JPH021003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thermoplastic resin foam board. More specifically, this invention extrudes a thermoplastic resin containing a foaming agent into a tube shape to foam it, and while the tube's inner surface is still softened, the tube is flattened and the inner surfaces are fused together to form a resin. The present invention relates to a method for obtaining a foam board.

A die with a circular slit is attached to the tip of the extruder, a thermoplastic resin containing a foaming agent is melted within the extruder, the molten resin is extruded through the slit to form a tube, and the tube is foamed. A method is already known in which a tube is flattened while the inner surface of the tube is still softened and the inner surfaces are fused together to obtain a foam board. According to this method, a resin plate foamed to a low magnification can be easily produced, but it is not easy to obtain a resin plate foamed to a high magnification. This is because when trying to foam at a high magnification, the extruded tube-shaped resin rapidly increases in volume, and as the length in the circumferential direction increases, the cross-sectional shape bends into a petal-like shape. It becomes impossible to maintain the circular shape, resulting in many unevenness, and as a result,
This is because a large number of wrinkles extending in the longitudinal direction will be generated, making it impossible to obtain a foam board of good quality. The above-mentioned wrinkles can be corrected to some extent by pressing the surface, but even if the wrinkles are corrected in this way, the wrinkles remain as stripes on the surface, deteriorating the appearance of the foam board.

Various attempts have been made to prevent the occurrence of stripes as described above. One method is to attach a core mold to the tip of the mouthpiece, and make the extruded tube advance along the core mold. It is to take it as a thing. However, in order to advance the tube along the core mold, it is necessary to cool the inner surface of the tube to some extent, and if the inner surface is cooled, it is not possible to fuse the inner surface later, which causes a problem. In addition, in a state where the inner surfaces can be fused together,
It is difficult to advance along the core mold. Therefore, in any case, it is inappropriate to use a core type.

Additionally, Japanese Patent Publication No. 52-44355 describes a method for producing a striped foam sheet as described above. That is, this publication proposes that a cooling outer cylinder is attached to the tip of the mouthpiece, the extruded resin tube is made to advance along the inner surface of the outer cylinder, and a notch is provided on the side of the outer cylinder that contacts the mouthpiece. This paper describes a method for obtaining a foam sheet by preventing the tube extruded from the outer cylinder from coming into immediate contact with the outer cylinder. Additionally, this publication exemplifies a cooling outer tube that is shaped to become wider toward the tip, and also states that air may be blown from the cap into the tube between the inner welding roll and the cap. There is. However, since the method of this publication requires that the tube not come into contact with the outer cylinder at the above-mentioned notch, the amount of blown air cannot be high enough to bring the tube into close contact with the outer cylinder. Therefore, the cooling outer cylinder only cools the tube from the outside, and does not play a role in regulating the outer diameter.
Therefore, with the method of this publication, a foam with a very good surface condition cannot be obtained.

On the other hand, there is also known an attempt to improve the fusion of the inner surface of the tube by pressurizing water vapor into an extruded polystyrene tube when manufacturing a foamed polystyrene sheet. That is the special public service in 1973.
It is described in Publication No. 40789. However, this attempt is not concerned with improving the surface condition in the foam.

The inventor attempted to obtain a highly foamed foam board with a good surface condition and free from the above-mentioned stripes. To do this, the foaming resin tube that has come out of the mouthpiece is surrounded by an outer cylinder, and the resin tube is made to advance along the inner surface of the cylinder, and the cylinder is shaped like a funnel that widens toward the entrance. In addition, it has been found that it is effective to make the exit side and the inside side the same or slightly smaller. Furthermore, the inventor found that it is effective to maintain the inside of the tube under pressure in order to bring the resin tube into close contact with the inner surface of the cylinder. This invention was made based on such knowledge.

This invention extrudes a thermoplastic resin containing a foam plate from a die into a tube shape, passes the extruded tube through a cylinder, and foams exclusively within the cylinder, so that the inner surface of the tube is still softened when it exits the cylinder. In a method of manufacturing a thermoplastic resin foam board by sandwiching a tube between a pair of rolls and fusing the inner surface of the tube, the inner surface of the tube is widened into a funnel shape at the entrance in the direction of travel, and the exit is The method is characterized in that the tube remains in the expanded shape, and pressurized gas is injected into the tube through the mouthpiece, the tube is maintained in a pressurized state, and the tube advances while being brought into close contact with the inner surface of the tube. , relates to a method for manufacturing a thermoplastic resin foam board.

