JPH0224648B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for molding a tetrafluoroethylene copolymer that provides molded products with good releasability and does not generate bubbles, and a mold used for this molding. (Prior art) Tetrafluoroethylene copolymer resin has excellent heat resistance, chemical resistance, electrical properties, non-stick properties, low friction properties, and other properties unique to fluororesins, and it melts at high temperatures and becomes plastic. For, injection,
It is known as a resin that can be used to produce molded products using molding methods such as transfer, compression, rotation, and casting. (Problems to be Solved by the Invention) The first problem in molding such a tetrafluoroethylene copolymer is that the resin sticks to the mold. As mentioned above, the tetrafluoroethylene copolymer is a non-adhesive polymer, and in its non-molten state (solid state), it is hardly wetted by fluids and viscous substances such as adhesives. However, when the tetrafluoroethylene copolymer resin melts into a liquid state, the surface tension decreases and it becomes possible to wet many solid substances, and when this resin solidifies, it will be able to wet the surface of the solid substance it comes in contact with. stick. Therefore, a phenomenon of sticking to the mold occurs. The second problem is foaming of the molded product. When molding tetrafluoroethylene copolymer under high pressure such as injection molding or extrusion molding, even if the molten resin contains gaseous substances such as resin decomposition gas and air, degassing is compared. This is not a problem because it is easy to carry out, but when there is no pressure and the temperature of the mold is high, as in rotational molding, a large amount of decomposed gas is generated, and it is difficult to remove the gas. This causes bubbles to form in the molded product. The first problem, that is, the release of the molded product from the mold, can be solved by polishing the mold surface or applying a mold release agent such as a silicone mold release agent to the mold surface. However, surface polishing requires a lot of time and effort, has a short service life, and does not have sufficient mold releasability. In addition, the method of using a mold release agent is such that even silicone mold release agents cannot withstand the molding temperature of fluororesin, and furthermore, the mold release agent adheres to the surface of the molded product, worsening the surface condition of the molded product. However, it also has the disadvantage that the time period during which the mold release effect is effective is short. In addition, to solve the second problem, that is, the problem of air bubbles occurring in molded products, it has been proposed to add stabilizers such as zinc and tin to the resin, but the addition of these metals improves acid and alkali resistance. This is not preferable because it impairs the properties of fluororesin, such as lowering the electrical insulation properties and not containing impurities. [Means for Solving the Problems] In order to solve the above problems, the first invention of the present application provides tetrafluoroethylene and the following formula:

