JP2942331B2 - Ethylene-vinyl alcohol copolymer composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention relates to the formability in packaging in the food packaging field,
The present invention relates to a resin composition having a high gas barrier property, which has significantly improved the appearance quality after packaging.

B. Conventional technology Ethylene-vinyl alcohol copolymer (EVOH) is recognized for its high gas barrier properties, and is widely used in the field of food packaging. It is not necessarily satisfactory in terms of suitability for packaging foods (secondary processing), appearance quality after packaging, performance (drop strength, pinhole resistance, etc.), and as a result, gas barrier properties Such as variations
There was a need for improvement in reliability.

To solve these problems, attempts have been made to blend EVOH with ethylene-vinyl acetate copolymer (EVA), polyamide (PA), and various elastomers. In addition, vinylsilane-modified polyolefin and the like are blended. Although methods (Japanese Patent Application Laid-Open No. 61-155412) are known, in any case, none of them satisfy the above-mentioned suitability for secondary processing, appearance quality after packaging, or performance.

In other words, EVA or maleic anhydride-modified EVA
Although the effect of improving flexibility is recognized in the EVOH composition blended with, there is a problem in terms of appearance quality (decrease in transparency) and suitability for secondary processing (whitening during stretching and generation of pinholes).

Although the EVOH composition in which PA is blended with EVOH has good appearance quality, the effect of improving flexibility is small, and coloring and gelation are liable to occur during recovery use.

In addition, an EVOH composition in which a vinylsilane-modified polyolefin is blended with EVOH has an effect of improving flexibility to some extent, but is not always sufficient, and worse, coloring, gelation, etc. are liable to occur at the time of blending and collection and use. There is a problem.

C. Problems to be Solved by the Invention The present invention provides high flexibility by imparting flexibility to EVOH, and significantly improving the suitability for secondary processing, appearance quality, performance (drop strength, pinhole resistance, etc.) and recoverability. An object of the present invention is to provide a gas barrier EVOH resin composition.

D. Means for Solving the Problems The present inventors have proposed an EVOH composition obtained by blending various thermoplastic resins with EVA (A ′) in a solution and saponifying the mixture.
A film of an EVOH composition blended with various thermoplastic resins was formed and evaluated for flexibility (normal temperature and high temperature) and appearance (gel, spot, streak and transparency).

First, a saponified EVOH composition was formed by blending EVA (A ') with various thermoplastic resins, for example, polyvinyl acetate (PVAc), ionomer (IO), and the like in a solution.
As a result, the flexibility at room temperature (20 ° C.) was relatively good, but the transparency and appearance of the film such as lumps were poor. In addition, as a result of blending a modified polyethylene containing a vinylmethoxysilane-based compound with EVOH and evaluating the film formation, there were many spots and the like, and the appearance of the film was poor.

The present inventors have further studied and, surprisingly, surprisingly, obtained a film-formed EVOH composition (C) obtained by blending EVA (A ') with a vinylsilane-modified olefin copolymer (B) in a solution and saponifying the mixture. As a result, there was a case where a film having good flexibility, few bumps and the like, and a transparent and good appearance was obtained. Furthermore, as a result of intensive study, the EVOH composition,
It has been found that when the following conditions (I) to (II) are satisfied, a film having a very good appearance can be obtained, and the present invention has been completed.

5 ≦ Met ≦ 500 (I) 10 ≦ HAc ≦ 1000 (II) where Met: the content of calcium and sodium in the composition (ppm) HAc: the content of the acid component in the composition (ppm) By the way, EVOH (A) The EVOH composition obtained by blending the vinylsilane-modified polyolefin (B) with the polyolefin (B) under the melting conditions is present in the resin (B) when the EVA (A ') before saponification and the resin (B) are solution-blended and saponified. Si (OCH ₃ ) _n
Because the groups react preferentially with the -OH group of EVA (A ') generated in the saponification reaction without self-condensation, thickening and gelling, the transparency and flexibility are good and the gel No composition is obtained. This is clear from the embodiments described later.

 Hereinafter, the present invention will be described in more detail.

In the present invention, EVA (A ') is an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 65 mol%, preferably 25 to 58 mol%. If the ethylene content is less than 20 mol%, the melt moldability of the saponified EVOH composition is poor, while if it exceeds 65 mol%, the gas barrier properties of the saponified EVOH composition become insufficient. One of the more preferable requirements is that the EVA (A ') is obtained by copolymerizing 0.005 to 0.5 mol%, preferably 0.008 to 0.2 mol% of the vinylsilane compound.
(A ') is to be used. By using such EVA (A '), the improvement effect becomes more remarkable.

