JPH05179010A - Molded structure of ethylenic copolymer composition - Google Patents

Abstract

PURPOSE:To obtain a molded structure, composed of an ethylene-unsaturated carboxylic acid copolymer and ethylene-vinyl alcohol copolymer in which the latter is uniformly dispersed in the form of a thin layer and excellent in gas barrier properties, pinhole resistance and thermal stability. CONSTITUTION:The objective molded structure is obtained by kneading a composition composed of (A) 50-80wt.%, preferably 55-70wt.% ethylene-unsaturated carboxylic acid copolymer or its metallic salt having 0.5-30g/10min melt flow rate (at 190 deg.C under 2160g load) and 5-30wt.% content of the unsaturated carboxylic acid [preferably (meth)acrylic acid] and (B) 45-20wt.%, preferably 45-30wt.% ethylene-vinyl alcohol copolymer having 50-80mol%, preferably 55-75mol% vinyl alcohol content and an apparent melt viscosity (at 220 deg.C and 100/sec shearing rate) lower than that of the component (A) by 120-1000Pa.S under conditions of 170-235 deg.C 10-2000/sec shearing rate, 10sec to 5min residence time, etc., and molding the resultant kneaded composition. The component (B) is uniformly dispersed in the form of a thin layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded structure of an ethylene copolymer composition which is excellent in gas barrier properties, pinhole resistance, thermal stability during molding and the like.

[0002]

2. Description of the Related Art Ethylene / vinyl alcohol copolymers having a high vinyl alcohol content are widely used as packaging materials because of their excellent gas barrier properties.
However, this polymer easily absorbs water, and the gas barrier property is significantly lowered by the water absorption, and the pinhole resistance,
It also has major drawbacks such as poor stretchability, insufficient impact resistance in the dry state, poor heat resistance and inability to be molded at high temperatures. For this reason, the copolymer is rarely used alone, and is often used exclusively as an intermediate layer by laminating it with another material.

On the other hand, many proposals have been made to improve such a defect by blending it with another resin. Among them, it is difficult to remarkably improve the above-mentioned drawbacks in a system containing an ethylene / vinyl alcohol copolymer as a main component.

On the other hand, in a system containing other resin in a major amount, the excellent gas barrier property of the ethylene / vinyl alcohol copolymer is generally impaired, so that it cannot be said to be a practical solution. The method of forming a layered structure having different ethylene / vinyl alcohol contents by molding a polyolefin and an ethylene / vinyl alcohol copolymer under specific conditions, which is proposed in Japanese Patent Publication No. 51-30104, has a gas barrier property. It attracts attention as an improvement of the drawbacks of ethylene-vinyl alcohol copolymer while maintaining a high level. However, this proposal has a drawback in that the compatibility between the polyolefin and the ethylene / vinyl alcohol copolymer is not good, so that it is not possible to obtain the properties which are satisfactory for use as a thin film. That is, it was not always easy to produce a thin film, and the gas barrier property of the produced film was not sufficiently satisfactory.

On the other hand, in Japanese Unexamined Patent Publication No. Sho 62-246934, a blend having a good barrier property is obtained by causing partial cross-linking of the gas permeable polymer from a blend of a gas permeable polymer and a gas barrier polymer. A method of manufacturing has been proposed. In this proposal, ethylene / vinyl alcohol copolymer is exemplified as the gas barrier polymer, but there is no specific blend example, and the main objects are exclusively directed to polyamide and polyester. This method requires crosslinking, albeit partially, and it can be said that there is a problem in the molding process because it also causes an increase in the melt viscosity of the gas-permeable polymer.

[0006]

In view of the above situation, the present inventors have improved the above-mentioned drawbacks of the ethylene / vinyl alcohol copolymer as much as possible and have sufficient gas barrier property even in a thin film. A study was conducted to obtain a molded structure. As a result, a sufficient gas barrier property can be obtained by molding a composition of two kinds of ethylene copolymers described later and by uniformly dispersing the ethylene / vinyl alcohol copolymer in a thin layer,
Moreover, it has been found that a molded structure in which the drawbacks of the copolymer are reduced can be obtained without processing difficulties.

