JPS6226312B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite film for deep drawing,
More specifically, when used as a bottom material for deep drawing to obtain a package containing contents such as sliced ham, it has good deep drawability and barrier properties against oxygen and moisture, and the gloss and transparency of the package. The present invention relates to a composite film which is characterized in that it has good properties, can be sterilized by boiling, and is free from wrinkles in the top of the package, which is most important in terms of appearance, and is prevented from curling. Deep drawing is a method in which the composite film is formed into a predetermined shape with a certain depth using a deep drawing machine such as the FV-600 series manufactured by Omori Kikai Co., Ltd., and then the contents such as sliced ham are removed. After filling, the composite film for the bottom material is molded using the machine described above in order to seal it with the composite film for the lid material and obtain a package, and the film referred to here is generally called a sheet. However, it is used as a general term that includes relatively thick products.
In the case of packages for sliced ham, etc., there are packages that are sterilized by boiling in order to be filled with ham in a general room, and non-boiled packages that are packaged in a sterile packaging room, and the composite film for bottom material of the present invention can be used for both. It is a composite film that can be used. Currently, deep drawing packaging is being widely adopted for packaging foods such as sliced ham, and the packaging materials used are also made by dry lamination, kneelam, tandem, or coextrusion methods. Although it is possible to make it by any method or a combination of these methods, as will be explained later, a composite film made by coextrusion has the desired performance, that is, good deep drawability, and is easy to package. The composite film of the present invention is preferably made by coextrusion because it does not cause wrinkles on the top of the body and has a more desirable anti-curl effect than those made by other methods. Conventional composite films for deep drawing include sealing resin layer/polyamide resin layer (Ny)/saponified ethylene-vinyl acetate copolymer layer (saponified EVA)/polyamide resin layer (Ny) (referred to as film) and seals. Polymer resin layer / Adhesive / PVDC cord polyamide resin layer (KNy) / Adhesive / Polypropylene resin layer (PP)
However, in the case of film, if the ambient air condition of the store where the package is placed is high, the surface layer may deteriorate.
The package curls outward due to the swelling of Ny, and when the humidity is low, the Ny in the surface layer is dehydrated and the package becomes the first layer.
As seen in the figure, the brim portion 1 of the package curled inward. In other words, NY is highly dependent on humidity among the external ambient conditions, making it difficult to obtain a curl-free package. Therefore, in order to obtain a package that is always curl-free and has good barrier properties regardless of the external ambient air conditions, we need a surface layer that is less dependent on humidity, in other words, has good moisture resistance and is advantageous in terms of cost. Polypropylene (PP) was selected for this reason, and an example of the composition is something like that seen in film, but the packaging obtained using this film has a surface layer that is
Because PP is less dependent on external humidity conditions, there was almost no curling at the store, but the corner 2 of the filling part was not reproduced exactly as the mold and had a rounded shape, and the contents such as film and sliced ham Due to poor adhesion to the top 3, radial wrinkles 4 appeared on the top 3, resulting in an unattractive appearance. It was found that wrinkles were caused by the surface layer PP grating and the adhesive layer during dry lamination, which inhibited elongation during molding. Therefore, the present inventors have conducted various studies to develop a composite film for deep drawing in order to obtain a package with good deep drawability, no curls or wrinkles, and good barrier and transparency properties. As a result, a composite film of the present invention was obtained. The key point in the composition of the composite film of the present invention is the material of the surface layer, and the material of the surface layer should be one that has little dependence on humidity in terms of curling, that is, has good moisture resistance and is free from wrinkles. As a result of various studies, we found that PP is basically suitable for the purpose of finding a material that has good deep drawability and good transparency so that it can adhere tightly to the contents of sliced ham, etc., and is also advantageous in terms of cost. The study revealed that the selection of PP grade is important. In other words, when it comes to curling of packaging, there are two types: curling at the store and curling during deep drawing.The curling at the store is largely due to the humidity dependence of the surface layer, as mentioned above.
However, the curl during molding differs considerably depending on the selection of the PP grade. In other words, in the case of crystalline resin such as PP, if it is molded at a temperature above the primary transition point, for example around 160°C, there will be less molding distortion, in other words, there will be less residual stress and there will be no curling during molding, but from the viewpoint of the material of the intermediate layer and sealing layer. There is a constraint that the molding temperature cannot be raised too much, and it is generally done at around 110℃, so the surface layer
PP is undesirable because it has large molding distortion and tends to curl during molding. Therefore, in order to find a grade of PP that does not require raising the molding temperature, the present inventors blended homopolymer PP and random copolymer PP and varied the blend ratio to select a grade that was less likely to crystallize. However, we decided to reduce the change in volume during the process from molding to cooling and to prevent curling. Random copolymer PP is a random copolymer of ethylene and propylene with an ethylene content of 3.
-8% range was used. We also investigated varying the melt index (MI) of blended PP in order to reduce molding distortion during molding, that is, to make it easier to mold.
Note that MI of PP indicates the flow characteristics of PP and is a representative value representing the characteristics of PP. The melt index of the blended PP is a value calculated from the following formula. log ^-1 (logA×CH/100+logB×CR/100) where A: Melt index of homopolymer B: Melt index of random polymer CH: Blend ratio of homopolymer (%) CR: Blend ratio of random polymer ( %) In addition, changing the thickness composition ratio of PP in the surface area of the composite film also affects the formability, which affects curls and wrinkles as well as the physical properties of the package. We investigated by changing the thickness composition ratio. As shown in Table 1, all of the surface layers of the investigated film configurations were made of PP, and the grade was varied as shown in Table 2. PVDC coated Ny (KNy), EVA as the middle layer
Saponified material, Ny, Ny/EVA saponified material, EVA saponified material/Ny and Ny/EVA saponified material/Ny are selected respectively, and the sealing layer that seals with the lid material is ionomer resin, ethylene-vinyl acetate copolymer resin. (EVA) and polyethylene (PE) to make 18 types of composite films as shown in Table 1. The surface layer of each composite film is PP.
An experiment was conducted by changing the grade of the sample as shown in Table 2. The resins used in Table 1 are as follows. KNy: Vinylidene chloride coated 6 nylon EVA Saponified product: Kuraray Co., Ltd. EVAL F Ny: 6 nylon ionomer resin: DuPont Surlyn 1601 EVA: Vinyl acetate content 7%, melt index 1.5 g/10 min ethylene vinyl acetate Copolymer PE: low-density polyethylene with specific gravity 0.92 and melt index 2.0 g/10 min. The thickness of all composite films was 150 μm. The thickness of KNy and saponified EVA in the middle layer is 15μ, and the thickness of Ny is 15μ in films No. 9 to 11.
20μ, 15μ for No.12-17, 10μ each for No.18-20
μ was used. Among them, film No. 7
The third one was the result of considering No. 12.
It is a table. From these results, homopoly