The EVOH (A) and EVA (A ') may contain other monomers, for example, propylene, butylene, unsaturated carboxylic acid or its ester (meth) acrylic acid, as long as the object of the present invention is not impaired. (Meth) acrylic acid ester (methyl, ethyl) or the like; or vinylpyrrolidone (N-vinyl-2-pyrrolidone or the like).

Incidentally, as the vinylsilane-based compound used for EVA (A '), compounds represented by the following (X), (Y) and (Z) are preferable.

[Where n is 0 to 1, m is 0 to 2, R1 is a lower alkyl group, an allyl group, or a lower alkyl group having an allyl group, R2 is an alkoxyl group having 1 to 40 carbon atoms, and the alkoxyl The group may have a substituent containing oxygen. R3 is hydrogen or a methyl group; R4 is a hydrogen atom or a lower alkyl group; R5 is a divalent organic residue in which an alkyl group or a chain carbon atom is bonded to oxygen or nitrogen; R6 is hydrogen, a halogen, a lower alkyl group; An alkyl group, an allyl group, or a lower alkyl group having an allyl group, R7 is an alkoxyl group or an acyloxyl group (where the alkoxyl group or the acyloxyl group may have a substituent containing oxygen or nitrogen), R8. Is hydrogen, halogen,
R9 is a lower alkyl group, an allyl group, or a lower alkyl group having an allyl group, and R9 is a lower alkyl group. More specifically, R1 is a lower alkyl group having 1 to 5 carbon atoms, an allyl group having 6 to 18 carbon atoms, or a lower alkyl group having 1 to 5 carbon atoms having an allyl group having 6 to 18 carbon atoms, and R4 is R 5 represents a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, R 5 represents an alkyl group having 1 to 5 carbon atoms or a divalent organic residue in which chain carbon atoms are mutually bonded to oxygen or nitrogen; R6 is hydrogen, halogen, a lower alkyl group having 1 to 5 carbon atoms, an allyl group having 6 to 18 carbon atoms, or a lower alkyl group having 1 to 5 carbon atoms having an allyl group having 6 to 18 carbon atoms,
R7 is an alkoxyl group or an acyloxyl group (where the alkoxyl group or the acyloxyl group may have a substituent containing oxygen or nitrogen), R8 is hydrogen, halogen, a lower alkyl group having 1 to 5 carbon atoms, 6-18 carbon atoms
Represents an allyl group or a lower alkyl group having 1 to 5 carbon atoms having an allyl group having 6 to 18 carbon atoms, and R9 represents 1 to 5 carbon atoms.
Represents a lower alkyl group. Vinylsilane compound (X),
Specific examples of the compounds (Y) and (Z) include, for example, vinyltrimethoxysilane, vinyltriethoxysilane,
Vinylmethyldimethoxysilane and γ-methacryloxypropylmethoxysilane are exemplified. Among them, vinyltrimethoxysilane and vinyltriethoxysilane are preferably used.

Next, the vinylsilane-modified olefin copolymer (B)
Is described. The resin (B) used in the present invention is an olefin-based copolymer obtained by copolymerizing or grafting a vinylsilane-based compound. More specifically, the formula (X),
It is a silane-modified olefin-based copolymer modified with vinylsilane represented by (Y), (Z) or the like. More specifically, there are, for example, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacecoxysilane. It is also possible to use an unmodified olefin-based copolymer (which may be the same or different from the silane-modified olefin-based copolymer) as a blend with the silane-modified olefin-based copolymer.

A method for obtaining the silane-modified olefin-based copolymer (B) by copolymerization is disclosed in, for example, JP-A-55-9611. For example, the vinylsilane-based compound and ethylene are subjected to a pressure of 500 to 4000 kg /. Copolymerization is performed using a radical polymerization initiator under the conditions of cm ² and a temperature of 100 to 400 ° C., and in the presence of a chain transfer agent if necessary. In this case, a third monomer such as vinyl acetate, acrylic acid, methacrylic acid and esters thereof may be copolymerized. on the other hand,
Examples of a method for introducing a silyl group by grafting include a method disclosed in JP-A-48-1711. For example, there is a method in which the vinylsilane-based compound and the radical generator are supplied to an olefin-based copolymer to an extruder and extruded at a cylinder temperature of 180 to 240 ° C. In this case, organic peroxides such as dicumyl peroxide and benzoyl peroxide are preferred examples of the radical generator.

