JPS6328018B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for forming a moisture-proof transparent film, and more particularly to a method for manufacturing a moisture-proof transparent film with excellent adhesion by obliquely vapor-depositing magnesium oxide onto a transparent plastic film substrate. BACKGROUND ART Packaging materials, particularly packaging materials used for packaging foods, medicines, chemical products, etc., must have a moisture-proof function to prevent the contents from deteriorating. In order to make bags using it, it is also necessary that heat sealing is possible. On the other hand, in the electronics industry, there is a demand for transparent films with extremely excellent moisture-proofing properties that can be used as protective layers for EL devices, solar cells, etc. Japanese Patent Publication No. 51-48511 discloses forming a vapor-deposited thin film of Six Oy on the surface of a plastic film, and then laminating a plastic film having heat-sealing properties thereon. However, the film obtained in this manner is not practical as a protective coating for packaging materials or EL devices because the vapor-deposited thin film of silicon oxide has poor moisture-proofing performance. JP-A-56-142059 and JP-A-Sho
Publication No. 54-118479 discloses a method for manufacturing a laminated plastic film having a vapor-deposited aluminum film, and a tubular composite film having a polyamide resin layer with a polyolefin resin on the inner surface and a metal vapor-deposited resin on the outer surface, respectively. . Since all of these methods involve laminating a film on which a metal such as aluminum is vapor-deposited onto a film base material, the resulting film cannot be transparent. Films whose contents cannot be seen through are also
It cannot be put to practical use as a packaging material or protective coating. OBJECT OF THE INVENTION An object of the present invention is to provide a method for producing a transparent film that has heat sealability and excellent moisture resistance. Another object of the present invention is to provide a method for producing a transparent laminate film having excellent adhesiveness and moisture resistance. Still another object of the present invention is to provide a method for manufacturing a transparent laminate film that does not require an anchor treatment step and has excellent moisture resistance and adhesion. SUMMARY OF THE INVENTION The method for producing a transparent film having moisture-proof properties of the present invention comprises applying evaporated particles of magnesium oxide obliquely to the surface of a transparent plastic film base material at an inclination angle of 30° or more to the normal line of the base material. The above object is achieved by forming a transparent thin film of magnesium oxide on the surface of the substrate by vapor deposition, and laminating a heat-sealable transparent plastic film on the transparent thin film. Ru. Transparent plastic film base materials include, for example, polyvinyl chloride, polystyrene, polypropylene, polyethylene, polyester, nylon,
Vinylidene chloride, polyvinyl alcohol, etc. are used. Of course, there is no need to be limited to this. There is no particular restriction on the shape of the film base material, and it may be a lens-shaped molded body as well as a plate shape. A thin film of magnesium oxide is formed on this film base material by a method such as vacuum evaporation, ion plating, or sputtering. The magnesium oxide is heated and evaporated by an appropriate heating means such as an electron gun or resistance heating, and as shown in the figure, the incident angle of the evaporated particles 3 of the magnesium oxide 2 with respect to the normal 10 of the transparent film base 1 is adjusted. A vapor-deposited thin film is formed on the film base material 1 at an inclination angle such that θ is 30° or more. The obtained magnesium oxide thin film has transparency and is also excellent in moisture resistance. Its surface has minute irregularities due to the self-shading effect during oblique deposition. Preferably, the layer thickness is in the range 100 to 5000 Å. If the layer thickness is too small, it will be difficult to form a deposited layer uniformly, resulting in poor moisture resistance. If it is too large, cracks are likely to occur in the deposited layer, which may reduce moisture resistance. Further, on the magnesium oxide thin film,
A transparent plastic film for heat sealing is laminated. Although there are no particular restrictions on the lamination method, extrusion lamination is most preferred. In this method, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer, etc. are melted and extruded into a film, and then, while the film is in a molten state, it is pressed onto a magnesium oxide thin film and cooled. This laminated heat-sealable film firmly adheres to the deposited thin film, so no anchoring is required. The reason why the heat-sealable film is firmly adhered to the vapor-deposited thin film is unknown, but the surface of the magnesium oxide thin film diagonally vapor-deposited on the film base material becomes many microscopic irregularities due to the self-shading effect during vapor deposition, which is due to the anchoring effect. It can be presumed that this is the case. Examples The present invention will be described below with reference to examples. Example 1 Magnesium oxide with a purity of 99% was heated and evaporated with an electron gun under a vacuum of 1×10 ^-4 Torr, and the OPP was evaporated onto a 90 μm thick biaxially oriented polypropylene (OPP) film at an incident angle of 60° ± 7°. It was deposited on a film. The layer thickness of the obtained magnesium oxide thin film is approximately
It was 1500Å. On this thin film, then the density
0.92 and low density polyethylene having a melt index (MI) of 2.0 was laminated to a thickness of 50 μm by extrusion lamination under normal conditions. The laminating strength, heat sealing strength, and moisture permeability of the obtained moisture-proof transparent film are shown in the table. Laminate strength and heat strength are 15mm
This is the peel strength in the 180° direction of the width of the strip. Moisture permeability is the water vapor permeability at 40°C and 90% RH based on JIS Z-0208. Example 2 Everything was the same as in Example 1 except that the incident angle of the evaporated particles of magnesium oxide with respect to the OPP film was set at 35°±5°. Comparative Example 1 Everything was the same as in Example 1 except that the incident angle of the evaporated particles of magnesium oxide with respect to the OPP film was set to 0°. Comparative Example 2 The same as Example 1 except that no magnesium oxide vapor deposited film was formed and an isocyanate anchor agent was applied on the film base material. Comparative Example 3 Everything was the same as in Example 1 except that no magnesium oxide vapor deposited film was formed.

[Table] Effects of the Invention In the present invention, as described above, since magnesium oxide is vapor-deposited obliquely to the film base material, the surface of the obtained magnesium oxide thin film has an excellent anchoring effect. Therefore, the heat-sealable film laminated on the magnesium oxide thin film can be firmly adhered to the vapor-deposited film without anchoring. Since anchor treatment is not required, there is no need to use harmful organic solvents, which improves the working environment and reduces operational constraints. The resulting transparent film is highly moisture-proof, so it is useful not only as a packaging material for foods, medicines, chemicals, etc., but also as a protective coating for EL devices, solar cells, etc.

[Brief explanation of the drawing]

The figure is an explanatory diagram illustrating a method of vapor-depositing magnesium oxide onto the film base material 1. 1... Transparent film base material, 2... Magnesium oxide, 3... Vaporized particles of magnesium oxide,
10... Normal line of the film base material.

Claims (1)

[Claims] 1. Magnesium oxide is deposited on the surface of a transparent plastic film substrate by obliquely depositing evaporated particles of magnesium oxide on the surface of the substrate at an angle of inclination of 30° or more with respect to the normal line of the substrate. 1. A method for forming a transparent film having moisture-proof properties, which includes the steps of forming a transparent thin film of an object, and laminating a heat-sealable transparent plastic film on the transparent thin film. 2. The method of claim 1, wherein the vaporized particles of magnesium oxide are deposited onto the plastic film substrate at an inclination angle of 30° C. or more relative to the normal to the substrate. 3 The layer thickness of the transparent thin film of magnesium oxide is
A method according to claim 1 in the range of 100 to 5000 Å. 4. The method of claim 1, wherein the heat-sealable transparent plastic film is laminated by extrusion lamination.