JPH07232399A - Formation of fluoroplastic film - Google Patents

Abstract

PURPOSE:To enhance the close adhesiveness with coated fluoroplastic by preparing a soln. by adding water and an acid to a mixture of alkoxide and substituted alkoxide and applying the same to a substrate to form a film by a sol-gel method. CONSTITUTION:A metal oxide intermediate layer 2 is formed on a substrate l from alkoxide represented by M(OR)n (wherein M is a metal, R is an alkyl group and n is an integer) and substituted alkoxide represented by RfxM(OR)n (wherein Rf is a fluoroalkyl group or a fluoroalkylene group and x is 1<=x<=n-1) by a sol-gel method. A fluoroplastic film 3 is formed on the intermediate layer 2. The intermediate layer 2 becomes a state having a fluoroalkyl group or a fluoroalkylene group on its surface to be enhanced in the close adhesiveness with the fluoroplastic film 3 and becomes low in the content of a fluoroalkyl group on the side of the substrate to be enhanced in the close adhesiveness with the substrate and the close adhesiveness with both of the fluoroplastic film 3 and the substrate l thereof can be enhanced.

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 a fluororesin coating film. More specifically, the present invention provides a metal oxide intermediate layer formed by a sol-gel method as a binding inclusion without using a binder. The present invention relates to a method for forming a fluororesin coating used.

[0002]

2. Description of the Related Art Fluorocarbon resins have excellent heat resistance, chemical resistance, electrical insulation properties, low adhesiveness and low frictional resistance, and are used for many purposes. The fluororesin coating film that makes full use of such characteristics of the fluororesin is generally coated on the surface of the substrate through a primer containing a binder such as polyamideimide. However, the fluororesin has low reactivity with the binder and is easily peeled off.

Japanese Patent Laid-Open No. 153859/1993 discloses that a mixture of a fluororesin and a metal oxide is formed as an intermediate layer on the surface of a plastic, and the fluororesin is laminated on the surface of the plastic to adhere the plastic to the fluororesin. Is improving. By including fluorine in this intermediate layer, the adhesion with the fluororesin is improved, but this fluororesin is evenly distributed in the intermediate layer, and therefore the adhesion with the substrate is better than that without the fluororesin. Is also declining. Therefore, it is difficult to adhere the fluororesin coating to the substrate with sufficient strength.

[0004]

DISCLOSURE OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks in the formation of a fluororesin coating and to provide a method for forming a fluororesin coating having sufficient adhesion and strength.

[0005]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the problems of the above-mentioned fluororesin coating, a fluoroalkyl group, which is well compatible with fluororesins, has been incorporated into the fluorine of the intermediate layer. By being unevenly distributed on the resin side, an intermediate layer having high adhesion to the fluororesin and high adhesion to the substrate can be obtained, and by using this intermediate layer, a fluororesin film having sufficient adhesion and strength can be obtained. It was found that the present invention has been completed.

That is, the method for forming a fluororesin film of the present invention is represented by M (OR) _n (wherein M is a metal, R is an alkyl group, and n is an integer determined by M). Alkoxide and Rf _x M (OR) _nx (wherein 1
≦ x ≦ n−1, Rf is a fluoroalkyl group or a fluoroalkylene group, and M, R and n are the same as those defined above) and a metal oxide on the substrate by a sol-gel method. It is characterized by comprising a step of forming an intermediate layer and a step of forming a fluororesin coating film on the intermediate layer.

The alkoxide represented by the above formula used for forming the intermediate layer of the present invention is used in the so-called sol-gel method, and the kind thereof is not particularly limited. As the metal M, for example, silicon, aluminum, titanium, zirconium, or the like can be used. Further, as the alkyl group, methyl, ethyl, propyl, butyl, etc. can be used. Specifically, alkoxides include tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ), aluminum isopropoxide (Al (OC ₃ H ₇ ) ₃ ), titanium isopropoxide (Ti (OC ₃ H ₇ )). ₄ ), etc. are exemplified.

