JP4758265B2 - Multilayer shrink film - Google Patents

Description

  The present invention relates to a multilayer shrink film having a layer containing an ethylene-vinyl alcohol copolymer (hereinafter abbreviated as EVOH). More specifically, the present invention relates to creep resistance, heat resistance, and the like not found in conventional EVOH multilayer films. The present invention relates to a multilayer shrink film having shrinkage, gas barrier properties, transparency, delamination resistance and low environmental load.

EVOH is excellent in transparency, gas barrier properties, fragrance retention, solvent resistance, oil resistance, etc., making use of such properties, food packaging materials, pharmaceutical packaging materials, industrial chemical packaging materials, agricultural chemical packaging materials, etc. These are used after being formed into a film or sheet, or a container such as a tube, cup, tray or bottle.
In particular, because many of the fatty foods such as meat and processed foods are irregular in shape and irregular in size, in such a food packaging field, in order to preserve the freshness of the contents and improve the appearance There are many uses for shrink wrapping, and a multilayer shrink film excellent in heat shrinkability and gas barrier properties is desired. For the purpose of improving such performance, two types having different ethylene contents and saponification degrees are provided. A method of blending and using EVOH (see, for example, Patent Documents 1 and 2) has been proposed.
Japanese Patent Laid-Open No. 05-200865 Japanese Unexamined Patent Publication No. 2000-211068

  However, the multilayer shrink film according to the methods described in Patent Documents 1 and 2 is excellent in heat shrinkability, gas barrier properties, etc., but it is necessary to blend EVOH having greatly different compositions in order to obtain desired properties. As a result, the compatibility is insufficient, and a portion where the transparency is lowered after heat shrinkage is partially generated, or the adhesive force between the adhesive resin layer and the EVOH layer for bonding the EVOH layer and the thermoplastic resin layer is reduced. It has also been found that there is a problem that delamination occurs in the multilayer film after shrinking. It was also found that the deformation under a long-term load is large and the creep resistance is insufficient. That is, an EVOH layer-containing multilayer shrink film excellent in stretchability, heat shrinkability, gas barrier properties, transparency after heat shrinkage, delamination resistance, and creep resistance is desired.

（ここで、Ｒ¹は水素または有機基を表し、Ｘはエーテル結合を除く任意の結合鎖を表し、ｎは０または１を表し、Ｒ²〜Ｒ⁴はそれぞれ水素または有機基を表す）
As a result of intensive studies in view of the above circumstances, contain the following structural units (1), ethylene ethylene content of Ru 20-60 mol% der - vinyl alcohol copolymer polymer (A), the structure An ethylene-vinyl alcohol copolymer (B) containing no unit (1) and having an ethylene content of 20 to 70 mol% , and an ethylene-vinyl alcohol copolymer (A) and ethylene-vinyl A multilayer shrink film characterized by having a layer in which the blend ratio of the alcohol-based copolymer (B) is (A) / (B) = 95/5 to 50/50 by weight ratio meets the above-mentioned purpose As a result, the present invention has been completed.

(Here, R ¹ represents hydrogen or an organic group, X represents an arbitrary bond chain excluding an ether bond , n represents 0 or 1, and R ^{2 to} R ⁴ each represents hydrogen or an organic group)

  The multilayer shrink film of the present invention is characterized in that EVOH (A) containing the structural unit (1) and EVOH (B) not containing the structural unit (1) are used in combination as EVOH in the EVOH-containing layer. Therefore, by adopting such a configuration, an effect peculiar to the present invention that cannot be obtained when each EVOH is used alone is obtained.

In the present invention, the blending ratio of EVOH (A) and EVOH (B) having a 1,2-glycol bond as a partial structure in the side chain is (A) / (B) = 95/5 to 50 / 50 , the content of the structural unit (1) in EVOH (A) is 0.1 to 30 mol%, and the area shrinkage ratio when immersed in hot water at 90 ° C. for 30 seconds is 20 to 90. % Is a preferred embodiment.

  Since the multilayer shrink film of the present invention has a layer of EVOH having a specific structural unit, it is excellent in creep resistance, heat shrinkability, gas barrier properties, transparency, and delamination resistance.

Hereinafter, the present invention will be specifically described.
In addition, description of the component requirement described below is an example (representative example) of the embodiment of this invention, and is not specified by these content.

First, EVOH (A) used in the present invention will be described.
EVOH (A) used in the present invention is EVOH containing the following structural unit (1), R ^{1 in the} structural unit (1) represents hydrogen or an organic group, and X represents any bond excluding an ether bond. Represents a chain, n represents 0 or 1, and R ^{2 to} R ⁴ each represents hydrogen or an organic group.

In the structural unit (1) in the EVOH (A), the main chain substituent R ¹ and the side chain substituents R ^{2 to} R ⁴ are all hydrogen atoms, and the bonding chain (X) It is desirable that _n of n is 0, that is, a single bond, and the hydrogen atom may be substituted with an organic group that does not significantly impair the resin properties.
Such EVOH (A) contains 0.1 to 30 mol% of structural unit (1) and 10 to 60 mol% of structural unit derived from ethylene, and 90 mol% or more of the remaining portion is a vinyl alcohol structural unit. Are preferably used.

