JPH043740B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a multilayer container having a saponified ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH resin) as an intermediate layer, and is filled with an aqueous mixture under pressure by providing a specific layer configuration. The present invention relates to a pressure-resistant barrier container that most effectively demonstrates the gas barrier properties of EVOH resin. Conventionally, EVOH resin has been widely used as a thermoplastic resin with excellent gas barrier properties in food and other packaging applications, along with polyvinylidene chloride resin and polyacrylonitrile resin. but
One drawback of EVOH resins is the humidity sensitivity of their barrier performance. In other words, EVOH resin has the disadvantage that its barrier performance against oxygen, carbon dioxide, etc. decreases when it absorbs water, and the degree of this decrease is small for all other thermoplastic barrier resins, so this phenomenon is not practical. It is not observed to the extent that it becomes a problem at the stage, and is unique to EVOH resin. EVOH resin also has relatively high water vapor permeability. To avoid these drawbacks
In most cases, hydrophobic resins such as polyethylene and polypropylene are laminated on both sides of the EVOH resin layer for practical use. In this case, the hydrophobic resin layers laminated on both sides serve to shield the EVOH resin layer from moisture, and at the same time provide properties such as mechanical properties, heat sealability, and appearance. Plastic containers that require gas barrier properties, especially oxygen barrier properties, are often used for food packaging, and familiar examples include mayonnaise, ketchup, shaved bonito, takuan, miso, syouyu, and so on.
Examples include edible oil, cheese, furikake, snack food, jam, pudding, etc. All of these examples are packaged with almost no pressure difference between the inside and outside, but barrier properties are required not only against oxygen but also against carbon dioxide gas. Glass and metal cans are the main containers for aqueous liquid drinks with an internal pressure of at least 0.5 kg/cm ² G, such as beer and cola, and plastic containers are used for some large cola bottles. It's nothing more than that. The main reason why plastic containers are not used in the field of pressure containers is that plastic has inferior gas barrier properties compared to glass and metal. In order to overcome these drawbacks of plastic containers, various attempts have been made to create pressure-resistant containers by combining barrier resins with other thermoplastic resins, but none have been fully satisfactory. EVOH resin has better processability and thermal stability than other thermoplastic barrier resins such as vinylidene chloride resin, and when distributed to a multi-manifold die device when compounding with other thermoplastic resins. As with other barrier resins such as vinylidene chloride resins, they may be exposed to relatively high temperatures due to heat from other adjacent resins, which must be processed at higher melt extrusion temperatures. It is an extremely preferable resin that does not generate gaseous products or the like. On the other hand, the reasons for this are not clear, but one possibility is that tension is applied to the container's constituent materials, and furthermore, it is thought that the content is an aqueous mixture and factors that affect the barrier properties. Composite containers with an intermediate layer of EVOH resin have traditionally been used as containers for aqueous liquid beverages with an internal pressure of at least 0.5 Kg/cm ² G (especially 1 Kg/cm ² G) such as beer, cola, etc. It has been found that these containers do not exhibit the barrier properties as well as containers that are used to package foods in a wet state with almost no pressure difference. In view of this situation, the inventors have developed an EVOH
As a result of various studies on multilayer containers that use resin as an intermediate barrier layer, we have largely eliminated various drawbacks when using EVOH resin as a material for multilayer pressure-resistant barrier containers for pressurized aqueous mixtures where the container components are subject to tension. This led to the completion of a new container. That is, the present invention has an ethylene content of 25 to 55 mol% and a saponification degree of vinyl acetate component of 96% or more.
A multilayer container including at least one intermediate barrier layer B formed mainly of EVOH resin, wherein 1 or 2 layers formed on the inner side of B
Inner layer group consisting of the above layers An and outer layer group consisting of one or more layers formed outside of B
A pressure-resistant barrier container having Cn and configured to satisfy the following formula (), and containing at least 0.5Kg/cm ² G (especially 1Kg/cm ² G) of beer, cola, etc.
