JPH0157674B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a saponified ethylene-vinyl acetate copolymer (hereinafter, a saponified ethylene-vinyl acetate copolymer is referred to as EVOH in this specification).
The invention relates to a laminated stretched film made by stretching a laminate consisting of a polyamide resin and a polyamide resin. When used as a base material film, the gas barrier properties do not deteriorate even in humid outside air.
The present invention relates to a laminated stretched film that can always maintain a high gas barrier and is optimal as a base film for lamination, and a laminated film using the laminated stretched film. In general, biaxially stretched polyamide films have excellent physical strength and are therefore widely used as packaging materials, particularly as base films for laminates.
However, although this film has superior gas barrier properties compared to films made of polyethylene, polypropylene, or ethylene-vinyl acetate copolymer, it still does not have sufficient gas barrier properties for food packaging, etc. I can't say it's what I'm doing. In addition, EVOH film has excellent gas barrier properties, and its characteristics are further improved by stretching, and it also has excellent transparency and gloss, so it can be used as a useful packaging material. generally known. For films with such high gas barrier properties, the ethylene content should be between 25 mol% and 45 mol%, and the degree of saponification should be 98% or higher.
EVOH is commonly used. However, since the film is hydrophilic, it has poor water resistance, boiling resistance, and moisture permeability, and has water absorption. Moreover, in the state of water absorption, the gas barrier properties are significantly reduced. Although such properties can be improved through a stretching process, it is still not sufficient. or,
Since EVOH is expensive, it is necessary to make it as thin as possible. Therefore, in order to combine the physical properties of biaxially oriented polyamide film with the gas barrier properties of biaxially oriented EVOH film, a film made by laminating these two types of films exhibits extremely excellent performance. considered to be a thing. As a method for producing such a laminated stretched film, there is a method in which each film is separately stretched and then dry laminated. However, with this method, the manufacturing process is complicated, and furthermore, it is difficult to make the EVOH layer thin. Therefore,
Another manufacturing method is to use polyamide resin and
Taking advantage of the very good adhesion with EVOH, the method of simultaneously biaxially stretching the coextruded laminated film is considered to be a preferable method because the process is simple and the EVOH layer can be made thin. This method is described in JP-A-52-115880 and the like. However, polyamide resin produced by the above method etc.
A two-layer stretched film with EVOH will suffer from curling due to the difference in the amount of shrinkage and heat shrinkage due to stress relaxation after stretching between the polyamide resin and EVOH, or the amount of natural expansion and contraction due to moisture absorption. Furthermore, when the two-layer stretched film is used for packaging bags etc. by laminating a sealant material on the polyamide resin layer side,
The outermost EVOH layer absorbs moisture from the outside air, significantly reducing the gas barrier properties that are the most important feature of this layer. Also, even when a polyamide resin layer is used as the outermost layer, the EVOH in the middle layer absorbs moisture due to the high moisture permeability of the polyamide resin layer.
This also impairs gas barrier properties. The inventors of the present application have conducted intensive research in order to eliminate the curling phenomenon in a laminated stretched film of polyamide resin and EVOH, and to prevent the deterioration of gas barrier properties due to humidity in a laminate film made of the laminated stretched film. As a result, a saponified ethylene-vinyl acetate copolymer layer A with an ethylene content of 25 mol% to 45 mol% and a saponification degree of 98% or more, a polyamide resin layer B, and an ethylene content of 35%
A laminated and biaxially stretched film (first invention of the present application) has been found in which saponified ethylene-vinyl acetate copolymer layer C having a saponification degree of 50% or more is laminated and biaxially stretched in the above order with a saponification degree of from 70 mol% to 70 mol%. . In addition, the laminated film (second invention of the present application), which is formed by laminating a sealant material on the saponified ethylene-vinyl acetate copolymer layer A side of this laminated stretched film (second invention of the present application), is highly gas resistant from dry to humid conditions regardless of the humidity of the outside air. In addition to exhibiting barrier properties, they have also found boiling resistance sufficient to withstand boiling sterilization. The laminated stretched films of the various inventions of the present application and the laminated films made of the laminated stretched films will be explained below. As mentioned above, the curling phenomenon of a two-layer stretched film made of polyamide resin and EVOH is thought to be due to the difference in the shrinkage rate and amount of thermal shrinkage due to stress relaxation after stretching of both layers, or the amount of natural expansion and contraction due to moisture absorption. It will be done. Therefore, in order to eliminate this curl phenomenon, a significant improvement can be made by devising the heat treatment method after stretching. However, it is extremely difficult to completely eliminate the curling phenomenon through the heat treatment process alone.
