JP2014000683A - Method for manufacturing stretched multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a stretched multilayer film excellent in a gas barrier property.SOLUTION: A multilayer film, which comprises thermoplastic resin layers laminated on both sides of an interlayer whose main constituent is a polyvinyl alcohol-based resin (A) having a structural unit represented by the following general formula (1), is stretched at a temperature lower than the glass transition temperature of the polyvinyl alcohol-based resin (A). [In the formula, R, Rand Reach independently represent a hydrogen atom or a 1-3C alkyl group; X represents a single bond or a joining chain; and R, R, and Reach independently represent a hydrogen atom or a 1-3C alkyl group.]

Description

  The present invention relates to a method for producing a multilayer stretched film obtained by stretching a multilayer film in which a thermoplastic resin layer is laminated on both sides of an intermediate layer mainly composed of a polyvinyl alcohol-based resin, and more specifically, has excellent gas barrier properties. The present invention relates to a method for producing a multilayer stretched film.

Polyvinyl alcohol resin is excellent in strength, transparency, gas barrier properties, etc., so it can be molded into a film and used as a packaging material for various packaging materials, especially foods, chemicals, etc. that need to be inhibited from deterioration due to oxygen. Widely used.
However, the properties of polyvinyl alcohol resins (hereinafter abbreviated as PVA resins) are greatly affected by humidity. For example, strength and gas barrier properties are significantly reduced in a high humidity environment. A layer made of a thermoplastic resin having low wettability is used as a multilayer structure in which both sides of a PVA resin layer are laminated.

In addition, since the PVA resin has a melting point and a decomposition point close to each other, melt molding is substantially difficult. Usually, the PVA resin is formed into a film by a casting method from an aqueous solution and used as various packaging materials. .
In PVA-based resins, such restrictions on molding methods have been barriers to expansion of use, but in recent years, melting points are lower than that of unmodified PVA, so that hot melt molding is possible, and gas barrier properties at the same level PVA-based resins having a 1,2-diol structure in the side chain have been proposed as the PVA-based resins that can be obtained, and multilayer structures by co-extrusion molding of such PVA-based resins and other thermoplastic resins have been studied. Yes. (For example, refer to Patent Document 1.)

JP 2006-31313 A

It is known that in a molded article of a plastic material, molecular chains are highly oriented by stretching and various properties are improved. Even in the PVA-based resin, improvement in strength and gas barrier properties can be expected by stretching.
Such stretching is usually performed in a state where the molded product is heated, and the temperature thereof is not less than the rubber region, that is, the glass transition point (hereinafter abbreviated as Tg) because of the necessity of moving and arranging molecular chains. It is common technical knowledge to be carried out below the melting point.

However, in the case of a multilayer structure including a layer of a PVA resin having a 1,2-diol structure in the side chain obtained by Patent Document 1 or the like, even if stretched at a temperature higher than the Tg of the PVA resin, It has been found that the effect of improving the gas barrier property cannot be obtained sufficiently.
That is, the present invention was made for the purpose of developing a stretching method capable of obtaining a high gas barrier property in a multilayer structure including a layer made of a PVA resin having a 1,2-diol structure in the side chain. It is an object of the present invention to provide a method for producing a multilayer stretched film excellent in the above.

［式中、Ｒ^１、Ｒ^２及びＲ^３はそれぞれ独立して水素原子または炭素数１〜３のアルキル基を示し、Ｘは単結合または結合鎖を示し、Ｒ^４、Ｒ^５、及びＲ^６はそれぞれ独立して水素原子または炭素数１〜３のアルキル基を示す。］ In the present invention, as a result of intensive studies in view of the above circumstances, a thermoplastic resin layer is formed on both sides of an intermediate layer mainly composed of a PVA resin (A) containing a structural unit represented by the following general formula (1). The inventors have found that the object of the present invention can be achieved by a method for producing a multilayer stretched film in which the laminated multilayer film is stretched at a temperature lower than the Tg of the PVA-based resin (A), thereby completing the present invention.

[Wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, 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 alkyl group having 1 to 3 carbon atoms. ]

As described above, generally, stretching of a polymer is performed at a temperature higher than the rubber region, that is, Tg, and is not usually performed because it is likely to break when stretched at a temperature lower than Tg.
In the case of a multilayer film in which a thermoplastic resin layer is laminated on both sides of an intermediate layer mainly composed of a specific PVA resin, the present invention is stretched at a temperature lower than the Tg of the PVA resin. The present invention has been completed by finding that a multilayer stretched film having excellent gas barrier properties can be obtained without breaking.