It is an object of the present invention to provide a pressure-resistant barrier container in which the oxygen and carbon dioxide gas barrier properties are less deteriorated even when used for an aqueous liquid beverage with an internal pressure of 2,000 yen, especially an internal pressure aqueous carbonated beverage. Until now, little has been known about the relationship between the gas barrier properties and layer structure of pressurized aqueous liquid containers, and the reality is that they are considered to be the same as containers for non-pressurized aqueous liquids where no tension is applied to the container components. However, when the present inventors use EVOH resin, which is particularly sensitive to humidity and water content, in a composite form as a material for the pressurized aqueous liquid container, the present inventors found that when the EVOH resin is particularly sensitive to humidity and water content, it can be used in a composite manner as a material for the pressurized aqueous liquid container. We found that the pressure and water content during filling of pressurized aqueous mixtures were
As a result of studying the effect on the barrier properties of multilayer containers containing at least one layer of EVOH resin, we found that by creating a layer structure that satisfies specific conditions, it is possible to increase the tension in the container components when filling with an aqueous mixture. The present invention has completed a pressure-resistant barrier container for the pressurized aqueous mixture that has excellent oxygen and carbon dioxide gas barrier properties even when exposed to water. k≦0.75 () k= P alc/ P cla Here, la and lc are the total layer thicknesses of An and Cn, respectively, and P a and P c are the moisture permeability coefficients of the composite layer of An and Cn, respectively. As mentioned above, the inner layer group An is centered on the intermediate barrier layer B, which is mainly composed of EVOH resin with 25 to 55 mol% ethylene and a saponification degree of vinyl acetate component of 96% or more.
and the outer layer group Cn are disposed asymmetrically with respect to P/l, and the asymmetry is within a specific range defined by the formula (), only when the filling is an aqueous mixture and at least 0.5 kg/l cm ² G (especially 1Kg/cm ²
G) It is possible to significantly suppress the deterioration of the barrier performance of the EVOH resin layer under the practical conditions of a pressurized system in which tension is applied to the container constituent materials with internal pressure. This effect cannot be obtained when other barrier thermoplastic resins such as vinylidene chloride resins and acrylonitrile resins are used as the intermediate layer, and the effect is noticeable even for EVOH resins when the EVOH resin contains 55 mol% or less of ethylene. This is a unique property that can only be recognized when a resin is used as the intermediate layer B. The moisture permeability coefficients P a and P c in the present invention are values for the entire inner layer group An and the entire outer layer group Cn, respectively, and for the former, one side is 100% RH on the high humidity side (RH represents relative humidity). smell,
The value was measured at 30℃ with the other side set at 75% RH on the low humidity side, and for the latter, one side was set at the high humidity side.
This is a value measured at 30℃ with the other side at 75% RH and 50% RH on the low humidity side, and the P a, P
The effects of the present invention can only be enjoyed by providing the asymmetry that satisfies the expression () with respect to c. Regarding P a/la and P c/lc, a sheet with the same type of resin, density, and thickness as each layer of the inner layer group An and outer layer group Cn constituting the container was produced, and the sheet was subjected to the above conditions. It can be determined from the moisture permeability coefficient measured in The moisture permeability coefficient is usually calculated by determining the moisture permeability, and the moisture permeability can be measured according to ASTME96-63T. In the present invention, the value of k in equation () is 0.75
or less, preferably 0.005 to 0.5, more preferably 0.3 or less. That is, the remarkable effects of the present invention can only be enjoyed by configuring the container by increasing the degree of asymmetry with respect to P /l so that the value of k falls within the range. In other words, the value of k is
If it exceeds 0.75, the degree of improvement in barrier properties against oxygen and carbon dioxide gases will be reduced, and the effects of the present invention will be diminished. In addition, when the EVOH resin layer is located on the outermost side, the value of k is at least 0.005 to eliminate physical damage caused by friction, scratches, etc. during handling of the container and protect the barrier layer. It is more desirable to provide a protective layer. Further, the effect of the present invention is influenced by the relative humidity of the atmosphere with which the outermost layer of the outer layer group Cn is in contact, and the effect becomes more pronounced as the humidity decreases. However, the dependence of the effect on relative humidity does not impair the usefulness of the present invention, and as shown in the examples below, the barrier properties of the pressure-resistant barrier container of the present invention even at a relative humidity of 85%. is not out of the practically desirable range. However, in order to bring out the effects of the present invention more markedly, the relative humidity must be at least 95%.
% or less. The EVOH resin used in the present invention has an ethylene content of 25 to 55 mol% and a saponification degree of vinyl acetate component of 96.