In addition, when _n of the bond chain (X) _n of the structural unit (1) is 1, any bond chain other than an ether bond can be applied, and is not particularly limited, but other than alkylene, alkenylene, alkynylene, phenylene, hydrocarbons (these hydrocarbons fluorine, chlorine, may be substituted with halogen such as bromine and the like) of the naphthylene other, -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 (OR) - -OAl (OR) O-, etc. (R is each independently an optional substituent, preferably a hydrogen atom or an alkyl group, and m is a natural number). Of these, alkylene having 6 or less carbon atoms is preferably used.
In addition, it is not preferable that the bond chain X is an ether bond because the ether bond portion is easily thermally decomposed at the time of film production by melt molding, at the time of stretching or at the time of heat setting, and the thermal stability is insufficient.

In addition, when R ¹ and R ^{2 to} R ^{4 of} the structural unit (1) are organic groups, the organic group is not particularly limited, but for example, a methyl group, ethyl group, n-propyl group, isopropyl group, n- C1-C4 alkyl groups, such as a butyl group, an isobutyl group, a tert-butyl group, are preferable, and it has substituents, such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, and a sulfonic acid group, as needed. It may be.

The production method of EVOH (A) used in the present invention is not particularly limited, but the EVOH containing the structural unit (1) in which the bond chain which is the most preferable structure is a single bond ( _n in (X) n is 0) is used. Taking (A) as an example, 3,4-diol-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-ol-1-butene, 4-acyloxy-3-ol- as comonomers 1-butene, 3,4-diacyloxy-2-methyl-1-butene, 2,2-dialkyl-4-vinyl-1,3-dioxolane, copolymerized with vinyl ester monomers and ethylene Examples thereof include a method of saponifying the obtained copolymer, or a method of saponifying and decarboxylating the obtained copolymer using vinyl ethylene carbonate as a comonomer.

  Among these, 3,4-diacyloxy-1-butene is preferable because it is excellent in copolymerization reactivity with a vinyl ester monomer and ethylene, and further, a by-product formed by a saponification reaction is common with vinyl acetate. It is preferable to use diacetoxy-1-butene. Further, the monomer may contain 3,4-diacetoxy-1-butane, 1,4-diacetoxy-1-butene, 1,4-diacetoxy-1-butane or the like as a small amount of impurities.

  In addition, examples in which the bonding chain X is alkylene include 4,5-diol-1-pentene, 4,5-diacyloxy-1-pentene, 4,5-diol-3-methyl-1-pentene, 4,5- Copolymers obtained by copolymerizing diol-3-methyl-1-pentene, 5,6-diol-1-hexene, 5,6-diacyloxy-1-hexene, etc. with vinyl ester monomers and ethylene The method of making it.

  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, Although vinyl versatate etc. are mentioned, vinyl acetate is preferably used especially from an economical viewpoint.

  Hereinafter, the copolymerization method using 3,4-diacetoxy-1-butene as a comonomer will be described in detail, but the present invention is not limited thereto.

  There are no particular limitations on the copolymerization of 3,4-diacyloxy-1-butene with vinyl ester monomers and ethylene, and known methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization In general, solution polymerization is 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 employed.
The copolymerization ratio of 3,4-diasiloxy-1-butene and the like is not particularly limited, but the copolymerization ratio may be determined in accordance with the amount of the structural unit (1) introduced.
Further, the ethylene content in the copolymer can be controlled by the ethylene pressure during the polymerization, and it cannot be generally determined by the intended ethylene content, but is usually in the range of 25 to 80 kg / cm ² . Selected from.

Examples of the solvent used in such copolymerization include usually lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone and methyl ethyl ketone, and industrially, 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 7 (weight ratio).

  In the copolymerization, a polymerization catalyst is used. Examples of the polymerization catalyst include known radical polymerization catalysts such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauryl peroxide, and t-butylperoxyneodeca Noate, t-butylperoxypivalate, α, α′bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3, -tetramethylbutylperoxyneodeca Peroxyesters such as noate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-hexylperoxypivalate, di-n-propylperoxydi Carbonate, di-iso-propyl peroxydicarbonate, di-sec-butyl Ruperoxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, dimethoxybutylperoxydicarbonate, di ( Low temperature such as peroxydicarbonates such as 3-methyl-3-methoxybutylperoxy) dicarbonate, diacyl peroxides such as 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide, lauroyl peroxide Examples include active radical polymerization catalysts.

The amount of the polymerization catalyst used varies depending on the type of catalyst and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate. For example, when azobisisobutyronitrile or acetyl peroxide is used, 10 to 2000 ppm is preferable with respect to the vinyl ester monomer, and 50 to 1000 ppm is particularly preferable.
Moreover, although the reaction temperature of a copolymerization reaction changes with the solvent and pressure to be used, it is preferable to select normally from the range of about 40 degreeC-a boiling point.

