JPH0231658B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a vent plug structure for a mold for urethane resin foam molding, which is used when foaming a foamable urethane resin composition to produce a urethane resin foam molded product. The present invention relates to a venting plug structure for a urethane resin foam mold that is easy to use, does not cause troubles such as clogging or rusting of the structure, and is durable enough to maintain excellent venting performance over a long period of use.

When molding a urethane resin foam molded product, a foamable urethane resin composition is placed in a foam molding mold, and heated if desired to increase the foaming volume, thereby obtaining a urethane resin foam molded product that fills the mold. The method has been widely adopted. In such a foam molding method for foamable urethane resin compositions, the discharge of gas accompanying foam molding is performed under open conditions or with appropriate valve means in response to an increase in mold internal pressure. It is carried out under substantially closed conditions with the possibility of evacuation.

The urethane resin foam molded product obtained by the conventional method as described above has a disadvantage in that it has a protrusion which requires work to cut and remove because it fills up to the inside of the gas discharge part. In addition to this, there is the disadvantage that the foamable urethane dendritic composition is wasted.

Conventionally, overcoming the above-mentioned troubles in foam molding of expandable urethane resin compositions has been overlooked. The inventors of the present invention have conducted research in order to develop means that can industrially advantageously avoid the disadvantages and inconveniences described above.

As a result, the thickness is 0.5 mm or more, the apparent specific gravity is 0.8 to 1.8,
By providing an air vent structure made of a polytetrafluoroethylene porous material with a non-fibrillar structure with an air permeation resistance of 0.1 to 2 as an exhaust means for a mold for urethane resin foam molding, the above-mentioned method can be achieved. Disadvantages and inconveniences can be overcome at once, simple structure,
It has been discovered that it is easy to manufacture, does not cause clogging due to the intrusion of the foamable urethane resin composition into the structure, and can achieve outstanding improvement effects such as maintaining excellent air removal performance for a long period of time.

Furthermore, regarding rubber materials whose molded product forming mechanism and moldability are significantly different from those of foamable urethane resin compositions, during vulcanization molding under heating and pressurizing conditions, the mold surface of the rubber mold and If gas is sealed between the rubber material and the rubber material, the rubber material will be vulcanized and molded without sufficient pressure on the mold surface.
As a conventional proposal to overcome the problem of unavoidable surface failure of the resulting vulcanized rubber molded product, which often causes a loss of commercial value, a porous metal such as a sintered metal material was used in the vent hole of the rubber mold. Insert the body,
It is also known to use a vent plug structure to escape and remove the gas enclosed in the rubber molding mold through the pores of the metal material. However, in addition to the drawback that it is difficult to avoid the intrusion of rubber materials into the pores of the vent plug structure, there is also the problem of rusting, and a clogging phenomenon occurs in a relatively short period of time, resulting in the expected failure. There are deficiencies that prevent the goal from being achieved over a long period of time. Furthermore, the fact that it is difficult to industrially easily and inexpensively manufacture a porous metal body that matches the shape of the vent hole of a rubber molding die is a bottleneck, and the reality is that it is difficult to put it into practical use. . In addition, various proposals have been made regarding metal vent plug structures for rubber molding molds that require a complex structure with a special shape, but these structures are complex, difficult to manufacture, and expensive. The reality is that it is difficult to put it into practical use because it has many technical defects.

According to the research conducted by the present inventors, non-fibrillar structure polytetrafluoroethylene porous materials, especially non-fibril structure polytetrafluoroethylene porous materials having a thickness of 0.5 mm or more, an apparent specific gravity of 0.8 to 1.8, and an air permeation resistance of 0.1 to 2. The venting plug structure for urethane resin foam molding molds made of a porous tetrafluoroethylene material is completely different from the metal porous material, and has excellent venting performance without the trouble of clogging. can be maintained for a long time,
Furthermore, it has been discovered that it has the advantage of being simple and easy to manufacture, has no fear of rusting problems, and has excellent performance as a vent plug structure for urethane resin foam molds.

According to the research conducted by the present inventors, the polytetrafluoroethylene porous material with a non-fibrillar structure exhibits non-adhesive properties due to the low surface tension, and furthermore, the communicating pore structure of the porous material is extremely complicated and curved. It is presumed that the pores are connected to each other by showing a constricted partial structure where the polytetrafluoroethylene particles are fused and bonded to each other. It has been discovered that the problem of intrusion into the communicating hole structure of the mass body is effectively prevented, and it exhibits durability that maintains its excellent air extraction performance for a long period of time.

