, —COCO—, —CO (CH ₂ ) _m CO— _{, -CO (C 6 H 4)} CO -, - S -, - CS -, - SO -, - SO 2 -, - NR -, - CONR -, - NRCO -, - CSNR -, - NRCS -, - _{NRNR -, - HPO 4 -,} - Si (OR) 2 -, - OSi (OR) 2 -, - OSi (OR) 2 O -, - Ti (OR) 2 -, - OTi (OR) 2 -, - _{OTi (OR) 2 O -,} - Al (OR) -, - OAl ( R) -, - OAl (OR) O-, etc. (R is an optional substituent each independently, a hydrogen atom, an alkyl group are preferred, and m is a natural number) and the like. Among them, an alkylene group having 6 or less carbon atoms, particularly a methylene group or —CH ₂ OCH ₂ — is preferable from the viewpoint of stability during production or use.

  The PVOH-based resin used in the present invention usually contains 1 to 15 mol%, preferably 2 to 10 mol%, more preferably 3 to 9 mol% of the structural unit represented by the general formula (1). When the molar fraction of the structural unit represented by the general formula (1) is excessively high, it tends to be difficult to obtain a PVOH-based resin having a desired degree of polymerization. On the other hand, if the molar fraction is too low, the melting point becomes high and the temperature is close to the thermal decomposition temperature, so that there is a tendency that scorching, gel, and fish eyes are easily caused by thermal decomposition during melt molding.

In the PVOH-based resin, the content (molar fraction) of the 1,2-diol structural unit represented by the general formula (1) is the ¹ H-NMR spectrum (solvent: DMSO-) of the completely saponified PVOH-based resin. d6, internal standard: tetramethylsilane), specifically, hydroxyl group protons in the 1,2-diol unit, methine protons, and methylene protons, methylene protons in the main chain, and hydroxyl groups linked to the main chain. It can be calculated from the peak area derived from protons and the like.

  The degree of saponification (measured in accordance with JIS K6726) of the PVOH resin used in the present invention is usually 80 to 100 mol%, particularly 85 to 99.9 mol%, more preferably 88 to 99.5 mol%. preferable. If the degree of saponification is too low, the stability of melt viscosity tends to be insufficient at the time of melt molding, and the odor of acetic acid generated by the decomposition of the vinyl acetate structural unit portion tends to be significant.

  Moreover, the average degree of polymerization (measured according to JIS K6726) of the PVOH-based resin is usually 200 to 1800, particularly 300 to 1500, and more preferably 300 to 1000. When the average degree of polymerization is too high, the melt viscosity becomes high and the moldability tends to be lowered. On the other hand, if the average degree of polymerization is too low, the mechanical strength of the molded product tends to be insufficient.

The PVOH resin used in the present invention usually has an absorbance at 280 nm in an ultraviolet absorption spectrum of a 4% by mass aqueous solution of 0.1 to 0.3, particularly 0.1 to 0.28, and further 0.1 It is preferably ˜0.25. Absorption at 280 nm is due to the isolated carbonyl group in the case of n = 0 and the conjugated carbonyl group in the case of n = 2 in the —CO— (CH═CH) _n — structure contained in the PVOH-based resin. When the absorbance is too large, the conjugated system tends to be extended to the long wavelength side and easily colored, and the thermal stability tends to decrease. On the other hand, in a general industrial production method, what has an absorbance of less than 0.1 cannot be obtained, and PVOH-based resin having a low absorbance needs to employ a production method with low production efficiency such as cryogenic polymerization. Such a PVOH resin is not preferable in terms of productivity and cost. The absorbance can be measured using a UV spectrophotometer after preparing a 4% by mass aqueous solution of a PVOH resin, but the PVOH resin composition further contains a carboxylic acid and an alkali (earth) metal salt. May be used to prepare an aqueous solution so that the content of the PVOH-based resin is 4% by mass, and measurement may be performed using a UV spectrophotometer.

