JP2001277245A - Mold for molding crosslinked rubber product and method for producing the product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold for molding a crosslinked rubber product which is effective for preventing the generation of defects and cracks especially in the production of a crosslinked rubber product of a large volume and can facilitate the finish of the product and a method for producing the crosslinked rubber product by using the mold. SOLUTION: In the mold 10 having a hollow sacrifice layer forming part 11 on the split surfaces 4 of molds 2, 2. the part 11 is composed of a shallow part 12 communicating directly with the cavity 3 and a deep part 13 communicating with the cavity 3 through the part 12, and the depth of the part 13 is larger than that of the part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die used for producing a rubber crosslinked product, and more particularly, to a rubber crosslinked product molding die suitable for molding a large-capacity product, and using the same. And a method for producing a crosslinked rubber product.

[0002]

2. Description of the Related Art Rubber crosslinked products (rubber molded products)
After heating the molding die processed according to the product shape to an appropriate temperature, filling the cavity of this mold with uncrosslinked rubber, sulfur and peroxide previously compounded in the uncrosslinked rubber By subjecting the rubber to a crosslinking reaction. FIG.
FIG. 2 is a view showing an example of a mold for molding a rubber crosslinked product used in such a manufacturing method, and reference numeral 1 in FIG. 2 denotes a mold for molding a rubber crosslinked product (hereinafter abbreviated as a molding mold). .

The molding die 1 has a pair of dies 2, 2, and a cavity 3 having a circular vertical section is formed inside the dies 2, 2. In addition, a cracking surface of the molding die 1, that is, a parting surface (cracked surface) 4 serving as a joining surface of the molds 2 and 2 as shown by a solid line in FIG. A hollow sacrificial layer forming portion 5 is formed. The sacrifice layer forming portion 5 is formed by extruding rubber called burrs (sacrifice layer) as described later.
It is formed for the purpose of taking charge.

By the way, in general, molded products (crosslinked rubber products)
The following two methods are mainly adopted as a method for producing the rubber according to the method of filling a mold with rubber. One is to apply or wind uncrosslinked rubber, which has been molded into a sheet or tape shape, etc., according to the shape of the mold in advance, around the product forming portion (cavity) of the mold, and then press the heated press This is a method of pressure molding with a molding machine, and is a method generally called a press molding method. The other is a method of injecting and filling a pre-heated and pressurized uncrosslinked rubber into a mold as shown in FIG. 2 by an injection molding machine and molding, and is generally called an injection molding method. Is the way.

In any of these methods, the mold is used while being heated and kept at a predetermined temperature by a heat source such as a hot platen or a heater built in the mold. The uncrosslinked rubber to be injected and filled into the mold is kept at room temperature in press molding, whereas in injection molding, it is stored in a measuring device in advance.
Generally, it is heated to a temperature of 00 ° C. or less.

The uncrosslinked rubber is filled into, for example, the cavity 3 of the molding die 1 shown in FIG.
Heated by Then, the uncrosslinked rubber thermally expands due to a temperature difference at the time of filling or heat generated by a crosslinking reaction, whereby the rubber pressure in the molding die 1 gradually increases. In this way, the cross-linking reaction is carried out, and the rubber cross-linked product obtained after the molding is completed retains its product shape even at the molding temperature. (Release). Therefore, such a manufacturing method does not need to cool the mold, which is advantageous in terms of thermal energy and time required for the manufacturing.

[0007]

By the way, especially in the case of manufacturing a large-capacity thick-walled cast product by an injection molding method, the pressure in the mold at the time of cross-linking greatly increases, and the internal pressure cannot withstand this increase. In some cases, rubber may gradually protrude from the cracked surface (parting surface) of the molding die during molding.
If such protrusion occurs after cross-linking of the surface, the protrusion is lost from the product portion, resulting in a product defect. In addition, when the molding die is opened at the time of mold release, the pressure is rapidly and locally released at the cracked surface, so that the obtained product may be cracked and defective.

In order to prevent such inconvenience, a sacrificial layer forming portion 5 is usually provided in the molding die 1 as shown in FIG. The crack is prevented from reaching the rubber, and the crack is prevented from reaching the product even when a sudden pressure is released at the time of demolding.

However, since the burrs formed in the sacrificial layer forming portion 5 are unnecessary portions for the obtained product, the boundary with the product portion formed in the cavity 3 is finally cut off. A finishing operation called deburring for smoothing is required. Therefore, it is desired that the shape of the burr formed by the sacrificial layer forming portion 5 be as thin and small as possible so that the product can be easily finished.

