JP7259296B2 - Modified polyvinyl alcohol resin and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a modified polyvinyl alcohol-based resin, and more particularly to a modified polyvinyl alcohol-based resin grafted with an aliphatic polyester and a method for producing the same.

Polyvinyl alcohol-based resins (hereinafter sometimes referred to as “PVA-based resins”) have hydroxyl groups, so they have a high affinity for water and are water-soluble. In addition, the hydrogen bond of the hydroxyl group provides a strong bonding force between molecular chains, making the resin highly crystalline.
Due to its high crystallinity, it has high gas barrier properties and is useful for applications that require barrier properties such as packaging materials. rice field.

Therefore, for the purpose of improving flexibility, a lactone-modified PVA-based resin obtained by addition-polymerizing a lactone monomer to a PVA-based resin has been proposed (see, for example, Patent Document 1). Such a lactone-modified PVA-based resin has a low melting point and is suitable for melt molding.

In addition, as PVA-based resins suitable for melt molding, PVA-based resins having 1,2-diol structures in side chains and PVA-based resins containing oxyalkylene groups have been proposed (see, for example, Patent Documents 2 and 3). .).

JP-A-08-151411 JP 2008-208347 A JP 2015-117286 A

However, conventional lactone-modified PVA-based resins are melt-kneaded with unmodified PVA-based resins and lactone-modified. However, the gas barrier property was not satisfactory because PVA-based resin with a low degree of saponification, which is relatively easy to melt and mold, was used.
Moreover, since the PVA-based resin having a low degree of saponification is modified with a lactone group, which is a hydrophobic group, there is a problem of poor water solubility.
Therefore, a PVA-based resin having a 1,2-diol structure in a side chain has been proposed, which is relatively easy to melt-mold, has excellent gas barrier properties, and is also excellent in water solubility. However, such a PVA-based resin having a 1,2-diol structure in its side chain still has room for improvement in terms of biodegradability and melt moldability.
Accordingly, an object of the present invention is to provide a modified PVA-based resin having three properties of gas barrier properties, water solubility and biodegradability.

As a result of intensive studies, the present inventors have found that a modified PVA-based resin having a specific structural unit can solve the above problems, and completed the present invention.

（化学式（１）中、Ｘはヘテロ原子を有する有機鎖を表し、ｎは正の整数を表す。） That is, the gist of the present invention is a modified polyvinyl alcohol resin having a structural unit (A) and a structural unit (B) in its main chain,
Structural unit (A) is a structural unit represented by the following general formula (1),
The structural unit (B) relates to a modified polyvinyl alcohol-based resin characterized by being a structural unit having an alkyl group having a hydroxyl group at the end of a side chain.

(In chemical formula (1), X represents an organic chain having a heteroatom, and n represents a positive integer.)

Furthermore, the present invention also provides a method for producing the above-mentioned modified PVA-based resin.

A melt-molded article obtained using the modified PVA-based resin of the present invention is excellent in flexibility and biodegradability. In addition, since it also retains gas barrier properties, it is useful as various packaging materials.

¹ H-NMR chart of the modified PVA-based resin of the present invention ¹³ C-NMR chart of the modified PVA-based resin of the present invention

The invention of the present invention will be described in more detail below, but the invention is not limited to the following embodiments.

[Modified PVA-based resin]
The modified PVA-based resin of the present invention is a modified polyvinyl alcohol-based resin having structural units (A) and (B),
Structural unit (A) is represented by the following general formula (1), is bound to the main chain,
Structural unit (B) is a modified polyvinyl alcohol-based resin characterized by being a structural unit having an alkyl group having a hydroxyl group at the end of a side chain.

(In chemical formula (1), X represents an organic chain having a heteroatom, and n represents a positive integer.)

First, the structural unit (A) will be explained.
In chemical formula (1), X represents an organic chain having a heteroatom. Heteroatoms include, for example, an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a silicon atom, and the like. Among these, from an industrial point of view, the heteroatom is preferably an oxygen atom, a nitrogen atom or a sulfur atom, and particularly preferably an oxygen atom.

Furthermore, from the viewpoint of production, X is an organic chain having a hydrocarbon chain which may have a substituent starting from a carbonyl group and having a hetero atom which may have a repeating group at the end. Preferably. In addition, X may have another heteroatom as long as it has a heteroatom at least at the repeating end of the carbonyl group as a starting point.

When the hydrocarbon chain that may have a substituent is Rx, and the heteroatom that may have a substituent at the repeating end is Z, chemical formula (1) is represented by the following chemical formula (2). be.

