JPH0579229B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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] For this type of container, it is preferable to use a container that has low oxygen gas permeability, low moisture loss, and high impact resistance in terms of preserving the contents. However, to date, no single material has been found 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 material combinations for hollow containers include polyolefin for the inner and outer layers, saponified ethylene-vinyl acetate copolymer for the middle layer, and modified polyolefin, etc. between each layer as necessary 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 disadvantage of high gas permeability to oxygen gas, carbon dioxide gas, etc., and the long-term storage stability of the contents is poor. on the other hand,
Saponified ethylene-vinyl acetate copolymers have the advantage of significantly lower gas permeability than polyolefins, but because they are hydrophilic, they have high permeability to water vapor, and when exposed to a high humidity atmosphere, There is a drawback 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, we created a laminated structure with polyolefin in the inner and outer layers and saponified ethylene-vinyl acetate copolymer in the middle layer. In particular, blow molding by coextrusion is generally practiced. With a hollow container made of such a laminated structure,
It has become 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 plastic containers, which have the greatest characteristics of being lightweight and unbreakable, can be made transparent and glossy, they can be used safely in the medical field, and their commercial value will 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 such demands, US Pat. No. 4,608,311 discloses a polycarbonate layer/
A laminated structure consisting of adhesive resin layer/saponified ethylene-vinyl acetate copolymer layer/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,
It is necessary to melt each resin at different heating temperatures, and to provide a temperature shield wall to prevent the resin layers from coming into contact with each other in a certain section of the extrusion head, so that they only come together at the tip of the head. An extrusion head is required. Another drawback is that polycarbonate itself is expensive. Therefore, an object of the present invention is to provide a material that can be easily blow molded by coextrusion without using such a special extrusion head, has excellent gas permeation resistance, moisture permeation resistance, impact resistance, etc., and is transparent. It is an object of the present invention to provide a hollow container made of a multilayer structure having excellent properties and gloss. [Means for Solving the Problems] 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, in which the inner layer is made of a propylene homopolymer or Consisting of a propylene copolymer containing up to 20 mol% ethylene,
The intermediate layer is made of a saponified ethylene-vinyl acetate copolymer, and the outer layer has a gloss of 95% or more and has a melt flow temperature T ₀ (melting It is characterized in that it is made of an aromatic polyester having a viscosity of 20,000 poise (temperature at which the viscosity is 20,000 poise). [Operations and Modes 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. However, in this case, as mentioned above, a special extrusion head is required to prevent gelation of the saponified ethylene-vinyl acetate copolymer, and because of the cost for this and the expensive polycarbonate itself, the yield is low. The hollow containers that can be used are also expensive, making it difficult to use them 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 of inexpensive materials for the outer layer that have excellent coextrusion moldability and transparency, we have developed an aromatic material with a melt flow temperature T ₀ that does not exceed 30°C, the melting point of the resin used for the intermediate layer. The inventors have discovered that polyesters of the above group satisfy the above requirements, and have completed the present invention. 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 has a gloss level of 95% or more and the melting point of the resin used in the intermediate layer is low.
Because it uses a combination of aromatic polyesters with a melt flow temperature not exceeding 30℃, the saponified ethylene-vinyl acetate copolymer used for the intermediate layer during coextrusion does not gel.
It has excellent gas permeability, moisture permeability, impact resistance, etc., as well as transparency and gloss, and can be obtained at a relatively low cost. Note that the melting point of the intermediate layer resin as used herein 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 type flow tester having a capillary die with a length L and a radius R, the discharge volume is Q, and the apparent The shear rate γ, the apparent shear rate γ, and the apparent viscosity μ are defined as follows. τ=(R・P)/2L γ=(4Q)/(πR ³ ) μ=τ/γ At this time, μ at various temperatures T
The curve obtained by plotting μ = μ of (T) =
Melt flow temperature with value at 20000 (poise)
Let it be T ₀ . In the present invention, L=10mm, R=
A value measured using a 0.5 mm die at τ=2×10 ⁶ dyne/cm ² was used. The above viscosity of 20,000 poise is a normal extrusion state viscosity that provides similar flow characteristics, and therefore the above melt flow temperature can be seen as another way of forming 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, neo Examples include pentyl 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 1×10 ^-11 cc
A saponified ethylene-vinyl acetate copolymer having a concentration of x cm/cm ² ·sec·cmHg (37° C., RHO%) or less, a modified product thereof, or a mixture mainly composed of them is used. Among these, ethylene content 25
A saponified ethylene-vinyl acetate copolymer having a saponification degree of 96% or more and 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 is improved,
On the other hand, by controlling the saponification degree to 50 mol% or less, good oxygen barrier properties are exhibited, and by controlling the saponification degree to 96% or more, oxygen barrier properties are improved. As described in Japanese Patent Publication No. 59-47994, an ethylene-vinyl acetate copolymer having an ethylene content of 60 to 95 mol% and a saponification degree of 50% or more is Saponified polymers are mixed at a weight ratio of 95:5 to 50:50, and 5 to 100 weight of polyvinyl alcohol with an average degree of polymerization of 300 to 2000 and a saponification degree of 70% or more is added per 100 parts by weight of the total amount of these saponified substances. By using a partially mixed mixture as an intermediate layer or by blending a polymer with affinity with the resins of other layers, a multilayer structure can be obtained without intervening an adhesive resin layer. 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,
Ethylene is added between each layer to increase interlayer adhesion strength.
An adhesive resin layer such as vinyl acetate copolymer or modified polyolefin is interposed. Furthermore, in the present invention, in order to impart other desired physical properties, other resin layers may be interposed, or each of the above layers may be formed into a plurality of layers, as long as transparency is not impaired. The hollow container obtained by the present invention can be used for alcoholic beverages,
Various beverage containers such as carbonated drinks, youth drinks including fruit juice and vegetable juice, synthetic drinks including vitamin-enriched drinks, lactic acid bacteria drinks; mayonnaise, dressing, ketchup, soybean oil, sauce, mirin,
Containers for various seasonings such as vinegar, edible oil, and miso; soups,
Containers for liquid foods such as stew and curry; carbohydrate infusions, electrolyte infusions, plasma expanders, osmotic diuretics,
Containers for infusions such as amino acid infusions, fat emulsions, high-calorie infusions, medical liquid foods such as high-calorie foods, high-protein foods, and blood; Suitable as containers for detergents, cosmetics, agricultural chemicals, industrial chemicals, etc. It can be used for. [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: Height 60mm x
The width was 80 mm, the height to the lower end of the neck was 160 mm, and the height to the end of the mouth was 200 mm). 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: According to the specular gloss measurement method specified in JIS Z8741, the specular reflected luminous flux φs from the sample surface and the reflected luminous flux φ ₀ from the standard surface are measured at an incident angle of 60°, and Gs (% ) = φs/φ ₀ ×100. The measuring device used was an IG-310 gloss meter manufactured by Horiba, Ltd. Transparency: Total light transmittance, defined in JIS K6714
It is expressed as the ratio between the incident amount of light with a wavelength of 420 nm and the total amount of light transmitted.