The method of this invention will be explained as follows based on the drawings. FIG. 1 is a partially cutaway sectional view showing one embodiment of the method of the present invention. FIG. 2 is a partially cutaway perspective view of a foam board obtained by the method of this invention.

In FIG. 1, 1 is an extruder, 2 is a die, 3 is a tube, 4 is a pair of rolls, 5 is a take-up roll, and a is a foamed resin tube. Base 2
is attached to the tip of the extruder 1. Base 2
is constructed by inserting a core mold 22 into an outer mold 21 and fixing them together. Fixation is achieved by supporting the core mold 22 at some places with the support bridges 23. Reference numeral 24 denotes a gas supply pipe which passes through the inside of the branch 23 and opens at the tip of the core mold 22. Reference numeral 25 denotes a gas discharge pipe, which similarly opens at the tip of the core mold 22.

The tube 3 has an inlet side part 31 and an outlet side part 32.
It is made up of. The entrance side portion 31 has an inner surface widened into a funnel shape in the direction of travel, and the exit side portion 32 has an expanded inner surface and has substantially the same cross-sectional shape. I have it. Therefore, the inner cavity of the cylinder 3 is located at the entrance side 31.
Although the cross section is suddenly enlarged at the exit wall 32, the cross section is substantially the same throughout the exit wall 32, and there is no step between the entrance wall 31 and the exit wall 32. However, the lumen of the outlet sill 32 may be very slightly reduced in the direction of travel, specifically by about 3% or less of the enlarged diameter.
Further, a cooling medium passage 33 is buried inside the cylinder 3.

The method of this invention is carried out as follows. A thermoplastic resin containing a blowing agent is melted and kneaded in an extruder 1, the molten resin is press-fitted into a die 2, and an outer mold 2 is formed.
1 and the core mold 22 in the shape of a tube. The extruded resin is guided into the tube 3 while remaining in a tube shape, and is allowed to advance along the inner wall of the tube 3. The tube coming out of the cylinder 3 is flattened and sandwiched between a pair of rolls 4, and while the inner surface of the tube is still softened, the inner surfaces of the tube are fused to each other to form a two-ply foam board. At this time, on the other hand, pressurized gas is sent from the pipe 24 and stored in the tube a to forcibly increase the inner diameter of the tube a, so that the tube a is brought into close contact with the inner wall of the cylinder 3. On the other hand, in order to prevent excess gas generated from the resin from accumulating in the tube a, the gas in the tube a is appropriately discharged from the pipe 25. In this way, the inside of tube a is maintained in a pressurized state,
By bringing the tube a into close contact with the inner wall of the cylinder 3, the tube a is prevented from forming wrinkles on its outer surface. Note that cooling water is circulated through the cooling passage 33 of the tube 3 to cool the tube a from the outside.
Fix the tube quickly.

According to the method shown in FIG. 1, the tube a is prevented from forming wrinkles based on the following principle. The resin extruded from the die foams because it contains a foaming agent, increasing its apparent volume. This volume increase occurs in three directions of tube a.
That is, the length of tube a increases in three directions: the extrusion direction of tube a, the circumferential direction, and the thickness direction. Among these, the increase in the extrusion direction can be easily absorbed and adjusted so as not to become excessive by increasing the take-up speed of tube a. Further, the increase in the thickness direction can be easily caused because there is nothing inside the tube a that prevents foaming. The problem is the increase in the length in the circumferential direction, but since there is a cylinder 3 on the outside in the circumferential direction and pressurized gas exists on the inside, the tube is forced to expand into the cylinder 3 by the pressurized gas. As a result of being pressed against it, it follows the inner wall of the tube, thus preventing wrinkles from forming on the outer surface of the tube.

