JPH02175244A - Hollow container - Google Patents

Abstract

PURPOSE:To enhance gas impermeability, humidity, impermeability, impact resistance, transparency and glossiness by constituting the title container of an inner layer composed of a propylene homopolymer or a propylene copolymer containing specific ethylene, an intermediate layer composed of a saponified ethylene/vinyl acetate copolymer and an outer layer having specific gloss and composed of aromatic polyester having melt flow temp. not exceeding the specific m.p. value of the resin used in the intermediate layer. CONSTITUTION:A saponified ethylene/vinyl acetate copolymer excellent in oxygen barrier properties is used in an intermediate layer and a propylene homopolymer or ethylene/propylene copolymer containing 20mol.% or less of ethylene especially excellent in transparency among polyolefins excellent in humidity impermeability and chemical resistance is used in an inner layer. Aromatic polyester having gloss of 95% or more and having melt flow temp. not exceeding the m.p. of 30 deg.C of the resin used in the intermediate layer is used in an outer layer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to hollow containers for storing foods, medicines, cosmetics, etc., and particularly to hollow containers that require oxygen barrier properties, surface gloss, and transparency. [Prior Art] From the viewpoint of preserving the contents, it is preferable for containers of this type to have particularly low oxygen gas permeability, low water loss, and high impact resistance.

However, no single volatile material has been found to date that can satisfy these conditions. Therefore, it is common practice to laminate various materials and utilize the excellent characteristics of each material in combination.

Conventionally, the combination of materials for hollow containers has been to use polyolefin for the inner and outer layers, a saponified ethylene-vinyl acetate copolymer for the middle layer, and, if necessary, add modified polyolefin or the like between each layer to increase the adhesive strength between each layer. It has been widely adopted to provide an adhesive resin layer. That is, although polyolefins have excellent water resistance, moisture permeability, and chemical resistance, they have the drawback of high permeability to gases such as oxygen gas and carbon dioxide gas, and the long-term storage stability of the contents is poor. On the other hand, saponified ethylene-vinyl acetate copolymers have the advantage of having significantly lower gas permeability than polyolefins, but because they are hydrophilic, they have high permeability to water vapor and are susceptible to exposure to high humidity environments. This has the disadvantage that gas permeability to oxygen gas and the like increases. Therefore, in order to utilize the strengths of each of these resins in combination and cover each other's weaknesses with other resins, polyolefin was added to the inner and outer layers.
Blow molding, particularly by coextrusion, is generally carried out using a laminated structure in which a saponified ethylene-vinyl acetate copolymer is disposed in the intermediate layer.

Hollow containers made of such laminated structures have made it possible to satisfy the characteristics requirements to a certain extent. However, in recent years, it has been desired to provide such plastic containers with the transparency and glossiness of glass containers.

This demand is particularly high for medical containers. That is, in medical containers, it is desirable to visually confirm the presence or remaining amount of contents, and a transparent container is a basic requirement. Containers in other fields are also desired to be transparent and glossy to varying degrees.

Glass containers are a container that meets these demands, but they have the fatal disadvantage of being brittle and easily broken, and are also heavy.

Therefore, if transparency and gloss could be added to plastic containers, which have the greatest characteristics of being lightweight and unbreakable, they could be used safely in the medical field, and their commercial value would be significantly higher as containers for other fields. . However, in the case of a hollow container made of a laminated structure as described above, since polyolefin is used for the inner and outer layers, the container has poor transparency and gloss.

In particular, when polyethylene is used for the inner and outer layers, the transparency becomes considerably poor.

In response to this request, U.S. Patent Section 4.6
08,311, polycarbonate layer/adhesive resin layer/saponified ethylene-vinyl acetate copolymer layer/
A laminated structure consisting of an adhesive resin layer/polyolefin layer has been proposed.

[Problem to be solved by the invention]

If polypropylene is used for the inner polyolefin layer and polycarbonate is used for the outer layer, as in the laminated structure described in the above US patent, a hollow container with good transparency can be obtained. However, this laminated structure has a serious drawback of poor moldability. That is, since the melting point of the saponified ethylene-vinyl acetate copolymer in the intermediate layer is lower than the melting temperature of polycarbonate, the saponified ethylene-vinyl acetate copolymer is heated to a temperature higher than the melting point during coextrusion. However, under such temperature conditions, gelation occurs from the saponified ethylene-vinyl acetate copolymer in the intermediate layer, conversely impairing transparency. Therefore, in order to solve this problem, each resin is melted at different heating temperatures, and a temperature shielding wall is installed to prevent the resin layers from coming into contact with each other in a certain section of the extrusion head, so that they are integrated only at the tip of the head. This requires a special extrusion head. Another drawback is that polycarbonate itself is expensive.

Therefore, an object of the present invention is to easily perform blow molding by coextrusion without using such a special extrusion head, and to have excellent gas permeation resistance, moisture permeation resistance, impact resistance, etc., as well as transparency. Another object of the present invention is to provide a hollow container made of a multilayer structure that also has excellent gloss.