Further, in the formation of the intermediate layer, a substituted alkoxide in which a part of the OR group of the above alkoxide is substituted with a fluoroalkyl group or a fluoroalkylene group is used. The fluoroalkyl group of the formula _{CF 3 (CF 2) n C} 2 H 4 - are those represented by, and the fluoroalkylene group, for example,
_{CF 2 = CF (CF 2)} n C 2 H 4 - is represented as being at. In the fluoroalkylene group, the number of double bonds is not limited to one,
There may be more than one.

An intermediate layer is formed by forming a film of these alkoxides on a substrate by using a sol-gel method. Specifically, alcohol, water and acid are added to a mixture of alkoxide and substituted alkoxide to prepare a solution of alkoxide. The gel film is formed on the substrate by immersing the substrate in this alkoxide solution and pulling it up. Next, the coating is dried and baked to fix the coating to the substrate. This method of forming a coating film by the sol-gel method is a known means, and its conditions are appropriately selected within the range of conditions known to those skilled in the art. The thickness of the intermediate layer coating is not particularly limited, but is preferably 0.1 μm or less. From the viewpoint of strength, the amount of the substituted alkoxide is preferably 10 mol% or less of the total alkoxide. The substrate is also not particularly limited, and glass, aluminum, stainless steel or the like can be used.

During the above drying process, fluoroalkyl or fluoroalkylene groups tend to collect on the surface of the intermediate layer. In the resulting intermediate layer,
The surface is rich in fluoroalkyl or fluoroalkylene groups, and the substrate side is rich in metal oxides.

A fluororesin is coated on the intermediate layer thus formed. There is no limitation on the fluororesin, for example,
Polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTF)
E), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer copolymer A combination (ECTFE) and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) can be used.

Fluorocarbon gas such as CF
₄ and C ₃ F ₆ may be used to coat the fluororesin by the plasma CVD method (chemical vapor reaction method). That is, the substrate on which the intermediate layer is formed is placed in a plasma CVD apparatus and vacuumed. Next, argon is introduced as a carrier gas, and a monomer gas is flown. After that, a high frequency is applied to generate plasma, and radicals of the monomer gas are generated, which are deposited on the substrate while forming a film. In this way, a fluororesin film is formed. The monomer gas used here preferably has a double bond. It is considered that the presence of the double bond causes a load-polymerized reaction and bonds with the fluoroalkyl group by a chemical bond, which is considered to enhance the adhesiveness. For the same reason, a fluoroalkylene group having a double bond is preferable to fluoroalkyl.

[0013]

According to the method of the present invention, an intermediate layer containing a large amount of fluoroalkyl groups or fluoroalkylene groups on the surface can be obtained by forming the intermediate layer by the sol-gel method. This is because fluoroalkyl groups are concentrated on the surface during the drying process in order to reduce the surface energy of the film. Since the fluoroalkyl groups of the same kind as the fluororesin are unevenly distributed on the surface, this intermediate layer has high adhesiveness with the fluororesin, while the substrate side has very few fluoroalkyl groups and therefore has high adhesiveness with the substrate. As described above, the intermediate layer used in the present invention has high adhesion to both the fluororesin and the substrate, so that the fluororesin can be more strongly coated.

[0014]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention.

Example 1 Tetraethoxysilane (Si (OC ₂ H
₅ ) ₄ ) 200 g, fluoroalkylsilane (CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (O
20 g of CH ₃ ) ₃ ) and 430 g of ethanol were added and mixed with stirring for 20 minutes. Then, 83 g of water and 105 g of 0.1N hydrochloric acid were added, and the mixture was stirred for 2 hours. Transfer the solution to a sealed container and store at 25 ° C for 24 hours.
Aged for hours. The stainless steel substrate was immersed in the metal alkoxide solution produced in this manner, and the substrate was pulled up at a pulling rate of 30 mm / min to form a gel coating film on the substrate. Then, this film was baked at 250 ° C. for 1 hour to form a fluoroalkyl group-containing SiO ₂ film.