  Since the multilayer stretched film obtained by the production method of the present invention is excellent in gas barrier properties, it is useful as a packaging material for articles, such as foods, medicines and metal parts, whose characteristics can be degraded or deteriorated by oxygen.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

The method for producing a multilayer stretched film of the present invention is a multilayer film in which a thermoplastic resin layer is laminated on both sides of an intermediate layer mainly composed of a specific PVA resin (A) having a 1,2-diol structure in the side chain. Is stretched at a temperature lower than the Tg of the PVA resin (A).
Hereinafter, the configuration of each layer of the multilayer stretched film and the production method will be described in detail.

[PVA resin (A)]
First, the PVA resin (A) used as the main component of the intermediate layer in the multilayer stretched film of the present invention will be described.
The PVA-based resin (A) 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 A hydrogen atom or an alkyl group having 1 to 3 carbon atoms, 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 alkyl group having 1 to 3 carbon atoms. Is.

Particularly, it is most preferable that R ^{1 to} R ³ and R ^{4 to} R ⁶ in the 1,2-diol structural unit represented by the general formula (1) are all hydrogen atoms, and X is a single bond. A PVA resin having a structural unit represented by the general formula (1 ′) is preferably used.

The X in the 1,2-diol structural unit represented by the general formula (1) is most preferably a single bond from the viewpoint of thermal stability and stability under high temperature and acidic conditions. As long as it does not inhibit the effect of the above, it may be a linking chain. Examples of the linking chain include hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, and naphthylene (these hydrocarbons are halogens such as fluorine, chlorine, and bromine). another may be substituted) in _{such, -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-, -HP _{4 -, - Si (OR)} 2 -, - OSi (OR) 2 -, - OSi (OR) 2 O -, - Ti (OR) 2 -, - OTi (OR) 2 -, - OTi (OR) 2 O-, -Al (OR)-, -OAl (OR)-, -OAl (OR) O-, etc. (R is each independently an optional substituent, preferably a hydrogen atom or an alkyl group, m is a natural number).
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.

  Although it does not specifically limit as a manufacturing method of PVA-type resin (A) used by this invention, (i) The method of saponifying the copolymer of a vinyl ester type monomer and the compound shown by following General formula (2) (Ii) a method of saponifying and decarboxylating a copolymer of a vinyl ester monomer and a compound represented by the following general formula (3), or (iii) a vinyl ester monomer and the following general formula (4) A method of saponifying and deketalizing a copolymer with the compound shown is preferably used.

In the general formulas (2), (3) and (4), R ¹ , R ² , R ³ , X, R ⁴ , R ⁵ and R ⁶ are all the same as in the case of 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 having 1 to 4 carbon atoms). R ¹⁰ and R ¹¹ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

As the methods (i), (ii), and (iii), for example, the method described in JP-A-2006-95825 can be used.
Of these, it is preferable to use 3,4-diacyloxy-1-butene as the compound represented by the general formula (2) in the method (i) from the viewpoint of excellent copolymerization reactivity and industrial handleability. In particular, 3,4-diacetoxy-1-butene is preferably used.

  Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, versatic. Although vinyl acid acid etc. are mentioned, vinyl acetate is preferably used economically.

  In addition to the above-mentioned monomers (vinyl ester monomers, compounds represented by the general formulas (2), (3), (4)), a range that does not significantly affect the physical properties of the resin, specifically 10 mol% If within, α-olefin such as ethylene or propylene as a copolymerization component; hydroxy group-containing α- such as 3-buten-1-ol, 4-penten-1-ol, 5-hexene-1,2-diol Derivatives such as olefins and acylated products thereof; unsaturated acids such as itaconic acid, maleic acid and acrylic acid or salts or mono- or dialkyl esters thereof; nitriles such as acrylonitrile; amides such as methacrylamide and diacetone acrylamide; Olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, AMPS or the like A compound such as a salt thereof may be copolymerized.

  The degree of saponification (measured according to JIS K6726) of the PVA resin (A) used in the present invention is usually 90 to 100 mol%, particularly 95 to 99.99 mol%, particularly 98 to 99.99. Those of 9 mol% are preferably used. If the degree of saponification is too low, the resulting multilayer stretched film tends to have insufficient gas barrier properties.

Moreover, the average degree of polymerization (measured according to JIS K6726) of the PVA resin (A) is usually 200 to 1800, particularly 300 to 1500, and more preferably 300 to 1000.
If the average degree of polymerization is too small, the mechanical strength of the obtained molded product may be insufficient. Conversely, if the average degree of polymerization is too large, the fluidity at the time of hot melt molding will be insufficient and the moldability will deteriorate. There is also a tendency for shear heat generation during molding to occur abnormally and the resin to be easily thermally decomposed.