[Means to solve the problem]

In order to achieve the above object, the hollow container of the present invention is a hollow container consisting of a laminated structure of at least an outer layer, an intermediate layer, and an inner layer formed by coextrusion, wherein the inner layer is a homopolymer of propylene or propylene containing 20 mol% or less of ethylene. The intermediate layer is composed of a saponified ethylene-vinyl acetate copolymer, and the outer layer has a gloss of 95% or more and has a melting point that does not exceed 30°C, which is the melting point of the resin used for the intermediate layer. It is characterized by being made of an aromatic polyester having a flow temperature T0 (temperature when the melt viscosity is 20,000 poise).

[Operation and mode of the invention]

As described above, if polycarbonate is used for the outer layer, since this polycarbonate has excellent transparency, it becomes possible to manufacture a laminated structure with good transparency. but,
In this case, as mentioned above, a special extrusion head is required to prevent gelation of the saponified ethylene-vinyl acetate copolymer, and since the cost for this and the polycarbonate itself are expensive, the resulting hollow The container is also expensive, making it difficult to use it for anything other than special purposes.

The present inventors focused on the fact that the above-mentioned phenomenon is caused by the difference in melting temperature and flow behavior of the resins used for the intermediate layer and the outer layer. As a result of intensive research and exploration into an inexpensive material for the outer layer that has excellent coextrusion moldability and transparency, we found an aromatic polyester that has a melt flow temperature T0 that does not exceed 30°C, the melting point of the resin used for the intermediate layer. The present invention has been completed based on the discovery that the above-mentioned requirements are met.

That is, in the hollow container of the present invention, a saponified ethylene-vinyl acetate copolymer with excellent oxygen barrier properties is used in the intermediate layer, and a particularly transparent polyolefin with excellent moisture permeability and chemical resistance is used in the inner layer. In addition to using a propylene homopolymer with excellent properties or an ethylene-propylene copolymer containing 20 mol% or less of ethylene, the outer layer contains 9
Because it uses a combination of aromatic polyester that has a gloss level of 5% or more and a melt flow temperature that does not exceed 30°C, which is the melting point of the resin used for the intermediate layer, it cannot be used for the intermediate layer during coextrusion. The saponified ethylene-vinyl acetate copolymer does not undergo gelation, has excellent gas permeability, moisture permeation resistance, impact resistance, etc., as well as transparency and gloss, and is relatively inexpensive. can be obtained.

Note that the melting point of the intermediate layer resin in this specification refers to the melting point measured with a differential scanning calorimeter.

Further, the melt flow temperature is defined as follows. In other words, when a synthetic resin is extruded at a temperature T and a pressure P using a Koka flow tester having a capillary die with a length of 1 radius R, the discharge volume is Q, and the apparent The shear stress T1, apparent shear rate γ, and apparent viscosity μ are defined as follows.

τ-(R-P)/2L γ-(4Q)/(πR3) μ-τ/γ Curve obtained by plotting μ at various temperatures T at this time μ-f (T) μm20. 00
The melt flow temperature T with the value at 0 (poise)
Set to 0. In the present invention, L-10mm, R=0.
Using a 5mm die, r-2X10' dyne/cm
'The value determined by n1 was used. In addition, the above viscosity is 20.00
0 poise is a normal extrusion state viscosity at which similar flow characteristics can be obtained, and therefore the above melt flow temperature can be seen as another way of expressing the molding temperature.

The aromatic polyester used in the present invention refers to a polyester having an aromatic ring in the main chain, and uses terephthalic acid, isophthalic acid, etc. alone or in combination as an acid component, and bis(2-hydroxyethoxy) as a diol component. ) It can be obtained by using benzene alone or in combination with other diols and esterifying them.

As other diols that can be used in combination with bis(2-hydroxyethoxy)benzene, all diols having ester-forming ability can be used, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl, etc. Examples include glycol, cyclohexanediol, xylylene glycol, hexahydroxylylene glycol, and bis(4-β-hydroxyethoxyphenyl)sulfone.

The saponified ethylene-vinyl acetate copolymer used for the intermediate layer has an oxygen permeability coefficient of lXl0-"c a
cm/Cm2 #sec*cm
Saponified ethylene-vinyl acetate copolymers with Hg (37"C1R,) 1.0%) or less, modified products thereof, or mixtures mainly composed of them are used. Among these, ethylene containing ji of 25 to 50 mol% is used. A saponified ethylene-vinyl acetate copolymer having a saponification degree of 96% or more is particularly preferred.By setting the ethylene content to 25 mol% or more, moldability such as extrusion moldability and blow moldability becomes good; By controlling the saponification degree to 96% or more, good oxygen barrier properties are exhibited.