  In the present invention, an ethylenically unsaturated monomer that can be copolymerized may be copolymerized as long as the effects of the present invention are not impaired during the above copolymerization. Examples of such monomers include propylene, 1 -Olefins such as butene and isobutene, unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid and (anhydrous) itaconic acid, or salts thereof, or those having 1 to 18 carbon atoms Mono- or dialkyl esters, acrylamide, N-alkyl acrylamide having 1 to 18 carbon atoms, N, N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salt, acrylamidopropyldimethylamine or its acid salt or its quaternary salt, etc. Acrylamides, methacrylamide, N-alkyl methacryl having 1 to 18 carbon atoms Methacrylamides such as amide, N, N-dimethylmethacrylamide, 2-methacrylamide propanesulfonic acid or salts thereof, methacrylamide propyldimethylamine or acid salts thereof or quaternary salts thereof, N-vinylpyrrolidone, N-vinylformamide N-vinylamides such as N-vinylacetamide, vinyl cyanides such as acrylonitrile and methacrylonitrile, vinyl ethers such as alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers, alkoxyalkyl vinyl ethers, vinyl chloride, vinylidene chloride , Vinyl halides such as vinyl fluoride, vinylidene fluoride, vinyl bromide, vinyl silanes, allyl acetate, allyl chloride, allyl alcohol, dimethylallyl alcohol, trimethyl- (3- Acrylamide-3-dimethylpropyl) - ammonium chloride, acrylamido-2-methylpropanesulfonic acid, glycerol monoallyl ether, ethylene carbonate, and the like.

  Furthermore, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidopropyltrimethylammonium chloride, 2-acryloxyethyltrimethylammonium chloride, 2-methacryloxyethyltrimethylammonium chloride, 2-hydroxy-3- Cationic group-containing monomers such as methacryloyloxypropyltrimethylammonium chloride, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, 3-butenetrimethylammonium chloride, dimethyldiallylammonium chloride, diethyldiallylammonium chloride, acetoacetyl group-containing monomers And so on.

  Further, the above-mentioned vinylsilanes include vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinyl Methoxydibutoxysilane, vinyldimethoxybutoxysilane, vinyltributoxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyhexyloxysilane, vinyltrihexyloxysilane, vinylmethoxydioctyloxysilane, vinyldimethoxyoctyloxysilane, vinyltrioctyl Loxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleoxy Run, and vinyl dimethoxy I acetoxyphenyl silane.

  In addition, it is preferable in terms of improving the color tone of EVOH (A) obtained by allowing a hydroxylactone compound or hydroxycarboxylic acid to coexist with the above catalyst during polymerization, and the hydroxylactone compound may be a molecule. It is not particularly limited as long as it is a compound having a lactone ring and a hydroxyl group, and examples thereof include L-ascorbic acid, erythorbic acid, glucono delta lactone, etc., preferably L-ascorbic acid and erythorbic acid are used. Examples of the hydroxycarboxylic acid include glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid, and the like, and citric acid is preferably used.

  The amount of the hydroxylactone compound or hydroxycarboxylic acid used is 0.0001 to 0.1 parts by weight, more preferably 0.0005 to 0.05 parts by weight, particularly 0.001 to 100 parts by weight of vinyl acetate. 0.03 part by weight is preferable, and if the amount used is too small, these addition effects may not be obtained. On the other hand, if the amount used is too large, polymerization of vinyl acetate is inhibited, which is not preferable.

  There is no particular limitation on charging such a compound into the polymerization system, but it is usually charged into a polymerization reaction system by diluting with a solvent such as an aliphatic ester containing lower aliphatic alcohol or vinyl acetate, water, or a mixed solvent thereof. .

  The obtained copolymer is then saponified. In such saponification, an alkali catalyst or an acid catalyst is used in a state where the copolymer obtained above is dissolved in alcohol or hydrous alcohol. Done. Examples of the alcohol include methanol, ethanol, propanol, tert-butanol and the like, 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.
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, a vinyl ester monomer and 3,4-diacyloxy-1- 0.001-0.1 equivalent with respect to the total amount of monomers, such as butene, Preferably 0.005-0.05 equivalent is suitable.

With regard to such a saponification method, batch saponification, continuous saponification on a belt, and continuous saponification of a tower type are possible depending on the target saponification degree, etc., and the amount of alkali catalyst during saponification can be reduced and saponification reaction is high. For reasons such as efficiency and ease of progress, tower saponification under constant pressure is preferably used. The pressure during saponification cannot be generally specified depending on the target ethylene content, but is selected from the range of ^{2 to} 7 kg / cm ² , and the temperature at this time is 80 to 150 ° C., preferably from 100 to 130 ° C. Selected.

Thus, ethylene content and degree of saponification of the resulting EVOH (A) is not particularly limited, ethylene content 2 0-60 mol%, 25 to 48 mol% in particular, saponification degree 90 mol% In addition, 95 mol% or more, particularly 99 mol% or more is preferably used, and if the ethylene content is too low, gas barrier properties under high humidity conditions tend to deteriorate or the appearance tends to deteriorate. On the other hand, if the amount is too large, the gas barrier property tends to decrease, which is not preferable. On the other hand, when the degree of saponification is too low, gas barrier properties and moisture resistance tend to be lowered, which is not preferable.