Moreover, if the heat treatment conditions are adapted only to eliminate the curling phenomenon, polyamide resin and
This may destroy the excellent characteristics of EVOH. Further, when the laminated stretched film is used as a heat-shrinkable laminate, sufficient heat treatment cannot be performed, and it is difficult to eliminate the curling phenomenon. However, in order to eliminate this curl phenomenon,
When considering the structure of the laminated stretched film, it is considered preferable to have a laterally symmetrical structure, that is, a polyamide resin layer, an EVOH layer, and a polyamide resin layer in this order, or an EVOH layer, a polyamide resin layer, and an EVOH layer in this order. Therefore, we made various prototypes of laminated stretched films with these configurations, and found that in both configurations, when both outer layers had approximately the same thickness, after heat treatment,
No curling phenomenon was observed even immediately after stretching. In addition, even if the thickness of one of the outer layers is within 3 to 4 times the thickness of the other layer, curling phenomenon is hardly observed and there is no problem in practical use. It seems that the curling phenomenon does not always occur depending on the thickness structure. Next, as mentioned above, the two-layer stretched film of polyamide resin and EVOH is made of polyamide resin layer and EVOH.
When a laminate film with either of the EVOH layers as the outermost layer is used for packaging bags, etc., it is affected by the humidity of the outside air and its gas barrier properties are significantly reduced. This is because the EVOH layer absorbs moisture from the outside air or moisture from the outside air permeates through the polyamide resin layer.
It is absorbed into the EVOH layer, and as a result,
This is thought to be because EVOH lost its original gas barrier properties. Conventionally, as a method for improving this point, a method has been considered in which a hydrophobic resin such as polyethylene, polypropylene, polyethylene terephthalate, etc. is laminated on the outermost layer. As a manufacturing method, there is a method in which these resins are formed into a film and dry laminated as the outermost layer. However, this method requires complicated steps such as forming these films and dry laminating them, resulting in a significant increase in the cost of the finished product. There is also a method of extrusion laminating these hydrophobic resins onto the laminated stretched film, but the interlayer adhesive strength is insufficient. In addition, hydrophobic resins such as polyamide resin and EVOH
A method of coextrusion stretching with polyamide resin or EVOH is also considered, but these hydrophobic resins do not have sufficient adhesion with polyamide resin or EVOH, and delamination occurs during coextrusion, so even if there is interlayer adhesion, the stretching process Sometimes delamination occurs. Based on the above, we have found a laminated stretched film consisting only of a polyamide resin layer and an EVOH layer, which has a structure that is not affected by the humidity of the outside air, and obtained a laminated film using this laminated stretched film. This was more strongly desired than before. However, when considering the structure of such a laminated stretched film, it is necessary that both outer layers be made of the same resin, either polyamide resin or EVOH, from the viewpoint of curling, as described above. Therefore, the order of polyamide resin layer, EVOH layer, polyamide resin layer,
Using a laminated stretched film consisting of an EVOH layer, a polyamide resin layer, and an EVOH layer in this order, a laminate film was prototyped and its gas barrier properties under humid conditions were investigated. As a result, both of the laminated films had poor gas barrier properties and were unsuitable for food packaging, which requires a high degree of gas barrier. The reason for this is thought to be the same as the reason for the laminate film consisting of a two-layer stretched film of polyamide resin and EVOH. The inventors of the present application have repeatedly investigated in detail the moisture permeability of the polyamide resin and EVOH film that serve as the outermost layer of the laminate film. As a result, the moisture permeability of unstretched polyamide film (30μ) is more than 100g/ ^m2・20hr, and even the biaxially stretched film (30μ) is about 60-80g/ ^m2・24hr, and the EVOH The unstretched laminate (30μ) also showed a large moisture permeability of 40 to 60 g/m ² ·24 hr. However, for highly gas barrier films, the
It has been found that EVOH, ie, EVOH with a high ethylene content and a low degree of saponification, exhibits a moisture permeability value close to that of hydrophobic resins. Therefore, the ethylene content of EVOH is 35 mol%.
When polyamide resin is laminated and stretched with 70 mol% of EVOH and a degree of saponification of 50% or more (hereinafter such EVOH is referred to as partial EVOH), ethylene, which is an EVOH with a conventional high gas barrier property, is produced. EVOH with a content of 25 mol% to 45 mol% and a degree of saponification of 98% or more (hereinafter such EVOH is referred to as high EVOH).