  A method for bringing the absorbance of the PVOH-based resin aqueous solution into the specified range of the present invention is not particularly limited. For example, a) hydroxycarboxylic acid such as tartaric acid or citric acid, polyvalent carboxylic acid, L-scorbic acid, D -Polymerization in the presence of chelating agents such as hydroxy lactones such as araboascorbic acid and D-glucono-1,5-lactone, polyhydric alcohols such as D-sorbitol and D-xylose, and polyvalent amines such as tetramethylethylenediamine. B) a method of reducing the amount of aldehyde compound in the polymerization system, b) a method of using a polymerization initiator having a short half-life, c) a method of polymerizing at a low temperature using a low-temperature active polymerization initiator, d E) A method using a polymerization initiator having a weak oxidizing power, e) A recovered vinyl ester monomer such as vinyl acetate is not used, or When used, a method of reducing the content of the aldehyde compound as much as possible by distillation or the like, and f) a long wavelength of a conjugated system at the end of PVOH resin such as p-methoxyphenol or α-methylstyrene dimer as a polymerization inhibitor Examples thereof include a method that does not promote side elongation, or a method that minimizes the amount of the inhibitor used. Among these, the method b) is preferably used because it is excellent in productivity and has little influence on other resin physical properties.

  Next, the manufacturing method of PVOH-type resin which has a structural unit shown by General formula (1) is demonstrated. The method for producing such a PVOH resin is not particularly limited. For example, a copolymer obtained by copolymerizing a vinyl ester monomer and a compound having a 1,2-diol structure represented by the following general formula (2) or a derivative thereof: The method of saponifying a thing is mentioned. Two or more vinyl ester monomers may be copolymerized with two or more compounds of the general formula (2) or derivatives thereof.

R ¹ , R ² , R ³ , X, R ⁴ , R ⁵ and R ⁶ in the structural unit represented by the general formula (2) are all the same as in the case of the general formula (1).

  The vinyl ester monomers used for the production of PVOH resins include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, stearic acid. Vinyl, vinyl benzoate, vinyl versatate, vinyl trifluoroacetate and the like can be mentioned, but vinyl acetate is preferably used among them economically.

  A method for producing a PVOH resin from a compound having a 1,2-diol structure represented by the general formula (2) or a derivative thereof and a vinyl ester monomer is not particularly limited, and (i) a vinyl ester monomer and A method of saponifying a copolymer with a compound represented by the following general formula (3), or (ii) saponifying and depolymerizing a copolymer of a vinyl ester monomer and a compound represented by the following general formula (4) A method of carbonation and a method of (iii) saponifying and deketalizing a copolymer of a vinyl ester monomer and a compound represented by the following general formula (5) are preferably used. In addition, about the method of (i), (ii), and (iii), the method demonstrated by Unexamined-Japanese-Patent No. 2006-95825 is employable, for example.

In the general formulas (3), (4) and (5), R ¹ , R ² , R ³ , X, R ⁴ , R ⁵ and R ⁶ are all the same as in the general formula (1). . R ⁷ and R ⁸ are each independently a hydrogen atom or R ⁹ —CO— (wherein R ⁹ is an alkyl group). R ¹⁰ and R ¹¹ are each independently a hydrogen atom or an organic group similar to R ^{1 to} R ⁶ .

Examples of the compound represented by the general formula (3) include 3,4-dihydroxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-hydroxy-1-butene, and 4-acyloxy-3- Hydroxy-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene, 4,5-diasiloxy-1-pentene, 4,5-dihydroxy-3-methyl- Examples include 1-pentene, 4,5-diacyloxy-3-methyl-1-pentene, 5,6-dihydroxy-1-hexene, 5,6-diacyloxy-1-hexene, glycerin monoallyl ether, and the like. Among these, from the viewpoint of excellent copolymerization reactivity and industrial handling, in the general formula (3), R ^{1 to} R ⁶ are hydrogen, X is a single bond, and R ^{7 to} R ⁸ are R ⁹ —CO—. 3,4-diacyloxy-1-butene in which R ⁹ is an alkyl group is preferable, and among these, 3,4-diacetoxy-1-butene in which R ⁹ is a methyl group is particularly preferable.

  In the method (i) above, vinyl acetate is used as the vinyl ester monomer, and the reactivity ratio of each monomer when 3,4-diacetoxy-1-butene is copolymerized is r (vinyl acetate) = In the case of vinyl ethylene carbonate, which is a compound represented by the general formula (4) used in the method (ii), 0.710, r (3,4-diacetoxy-1-butene) = 0.701 Compared with r (vinyl acetate) = 0.85 and r (vinyl ethylene carbonate) = 5.4, 3,4-diacetoxy-1-butene is excellent in copolymerization reactivity with vinyl acetate. Is.

