JPH0480015A - Screw for extrusion molding machine - Google Patents

Abstract

PURPOSE:To prevent a thermoplastic resin, especially a resin with a small frictional coefficient such as fluororesin from fluctuation of amt. of extrusion by making the surface of a channel part of a screw to be a rough face. CONSTITUTION:A processing range for making a rough face on the feeding part of a screw is pref. in such a way that at least two pitches of the channel part of a screw are made into a rough face from a solid material feeding inlet 8 just below a hopper to the flow direction of a resin and the whole region corresponding to the feeding part of the screw may be processed in some cases. In addition, the surface of the channel part of the screw means the surface area from 50-60% of the whole surface area of the channel part where the bottom part of the channel part as a center to the whole surface area of the channel part and this processing range for making the rough surface is properly selected in relation with kind of the resin and degree of surface roughness of the rough surface. In addition, it is pref. that the surface roughness Rmax of the rough surface is in the range of 20-300mum. If it is less than 20mum, it is not enough for obtaining stabilization of a const. atm. of extrusion and if it exceeds 300mum, it results decrease in the amt. of extrusion. There exists no special restriction on the shape of applied screw but the effect can be exhibited especially when a rapid compression type screw is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to improvements in screws for extrusion molding machines used in extrusion molding of thermoplastic resins.

(Prior art) Extrusion molding of thermoplastic resins uses a screw in an extrusion molding machine, and by exchanging dies, films, sheets,
It is widely used because it can produce products of various shapes, such as members with irregular cross sections and filaments produced by melt spinning. Figure 2 shows the internal structure of a single screw extruder.
Generally, the resin is put into the hopper 10 as a solid in the form of pellets or powder, and is transported toward the die 12 by the rotational movement of the screw 4, and is heated by the frictional heat of the resin and the heat transferred from the wall of the cylinder 9 by the heater. The material is melted and then extruded from the die 12 while generating pressure to form a desired cross-sectional shape.

A screw for an extrusion molding machine usually consists of three sections: a supply section 1, a compression section 2 (plasticization section), and a melt metering section 3, and the supply section 1 efficiently transports solid materials in the form of pellets or powder. The compression section 2 heats and melts the solid material and removes the contained air and volatile matter to form a gel, and provides uniform kneading to ensure uniform dispersion of the ingredients.The melting and measuring section 3 allows the gel to pass through the die. It has functions such as providing optimal temperature and pressure and stabilizing the extrusion rate. In addition, it is generally said that the friction between the resin and the inner surface of the cylinder is greater (and the smaller the friction between the resin and the screw surface, the better. Therefore, the screw surface is highly polished and plated, and the inner surface of the cylinder is It was considered to have a somewhat rough surface.

(Problems to be Solved by the Invention) However, among thermoplastic resins, there are very few other resins that are compatible with it, such as fluorine-based resins, and when extrusion molding of resins with a small coefficient of friction is carried out, Even when melted, the resin pressure and therefore the extrusion rate fluctuate greatly, making it difficult to continuously produce products with uniform density, shape, etc. compared to other resins, so compactors, rotary valves, etc. are installed. The resin was fed into the screw supply section using the same method, but the results were not always satisfactory in terms of stable supply. Therefore, the purpose of the present invention is to stabilize the extrusion amount at a constant level during extrusion molding of thermoplastic resins, especially fluororesins, and
The goal is to continuously produce extruded products with uniform density, shape, etc.

(Means for Solving the Problems) Therefore, the present inventors have conducted intensive research on a method for stabilizing the extrusion rate at a constant level when extruding thermoplastic resins, particularly fluororesins, and have found that the screw They discovered that it is sufficient to roughen the surface of the supply section, and after studying various conditions in detail, they have completed the present invention.

That is, the present invention provides a screw for an extrusion molding machine, characterized in that the screw groove surface in the feed section of the screw is roughened, and the roughened surface has a surface roughness Rmax of 20 to 300 μm.

The present invention will be explained in detail below.

Examples of thermoplastic resins used in the present invention include PE-based resins, PP-based resins, vinyl chloride-based resins, and fluorine-based resins, among which fluorine-based resins with a small coefficient of friction are effective.
Specific examples include homopolymer resins of monomers such as vinyl fluoride, vinylidene fluoride, dichlorodifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, hexafluoroisobutylene, copolymer resins of these, and ethylene. Examples include copolymer resins with other monomers.

In addition, pigments such as titanium oxide, zinc oxide, aluminum oxide, and chromium oxide, ultraviolet absorbers such as benzotriazole type, benzophenone type, and hindered amine type, inorganic fillers such as glass fiber, glass beads, and silica, and methyl methacrylate type It is optional to mix an acrylic processing aid such as a resin with the resin and perform extrusion molding.

