JPH02102019A - Manufacture of polyoxymethylene hollow member - Google Patents

Abstract

PURPOSE:To mold a hollow member without surface defect, inner defect, disconnection stably for a long period of time by specifying the pressure condition of pressurized fluid to be fed to the hollow part of resin. CONSTITUTION:Polyoxymethylene supplied from a hopper 1 is melted and plasticized by an extruder 2, then guided through a heated double die 3 to a sizing die 4 without exposing with the air to be specified in the outer diameter of a hollow part, and manufactured while cooling. The die 3 has an inner die 11 having a hole for feeding pressurized fluid such as air, nitrogen, and an outer die 12 provided at an annular gap outside the die 11, and the pressure of the fluid fed from the die 11 is maintained at a predetermined value of 0.5-5kg/cm<2>. Thus, surface, inner or shape defect is suppressed thereby to stably mold for a long period of time, thereby manufacturing a hollow member with high productivity and high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing polyoxymethylene hollow bodies. More specifically, the present invention relates to a method for producing polyoxymethylene hollow bodies that can be stably molded for a long period of time without generating surface or internal defects.

(Prior art) In extrusion molding of hollow bodies, the molten resin extruded from the double die is normally guided to the sizing die in a molten state, but the outer diameter is regulated by contacting the inner wall of the sizing die. ing. The contact of the resin with the inner wall of the sizing die is achieved by increasing the pressure in the hollow part of the resin, reducing the pressure on the outside and using the pressure difference between the inside and outside, or by using both in combination to spread the resin and spread it against the inner wall of the sizing die. This is done by placing them in close contact. (For example, "Extrusion Molding" 7th edition, p. 268, publisher, Plastic Age) (Problem to be solved by the invention) The regulation of the outer diameter of the molten resin extruded from the double die is typically as described above. The sizing is done by contacting the inner wall of the sizing die.

However, this sizing method has the risk of quality deterioration or breakage during molding due to direct contact of the molten resin with the sizing die. especially,
Inching of the resin in the sizing die, surface defects caused by so-called stick-slip, internal defects such as changes in the diameter of the hollow part, and cutting are major obstacles to long-term stable molding using this method. The present invention has been made to address these problems and to provide a method for producing polyoxymethylene hollow bodies that can be stably molded for a long period of time without causing surface or internal defects.

(Means for Solving the Problems) As a result of conducting various studies on the method of producing polyoxymethylene hollow bodies by extrusion molding, the present inventor has found that stick-slip or other factors may cause the problem. The present invention was developed based on the knowledge that the pressure conditions of the pressurized fluid fed into the hollow part of the resin are important in order to achieve stable molding for a long time without causing surface defects, internal defects, or cuts. I arrived at the eggplant.

That is, the present invention continuously extrudes molten polyoxymethylene from between a double die consisting of an outer die and an inner die having a pressurized fluid inlet hole in the center, and then places the polyoxymethylene at the rear of the double die. A method for producing a polyoxymethylene hollow body by external cooling using a sizing die, characterized in that the pressure of the pressurized fluid is maintained at a constant value in the range of 0.5 to 5 kg/d. It is a method of manufacturing the body.

In the method for manufacturing polyoxymethylene hollow bodies of the present invention, it is necessary to maintain the pressure of the pressurized fluid at a constant value in the range of 0.5 to 5 kg/ctl. The pressure is 5kg/cJ
Exceeding this may lead to undesirable situations, such as being prone to breakage during long-term molding or making it difficult to take the molded hollow body stably. On the other hand, the pressure is 0.5 kg/c1
If it is less than i, the above-mentioned stick-slip tends to occur, resulting in surface defects and internal defects,
If left untreated, it can lead to amputation. In addition, the resin tends to spread incompletely, resulting in significant fluctuations in the outer and inner diameters.

Preferably, the pressure of the pressurized fluid is kept at a constant value in the range of 1-4 kg/ctA.

Next, a preferred example of the method for producing a polyoxymethylene hollow body of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an apparatus for producing a hollow body according to the present invention, and polyoxymethylene supplied from a hopper 1 is
After being melted and plasticized in the extruder 2, it passes through a heated double die 3 and is led to a sizing die 4 without being exposed to the air, where the outer diameter of the hollow body is regulated and it is manufactured while being cooled. Ru. The hollow body exiting the sizing die 4 is completely solidified in a cooling tank 5 filled with a coolant such as water. Thereafter, the hollow body is taken up by a take-up machine 7 and then passed through a guide 8 and wound up by a take-up machine 9. The tip of the hollow body is sealed. The pressurized fluid is connected to the pressurized fluid supply pipe IO
is supplied to the double die 3.