  The chain transfer constant of 3,4-diacetoxy-1-butene at the time of copolymerization with vinyl acetate is Cx (3,4-diacetoxy-1-butene) = 0.003 (65 ° C.). In the case of vinyl ethylene carbonate, Cx (vinyl ethylene carbonate) = 0.005 (65 ° C.) and 2,2-dimethyl-4 which is a compound represented by the general formula (5) used in the method (iii) -Compared with Cx (2,2-dimethyl-4-vinyl-1,3-dioxolane) = 0.023 (65 ° C) in the case of vinyl-1,3-dioxolane, This indicates that it is difficult to cause a decrease in the polymerization rate.

  In such 3,4-diacetoxy-1-butene, a by-product generated when the copolymer is saponified is by-produced during saponification from a structural unit derived from vinyl acetate that is frequently used as a vinyl ester monomer. It is an industrially significant advantage that it is the same as the compound, and it is not necessary to provide a special apparatus or process for the subsequent treatment or solvent recovery system, and conventional equipment can be used.

  The 3,4-diacetoxy-1-butene is described in, for example, a product produced by a synthesis route using 1,3-butadiene as a starting material described in International Publication No. 00/24702, USP56223086, USP6072079. A product produced by using an epoxybutene derivative by the above technique as an intermediate can be obtained, and a product of Acros can be obtained from the market at the reagent level. Further, crude 3,4-diacetoxy-1-butene obtained as a by-product during the production process of 1,4-butanediol can be purified and used.

  Further, by isomerizing 1,4-diacetoxy-1-butene, which is an intermediate product in the production process of 1,4-butanediol, by a known isomerization reaction using a metal catalyst such as palladium chloride, It can also be converted to 4-diacetoxy-1-butene. Moreover, it is also possible to manufacture according to the manufacturing method of the organic diester described in International Publication No. 00/24702.

  When the degree of saponification is low or when decarboxylation or deacetalization is insufficient, the PVOH resin obtained by the above method (ii) or (iii) has a carbonate ring or acetal ring in the side chain. As a result, when such a PVOH-based resin is used for melt molding, there is a tendency that foreign matters are generated due to gel and cross-linking. From these points, the PVOH obtained by the method (i) System resins are preferred.

In addition to the above-mentioned monomers (vinyl ester monomers, compounds represented by the general formulas (2) to (5)), ethylene or propylene can be used as a copolymerization component as long as the physical properties of the resin are not significantly affected. Α-olefin such as 3-buten-1-ol, 4-penten-1-ol, 5-hexene-1,2-diol and the like, and derivatives such as acylated products thereof; itaconic acid , Unsaturated acids such as maleic acid and acrylic acid, or salts or mono- or dialkyl esters thereof; nitriles such as acrylonitrile; amides such as methacrylamide and diacetone acrylamide; ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, Olefins such as AMPS (2-acrylamido-2-methylpropanesulfonic acid) A compound such as sulfonic acid or a salt thereof, and an allyl compound such as ethylene oxide monoallyl ether may be copolymerized.
Moreover, what made the 1, 2- glycol bond amount of the main chain 1.5 to 3 mol% by copolymerizing with vinylene carbonate or making the temperature condition at the time of superposition | polymerization into high temperature can also be used.

  The method for copolymerizing the above monomers is not particularly limited, and a known method such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be employed. From the viewpoint of being easily obtained, solution polymerization is usually performed. The method for charging the monomer component at the time of copolymerization is not particularly limited, and any method such as batch charging, split charging, continuous charging, etc. may be adopted, but the compounds represented by the general formulas (2) to (5) may be used. Drop polymerization is preferred from the viewpoint of being uniformly distributed in the molecular chain of the polyvinyl ester polymer, and a polymerization method based on the HANNA method is particularly preferred.