Further, the content of the structural unit (1) introduced into EVOH (A) by copolymerization is not particularly limited, but is 0.1 to 30 mol%, more preferably 0.5 to 20 mol%, In particular, the content is preferably 1 to 10 mol%. If the content is too small, the effect of the present invention is not sufficiently exhibited.
Moreover, in adjusting this content, it is also possible to adjust by blending two or more types of EVOH (A) having different contents of the structural unit (1).
Regarding EVOH (A) obtained by such blending, the content of the structural unit (1) may be calculated by weight average, and the ethylene content may be determined by weight average. The content of ethylene and the content of structural unit (1) can be calculated from ¹ H-NMR measurement results.

  Further, the melt flow rate (MFR) (210 ° C., load 2160 g) of the EVOH (A) is 0.1 to 100 g / 10 minutes, further 1 to 50 g / 10 minutes, and particularly 2 to 35 g / 10 g. If the melt flow rate is too small, the inside of the extruder may be in a high torque state at the time of molding, which may make extrusion difficult. Conversely, if it is too large, the thickness accuracy of the resulting film or sheet will be reduced. Is not preferable.

Next, EVOH (B) used in the present invention will be described.
Any EVOH can be used as the EVOH (B) used in the present invention as long as it does not contain the structural unit (1). Usually, the ethylene structural unit, the vinyl alcohol structural unit, and the vinyl acetate structure are used. Conventionally known EVOH having only units is preferably used. In addition, the above-described copolymerizable ethylenically unsaturated monomer may be copolymerized as long as the effects of the present invention are not impaired.
The ethylene content of such EVOH (B) is 20 to 70 mol%, more preferably 23 to 58 mol%, particularly 25 to 55 mol%, and the degree of saponification of the vinyl acetate component is 90 mol% or more, further 95 mol. %, Particularly 99 mol% or more is preferably used. If the ethylene content is too low, melt molding is reduced. On the other hand, if the ethylene content is too high, sufficient gas barrier properties cannot be obtained. If the degree of conversion is too small, gas barrier properties, thermal stability, moisture resistance and the like are lowered, which is not preferable.
Further, the difference in ethylene content between EVOH (A) and EVOH (B) is preferably 20 mol% or less, more preferably 15 mol% or less, and particularly preferably 10 mol% or less, and the difference in saponification degree is 5 It is preferably at most 3 mol%, more preferably at most 1 mol%. If the difference in the ethylene content and the difference in the saponification degree are too large, the compatibility between EVOH (A) and EVOH (B) decreases, making it difficult to form a uniform resin composition, Since stretchability may be reduced, it is not preferable.

Further, the melt flow rate (MFR) (210 ° C., load 2160 g) of the EVOH (B) is 0.5 to 100 g / 10 minutes (further 1 to 50 g / 10 minutes, particularly 3 to 35 g / 10 minutes). If the melt flow rate is less than 0.5 g / 10 minutes, the inside of the extruder may be in a high torque state during molding, making extrusion difficult. Conversely, if the melt flow rate exceeds 100 g / 10 minutes, The thickness accuracy of the film or sheet to be produced may decrease, which is not preferable.
Further, the difference in MFR between EVOH (A) and EVOH (B) is preferably 20 or less, more preferably 10 or less, and particularly preferably 5 or less. If the difference is too large, both are mixed to obtain a uniform resin composition. Since it may become difficult to obtain a thing, it is not preferable.

Compounding ratio of the two EVOH in the multilayer shrink film of the present invention, the EVOH (A) containing a structural unit (1), the blending ratio of EVOH containing no structural unit (1) (B), by mass, (A) / (B) = 95/5 to 50/50 is preferable. Moreover, particularly good in the case of obtaining the stretchability and heat shrinkability are not preferable to be a (A) / (B) = 9 4 / 6~55 / 45.

  The method of mixing the two types of EVOH is not particularly limited. For example, (a) a method of mixing ethylene-vinyl acetate methanol paste before saponification and then saponification, and (b) each EVOH after saponification. (C) A method of extruding the solution into a coagulation bath in a strand shape, cutting and pelletizing the solution, and (c) a method of dry blending each EVOH pellet and then melt-kneading. ) To form a multilayer film as it is.

Furthermore, in the EVOH-containing layer in the multilayer shrink film of the present invention, an acid such as acetic acid and phosphoric acid, boric acid or its alkali metal, alkaline earth metal salt, and various organic compounds are included in the range not impairing the object of the present invention. It is preferable to add a metal salt of an acid or an inorganic acid from the viewpoint of improving the thermal stability during melt molding.
The method for adding the following additives is not particularly limited, and may be added at the time of production of EVOH (A) and EVOH (B), or may be added at the time of mixing EVOH (A) and EVOH (B). Also good.