The content of the vinylsilane-based compound in the copolymerized or grafted olefin-based copolymer is 0.0005 to 5 mol%, preferably 0.01 to 4 mol%, more preferably 0.1 to 2 mol%. When the content of the vinylsilane-based compound is less than 0.0005 mol%, good transparency cannot be obtained. On the other hand, when the content is 5 mol% or more, there is a problem that gels and bumps frequently occur during film formation.

As the olefin-based copolymer which is a base material of the silane-modified olefin-based copolymer (B), olefin is 67 to 100.
Molar% is preferably used, and specifically, polyethylene, polypropylene, especially 39% by mole or less, preferably 3 to 39% by mole of ethylene, propylene, vinyl acetate, acrylic acid, methacrylic acid, and the like. A resin obtained by copolymerizing at least one of the above esters is preferable. Among them, ethylene-propylene copolymer, ethylene-
A vinyl acetate copolymer and an ethylene-acrylate (methyl ester, ethyl ester) copolymer are more preferred.

By the way, in the present invention, a method of blending EVA (A ') with a vinylsilane-modified olefin-based copolymer (B) is important. As a solvent for obtaining the solution of (A ') and (B), a solvent in which both are uniformly dissolved at the temperature during saponification, for example, methanol, ethanol, propanol, butanol, benzene, toluene, xylene, dimethyl sulfoxide, For example, dimethylformamide and the like, preferably methanol, toluene, xylene and the like are used.
The solution of (A ') and the solution of (B), or the solution of (A') and (B) are mixed by a stirrer, static mixer, twin-screw kneading extruder or by a distillation tower tray. It is important to mix as thoroughly as possible, such as by bubbling or a combination of these.
Regarding the blend ratio of EVA (A ′) and vinylsilane-modified olefin copolymer (B), the weight ratio was (A ′) /
(B) is 5/95 to 95/5, preferably 30/70 to 94/6, more preferably 50/50 to 93/7. If (A ') / (B) is less than 5/95, the gas barrier properties of the saponified EVOH composition will not be sufficient, while if it exceeds 95/5, the effect of improving flexibility and the like will be insufficient.

The blend ratio of EVOH (A) and (B) after saponification of EVA (A ') is the ratio of the weight of EVOH reduced by saponification to the weight of (B).

The above mixed solution is treated with an acid (eg, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid) or an alkali (eg, caustic soda, caustic potash, lithium hydroxide, etc.) with respect to the resin at a concentration of 0.
Add 001-5 mol% and saponify at a temperature of 60-200 ° C. At this time, it is important to suppress the amount of the catalyst to suppress the coloring of the resin, and for that, it is important to remove by-products generated during saponification, such as methyl acetate, out of the reaction system as quickly as possible. . It is important that the reaction temperature be as high as possible in order to avoid the above-mentioned raw material or its saponified product being precipitated during the reaction.

The average degree of saponification of the vinyl acetate component in the composition obtained by saponifying the mixed solution is 90% or more, preferably 95% or more,
More preferably, it is 97% or more. If the degree of saponification is less than 90%, the gas barrier properties and the thermal stability deteriorate.

The solution of the saponified composition is solidified by cooling or solvent replacement with water or the like, and then alcohol-water,
Impurities such as solvents, catalysts and oligomers contained therein are removed with acetic acid-water, distilled water or water, and further, sodium and / or calcium metal salts and acids are added so as to satisfy the above formulas (I) to (II). And then dehydrated and dried at 60 to 150 ° C. to obtain the composition. The composition is used as it is or after being melted and pelletized.

By the way, when Met of the formulas (I) and (II) is less than 5 ppm and / or when HAc is 1000 ppm or more,
Not only does the transparency of the film deteriorate, but gels,
Streaks increase. On the other hand, Met is 500 ppm or more and / or H
If the Ac content is less than 10 ppm, not only does the transparency deteriorate, but the film is too colored to withstand use. Therefore, it is necessary to satisfy the formulas (I) and (II) simultaneously, preferably 10 ≦ Met ≦ 400, 20 ≦ HAc ≦ 800, more preferably 20 ≦ Met ≦ 300, 50 ≦ HAc ≦ 500. It is.