(In chemical formula (2), Rx represents an optionally substituted hydrocarbon chain, Z represents an optionally substituted heteroatom, and n represents a positive integer.)

In the chemical formula (2), when Z is an oxygen atom, the repeating unit includes -CO-Rx-O-, and when Z is a nitrogen atom, the repeating unit is -CO-Rx-NH-, -CO- Rx-NR ¹ -, and when Z is a sulfur atom, repeating units include -CO-Rx-S-. Examples of substituents that the hydrocarbon and heteroatom may have include alkyl groups such as methyl and ethyl groups, aryl groups such as aromatic rings, and acyl groups such as acetyl groups. That is, R ¹ in -Rx-NR ¹ - represents an alkyl group such as a methyl group or an ethyl group, an aryl group such as an aromatic ring, or an acyl group such as an acetyl group.
Among these, from the viewpoint of improving gas barrier properties, the repeating unit is preferably -CO-Rx-O-, -CO-Rx-NH- or -CO-Rx-S-, and particularly Z is an oxygen atom. Specifically, when the repeating unit is -CO-Rx-O-, the chemical formula (1) is represented by the following chemical formula (3).

(In chemical formula (3), Rx represents a hydrocarbon chain which may have a substituent, and n represents a positive integer.)

The hydrocarbon chain Rx in chemical formulas (2) and (3) is preferably a straight or branched chain having 1 to 10 carbon atoms. The linear or branched hydrocarbon chain having 1 to 10 carbon atoms includes, for example, a methylene group ( _--CH.sub.2-- ), a methine group ( ^{--CHR.sub.2--} ), and a quaternary carbon having no hydrogen atom ( ^--CR.sub.3-- ). R ⁴ -), propylene group, isopropylene group, butylene group, isobutylene group, phenylene group and the like. R ² , R ³ and R ⁴ in the methine group and quaternary carbon atoms represent alkyl groups such as methyl and ethyl groups, and aryl groups such as aromatic rings. Among them, the hydrocarbon chain is more preferably a straight or branched alkyl chain having 2 to 8 carbon atoms, and more preferably a straight or branched alkyl chain having 3 to 7 carbon atoms. Among these, from the viewpoint of improving the storage stability and processing stability of the resin, it is preferably a straight hydrocarbon chain, more preferably a straight alkyl chain having 2 to 8 carbon atoms, and 3 to 7 carbon atoms. is particularly preferred.

In chemical formulas (1) to (3), n represents a positive integer. n is preferably an integer of 1-10, more preferably an integer of 1-5. When n is 1 to 10, it is possible to suppress the deterioration of the barrier properties due to the introduction of the modifying group.

In chemical formulas (1) to (3), when n is 2 or more, a plurality of X's may be the same or different, but are preferably the same from the viewpoint of barrier properties.

In the modified PVA-based resin of the present invention, the average value of n in the chemical formulas (1) to (3) (that is, sometimes referred to as the average chain length of the graft chain) is in the range of 1 to 10. 1 to 8 is more preferred, 1 to 5 is even more preferred, and 1 to 3 is particularly preferred. If the average value of n is too large, the gas barrier properties tend to deteriorate, so it is preferably 10 or less.

The content of the structural unit (A) in the modified PVA-based resin of the present invention is usually 0.1 to 30 mol%, more preferably 1 to 20 mol%, particularly preferably 5 to 15 mol%. be. The modification rate means the proportion of the PVA resin structural units grafted with the structure of the structural unit represented by any one of the chemical formulas (1) to (3). If the modification rate in the modified PVA-based resin is too low, the flexibility tends to decrease. On the other hand, if the modification rate in the modified PVA-based resin is too high, the gas barrier properties tend to decrease.
The modification rate in the modified PVA-based resin of the present invention can be calculated from the results of measurement by nuclear magnetic resonance spectroscopy.

Structural units represented by chemical formulas (1) to (3) can be identified by general organic chemical techniques such as nuclear magnetic resonance spectroscopy (NMR), infrared spectrophotometry, and mass spectrometry. can.
The average chain length of the grafted chains in chemical formulas (1) to (3) in the modified PVA-based resin of the present invention can be calculated from the results of measurement by nuclear magnetic resonance spectroscopy.

Next, the structural unit (B) will be explained.
Structural unit (B) is a structural unit having an alkyl group having a hydroxyl group at the end of the side chain, and includes, for example, a structural unit having a 1,2-diol structural unit and a hydroxymethyl group in the side chain.
Among them, 1,2-diol structural units and oxyalkylene group-containing structural units are preferable in the side chain from the viewpoint of productivity.