  The amount of acetic acid added is preferably 0.001 to 1 part by weight (more preferably 0.005 to 0.2 part by weight, particularly 0.010 to 0.1 part by weight) with respect to 100 parts by weight of EVOH. If the amount added is less than 0.001 part by weight, the content effect may not be sufficiently obtained. Conversely, if it exceeds 1 part by weight, it is difficult to obtain a uniform film.

  Moreover, as an addition amount of a boron compound, 0.001-1 weight part in conversion of boron with respect to 100 weight part of EVOH, Furthermore, 0.002-0.2 weight part, Especially 0.005-0.1 weight part If the amount added is too small, the content effect may not be sufficiently obtained. On the other hand, if the amount is too large, it is difficult to obtain a uniform film.

  Examples of metal salts of organic acids or inorganic acids include sodium, potassium, calcium, magnesium, and other organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid, sulfuric acid, and sulfurous acid. Metal salts of inorganic acids such as carbonic acid and phosphoric acid are preferable, and acetate, phosphate and hydrogen phosphate are preferred. Moreover, as addition amount of this metal salt, 0.0005 to 0.1 weight part in conversion of a metal with respect to 100 weight part of EVOH, Furthermore, 0.001 to 0.05 weight part, Especially 0.002 to 0.00. The content is preferably 03 parts by weight. If the amount added is too small, the content effect may not be sufficiently obtained. On the other hand, if the amount added is too large, it is difficult to obtain a uniform film. In addition, when adding 2 or more types of alkali metal and / or alkaline-earth metal salt to EVOH, it is preferable that the total is in the range of said addition amount.

  There is no particular limitation on the method of adding acids or metal salts thereof to a mixture of EVOH. A) A porous precipitate of EVOH having a water content of 20 to 80% by weight is brought into contact with an aqueous solution of acids or metal salts thereof. , A method of drying after containing an acid or its metal salt, and b) adding an acid or its metal salt to a uniform EVOH solution (water / alcohol solution, etc.) and then extruding it into a coagulation liquid, A method in which the obtained strand is cut into pellets and further dried, c) a method in which EVOH and acids and their metal salts are mixed together and then melt-kneaded with an extruder, etc., d) at the time of production of EVOH In the saponification step, the alkali (sodium hydroxide, potassium hydroxide, etc.) used in the saponification step is neutralized with acids such as acetic acid, and the remaining acids such as acetic acid and by-product sodium acetate and potassium acetate And a method such that the amount of the alkali metal salt or adjusted by water washing treatment. In order to obtain the effects of the present invention more remarkably, the methods a), b) and d), which are excellent in dispersibility of acids and metal salts thereof, are preferred.

  It should be noted that a mixture of EVOH, or a composition thereof, may contain some monomer residue or saponified monomer, specifically 3,4-diacetoxy-1-butene, 3 to the extent that the object of the present invention is not impaired. , 4-diol-1-butene, 3,4-diacetoxy-1-butene, 3-acetoxy-4-ol-1-butene, 4-acetoxy-3-ol-1-butene, and the like. .

  The resin composition containing EVOH thus obtained can be processed into a film as it is, but in the present invention, various additives are added to the resin composition as long as the object of the present invention is not impaired. You can also. Such additives include saturated aliphatic amides (such as stearic acid amide), unsaturated fatty acid amides (such as oleic acid amide), bis fatty acid amides (such as ethylene bisstearic acid amide), fatty acid metal salts (such as calcium stearate) , Magnesium stearate, etc.), lubricants such as low molecular weight polyolefins (for example, low molecular weight polyethylene having a molecular weight of about 500 to 10,000, or low molecular weight polypropylene), inorganic salts (for example, hydrotalcite), plasticizers (for example, ethylene glycol) , Aliphatic polyhydric alcohols such as glycerin and hexanediol), heat stabilizers, light stabilizers, antioxidants, UV absorbers, colorants, antistatic agents, surfactants, antibacterial agents, antiblocking agents, slips Agent, filler (for example, inorganic filler), oxygen absorbent, other resin Such as polyolefin, polyamide, etc.) and the like.

Next, the manufacturing method of the multilayer shrink film of this invention is demonstrated.
The EVOH-containing layer in the multilayer shrink film of the present invention contains two different types of EVOH, EVOH (A) and EVOH (B) as described above. As a method of mixing the two types of EVOH, Although not limited, it is usually carried out by a method in which each EVOH pellet is dry blended and then formed into a multilayer film.
Although the EVOH composition used for the multilayer shrink film of the present invention is obtained, in producing the multilayer shrink film, it is laminated with another substrate. As a lamination method when laminating with another base material, for example, a method of melt extrusion laminating another base material on the film, sheet or the like of the above EVOH composition, and conversely melt extruding the resin to another base material A method of co-extrusion of the resin and another substrate, a known adhesion of the resin (layer) and another substrate (layer) to an organic titanium compound, an isocyanate compound, a polyester compound, a polyurethane compound, etc. Examples include a method of dry laminating using an agent, a method of removing a solvent after coating a solution containing the resin composition on another substrate, and the laminate has good stretchability and shrinkability. In particular, a method of co-extrusion is preferable.

