JPH032052B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for adhering fluorine-based resins such as polytetrafluoroethylene. Conventional technology Polytetrafluoroethylene and tetrafluoroethylene copolymer resins modified to provide thermoplasticity have excellent heat resistance, chemical resistance, and weather resistance, but have extremely low adhesion and are difficult to bond with different materials. It is difficult to adhere these materials, and surface chemical treatment methods such as a graft reaction method and a sodium-ammonia method are used for adhesion. In addition, for coating film formation on the surface of metal etc., for example,
A complicated method is used, such as sandblasting the metal surface to an appropriate roughness, baking a primer on that surface, and then baking a fluorine-based resin on that surface.This method involves adjusting the thickness of the baking,
Careful attention must be paid to adjusting the baking temperature and baking time, as well as to rapid cooling after coating, and in order to thicken the coating, it is necessary to increase the number of baking cycles. Further, in practical terms, the thickness is limited to several μm. Problems to be Solved by the Invention The present invention enables polytetrafluoroethylene and polytetrafluoroethylene copolymer resin surfaces and adherend surfaces to be converted into polytetrafluoroethylene without any special chemical or physical treatment. The purpose is to bond ethylene resin moldings to metals or ceramics. Measures to solve the problem Polytetrafluoroethylene resin and tetrafluoroethylene-hexafluoropropylene resin are materials with low surface energy, and their molded products and metals can be easily cooled even if they are pressurized above their melting point. It is well known that the film can peel off. However, a thermal fusion phenomenon can be observed between the two resins having similar surface energies. For example, two polytetrafluoroethylene sheets can be bonded together by heating and pressurizing them above their melting point and then cooling them. Also, between two sheets of polytetrafluoroethylene,
When polytetrafluoroethylene sheets are sandwiched and heated and pressed to a temperature above the melting point, it is possible to bond polytetrafluoroethylene to each other, but the adhesive strength is not very strong. The results regarding these adhesion are described in Reference Example 1. This level of adhesive strength is insufficient for practical use. The inventor has already discovered that the presence of ultrafine particles with a particle size of 1 μm or less at the adhesive interface can make it possible to bond combinations of adherends and adhesives that are difficult to bond to (Kobunshi Proceedings vol. 33No.2
PP55−61). However, experimental proof is required to clarify the range to which this phenomenon can be applied. As a result of experiments, it was found that dope cement mixed with ultrafine particles has difficulty adhering to rolled polytetrafluoroethylene sheets. Furthermore, ultrafine particles were mixed with polypropylene and polyvinylidene fluoride resin, which have low surface energy, and attempts were made to thermally bond them to polytetrafluoroethylene, but no adhesion was observed at all. These experimental results are described in Reference Example 2. However, strong adhesive strength can be obtained by heat fusion using polytetrafluoroethylene as an adhesive by mixing ultrafine particles into a tetrafluoroethylene-hexafluoropropylene copolymer and using polytetrafluoroethylene as an adherend. When adhering the fluorinated ethylene sheet, a peel strength of 2 to 6 kg/25 mm was obtained, which was nearly 10 times as strong as when thermal fusion was used without an adhesive. Although the example was described in Example 1, it will be described in more detail. It is essential that the heating temperature during bonding be above the melting point (327°C) of polytetrafluoroethylene and below the decomposition point; adhesive strength is extremely low at temperatures below the melting point of polytetrafluoroethylene. It was a good result. The temperature range of heating is important to obtain strong adhesion. The required crimping force depends on the shape of the adherend, surface condition,
Although it is related to the melt viscosity of the adhesive, it is sufficient that the melted adhesive sufficiently wets the surface of the adherend, and the pressure is far lower than the pressure required to mold polytetrafluoroethylene. On the contrary, if the pressure is too high, the adhesive will flow out from the adhesive interface, which is not preferable. The pressure level seen in normal bonding is 0.1 to several kg/cm ² . As with normal fusion bonding, it is preferable to cool under pressure in order to obtain an actual bonded sample. Since polytetrafluoroethylene has high viscosity even above its melting point, the polytetrafluoroethylene molded product deforms slightly under this pressure, but unlike other molten resins, it does not flow and retains its shape as an adherend. can be kept. It is also recognized that the tetrafluoroethylene-hexafluoropropylene copolymer mixed with ultrafine particles in Example 1 can be bonded to various materials by a heat fusion method. This phenomenon is considered to belong to the phenomenon described in the literature mentioned above. Adhesion phenomena have been found at low filling rates. Therefore, by using a polytetrafluoroethylene-hexafluoride propylene molded product mixed with ultrafine particles as an adhesive, it was possible to bond the polytetrafluoroethylene molded product and different materials. As described in Example 2, a 0.5 mm thick Teflon sheet is made of stainless steel, iron,
Can be bonded to metal plates such as copper, brass, nickel plating, and tin plating, with a peel strength of 3 to 6 kg/25 mm.
The result is as follows. It was also possible to bond ceramics such as ceramics. Tetrafluoroethylene-hexafluoropropylene copolymers usually have a melting point of about 270°C, but some low polymers are oily. Such copolymers cannot be used in adhesives. The copolymer used in the present invention is of a grade used for resin molding. Furthermore, since it is possible to obtain a three-component copolymer by adding some third monomer to the copolymer, it is possible to obtain a three-component copolymer by adding a small amount of a third monomer. Copolymers to which components have been added are also included in the term copolymers in the present invention. The ultrafine particles used cannot be of the type that chemically reacts with the resin and ceases to be particles. Inert means that there is no significant chemical reaction. It is generally known that the surface of ultrafine particles has a different activity from the surface of a normal object, and even if the surface of an ultrafine particle does not react with a normal surface, it does not necessarily mean that a chemical reaction will not occur. However, it is difficult to prove such a chemical reaction, and this type of chemical reaction is excluded from the discussion here. As for the type of fine particles, inorganic and hard metals can be used, and as a result of using crushed glass, ultrafine alumina powder, ultrafine powder for magnetic materials (iron oxide), etc. as fillers, high adhesive strength was obtained for all of them. Examples are described in Examples 1 and 2. Regarding the mixing volume ratio, the maximum limit of mixing is determined by the viscosity of the melted resin at the time of mixing, and high viscosity resins have poor flow on the surface of the adherend during adhesion and are not suitable for adhesion. In addition, viscosity is related not only to the capacity ratio and temperature of the particles, but also to the distribution of the viscosity form, size, etc., and it is known that in the case of ultrafine particles, the viscosity becomes larger than the capacity ratio. For this reason, the maximum capacity rate is 30 from experience.
%. The lower limit was set at approximately 3%, as results of experiments showed that adhesive strength was observed even at low rates. As a result of the above experiments, we found that ethylene tetrafluoride-propylene hexafluoride copolymer (hereinafter referred to as
It is possible to bond polytetrafluoroethylene (hereinafter also referred to as PTFE) onto metal etc. using FEP), which protects the surface of iron products, and equipment that utilizes the non-adhesive properties of polytetrafluoroethylene. This makes manufacturing extremely easy. Examples and reference examples regarding experimental conditions will be described below. Example 1 1. Iron oxide fine particles for magnetic materials manufactured by Toda Kogyo (particle size
0.5μm) and FEP in the capacities shown in the table in advance, heated the mixing cell of Toyo Seiki Plastomill (capacity 30c.c. type) to 320℃, and set the mixing blade rotation speed to 50rpm. Add the resin little by little into the cell, melt and knead, and after the melting is complete, add the fine powder little by little, and after feeding, further increase the rotation speed.
Continue mixing at 100 rpm for about 10 minutes, then take out the mixed molten resin from the cell, make it into a suitable lump, and use a heat press to form a sheet with a thickness of about 0.3 mm (hereinafter referred to as
Using a material formed into a FEP composite sheet (FEP composite sheet) as an adhesive, the adhesive surface is 25mm between a PTFE sheet with a thickness of 0.5mm and a width of 25.0mm and a stainless steel plate with a thickness of 3mm and a width of 25mm.
x 25 mm, inserted between heating plates controlled at 340°C to 350°C, pressurized and heated at a pressure of 1 kg/cm ² (calculated), and heated for about 10 minutes. The sample was allowed to cool down to 240°C while still being pressurized, and when the temperature reached 240°C, the pressure was released, the sample was taken out, and the bonded sample was rapidly cooled with water, and the PTFE and stainless steel plates could be bonded together. A peel test was conducted on this adhesive sample at room temperature and at a pulling speed of 20 mm/min.
A high adhesive strength of 2 to 6 kg/25 mm was obtained. The results are shown in Table 1.