The structure of the screw, which is the most distinctive feature of the present invention, will be explained using drawings. Figure 1 shows an example of an embodiment of the present invention, and the concept is an enlarged view of the screw feeding section of the single-screw extruder shown in Figure 2. It is a diagram. Here, as for the roughening processing range of the screw supply section, it is desirable that the groove portion of the screw is roughened by at least two pitches from the solid material supply port 8 directly below the hopper toward the flow direction of the resin. In addition, the screw groove surface refers to 50 to 60% of the total surface area of the groove, centering on the bottom of the groove, as shown in Fig. 1, 7a. % to 7b refers to the entire surface of the groove, but the range of this roughening process is selected appropriately depending on the type of resin, the degree of surface roughness of the rough surface, etc. Furthermore, the surface roughness of the rough surface Raaax is preferably in the range of 20 to 300 μm; if it is less than 20 μm, it is not sufficient to obtain a constant stabilization of the extrusion rate, which is the objective of the present invention, and if it exceeds 300 μm, the extrusion rate will decrease and productivity will be reduced. decreases.

This surface roughening processing method includes lathe processing, sandblasting, etching processing, electrical discharge machining, ultrasonic processing, etc., but etching processing and electrical discharge machining have relatively high accuracy.
It is easy and economical.

There are no particular restrictions on the shape of the screw to which the present invention is applied, but usually continuous compression type, rapid compression type, torbead type,
Examples include screws called Dalmage type. In addition, the most suitable screw is selected taking into consideration the thermal stability of the resin, the shape and size of the molded product, extrusion efficiency, etc.
The effects of the present invention are particularly exhibited when a rapid compression type screw as shown in FIG. 3 is used. Furthermore, it is also effective for twin screw types. In addition, from the viewpoint of screw maintenance, it is optional to perform processing such as metal plating, metal or ceramic lining, metal or ceramic coating, etc., as long as the roughening of the surface is not impaired.

Hereinafter, specific embodiments of the present invention will be described with reference to Examples, but the present invention is not limited thereto.

(Example 1) Polychlorotrifluoroethylene (manufactured by 3M, KeL-F
6050) with a width of 42 mm using a T-die under the following conditions.
A film having a thickness of 0 mm and a thickness of 0.1 mm was extruded and the amount of extrusion was measured. The extruder is a 40mmφ rapid compression type screw D = 25, compression ratio: 23, rotation speed: 8 rpm.
, Cylinder temperature: C, 290'C, C2310''C
, C, 320' CT die temperature: 300°C. To roughen the surface of the screw, as shown in FIG. 1, the entire surface of the groove of the screw supply section for 3 pitches from just below the hopper was processed by electrical discharge machining to a surface roughness Rmax of 1100LL. Table 1 shows the extrusion conditions and results.

(Example 2) Extrusion molding was carried out under the same conditions as in Example 1, except that the surface roughness was set to Rmax 30 μm by etching with 30% hydrochloric acid, and the results are also shown in Table 1. Comparative Example 1) Roughness Extrusion molding was carried out in the same manner as in Example 1, except that the entire screw surface was finished smooth (surface roughness 08 μm) by grinding without surface treatment, and the screw was hard chrome plated. It is also listed in Table 1.

(Effects of the Invention) The present invention relates to an improvement of a screw for an extrusion molding machine for thermoplastic resin, and by roughening the groove surface of the feed section of the screw, friction of thermoplastic resin, especially fluororesin, etc. Even with a resin having a small coefficient, it is possible to continuously produce products with uniform density, shape, etc. without fluctuation in the extrusion rate, and its utility value in industry is extremely high.

No. ■ table

[Brief explanation of drawings]

FIG. 1 is a partial conceptual diagram of a screw for an extrusion molding machine showing one example of an embodiment of the present invention. The 20th is a conceptual diagram of a single screw extrusion molding machine. FIG. 3 shows a side view of the rapid compression type screw. 1. Supply section 2. Compression section 3. Melt metering section 4. Screw 5. Flight section 6. Groove sections 7a, 7b.. Roughened section 8. Supply port 9.. Cylinder 10. Hopper 11, screen pack, breaker plate 12, Gui patent applicant Shin-Etsu Chemical Co., Ltd.

Claims (1)

[Scope of Claims] 1. A screw for an extrusion molding machine, characterized in that a screw groove surface in a feeding section of the screw is roughened. 2. The screw for an extrusion molding machine according to claim 1, wherein the rough surface has a surface roughness Rmax of 20 to 300 μm.