[0007]

That is, according to the present invention, the melt flow rate at 190 ° C. and a load of 2160 g is 0.5 to 30 g / 10 minutes, and the unsaturated carboxylic acid content is 5 to 30% by weight. An ethylene / unsaturated carboxylic acid copolymer or its metal salt (A) of 55 to 80 wt% and a vinyl alcohol content of 50 to 80 mol%
And the apparent melt viscosity at 220 ° C. and a shear rate of 100 sec ⁻¹ is 120 to 1,000 pa than that of the above (A).
・ S-low ethylene / vinyl alcohol copolymer (B) 4
It relates to a molded structure comprising a composition of 5 to 20% by weight and (B) being in a thin layer and uniformly dispersed.

It should be noted that the Japanese Patent Publication No. 51-30104 mentioned above describes that an olefin copolymer containing a small amount of other ethylenically unsaturated monomers up to 5 mol% may be used as the polyolefin. However, there is no specific example thereof, and the manufacturability of the molded structure as in the present invention is not taught at all. In the same publication, these olefin copolymers are rather used exclusively as thermoplastic polymers having a carbonyl group, which is recommended to be added as an optional component.

The ethylene / unsaturated carboxylic acid copolymer or its metal salt (A) used in the present invention has an unsaturated carboxylic acid copolymerization amount of 5 to 30% by weight, preferably 6 to 25% by weight. It is a combination or a metal salt thereof.
Acrylic acid and methacrylic acid are preferable as the unsaturated carboxylic acid. When a copolymer having an unsaturated carboxylic acid copolymerization amount less than the above range or a metal salt thereof is used, it is difficult to obtain a molded structure having excellent gas barrier properties, and the copolymerization ratio is more than the above range. The material is not suitable as a packaging material for films, containers, etc. because of its low strength. Here, the ethylene / unsaturated carboxylic acid copolymer is another unsaturated monomer such as an acrylic ester,
It may be a copolymer of an unsaturated carboxylic acid ester such as methacrylic acid ester and a vinyl ester such as vinyl acetate. When such other unsaturated monomer is copolymerized, for example, 30% by weight or less,
Although it may be contained in an amount of preferably 25% by weight or less, the total amount thereof together with the unsaturated carboxylic acid is 45% by weight or less, particularly 40
The polymerization ratio is preferably such that it is not more than weight%.

When the metal salt of the above copolymer is used, for example, lithium, sodium, potassium, magnesium,
A salt such as zinc can be used. The degree of neutralization with these metal ions is 1 to 100%, preferably 5 to 80%.

In order to use the molded structure of the present invention preferably as a packaging material, the above-mentioned component (A) is 190 ° C.,
Melt flow rate under a load of 2160 g is 0.5 to
It is preferable to use 30 g / 10 min, especially 1 to 25 g / 10 min.

The ethylene / vinyl alcohol copolymer (B) used in the present invention has a vinyl alcohol content of 5
0 to 80 mol%, preferably 55 to 75 mol%. Such a copolymer has a saponification degree of 95% or more, preferably 99% or more, of the corresponding ethylene / vinyl acetate copolymer.
It is obtained by saponification at a ratio of at least%.
The ethylene / vinyl alcohol copolymer also has 2
It is preferable to use a melt flow rate of 0.5 to 30 g / 10 minutes, particularly 1 to 20 g / 10 minutes at 10 ° C. and a load of 2160 g.

In order to easily obtain a molded structure having a good gas barrier property in the present invention, the ethylene / vinyl alcohol copolymer (B) has a melting apparent viscosity at 220 ° C. and a shear rate of 100 sec ^−1. 1 more than that of (A) above
20-1,000 pa · S, preferably 300-900
The one with lower pa · S should be used.

In the ethylene copolymer composition constituting the molded structure of the present invention, the component (A) is 55 to 80% by weight, preferably 55 to 70% by weight, and the ethylene / vinyl alcohol copolymer (B) is 45. -20% by weight, preferably 45-3
It consists of 0% by weight. If the amount of component (B) is less than 20% by weight, it is difficult to obtain a molded product having a high gas barrier property. Further, when the content is more than 45% by weight, the drawback of the component (B),
That is, the pinhole resistance, the thermal stability during molding, and the like are poor, which is not preferable.

The molded structure of the present invention must be composed of the above copolymer composition, and the component (B) must be in a thin layer and uniformly dispersed. Here, the thin layer form means that the component (B) forms a discontinuous thin layer in the surface direction of the molded structure. Further, being uniformly dispersed means a state in which the uneven distribution of the component (B) is not substantially recognized in the main part of the molded structure.