In particular, in the method shown in FIG. 1, since the tube 3 has a continuous inner cavity that expands in a funnel shape and an inner cavity that does not expand, the tube can be reliably aligned with the inner wall of the tube. In other words, when the tube 3 has only an inner cavity that expands like a funnel, increasing the internal pressure of the tube will cause the tube to expand its inner diameter indefinitely or expand its inner diameter after leaving the tube 3. , it is difficult to reliably align the tube with the inner wall of the cylinder. However, if there is a lumen part at the tip of the tube 3 with an inner diameter that is substantially the same as the inner diameter of the funnel-shaped enlarged end, the inner diameter of the tube a cannot be increased any further, so the air pressure inside the tube cannot be increased. It is allowed to increase in size, so that the tube can be reliably aligned with the inner wall of the cylinder 3.

In the method of this invention, the tube 3 has, in addition to a lumen that expands in a funnel shape (this is called a funnel-shaped lumen), a lumen that has an inner diameter that is substantially the same as the enlarged part of the funnel-shaped lumen (this is called a funnel-shaped lumen). One of its characteristics is that it has a parallel lumen (called a parallel lumen). Parallel lumens, as already mentioned, have essentially the same lumen from start to finish, but as they approach the other end from the funnel-shaped lumen side, It also includes those whose surface shape is slightly narrowed. It is desirable that the funnel-shaped lumen has a shape that expands as rapidly as possible depending on the degree of foaming of the foaming tube.
That's not absolutely necessary.

The shape and size of the funnel-shaped lumen and the parallel lumen are appropriately determined depending on the foaming ability of the resin and the desired shape of the tube. In particular, the shape of the funnel-shaped lumen can be greatly changed depending on the expansion ratio of the resin to be obtained. For example, if the resin is to be expanded 25 times, the widening angle of the funnel-shaped lumen should be approximately 120 degrees, and the maximum diameter of the lumen should be approximately 2.5 times the diameter of the inlet. When attempting to foam the resin 25 times or more, the expansion angle of the funnel-shaped lumen is made larger than 120 degrees. In addition, the shape of the parallel lumen is such that its inner diameter remains equal to the maximum diameter of the funnel-shaped lumen from beginning to end, or decreases by about 3% or less at the exit side, and in the parallel direction Regarding the length, the aim is to ensure that the tube is cooled in the parallel lumen and that the diameter does not increase any further after exiting from there, but that the inner surface can still be fused. stipulate.

One feature of the method of this invention is that pressurized gas is injected into the resin tube a through a mouthpiece. The pressure of the pressurized gas inside the tube is
0.01 to 2 atmospheres (gauge pressure) G. This pressure is caused by the pressurized gas from the gas supply pipe 24,
This occurs as a difference from the gas discharged from the gas discharge pipe 25. Due to the presence of such pressurized gas, the resin tube a comes into close contact with the funnel-shaped lumen and the parallel lumen, and therefore its outer shape is regulated within the tube 3, resulting in a good outer surface. .

In the method of this invention, even when the expanded shape of the funnel-shaped lumen does not match the natural expansion state of the resin tube, the pressurized gas within the tube prevents unevenness from occurring on the outer surface of the tube. Therefore, the outer surface is good. However, if the funnel-shaped lumen is smaller than the naturally expanded state of the tube, unevenness will occur on the inner surface of the tube. When a tube with an uneven inner surface is passed through the roll 4 and the inner surface is fused, the fused surface becomes a curved surface and remains inside the foam board. A foam whose fused surface is bent in this manner becomes a foam board with high bending strength in the longitudinal direction.

Various types of thermoplastic resins can be used in the method of this invention. Typical among these are styrene resins and olefin resins. As the styrene resin, in addition to polystyrene, a copolymer of maleic anhydride and styrene can be used.As the olefin resin, in addition to polyethylene and polypropylene, a copolymer of olefin, such as ethylene and styrene or acetic acid, can be used. Copolymers with vinyl can be used.

Various blowing agents can be used in the method of this invention. For example, aliphatic hydrocarbons, halogenated hydrocarbons, ethers, thermally decomposable blowing agents, and the like can be used. Propane, butane, pentane, hexane, petroleum ether, etc. can be used as aliphatic hydrocarbons, methyl chloride, monofluorotrichloroethane, etc. can be used as halogenated hydrocarbons, and dimethyl ether, diethyl ether can be used as ethers. As the thermally decomposable blowing agent, soda carbonate, azodicarbonamide, etc. can be used.

