JPS6330988B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field: The present invention relates to a method for forming a transparent thin film having moisture resistance;
In particular, the present invention relates to a method of forming a transparent and highly moisture-proof thin film on an organic substrate. Prior Art: Packaging materials, especially packaging materials used for packaging foods, medicines, chemical products, etc., must have a moisture-proofing function to prevent the contents from deteriorating.
To this end, conventionally, for example, aluminum foil has been bonded to a base plastic film to take advantage of the moisture-proof properties of the aluminum foil. Although the packaging material in this case has excellent moisture resistance, the transparency of the base plastic film is impaired and the contents cannot be seen through. Moreover, since the flexibility is extremely reduced, pinholes may occur. Other examples of packaging materials include vinylidene chloride-based and fluorine-based resin films which themselves have moisture-proof properties. These films must be thick for applications where moisture resistance is strictly required, and various problems arise in the manufacturing process. Attempts have also been made to improve moisture resistance by vacuum-depositing metallic aluminum onto the surface of plastic. However, since the aluminum vapor-deposited film is opaque, when it is used as a packaging material, the contents cannot be seen through. Furthermore, since the adhesion strength between the vapor-deposited aluminum and the base film is relatively low, there is a risk that peeling may occur at the interface. In order to improve these drawbacks of conventional packaging materials, for example, Japanese Patent Publication No. 51-48511 proposes providing a vapor-deposited layer of silicon oxide on the surface of a plastic film to obtain a transparent moisture-proof film. In this silicon oxide vapor-deposited film, the silicon oxide is slightly dissolved in water, so its moisture-proofing performance deteriorates over time. Also, JP-A-54-
Publication No. 152089 discloses a polyester film on which metals, metal oxides, and silicon oxides are deposited. This vapor-deposited film can exhibit its moisture-proofing performance only when a polyester film is used as the base material. In recent years, EL has been increasingly used in the electronics industry.
A transparent film having a high degree of moisture resistance is increasingly required as a protective film for elements, solar cells, and the like. OBJECT OF THE INVENTION: An object of the present invention is to provide a method for forming a transparent thin film having high moisture resistance on an organic substrate. Another object of the present invention is to provide a method for forming a thin film with excellent adhesion to a substrate. Summary of the invention: The thin film forming method of the present invention is to form a transparent magnesium oxide thin film on an organic substrate by heating and evaporating metallic magnesium while introducing oxygen gas into a vacuum chamber. The above objective is achieved. The base material used is an organic film made of transparent and highly flexible polyvinyl chloride, polypropylene, polyethylene, polyester, polyvinylidene chloride, nylon, polyvinyl alcohol, fluororesin, or the like. Note that the base material may be plate-shaped or may be a lens-shaped plastic molded body. There is no particular limit to the thickness of the film, but considering workability, it should be 5 μm or more.
300 μm is preferred. Oxygen gas is supplied to this transparent film and a magnesium oxide thin film is formed by reactive vapor deposition. Specifically, the film is placed in a vacuum chamber, and while the vacuum chamber is evacuated by a vacuum pump, oxygen gas is introduced, and metal magnesium is heated by a known heating method such as resistance heating or electron beam heating. This heating generates magnesium vapor. This magnesium vapor reacts with the introduced oxygen gas to form a magnesium oxide thin film on the substrate. The amount of oxygen gas to be introduced is normally determined appropriately depending on the container of the vacuum chamber, the exhaust capacity of the vacuum pump, the evaporation rate ^{of magnesium} , etc. It is preferable to adjust it so that it becomes tall. When the oxygen partial pressure is lower than 1×10 ⁻⁴ Torr, the amount of oxygen in the formed magnesium oxide thin film decreases, resulting in coloration and loss of transparency. If the oxygen partial pressure is higher than 1×10 ⁻³ Torr, the quality of the formed magnesium oxide thin film becomes porous and the moisture proofing property decreases. The magnesium oxide thin film can be formed not only by reactive vapor deposition but also by reactive ion plating. The thin film obtained by this method has no difference in performance from the thin film obtained by the above-mentioned reactive vapor deposition method. The thickness of the magnesium oxide thin film is 0.01μ.
m to 0.5 μm is preferable. If the film thickness is less than 0.01 μm, it is difficult to form a uniform continuous film. As a result, moisture resistance is significantly reduced. If the thickness is 0.5 μm or more, cracks are likely to occur in the formed magnesium oxide thin film, resulting in a decrease in moisture resistance. Examples: The present invention will be described below with reference to Examples. Example 1 A polyethylene terephthalate (PET) film with a thickness of 15 μm was used as a base film, and this was placed in a vacuum chamber. After the inside of the tank was evacuated to 1×10 ⁻⁵ Torr, oxygen gas was introduced so that the oxygen gas partial pressure during vapor deposition became 3×10 ⁻⁴ Torr. purity
When 99.9% metallic magnesium is heated by resistance heating and the distance between the evaporation source and the PET film is 25cm, the film formation rate of magnesium oxide is approximately 100%.
Vapor deposition was carried out at a rate of Å/min. Two types of deposited thin films with thicknesses of 1000 Å and 2000 Å were obtained.
The moisture permeability of the transparent vapor-deposited film thus obtained is shown in the table together with the transparency. Moisture permeability is JISZ−
Shows the water vapor transmission rate at 40℃ and 90%RH based on 0208. Transparency was measured by visual observation, and those with excellent transparency are indicated as +, those with good transparency are indicated as +, and those that are opaque are indicated as -. Example 2 The same as Example 1 except that the oxygen gas partial pressure was adjusted to 6×10 ⁻⁴ Torr. The results are shown in the table. Example 3 The same as Example 2 except that a biaxially stretched polypropylene film was used as the base film. The results are shown in the table. Comparative example 1 PET with a thickness of 15 μm under a vacuum degree of 5 × 10 ^-5 Torr
SiO was deposited on the film to two thicknesses of about 1000 Å and 2000 Å. The moisture permeability and transparency are shown in the table. Comparative example 2 PET with a thickness of 15 μm under a vacuum degree of 5 × 10 ^-5 Torr
SiO ₂ was deposited on the film to two thicknesses of about 1000 Å and 2000 Å. The moisture permeability and transparency are shown in the table. Comparative Example 3 Everything was the same as in Example 1 except that the oxygen partial pressure during vapor deposition was 5×10 ⁻⁵ Torr.
The results are shown in the table.

[Table] Effects of the invention: The thin film obtained by the method of the invention is transparent and has excellent moisture resistance, regardless of the type of organic base film. Moreover, its moisture resistance is extremely improved compared to conventional silicon oxide vapor-deposited films.
The adhesion of the magnesium oxide film according to the present invention to the base film was also good, and it passed the peel test according to JISD-0202. The transparent plastic film coated with the transparent thin film of the present invention has unprecedented moisture-proofing performance, and is therefore useful as a packaging material for foods, pharmaceuticals, and chemicals, as well as for protecting EL elements and solar cells in the electronics industry. Ideal as a membrane.

Claims (1)

[Scope of Claims] 1. A method for forming a transparent thin film having moisture-proof properties, which forms a transparent thin film of magnesium oxide on an organic substrate by heating and evaporating metallic magnesium while supplying oxygen gas in a vacuum chamber. 2 By controlling the supply amount of the oxygen gas, the oxygen partial pressure during metal magnesium vapor deposition is set to 1 × 10 ^-4 ~
1. The method according to claim 1, wherein the torr is 1×10 ⁻³ Torr. 3. The method according to claim 1, wherein the base material is a transparent flexible sheet or film.