  The solvent used in such copolymerization usually includes lower alcohols such as methanol, ethanol, isopropyl alcohol, n-propanol and butanol, ketones such as acetone and methyl ethyl ketone, or a mixed solvent thereof. Methanol is preferably used. The amount of the solvent used may be appropriately selected in consideration of the chain transfer constant of the solvent in accordance with the degree of polymerization of the target copolymer. For example, when the solvent is methanol, S (solvent) / M ( Monomer) = 0.01 to 10 (weight ratio), preferably 0.05 to 3 (weight ratio).

  In the copolymerization, a polymerization initiator is usually used. The polymerization initiator is not particularly limited. For example, known radical polymerization initiators such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauryl peroxide, azobisdimethylvaleronitrile, azobismethoxydimethylvalero And low temperature active radical polymerization initiators such as nitriles. However, in order to reduce the content of the carbonyl group in the PVOH resin and adjust the absorbance as defined in the present invention, it is preferable to use a polymerization initiator having a short half-life. Specifically, it is preferable to use an organic peroxide having a half-life at 60 ° C. of usually 10 to 300 minutes, particularly 15 to 250 minutes, and further 20 to 200 minutes. When the half-life of the polymerization initiator is too long, the YI value of the produced PVOH-based resin tends to be high, and when the half-life is too short, it is difficult to control the polymerization. In addition, the half-life said here is measured in 60 degreeC toluene (azo compound) or benzene (other polymerization initiator).

  Specific examples of the organic peroxide having a half-life of 10 to 300 minutes at 60 ° C. include 2,2′-azobis- (2,4-dimethylvaleronitrile) [half-life of 150 minutes], 2,2′- Azo compounds such as azobis- (4-methoxy-2,4-dimethylvaleronitrile) [half-life 11 minutes], t-butylperoxyneodecanoate [half-life 102 minutes hours], t-butylperoxypivalate Peroxyesters such as [half-life 288 minutes], t-hexylperoxypivalate [half-life 222 minutes], bis- (4-t-butylcyclohexyl) peroxy-di-carbonate [half-life 40 minutes], di 2-ethylhexylperoxy-dicarbonate [half-life 50 minutes], di-isopropylperoxy-dicarbonate [half-life 36 minutes], di-n-propylper Carboxymethyl dicarbonate [half-life 42 minutes], such as peroxy - di - carbonates, diacyl peroxides such as isobutyl butyral peroxide [half-life 16 minutes] and the like.

The amount of the polymerization initiator used varies depending on the type of the polymerization initiator and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate. For example, when an organic peroxide having a half-life at 10 ° C. of 10 to 300 minutes is used, it is usually 1 × 10 ⁻⁷ to 1 × 10 ⁻² mol%, preferably 1 × 10 6 with respect to the vinyl ester monomer. ⁻⁶ to 1 × 10 ⁻³ mol%. When the amount of the polymerization initiator used is too large, it tends to be difficult to control the polymerization rate and the heat generation amount, and when it is too small, the polymerization takes a long time and the productivity tends to decrease. The reaction temperature of the polymerization reaction varies depending on the solvent used, the pressure used, and the heat removal ability of the polymerization canister and cannot be determined unconditionally. When the reaction temperature is too high, it tends to be difficult to control the polymerization, and when it is too low, the polymerization tends to be difficult to proceed. Two or more polymerization initiators having different half-lives may be used, and two or more polymerization initiators may be charged sequentially or simultaneously.

The copolymer obtained by copolymerization is then saponified. Such saponification is performed by dissolving the copolymer obtained above in an alcohol or hydrous alcohol and using an alkali catalyst or an acid catalyst. Examples of the alcohol include methanol, ethanol, propanol, tert-butanol, mixed solvents such as methanol / methyl acetate and methanol / benzene, and methanol is particularly preferably used. The concentration of the copolymer in the alcohol is appropriately selected depending on the viscosity of the system, but is usually selected from the range of 10 to 60% by weight. Catalysts used for saponification include alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, lithium methylate, etc., sulfuric acid, Examples include acid catalysts such as hydrochloric acid, nitric acid, metasulfonic acid, zeolite, and cation exchange resin.
Examples of the apparatus used for the saponification reaction include a kneader and a belt-like continuous saponification apparatus, a twin screw extruder, and the like.