Similarly, the adhesiveness with the polyamide resin was good, and laminated stretching was possible, and no delamination occurred after stretching. However, parts like this
EVOH generally has low gas barrier properties, and when used for laminated stretched films with high gas barrier properties, it has been necessary to use a high EVOH layer in combination. Based on the above results, a laminated stretched film was produced by laminating partial EVOH and high EVOH on both outer layers of a polyamide resin layer and stretching. Similar to the laminated stretched film, no curling phenomenon occurred. Furthermore, when we investigated the gas barrier properties in humid conditions of the laminated film in which a sealant material was laminated on the high EVOH layer side of the prototype laminated stretched film, we found that the outermost layer had a high EVOH
Because the permeability of the layer is low and good, the high EVOH layer located in the middle does not absorb moisture from the outside air by passing through the partial EVOH and polyamide resin layer, always maintaining high gas barrier properties. The inventions of the present application have been achieved by discovering the following. Furthermore, since hydrophobic resin is generally used as the sealant material, the moisture permeability is low, and it is unlikely that the high EVOH layer will penetrate the sealant layer and absorb moisture, thereby impairing the gas barrier properties. Polyamide resins that can be used in each invention of the present application include:
Examples include polyε-caprolactam and polyhexamethylene adipamide, and these are preferred for packaging. However, copolymers or blends of these resins or other resins can also be used without departing from the gist of the present invention. Furthermore, there are no restrictions on adding additives such as heat stabilizers, plasticizers, lubricants, and ultraviolet absorbers. In addition, as for high EVOH, food packaging films with high gas barrier properties generally have an oxygen permeability of 2 to 5 c.c./m not only in a dry state but also at 25°C and 70% RH. Since it is required to be ^2.24 hours or less, it is necessary to meet the following conditions. That is, the ethylene content ranges from 25 mol% to 45 mol%.
The saponification degree is more than 98% EVOH. If the ethylene content exceeds 45 mol %, the gas barrier properties will be reduced and the film cannot be used as a high gas barrier film. If the ethylene content is less than 25 mol %, the ethylene content will be so low that extrusion and stretching will be difficult. Further, even if the ethylene content is from 25 mol% to 45 mol%, if the degree of saponification does not reach 98%, the gas barrier properties will deteriorate. Part that maintains gas barrier properties of high EVOH layer
As EVOH, it is necessary to select an EVOH that has lower moisture permeability than gas barrier properties, and has good water resistance and boiling resistance. From this point of view, it is considered that the EVOH having a higher ethylene content and a lower degree of saponification are more preferable. However, if the ethylene content becomes too high or the degree of saponification becomes too low, the adhesiveness with polyamide resin will decrease, and moreover, if the ethylene content becomes too high or the degree of saponification becomes too low, the
The stretching conditions, stretching stress, etc. are too different between the two, making lamination stretching impossible or causing delamination. Even more like this
When EVOH is used, even if lamination stretching is possible, the amount of shrinkage due to stress relaxation after stretching, the amount of heat shrinkage, or the amount of natural expansion and contraction due to moisture absorption, etc., are significantly different from those of high EVOH, resulting in curling phenomenon. This does not meet the purpose of the inventions of the present application, which attempts to eliminate the curling phenomenon by laminating EVOH on both outer layers of the resin. Based on the above, the parts used in each invention of the present application
EVOH must have an ethylene content of 35 mol% to 70 mol% and a saponification degree of 50% or more. If the ethylene content is less than 35 mol%, the moisture permeability, water resistance, and boiling resistance will be poor, and the high gas barrier properties of the high EVOH layer will not be able to protect from the humidity of the outside air. In addition, the ethylene content
If it exceeds 70 mol%, polyamide resin and high
Lamination and stretching with EVOH becomes difficult. Even if lamination and stretching were possible, delamination or curling would occur, making it unusable. Furthermore, even if the ethylene content is between 35 mol% and 70 mol%, if the degree of saponification is less than 50%, lamination and stretching may be difficult, and delamination or curling may occur, just as in the case of high ethylene content. As a result, it was still unusable. In addition, in terms of the gist of the second invention of the present application, when a sealant material is laminated on a laminated stretched film,
The part used as the outermost layer to prevent moisture permeation.