  As the co-extrusion method, specifically, a known method such as a multi-many hold die method, a feed block method, a multi-slot die method, or a die external bonding method can be employed. As the shape of the die, a T die, a round die or the like can be used, and the melt molding temperature at the time of melt extrusion is preferably 150 to 300 ° C.

  As such other base materials, thermoplastic resins are useful. Specifically, linear low density polyethylene, low density polyethylene, ultra-low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer Polymer, ionomer, ethylene-propylene (block and random) copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) ) Polyolefin resins and polyesters in a broad sense, such as copolymers, polybutenes, polypentenes and other olefins or copolymers, or those olefins alone or copolymers grafted with unsaturated carboxylic acids or esters thereof Resin, polyamide resin (including copolyamide) ), Polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene, aromatic or aliphatic polyketone, and further reducing these Polyalcohols, and other EVOH, etc., but from the point of practicality such as physical properties (particularly strength) of the laminate, polypropylene, ethylene-propylene (block or random) copolymer, polyamide, polyethylene, An ethylene-vinyl acetate copolymer, polystyrene, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN) are preferably used.

  Further, when the shrink film of the present invention is extrusion coated with another substrate, or when a film, sheet, or the like of another substrate is laminated using an adhesive, the substrate is not limited to the thermoplastic resin described above. Any substrate (paper, metal foil, uniaxial or biaxially stretched plastic film or sheet and its inorganic deposit, woven fabric, non-woven fabric, metallic cotton, wood, etc.) can be used.

  The layer structure of the laminate is such that when the EVOH-containing layer is a (a1, a2,...) And another substrate, for example, the thermoplastic resin-containing layer is b (b1, b2,...) If it is a sheet, not only a / b two-layer structure, but also b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2 , B2 / b1 / a / b1 / a / b1 / b2, etc. are possible. Furthermore, when R is a regrind layer comprising at least a mixture of the EVOH composition and a thermoplastic resin, b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, etc. Is possible. In the above layer structure, an adhesive resin layer can be provided between the respective layers as necessary, and various adhesive resins can be used, and the stretchability is excellent. It is preferable in that a laminate can be obtained. It varies depending on the type of resin b, but cannot be generally stated. However, an unsaturated carboxylic acid or its anhydride is added to an olefin polymer (the above-mentioned polyolefin resin in the broad sense) or a graft reaction. Examples thereof include modified olefin polymers containing carboxyl groups obtained by chemically bonding such as maleic anhydride graft modified polyethylene, maleic anhydride graft modified polypropylene, maleic anhydride graft modified. Ethylene-propylene (block and random) copolymer, maleic anhydride graft modified ethylene-ethylene Le acrylate copolymer, maleic anhydride graft-modified ethylene anhydride - one or a mixture of two or more species selected from vinyl acetate copolymers and the like as preferred. At this time, the amount of the unsaturated carboxylic acid or anhydride thereof contained in the thermoplastic resin is preferably 0.001 to 3% by weight, more preferably 0.01 to 1% by weight, particularly preferably 0.03. ~ 0.5 wt%. If the amount of modification in the modified product is small, the adhesiveness may be insufficient. On the other hand, if the amount is too large, a crosslinking reaction may occur and the moldability may be deteriorated. Further, these adhesive resins can be blended with the EVOH composition of the present invention, other EVOH, rubber / elastomer components such as polyisobutylene, ethylene-propylene rubber, and the resin of the b layer. In particular, blending a polyolefin resin different from the base polyolefin resin of the adhesive resin is useful because the adhesiveness may be improved.

The thickness of each layer of the laminate cannot be generally stated depending on the layer configuration, the type of thermoplastic resin, the type of adhesive resin, the use and packaging form, the required physical properties, etc. The adhesive resin layer is selected from a range of about 5000 μm, further 3 to 1000 μm, and 0.1 to 400 μm, and further about 0.2 to 150 μm.
The thickness of the EVOH-containing layer varies depending on the required gas barrier properties, but is usually 0.5 to 30 μm, more preferably 0.8 to 10 μm, and particularly preferably 1 to 5 μm, and the thickness is too thin. In some cases, sufficient gas barrier properties may not be obtained. On the other hand, if the thickness is too thick, the flexibility of the film tends to be insufficient.

  The base resin layer may contain an antioxidant, an antistatic agent, a lubricant, a core material, an antiblocking agent, an ultraviolet absorber, a wax and the like as conventionally known.

  In order to impart shrink properties to the multilayer film (laminated body) as described above, usually (heating) stretching treatment is performed. Such (heating) stretching treatment is an operation for uniformly forming a film or a sheet-like laminate that has been uniformly heated into a tube or a film by chucking, plugging, vacuum force, pneumatic force, blowing, or the like. Meaning, such stretching may be either uniaxial stretching or biaxial stretching, and it is better to perform stretching at as high a magnification as possible (about 1.5 to 9 times each in length and / or width). Thus, a multi-layer stretched film excellent in gas barrier properties that does not cause pinholes, cracks, stretch unevenness, uneven thickness and the like during stretching can be obtained.