[Table] In addition, under the above conditions, various materials were used instead of stainless steel as the adherend, and an FEP composite with a filling rate of 10% by volume of Fe ₂ O ₃ ultrafine powder was used to bond the PTFE sheet. The resulting peeling forces were as shown in Table 2. It was also possible to adhere to pieces of ceramics.

[Table] Example 2 Gamma alumina A125 manufactured by Baikowski (particle size 0.01 μm) was used instead of the iron oxide powder in Example 1.
FEP composites were prepared in the same manner using micronized glass and micronized glass (average particle size 0.2 μm);
As a result of trying to bond PTEF and stainless steel, good adhesive strength was obtained. Reference example 1 A sheet of 0.3 mm thick polytetrafluoroethylene-propylene hexafluoride is placed on a 3 mm thick polytetrafluoroethylene plate, and then a 0.5 mm thick sheet of polytetrafluoroethylene is placed on top of that. Heat for 10 minutes at a pressure of 1 kg/cm ² using a heating plate heated to 340°C from above and below.
A peel test was conducted on the adhesive strength of the polytetrafluoroethylene plate and sheet, which were left as they were and then the heating plate was removed and taken out, at a speed of 20mm for 1 minute.The average adhesive strength of the four pieces was 0.784Kg/25mm. It was hot. In addition, when preparing the upper test bonded sample, ethylene tetrafluoride
When the hexafluoropropylene sheet was excluded, the adhesive strength was as low as 0.705 kg/25 mm on average for four sheets. Reference Example 2 In the method described in Example 1, polyvinylidene fluoride or polypropylene resin was used instead of the tetrafluoroethylene-hexafluoropropylene copolymer, but no adhesive effect was observed.

Claims (1)

[Claims] 1 When bonding a polytetrafluoroethylene resin surface and a metal or ceramic surface, a particle size of 1 μm is used.
An adhesion method characterized by using as an adhesive a tetrafluoroethylene-hexafluoropropylene copolymer containing about 3 to 30% by volume of the following inert ultrafine particles, and press-bonding under heat.