As described in Japanese Patent Publication No. 59-47994, the ethylene content is 60 to 95 mol% and the degree of saponification is 50 to the above-mentioned preferred saponified ethylene-vinyl acetate copolymer.
95% or more of saponified ethylene-vinyl acetate copolymer
=5 to 50: Mixed at a weight ratio of 50, and the average degree of polymerization is 300 to 2 per 100 parts by weight of the total amount of these saponified materials.
000, by using a mixture of 5 to 100 parts by weight of polyvinyl alcohol with a saponification degree of 70% or more as an intermediate layer, or by blending a polymer with affinity with the resin of other layers, an adhesive resin layer can be formed. A multilayer structure can be obtained without intervening. That is, in this case, a three-layer structure consisting of an outer layer/intermediate layer/inner layer made of each of the resins described above can be provided. However, in general, an adhesive resin layer such as ethylene-vinyl acetate copolymer or modified polyolefin is interposed between each layer in order to increase the interlayer adhesive strength.

Furthermore, in the present invention, other resin layers may be interposed to impart other desired physical properties within the range of not impairing transparency, or the above-mentioned layers may be formed into a plurality of layers.

The hollow containers obtained by the present invention are containers for various beverages such as sake-soaked drinks, carbonated drinks, juice drinks including fruit juice and spinach juice, synthetic drinks including vitamin-enriched drinks, and lactic acid bacteria drinks;
Containers for various seasonings such as mayonnaise, dressing, ketchup, soy sauce, sauce, mirin, vinegar, cooking oil, miso, etc.;
Liquid food containers for soups, stews, curries, etc.; infusions such as carbohydrate infusions, electrolyte infusions, plasma expanders, osmotic diuretics, amino acid infusions, fat emulsions, high-calorie infusions, high-calorie foods, and high-protein foods. It can be suitably used as a container for liquid medical foods such as blood, etc.; and containers for detergents, cosmetics, agricultural chemicals, industrial chemicals, etc.

[Examples] Hereinafter, the present invention will be specifically explained with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples.

Examples 1 to 3 and Comparative Examples 1 to 2 Using the synthetic resins shown in Table 1 below, infusions were made with the layer configuration shown in Table 2 using a coextrusion blow molding machine with a 5-layer coextrusion die. Container (size: length 60s x width 80+gm, height to the bottom of the neck 160cm, height to the end of the eye 200mm
m5) was blow molded. The glossiness and transparency of the obtained container are also shown in Table 2.

Note that the glossiness and transparency are values measured as follows.

Glossiness: Specular gloss ΔpJ determination method specified in JIS 28741. Specularly reflected luminous flux ψS from the sample surface and reflected luminous flux ψ0 from the standard surface are measured at an incident angle of 60'', and according to These are the determined values.The measuring a! device used was ① IG-310 type gloss meter manufactured by Horiba, Ltd.

Transparency: It was expressed as the total light transmittance, that is, the ratio of the incident amount of light with a wavelength of 420 nm defined in JIS K6714 to the total light transmitted amount.

Table 2 N) Melting Point As is clear from the results shown in Table 2 above, in the hollow container of the present invention, the melt flow temperature in the outer layer is relatively low and the melt flow temperature is close to the melting point of the resin used in the intermediate layer. Since we used an aromatic polyester with a polyester, it is possible to stably coextrude it with saponified ethylene-vinyl acetate copolymer, which is an oxygen barrier resin that has a narrow heating temperature range and easily gels even with a slight temperature increase. (See comparison of Examples 1 to 3 and Comparative Example 2), and both gloss and transparency were significantly improved compared to when polypropylene was used for the outer layer (Comparative Example 1).

In addition, in the case of saponified ethylene-vinyl acetate copolymer,
Since gelation begins when the temperature exceeds the melting point by 30°C (see Comparative Example 2), it is necessary to keep the temperature below 30°C, and preferably below 20°C is stable.

In addition, since polypropylene, which is a hydrophobic synthetic resin and has high heat resistance, is used for the inner layer, it is possible to prevent moisture from entering the oxygen barrier resin in the middle layer when contents such as liquid are placed inside the container. Furthermore, when a container is formed by heat welding a coextruded sheet, the heat sealing strength is increased.

〔Effect of the invention〕

As described above, the hollow container of the present invention has excellent gas permeation resistance, moisture permeation resistance, impact resistance, heat resistance, and heat sealability, as well as excellent transparency and gloss, and can be used as an intermediate layer. The saponified ethylene-vinyl acetate copolymer can be extruded using a normal extrusion die without gelling.Moreover, the aromatic polyester used for the outer layer is more durable than polycarbonate conventionally used for the same purpose. Because it is durable and durable, it can be used not only as a medical container but also as a hollow container in other fields at a low cost, and its commercial value is extremely high.

Claims (1)

[Claims] A hollow container consisting of a laminated structure of at least an outer layer, an intermediate layer, and an inner layer formed by coextrusion, the inner layer consisting of a propylene homopolymer or a propylene copolymer containing 20 mol% or less of ethylene, and the intermediate layer consisting of an ethylene-vinyl acetate copolymer. It is made of a saponified polymer, and the outer layer has a gloss of 95% or more, and the melt flow temperature T_0 (melt viscosity of 20°C) does not exceed the melting point of the resin used for the intermediate layer.
,000 poise).