JPH02235731A - Manufacture of polyoxymethylene hollow body - Google Patents

Abstract

PURPOSE:To enable the resin-blocking or the breakage of a hollow body in the beginning of extrusion forming to be remarkably reduced by using the sizing die in which the ratio of the length of the sizing die to the inner diameter thereof satisfies a specified formula. CONSTITUTION:As a sizing die 4, the sizing die in which the ratio of its length (Lmm) to its inner diameter (Dmm) satisfies following formula is used, and said formula is 0.46XDp+0.16<L/D<0.65XDp+3.23, and then Dp is the outer diameter (mm) of a polyoxymethylene hollow body and is equal to or larger then 3.5. In the case of L/D<=0.46XDp+0.16, at the beginning of extrusion, the resin-blocking or the breakage of a hollow body in the sizing die does not occur easily, but a prescribed wall thickness is not easily obtained, whereby only the hollow body with thin wall thickness is obtained, and the dimension control of the outer diameter is not sufficient, whereby the deviation of the outer diameter becomes large. On one hand, in the case of L/D>=0.65XDp+3.23, the resin-blocking or the resin breakage at the beginning of extrusion occurs easily and stable forming is not achieved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing polyoxymethylene hollow bodies.

For further details, please refer to the polyoxymethylene hollow body, which can stably start extrusion molding without causing resin clogging in the sizing die, and can be stably molded for long periods of time under specified molding conditions. It is related to the manufacturing method.

[Conventional technology]

In extrusion molding of hollow bodies, much research and technological development has been conducted regarding sizing dies. Particularly regarding outer diameter sizing, vacuum sizing, prevention of dirt inside the sizing die (e.g., JP-A-58-142826), smoothing of the surface of hollow bodies (e.g., JP-A-56-82223), starting extrusion molding. There is a structure in which the sizing die can be divided in order to simplify the treatment at the time of cutting (Japanese Patent Application Laid-Open No. 55-95538).

[Problem to be solved by the invention]

The molten resin extruded from the double die is normally guided in a molten state to the sizing die, but the outer diameter is forcibly regulated by contacting the inner wall of the sizing die. Therefore, if the contact length or contact time between the sizing die and the resin is short, the start-up performance at the start of extrusion molding is good, but the molding is difficult to stabilize.On the other hand, if the contact length or contact time is long, The opposite tends to be true.

Start-up performance at the start of extrusion refers to the ease or difficulty of clogging or cutting of the resin in the sizing die due to contact with the sizing die.Good start-up performance means that these do not occur. means. In addition, stable molding is a state in which the outer diameter of the resin is sufficiently regulated by the sizing die, the hollow body is taken up without any jitter or sagging of the hollow body, and there is little variation in the outer and inner diameters and there are almost no surface defects. means. In the past, startup performance and stable moldability have hardly been studied starting from the sizing die. The present invention has been made with the object of providing an excellent method for manufacturing a hollow body that can sufficiently solve both of these contradictory problems.

As a result of various research into methods for manufacturing polyoxymethylene hollow bodies by extrusion molding, the present inventors have found that if the resin sizing die becomes clogged, extrusion molding can be started without cutting, and the prescribed molding can be carried out. It was discovered that the shape and dimensions of the sizing die are required to be suitable for the outer diameter of the hollow body in order to perform stable molding under various conditions, and the present invention was developed based on this knowledge.

[Means to solve the problem]

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 extrudes the polyoxymethylene at the rear of the double die. In the method of manufacturing a polyoxymethylene hollow body by external cooling using a sizing die, the length (L (picture)) and inner diameter (D (
A method for producing a polyoxymethylene hollow body characterized by using a sizing die whose ratio of mm) ) satisfies the following formula.
．． 46×Dp+0.16<L/D<0.65×Dp+3
．． 23 However, Dp is Borioki. The outer diameter (am) of the simethylene hollow body is Dp≧3.5.

In the method for producing polyoxymethylene hollow bodies of the present invention, the length (L (mm)) of the sizing die and the inner diameter (
The ratio of D (mm)) is the following formula, 0.46×Dp+0.1
6<L/D<0.65×Dp+3.23 However, Dp is the outer diameter (mm) of the polyoxymethylene hollow body, and Dp≧3.
5 must be satisfied.

When L/D≦0.46×Dp+0.16, resin clogging and cutting in the sizing die are unlikely to occur at the start of extrusion, but it is difficult to achieve a predetermined wall thickness, and only a thin hollow body can be obtained. Furthermore, the outer diameter is insufficiently regulated, resulting in large variations in the outer diameter. On the other hand, L/D≧0.65×Dp+3
．． With No. 23, resin clogging and cutting are likely to occur at the start of extrusion, and stable molding cannot be achieved. The sizing die is preferably made of brass with a mirror-finished inner wall.