【table】

[Table] As is clear from the results shown in Table 2 above, in the hollow container of the present invention, an aromatic compound having a relatively low melt flow temperature in the outer layer and a melt flow temperature close to the melting point of the resin used in the intermediate layer. Since polyester is used, coextrusion 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 rise, can be carried out stably. (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, 30
If the temperature exceeds 30°C, gelation will begin (see Comparative Example 2), so the temperature must be 30°C or lower, preferably 20°C.
It is stable below ℃. 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. Also,
When coextruded sheets are thermally welded to form a container, the heat sealing strength increases. [Effects of the Invention] As described above, the hollow container of the present invention has excellent gas permeability, moisture resistance, impact resistance, heat resistance, and heat sealability, as well as excellent transparency and gloss. Furthermore, the saponified ethylene-vinyl acetate copolymer used in the intermediate layer does not gel and can be coextruded using a common extrusion die. Moreover, the aromatic polyester used for the outer layer is cheaper than polycarbonate, which is conventionally used for the same purpose, so it can be used not only for medical containers but also for hollow containers in other fields at a cost-effective level.
Product value increases significantly.

Claims (1)

[Claims] 1. 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,
The intermediate layer is made of a saponified ethylene-vinyl acetate copolymer, and the outer layer has a gloss of 95% or more and has a melt flow temperature T ₀ (melting A hollow container characterized in that it is made of an aromatic polyester having a viscosity of 20,000 poise.