The fluoroalkyl group-containing SiO ₂ film thus formed is set in a plasma CVD apparatus and evacuated to a vacuum degree of 10 ⁻³ Pa by a rotary pump and an oil diffusion pump, and then 10 vol% CF ₄ is added to argon. The mixed gas was introduced, and the flow rate was adjusted so that the pressure inside the device was 0.1 Pa. Next, RF power of 500 W was introduced and left for 60 minutes. Thus, a fluororesin film having a thickness of about 1000 angstrom was formed on the fluoroalkyl group-containing SiO ₂ film.

Example 2 Si containing fluoroalkyl group produced in Example 1
The O ₂ film was set in a plasma CVD apparatus, and a rotary pump and an oil diffusion pump were evacuated to a vacuum degree of 10 ⁻³ Pa, and then a gas containing 10 vol% C ₃ F ₆ mixed in argon was introduced. The flow rate was adjusted so that the pressure inside the device was 20 Pa. Next, introduce RF power of 500W,
Let stand for 10 minutes. Thus, fluoroalkyl group-containing Si
A fluororesin film having a thickness of about 1000 angstrom was formed on the O ₂ film.

Example 3 Si containing fluoroalkyl group produced in Example 1
Place the O ₂ film in the reaction furnace as shown in Fig.
A crucible containing 10 g of a PTFE chip was set at the position of mm. Then, the inside of this reactor was rotary pumped
Vacuum was drawn to the order of 0.1 Pa, then argon was introduced and the pressure was returned to atmospheric pressure. After that, 100 cc / min of argon
The vaporized substance from the crucible was caused to flow in the direction of flowing through the SiO ₂ film at a flow rate of, and the temperature was kept at 400 ° C. and left for 3 hours. Thus, a fluororesin film having a thickness of about 1000 angstrom was formed on the fluoroalkyl group-containing SiO ₂ film.

Example 4 200 g of tetraethoxysilane and silane having a fluoroalkylene group (CF ₂ = CF (CF ₂ ) ₆ C ₂ H ₄ S in a 1 liter beaker)
20 g of i (OCH ₃ ) ₃ ) and 430 g of ethanol were added, and the mixture was stirred and mixed for 20 minutes. Then, 83 g of water and 105 g of 0.1N hydrochloric acid were added, and the mixture was stirred for 2 hours. Transfer the solution thus produced to a sealed container,
It was aged at 25 ° C for 24 hours. Immerse the stainless steel substrate in the metal alkoxide solution produced in this way, and 30 mm / min
The substrate was pulled up at a pulling speed of 1 to form a gel coating film on the substrate. Then, this film was baked at 250 ° C. for 1 hour to give a fluoroalkyl group-containing SiO ₂ film.
A film was formed.

The fluoroalkyl group-containing SiO ₂ film thus formed is set in a plasma CVD apparatus and evacuated to a vacuum degree of 10 ⁻³ Pa by a rotary pump and an oil diffusion pump, and then 10 vol% CF ₄ is added to argon. The mixed gas was introduced, and the flow rate was adjusted so that the pressure inside the device was 0.1 Pa. Next, RF power of 100 W was introduced and left for 60 minutes. Thus, a fluororesin film having a thickness of about 1000 angstrom was formed on the fluoroalkyl group-containing SiO ₂ film.

Example 5 Si containing fluoroalkyl group produced in Example 4
The O ₂ film was set in a plasma CVD apparatus, and a rotary pump and an oil diffusion pump were evacuated to a vacuum degree of 10 ⁻³ Pa, and then a gas containing 10 vol% C ₃ F ₆ mixed in argon was introduced. The flow rate was adjusted so that the pressure inside the device was 20 Pa. Next, introduce RF power of 500W,
Let stand for 10 minutes. Thus, fluoroalkyl group-containing Si
A fluororesin film having a thickness of about 1000 angstrom was formed on the O ₂ film.