  The content of the 1,2-diol structural unit contained in the PVA resin (A) is usually 1 to 15 mol%, particularly 2 to 10 mol%, and more preferably 3 to 9 mol%. . If the content is too low, the melting point becomes high, and it becomes close to the thermal decomposition temperature, so that it is easy to cause scorching, gel, and fish eyes due to thermal decomposition during melt molding, and conversely, if it is too high, metal adhesion is improved. However, during melt molding, the flowability is poor, and thermal deterioration due to stagnation or the like is likely to occur.

Incidentally, the content of 1,2-diol structural unit represented by the general formula in PVA-based resin (A) (1), although completely saponified PVA-based resin ¹ H-NMR spectrum (solvent: DMSO -D6, internal standard: tetramethylsilane), specifically hydroxyl group protons in 1,2-diol units, methine protons, and methylene protons, methylene protons in the main chain, hydroxyl groups linked to the main chain What is necessary is just to calculate from the peak area derived from the proton etc.

Moreover, Tg of PVA-type resin (A) used by this invention is 60-90 degreeC normally, Especially the thing of 65-90 degreeC, especially 70-85 degreeC is used preferably. If the Tg is too high, the glass tends to break during stretching, and if it is too low, the barrier performance tends to be low.
The melting point of the PVA resin (A) is usually 170 to 230 ° C., particularly 175 to 210 ° C., particularly 180 to 200 ° C. is preferably used. If the melting point is too high, there is a possibility of causing thermal degradation during melt molding. Conversely, if the melting point is too low, the barrier performance tends to be low.
Such Tg and melting point were measured using “DSC7” manufactured by PerkinElmer Co., Ltd. under a temperature increase rate of 10 ° C./min.
In addition, Tg and melting | fusing point of this PVA-type resin (A) can be controlled by content of the structural unit represented by the above-mentioned saponification degree and Formula (1).

In addition, the PVA resin (A) used in the present invention may be one kind or a mixture of two or more kinds. When a mixture is used, the polymerization degree, the saponification degree, It is preferable that the average value of the content of the 2-diol structural unit, the Tg of the mixture, and the melting point are within the above-described ranges.
In addition, it is possible to use a PVA resin that does not contain a 1,2-diol component in the side chain as the PVA resin, for example, unmodified PVA, but in that case, 1,2- The PVA resin (A) having a diol component is the main component, specifically, 50% by weight or more, particularly preferably 80% by weight or more of the total amount of the PVA resin.

  Unlike general unmodified PVA, the PVA-based resin (A) of the present invention is characterized by having a good thermal melting property without blending a plasticizer. A compound obtained by adding ethylene oxide to a polyhydric alcohol such as an aliphatic polyhydric alcohol (for example, ethylene glycol, hexanediol, glycerin, trimethylolpropane, diglycerin, etc.) or glycerin can be blended. , Various alkylene oxides (ethylene oxide, propylene oxide, mixed adducts of ethylene oxide and propylene oxide, etc.), sugars (for example, sorbitol, mannitol, pentaerythritol, xylol, arabinose, ribulose, etc.), phenols such as bisphenol A and bisphenol S Derivatives, - amide compounds such as methyl pyrrolidone, glucosides such as α- methyl -D- glucoside, water and the like. The blending amount is preferably 100 parts by weight or less, more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less with respect to 100 parts by weight of the PVA resin (A).

  The PVA resin (A) containing a 1,2-glycol component in the side chain obtained as described above or a composition thereof can be used for hot melt molding as it is, but workability at the time of molding, etc. In view of the above, it is preferable to use a material that has been once kneaded in a molten state and then cooled and solidified to form a pellet.

The intermediate layer in the multilayer stretched film of the present invention is mainly composed of the above-mentioned PVA resin (A), and usually contains 80% by weight or more, particularly 90% by weight or more of the PVA resin (A). It is.
In addition, various additives can be blended in the intermediate layer as necessary. Specifically, a thermoplastic resin (for example, polyethylene, polypropylene, polyester in the presence of a compatibilizer), a filler ( Organic fillers such as talc, clay, montmorillonite, calcium carbonate, glass beads, glass fiber, silica, mica, alumina, hydrotalcite, titanium oxide, zirconium oxide, boron nitride, aluminum nitride, and organic such as melamine-formalin resin Fillers), ultraviolet absorbers, antioxidants, processing stabilizers, and the like.

