JPS6230912B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a highly transparent multilayer container with excellent gas barrier properties. More specifically, the container has a multilayer structure made of at least two types of thermoplastic resins, the outermost layer and the innermost layer are made of a thermoplastic polyester resin, the middle layer is made of a metaxylylene group-containing polyamide polymer, and The present invention relates to a highly transparent multilayer container with excellent gas barrier properties and mechanical properties, characterized in that the thin wall portion is oriented in at least one direction. Thermoplastic polyester resins, mainly composed of polyethylene terephthalate, have been used for various containers, films, sheets, etc. due to their excellent mechanical properties, gas barrier properties, chemical resistance, fragrance retention, and hygienic properties. It is processed and widely used as packaging material. In particular, in recent years, advances in blow molding technology, especially biaxial stretch blow molding technology, have led to remarkable use of hollow containers such as bottles and cans. However, biaxially oriented containers made of thermoplastic polyester resin mainly composed of polyethylene terephthalate do not have perfect performance, especially as food containers whose contents require gas barrier properties. It was unsuitable due to its lack of gas barrier properties against oxygen. So far, saponified ethylene-vinyl acetate copolymers and styrene-acrylonitrile copolymers have been known as thermoplastic resins with high gas barrier properties. There was nothing that could be put to practical use in terms of durability, impact resistance, or hygiene. The present inventors have conducted extensive research in order to improve the oxygen barrier properties of thermoplastic polyester resins without impairing their excellent mechanical properties, transparency, chemical resistance, and hygiene properties, and have found that thermoplastic polyester resins containing metaxylylene groups A solution to the problem was found by combining it with a polyamide resin, leading to the present invention. That is, the present invention provides a container having a multilayer structure made of at least two types of thermoplastic resins, wherein the outermost layer and the innermost layer are made of a thermoplastic polyester resin whose main repeating unit is ethylene terephthalate, and the middle layer is made of a metaxylylene group-containing polyamide. The present invention relates to a highly transparent multilayer container that is made of resin and has excellent gas barrier properties and mechanical properties, and is characterized in that the thin wall portion of the container is oriented in at least one direction. The thermoplastic polyester resin containing ethylene terephthalate as a main repeating unit in the present invention usually has an acid component of 80 mol% or more, preferably 90 mol% or more of terephthalic acid, and a glycol component of 80 mol% or more, preferably 90 mol% or more. It means a polyester in which ethylene glycol accounts for mol% or more, and the remaining acid components include isophthalic acid, diphenyl ether 4,4'-dicarboxylic acid, and naphthalene 1,4-
or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane 1,10-dicarboxylic acid, hexahydroterephthalic acid, and other glycol components such as propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, cyclohexane. Dimethanol, 2,2-bis(4-hydroxyphenyl)propane, 2,2
- bis(4-hydroxyethoxyphenyl)propane or p-oxybenzoic acid as oxyacid,
It means a polyester resin containing p-hydroethoxybenzoic acid or the like. Alternatively, a blend of two or more types of polyester may be used so that ethylene terephthalate falls within the above range. The polyester resin in the present invention may contain additives such as colorants, ultraviolet absorbers, antistatic agents, thermal oxidative deterioration inhibitors, antibacterial agents, and lubricants in appropriate proportions, if necessary. When this additive is used, it is particularly preferable to add it to the polyester resin for the outer layer. The thermoplastic polyester resin of the present invention must have an intrinsic viscosity of 0.55 or more, more preferably 0.65 to 1.4. If the intrinsic viscosity is less than 0.55, it is difficult to obtain a parison, which is a precursor molded body of a container, in a transparent amorphous state, and the resulting container also has insufficient mechanical strength. The meta-xylylene group-containing polyamide resin used in the present invention is composed of meta-xylylene diamine or a mixed xylylene diamine containing meta-xylylene diamine and para-xylylene diamine in an amount of 30% or less of the total amount, and a carbon number of 6 to 10. It is a polymer containing in its molecular chain at least 70 mol % of a structural unit formed from an α·ω-aliphatic dicarboxylic acid. Examples of these polymers include polymethaxylylene adipamide, polymethaxylylene sebacamide,
Homopolymers such as polymethaxylylenesperamide, and metaxylylene/paraxylylene adipamide copolymers, metaxylylene/paraxylylene pimeramide copolymers, metaxylylene/paraxylylene azeramide copolymers, etc. copolymers such as, as well as components of these homopolymers or copolymers with aliphatic diamines such as hexamethylene diamine, cycloaliphatic diamines such as piperazine,
