JPH02191B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite stretched film with excellent strength and oxygen and water vapor barrier properties, and a method for producing the same. Among the qualities generally required for food packaging films, strength, especially flexural strength, is extremely important, but other qualities, such as transparency, heat resistance, dimensional stability, etc., must be met and the flexural strength is There are very few films that are excellent. Polyamide biaxially stretched film is one of the few films that satisfy these conditions and is widely used in food packaging applications. Next, if the film has oxygen gas and water vapor barrier properties, when the film is used for food packaging, it will have the effect of extending the shelf life of the food, making it useful as a high-grade packaging film. Saponified ethylene-vinyl acetate copolymer (EVOH)
(abbreviated as ) film has excellent barrier properties and is a material that can be used as a high-grade food packaging film, but both non-oriented and oriented films have a drawback of low bending strength. This tendency is particularly strong when the ethylene component in EVOH is reduced in order to improve barrier performance. Furthermore, when the ethylene component is reduced, the barrier performance in a dry state becomes good, but the moisture resistance decreases and the barrier performance under high humidity conditions rapidly decreases. The inventors of the present invention have arrived at the present invention as a result of research into a method of effectively utilizing the qualities of polyamide film and EVOH film. In other words, a polyamide film and an EVOH film are laminated to cover the strength defects of the EVOH film, and a polyvinylidene chloride (hereinafter abbreviated as PVDC) layer with excellent moisture resistance is provided on the surface of the EVOH film to prevent the EVOH film from being exposed to high humidity. This is a film that takes full advantage of the properties of each polymer by preventing the barrier properties from deteriorating during the process, and then by biaxially orienting these laminated films. Biaxial orientation not only improves the strength of polyamide film, the strength, transparency, and barrier properties of EVOH film, but also surprisingly improves the strength of PVDC.
The barrier properties of the layers and the adhesion strength between the EVOH/PVDC layers are also significantly improved. The function of the polyamide film in the composite stretched film of the present invention is not only to improve the quality of the product film, that is, the practical strength that a packaging film should have, such as bending strength, pinhole strength, and drop bag strength, but also to produce a composite stretched film. It also has the effect of improving the process, that is, biaxial ductility. EVOH film especially has low ethylene content
The stretchability of EVOH film is not necessarily good.
When stretching a single film, non-uniform stretching and breakage during stretching tend to occur, and there are many restrictions on the composite magnification, stretching temperature, stretching speed, etc. However, when it is laminated with a polyamide film and stretched, Since it serves as a carrier for the stretching and deforming process and mainly controls the stretching ratio in the longitudinal and lateral directions throughout the entire stretching process, the EVOH film laminated to the polyamide film is also stretched uniformly over a wide range of conditions. The EVOH film constructed according to the present invention not only has gas barrier properties in terms of quality, but also has a relatively high Young's modulus that covers the low Young's modulus of polyamide film, strengthens the stiffness of the composite stretched film, and allows it to be used in the post-processing process. Improve work efficiency. For example, a biaxially stretched nylon 6 film is desired to have a thickness of 15μ or more from the viewpoint of workability, but in the composite film of the present invention, if the polymer and thickness structure are well designed, a thickness of 12μ can be sufficient for workability. There are things you can get. The polyamide film that is a component of the present invention includes linear polyamides such as nylon 6, nylon 66, and nylon 12, as well as copolymers and mixtures containing these components, and additives such as lubricants and antistatic agents. Including those with added. EVOH has an ethylene content of 15 to 59 mol% and a saponification degree of 98%.
That's all. The lower the ethylene content, the better the quality of the composite stretched film in terms of barrier properties and heat resistance, but the prevention of fish eyes during melt extrusion and the operability of biaxial stretching become more difficult. PVDC refers to vinyl chloride, acrylonitrile,
These PVDCs are copolymerized with acrylic acid esters, etc., and these PVDCs are applied to the EVOH film surface as an aqueous latex or solvent solution. The greater the polyvinylidene chloride component, the better the moisture-proofing performance, but the pot life of the latex or solution becomes too short and the uniform coating properties deteriorate. In the composite film of the present invention, the PVDC layer is
0.5~2μ is suitable, and the polyamide layer and
The thickness ratio of the EVOH layer is in the range of 3:7 to 7:3, and the optimal composition ratio is determined depending on the purpose of use. Further, the effects of the present invention are most clearly exhibited when the total thickness of the composite stretched film is in the range of 12 to 30 microns. Next, the manufacturing method of the present invention will be explained. Lamination of a polyamide film and an EVOH film is at least basically carried out using a coextrusion device that is a combination of three extruders and a three-layer T-die. The third extruder here is for the adhesive resin poured between the polyamide layer and the EVOH layer.
Modified polyolefin resin is generally used as the adhesive resin, but in the method of the present invention, shearing force may act on the interface during biaxial stretching in the post-process and inhibit adhesion, so the type of adhesive resin is Sufficient care must be taken in selecting the layer thickness. If particularly strong adhesive strength is required, it may be desirable to use a crosslinkable adhesive. Polyamide/
After obtaining an EVOH laminated non-oriented film, a PVDC aqueous latex or solvent solution is applied to the EVOH side of the film to form a multilayer film and dried until at least the coated surface loses its tackiness. Coating is performed using an air knife method, gravure roll method, reverse roll method, bar coating method, etc., and drying is performed using an arch type, floating type, etc. drying oven. before stretching
