JPH0565375A - Molded structure of ethylene copolymer composition - Google Patents

Abstract

PURPOSE:To provide a molded structure of an ethylene copolymer composition having good gas barrier properties, good pinhole resistance, and good thermal stability during molding and suitable as a packaging material. CONSTITUTION:The objective molded structure is made of a composition consisting of 55-80wt.% ethylene/unsaturated ester copolymer (A) having an unsaturated ester content of 15-35wt.% and a melt flow rate of 0.5-20g/10min at 190 deg.C under a load of 2160g and 45-20wt.% ethylene/vinyl alcohol copolymer (B) having a vinyl alcohol content of 50-80mol%, a melt flow rate of 0.5-30g/10min at 210 deg.C under a load of 2160g, and an apparent melt viscosity at 220 deg.C under a shear rate of 100sec<-1> lower than that of component A by 300-1000Pa.S and in which the component B forms uniformly dispersed thin layers.

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 an ethylene / vinyl alcohol copolymer is generally impaired, and thus it cannot be said to be a practical solution, but JP-B-51-
A 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 proposed in Japanese Patent No. 30104 has a high gas barrier property. It is noted as improving the shortcomings of ethylene-vinyl alcohol copolymer while maintaining. 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.

[0004]

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,
It has also been found that a molded structure can be obtained in which the drawbacks of the copolymer are reduced.

[0005]

That is, according to the present invention, an unsaturated ester content of 15 to 35% by weight, 190
The melt flow rate under a load of 2160 g is 0.
55 to 80% by weight of an ethylene / unsaturated ester copolymer (A) of 5 to 20 g / 10 minutes, a vinyl alcohol content of 50 to 80% by mole, a melt flow rate at 210 ° C. and a load of 2160 g of 0.5 to The melting apparent viscosity of the ethylene / unsaturated ester copolymer (A) is 30 g / 10 minutes and the shear rate is 220 ° C. and 100 sec ^−1.
300-1000 Pa · S smaller ethylene than that of
Provided is a molded structure comprising a composition of 45 to 20% by weight of a vinyl alcohol copolymer (B), wherein (B) is in a thin layer and uniformly dispersed.

The ethylene / unsaturated ester copolymer (A) used in the present invention has an unsaturated ester content of 15 to 35% by weight, preferably 15 to 28% by weight. When a copolymer having an unsaturated ester content less than the above range is used, it is difficult to obtain a composition having excellent gas barrier properties, and a polymer having a content higher than the above range is a film container or the like. Is not suitable as a packaging material because of its low strength. As the copolymer, 190 ° C., 2
The melt flow rate measured with a 160 g load is 0.5 to
It is preferable to use 20 g / 10 minutes, especially 1 to 15 g / 10 minutes. The unsaturated ester which is a polymerization component of the copolymer may be either a carboxylic acid unsaturated ester or an unsaturated carboxylic acid ester, and vinyl acetate, acrylic acid ester, methacrylic acid ester and the like are exemplified as typical examples. be able to. As the ester of acrylic acid or methacrylic acid, for example, a carbon number of 1 to
Preferred are alkyl esters of 8, especially methyl or ethyl esters.

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 one having a melt flow rate of 0.5 to 30 g / 10 minutes, especially 1 to 20 g / 10 minutes under a load of 10 ° C. and 2160 g.

In order for the molded structure to have an excellent gas barrier property in which the ethylene / vinyl alcohol copolymer, which is the object of the present invention, is uniformly dispersed in a thin layer, ethylene.
220 ° C. as vinyl alcohol copolymer (B), 10
The melt apparent viscosity of the ethylene / vinyl alcohol copolymer (B) at a shear rate of ⁰ sec ⁻¹ is 300 to 1,000 than that of the ethylene / unsaturated ester copolymer (A).
It is necessary to use a material having a small Pa · S, preferably 400 to 900 Pa · S.