Aromatic diamines such as para-bis-(2-aminoethyl)benzene, aromatic dicarboxylic acids such as terephthalic acid, lactams such as ε-caprolactam, ω-aminocarboxylic acids such as γ-aminoheptanoic acid, Examples include copolymers obtained by copolymerizing aromatic aminocarboxylic acids such as para-aminomethylbenzoic acid. In the above copolymer, paraxylylene diamine accounts for 30% or less of the total xylylene diamine, and the constituent units formed from xylylene diamine and aliphatic dicarboxylic acid account for at least 70 mol% in the molecular chain. That's all. In addition, these polymers include, for example, nylon 6, nylon 6, 6, nylon 6, 10, nylon
11, polymers such as nylon 12, antistatic agents, lubricants,
Anti-blocking agents, stabilizers, dyes, pigments, etc. may also be included. Meta-xylylene group-containing polyamide resin (hereinafter referred to as
Since SM resin (abbreviated as SM resin) itself is inherently brittle in an amorphous state, it is necessary to have a relative viscosity of 1.5 or more, more preferably 2.0 or more. The multilayer container according to the present invention has inner and outer layers made of thermoplastic polyester resin and an intermediate layer made of metaxylylene group-containing polyamide resin, but in some cases an adhesive layer is provided between the intermediate layer and the outer layer and/or between the intermediate layer and the inner layer. It is also possible to form. Conventionally, when a saponified ethylene-vinyl acetate copolymer known as a high gas barrier resin is used, since the resin itself is a crystalline resin, devitrification occurs during parison molding, resulting in a significant decrease in transparency. Of course, transparency can be improved by thinning the layer by stretching, but the portions that are not stretched, such as the bottom of the bottle, remain in a devitrified state, which is unfavorable in terms of appearance. Furthermore, when using a styrene-acrylonitrile copolymer, since it is an amorphous resin itself, it will not devitrify during molding, but its glass transition temperature is high, so it cannot be used under the stretching temperature suitable for polyester resin. It has the disadvantage that it cannot be extended sufficiently. Furthermore, since it is an amorphous resin and does not induce oriented crystallization even when stretched, it also has the disadvantage that the container deforms due to residual stretching stress. For these resins, SM resin itself is originally a crystalline resin, but since it has a relatively high Tg, it is easily amorphized by rapid cooling treatment from the molten state, giving it good transparency, and its Tg is higher than that of polyester resin. Since this is almost the same, oriented crystallization by stretching is sufficiently induced, and unlike the high gas barrier resins, the container has excellent transparency, gas barrier properties, and other physical properties, and has high commercial value. In the multilayer container of the present invention, the thickness of the intermediate layer made of SM resin in the main body is practically 5 .mu.m to 1 mm, preferably 10 .mu.m to 500 .mu.m. In addition, it is practical that the thickness of the polyester resin layer forming the inner layer and outer layer is 50 μ to 1 mm.
Preferably it is 100μ to 500μ. Further, the total thickness of the inner, outer and intermediate layers is practically 100μ to 2mm, preferably 200μ to 1mm. The container of the present invention can be manufactured according to conventional container manufacturing methods, but it is necessary that at least the thin wall portion of the container is oriented in at least one direction. The degree of orientation can be detected by measuring the difference in refractive index between the thickness direction and the plane direction of the thin wall portion of the container. If you expect excellent gas barrier properties and high transparency, it is desirable that the difference in refractive index between the plane direction and the thickness direction is 0.02 or more, and even more preferably 0.05 or more.If the difference in refractive index is 0.02 or less, sufficient mechanical strength is achieved. No improvement in physical properties or gas barrier properties can be expected. If it is difficult to measure by refractive index, it can also be detected by anisotropy of mechanical properties. Examples of the container of the present invention include containers obtained by a molding method involving stretching, such as bottles and pots. For example, in the case of bottles, methods for obtaining these containers include conventionally known extrusion blow molding methods or
Although there are axial stretch blow molding methods, biaxial stretch blow molding methods are preferred. In the case of the biaxial stretch blow molding method, after heating the expandable geometric shape with a multilayer structure (hereinafter referred to as parison) to the stretching temperature, a stretching rod and a compressed gas are moved axially in the blow mold. It can be expanded and shaped into a bottle by blowing into it. A parison having a multilayer structure is formed by forming one end of a multilayer pipe in a stepwise manner starting from the inner layer using a normal injection molding machine or a molding machine with multiple melt injection devices, or by using a multilayer extrusion molding machine. Obtained by bottoming out, etc. The parison can also be heated in a heating oven equipped with a conventional heating element such as a block heater or an infrared heater. The stretching temperature in the case of a multilayer parison made of the constituent components of the present invention may be approximately the same as that of a parison made of a single polyester resin, and is related to the glass transition temperature (Tg) of the polyester resin.
15〔℃ or more, [2 (Tg) + 15〕℃ or less, especially
80-150°C is preferred. Stretching is 1 to 4 in the axial direction.