In the method of this invention, it is possible to add a small amount of a foam control agent in addition to the blowing agent. The bubble regulator is used to make the bubbles that are generated finer. Foam control agents are, for example, talc.

According to the method of this invention, a foam board with a good surface condition can be easily obtained. Since the foam board is made by flattening the tubes, it can be made into a thick board. Therefore, according to the method of this invention, thick plates can be easily manufactured. Further, in the method of the present invention, the surface condition is always good even when foaming is performed at a high magnification, so a foam board with a high magnification can be easily obtained. moreover,
By creating a funnel-shaped inner cavity that suppresses natural foaming of the resin from the outside, unevenness is formed on the inner surface of the tube, thereby forming a curved fusion surface within the foam board, resulting in a foam board with high bending strength. can be obtained. The method of this invention provides the advantages described above.

The following is a supplementary explanation of the fact that the foam board with the above-mentioned bent fused surface has a large bending strength. In Figure 2, foam plates b and c
The foamed board of the present invention is obtained by flattening a tube, such as tube a in FIG. The welding surface 6 in the foam board has a small thickness, but is present as a high-density surface and extends through the foam board in the longitudinal direction.
When looking at the cross section of the fused surface 6, as shown in FIG. 2, it is bent in the middle of the thickness. Although the bending is not exactly a repetition of the same waveform, when the amplitude D of the waveform is large, the foam board has a large bending strength in the longitudinal direction E. Specifically, when the length of the amplitude D becomes one-tenth or more of the thickness T of the entire foam board, the foam board has a high bending strength. The method of the present invention is advantageous in obtaining such a foam board.

Next, the method of this invention will be specifically explained with reference to Examples.

Example: Add 1 part by weight of talc powder as a foam regulator to 100 parts by weight of polystyrene, put this into an extruder, heat knead it, press-fit 8 parts by weight of butane as a blowing agent into this kneaded product, and insert it into the nozzle. It was extruded from the circular space in a tube shape. As shown in FIG. 1, the extruded tube was advanced along the tube 3 attached to the tip of the mouthpiece.

The outer diameter of the circular tube is 95 mm, the width of the tube is 1.2 mm, the inner cavity at the end of the cap is 100 mm in diameter, the enlarged end of the funnel-shaped bore is 250 mm in diameter, and the length along the axis is 70 mm.
In addition, the parallel lumens began and ended with a diameter of 250 mm and a length along the axis of 50 mm.

Pressurized gas was sent from the gas injection pipe 24 and exhausted from the gas discharge pipe 25 to maintain air at a gauge pressure of 0.12 atmospheres in the tube a, thereby bringing the tube a into close contact with the inner surface of the cylinder. .

In this way, a good foam with a uniform surface and no irregularities or stripes was obtained. The foam is 25mm thick, 400mm wide,
The density was 0.042 g/cc. In addition, the fused surface is curved in the cross section, and the amplitude of the fused surface is approximately
It was 20mm. When the bending strength was measured, the bending strength in the longitudinal direction was 11.5 Kg/cm ² , and it was found that the bending strength was high.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway sectional view showing one embodiment of the method of the present invention. FIG. 2 is a partially cutaway perspective view of a foam board obtained by the present invention.

Claims (1)

[Claims] 1. Extrude thermoplastic resin containing a foaming agent into a tube shape from a mouthpiece, pass the extruded tube through a cylinder to foam exclusively within the cylinder, and while the inside of the tube exits the cylinder is still softened. In a method of manufacturing a thermoplastic resin foam board by sandwiching a tube between a pair of rolls and fusing the inner surface of the tube, the inner surface of the tube is expanded into a funnel shape at the entrance in the direction of travel, and at the exit. The heat treatment is characterized by keeping the tube in its expanded shape, injecting pressurized gas into the tube through the mouthpiece, keeping the tube in a pressurized state, and advancing the tube while bringing it into close contact with the inner surface of the tube. A method for producing a plastic foam board.