（化学式（４）中、Ｒ^５～Ｒ^８はそれぞれ独立して水素原子又は炭素数１～４のアルキル基を表し、Ｘ^２は単結合又は炭素数１～４アルキレン鎖を表す。） First, the 1,2-diol structural unit in the side chain will be explained.
The 1,2-diol structural unit in the side chain is represented by the following general formula (4).

(In chemical formula (4), R ⁵ to R ⁸ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ² represents a single bond or an alkylene chain having 1 to 4 carbon atoms.)

All of R ⁵ to R ⁸ in the 1,2-diol structural unit represented by the general formula (4) are hydrogen atoms, so that the terminal of the side chain becomes a primary hydroxyl group and further reacts with the functional group of the block copolymer. However, it may be substituted with an alkyl group having 1 to 4 carbon atoms in an amount that does not significantly impair the properties of the resin. The alkyl group having 1 to 4 carbon atoms is, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group and the like, and optionally halogen group, hydroxyl group. , an ester group, a carboxylic acid group, a sulfonic acid group, or the like.

The content of the 1,2-diol structural unit in the side chain is usually 0.5 to 20 mol%, preferably 1 to 10 mol%, based on the total structural units of the modified PVA-based resin of the present invention. More preferably 2 to 8 mol %, the remaining portion contains vinyl alcohol structural units corresponding to the usual degree of saponification, vinyl acetate structural units other than that, and structural units represented by general formula (1).

Next, a structural unit having a hydroxymethyl group will be explained.
A hydroxymethyl group is represented by the following general formula (5).

The content of the structural unit having such a hydroxymethyl group is usually 0.5 to 10 mol%, preferably 1 to 5 mol%, based on the total structural units of the modified PVA-based resin of the present invention. , the remaining portion contains vinyl alcohol structural units corresponding to the usual degree of saponification, vinyl acetate structural units other than that, and structural units represented by general formula (1).

[Production of modified PVA-based resin]
The modified PVA-based resin of the present invention can usually be obtained by graft reaction of a PVA resin having the structural unit (B) and a compound having a heterofunctional group.
Formation of the repeating unit represented by the chemical formula (1) in the main chain of the modified PVA-based resin, that is, the formation of the side chain graft structure by the graft reaction, starts from the hydroxyl group of the PVA resin having the structural unit (B) used as the starting material. It is.

(PVA resin having structural unit (B))
The PVA resin having the structural unit (B) used in the present invention is a resin obtained by saponifying after copolymerizing a modified monomer having copolymerizability with a vinyl ester monomer, and is produced by a known method. be able to.
A PVA-based resin having a 1,2-diol structure in a side chain and an oxyalkylene group-containing PVA-based resin can be produced by the method described in JP-A-2015-117286. Hydroxymethyl group-containing PVA-based resin can be produced by the method described in JP-A-2013-177576.

Moreover, the PVA resin having the structural unit (B) may further contain a structural unit derived from a comonomer shown below. The comonomers include α-olefins such as propylene, isobutene, α-octene, α-dodecene, α-octadecene, 3-butene-1-ol, 4-pentene-1-ol, 3-butene-1,2-diol. hydroxy group-containing α-olefins such as esters thereof, hydroxy group-containing α-olefin derivatives such as acylated products, hydroxymethyl such as 1,3-hydroxy-2-methylenepropane and 1,5-hydroxy-3-methylenepentane vinylidenes; vinylidenes such as 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyronyloxy-2-methylenepropane, which are esters thereof; Acetates; comonomers such as unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides, unsaturated sulfonic acids or their salts, vinylsilane compounds, vinyl chloride, and styrene.

The average degree of polymerization of the PVA resin having the structural unit (B) is preferably 200-1000, more preferably 250-800, even more preferably 300-600. If the average degree of polymerization is too low, the material tends to be brittle.
In addition, the said average degree of polymerization is measured according to JISK6726.

The saponification degree of the PVA resin having the structural unit (B) is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, even more preferably 85 to 100 mol%. When the degree of saponification is within this range, efficiency in melt-kneading tends to be improved. On the other hand, if it is too low, the heat resistance tends to decrease.
The degree of saponification is measured according to JIS K6726.

The melt flow rate (MFR) (210° C., load 2,160 g) of the PVA resin having the structural unit (B) is usually 0.5 to 50 g/10 minutes, preferably 1.5 to 25 g/10 minutes, Particularly preferably, it is 2 to 20 g/10 minutes. If the MFR is too large, the barrier properties tend to deteriorate, and if it is too small, the workability tends to deteriorate.