The microstructure of such a molded structure can be judged by a micrograph as shown in FIG. 1 5 of the compositions of the resulting ethylene-methacrylic acid copolymer metal salt and an ethylene-vinyl alcohol copolymer in the present invention
It is an electron micrograph which the cross section of the film of 0 micrometer thickness was dye | stained by osmic acid and ruthenium, and was image | photographed with the scanning electron microscope. The black portion in Fig. 1 is the metal salt of the ethylene / unsaturated carboxylic acid copolymer as the matrix layer, and the ethylene / vinyl alcohol copolymer uniformly dispersed in a thin layer in the film surface direction is not contained therein. It is observed as a part surrounded by a continuous white line. The molded structure of the present invention has such a fine structure,
Despite being a resin composition in which the ethylene / vinyl alcohol copolymer does not occupy a major amount, it exhibits excellent gas barrier properties.

The molded structure of the present invention has a shape having a relatively large area and a small thickness, and can take various shapes such as a film, a sheet, a tube and a container. The thickness of the molded structure of the present invention is, for example, 5 to 1000.
μm, preferably 20 to 500 μm, 30 to 50
It exhibits excellent gas barrier properties even in thin layers such as μm.

In the molded structure of the present invention, the component (B) must be a thin layer and uniformly dispersed. For this purpose, it is necessary to knead the components (A) and (B) to a desired degree and then mold. In addition, it is necessary to use a molding method that causes resin to flow in the area direction during molding.
The resin composition comprising the two components (A) and (B) of the present invention is a thin layer and uniform component (B) by various molding methods such as extrusion molding, hollow molding, injection molding, injection-hollow molding, and vacuum molding. It is possible to easily mold the molded structure dispersed in the. To obtain such a molded structure, (A)
After melting and kneading (B) and (B), they may be subjected to a molding machine, but in any case, the kneading temperature is 170 to 235 ° C., the shear rate is 10 to 2000 / sec, and the residence time is 10 sec to 5
It suffices to knead and mold under conditions such as min. In the present invention, the difference in the melt apparent viscosity between the two resins (A) and (B) is set within the specific range as described above, and by adopting the molding conditions as described above, the component (B) is formed into a thin layer. It becomes easier to uniformly disperse.

In producing the molded structure of the present invention, various additives may be added to the ethylene copolymer composition. Examples of such additives include antioxidants, heat stabilizers, desiccants, nucleating agents, antistatic agents, and barrier property-imparting fillers such as mica.

The molded structure of the present invention may have a laminated structure with other materials. Examples of such other materials include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, polyolefins such as poly-4-methyl-1-pentene, polyethylene terephthalate, polybutylene terephthalate, and the like. Examples include thermoplastic resins represented by polyesters, polyamides such as nylon-6 and nylon-6,6, thermosetting resins such as polyurethane, various elastomers, metallic materials such as aluminum foil, and paper. be able to. In the case of taking a multilayer structure, the molded structure portion of the present invention may occupy one layer or two or more layers,
Further, a surface layer or an intermediate layer may be formed.

[0020]

The present invention will be described in more detail with reference to the following examples. The resin kneading method, molding method and evaluation, and analysis method in Examples and Comparative Examples were performed under the following conditions and methods.

1) Method of kneading resin A predetermined proportion of resin was melt-mixed under the following conditions. Kneader ・ ・ ・ 30mmφ Single screw extruder Screw ・ ・ ・ Dullamage type single flight screw L / D = 33 Barrel temperature (℃) C ₁ C ₂ C ₃ C ₄ C ₅ D 80 150 180 180 200 200 200 180 Screw Rotation speed ... 40 rpm

2) Film forming method An inflation film was formed under the following conditions using an inflation forming machine consisting of a 30 mm diameter single-screw full light extruder. Barrel temperature (° C.) C ₁ C ₂ C ₃ C ₄ HD 150 200 200 200 200 200 200 Other than Example 2 Example 2 Screw rotation speed rpm ... 45 60 Take-up speed m / min ... 3 4 Film thickness μm ... 50 50 Blow-up ratio ... 2.8 2.8 Except for Example 2, the screw rotation speed was 45 rpm.
Example 2 was molded by increasing the resin discharge speed from the extruder and the film take-up speed.

These molding conditions are the usual blown film molding method, and are not such that the dispersion and flow state of the ethylene / vinyl alcohol resin are controlled.

