JPH05140750A - Formation of organic polymer film - Google Patents

Abstract

PURPOSE:To form a Parylene film excellent in characteristics on one of various substrates with satisfactory adhesion by subjecting the surface of a plasma polymerized film formed on the surface of the substrate to plasma treatment in gaseous oxygen and synthesizing poly-p-xylylene in a vapor phase. CONSTITUTION:An Mg alloy casting 10 as a substrate is subjected to plasma treatment in an atmosphere based on gaseous hydrocarbon or an organosilicone compd. to form a plasma polymerized film 20 of about 100-200nm thickness on the surface of the substrate. This film 20 is subjected to plasma treatment in an atmosphere contg. gaseous oxygen or argon to etch the surface of the film 20 to about 20nm depth. By this etching, carbonyl and hydroxyl groups on the surface are decomposed and contaminants are removed. A Parylene film 30 is then formed on the film 20 by vapor phase synthesis in about 2nm thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an organic polymer film, and more particularly to a method for improving the adhesion of a parylene film to a substrate by a vapor phase synthesis method.

[0002]

2. Description of the Related Art A parylene film is a coating film made of a polyparaxylylene resin developed by Union Carbide Chemicals & Plastics Company of the United States by a vapor phase synthesis method. This coating film is formed by vaporizing and thermally decomposing the raw material diparaxylylene solid dimer, and the stable diradical paraxylylene monomer generated at this time causes a simultaneous reaction of adsorption and polymerization on the substrate. This coating film is capable of precision coating, which is not possible with conventional liquid coating or powder coating, as well as the shape and material of the adherend during coating, and coating at room temperature. By having many excellent characteristics,
It is known as the most suitable conformal coating film, from coating of ultra-precision parts to coating of general-purpose products. Specifically, its application examples can be seen in the insulation film coating of hybrid ICs, the prevention of dust generation of disk drive parts, the lubrication film of stepping motors, and the corrosion prevention film of biomaterials.

[0003]

However, the adhesiveness of the parylene film to the base material varies greatly depending on the type of the base material. For example, the adhesion to ceramic substrates is generally excellent, but the adhesion to glass or metal substrates is extremely poor. It is easily peeled off by peeling off with an adhesive tape. Further, it is difficult to say that even a ceramic base material that is said to have good adhesiveness will sufficiently satisfy the required characteristics depending on its type and use environment conditions. As a countermeasure against this, a generally performed method is to perform degreasing cleaning as a pretreatment before forming a parylene film, and then perform a silane treatment. This is a method in which a base material before coating with a parylene film is immersed in an alcohol solution in which an organosilane coupling agent is dissolved and dried to form a silane-treated layer on the surface of the base material, and then a parylene film is formed. However, even if such a silane treatment is performed, the silane-treated layer is only bonded to the substrate and the parylene film by chemisorption, so that sufficient adhesion cannot be obtained depending on the required characteristics. For example, when a ceramic substrate having a parylene film that has been subjected to such a treatment is cut as a secondary process, a phenomenon of gradually peeling from the cut surface is observed.

An object of the present invention is to provide a method for forming a parylene film having excellent properties on various substrates with good adhesion.

[0005]

To achieve the above object, in the present invention, a plasma polymerized film is formed on the surface of a substrate by plasma polymerization in an atmosphere containing a hydrocarbon gas or an organic silicon compound as a main component, and then, The surface of the plasma-polymerized film is treated by plasma treatment in an atmosphere containing oxygen gas or argon gas to remove surface contaminants and to form a carbon-carbon covalent bond between the parylene film present on the surface of the plasma-polymerized film and the plasma-polymerized film. Decomposes carbonyl groups and hydroxyl groups that interfere. After that, the parylene film was formed by the vapor phase synthesis method described above.

[0006]

Embodiment 1 An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view showing a part of a magnesium alloy casting constituting a hard disk drive component coated with a parylene film according to the present invention. Since this material is very likely to generate dust powder, a parylene film is coated to prevent the generation of dust powder, but its adhesiveness is not excellent and often peels off partially. Therefore, according to the present invention, a plasma polymerized ethylene film 20 having a film thickness of about 100 nm is first formed on the casting 10 by the plasma polymerization method. It is generally known that a plasma-polymerized film exhibits excellent adhesion to various substrates due to its film formation mechanism. The conditions are shown below.