The viscosity of a 4% by weight aqueous solution of the PVA resin having the structural unit (B) at 20° C. is preferably 2.5 to 70 mPa·s, more preferably 3 to 12 mPa·s, and even more preferably 3.5 to 6 mPa·s. . If the viscosity is too low, the mechanical properties such as film strength tend to be poor, and if it is too high, the ability to form a film tends to be low.
The above viscosity is measured according to JIS K6726.

As the PVA resin having the structural unit (B), two or more PVA resins having different ethylene content, degree of saponification, MFR, and modified species are mixed as long as the average value thereof satisfies the above requirements. may be used.

(Compound with heterofunctional group)
Next, a compound having a heterofunctional group will be explained. The hetero functional group is a functional group having a hetero atom, and the hetero atom includes an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a silicon atom and the like. Examples include an ester group, a carboxylic acid group, an acyl group, a thioester group, an amide group, a carbonate group, a carbamate group, a thiocarbamate group, a carbamide group, an N-acyl group, and an N,N'-diacyl group.

Compounds having a heterofunctional group include cyclic compounds, carboxylic acid compounds, carbonate compounds, carbamate compounds, thiocarbamate compounds, diacyl compounds, triacyl compounds, and analogues thereof having a heterofunctional group.

<Cyclic compound having a heterofunctional group>
As the cyclic compound having a heterofunctional group, a heterocyclic compound having 2 or more carbon atoms is preferable. Examples of the cyclic compound having a heterofunctional group include cyclic esters such as lactones, cyclic amides such as lactams, cyclic carbonates such as ethylene carbonate and propylene carbonate, thietan-2-one, 3,3-dimethylthietane- Cyclic thioesters such as 2-one, 4-methylthietane-2-one, 3-methylthietane-2-one, 3-ethylthietane-2-one, 3-methyl-3-ethylthietane-2-one, and cyclic carbamates such as ethylene carbamate , phenylphthalimide and cyclohexanedicarboximide, etc., cyclic urea derivatives such as N,N'-dimethylpropylene urea and 1,3-dimethyl-2-imidazolidison, and cyclic N compounds such as N-acyl-substituted caprolactam. , N′-diacyl compounds, etc. Among these, cyclic esters are preferred, and lactones are more preferred.

Lactones include lactones having 3 to 15 carbon atoms that form aliphatic polyesters by ring-opening polymerization. Such lactones, when not having a substituent, are represented by the following general formula, where n is an integer of 2-14, preferably 4-5. Any carbon atom of the alkylene chain —(CH ₂ )n— in the following formula may be at least one lower alkyl group having about 1 to 8 carbon atoms, or a lower alkoxy group having about 1 to 8 carbon atoms. It may have a substituent such as a group, a cycloalkyl group, a phenyl group, an aralkyl group, or the like.

Specific examples of lactones include β-propiolactones, γ-butyrolactones, ε-caprolactones, δ-valerolactones and the like.

Examples of β-propiolactones include β-propiolactone and dimethylpropionolactone.

Examples of γ-butyrolactones include butyrolactone, γ-valerolactone, γ-caprolactone, γ-caprylolactone, γ-laurolactone, γ-palmitolactone, γ-stearolactone, crotonolactone, and α-angelica. lactones, β-angelical lactones, and the like.

Examples of ε-caprolactones include monoalkyl-ε-caprolactones such as ε-caprolactone, monomethyl-ε-caprolactone, monoethyl-ε-caprolactone, monodecyl-ε-caprolactone, monopropyl-ε-caprolactone; dialkyl-ε-caprolactone in which groups are respectively substituted on carbon atoms other than the ε-position; trialkyl-ε-caprolactones in which three alkyl groups are respectively substituted on carbon atoms other than the ε-position; ethoxy-ε-caprolactone cycloalkyl-lactones such as cyclohexyl-ε-caprolactone; aralkyl-ε-caprolactones such as benzyl-ε-caprolactone; aryl-ε-caprolactones such as phenyl-ε-caprolactone;

δ-valerolactones include, for example, 5-valerolactone, 3-methyl-5-valerolactone, 3,3-dimethyl-5-valerolactone, 2-methyl-5-valerolactone, 3-ethyl-5- valerolactone and the like.

These lactones can be used singly or in combination of two or more.

Among these, the lactones used in the present invention are preferably ε-caprolactones or δ-valerolactones from the viewpoint of reactivity, and more preferably ε-caprolactones from the viewpoint of low cost and easy availability. .