3) MFR (melt flow rate) JIS K-6760 temperature 190 ° C. load 2160 gr

4) Measurement of oxygen gas permeation amount Using a gas permeation tester (differential pressure method) manufactured by Toyo Seiki, the oxygen gas permeation amount of the 50 μm thick film obtained in 2) was measured under an atmosphere of 23 ° C. × 50% RH. did.

5) Apparent Melting Viscosity Capillary Rheometer 3211 manufactured by Instron (USA)
Using a mold, the shear stress under a specified melting temperature and shear rate was detected, and the apparent melting viscosity was calculated. Details are given below. Capillary rheometer 3211 type Plunger speed ・ ・ ・ 0.06〜20 cm / min Load capacity ・ ・ ・ 500〜2000 Kg Measurement temperature ・ ・ ・ 40〜399 ℃ Temperature control ・ ・ ・ Barrel ± 2 ℃ Capillary ± 0.5 ℃ barrel ・ ・ ・ Diameter 0.953 ± 0.0013cm Effective length 25cm (including capillary part) Capillary ・ ・ ・ Diameter 0.0762cm Length 2.54cm Material Tungsten carbide Inflow angle ・ ・ ・ 90 degrees

6) Measurement of Dispersion State of Ethylene / Vinyl Alcohol Copolymer A film having a thickness of 50 μm obtained by the method of 2) above was used for 20 using an RM type microtome manufactured by Japan Microtome Institute.
Cut to a width of μm to obtain a section sample having a smooth cross section. Further, this section sample was surface-treated with osmium acid and ruthenium, and was subjected to 1 with a Hitachi 80 type scanning electron microscope under the conditions of an accelerating voltage of 6 KV and a working distance of 15 mm.
It was observed at a magnification of 000 times. From the photograph (FIG. 1) taken, the presence of a thin layer and uniformly dispersed ethylene / vinyl alcohol copolymer was visually determined.

The resins used in the examples and comparative examples are shown in Table 1 (ethylene copolymer) and Table 2 (ethylene / vinyl alcohol copolymer).

[0029]

[Table 1]

[0030]

[Table 2]

Examples 1 to 4 Ethylene copolymers (A) listed in Table 1 and ethylene
The vinyl alcohol copolymer (B) was kneaded by the method of 1) above, and the MFR and oxygen permeation amount were measured. The results are shown in Table 3.

[0032]

[Table 3]

Comparative Examples 1 and 2 Compositions obtained by kneading the ethylene polymer (A) and the ethylene / vinyl alcohol copolymer (B) listed in Table 1 by the method of 1) above, and The MFR and oxygen permeation amount of the ethylene polymer alone were measured. The results are shown in Table 4.

[0034]

[Table 4]

[0035]

According to the present invention, a specific ethylene / unsaturated carboxylic acid copolymer and an ethylene / vinyl alcohol copolymer are combined, and the difference in the apparent melting viscosities of both components is within a specific range. Thereby, a structure in which the ethylene / vinyl alcohol copolymer content is not more than half but the copolymer is a thin layer and uniformly dispersed is obtained,
Shows excellent gas barrier properties. Therefore, the water absorption is low and the gas barrier property is less dependent on humidity. Further, it has good thermal stability during molding, and has excellent pinhole resistance even when formed into a film or the like, and is therefore useful as various packaging materials such as food packaging.

[Brief description of drawings]

FIG. 1 is an electron micrograph of a cross section of a molded structure of the present invention.

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[Procedure amendment]

[Submission date] December 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an electron micrograph of a cross section of a thin film that is a molded structure of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C08L 23/08 LCK 7107-4J // (C08L 23/08 29:04) 6904-4J

Claims (1)

[Claims] 1. Ethylene having a melt flow rate of 0.5 to 30 g / 10 minutes at 190 ° C. and a load of 2160 g and an unsaturated carboxylic acid content of 5 to 30% by weight.
Unsaturated carboxylic acid copolymer or its metal salt (A) 5
5-80% by weight and vinyl alcohol content of 50-8
At 0 mol%, the apparent melt viscosity at 220 ° C. and a shear rate of 100 sec ⁻¹ is 120 to 1.0 from that of the above (A).
A molded structure comprising a composition of 45 to 20% by weight of an ethylene / vinyl alcohol copolymer (B) having a low 00 pa · S, wherein (B) is a thin layer and uniformly dispersed.