  The amount of the saponification catalyst used is appropriately selected depending on the saponification method, the target degree of saponification, and the like. Usually, when an alkali catalyst is used, the vinyl ester monomer and the general formulas (2) to (5) ) To 0.1 to 30 mmol, preferably 2 to 17 mmol, per 1 mol of the total amount of the compounds shown. The reaction temperature for the saponification reaction is not particularly limited, but is preferably 10 to 60 ° C, more preferably 20 to 50 ° C.

The PVOH resin composition of the present invention contains a carboxylic acid and at least one of an alkali metal salt and an alkaline earth metal salt together with the PVOH resin.
Examples of the carboxylic acid include aliphatic carboxylic acids and aromatic carboxylic acids. Among them, aliphatic carboxylic acids are preferably used, and monocarboxylic acids and dicarboxylic acids are preferable. Monocarboxylic acids are preferably used. Moreover, the carbon number is 2-18 normally, Preferably it is 2-10, More preferably, what is 2-5 is used, and what is especially water-soluble is used preferably. Specific examples include acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, and succinic acid. Among them, acetic acid is preferably used.

  The content of the carboxylic acid is usually 0.001 to 0.2 parts by mass with respect to 100 parts by mass of the PVOH-based resin, particularly 0.002 to 0.15 parts by mass, and further 0.002 to 0.1 parts by mass. Part is preferred. The method for containing the carboxylic acid is not particularly limited, but it is efficient to add it in the PVOH resin production process. In particular, the carboxylic acid is added after the copolymer is saponified using an alkali catalyst. In this case, the consumption due to neutralization is appropriately adjusted and contained. Two or more carboxylic acids may be included.

  Alkali (earth) metal salts are organic acid salts and inorganic acid salts of alkali metals, and organic acid salts and inorganic acid salts of alkaline earth metals. In the present invention, at least one of these salts is used. It is done. Examples of the alkali metal include potassium and sodium, and examples of the alkaline earth metal include calcium and magnesium. Among these, alkali metals are preferable from the viewpoint of a large effect on the amount used, and sodium salts are particularly preferably used.

Examples of organic acid salts include carboxylic acid salts such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid, and inorganic acid salts include salts such as sulfuric acid, sulfurous acid, carbonic acid, and phosphoric acid. Is mentioned.
The content of the alkali (earth) metal salt is usually 0.0002 to 1 mol%, particularly 0.001 to 0.6 mol%, more preferably 0.002 to 0, in terms of metal with respect to the PVOH resin. .2 mol% is preferred. In addition, when two or more alkali (earth) metal salts are contained, the content represents the total amount of two or more salts.

The method of containing an alkali (earth) metal salt is not particularly limited. For example, an alkaline substance containing an alkali metal is used as a saponification catalyst during the production (saponification) of a PVOH resin, and PVOH after saponification is used. A method of washing and neutralizing with an acid to control the amount of alkali metal salt contained in the resin, a method of mixing an aqueous metal salt solution with the PVOH resin before the drying step in the production of the PVOH resin, Examples include a method of mixing a metal salt with a molten PVOH resin. Among them, a method of using an alkaline substance containing an alkali metal as a saponification catalyst and using a carboxylic acid when neutralizing it with an acid is used for each of the carboxylic acid and alkali (earth) metal salt of the resin composition. Since content can be controlled simultaneously, it is suitable as a manufacturing method of the resin composition of this invention.
The content of the alkali (earth) metal salt in the PVOH resin can be determined by atomic absorption analysis.

  In the PVOH-based resin composition of the present invention, the pH at 20 ° C. of an aqueous solution prepared so that the content of the PVOH-based resin is 4% by mass is usually 5.5 to 7, particularly 6 to 7, particularly 6 .2 to 6.8 are preferred. If the pH of the aqueous solution is too high, the stability of the melt viscosity tends to be insufficient or tends to be colored, and if the pH is too low, the stability of the melt viscosity tends to be insufficient. The pH of the aqueous solution can be adjusted, for example, by controlling the content ratio between the carboxylic acid and the alkali (earth) metal salt. The pH of the aqueous solution is an aqueous solution prepared using the PVOH resin composition containing the carboxylic acid and the alkali (earth) metal salt so that the content of the PVOH resin is 4% by mass. Measured.