  As the stretching method, a roll stretching method, a tenter stretching method, a tubular stretching method, a stretching blow method, a vacuum / pressure forming method, or the like having a high stretching ratio can be employed. In the case of biaxial stretching, both a simultaneous biaxial stretching method and a sequential biaxial stretching method can be employed. The stretching temperature is selected from the range of about 40 to 140 ° C, preferably about 60 to 100 ° C. If the stretching temperature is less than 40 ° C, the stretchability is poor, and if it exceeds 140 ° C, the heat shrinkability is insufficient. Prior to stretching, the thermoplastic laminate, especially the polyolefin resin layer, can be cross-linked by irradiating the laminate of the original fabric with radiation, electron beam, ultraviolet rays, etc. This is preferable in terms of improving the mechanical strength.

  The thermal shrinkage rate of the multilayer shrink film of the present invention obtained by such a method is determined by the above-mentioned stretching ratio, but the area shrinkage rate when immersed in hot water at 90 ° C. for 30 seconds is 20 to 90%, Furthermore, what is 60 to 90% is preferable.

  When the multilayer shrink film thus obtained is used for shrink packaging of raw meat, processed meat, cheese, etc., the raw meat, processed meat, cheese, etc. are stored in a bag made of the film, and then the bag is subjected to reduced pressure. After removing the air inside and sealing the opening of the bag, heat treatment is performed at 50 to 130 ° C., preferably 70 to 120 ° C. for about 2 to 300 seconds, and the film is thermally shrunk into the contents. Use close-packaging. By this operation procedure, a package having excellent appearance can be obtained. The inside of the packaging bag can be replaced with carbon dioxide gas, nitrogen gas or the like for packaging. Furthermore, it can use suitably also for what is called stretch shrink packaging which heat-shrink-wraps the goods piled up on the tray.

  On the other hand, when used for skin pack packaging, an unstretched multilayer film (laminate) is put into a skin pack packaging machine, and the film is stretched at 60 to 200 ° C., and in some cases after thermoforming with a mold. Immediately, the substrate is placed on a substrate film, sheet, or tray on which the contents are placed under vacuum, and the surroundings are sealed. Then, the contents are returned to atmospheric pressure and contracted, and the contents and the surrounding films are brought into close contact with each other. By this operation procedure, a package having excellent appearance can be obtained. Even in the skin pack packaging application, it is possible to crosslink the thermoplastic resin layer, particularly the polyolefin resin layer, by irradiating the raw multilayer film with radiation, electron beam, ultraviolet ray, etc., thereby improving the stretchability of the raw fabric. It is preferable in that the mechanical strength of the product is improved.

  The multilayer shrink film of the present invention is very useful for shrink packaging or skin pack packaging of foods such as raw meat, processed meat and cheese as described above, but besides this, pharmaceuticals, industrial chemicals, agricultural chemicals, electronic components It is also useful as various gas barrier packaging materials such as machine parts.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the examples.
In the following, “%” and “parts” refer to the weight basis unless otherwise specified.

Example 1
EVOH (A) [ethylene content 38 mol%, saponification degree 99.5 mol%, structural unit (1) content 3 mol%, MFR 4.0 g / 10 min (210 ° C., 2160 g)] and EVOH composition (B1) [ethylene Content 44 mol%, saponification degree 99.6 mol%, MFR 3.6 g / 10 min (210 ° C., 2160 g), boric acid content (boron conversion) 0.015 parts by weight with respect to EVOH 100 parts by weight, phosphoric acid with respect to EVOH 100 parts by weight Multi-layer T-die of feed block 3 types and 5 layers of composition [MFR 4.0 g / 10 min] obtained by blending 0.005 parts by weight of calcium dihydrogen (in terms of phosphate radical) at a ratio of 50/50 Polyethylene (Novatech C6 / Novatech EVA = 70/30 wt%) layer / adhesive tree (Mitsubishi Chemical "Modic AP M533") layer / EVOH layer / adhesive resin layer (same as left) / polyethylene layer (same as left) layer structure (thickness 100/20/40/20/100 μm) The multi-layered film is successively biaxially stretched 3.5 times in length and 3.5 times in width at 80 ° C. with a biaxial stretching machine, and then the film is cooled and fixed with cold air at 20 ° C. A film was obtained. The stretchability when producing a multilayer shrink film, the heat shrinkability, gas barrier properties, transparency after heat shrinkage, and delamination resistance of the obtained multilayer film were evaluated as follows.

(appearance)
The obtained laminate was visually observed and the appearance was evaluated as follows.
○: Stretching unevenness and uneven thickness are not recognized, and the appearance is good.
Δ: Uneven stretching and uneven thickness are observed, but can be used.
X: It breaks at the time of extending | stretching and a stretched film cannot be obtained.