Next, a preferred example of the method for manufacturing the polyoxymethylene hollow body of the present invention will be explained with reference to the accompanying drawings. Figure 1 shows
FIG. 1 is a schematic diagram of an apparatus for manufacturing a hollow body of the present invention, in which polyoxymethylene supplied from hopper 1 is
After being melted and plasticized in the extruder 2, it is guided through a heated double die 3 to a sizing die 4 without being exposed to the air, and the hollow body is manufactured while being cooled. The hollow body leaving 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 taking machine 7. Next, it passes through a guide 8 and is wound up by a winding machine 9.

FIG. 2 is a schematic cross-sectional view of the vicinity of the tip of the double die 3 shown in FIG. From an outer die 11 provided on the outside with an annular gap in between, and a sizing die 4 provided adjacent to the end of the outer die 11,
It consists of a cooling tank 5. The sizing die 4 is one in which, for example, water 12 flows as a refrigerant, and the cooling tank 5 is filled with, for example, water 13 as a refrigerant. The outer die 11 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 11 and the sizing die 4. Yes, they may also be integrated. In any case, it is necessary that the connection surface between the outer die 11 and the sizing die 4 has a sealed structure in which the resin is not exposed to the outside. The sizing 4 and the cooling tank 5 may be connected directly as shown in FIG. 2, or may be separated from the sizing 4. Further, the sizing die 4 does not have to have a double-tube jacket structure as shown in FIG. 2, but may have a single-tube structure and be connected to the outer die 11.

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 a main raw material, and may be a polyoxymethylene homopolymer, a polyoxymethylene copolymer, or a blend of both polymers. Furthermore, various additives for modifying polyoxymethylene, antistatic agents, plasticizers, and weather resistance improvers may be included.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to this in any way.

Examples 1 to 10, Comparative Examples 1 to 5 Polyoxymethylene (manufactured by Asahi Kasei Kogyo ■, Tenac (registered trademark) 3010) was used to prepare an outer diameter of 3.7 to 9.6 using the apparatus shown in FIGS. 1 and 2. A hollow body was molded. Resin temperature 1
The resin is extruded at 90°C, water at 10°C is used as a refrigerant in the sizing die and the cooling tank, and compressed air is pumped from the inner die at a rate of 2 kg/af for the hollow body with outer diameters of 3.7 and 4.0 mm.
1, and the other hollow bodies were delivered at 4 kg/ci. The shape, dimensions, and molding conditions of the sizing die are summarized in Table 1. Further, FIG. 3 shows the relationship between the outer diameter of the hollow body and the L/D of the sizing die in each example and comparative example, together with the range specified by ``2'' in the claims.

In the figure, the circle plots represent examples, the triangular plots represent comparative examples, and the numbers indicate the numbers of each example and comparative example. According to the method for producing a hollow body of the present invention, stable molding can be achieved without resin clogging or cutting at the start of extrusion molding. On the other hand, if extrusion molding is performed using L/D sizing outside the range specified by the formula described in the claims, resin clogging occurs at the start of molding, and molding is not even completed.

Even if molding can be started without causing resin clogging, the hollow body begins to sag during molding, the take-up condition becomes unstable, and stable molding cannot be achieved.

Table 1 et seq. Margins [Effects of the Invention] According to the hollow body manufacturing method of the present invention, resin clogging and cutting of the hollow body at the start of extrusion molding are significantly reduced, and stable molding is easily achieved, resulting in raw material loss. It is an industrially superior manufacturing method, as it enables labor savings by eliminating the need for troubleshooting and troubleshooting work, and allows hollow bodies to be manufactured extremely efficiently.

By stretching the polyoxymethylene hollow body obtained by the hollow body manufacturing method of the present invention, it can be suitably used as industrial materials such as lobes, various control cables, and various rubber reinforcing materials.

[Brief explanation of the drawing]

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 cross-sectional view of the vicinity of the tip of the double die of the apparatus of FIG. Code: 1 is hopper, 2 is extruder, 3 is double die, 4 is sizing machine,
5 is a cooling tank, 6 is a hollow body, 7 is a take-up machine, 9 is a winding machine, 1
0 is the inner die, 1l is the outer die, 12 is the refrigerant of the sizing die, 13 is the refrigerant of the cooling tank, L is the length of the sizing die,
D indicates the inner diameter of the sizing die. FIG. 3 is a graph showing the relationship between the outer diameter of the hollow body and the L/D of the sizing die in each example and comparative example, together with the range specified by the formula described in the claims. . In the figure, the circle plots represent Examples, the triangular plots represent Comparative Examples, and the reference numbers indicate the numbers of each Example and Comparative Example. Patent Applicant: Asahi Kasei Kogyo Co., Ltd. Figure 3 Figure IrlA Figure 2 Intracorporeal Dρ (mm)

Claims (1)

[Claims] Molten polyoxymethylene is continuously extruded 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 installed at the rear of the double die. In the method of manufacturing a polyoxymethylene hollow body by external cooling using a sizing die, the sizing die has a ratio of length (L (mm)) to inner diameter (D (mm)) that satisfies the following formula. A method for producing a polyoxymethylene hollow body characterized by using 0.46×Dp+0.16<L/D<0.65×Dp+
3.23 However, Dp is the outer diameter (mm) of the polyoxymethylene hollow body
, Dp≧3.5