  The PVOH-based resin composition of the present invention can obtain good melt moldability without blending a plasticizer, but it can also be blended with a plasticizer if necessary. Such plasticizers include aliphatic polyhydric alcohols (eg, ethylene glycol, hexanediol, glycerin, trimethylolpropane, diglycerin, etc.), compounds obtained by adding ethylene oxide to polyhydric alcohols such as glycerin, various alkylene oxides (ethylene Oxides, propylene oxide, mixed adducts of ethylene oxide and propylene oxide, etc.), saccharides (eg, sorbitol, mannitol, pentaerythritol, xylol, arabinose, ribulose, etc.), phenol derivatives such as bisphenol A and bisphenol S, N-methylpyrrolidone Amide compounds such as glucosides such as α-methyl-D-glucoside, water and the like. In addition, as the compounding quantity, it is preferable to set it as 100 mass parts or less with respect to 100 mass parts of PVOH-type resin, Furthermore, 20 mass parts or less, Especially 10 mass parts or less.

  Also, thermoplastic resins (eg polyethylene, polypropylene, polyester in the presence of compatibilizers), fragrances, foaming agents, deodorants, extenders, fillers (talc, clay, montmorillonite, calcium carbonate, glass beads, glass fibers , Silica, mica, alumina, hydrotalcite, titanium oxide, zirconium oxide, boron nitride, aluminum nitride and other inorganic fillers, melamine-formalin-based organic fillers, etc.), release agents, UV absorbers, antioxidants In addition, additives such as processing stabilizers, weather resistance stabilizers, fungicides, and preservatives can be appropriately blended. The filler is suitably used for the purpose of adjusting the water decomposability and biodegradability of the PVOH-based resin, and providing the resin with anti-blocking properties and printability.

  The PVOH-based resin composition obtained as described above can be used for melt molding as it is, but considering the workability and discharge stability at the time of melt molding, once kneaded in a molten state, It is preferable to cool and solidify into pellets or the like.

  As such means, for example, known kneaders such as a kneader ruder, an extruder, a mixing roll, a Banbury mixer, a blast mill can be used, but usually a single-screw or twin-screw extruder is used. It is industrially preferable, and it is also preferable to provide a vent suction device, a gear pump device, a screen device, a strand support belt, a dry fog generator, and the like as necessary. In particular, in order to remove moisture and by-products (pyrolysis low molecular weight products, etc.), one or more vent holes are provided in the extruder, and suction is performed under reduced pressure, and mixing of oxygen into the extruder is prevented. Therefore, by continuously supplying an inert gas such as nitrogen into the hopper, pellets of PVOH-based resin composition having excellent quality with reduced thermal coloring and thermal deterioration can be obtained.

The PVOH-based resin composition of the present invention has unique non-coloring properties and melt viscosity stability over time. Specifically, using an extruder, the YI (Yellow Index) value of an extrudate (melt extruded pellet) obtained under the conditions of a resin temperature of 210 ° C. and a residence time of 3 minutes is 50 or less, preferably 5 to 48, Especially preferably, it is 10-45. The YI value can be measured using a spectral color difference meter.
Further, the PVOH-based resin composition of the present invention has a ratio of torque 60 minutes after the start of kneading to torque 10 minutes after the start of kneading when the resin temperature is 230 ° C. by plastograph (torque after 60 minutes) (Torque after 10 minutes) is 3 or less, preferably 0.3 to 3, particularly preferably 1 to 2.8.

  The PVOH-based resin composition of the present invention can be suitably used for melt molding. The melt-molded product using the PVOH-based resin composition of the present invention is not particularly limited, and is a film, sheet, bottle, pipe, tube, injection-molded product, atypical cross-section extrudate, etc. Is exemplified. As a melt molding method for obtaining such a melt molded product, a compression molding method, a transfer molding method, an extrusion molding method, an injection molding method, an inflation molding method, a hollow molding method, a blow molding method, a calendar molding method, a foam molding method, A vacuum molding method or the like is mainly employed, and the melting temperature is usually selected from the range of 150 to 250 ° C., but in the PVOH resin composition of the present invention, 150 to 220 ° C. (more preferably 185 to 210 ° C.). ) Can be melt-molded at a low temperature, and if the degree of saponification of the PVOH resin is further lowered, molding at a lower temperature is possible.