[Thermoplastic resin layer]
Next, the thermoplastic resin layers laminated on both sides of the intermediate layer in the multilayer stretched film of the present invention will be described.
As the thermoplastic resin used in such a thermoplastic resin layer, known resins can be used, and specifically, polyolefin resins, aromatic and aliphatic polyester resins, polyamide resins, polystyrene resins, polychlorinated resins. Examples include vinyl resins, polyvinylidene chloride, acrylic resins, vinyl ester resins, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene, aromatic and aliphatic polyketones, and aliphatic polyalcohols. Examples thereof include a polyolefin resin, a polyester resin, and a polyamide resin.

As the thermoplastic resin used for the thermoplastic resin layer in the multilayer stretched film of the present invention, it is preferable to use one having Tg and melting point within a specific range.
For example, the Tg of the thermoplastic resin is usually preferably 60 ° C. or lower. If the Tg of the thermoplastic resin is too high, the stretching temperature tends to increase, such being undesirable.
Moreover, melting | fusing point is 80-300 degreeC normally, Especially 90-280 degreeC, especially 100-270 degreeC thing is used preferably. If the melting point is too high, the processing temperature tends to be too high, and conversely if it is too low, it tends to break during stretching.

Due to recent environmental protection requirements, the application of biodegradable resins to plastic materials is accelerating, and there is a strong demand for multilayer films in which all the layers constituting them are biodegradable. Yes.
In the multilayer stretched film of the present invention, the PVA-based resin (A) used for the intermediate layer is biodegradable like a general unmodified PVA-based resin, and the thermoplastic resin layers disposed on both sides thereof are also biodegradable. Desirable to be degradable.
As such a biodegradable resin, an aliphatic polyester-based resin is generally used. A dibasic acid having 2 to 6 carbon atoms such as succinic acid, glutaric acid, and adipic acid, ethylene glycol, propylene glycol, 1, 4 A polycondensation product of diols having 2 to 6 carbon atoms such as butanediol, or a polycondensation product of 2 to 6 hydroxycarboxylic acids such as glycolic acid, lactic acid, 4-hydroxybutyric acid, etc. It is preferably used from the point of balance of various characteristics.
Among them, polylactic acid is suitable as a packaging material since it is excellent in heat resistance, strength, and transparency.

Hereinafter, the case where polylactic acid is used as the thermoplastic resin layer in the multilayer stretched film of the present invention will be described in detail.
Polylactic acid is an aliphatic polyester resin having a lactic acid structural unit as a main component, and L-lactic acid, D-lactic acid, or L-lactide, D-lactide, and DL-lactide, which are cyclic dimers thereof, as raw materials. Polymer.
The polylactic acid used in the present invention is preferably a homopolymer of these lactic acids, but contains a copolymer component other than lactic acids if the amount does not hinder the properties, for example, 10 mol% or less. It may be a thing.
Examples of the copolymer component include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, aliphatic hydroxycarboxylic acids such as 6-hydroxycaproic acid, and lactones such as caprolactone. Aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol and 1,4-butanediol; aliphatic dibasic acids such as succinic acid, oxalic acid, malonic acid, glutaric acid and adipic acid Can be mentioned.

  The content ratio (L / D) of the L-lactic acid component to the D-lactic acid component in the polylactic acid is usually 95/5 or more, particularly 99/1 or more, especially 99.8 / 0.2. Is preferably used. The larger the value, the higher the melting point and the higher the heat resistance. On the contrary, the smaller the value, the lower the melting point and the heat resistance tends to be insufficient. Specifically, in the case of a homopolymer of polylactic acid, the melting point of L / D of 95/5 is 152 ° C., and the melting point of 99/1 is 171 ° C. and 99.8 / 0.2. Some are above 175 ° C.

  The weight average molecular weight of the polylactic acid used in the present invention is usually from 20,000 to 1,000,000, particularly from 30,000 to 300,000, particularly from 40,000 to 200,000. If the weight average molecular weight is too large, the melt viscosity at the time of hot melt molding tends to be too high, and good film formation tends to be difficult. Conversely, if it is too small, the mechanical strength of the obtained laminate is insufficient. Tend to be.

  Examples of commercially available products of such polylactic acid-based resins include “Ingeo” manufactured by NatureWorks, “Lacea” manufactured by Mitsui Chemicals, “REVODE” manufactured by Zhejiang Kaisei Biological Materials Co., Ltd., and “Toyobo” manufactured by Toyobo Co., Ltd. Can be mentioned.