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[Table] Blending ratio of remer and random copolymer,
It was found that by selecting the melt index and the thickness composition ratio of the PP surface layer in the composite film, a package with good gloss and no curls or wrinkles could be obtained.As a result of further investigation, a combination within the following range was found. I found that it gave better results. Blend ratio of homopolymer/random copolymer: 30-70/70-30 MI: 2.0-6.0 Thickness composition ratio of surface layer PP in composite film:
5 to 25% Table 4 shows examples of composite films made with this combination range.
As can be seen from this table, no matter which film structure a composite film is used, if the surface layer PP material is within the above range, the package will not wrinkle or curl, and will have good barrier properties and transparency. In addition, the molding temperature was around 110°C, which was almost the same as the molding temperature of conventional composite films, so there was no particular problem in that the molding cycle did not decrease. In addition, the surface layer
Looking at the effect on the package when a combination of PPs outside the above range is selected, first of all, the blend ratio of homopolymer and random copolymer is 70%. This results in poor deep drawability and further deterioration in gloss and transparency. If the random copolymer blend ratio exceeds 70%, the softening temperature will drop too much and the film will stick to the mold during molding, making continuous molding impossible. Therefore, the homopolymer blend ratio should preferably be in the range of 30 to 70%.
40-60% is preferred. Next, regarding the surface area MI of PP, if it is less than 6, the softening temperature will drop too much and the film will stick to the mold, resulting in poor mechanical suitability.On the other hand, if it is less than 2, moldability will be poor and wrinkles will occur on the package. It becomes easier.
In this way, MI is preferably 2 to 6, preferably 3 to 5. If the thickness composition ratio of the surface layer PP to the composite film is lower than 5%, the moisture resistance, heat resistance, etc.
If the properties of PP are not utilized, and if 25% is rubbed, molding distortion will increase, which will have an adverse effect on curls and wrinkles.
Therefore, the thickness composition ratio of PP in the surface layer to the composite film is preferably 5 to 25%, preferably 10 to 20%. As described above, the composite film of the present invention has a surface layer of
By selecting a grade of PP, there will be no wrinkles on the top of the package, no curling of the package during molding or store display, and it has good barrier properties and is also heat resistant, so it can be packaged at temperatures above 80℃ for 10 to 30 minutes. It can withstand boiling sterilization, which is used to sterilize human bodies, has good transparency, and has good suitability for deep-draw packaging machines, that is, moldability, which is a basic requirement for obtaining packages. In addition, when this composite film is made by dry lamination, the surface layer and the intermediate layer and the intermediate layer and the sealing layer are bonded with adhesive, so this adhesive layer inhibits elongation during molding, resulting in deep drawing with a uniform thickness. In addition to being difficult to obtain molded products, the gas barrier properties deteriorate, and physical properties such as elongation between layers rapidly change, making wrinkles more likely to occur.In contrast, coextruded products simultaneously use an adhesive resin layer of polyolefin resin between the layers. Coextrusion is suitable as a method for manufacturing the composite film of the present invention because extrusion lamination slows the change in physical properties between layers and causes almost no wrinkles or deterioration of barrier properties. As described above, the composite film of the present invention has a homopolymer in the surface layer.
A blend of PP and random copolymer PP
By using PP (homopolymer bilend ratio of 30 to 70%), which has an MI of 2.0 to 6.0 and a thickness composition ratio of 5 to 25% of the composite film, wrinkles do not occur on the top of the package. A composite film for deep-drawn packaging that does not curl during molding or on store shelves, has good transparency, and has good barrier properties, and can be applied to both non-boiled and boiled packaging, and has good suitability for deep-drawn packaging. be.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing curling of the package. FIG. 2 is a perspective view showing the occurrence of wrinkles in the package.

Claims (1)

[Claims] 1 In a composite film consisting of a surface layer, an intermediate layer, and a sealing layer, the surface layer is a polypropylene resin that is a blend of a homopolymer polypropylene resin and a random copolymer polypropylene resin, and the blend ratio is 30 to 70% homopolymer. 1. A composite film for deep drawing, comprising a polypropylene resin layer having an index of 2 to 6, and a surface layer having a thickness composition ratio of 5 to 25% with respect to the composite film.