<Carboxylic acid compound>
Examples of the carboxylic acid compound include linear carboxylic acid esters, linear carboxylic acid thioesters, linear carboxylic acid amides, acyl halides of carboxylic acids, acid anhydrides, and the like. Among these, linear carboxylic acid esters are preferred.

<Carbonate compound>
Examples of carbonate compounds include various dialkyl carbonates, diaryl carbonates, arylalkyl carbonates, and the like.

<Carbamate compound>
Examples of carbamate compounds include methyl carbamate and ethyl carbamate.

<Thiocarbamate compound>
Thiocarbamate compounds include derivatives such as dimethylamino-S-arylthiocarbamate.

<Diacyl compound>
Examples of diacyl compounds include diacetamide and diacetyl(cyclopentyl)azane.

<Triacyl compound>
Examples of triacyl compounds include triacetamide and tribenzamide.

In addition, as the compound having a heterofunctional group, oligomers or polymers of repeating structural units represented by n in chemical formulas (1) to (3) can also be used. For example, polyesters such as poly-ε-caprolactone and polylactic acid, polyamides such as poly-ε-caprolactam, and polythioesters can be used.

As described above, the method for producing a modified PVA-based resin of the present invention having a structural unit represented by the chemical formula (1) comprises: (i) a PVA resin having a structural unit (B) and a compound having a heterofunctional group; (ii) a PVA-based resin obtained by dissolving a PVA-based resin having the structural unit (B) in a solvent; (iii) swelling a PVA-based resin having the structural unit (B) in a solvent; A method of producing by incorporating a compound having a functional group and performing a graft reaction, and the like can be mentioned.

When a cyclic compound having a heterofunctional group is used as the compound having a heterofunctional group, ring-opening polymerization reaction and graft reaction of the cyclic compound having a heterofunctional group are performed in the presence of the PVA resin having the structural unit (B). . Alternatively, when a carboxylic acid compound is used as the compound having a heterofunctional group, the nucleophilic substitution reaction or dehydration condensation reaction and graft reaction of the carboxylic acid compound are carried out in the presence of the PVA resin having the structural unit (B). Through such steps, the modified PVA-based resin of the present invention can be produced.

In the present invention, the above-described PVA resin and a compound having a heterofunctional group as a monomer are used as the polymerization material, and if desired, a polymerization catalyst is contained.

Each material may be charged one by one, or may be mixed in advance. Among them, the most preferable method is to charge the PVA resin first and then charge the compound having a heterofunctional group. A method of charging the compound having such a heterofunctional group while stirring the PVA resin is preferably used.

The amount of the compound having a heterofunctional group, which is a monomer, may be appropriately selected so as to obtain the desired grafted structural unit content. is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass. When the amount of the compound having a heterofunctional group used is too small, the flexibility tends to decrease, while when the amount used is too large, the gas barrier properties tend to decrease.

Examples of the polymerization catalyst include metal catalysts, and conventionally known catalysts such as a ring-opening polymerization catalyst for a cyclic compound having a heterofunctional group, a nucleophilic substitution reaction catalyst for a carboxylic acid compound, or a dehydration condensation reaction catalyst can be used.
Examples include titanium-based compounds, tin-based compounds, aluminum-based compounds, iron-based compounds, zirconium-based compounds, zinc-based compounds, and lead-based compounds. Specifically, titanium alkoxides such as tetra-n-butoxytitanium, tetraisobutoxytitanium and tetraisopropoxytitanium; tin alkoxides such as dibutyldibutoxytin; dibutyltin diacetate; tin (II) 2-ethylhexanoate; Among these, tin ester compounds are preferred in that the effects of the present invention can be obtained more effectively, and 2-ethylhexanoic acid is preferred in terms of compatibility with compounds having a heterofunctional group. Tin(II) is preferred.

When a polymerization catalyst is used, the amount used is preferably less than 5 parts by mass, preferably 3 parts by mass or less, more preferably 1 part by mass with respect to 100 parts by mass of the compound having a heterofunctional group that is a monomer. parts or less, more preferably 0.5 parts by mass or less.

As for the melt-kneading conditions in the production method (i), the heating temperature is preferably 180 to 240°C, more preferably 190 to 235°C, and even more preferably 195 to 210°C. If the heating temperature is too low, the efficiency of the graft reaction may decrease, and if the heating temperature is too high, the processability may decrease due to coloring of the resin or increase in viscosity, so heating within the above temperature range is preferable.