Furthermore, since there is no reduction in air extraction ability due to clogging, the long-term durability mentioned above is outstanding, and the product shows outstanding performance by being able to maintain its excellent air extraction ability even after repeated molding over 5000 times. Furthermore, it is possible to obtain a urethane resin foam molded product with an excellent finished surface without leaving any traces of vent holes on the finished surface of the urethane resin foam molded product, and also because it is inexpensive and easy to mass produce, it is industrially remarkable. It has been found that an excellent vent plug structure for a urethane resin foam molding mold can be provided.

Therefore, an object of the present invention is to provide a vent plug structure for a urethane resin foam mold, which has never been proposed before.

The above objects and many other objects and advantages of the present invention will become more apparent from the following description.

The vent plug structure for a urethane resin foam mold of the present invention has a thickness of 0.5 mm or more, preferably 1 mm or more,
More preferably about 5 mm or more and an apparent specific gravity of 0.8 to
1.8, preferably about 1 to about 1.8, more preferably about 1 to about 1.6, and an air permeation resistance of 0.1 to 2, preferably about 0.2 to about 1.

If the thickness of the porous body is too thin, less than 0.5 mm,
In addition to being unsatisfactory in terms of strength, the foamable urethane resin composition tends to invade the pores of the porous body and cause clogging. It is preferable to use a porous material with a diameter of about 5 mm or more.

In addition, if the apparent specific gravity of the porous body is less than 0.8, the mechanical strength of the porous body will deteriorate, and if it exceeds 1.8, the air permeation resistance will become too high and the air extraction capacity will decrease, so it should be 0.8 to 1.8. , preferably having an apparent specific gravity of about 1.8 to about 1.8, more preferably about 1 to about 1.6.

Further, the porous body preferably has an apparent specific gravity and an air permeation resistance related to its continuous porous structure of 0.1 to 2, preferably about 0.2 to about 1. in general,
The lower the air permeation resistance, the higher the air removal capacity.
If it is too small, less than 0.1, clogging of the air vent plug tends to occur, and the finished surface of the formed urethane resin foam molded product tends to be poor.
If the air permeation resistance is too high, exceeding 2, the air removal ability will deteriorate and a satisfactory air removal plug effect will be lost.

In the present invention, the air permeation resistance is determined by the portable dry gas meter model P-1-1 manufactured by Shinagawa Seisakusho.
Thickness: 10mm, diameter: 23mm (however, the contact area with air is 2.0mm)
It is expressed as the reciprocal of the air permeation rate (/min) per 1 cm ² measured at an air pressure of 1.0 Kg/cm ² G using a polytetrafluoroethylene porous body with a diameter ^of 16 mm.

The vent plug structure for a urethane resin foam mold of the present invention may have any shape that can be installed at an appropriate location to block the gas passage of the vent hole, and may be in the form of a sheet, block, or other various shapes. However, it is necessary to be composed of a polytetrafluoroethylene porous body with a non-fibrillar structure. Polytetrafluoroethylene porous material with a fibrillar structure has an open pore structure with a fibrillar structure, which makes the pores itself extremely flexible, and the pores are easily collapsed by molding pressure, making it difficult to vent air. There are defects that reduce performance, and there is also the disadvantage that a convex portion is formed at the part of the molded product that contacts the vent hole.

The polytetrafluoroethylene porous body having a non-fibrillar structure that forms the vent plug structure for a urethane resin molding die of the present invention can be produced by various methods known per se.

For example, it can be manufactured by utilizing the plastic memory of fired polytetrafluoroethylene powder, which is a preferred manufacturing method. According to this manufacturing mode, for example, the average particle size is about 10 to about 1000μ.
The ^fired polytetrafluoroethylene powder of
A polytetrafluoroethylene porous body having a non-fibrillar structure can be produced by free sintering at a temperature of about 330° to about 400°C. The fired polytetrafluoroethylene powder is
Polytetrafluoroethylene powder, e.g. 327
It can be obtained by heat treatment at a temperature of .degree. C. or higher. The compressed polytetrafluoroethylene sintered powder constituting the above preformed product is
Due to the memory, the powder is elastically restored and restored to its original shape as the fired polytetrafluoroethylene powder, and the powder particles are fused together to form a polytetrafluoroethylene porous body with a non-fibrillar structure.