  When polylactic acid is used for the thermoplastic resin layer of the present invention, a biodegradable resin other than polylactic acid is blended within a range of, for example, 20% by weight or less, particularly 10% by weight or less unless the effects of the present invention are significantly impaired. Is possible. Examples of such biodegradable resins include aliphatic polyester resins, modified starch resins, and the like. Among them, polymers of the above-mentioned aliphatic hydroxycarboxylic acids, ring-opening polymers of lactones, aliphatic diols and fatty acids. A polymer of an aromatic dibasic acid or a copolymer thereof is preferably used.

  Further, the thermoplastic resin layer of the present invention can be blended with various additives as necessary, for example, heat stabilizers, antioxidants, ultraviolet absorbers, crystal nucleating agents, antistatic agents, Flame retardants, plasticizers, lubricants, fillers, lubricants, crystal nucleating agents, plasticizers and the like may be blended.

[Adhesive layer]
In the multilayer stretched film of the present invention, the intermediate layer, the thermoplastic resin layer, and other layers may be directly laminated, but it is also a preferred embodiment that an adhesive layer is interposed in order to improve interlayer adhesion. .
As an adhesive used for such an adhesive layer, a preferable one may be selected as appropriate depending on the adherend, but a resin having a carboxyl group is preferable in terms of adhesiveness to a layer containing a PVA resin, for example, Polyolefin resins and aliphatic polyester resins having a carboxyl group at the side chain or terminal are preferably used.

In addition, as described above, the adhesive layer used for the multilayer stretched film is also preferably biodegradable, and examples of the adhesive resin that satisfies the requirement include aliphatic polyester resins in which carboxyl groups are introduced into the side chains. be able to.
As the aliphatic polyester-based resin having a carboxyl group in the side chain, known ones can be used, but as a preferred example, α, β-unsaturated carboxylic acid or its anhydride is graft-polymerized to the aliphatic polyester-based resin. Can be mentioned.

The aliphatic polyester resin used in such graft polymerization is required to have an alkylene chain having a specific chain length in order to graft polymerize with an α, β-unsaturated carboxylic acid or anhydride thereof. Those having 2 to 6 carbon atoms, particularly 2 to 4 carbon atoms are preferably used.
The aliphatic polyester-based resin preferably has all of the structural units satisfying the above conditions, but may contain other structural units within a range that does not impair the resin characteristics, for example, less than 20 mol%. .

  The weight average molecular weight of the aliphatic polyester-based resin is usually 5000 to 50000, preferably 5500 to 40000, and particularly preferably 6000 to 30000. If the weight average molecular weight is too large, melt viscosity tends to be high in the case of hot melt molding, and melt molding tends to be difficult. Conversely, if it is too small, sufficient adhesive strength tends not to be obtained.

  Examples of commercially available products of such aliphatic polyester resins include “Ecoflex” manufactured by BASF, which mainly contains a condensation product of adipic acid / terephthalic acid and 1,4-butanediol, and succinic acid / 1,4- Examples thereof include “GS-PLA” manufactured by Mitsubishi Chemical Co., Ltd., whose main component is a condensation polymer of butanediol / lactic acid.

Next, α, β-unsaturated carboxylic acid or an anhydride thereof used for introducing a carboxyl group by graft polymerization to the aliphatic polyester-based resin, specifically, α such as acrylic acid, methacrylic acid, β-unsaturated monocarboxylic acids; α, β- and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citrus acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, etc., preferably α, β -Unsaturated dicarboxylic acids are used.
These α, β-unsaturated carboxylic acid compounds are not limited to the use of one kind alone, and two or more kinds may be used in combination.

  The method for graft polymerization of an α, β-unsaturated carboxylic acid to an aliphatic polyester resin is not particularly limited, and a known method can be used, and only a thermal reaction is possible, but in order to increase the reactivity It is preferable to use a radical initiator. Examples of the reaction method include a solution reaction, a reaction as a suspension, a reaction in a molten state without using a solvent, and the like. Among them, the reaction is preferably performed in a molten state.

As a melting method, an aliphatic polyester-based resin, an α, β-unsaturated carboxylic acid compound, and a radical initiator are mixed in advance and then melted and kneaded in a kneader and reacted. A method of blending an α, β-unsaturated carboxylic acid compound and a radical initiator with the biodegradable polyester resin in the above can be used.
As a mixer used when mixing raw materials in advance, a Henschel mixer, a ribbon blender, or the like is used, and as a kneader used for melt kneading, a single screw or twin screw extruder, a roll, a Banbury mixer, a kneader, A Brabender mixer or the like can be used.
What is necessary is just to set the temperature at the time of melt-kneading suitably in the temperature range which is more than melting | fusing point of aliphatic polyester-type resin, and is not thermally deteriorated. It is preferably melt-mixed at 100 to 250 ° C, more preferably 160 to 220 ° C.