EVOH with higher ethylene content than high EVOH ethylene content as gas barrier layer
Of course you can choose. Moreover, it is natural from the gist of the second invention of the present application that the degree of saponification of partial EVOH is preferably lower than the degree of saponification of high EVOH. In addition, there are no restrictions on blending other resins or adding additives such as heat stabilizers, plasticizers, lubricants, colorants, and ultraviolet absorbers to both EVOHs without changing the gist of the inventions. It's not something you can do. Although the thickness of each layer of the laminated stretched film of each invention of the present application and the laminated film using the laminated stretched film is not particularly limited, the thickness of the polyamide resin layer is 5 μm or more from the viewpoint of physical properties when used as a packaging film. Approximately 15μ is preferable. Also, high
The EVOH layer is preferably 2μ or more from the viewpoint of gas barrier properties, and preferably 10μ or less from the viewpoint of product cost. Further, the partial EVOH layer preferably has a thickness of about 3μ to 15μ from the viewpoint of moisture permeability, and it is preferable that the thickness of the layer is not much different from that of the high EVOH layer from the viewpoint of curling of the obtained laminated stretched film. . However, if the thickness of one EVOH layer is up to about 3 to 4 times the thickness of the other EVOH layer, the curl phenomenon hardly becomes a problem.
Further, the layer thickness of the sealant material is generally about 20 to 30 microns. Furthermore, as for the stretching ratio of the laminated stretched film in each invention of the present application, it is preferable to stretch at a high ratio because this improves many physical properties such as gas barrier properties and moisture permeability resistance. Generally, the stretching ratio is 2.5 times or more, preferably 3.0 times or more in both the longitudinal and transverse directions. However, the possible stretching ratio of a laminated stretched film of polyamide resin and EVOH is about 4 times at most. It goes without saying that the laminated stretched films of each invention of the present application do not cause any curling phenomenon that would pose a practical problem.
Because it is stretched, it has significantly improved gas barrier properties and moisture permeability compared to unstretched films, and
This film has a high initial elastic modulus, is strong and has excellent optical properties. Furthermore, since polyamide resin is used for the intermediate layer, it has excellent physical strength such as tensile strength and impact strength, but the
Since an EVOH layer is also used, the tear strength, which is a common drawback of stretched products, is not significantly reduced. It also has many properties suitable as a base film for lamination, such as very good printing suitability for high EVOH layers. Furthermore, the laminated film of the second invention of the present application, in which a sealant material is laminated on the high EVOH layer side of the laminated stretched film, exhibits extremely high gas barrier properties in a dry state, but it also exhibits extremely high gas barrier properties in a humid state. It also maintained high gas barrier properties.
In addition, in terms of boiling resistance, high
EVOH is used as the middle layer and has good hot water resistance.
It was good because EVOH was on the surface layer.
Moreover, the laminate film has many useful features as a laminate film, particularly as a laminate film for food packaging, such as the high EVOH layer does not absorb moisture from the outside air, so the stiffness of the film does not decrease. The laminated stretched films of each invention of the present application have high EVOH,
It is obtained through a step of stretching an unstretched laminated film obtained by laminating a polyamide resin and a partial EVOH in this order. The lamination method includes a coextrusion method, an extrusion lamination method, a dry lamination method, etc., and the coextrusion method is preferable because the process is simple. The coextrusion method is not particularly limited, but in-die adhesion is generally preferred. In addition, there are two stretching methods: tenter method and inflation method, but simultaneous biaxial stretching is preferable for EVOH stretching, and considering that tenter method simultaneous biaxial stretching equipment is very expensive. and,
Simultaneous biaxial stretching using an inflation method seems to be effective. A specific example of a manufacturing method is to coextrude a tube-shaped laminated raw film in which these three types of resin are laminated in a predetermined order, and then heat the film between two sets of Nippro rolls with different peripheral speeds using an external heating device. There is also a method of simultaneous biaxial stretching using internal gas pressure. At this time, the moisture content of the original fabric is maintained at 2.0 wt % or less, and the original fabric is passed through a continuous heating zone that is preheated to 50°C to 100°C within 5 seconds, and then stretching is immediately started. Moreover, in the stretching zone,
The tube-shaped film is heated to a temperature higher than the preheating temperature, and then simultaneous biaxial stretching is performed under conditions such that the maximum temperature is approximately at the center of the stretching zone. When the obtained laminated stretched film is used as a heat-shrinkable film, it is used without heat setting or after some heat setting. When used as a general laminate base film, it is heat-set to eliminate heat-shrinkability. Note that heat fixing methods include an inflation method, a tenter method, or a combination of both methods. Moreover, the laminated film of the second invention of the present application has a higher height than the laminated stretched film of the first invention of the present application.