The primary purpose of applying PVDC is to also biaxially orient the PVDC layer to improve barrier performance, but the other effect is that this method improves the adhesion between EVOH/PVDC without anchoring. It turned out that it would. The reason for this is not clear even to the inventors, but it is thought to be related to the effect of the high-temperature heat treatment performed after stretching. Also, when applying PVDC water-based latex, water in the coating solution
Migrate into EVOH and plasticize EVOH, EVOH
The effect of increasing the stretchability is recognized.
A laminated film with a multilayer structure coated with PVDC is biaxially oriented by a simultaneous biaxial method, and the selection of simultaneous biaxial stretching as the stretching method is the biggest factor in realizing the present invention. Biaxial stretching methods of the flat method include a two-stage biaxial stretching method and a simultaneous biaxial stretching method, but the present invention cannot be realized with the two-stage biaxial stretching method.
Both polyamide and EVOH have strong crystallinity, and when a two-stage biaxial stretching method is applied, crystallization progresses in the first stage and inhibits the second stage's stretchability.The two-stage biaxial stretching method is used for longitudinal stretching. With hot roll drawing machine
The reason is that PVDC sticks to the heat roll. In a simultaneous biaxial stretching machine, both ends of a non-oriented film are gripped by clips attached to an endless link chain, and in a preheating zone where the clips advance in parallel, the film is heated to the stretching temperature, and in the next stretching zone, the distance between opposing clips is increased. The paper is stretched in the transverse direction by expanding in a divergent manner, and at the same time, the pitch between the clips in the machine direction gradually increases and the advancing speed of the clips increases, thereby causing the paper to stretch in the machine direction. Next to the stretching zone is a heat treatment zone where the clips run parallel to each other at a constant speed and hot air is blown at a high temperature, and the stretched film is thermally set in this zone. In the case of the present invention, the stretching ratio is 3 to 3.3 times in the longitudinal direction;
3 to 3.5 times in the transverse direction is suitable, and the stretching temperature is 60 to 150.
It is ℃. The heat treatment temperature is determined mainly by considering the melting point of EVOH, but in the case of EVOH of the same composition,
In the case of the present invention, since it is reinforced with polyamide having a higher melting point, it is possible to heat treat it at a higher temperature than when stretching it alone.
In the case of EVOH, when stretched alone, it may break due to the residual stretching stress at temperatures above 175°C, but when laminated with nylon 6, it does not break even when the temperature is raised to the melting point, and therefore, within the range where orientation relaxation is allowed. Can be heat treated at maximum temperature. In addition, polyamide/
Adhesion strength between EVOH is often increased,
The adhesive strength, which was reduced by the interfacial shear stress generated during the stretching process, is restored again. The heat-treated film is trimmed at both edges and then rolled up to form a product. The trimming edges must be made of polyamide alone or at least a polyamide/EVOH laminate. This is because when the PVDC layer is held by the clips of a stretching machine, it adheres and accumulates on the clips, causing stretching and cutting. If the coextrusion die is modified to laminate an EVOH layer narrower in width than the polyamide layer, the trimming selvage becomes a single polyamide layer and can be easily recycled. The biaxially stretched laminated film is subjected to post-treatments such as corona treatment and aging, if necessary. The thus obtained composite stretched film is printed and further laminated with a sealant to become a packaging material. The present invention provides at least polyamide/EVOH/
The present invention relates to a composite stretched film including a three-layer component of PVDC, and a film in which another layer is superimposed on the three-layer component is also included in the present invention. for example
This is a composite film in which a PVDC layer is provided not only on the EVOH side but also on the polyamide side, and in this case, the oxygen and water vapor barrier properties of the obtained film are further improved. The present invention skillfully combines materials such as polyamide, EVOH, and PVDC, each with its own characteristics.
Furthermore, the production method was achieved by making the most of the possibilities of in-line coating and simultaneous biaxial stretching, and this produced an ideal packaging film, which has great industrial value. Next, the present invention will be specifically explained with reference to Examples. Examples and Comparative Examples Nylon 6, EVOH with ethylene content of 30 mol%,
Three types of non-oriented laminated films with different thickness configurations were obtained by melting a carboxylic acid-modified polyolefin adhesive using three extruders, extruding it using a multi-manifold type three-layer die, and rapidly cooling it using a cooling roll. After applying a PVDC aqueous latex containing 92% by weight of vinylidene chloride to the EVOH side of the obtained film, it was fed into a simultaneous biaxial stretching machine and simultaneously biaxially stretched by 3.0 times in the longitudinal direction and 3.3 times in the transverse direction. A composite stretched film was obtained. The thickness structure of the obtained film (the thickness of the adhesive layer is 0.5 to 1μ) and the physical properties were compared to Nylon 6.
The table shows a comparison with that of a biaxially stretched film of EVOH alone.

【table】

[Table] As is clear from the table, the film of the present invention has EVOH
The bending resistance of the film has been improved without losing its oxygen gas barrier properties, and the moisture-proofing effect of the oriented PVDC layer means that the EVOH film's barrier properties do not deteriorate much even under high humidity conditions.

Claims (1)

[Scope of Claims] 1. A laminated film composed of at least multiple layers of polyamide/saponified ethylene/vinyl acetate copolymer/polyvinylidene chloride, and each of the multiple layers is biaxially oriented. A composite stretched film featuring: 2 Polyamide/ethylene laminated by coextrusion method
After applying an aqueous polyvinylidene chloride latex or a solvent solution to the ethylene/vinyl acetate copolymer saponified film surface of a non-oriented laminated film having a saponified vinyl acetate copolymer composition, the laminated film is simultaneously biaxially stretched. A method for producing a characteristic composite stretched film.