  The amount of α, β-unsaturated carboxylic acid to be used is usually 0.0001 to 5 parts by weight, particularly 0.001 to 1 part by weight, especially 0.02 to 100 parts by weight of the aliphatic polyester resin. A range of ˜0.5 parts by weight is preferably used. When the blending amount is too small, a sufficient amount of carboxyl groups is not introduced into the aliphatic polyester resin, and the interlaminar adhesion, particularly the adhesive force with the intermediate layer containing the PVA resin tends to be insufficient. Moreover, when there are too many compounding quantities, the (alpha) and (beta) -unsaturated carboxylic acids which were not graft-polymerized may remain in resin, and there exists a tendency for the appearance defect resulting from it to arise.

It does not specifically limit as a radical initiator, Although a well-known thing can be used, For example, t-butyl hydroperoxide, cumene hydroperoxide, 2,5-dimethyl hexane-2,5-dihydroperoxide 2,5-dimethyl-2,5-bis (t-butyloxy) hexane, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxybenzoate, benzoyl peroxide, m-toluoyl peroxide, Organic and inorganic peroxides such as dicumyl peroxide, 1,3-bis (t-butylperoxyisopropyl) benzene, dibutyl peroxide, methyl ethyl ketone peroxide, potassium peroxide, hydrogen peroxide; 2,2′- Azobisisobutyronitrile, 2,2'-azobis (isobutyl Bromide) dihalide, 2,2'-azobis [2-methyl-N-(2-hydroxyethyl) propionamide], azo compounds such as azodi -t- butane; and carbon radical generators such as dicumyl like.
These may be used alone or in combination of two or more.

The amount of the radical initiator is usually 0.00001 to 0.5 parts by weight, particularly 0.0001 to 0.1 parts by weight, especially 0.002 to 100 parts by weight of the aliphatic polyester resin. A range of 0.05 parts by weight is preferably used.
If the amount of the radical initiator is too small, graft polymerization may not occur sufficiently, and the effects of the present invention may not be obtained. If it is too large, the molecular weight may be lowered by decomposition of the aliphatic polyester resin. Occurrence tends to be insufficient adhesive strength due to insufficient cohesive strength.

The amount of carboxyl groups introduced into the aliphatic polyester resin by the α, β-unsaturated carboxylic acid is usually 0.0001 to 6 mol%, particularly 0.001 to 1 mol%, particularly 0.025 to 25 mol%. A range of 0.6 mol% is preferably selected.
If the amount introduced is too small, the interlaminar adhesion, particularly the adhesive strength with the PVA resin layer, tends to be insufficient. Moreover, when there is too much introduction amount, there exists a tendency for stability at the time of hot-melt molding to fall.

[Multilayer film]
The multilayer film used for producing the multilayer stretched film of the present invention has a thermoplastic resin layer laminated on both sides of an intermediate layer mainly composed of a PVA resin (A) having a structural unit represented by the general formula (1). Including other layers, usually 3 to 15 layers, preferably 3 to 7 layers, particularly preferably 5 to 7 layers.
The configuration is not particularly limited, but when the intermediate layer is a, the thermoplastic resin layer is b, and the adhesive layer is c, b / a / b, b / c / a / c / b, b / c / b Any combination is possible as long as the thermoplastic resin layer b is disposed on both sides of the intermediate layer a, such as / c / a / c / b / c / b and b / c / a / a / c / b. is there. Each of these layers may be the same or different.

Such a multilayer film can be produced by a conventionally known molding method. Specifically, dry lamination, a melt molding method, or a molding method from a solution state can be used.
For example, as a dry laminating method, a film containing a PVA resin (A) and a thermoplastic resin film are produced in advance by a hot-melt extrusion molding method or the like, and an adhesive is directly or between each film. A method of interposing and laminating and heating and pressure bonding as necessary is used.
In addition, as a melt molding method, a method in which a thermoplastic resin film or sheet is used as a base material and a resin for forming other layers on the base material is sequentially or simultaneously melt extrusion laminated, or each layer is melt extrusion laminated at the same time. Etc. are used.
In addition, as a molding method from a solution state, a method of sequentially coating a thermoplastic resin film with a solution obtained by dissolving a resin for forming another layer in a good solvent and drying the solution.
Among them, the melt molding method is preferable, and the coextrusion method is particularly preferably used in that a laminate that can be manufactured in one step and has excellent interlayer adhesion can be obtained.

Specific examples of the coextrusion method include an inflation method, a T-die method, a multimany hold die method, a feed block method, and a multi-slot die method. As the shape of the die such as an outside die bonding method, a T die, a round die or the like can be used.
The melt molding temperature at the time of melt extrusion is usually 190 to 250 ° C, preferably 200 to 230 ° C.