Source gas: ethylene Excitation method: high frequency (13.56 MHz) Excitation output: 100 W Gas flow rate: 50 cm ³ / min. Gas pressure: 0.5 Torr Film formation rate: 2 nm / min. Processing temperature: ≤150 ° C

The structure of the plasma-polymerized ethylene film 20 obtained under the above conditions has a branched or high-density cross-linked structure unlike ordinary polyethylene, and further, unsaturated double bonds or oxidation of aromatic compounds. A carbonyl group or a hydroxyl group generated by is attached. This is a major factor that hinders the adhesion between the plasma polymerized film and the parylene film. Further, the adhesion of the powdery polymer produced in the plasma space during the polymerization reaction to the film surface is also a factor that impedes the adhesion to the parylene film. Therefore, as a countermeasure, plasma treatment is continuously performed in the same treatment tank. The representative conditions are shown below.

Source gas: Argon Excitation method: High frequency (13.56 MHz) Excitation output: 20 W Gas flow rate: 50 cm ³ / min. Gas pressure: 0.2 Torr Treatment temperature: ≦ 150 ° C. Treatment time: 3 min.

By this treatment, the surface of the film is etched by about 20 nm, which becomes a cause of inhibition.
Carbonyl groups and hydroxyl groups on the surface are destroyed, and contaminants are also removed. A parylene film 30 of about 2 μm is formed on the plasma-polymerized ethylene film 20 that has been subjected to the above-mentioned treatment by the vapor phase synthesis method described above. It has been confirmed from the result of ESR (electron spin resonance) analysis that residual radicals exist on the surface and in the plasma-polymerized ethylene film 20, and this radical and the diradical paraxylylene monomer generated during the formation of the parylene film 30 are present. React to form a strong covalent bond. Therefore, the plasma polymerized ethylene film 20 and the parylene film 30 exhibit excellent adhesion. Also in this step, it is desirable to continuously form a parylene film in the same reactor.

In order to confirm the effect of the embodiment of the present invention, as a comparative sample, the same casting as that of the embodiment was subjected to the usual silane treatment, and then a parylene film of about 2 μm was coated by a vapor phase synthesis method. The sample obtained by the above was evaluated by a cross-cut tape peeling test. The results are shown in Table 1.

[0012]

[Table 1]

[0013]

[Embodiment 2] FIG. 2 is a sectional view showing a part of a ceramic piezoelectric element component used in an ink jet printer coated with a parylene film according to the present invention. At this time, in order to improve the hydrophilicity of the parylene film with respect to the aqueous ink, the surface of the parylene film is surface-modified by liquid phase graft polymerization of a hydrophilic monomer. The phenomenon of peeling was frequently observed. Therefore, according to the present invention, a plasma polymerized film 50 made of tetramethylsilane as a raw material was coated on the piezoelectric element 40 by about 200 nm and then surface-treated with oxygen plasma to form a parylene film 60 of about 2 μm. As a result, the peeling phenomenon due to graft polymerization was completely eliminated.

[0014]

As is clear from the above examples, according to the present invention, it becomes possible to coat a variety of substrates with a parylene film with good adhesion, and a practical range in which the properties of the parylene film are fully utilized. It will be possible to expand in many directions.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a magnesium alloy casting coated with a parylene film in Example 1 of the present invention.

FIG. 2 is a schematic cross-sectional view of a piezoelectric element part coated with a parylene film in Example 2 of the present invention.

[Explanation of symbols]

 10 Cast Magnesium Alloy 20 Plasma Polymerized Film 30 Parylene Film 40 Piezoelectric Element Component 50 Plasma Polymerized Film 60 Parylene Film

Claims (1)

[Claims] 1. A step of forming a plasma polymerized film on the surface of a substrate by plasma polymerization in an atmosphere containing a hydrocarbon gas or an organic silicon compound as a main component, and a plasma treatment in an atmosphere containing oxygen gas or argon gas. A method for forming an organic polymer film, comprising a step of treating a surface of a plasma polymerized film and a step of forming a parylene film by a vapor phase synthesis method.