It is preferable to stretch 2 to 7 times in the circumferential direction.In particular, by increasing the stretching ratio, the pressure bonding between the outer periphery and the intermediate layer, the intermediate layer and the inner layer, etc. improves, and the transparency also increases. More preferably, the area stretching ratio (stretching ratio in the axial direction x stretching ratio in the circumferential direction) is 5 to 18 times. The present invention will be explained below with reference to Examples. Furthermore, methods for measuring the main characteristics measured in the present invention are shown below. (1) Intrinsic viscosity of polyester resin [η]; Phenol/tetrachloroethane = 6/4 (weight ratio)
Measurement was performed at 80°C using a mixed solvent. (2) ηrel of polyamide resin: Relative viscosity measured at 25°C after dissolving 1 g of resin in 100 ml of 96% sulfuric acid. (3) Refractive index: Attach a polarizing plate to the Atsube refractometer,
Measured using sodium D line at 25°C.
Let the refractive index in the axial and circumferential directions (both plane directions) be nx and ny, and the refractive index in the thickness direction be nz, and calculate nx + ny/2-nz = △n (birefringence) to detect the degree of orientation. did. (4) Transparency and haze: Calculated using Hazemeter S manufactured by Toyo Seiki Co., Ltd. according to the following formula according to JIS-K6714. Transparency= _T2 / _T1 ×100(%) Haze= _T4 − _T3 ( _T2 / _T1 )/ _T2 ×100(
%) T ₁ ; Incident light amount T ₂ ; Total light transmission amount T ₃ ; Scattered light amount by the device T ₄ ; Scattered light amount by the device and sample (5) Oxygen permeation amount; Rika Seiki Kogyo dual-unit gas permeability meter It was measured by pressure change at 30°C using a method according to ASTM-D-1434-58.
(cc/m ²・24hr・atm) (6) Water vapor permeation rate; 40℃ according to JIS-Z-0208,
It was measured from the weight increase by the Cupp method at 90% RH. (g/m ²・24 hours) (7) Tensile properties: The yield strength was measured using a tanzag-shaped specimen with a width of 10 mm using a Tensilon manufactured by Toyo Baldwin Co., Ltd. under conditions of a chuck distance of 50 mm and a tensile speed of 50 mm/min. , the breaking strength and elongation were measured (23
℃). Examples 1, 2 and Comparative Example Polyethylene terephthalate (abbreviated as PET) with [η] = 0.72 was used as the polyester resin constituting the inner layer and the outer layer, and Example 1 was used as the meta-xylylene group-containing polyamide resin constituting the intermediate layer.
In the case of polymethaxylylene adipamide with ηrel=2.2 (methaxylylene/paraxylylene=99/
1 weight ratio) (abbreviated as SM-1), and in Example 2, polymethaxylylene adipamide (abbreviated as SM-2) obtained by copolymerizing SM-1 with 2.5% by weight of polyethylene glycol having a molecular weight of 4000 was used. Then, a multilayer parison with an outer diameter of 35 mm, a length of 140 mm, and a wall thickness of 5 mm was molded. In addition, in Comparative Example 1, [η]=
Using 0.72 polyethylene terephthalate,
A parison having the same shape as in Examples 1 and 2 was molded. The multilayer parison was first molded using polyester resin to form the innermost layer parison with a thickness of 2 mm, and then the molds were sequentially replaced to layer SM resin for the middle layer and polyester resin for the outermost layer. The thickness of each layer in this parison is inner layer: middle layer: outer layer = 2 mm: 1.5 mm: 1.5 mm. All molding was performed using an N-95 injection molding machine manufactured by Japan Steel Works. Table 1 shows the conditions at that time.
Shown below.

[Table] The open end of this parison was fitted into the parison fitting part equipped with a rotation drive device, and the parison was heated while rotating in an oven equipped with a far-infrared heater until the surface temperature of the parison reached 110℃. . After that, the parison was transferred into a blow mold and blow molded under the conditions of a stretching rod moving speed of 22 cm/sec and a compressed gas pressure of 20 Kg/cm ² to produce a beer with a total length of 265 mm, an outer diameter of the body of 80 mm, and an internal volume of 1000 ml. A bottle-shaped hollow container was obtained.
Table 2 shows the performance of these containers.

[Table]
The container obtained in this example has a lower transparency than a container made of polyethylene terephthalate alone.
It can be seen that the oxygen gas barrier properties are significantly improved without any sacrifice in mechanical properties.

Claims (1)

[Claims] 1 A container having a multilayer structure consisting of at least two types of thermoplastic resins, in which the outermost layer and the innermost layer are thermoplastic polyester resins with an intrinsic viscosity of 0.55 or more whose main repeating unit is ethylene terephthalate, and the middle layer contains metaxylylene groups. A multilayer container made of polyamide resin, characterized in that a thin wall portion of the container is oriented in at least one direction.