As the conditions for the solution reaction in the production method (ii), it is preferable to use a highly polar solvent capable of sufficiently dissolving the raw material PVA. Examples thereof include diprotic highly polar solvents such as dimethylsulfoxide, dimethylformamide, and dimethylacetamide, but dimethylsulfoxide is particularly preferred in terms of solubility and stability during the reaction. The heating temperature depends on the boiling point and decomposition temperature of the highly polar solvent, preferably 50 to 150°C, more preferably 80 to 140°C.

In the case of the production method (iii), as conditions for swelling the PVA-based resin in the solvent for reaction, it is preferable to use a solvent capable of sufficiently swelling the raw material PVA. For example, various carboxylic acids such as acetic acid, propionic acid, butyric acid and caproic acid can be used, but acetic acid is preferably used from the viewpoint of cost and swelling property. The heating temperature depends on the boiling point of the swelling solvent, preferably 50 to 180°C, more preferably 80 to 120°C.

After the graft reaction, it is preferable to remove unreacted monomers in order to prevent the odor of the resin.
Methods for removing the unreacted monomer include a method of immersion in a solution in which the unreacted monomer is dissolved and a method of removal under reduced pressure. From the viewpoint of production efficiency, the method of removal under reduced pressure is preferred.
For example, as conditions for removal under reduced pressure, it is preferable to carry out at the same set temperature as the reaction temperature under a pressure of 100 to 1200 Pa for 1 second to 10 hours.

The solvent that dissolves the unreacted monomer is preferably a solvent that dissolves the unreacted monomer but does not dissolve the modified PVA-based resin of the present invention. The solvent can be freely selected according to the monomers used, but lower alcohols such as methanol and ethanol are particularly preferred.

The number average molecular weight (measured by gel permeation chromatography (GPC) in terms of standard polystyrene) of the modified PVA-based resin of the present invention is usually 10,000 to 300,000, preferably 12,500 to 200,000, and particularly preferably 15,000 to 100,000. is. When the number average molecular weight of the modified PVA-based resin is too high, barrier properties tend to decrease, while when the number-average molecular weight of the modified PVA-based resin is too low, flexibility tends to decrease.
The number average molecular weight in the modified PVA-based resin can be calculated from the results of GPC measurement.

The melting point of the modified PVA-based resin of the present invention is preferably 100 to 190°C, more preferably 110 to 160°C, and particularly preferably 120 to 150°C. If the melting point of the modified PVA-based resin is too high, flexibility tends to decrease, while if the melting point of the modified PVA-based resin is too low, barrier properties tend to decrease.
In general, the grafting of the above monomers weakens the intermolecular forces such as hydrogen bonding between hydroxyl groups in the PVA resin skeleton. tends to be lower.
The melting point of the modified PVA-based resin can be measured using a differential scanning calorimeter.

The modified PVA-based resin of the present invention contains compounding agents that are generally blended with PVA resins, such as heat stabilizers, oxidation Antistatic agents, antistatic agents, colorants, UV absorbers, lubricants, plasticizers, light stabilizers, surfactants, antibacterial agents, desiccants, antiblocking agents, flame retardants, cross-linking agents, hardeners, foaming agents, crystals A nucleating agent, an antifog agent, a biodegradable additive, a silane coupling agent, an oxygen absorber, and the like may be contained.

Examples of plasticizers include compounds obtained by adding ethylene oxide to polyhydric alcohols such as aliphatic polyhydric alcohols (e.g., ethylene glycol, hexanediol, glycerin, trimethylolpropane, diglycerin, etc.), and various alkylene oxides (e.g., ethylene oxide, propylene oxide, mixed adducts of ethylene oxide and propylene oxide, etc.), sugars (e.g., sorbitol, mannitol, pentaerythritol, xylol, arabinose, ribulose, etc.), phenol derivatives such as bisphenol A and bisphenol S, N-methyl Examples include amide compounds such as pyrrolidone, glucosides such as α-methyl-D-glucoside, and the like.

<Application of modified PVA-based resin>
The modified PVA-based resin of the present invention thus obtained can be molded into films, sheets, cups, bottles, etc. by melt molding. As such a melt molding method, extrusion molding (T-die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, etc.) and injection molding are mainly employed. The melt-molding temperature is usually selected from the range of 120 to 300°C.

Since the molded article has a good appearance, it is suitably used as an optical material, a food packaging material, a surface coating agent for paper, a sizing agent for fibers, a binder for various pigments, and the like. In addition, in order to further increase the strength or impart other functions, it can be laminated with other base materials to form a laminate.
Thermoplastic resins other than PVA resins are useful as such other base materials. Thermoplastic resins include biodegradable resins such as aliphatic polyester resins.