The effect of the present invention is greater when the ethylene content is lower than 25 mol%, but when the ethylene content is less than 25 mol%, moldability deteriorates and satisfactory molding becomes difficult. Furthermore, if the ethylene content exceeds 55 mol%, the humidity sensitivity decreases, the effect of the present invention decreases, and the gas barrier properties decrease due to the increased ethylene content, making it impossible to maintain satisfactory barrier properties. . Furthermore, if the degree of saponification is less than 96 mol%, the gas barrier properties will be poor and it will not be possible to use it suitably in the present invention. The EVOH resin contains ethylene,
tertiary units other than vinyl alcohol and vinyl acetate units
Components and the like may be included within a range that does not significantly affect barrier performance, humidity sensitivity, etc. Intermediate barrier layer B is basically a single layer consisting of the above EVOH resin alone, but EVOH
In addition to a single resin layer, a blend layer of EVOH resin and other resins can be used within a range that does not impair the barrier performance, or a multi-layered layer of both can be used. In order for the effects of the present invention to be significantly exhibited, the layer thickness of the intermediate barrier layer must be at least 1 μm or more. If it is less than 1μ, it seems to be due to the occurrence of pinholes, cracks, etc. in the EVOH resin layer during molding, especially during stretch molding.
In many cases, the effects of the present invention are not substantially realized and the effects of the present invention cannot be enjoyed. Practically speaking, the EVOH resin layer serving as the intermediate barrier layer preferably has a thickness of 2 to 3 microns or more. Resins used for the inner layer group An include aromatic polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyolefin resins such as polyethylene and polypropylene,
Examples include combinations of one or more laminates and/or mixtures of polyamide resins such as 6-nylon, 66-nylon, and 12-nylon, and hydrophobic thermoplastic resins such as polycarbonate, polystyrene, and polyvinyl chloride. However, in view of the fact that the present invention is a container for an internally pressured aqueous mixture, the resin used for the innermost layer preferably has lower water absorption and moisture permeability, and for this reason, it is more preferable to use the resin after biaxial orientation crystallization. Furthermore, when the content is food, the resin used for the innermost layer _A1 is suitably selected from aromatic polyester resins and polyolefin resins from a hygienic standpoint. Among these, polyethylene terephthalate resin is preferred because it forms a bottle with excellent mechanical properties, particularly impact resistance and internal pressure resistance, by biaxial stretch blow molding of a preform such as a parison, and polypropylene resin is also preferred. Biaxially oriented crystallized hydrophobic thermoplastic resin is suitable for use in the innermost layer _A1 . Furthermore, when a layer containing recovered resin is used as one layer of the inner layer group An, it is preferable to use it as a layer other than the innermost layer A ₁ because the resin contains EVOH resin regardless of the amount. It is preferable that the layer in contact with the intermediate barrier layer B of the inner layer group An includes an adhesive resin layer that has adhesive properties to both the thermoplastic resin and the EVOH resin that are normally used in the layer. Depending on the type of hydrophobic thermoplastic resin used for the inner layer group, the adhesive resin may be carboxyl-modified polyolefin, carboxyl-modified ethylene-ethyl acrylate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, or modified SBR. , polyacrylate,
It can be appropriately selected from polyurethane, flexible polyamide, flexible polyester, and the like. Coextrusion, coextrusion lamination, coating, dry lamination, etc. can be used as a molding method for multilayer containers, and any combination of two or more of them can be used, so the adhesive resin can also be selected appropriately depending on the molding method. I can do it. As the resin used for the outer layer group Cn, hydrophobic thermoplastic resins and adhesive resins similar to those used for the inner layer group An can be used. In addition, solutions or emulsions of each resin can be used on the EVOH resin layer, and if necessary corona After surface treatment for improving adhesion such as treatment, it is also possible to coat directly or via an anchor coating agent. The fact that the outer layer group Cn is composed of the outermost coat layer and optionally an anchor coat layer means that the outer layer group can be easily made to a desired thickness, and that the inner layer group is biaxially oriented. In the case of a crystallized hydrophobic thermoplastic resin, this is a simple method to make the layer in the outer layer group Cn a biaxially oriented non-crystallized layer, and therefore the value of k can be kept in a smaller region. This is one of the preferred embodiments from the viewpoints of the above. The outermost layer may be printed, labeled, etc.
It also plays an important role in determining performance such as appearance gloss, mutual friction, and scratches, and also protects the EVOH resin layer from external water. More preferable resins from the above point of view include, but are not limited to, polyethylene terephthalate, ionomer resins, polyvinyl fluoride, polyvinylidene chloride, and polyacrylate. The resin used in the inner layer group An and the outer layer group Cn can contain antioxidants, ultraviolet absorbers, antistatic agents, colorants, fillers, lubricants, and other additives. For example, in the case of beer containers, it is necessary to block ultraviolet rays, so colored pigments such as iron oxide or ultraviolet absorbers can be added to one of the layers. In addition, resin layers and rejected containers generated during the container manufacturing process can be used as a single layer or mixed with new resin to form a single layer as part of the inner layer group An or outer layer group Cn. can. The present invention will be explained in detail below based on Examples, but the scope thereof is not limited. Examples 1 to 3 and Comparative Examples 1 to 3 EVOH resin with an ethylene content of 32 mol% and a saponification degree of vinyl acetate component of 99.5%, polyethylene terephthalate with an intrinsic viscosity of 0.85 dl/g, and a vinyl acetate content of 24% by weight as an adhesive resin. %, modified ethylene-vinyl acetate resin with maleic anhydride modification degree of 1.1% by weight was fed to three extruders, and the EVOH resin was
The molten resin is melted and kneaded at 220℃, 278℃ for polyethylene terephthalate, and 215℃ for adhesive resin, and the molten resins are bonded together in a die at a temperature of 250℃.