Example 6 Fluoroalkyl group-containing Si produced in Example 4
Place the O ₂ film in the reaction furnace as shown in Fig.
A crucible containing 10 g of a PTFE chip was set at the position of mm. Then, the inside of this reactor was rotary pumped
Vacuum was drawn to the order of 0.1 Pa, then argon was introduced and the pressure was returned to atmospheric pressure. After that, 100 cc / min of argon
The vaporized substance from the crucible was caused to flow in the direction of flowing through the SiO ₂ film at a flow rate of, and the temperature was kept at 400 ° C. and left for 3 hours. Thus, a fluororesin film having a thickness of about 1000 angstrom was formed on the fluoroalkyl group-containing SiO ₂ film.

Comparative Example 1 After setting an untreated stainless plate in a plasma CVD apparatus, a vacuum degree was set by a rotary pump and an oil diffusion pump.
Evacuate to the order of 10 ^-3 Pa, then place in argon for 10
A gas mixed with vol% C ₃ F ₆ was introduced, and the flow rate was adjusted so that the pressure in the apparatus became 20 Pa. Then, RF power of 500 W was introduced and left for 10 minutes. Thus, a fluororesin film having a thickness of about 1000 angstrom was formed on the stainless steel substrate.

The fluororesin film produced in each example was reciprocated 3000 times with a flannel cloth under a load of 300 g / cm ² , and a fastness test was conducted. The area of the fluororesin coating film peeled off in this test was measured, and the results are shown in Table 1 below.

[0025]

[Table 1]

From these results, it can be seen that when a fluoroalkyl group-containing SiO ₂ film is used as the intermediate film, the adhesiveness of the fluororesin film is significantly improved. Further, the adhesion is further improved when an alkoxide having a fluoroalkylene group having a double bond is used and when a fluorocarbon gas having a double bond is used as a CVD source gas.

Further, a thermal cycle test (holding in air at 300 ° C. for 20 minutes, rapid heating in water at 20 ° C.-quenching) was conducted on the fluororesin coating film produced in each example. After 10 thermal cycles, first attach water droplets to the surface of the membrane,
The repellency of water was observed, and unlike the state before the test, SEM observation was performed on a well-wetted one, and peeling of the film was confirmed. The results are shown in Table 2 below.

[0028]

[Table 2]

In Comparative Example 1, due to the difference in the coefficient of thermal expansion between the stainless steel and the fluororesin coating, a load is generated at the interface due to the thermal cycle, resulting in peeling.
On the other hand, in the film of the present invention, the intermediate film has extremely high adhesion and therefore does not peel off.

[0030]

As described in detail above, in the method of the present invention, by forming the intermediate layer from the alkoxide by the sol-gel method, an intermediate layer having high adhesion to both the substrate and the fluororesin can be obtained, which is further improved. The obtained fluororesin coating film is obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a fluororesin coating film obtained by the method of the present invention.

FIG. 2 is a schematic view of a reaction furnace used for coating a fluororesin.

[Description of Reference Signs] 1 ... Substrate 2 ... Intermediate layer 3 ... Fluororesin layer 4 ... Crucible 5 ... Substrate

Claims (3)

[Claims] 1. M (OR) _n (wherein M is a metal,
R is an alkyl group, and n is an integer determined by M) and Rf _x M (OR)
by a sol-gel method from an alkoxide represented by _nx (wherein 1 ≦ x ≦ n−1, Rf is a fluoroalkyl group or a fluoroalkylene group, and M, R and n are the same as the above definition). A method for forming a fluororesin coating, comprising the steps of forming a metal oxide intermediate layer on a substrate and forming a fluororesin coating on the intermediate layer. 2. The method according to claim 1, wherein Rf is a fluoroalkylene group. 3. The method according to claim 1, wherein in the step of forming the fluororesin coating on the intermediate layer, the fluorocarbon coating having a double bond is used to deposit the fluororesin coating.