The thickness of the thermoplastic resin layer and the adhesive resin layer of the laminate cannot be generalized depending on the layer structure, type of thermoplastic resin, type of adhesive resin, application, packaging form, required physical properties, etc. However, thermoplastic The resin layer is usually 10 to 1000 μm, preferably 50 to 500 μm, and the adhesive resin layer is 5 to 500 μm, preferably 10 to 250 μm.

The thickness of the modified PVA-based resin layer of the present invention varies depending on the required gas barrier properties, etc., but is usually 5 to 500 μm, preferably 10 to 250 μm, particularly preferably 20 to 100 μm. If it is too thick, there is a tendency that sufficient gas barrier properties cannot be obtained, and if it is too thick, the flexibility of the film tends to decrease.

Further, since the modified PVA-based resin of the present invention is water-soluble, it can be dissolved in water and applied as a coating liquid to various substrates.

The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. "Parts" and "%" in the examples are based on mass unless otherwise specified.

(Example 1)
[Production of modified PVA-based resin of the present invention]
Using a twin-screw extruder (manufactured by Technobel, L/D = 60, 15 mmφ) equipped with a screw having three kneading sections and a monomer introduction section, a 1,2-diol structure is added to the side chain from the raw material input section. 100 parts of PVA resin (1,2-diol structure of side chain 6 mol%, average degree of polymerization 470, saponification degree 99 mol%, MFR 3.3 g (210 ° C., load 2,160 g)), From the monomer introduction part, 30 parts of ε-caprolactone monomer ("PLACCEL M" manufactured by Daicel Corporation) containing 1% of tin (II) 2-ethylhexanoate (Sn(Oct)2) as a catalyst was continuously introduced. and kneaded at 230° C. in an extruder (screw speed: 200 rpm).

The resin after kneading was air-dried while being extruded in the form of strands, and then cut with a fan cutter to obtain modified PVA-based resin pellets of the present invention. Structural analysis using nuclear magnetic resonance spectroscopy revealed that the reaction rate between the PVA-based resin having a 1,2-diol structure in the side chain and the monomer was 94%, and the average chain length of the grafted chain was 1.7. rice field.
Structural analysis was performed as follows using an Ascend 400 device manufactured by Bruker Japan.

measuring device:
¹ H-NMR measurement conditions heavy solvent dimethyl sulfoxide-d6
Measured concentration 5% by weight
Measurement temperature 50℃
Accumulated times 16 times

¹ H-NMR chart (Fig. 1)
1.2 to 1.7 ppm: methylene protons of PVA 1.9 to 2.0 ppm: protons of residual acetic acid groups of PVA 2.1 to 2.3 ppm: carbonyl groups contained in the caprolactone chain grafted to the main chain α-methylene protons, and a ring-opened product hydrolyzed by the monomer 2.6 ppm: Remaining unreacted ε-caprolactone monomer 4.2 to 4.6 ppm: hydroxyl group protons

¹³ C-NMR measurement conditions (reverse gate decoupling method, relaxation time 2 seconds)
Heavy solvent dimethyl sulfoxide-d6
Measured concentration 5% by weight
Measurement temperature 80℃
Accumulated times 4096 times

^13C -NMR chart (Fig. 2)
· 60.4 ppm: Terminal carbon (a) of caprolactone chain grafted to the main chain
· 63.3 ppm: Terminal carbon (b) contained in the repeating chain of the caprolactone chain grafted to the main chain
Specific positions of terminal carbon (a) and terminal carbon (b) are shown below.

<Melting point evaluation>
The melting point of the modified PVA-based resin pellets of the present invention obtained above was measured by differential scanning calorimetry using a Mettler-Toledo DSC1 apparatus. The melting point of the 2nd run was adopted as the value. Measurement conditions are shown below.
1st Run: -30 to 215°C
2nd Run: -30 to 230°C
Heating rate: 10°C/min The results are shown in Table 1.

[Preparation of film]
Using the obtained modified PVA-based resin pellets of the present invention, hot press molding was performed at 200° C. using a compression molding machine (PRESS AH-10TD, manufactured by AS ONE) to obtain a film having a thickness of about 50 μm.

<Oxygen gas barrier property evaluation>
OTR (oxygen permeability, 23 ° C., internal 65% RH, external 50% RH) was measured using an oxygen gas permeation measuring device (manufactured by Mocon Co., Ltd., "OX-TRAN 2/20"). The obtained OTR values were compared in terms of 20 μm.
Table 1 shows the results.