[Formula] and

[Formula] (wherein Rf ₁ is H or a fluoroalkyl group having 1 to 5 carbon atoms, Rf ₂ is a fluoroalkyl group having 1 to 5 carbon atoms, and X ₁ , X ₂ and X ₃ are F or H) A copolymer with one or more types is heated and melted to produce polyarylene sulfide (hereinafter referred to as
This paper proposes a method for molding tetrafluoroethylene copolymers by cooling and solidifying them in a mold coated with PAS. The second invention of the present application proposes a mold for molding a tetrafluoroethylene copolymer coated with PAS. Examples of the PAS used in this invention include polyphenylene sulfide (hereinafter referred to as PPS). It should be noted that it is preferable that PAS is easily synthesized and has high purity.
Excessive addition of pigments or fillers, e.g. titanium oxide, e.g. containing more than 50% of these fillers
PAS often reduces mold release properties. Furthermore, it is preferable that the surface coated with PAS be smooth and easy to form, and if the surface condition of the coating film is poor, the mold releasability may be insufficient. If the surface condition of the coating film is poor and the mold releasability is insufficient, the mold releasability can be improved by polishing the surface and re-baking. The mold is coated with PAS according to a conventional method. For example, a PPS dispersion paint or powder paint is applied to the mold by spraying, dipping, brushing, rolling, fluid dipping, or other conventional techniques, and then baking is performed at a temperature of 300 to 450°C. On the other hand, examples of tetrafluoroethylene copolymers suitable for the molding method of the present invention include Teflon PFA,
(Registered Trademark) Teflon FEP, Teflon EPE (Mitsui-DuPont Fluorochemical Co., Ltd. product) and Tefzel ETEE (Registered Trademark) (DuPont Product). can. When using Tefzel ETFE
At a temperature of 300-400℃, Teflon PFA, Teflon
In the case of FEP and Teflon EPE, it is heated and melted at a temperature of 330 to 430°C. This heating and melting is performed outside the mold in the case of injection molding, transfer molding, etc. That is, in the case of injection molding, it is carried out in a barrel, and in the case of transfer molding, it is carried out in a pot, and then it is injected into a mold coated with PAS. On the other hand, in the case of compression molding, rotational molding, etc., a method is adopted in which the material is heated and melted in a mold coated with PAS, and then cooled and solidified in the mold. (Effects of the Invention) Such a molding method, that is, the molding method of the first invention of the present application, simultaneously solves the following phenomena, which have different causes: sticking of the tetrafluoroethylene copolymer to the mold and foaming of the molded product. This will solve the problem. On the other hand, in the second invention of the present application, the mold is coated with PAS, which not only reduces thermal decomposition of the tetrafluoroethylene copolymer itself, but also prevents corrosive thermal decomposition gas from coming into direct contact with the metallic mold surface. Therefore, the mold for molding tetrafluoroethylene copolymer can be made from inexpensive carbon steel, without using conventional corrosion-resistant alloys such as Hastelloy or stainless steel. Furthermore, since PAS is baked into the mold, it does not wear out like normal mold release agents, and its surface hardness allows it to maintain its mold release effect for a long time. (Example) Examples of the present invention will be shown below. Example 1 A 50 x 100 x 2.3 mm iron plate (material SS41) was degreased with a solvent, air-baked, and half of its surface was coated with PPS water-based dispersion paint (Sustain C-400 (registered trademark): Hodogaya Chemical Industry Product). After applying 20μ and drying, baking was performed at 390°C for 30 minutes. This iron plate was used as the bottom mold for a hot compression mold, and a 1 mm thick Teflon PFA sheet [Mitsui
Dupont Chemical Co., Ltd. product] was placed thereon and heated in a furnace at 340 to 350°C to melt the PFA sheet. Next, this was taken out of the furnace and compressed at a molding pressure of 30 kg/cm ² .
Cooling was carried out. After cooling, the iron plate (bottom mold) was removed from the outer cylinder of the mold, and PFA was not adhered to the PPS-coated portion (peel strength: 0 kg/cm). On the other hand, PFA was strongly adhered to the parts not coated with PPS, and its peel strength was 3.2 kg/cm. Example 2 PPS water-based dispersion paint (Sustain C-4000 Hodogaya Chemical Industry Product) was applied to a hemispherical depression mold with a diameter of 200 mm, and PPS powder (Ryton V-
1 (registered trademark) Hodogaya Chemical Industry Products),
Baking was performed at 330°C for 30 minutes. Then this PPS
Polish the coated surface with waterproof abrasive paper (CC-600),
Rebaking was performed at 360°C for 60 minutes. Put 270g of Teflon PFA powder (Mitsui Dupont Fluorochemical Products) with a particle size of 200μ into this mold.
The diameter was measured by two-axis rotation method for 2 hours in a furnace at a temperature of 370℃.
A hollow sphere with a diameter of 200 mm and a wall thickness of approximately 2 mm was molded. No foaming was observed in the molded product, and the molded product did not adhere to the mold.

Claims (1)

[Scope of Claims] 1 Tetrafluoroethylene, and the following formulas [Formula] and [Formula] (where Rf ₁ is H or a fluoroalkyl group having 1 to 5 carbon atoms, and Rf ₂ is a fluoroalkyl group having 1 to 5 carbon atoms) A copolymer with one or more comonomers (X ₁ , X _{2 and} 1. A method for molding a tetrafluoroethylene copolymer, which method comprises molding a tetrafluoroethylene copolymer. 2. A mold for molding a tetrafluoroethylene copolymer, characterized by being coated with polyarylene sulfide.