Met is the content of sodium and calcium in the sodium compound and calcium compound present in the EVOH composition, and examples of the sodium compound include sodium phosphate, sodium acetate, sodium carbonate, sodium hydroxide and the like. Examples of the calcium compound include calcium chloride, calcium phosphate, calcium acetate, calcium hydroxide and the like. HAc is the content of the acid present in the EVOH composition. Here, the acid includes an inorganic acid and an organic acid, and preferably acetic acid.

The composition contains a plasticizer, a heat stabilizer, an ultraviolet absorber, an antioxidant, a colorant, a filler, and other resins (polyamide, partially saponified ethylene-vinyl acetate copolymer) as long as the object of the present invention is not impaired. Blending) is free.

In addition, a suitable melt index (MI) of the composition
(At 190 ℃, under 2160g load) is 0.1 ~ 50g / 10min., Optimally
0.5 to 20 g / 10 min.

In the present invention, the EVOH composition (C) can be used as a single layer, but is usually used as a multilayer with a polyolefin resin layer, a sealant layer and the like. Therefore, the adhesive resin used for multilayering is not particularly limited as long as it can firmly bond the EVOH composition (C) layer, the polyolefin resin or the sealant layer, Unsaturated carboxylic acids or their anhydrides (such as maleic anhydride) are converted to olefin-based polymers or copolymers [polyethylene ｛low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (SLD)
PE)｝, ethylene-vinyl acetate copolymer, ethylene-
(Meth) acrylic acid ester (methyl ester or ethyl ester) copolymer] is preferably used.

As a method for obtaining a multilayer structure, for example, a multilayer film, the EVOH composition (C), a polyolefin resin, a sealant resin, or the like is laminated via an adhesive resin by an extrusion lamination method, a dry lamination method, a coextrusion lamination method, a coextrusion method. Examples thereof include a method of obtaining a laminate by a sheet molding method, a co-extrusion pipe molding method, a co-injection molding method, a solution coating method, and the like.

The method of collecting and reusing scraps such as trims and defective containers generated during molding is not particularly limited. The scrap is pulverized, dried if it absorbs moisture, and then dry-blended with the raw polyolefin resin, the pulverized scrap is pelletized, and then dry-blended with the raw resin. And a method of forming a blend pellet. The blending ratio between the raw resin and the scrap is not particularly limited, but is usually blended at a ratio of about 2 to 80%. At this time, maleic anhydride-modified polyolefins, maleic anhydride-modified polyolefin-polystyrene copolymer, One kind of metal Setsuken, hydrotalcite-based compound,
Alternatively, it may be preferable to add more.

Furthermore, the thickness configuration of the multilayer film is not particularly limited, but in consideration of moldability, cost, and the like, usually, the total layer thickness is 10 to 5000 μm, preferably 15 to 2000 μm, The thickness ratio of the EVOH composition (C) layer to the total thickness is from 1 to 40%, more preferably from 2 to 30%.
It is. In addition, as the configuration of the multilayer film, EVOH
(C) layer / adhesive resin layer / polyolefin resin layer, polyolefin resin layer / adhesive resin layer / EVOH (C) layer / adhesive resin layer / polyolefin resin layer, EVOH (C) layer / adhesive resin layer / recovery Layer, EVOH (C) layer / adhesive resin layer / collection layer / polyolefin resin layer, polyolefin resin layer / collection layer / adhesive resin layer / EVOH (C) layer / adhesive resin layer / polyolefin resin layer, polyolefin resin layer / Recovery layer /
Adhesive resin layer / EVOH (C) layer / Adhesive resin layer / Recovery layer /
Polyolefin resin layer, recovery layer / adhesive resin layer / EVOH
Typical examples include (C) layer / adhesive resin layer / polyolefin resin layer, collection layer / adhesive resin layer / EVOH (C) layer / adhesive resin layer / collection layer. When a polyolefin resin layer is provided on both outer layers, the resins may be different or the same. In general, a sealant layer is provided on one surface (the innermost layer or the outermost layer) or on both surfaces (the innermost layer and the outermost layer) of the multilayer body directly or via an adhesive resin layer.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