  Specific examples of melt-molded products obtained using the PVOH-based resin composition of the present invention include fibers, gas barrier films, water-soluble films (especially agricultural chemicals, detergents, laundry clothes, civil engineering additives, disinfectants) Water-soluble film for packaging of goods such as dyes, pigments, etc.), agricultural film, sheet, pipe, tube, leak-proof film, temporary coating, water-soluble fiber for chemical lace, PVDC (polyvinylidene chloride) substitute film for food packaging Etc. are exemplified. In addition, a sheet or film as a melt-molded product may be uniaxially or biaxially stretched, and if necessary, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making. Processing, deep drawing processing, box processing, tube processing, split processing, cutting processing, and the like may be performed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded. In the following, “%” means mass basis unless otherwise specified.

Example 1
[Production of PVOH resin]
A reactor equipped with a reflux condenser, a dropping funnel and a stirrer was charged with 321.4 g of vinyl acetate, 241.1 g of methanol, and 38.6 g of 3,4-diacetoxy-1-butene, and the temperature was maintained under a nitrogen stream while stirring. Then, 37.8 g of a 4% methanol solution of t-butylperoxyneodecanoate (half-life 102 minutes) was added over 610 minutes for polymerization. When 35 minutes had elapsed from the start of polymerization, 571.4 g of vinyl acetate and 68.6 g of 3,4-diacetoxy-1-butene were added over 480 minutes, and polymerization was further carried out for 105 minutes. When the polymerization rate of vinyl acetate reached 89.5%, 38 ppm of p-methoxyphenol (vs. vinyl acetate charged) was added as a polymerization inhibitor to complete the polymerization. Subsequently, unreacted vinyl acetate monomer was removed out of the system by a method of blowing methanol vapor to obtain a methanol solution of a copolymer.

  Next, the solution was diluted with methanol to adjust the copolymer concentration to 66% and charged into a kneader. While maintaining the solution temperature at 40 ° C., a 2% methanol solution of sodium hydroxide was added to vinyl acetate in the copolymer. And saponification was performed by adding at a ratio of 12 mmol to 1 mol of the total amount of 3,4-diacetoxy-1-butene. As saponification progresses, saponified product precipitates in the form of particles to form a slurry, and then acetic acid is added in an amount of 0.35 equivalent to the amount of added sodium hydroxide, and the resin concentration in the slurry is 9 % Methanol was added, and the mixture was stirred in a kneader for 15 minutes, filtered and dried in a hot air dryer to obtain a PVOH resin composition (pellets) containing acetic acid and sodium acetate.

The saponification degree of the PVOH-based resin in the obtained PVOH-based resin composition was analyzed by the alkali consumption required for hydrolysis of the residual vinyl acetate and the residual 3,4-diacetoxy-1-butene. It was 2 mol%, and the average degree of polymerization was 450 when analyzed according to JIS K6726. The amount of side chain introduced containing a 1,2-diol structure was 6 mol% when calculated by measurement with ¹ H-NMR spectrum (solvent: DMSO-d6, internal standard: tetramethylsilane). . Further, the absorbance at 280 nm in an ultraviolet absorption spectrum of an aqueous solution (hereinafter also referred to as a 4% by mass aqueous solution) of a PVOH resin composition prepared so that the content of the PVOH resin is 4% is 0.18, The aqueous solution had a pH of 6.2 at 20 ° C. This pH is measured using a glass electrode type pH meter (Horiba, Ltd., F-22) and a low conductivity pH electrode (Horiba, Ltd., 6377-10D).
Furthermore, the YI value and torque ratio of the PVOH-based resin composition were measured by the following measuring method. The above physical property values are summarized in Table 1.

[YI value measurement method]
The YI value of the extrudate (melt-extruded pellet) obtained under the following conditions using an extruder was measured under the following conditions.
Extruder: Twin screw extruder manufactured by Technobel, KZW-15-60MG, screw diameter 15 mm, L / D = 60,
Screw: Feed segment only (no kneading part),
Resin temperature: 210 ° C.
Residence time: 3 minutes
Measuring instrument: Nippon Denshoku Industries Co., Ltd., spectral color difference meter Σ90,
Measurement conditions: The hopper is nitrogen sealed.