[Stretching]
The multilayer film obtained in this way is made into a multilayer stretched film by stretching.
Such stretching is performed in a uniaxial direction, more preferably in a biaxial direction, and the stretching ratio is an area ratio, usually 2 to 100 times, particularly 4 to 50 times, especially 6 to 20 times. Used for. If the draw ratio is too small, sufficient gas barrier properties tend not to be obtained. Conversely, if the draw ratio is too large, it may break during stretching.

In the present invention, the stretching is performed at a temperature lower than the Tg of the PVA resin (A) used for the intermediate layer of the multilayer film, and in particular, the Tg of the PVA resin (A). It is preferable to carry out at a temperature lower by 1 to 30 ° C., particularly 5 to 20 ° C.
When the temperature at the time of such stretching is too low, it tends to break easily.

In the case of biaxial stretching, a sequential stretching method in which the multilayer film is first stretched in the longitudinal direction and then stretched in the transverse direction, a simultaneous stretching method in which the longitudinal direction and the transverse direction are simultaneously stretched, or the like is used.
Further, as a method of substantially stretching, a molding method using a die such as a deep drawing method, a vacuum forming method, a pressure forming method, a vacuum pressure forming method, etc., in which a multilayer film is drawn using a die is used. You can also.

[Multilayer stretched film]
The thickness of each layer constituting the multilayer stretched film obtained by the method of the present invention may be appropriately selected according to desired characteristics. For example, the thickness of the intermediate layer containing the PVA resin (A) Is usually 0.1 to 1000 μm, preferably 0.3 to 500 μm, particularly preferably 1 to 100 μm. If the intermediate layer is too thick, it tends to be hard and brittle, whereas if it is too thin, the gas barrier property tends to be low.
The thermoplastic resin layer is usually 0.4 to 14000 μm, preferably 1 to 6000 μm, particularly preferably 4 to 1400 μm, and the adhesive layer is usually 0.1 to 500 μm, preferably 0.15 to 250 μm, Especially preferably, it is 0.5-50 micrometers.
These thicknesses are all values in a single layer.
The total thickness of the multilayer stretched film is usually 1 to 30000 μm, preferably 3 to 13000 μm, particularly preferably 10 to 3000 μm.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
[Preparation of PVA resin (A)]
A reaction vessel equipped with a reflux condenser, a dropping funnel and a stirrer was charged with 68.0 parts of vinyl acetate, 23.8 parts of methanol, and 8.2 parts of 3,4-diacetoxy-1-butene, and azobisisobutyronitrile. Was added in an amount of 0.3 mol% (compared with vinyl acetate), and the temperature was raised under a nitrogen stream while stirring to initiate polymerization. When the polymerization rate of vinyl acetate reaches 90%, m-dinitrobenzene is added to complete the polymerization, and then unreacted vinyl acetate monomer is removed out of the system by blowing methanol vapor. A combined methanol solution was obtained.

Next, the methanol solution was further diluted with methanol, adjusted to a concentration of 45%, charged into a kneader, and a 2% methanol solution of sodium hydroxide was added to the vinyl acetate structural unit in the copolymer while maintaining the solution temperature at 35 ° C. And saponification was performed by adding 10.5 mmol with respect to 1 mol of the total amount of 3,4-diacetoxy-1-butene structural units. When saponification progresses and saponification precipitates and forms particles, it is filtered off, washed well with methanol and dried in a hot air drier to form a 1,2-diol structure on the target side chain. PVA-based resin (A) (in general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ are hydrogen atoms, and X is a single bond).

The saponification degree of the obtained PVA-based resin (A) was 99.2 mol% when analyzed by the alkali consumption required for hydrolysis of residual vinyl acetate and 3,4-diacetoxy-1-butene. . The average degree of polymerization was 450 when analyzed according to JIS K 6726. The content of the 1,2-diol structural unit represented by the general formula (1) is ¹ H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard substance: tetramethylsilane, 50 ° C.). It was 6 mol% when computed from the measured integral value.
Moreover, Tg of PVA-type resin (A) was 82 degreeC, and melting | fusing point was 190 degreeC.