Average particle size of about 20 to about 700 μ, especially special public 1970-
A porous body obtained from the above embodiment using a fired polytetrafluoroethylene powder with a small specific surface area, with an average particle size of about 300 μ or less and a sphericity of 1.2 or less, as described in No. 32098 and No. 53-13228. This further enhances the above-mentioned effect.

In the present invention, the term "polytetrafluoroethylene" includes not only a homopolymer of tetrafluoroethylene but also a polymer containing a modified amount of a copolymer component. Examples of such copolymer components include fluoroolefins, fluorovinyl ethers, and fluoroketones.

The vent plug structure for a urethane resin foam mold of the present invention can be used by being fixed at an appropriate position to block the gas passage of the vent hole, but preferably, it is screwed or fitted into the vent hole. It can also be used in a preferred embodiment in which it is fixed at a position that blocks the hollow part of the hollow protection tube which can be fixed by other removable means.

An example of the above preferred embodiment will be explained with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of an example of a urethane resin foam molding mold having vent holes;
The figure is a schematic cross-sectional view (cross-sectional lines are omitted) of a vent plug structure for a urethane resin foam molding mold of the present invention, showing an example of the preferred embodiment.

FIG. 1 shows a state in which a foamable urethane resin composition accommodated in a urethane resin foam molding mold 1 having two vent holes 4 is foam-molded to form a urethane resin foam 3. It is shown. According to a preferred embodiment of the present invention, a polytetrafluoroethylene porous body 11 having a non-fibrillar structure is provided in the hollow portion of the heat-resistant hollow protective tube 12 in the two vent holes 4, 4, which are provided by screwing means. It is shown as an air vent structure fixed in a position to block the air. In Fig. 1, no protrusions are formed due to the intrusion of the foamable urethane resin composition into the vent holes, and the venting is completed and the finished surface of the foam is aligned with the mold surface. has been done.

FIG. 2 shows an example of a preferred embodiment of the vent plug structure for a urethane resin foam mold of the present invention shown in FIG. 1 above. In FIG. 2, the polytetrafluoroethylene porous body 11 with a non-fibrillar structure covers the hollow part of the heat-resistant hollow protection tube 12.
It is fixed at the blocking position at the end of the mold surface. The outer peripheral surface of the protective tube 12 is provided with a thread 1 for removably fixing it to the mold 1 by screwing means.
3 has been applied. In this example, a sloped portion 14 is provided on the inner surface of the protective tube 12 near the end,
A mesh 16 is provided in contact with the surface of the porous body 11 in the direction of the outlet of the air vent 4, and a retaining pin 17 that crosses the protective tube and the porous body is attached to the end of the porous body 11. An example is shown in which . This fixing means can be changed as appropriate and the design can be changed freely by those skilled in the art, and these design changes are included in the scope of the present invention. In short, any fixing means that does not cause the porous body 11 to shift from its desired fixing position can be employed.

The material of the hollow protection tube may be any material that can withstand foam molding of the foamable urethane resin composition, and for example, metal materials, synthetic resin materials, etc. can be used. Specific examples of such materials include:
For example, iron, steel, aluminum, alloys containing the same, polyphenylene sulfide, polyimide resin, fluororesin, heat-resistant aromatic polyamide resin, etc. can be exemplified. The shape of the protective tube can also be selected appropriately, and there are no particular restrictions, but a cylindrical hollow tube having an inner diameter of about 5 to about 10 mm is usually preferably used. By using such a protection tube, the strength, dimensional stability, durability, etc. of the vent plug structure can be further enhanced, and the advantages include easier operations such as fabrication and replacement of the vent plug structure. There is.

[Brief explanation of drawings]

FIG. 1 of the accompanying drawings is a schematic cross-sectional view of an example of a mold for urethane resin foam molding having vent holes, and FIG. 2 is an example of a vent plug structure for a mold for urethane resin foam molding according to the present invention. FIG.

Claims (1)

[Scope of Claims] 1. Urethane resin foam molding characterized by being made of a polytetrafluoroethylene porous body with a non-fibrillar structure having a thickness of 0.5 mm or more, an apparent specific gravity of 0.8 to 1.8, and an air permeation resistance of 0.1 to 2. Vent plug structure for molds. 2. The vent plug structure according to claim 1, wherein the polytetrafluoroethylene porous material having a non-fibrillar structure is fixed at a position that blocks the hollow portion of the hollow protection tube.