[Torque ratio measurement method]
The torque ratio of the PVOH-based resin composition (torque 60 minutes after the start of kneading / torque 10 minutes after the start of kneading) was measured under the following conditions using a plastograph.
Plastograph: Brabender, Plastograph EC plus, Roller mixer R60B (chamber capacity 60 mL),
Resin input amount: 55 g,
Preheating time: 3 minutes,
Resin temperature: 230 ° C.
Kneading conditions: 50 rpm.

(Examples 2, 3, and 4)
In Example 1, by changing the content ratio of acetic acid / sodium acetate, the pH of the 4 mass% aqueous solution (20 ° C.) was 6.8 (Example 2), 6.2 (Example 3), or 5 8 (Example 4) PVOH-based resin compositions were obtained. Each physical property value is summarized in Table 1.

(Comparative Example 1)
A PVOH-based resin composition was obtained in the same manner as in Example 1, except that the polymerization initiator was changed to acetyl peroxide (half-life 1920 minutes). Each physical property value is summarized in Table 1.

(Comparative Examples 2 and 3)
In Example 1, by changing the content ratio of acetic acid / sodium acetate, PVOH having a 4% by mass aqueous solution (20 ° C.) having a pH of 5.3 (Comparative Example 2) or 7.2 (Comparative Example 3) Each resin composition was obtained. Each physical property value is summarized in Table 1.

  As shown in Table 1, the absorbance at 280 nm in the ultraviolet absorption spectrum of a 4% by mass aqueous solution is 0.1 to 0.3, and the pH of the aqueous solution at 20 ° C. is 5.5 to 7. The PVOH-based resin composition No. 4 has a low YI value of 50 or less and a low torque ratio of 3 or less. That is, the PVOH-based resin compositions of Examples 1 to 4 are all suitable for melt molding because the moldings are less colored (yellowing) and the melt viscosity is stable over time.

  On the other hand, in the PVOH resin composition of Comparative Example 1, the absorbance at 280 nm in the ultraviolet absorption spectrum of the 4% by mass aqueous solution is higher than 0.3, and the YI value exceeds 50. Moreover, the PVOH-type resin composition of the comparative example 2 has a pH at 20 ° C. of a 4 mass% aqueous solution smaller than 5.5 and a torque ratio exceeding 3. Furthermore, in the PVOH-based resin composition of Comparative Example 3, the pH of a 4% by mass aqueous solution at 20 ° C. is higher than 7, and the YI value exceeds 50. Accordingly, the PVOH-based resin compositions of Comparative Examples 1 to 3 have a problem that the molded product is easily colored and the resin viscosity increases with time in a molten state, and cannot be said to be suitable for melt molding.

Claims (3)

A polyvinyl alcohol resin having a structural unit represented by the following general formula (1) and having an absorbance at 280 nm of 0.1 to 0.3 in an ultraviolet absorption spectrum when a 4% by mass aqueous solution is obtained; The pH at 20 ° C. of an aqueous solution containing at least one of an alkali metal salt and an alkaline earth metal salt and having a polyvinyl alcohol resin content of 4% by mass is 5.5 to 7 The polyvinyl alcohol-type resin composition characterized by the above-mentioned.

[Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom. Or an organic group is shown. ] A polyvinyl alcohol resin having a structural unit represented by the general formula (1) is a polymerization initiator comprising a vinyl ester monomer and a compound having a 1,2-diol structure represented by the following general formula (2) or a derivative thereof. The polyvinyl alcohol according to claim 1, which is obtained by saponifying a copolymer obtained by copolymerization using an organic peroxide having a half-life of 10 to 300 minutes at 60 ° C. -Based resin composition.

[Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom. Or an organic group is shown. ]   Using an extruder, the extrudate obtained under the conditions of a resin temperature of 210 ° C. and a residence time of 3 minutes has a YI value of 50 or less, and 10 minutes from the start of kneading when melt-kneading at a resin temperature of 230 ° C. using a plastograph The ratio of the torque 60 minutes after the start of kneading with respect to the subsequent torque is 3 or less.