E. Examples Example 1 80 parts by weight of EVA (A ') having an ethylene content of 44 mol% and vinyltrimethoxysilane content of 0.012 mol, and a silane modification of ethylene content 70 mol% and vinylmethoxysilane content 0.55 mol%. After dissolving 20 parts by weight of the ethylene-vinyl acetate copolymer (B) in dimethyl sulfoxide under heating (concentration: 20% by weight), both were mixed and sufficiently homogenized with a stirrer. By-products (such as methyl acetate) were expelled with methanol vapor while dropping 10 parts by weight of a 120 g / concentration NaOH methanol solution. One hour later,
After cooling the solution to 60 ° C., it was poured into cold water with stirring,
An EVOH composition (C) was obtained. The composition was sufficiently washed with a large amount of 1 g / concentration aqueous acetic acid, and then further washed with distilled water.

Next, the composition was immersed in an aqueous solution in which 0.1 g / acetic acid and 0.07 g / sodium acetate and 0.04 g / calcium acetate were dissolved for 4 hours, then drained, and dried at 110 ° C. hot air drier for 24 hours. Was done. At this time, the EVOH composition
MI at 190 ℃ -2160g load is 1.5g / 10min., (A),
The saponification degree of the vinyl acetate component in (B) was 98.8%, the Ca + Na content (Met) in the composition was 58 ppm, and the acid (acetic acid) component content (HAc) in the composition was 90 ppm.

The EVOH composition (C) was pelletized at 180 ° C. under N ₂ under a 40φ extruder and dried under reduced pressure at 50 ° C. for 16 hours. Then, the composition (C) was treated with ethylene-vinyl acetate as a sealant layer. Copolymer (EVA) (Evaflexs E manufactured by Mitsui Polychemicals)
V-460) as a maleic anhydride-modified ethylene-vinyl acetate copolymer (Admer VF manufactured by Mitsui Petrochemical) as an adhesive resin.
600) to obtain a multilayer film having a composition (C) / adhesive resin / sealant composition by a three-type three-layer coextrusion film forming apparatus. At this time, the thickness of the film is 5/10 / 35μ.
It was.

To measure the characteristics of the film, width 15mm, length 10cm
And tensile tester with thermostat (AG-50 manufactured by Shimadzu Corporation)
0A), at 20 ° C and 120 ° C, check interval 50mm,
The tensile elongation was measured at a tensile speed of 100 mm / min. Moreover, the oxygen gas barrier property under 20 ° C.-60% RH was measured (a measuring device manufactured by Mocon Corporation). The results are shown in Table 1.

Examples 2 to 5 and Comparative Examples 1 to 8 Except as shown in Table 1, the procedure was performed under the same conditions as in Example 1. Table 1 shows the results.

F. Effects of the Invention The present invention is a high gas barrier EVOH composition having excellent flexibility and significantly improved appearance.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI C08L 51/06 C08L 51/06 (56) References JP-A-61-76545 (JP, A) JP-A-4-41536 (JP, A) JP-A-3-281542 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08L 29/04 C08L 23/00-23/36

Claims (4)

(57) [Claims] 1. Ethylene having an ethylene content of 20 to 65 mol%.
Modified with vinyl alcohol copolymer (A) and vinyl silane compound, and the content is 0.005 to 5 mol%
And a multilayer structure having an ethylene-vinyl alcohol copolymer composition layer satisfying the following formulas (I) to (II). 5 ≦ Met ≦ 500 (I) 10 ≦ HAc ≦ 1000 (II) where Met: calcium and sodium content in composition (ppm) HAc: acid component content in composition (ppm) 2. The multilayer structure according to claim 1, wherein (A) is an ethylene-vinyl alcohol copolymer modified with a vinylsilane compound and having a content of 0.0005 to 0.5 mol%. 3. Ethylene having an ethylene content of 20 to 65 mol%.
A liquid mixture of 5 to 95% by weight of a vinyl acetate copolymer (A ') and 5 to 95% by weight of an olefin copolymer (B) modified with a vinylsilane compound and having a content of 0.005 to 5% by mole An ethylene-vinyl alcohol copolymer composition obtained by saponifying
An ethylene-vinyl alcohol copolymer composition satisfying (II). 4. The ethylene-vinyl alcohol copolymer according to claim 3, wherein (A ') is an ethylene-vinyl acetate copolymer modified with a vinylsilane compound and having a content of 0.0005 to 0.5 mol%. Composition.