[Production of adhesive resin]
100 parts of adipic acid / 1,4-butanediol polycondensation product (“Ecoflex C1200” manufactured by BASF), maleic anhydride 0.1 part, 2,5-dimethyl-2,5-bis (t -Butyloxy) After 0.01 parts of hexane (“Perhexa 25B” manufactured by NOF Corporation) is dry blended, this is melt kneaded with a twin screw extruder under the following conditions, extruded into a strand, cooled with water, and cut with a pelletizer. Thus, an adhesive resin having a cylindrical pellet made of adipic acid / 1,4-butanediol polycondensate obtained by graft polymerization of maleic anhydride was obtained.
Twin screw extruder Diameter (D): 15mm,
L / D: 60
Screw rotation speed: 200rpm
Mesh: 90/90 mesh
Processing temperature: 210 ° C

[Production of multilayer film]
Polylactic acid (“Ingeo 4032D” manufactured by Nature Works, Tg 65 ° C., melting point 160 ° C.), PVA resin (A), adhesive, and three kinds of five-layer multilayer film apparatus equipped with three extruders, A multilayer film body having a three-kind five-layer structure of lactic acid layer / adhesive layer / PVA resin layer / adhesive layer / polylactic acid layer was produced. The thickness of the obtained laminate was 200 μm, and the thickness of each layer was 60 μm / 20 μm / 40 μm / 20 μm / 60 μm.
The set temperatures of each extruder and roll are as follows.
Setting temperature Polylactic acid: C1 / C2 / C3 / C4 / H / J = 180/190/200/200/200/200 ° C.
PVA resin: C1 / C2 / C3 / C4 / H / J = 180/200/210/210/210/210 ° C.
Adhesive resin: C1 / C2 / H / J = 180/200/210/210 ° C.
Dice: FD1 / FD2 / D1 / D2 / D3 = 200/200/200/200/200 ° C.
Roll: 60 ° C

[Production of multilayer stretched film]
The obtained multilayer film was cut into 90 mm × 90 mm, and stretched at a stretching temperature of 70 ° C., a preheating time of 40 seconds, a stretching speed of 100 mm / second using a stretching device (“Laboratory Strecher KARO4” manufactured by Bruckner) in the longitudinal direction. When the film was stretched 5 times and then stretched 2.5 times in the transverse direction, it was stretched well and a multilayer stretched film was obtained.

<Gas barrier property evaluation>
The oxygen permeability of the obtained multilayer stretched film was measured under conditions of 23 ° C. and 80% RH using “OXTRAN 2/20” manufactured by MOCON. The results are shown in Table 1.

Example 2
In Example 1, it carried out similarly to Example 1 except having made extending | stretching temperature 80 degreeC, it extended | stretched favorably and the multilayer stretched film was obtained. This was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1
In Example 1, it carried out similarly to Example 1 except having made extending | stretching temperature 90 degreeC, it extended | stretched favorably and the multilayer stretched film was obtained. This was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2
The multilayer film before stretching in Example 1 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Reference example 1
In Example 1, a single-layer film of PVA-based resin (A) was prepared without using a material other than PVA-based resin (A) at the time of multilayer film preparation, and stretched in the same manner as in Example 1. The film broke.

※他の例と厚さを揃えるため、実測値を６．２５倍（２．５倍×２．５倍）したもの。 [Table 1]

* Measured values 6.25 times (2.5 times x 2.5 times) to match the thickness with other examples.

As is clear from the results of Examples 1 and 2, a PVA resin (A) having a structural unit represented by the general formula (1) was used for the intermediate layer, and polylactic acid was disposed as a thermoplastic resin on both sides thereof. The multilayer film could be stretched at a temperature lower than Tg (82 ° C.) of the PVA resin, and the obtained multilayer stretched film was excellent in oxygen gas barrier properties.
On the other hand, the multilayer stretched film of Comparative Example 1 that was stretched at a temperature higher than the Tg of the PVA resin did not provide sufficient oxygen gas barrier properties.
Moreover, in the case of the single layer film of the PVA resin (A), it could not be stretched at a temperature lower than its Tg.

  The multilayer stretched film obtained by the method of the present invention is excellent in gas barrier properties, and thus is useful as a packaging material for articles that are desired to avoid contact with oxygen.

Claims (3)

A multilayer film in which a thermoplastic resin layer is laminated on both sides of an intermediate layer mainly composed of a polyvinyl alcohol-based resin (A) containing a structural unit represented by the following general formula (1) is used as the polyvinyl alcohol-based resin ( A method for producing a multilayer stretched film that is stretched at a temperature lower than the glass transition point of A).

[Wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, 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 alkyl group having 1 to 3 carbon atoms. ] 2. The method for producing a multilayer stretched film according to claim 1, wherein the thermoplastic resin layer is a layer containing polylactic acid as a main component. The method for producing a multilayer stretched film according to claim 1 or 2, wherein the intermediate layer and the thermoplastic resin layer are laminated via an adhesive layer.