FIG. 2 is a schematic cross-sectional view of the vicinity of the tip of the double die 3 shown in FIG. An outer die 12 provided on the outside with an annular gap therebetween, and a sizing die 4 provided adjacent to the end of the outer die 12;
It consists of a cooling tank 5. The sizing die 4 is one in which, for example, water 13 flows as a refrigerant, and the cooling tank 5 is filled with, for example, water 14 as a refrigerant.

The outer die 12 and the sizing die 4 may be connected directly mechanically as shown in FIG. 2, or may be connected via a heat insulating material between the outer die 12 and the sizing die 4. Yes, they may also be integrated. In any case, it is necessary that the inner diameter of the sizing die 4 is different from the inner diameter of the outer die 12, and that the resin is sealed so that it is not exposed to the outside at the connection surface between the outer die 12 and the sizing die 4. . The sizing die 4 and the cooling tank 5 may be connected directly as shown in FIG. 2, or may be separated from the sizing die 4, or the sizing die 4 may be connected in a double-layered manner as shown in FIG. It does not need to have a tube jacket structure, but may have a single tube structure and be connected to the outer die 12.

In this case, the cooling of the sizing die 4 is
The whole may be immersed in water as a coolant, for example.

Polyoxymethylene in the present invention is trioxane,
Alternatively, it may be obtained by a known polymerization method using formaldehyde as the main raw material, and may be a polyoxymethylene homopolymer, a polyoxymethylene copolymer, or a blend of both polymers. It may contain various additives, antistatic agents, plasticizers, and weather resistance improvers.

(Example) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto in any way.

Example 1. 2. Comparative Example 1.2 Polyoxymethylene (manufactured by Asahi Kasei Corporation, Tenac (registered trademark) 3010) was used to form a hollow body with an outer diameter of 4.6 mm at a distance of 4 m/min using the apparatus shown in Figures 1 and 2. Molding was performed at a speed of min. 0.3-6kg/cd as pressurized fluid
Compressed air was used and introduced from the inner die. Resin temperature 190
The resin was extruded at 10°C and water at 10°C was used as the coolant in the sizing die and cooling bath. The molding conditions are summarized in Table 1. When molding is performed with the compressed air pressure set within the range of the present invention, stable molding can be achieved for a long time without causing surface, internal or shape defects or cutting of the hollow body. It can be seen that the hollow body manufacturing method of the present invention is excellent.

Table 1 et seq. Margins (Effects of the Invention) According to the hollow body manufacturing method of the present invention, the occurrence of surface, internal, or shape defects can be suppressed and stable molding can be performed for a long time, resulting in high productivity and It can be said that this method is an excellent manufacturing method as it can produce hollow bodies extremely efficiently.

The polyoxymethylene hollow body obtained by the production method of the present invention is, for example, heated and stretched, and the resulting stretched filament is used in industries such as ropes, various control cables, and various rubber reinforcing materials. It is suitably used as a material.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of an example of an apparatus for carrying out the hollow body manufacturing method of the present invention, and FIG. 2 is a sectional view of the vicinity of the tip of the double die of the apparatus of FIG. In the figure, 1 is a hopper, 2 is an extruder, 3 is a double die, 4
is a sizing die, 5 is a cooling tank, 6 is a hollow body, 7 is a take-up machine, 9 is a winder, 10 is a pressurized fluid supply pipe, 11 is an inner die, 12 is an outer die, 13 is a refrigerant for the sizing die, 14
indicates the refrigerant in the cooling tank. Figure 1 Figure 2

Claims (1)

[Claims] Molten polyoxymethylene is continuously extruded from between a double die consisting of an outer die and an inner die with a pressurized fluid inlet hole in the center, and then extruded from the outside by a sizing die installed behind the double die. In the method of producing a polyoxymethylene hollow body by cooling, the pressure of the pressurized fluid is 0.5 to
A method for producing a polyoxymethylene hollow body characterized by maintaining a constant value in the range of 5 kg/cm^2