In the ethylene copolymer composition constituting the molded structure of the present invention, the ethylene / unsaturated ester copolymer (A) is 55 to 80% by weight, preferably 55 to 70% by weight. Polymer (B) is 45
-20% by weight, preferably 45-30% 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. On the other hand, if the content is more than 45% by weight, the drawbacks of the component (B), that is, the pinhole resistance, the thermal stability at the time of molding, etc. are unfavorable.

The molded structure of the present invention must be composed of the above copolymer composition, and the component (B) must be 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. FIG. 1 shows a cross section of a 50 μm-thick film of the composition of ethylene / vinyl acetate copolymer and ethylene / vinyl alcohol copolymer obtained in the present invention, which was dyed with osmic acid and ruthenium, and then observed with a scanning electron microscope. It is an electron microscope photograph taken. The black portion in Fig. 1 is the ethylene / unsaturated ester copolymer as the matrix layer, and the ethylene / vinyl alcohol copolymer uniformly dispersed in a thin layer in the film surface direction is a discontinuous white line. Observed as the enclosed area. By virtue of having such a fine structure, the molded structure of the present invention exhibits excellent gas barrier properties despite being a resin composition in which the ethylene / vinyl alcohol copolymer does not occupy a major amount.

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 melt flow rates of both component resins (A) and (B) are
By using the above-mentioned specific range and adopting the molding conditions as described above, it becomes easier to uniformly disperse the component (B) in a thin layer.

In producing the molded structure of the present invention, various additives can 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.

[0015]

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) Resin Kneading Method A predetermined ratio 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 molding method An inflation film was molded under the following conditions with an inflation molding machine composed 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 those in which 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 23 ° C. × 50% RH atmosphere. did.

5) Apparent viscosity of melting 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 Examples and Comparative Examples are shown in Table 1.

[0023]

[Table 1]

Examples 1 to 7 Ethylene / vinyl acetate copolymers (A) and ethylene / vinyl alcohol copolymers (B) listed in Table 1 were kneaded by the method of the above 1) to obtain MFR and oxygen permeation. The quantity was measured. The results are shown in Table 2.

[0025]

[Table 2]

Comparative Examples 1 to 5 The ethylene polymer (A) and the ethylene / vinyl alcohol copolymer (B) shown in Table 1 were kneaded by the method of 1) above, and the MFR and oxygen permeation amount were measured. did. The results are shown in Table 3.
Shown in.

[0027]

[Table 3]

As is clear from the results of Tables 2 and 3, a composition of an ethylene copolymer and an ethylene / vinyl alcohol copolymer having an unsaturated ester content within a specific range was used. The molded structure of the present invention in which the difference in melt apparent viscosity between the two is a certain value or more has extremely high gas barrier properties as compared with other copolymers or compositions of ethylene polymers and ethylene / vinyl alcohol copolymers. ..

[0029]

EFFECT OF THE INVENTION According to the present invention, the unsaturated ester content in the ethylene / unsaturated ester copolymer is set within a specific range, and there is a difference in the melting apparent viscosities of the two copolymers constituting the composition. As a result, a molded structure in which the ethylene / vinyl alcohol copolymer content is not more than half is obtained in which the copolymer is a thin layer and uniformly dispersed, and has excellent gas barrier properties. Show. Therefore, the water absorption is low and the gas barrier property is less dependent on humidity. In addition, it has good thermal stability during molding, and also has excellent pinhole resistance when molded into a film, etc.
It is 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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Claims (1)

[Claims] 1. An ethylene / unsaturated ester copolymer (A) 55 to 80 having an unsaturated ester content of 15 to 35% by weight, a melt flow rate at 190 ° C. and a load of 2160 g of 0.5 to 20 g / 10 min. % By weight and vinyl alcohol content 50 to 80 mol%, 210 ° C., 2160 g
Melt flow rate under load 0.5 to 30g / 1
An ethylene / vinyl alcohol copolymer (having an apparent melt viscosity at 220 ° C. and a shear rate of 100 sec ⁻¹ of 0 minutes, which is smaller than that of the ethylene / unsaturated ester copolymer (A) by 300 to 1000 Pa · S ( B) A molded structure comprising a composition of 45 to 20% by weight, wherein (B) is in a thin layer and uniformly dispersed.