<Water solubility evaluation>
The film obtained above was cut into a 2 cm x 2 cm test piece, heated in hot water at 80°C for 1 hour, then slowly cooled to room temperature while stirring, and the state of dissolution in water was visually observed. was evaluated according to the criteria of
◯: The film was dissolved in water and could not be visually observed. ×: The film was hardly dissolved in water and could be visually observed. Table 1 shows the results.

<Biodegradability Evaluation>
Each of the films obtained above was cut into a predetermined amount, and biodegradability was evaluated with reference to the biodegradability test method described in JIS K6950.
Apparatus: Closed system oxygen consumption measuring apparatus Inoculum source: Returned sludge from a sewage treatment plant in Osaka City Standard test culture solution: 300 mL
Seed concentration: 90mg/L
Temperature: 25±1°C
Period: 28 days Biodegradability was calculated based on the theoretical oxygen demand calculated from the elemental analysis values of the samples.
Table 1 shows the results.

Example 2
In Example 1, the ε-caprolactone monomer was ε-caprolactone containing 2% Sn(Oct)2 catalyst, and the amount introduced was 100 parts of the PVA resin having a 1,2-diol structure in the side chain. Resin pellets were obtained by reacting in the same manner as in Example 1, except that the amount was changed to 20 parts and the reaction temperature in the extruder was 220°C. Structural analysis using nuclear magnetic resonance spectroscopy revealed that the reaction rate between the resin and the monomer was 99%, and the average chain length of the grafted chains was 2.7.
Using the obtained modified PVA resin pellets of the present invention, a film was obtained in the same manner as in Example 1 and evaluated in the same manner. Table 1 shows the results.

Comparative example 1
100 parts of unmodified PVA (degree of saponification: 75 mol%, MFR: 5.2 g/10 min (210°C, load: 2160 g)) was melted at 220°C using a Brabender plasticorder. . After that, 30 parts of ε-caprolactone monomer (containing no catalyst) was added, and the reaction was carried out by melt-kneading for 10 minutes at 220° C. and 50 rpm to obtain a modified PVA-based resin. Structural analysis using nuclear magnetic resonance spectroscopy revealed that the reaction rate between the resin and the monomer was 93%, and the average chain length of the grafted chains was 1.0.
Using the obtained resin pellets, a film was obtained in the same manner as in Example 1 and evaluated in the same manner. Table 1 shows the results.

Comparative example 2
Various evaluations were performed on a PVA-based resin having a 1,2-diol structure in a side chain (degree of saponification: 99 mol%, 1,2-diol structure in the side chain: 6 mol%, average degree of polymerization: 1200).
After dissolving the resin in hot water at 90° C. to obtain an aqueous solution, a film was obtained by drying in an environment of 23° C. and 50% RH and evaluated in the same manner as in Example 1. Table 1 shows the results.

Examples 1 and 2 using the modified PVA-based resin of the present invention had gas barrier properties, water solubility, and biodegradability. On the other hand, Comparative Example 1 using an unmodified PVA having no structural unit (B) had poor gas barrier properties and was insoluble in water.
In Comparative Example 2, in which the PVA-based resin having the structural unit (B) was not modified with caprolactone, biodegradation took time.

Since the modified PVA obtained by the present invention has moldability and water solubility, it can be suitably used in the fields of various moldings, laminated structures, coating materials, emulsifiers, suspending agents, and the like. In particular, it can be suitably used as a hot-melt or heat-sealing material because of its low-temperature moldability and appropriate barrier properties. Furthermore, since it has good biodegradability, it can be suitably used for biodegradable packaging materials and moldings.

Claims (2)

A modified polyvinyl alcohol resin having a structural unit (A) and a structural unit (B) in its main chain,
Structural unit (A) is a structural unit represented by the following general formula (1),
A modified polyvinyl alcohol resin characterized in that the structural unit (B) has a side chain 1,2-diol structure represented by the following general formula (4).

(In chemical formula (1), X represents an organic chain having a heteroatom, and n represents a positive integer.)

(In chemical formula (4), R ⁵ to R ⁸ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ² represents a single bond or an alkylene chain having 1 to 4 carbon atoms.) A method for producing a modified polyvinyl alcohol-based resin according to claim 1,
A method for producing a modified polyvinyl alcohol-based resin, comprising a step of melt-kneading a polyvinyl alcohol-based resin and a compound having a heterofunctional group.

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