The outer layer group Cn is the adhesive resin (layer thickness 0.038 mm) and polyethylene terephthalate, the intermediate layer B is the EVOH resin (layer thickness 0.52 mm), and the inner layer group is the adhesive resin layer (layer thickness 0.038 mm) and polyethylene terephthalate. , and a composite pipe with an inner diameter of 9.5 mm and a total layer thickness of 4.7 mm of polyethylene terephthalate layers of Cn and An, cut this pipe into a length of 11.4 cm, heated both ends, and first cut one side. The end was welded blind and the other end was compression molded to form a thread to form the neck. The parison thus obtained is set in a blow mold, and the parison is approximately
After preheating to 90°C, biaxial stretch blow molding was performed at about 100°C. The outer diameter of the obtained hollow body is approximately 6.4 cm, the thickness of the adhesive resin layer is approximately 4μ for both An and Cn, the thickness of intermediate layer B is approximately 55μ, and the thickness of the adhesive resin layer is approximately 55μ for An and Cn.
The total polyethylene terephthalate layer in is
It was 350μ. Six hollow bodies with different k values were obtained by changing the layer configurations of the inner layer group An and the outer layer group Cn, and the oxygen permeation amount was measured by filling each hollow body with carbon dioxide saturated water. The results are shown in Table 1. It was shown to. The atmosphere in contact with the innermost layer and the outermost layer during the measurement is 20°C, respectively.
℃, 4atm・abs., relative humidity 100% and 20℃ atmospheric pressure, relative humidity 65%. The hollow bodies belonging to the invention exhibit good oxygen barrier properties.

[Table] Examples 4 to 7 and Comparative Examples 4 to 5 Inner layer group in Examples 1 to 4 and Comparative Examples 1 to 3
The procedure was as in Example 1, except that polypropylene resin was used instead of polyethylene terephthalate used in An, and 200°C was adopted as the melt-kneading temperature.The total thickness of the polypropylene resin layer and the polyethylene resin layer was 360μ, and the adhesive A hollow body was obtained in which the thicknesses of the agent layer and the EVOH resin layer were approximately the same as in Example 1, etc. 6 obtained by changing the layer composition of the inner layer group An and the outer layer group Cn
The hollow bodies with different numbers of k were each filled with carbon dioxide saturated water and the amount of oxygen permeation was measured, and the results are shown in Table 2. During this measurement, the atmosphere in contact with the innermost layer and the outermost layer was 20℃, 2.5atm.abs,
100% relative humidity and 20℃ atmospheric pressure, 50% relative humidity
It is. The hollow bodies belonging to the invention exhibit good oxygen barrier properties.

[Table] Examples 8 to 11 and Comparative Examples 6 to 7 In Examples 4 to 7, the ethylene content was 43 mol%,
A similar hollow body was obtained by carrying out the same procedure as in Examples 4 to 7 except that an EVOH resin whose vinyl acetate component had a saponification degree of 99.3 mol % was used. Six hollow bodies with different k obtained by changing the layer structure were each filled with carbon dioxide saturated water and the amount of oxygen permeation was measured, and the results are shown in Table 3. The atmosphere in contact with the innermost layer and the outermost layer during the measurement was 20℃, 3atm・abs., respectively.
100% relative humidity and 20°C atmospheric pressure, 50% relative humidity. The hollow bodies belonging to the present invention exhibited good oxygen barrier properties.

[Table] Examples 12 to 14 In Examples 1 to 3, the atmosphere in contact with the outermost layer at the time of oxygen permeation measurement was set at 20°C, atmospheric pressure, and relative humidity 85.
The same procedure as in Examples 1 to 3 was carried out except that % was used. The results are shown in Table 4 and show good oxygen barrier properties.