(Heat shrinkage)
The stretched multilayer film was cut into 10 cm × 10 cm and immersed in hot water at 90 ° C. for 30 seconds, and the area shrinkage (%) was calculated as follows.
Area shrinkage (%) = {(S−s) / S} × 100
S: Area of the film before shrinking s: Area of the film after shrinking

(Gas barrier properties)
The oxygen permeability of the stretched multilayer film was measured under conditions of 23 ° C. and 80% RH using “OXTRAN 2/21” manufactured by MOCON.

(transparency)
The appearance of the multilayer film after thermal contraction with hot water was visually observed and evaluated as follows.
○ ・ ・ ・ There was no abnormality in the appearance. △ ・ ・ ・ Opaque part was observed in part. × ・ ・ ・ Opaque part was recognized throughout.

(Delamination resistance)
The multilayer film after being thermally contracted with hot water was hand-held for 1 minute with a uniform force, and it was evaluated whether delamination occurred in the multilayer film by visual observation.
○: No delamination was observed in any of them.
Δ: Delamination was observed at the edge of the film, but it can be used.
X: Delamination was observed at the center of the film.

  Further, the EVOH composition (A) was supplied to a single-screw extruder equipped with a single-layer T-die and taken up at a cooling roll temperature of 30 ° C. to obtain a single-layer film having a thickness of 60 μm. This single layer film was cut into a width of 2.5 cm and a length of 6 cm, suspended with a clip in a hot air drier adjusted to 70 ° C., and further left under a load of 20 to 21 g for 30 seconds. At this time, in order to measure the elongation in the load direction of the film, creep resistance was evaluated by drawing a marked line at the center with a sense of 2 cm.

(Creep resistance)
The elongation between the marked lines of the obtained single layer film was evaluated.
○: The elongation between marked lines is less than 15%.
Δ: Elongation between marked lines is 15 to 25%.
X: The elongation between marked lines is 25% or more.

Example 2
A multilayer shrink film was similarly prepared and evaluated in the same manner as in Example 1 except that EVOH (A) and EVOH composition (B1) were blended at a ratio of 90/10.

Comparative Example 6
A multilayer shrink film was similarly prepared and evaluated in the same manner as in Example 1 except that EVOH (A) and EVOH (B1) were blended at a ratio of 30/70.

Comparative Example 1
A multilayer stretched film was prepared in the same manner as in Example 1 except that only the EVOH composition (B1) was used without using EVOH (A), and evaluation was performed in the same manner.

Comparative Example 2
In Comparative Example 1, instead of the EVOH composition (B1), the EVOH composition (B2) [ethylene content 38 mol%, saponification degree 99.5 mol%, MFR 3.5 g / 10 min (210 ° C., 2160 g), EVOH 100 weight Content of boric acid to boron parts (in terms of boron) 0.015 parts by weight, content of calcium dihydrogen phosphate to 100 parts by weight of EVOH 0.005 parts by weight (in terms of phosphate radicals)] A film was prepared and evaluated in the same manner.

Comparative Example 3
In Comparative Example 1, instead of the EVOH composition (B1), the EVOH composition (B3) [ethylene content 29 mol%, saponification degree 99.5 mol%, MFR 3.1 g / 10 min (210 ° C., 2160 g), EVOH 100 wt. Content of boric acid to boron parts (in terms of boron) 0.015 parts by weight, content of calcium dihydrogen phosphate to 100 parts by weight of EVOH 0.005 parts by weight (in terms of phosphate radicals)] A film was prepared and evaluated in the same manner.

  The evaluation results of Examples and Comparative Examples are summarized in Table 1.

[Table 1]

The multilayer shrink film of the present invention is composed of EVOH having a specific structural unit, and is excellent in creep resistance, heat shrinkability, gas barrier properties, transparency, delamination resistance, food, medical products, industrial chemicals, chemicals, agricultural chemicals. It is useful as a packaging material for electronic parts and machine parts.

Claims (4)

Contain the following structural unit (1), an ethylene content of Ru 20-60 mol% der ethylene - vinyl alcohol copolymer polymer (A), the ethylene content does not contain a structural unit (1) 20 The blending ratio of the ethylene-vinyl alcohol copolymer (B) which is ˜70 mol% and the ethylene-vinyl alcohol copolymer (A) and the ethylene-vinyl alcohol copolymer (B) is A multilayer shrink film comprising a layer having a weight ratio of (A) / (B) = 95/5 to 50/50 .

(Here, R ¹ represents hydrogen or an organic group, X represents an arbitrary bond chain excluding an ether bond , n represents 0 or 1, and R ^{2 to} R ⁴ each represents hydrogen or an organic group) R ¹ is hydrogen atom of the structural unit (1), n is 0, the multilayer shrink film of claim 1 Symbol mounting, characterized in that R ² to R ⁴ are each a hydrogen atom. The multilayer shrink film according to any one of claims 1 to 2 , wherein the content of the structural unit (1) in the ethylene-vinyl alcohol copolymer (A) is 0.1 to 30 mol%. The multilayer shrink film according to any one of claims 1 to 3, wherein an area shrinkage ratio when immersed in hot water of 90 ° C for 30 seconds is 20 to 90%.