Obtained by laminating a sealant material on the EVOH layer side. As the laminating method, a conventionally commonly used method can be used. However, in the case of extrusion lamination, the interlayer adhesion between the high EVOH layer and the sealant material, such as polyethylene or ethylene-vinyl acetate copolymer, is not sufficient, so it is necessary to use an adhesive resin or the like between the layers. It is necessary to devise measures such as inserting it using the following method. On the other hand, in the case of the dry lamination method, the adhesive strength between the high EVOH layer and the sealant material layer is strong and lamination can be easily performed if a conventional general adhesive is used and the sealant material layer is used in a conventional manner. Seems to be the preferred method. As described above, the laminated stretched film of the first invention of the present application does not have the curling phenomenon that poses a practical problem.
It has excellent physical properties such as tensile strength and impact strength, and optical properties, and is very useful as a base film for heat shrinkage or general lamination. Furthermore, the laminated film of the second invention of the present invention obtained by laminating the laminated stretched film of the first invention of the present application with a sealant material has not only the effects of the first invention described above, but also has always high gas barrier properties regardless of the humidity of the outside air. It continues to maintain the same properties and has good boiling resistance, so it exhibits its characteristics as a laminate film for heat-shrinkable packaging or a laminate film for general packaging that requires a high degree of gas barrier property. Therefore, the laminated stretched films of the present invention and the laminated films made of the laminated stretched films will greatly contribute to the industry, especially the food packaging field. Examples and comparative examples of each invention of the present application are shown below,
The usefulness of each invention of the present application will be further clarified. Example 1 High EVOH and polyε-caprolactam with an ethylene content of 29 mol% and a saponification degree of 99% or more and a part with an ethylene content of 45 mol% and a saponification degree of 96%
Co-extrude EVOH and EVOH in this order into a tube shape,
Unstretched laminated tubes with various thickness configurations were obtained by water cooling. The moisture content of these unstretched laminated tubes was maintained at 2.0wt% or less, and the continuous heating zone passage time for preheating to 70°C was 2.6 seconds, so that the tubes in the stretching zone were heated to a temperature higher than the preheating temperature, and moreover, at approximately the center of the stretching zone. While heating the film to a maximum temperature of 80° C., simultaneous biaxial stretching was carried out by 3 to 4 times in both the longitudinal and transverse directions using an inflation method to obtain laminated stretched films of various thickness configurations. Next, the laminated stretched film was heat-set by an inflation method at 170° C. while shrinking by 5% in both the longitudinal and transverse directions. Tables 1 and 2 show the presence or absence of curling phenomenon and various physical properties of the obtained laminated stretched film.

【table】

[Table] Example 2 Height of the laminated stretched film of Example 1 Test No. 2
A 30μ low density polyethylene film was dry laminated as a sealant on the EVOH layer side using a urethane adhesive. Table 3 shows the physical properties of the obtained laminate film, the physical properties of the bag made from the laminate film, and its packaging suitability.

[Table] Comparative Example 1 Part of the laminated stretched film of Example 1 Test No. 2
A 30μ low density polyethylene film was dry laminated on the EVOH layer side in the same manner as in Example 2. However, the obtained laminate film has a low oxygen permeability.
8.4cc/ ^m2・24hr at 23℃, 75%RH and Example 2
It showed a significantly inferior value, and could not be used as a laminate film with high gas barrier properties. Moreover, even in the boiling test, the height of the surface layer was
The EVOH layer was slightly whitened and could not be used as a laminated film for food packaging. Comparative Example 2 Various types with different ethylene content and saponification degree
EVOH was coextruded onto both outer layers of polyε-caprolactam, and various laminated stretched films were prototyped.
As a result, no good laminated stretched film was obtained in any of the configurations shown in Table 4. The thickness of each layer is 10μ for the polyamide resin layer.
When laminating, the sealant layer side
The EVOH layer was 5μ, and the outermost EVOH layer of the laminated film was 10μ.

【table】

Claims (1)

[Claims] 1. A saponified ethylene-vinyl acetate copolymer layer A having an ethylene content of 25 mol% to 45 mol% and a saponification degree of 98% or more, a polyamide resin layer B, and an ethylene content of 35 mol%. A laminated stretched film characterized in that a saponified ethylene-vinyl acetate copolymer layer C having a saponification degree of 50% or more and a saponification degree of 50% or more is laminated and biaxially stretched in the above order. 2 Ethylene-vinyl acetate copolymer saponified layer A having an ethylene content of 25 mol% to 45 mol% and a saponification degree of 98% or more, a polyamide resin layer B, and an ethylene content of 35 mol% to 70 mol% A saponified ethylene-vinyl acetate copolymer layer C having a degree of saponification of 50% or more is laminated in the above order and a sealant is applied to the saponified ethylene-vinyl acetate copolymer layer A side of the biaxially stretched laminated stretched film. A laminate film characterized by laminated materials.