[Table] Example 15 and Comparative Example 8 In Example 1 and Comparative Example 1, the atmosphere in contact with the outermost layer was set to a relative humidity of 50%, and the measurement temperature was
The same procedure was carried out except that the temperature was 30°C, and the amount of carbon dioxide permeation in a steady state was measured. The results are shown in Table 5. However, the amount of carbon dioxide permeation is expressed as a relative value based on Example 15.

[Table] Compared to the case of Example 15, which belongs to the present invention, the amount of carbon dioxide permeation in the comparative example, which does not belong to the present invention, was 5.8 times that of the former. Examples 16-17 and Comparative Examples 9-10 In Example 1, the thickness of the intermediate barrier layer B was
Example 1 was carried out in the same manner as in Example 1, except that a composite pipe having a thickness of 0.19 mm was extruded to obtain a hollow body in which the intermediate barrier layer B had a thickness of 20 μm. The measured values of oxygen permeation amount are shown in Table 6 together with the value of k.

[Table] Example 18 In Example 1, the inner layer group An consisted of a polyethylene terephthalate layer (4.7 mm layer thickness) and the same adhesive resin layer (0.038 mm layer thickness) as in Example 1, and the intermediate layer B consisted of an EVOH resin layer ( A hollow body was obtained by extruding a composite pipe having a layer thickness of 0.52 mm and having no outer layer group, and otherwise operating in the same manner as in Example 1. The thickness of each layer of the obtained hollow body was 350μ for the inner layer group, the polyethylene terephthalate layer, and about 4μ for the adhesive resin layer.
The EVOH resin layer was approximately 55μ. The hollow body is coated with an ionomer resin emulsion (Corpolene latex (resin content: 40%) manufactured by Asahi Dow Co., Ltd.) by dip coating, and the temperature of the polyethylene terephthalate resin portion of the hollow body is raised to 70°C or higher. It was dried with warm air at 80°C, being careful not to cause any damage. The thickness of the coating layer was approximately 4μ. The k of the hollow body provided with the coating layer was 0.02, and the oxygen permeation amount measured according to Example 1 was 0.1 cc/m ² ·24 hrs.

Claims (1)

[Scope of Claims] 1. At least one intermediate barrier layer B formed mainly of a saponified ethylene-vinyl acetate copolymer having an ethylene content of 25 to 55 mol% and a saponification degree of vinyl acetate component of 96% or more. A multilayer container containing layers 1 or 2 formed inside B
At least 0.5 kg, having an outer layer group Cn consisting of one or more layers formed outside the inner layer group An and B consisting of the above layers, and satisfying the following formula (). Pressure barrier vessel for pressurized aqueous mixtures having an internal pressure of /cm ² G. k≦0.75 () k= P a・lc/ P c・la However, P a and P c are each at 30℃
It is the moisture permeability coefficient of An and Cn, and la and lc are the layer thicknesses of An and Cn. 2. The pressure barrier container according to claim 1, wherein k is 0.005 to 0.5. 3. A pressure barrier container according to claim 1 or 2, having an internal pressure of at least 1 Kg/cm ² G. 4. The pressure-resistant barrier container according to any one of claims 1 to 3, wherein the inner layer group An includes at least one layer made of a biaxially oriented crystallized hydrophobic thermoplastic resin. 5. The pressure-resistant barrier container according to any one of claims 1 to 4, wherein the innermost layer _A1 of the inner layer group An is a polyethylene terephthalate resin. 6. The pressure-resistant barrier container according to any one of claims 1 to 4, wherein the innermost layer _A1 of the inner layer group An is a polypropylene resin. 7. A layer in which the inner layer group An is made of a biaxially oriented crystallized hydrophobic thermoplastic resin, and an adhesive resin layer that has adhesive properties to both the hydrophobic thermoplastic resin and the saponified ethylene-vinyl acetate copolymer. A pressure-resistant barrier container according to any one of claims 1 to 6, which comprises two layers. 8. Inner layer group An consists of polyethylene terephthalate resin layer A ₁ located at the innermost layer and adhesive layer A ₂ , and outer layer group Cn consists of polyethylene terephthalate resin layer C ₁ located at the outermost layer and adhesive layer C ₂ . The pressure-resistant barrier container according to claim 1, 2, 3, or 7, wherein the intermediate barrier layer B is one layer. 9. The pressure barrier according to any one of claims 1 to 7, comprising a hydrophobic thermoplastic resin layer formed by a coating in which the outer layer group Cn is located as the outermost layer, and optionally an anchor coat layer. container. 10. A pressure-resistant barrier container according to claims 1 to 9, wherein the pressurized aqueous mixture is a pressurized aqueous carbonated beverage.