However, as the size of the product increases, the rise in the internal pressure of the molding die 1 also increases. Therefore, it is necessary to increase the volume of the sacrificial layer forming portion 5 accordingly.
That is, as shown in FIG. 3, the depth d of the mold 2 from the parting surface 4 is increased in order to increase the depth D of the sacrificial layer formation portion 5, and the length L is also increased to increase the depth D. If the volume of the part 5 is not increased, the resulting product cannot be prevented from being broken or cracked.

Further, as shown in FIG. 3, a portion for forming a joint portion which is a boundary portion between the product portion and the burr, ie, a boundary portion between the cavity 3 and the sacrificial layer forming portion 5, is obtained. In order to prevent cracks in the product to be formed, the inner surface of the sacrificial layer forming portion 5 has a curved surface (usually an R surface) that expands toward the cavity 3. Therefore, the larger the radius of curvature R of the curved surface (R surface), the more difficult it is to crack. However, if the radius is too large, the boundary between the product portion and the burr becomes ambiguous, so that the finishing becomes more difficult. However, there is a limit in increasing the radius of curvature R.

Further, in order to prevent defects or cracks in the product portion, there is a measure in material composition such as using a filler having a higher reinforcing effect such as carbon. However, for example, when the product to be formed is used for an insulating layer of an electric component, carbon cannot be used as a filler, and its use is limited, and defects due to defects or cracks in the obtained rubber cross-linked product are reduced. It was not enough to ensure prevention.

The present invention has been made in view of the above circumstances, and has as its object to be particularly effective in preventing defects due to breakage or cracking when manufacturing a large-capacity rubber crosslinked product. It is an object of the present invention to provide a mold for molding a rubber crosslinked product, which can also facilitate finishing, and a method for producing a rubber crosslinked product using the same.

[0014]

Means for Solving the Problems Claim 1 of the present invention
In the rubber crosslinked product molding die according to the above, in the rubber crosslinked product molding die having a hollow sacrificial layer forming portion communicating with the cavity on the cracked surface of the mold, the sacrificial layer forming portion, Forming a shallow portion directly communicating with the cavity and a deep portion communicating with the cavity through the shallow portion, the depth of the deep portion being greater than the depth of the shallow portion is a means for solving the problem. .

According to this rubber crosslinked product molding die, the sacrificial layer forming portion is formed from the shallow portion and the deep portion, and the deep portion is made deeper than the shallow portion, so that the shallow portion directly communicating with the cavity is formed. It is possible to make the product sufficiently thin to easily finish the product such as deburring. Further, since the deep portion is provided, the volume of the entire sacrifice layer forming portion can be sufficiently secured, so that, for example, even when a large-capacity product is manufactured, the internal pressure of the molding die during cross-linking can be sufficiently increased. This can be alleviated.

According to a third aspect of the present invention, there is provided a method for producing a rubber cross-linked product, wherein the cavity is filled with an uncross-linked rubber by using the molding die according to the first aspect, and a cross-linking reaction is carried out. This is the solution to the above problem.

According to this method for producing a rubber crosslinked product, the use of the molding die makes it possible to easily finish the product after the crosslinking reaction, such as deburring. In addition, since the mold for molding is designed so that the increase in internal pressure at the time of cross-linking is sufficiently mitigated even in the case of producing a large-capacity product, a defect or a crack is generated in a product portion due to the increase in internal pressure. Ingress is prevented.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is an enlarged cross-sectional view of an essential part showing an embodiment of a mold for molding a rubber crosslinked product of the present invention. In FIG. 1, reference numeral 10 denotes a mold for molding a rubber crosslinked product (hereinafter, abbreviated as molding mold). Do). The molding die 10 differs from the molding die 1 shown in FIGS. 2 and 3 in that a sacrificial layer forming portion 11 is formed from a shallow portion 12 and a deep portion 13.

The molding die 10 shown in FIG. 1 forms a cavity 3 having a circular vertical section in the same manner as the conventional one, and a product part is formed therein.
The shallow portion 12 of the sacrifice layer forming portion 11 is directly connected to the sacrifice layer forming portion 11, and the deep portion 13 is further connected to the shallow portion 12.
The shallow portion 12 and the deep portion 13 constituting the sacrifice layer forming portion 11 are both hollow due to the combination of the grooves formed in the grooves (parting surfaces 4) of the molds 2 and 2 with the concave portions. These are all disposed along the outer periphery of the cavity 3.

The shallow portion 12 has a substantially rectangular cross section and the deep portion 13 has a circular cross section. The boundary portion where the shallow portion 12 is connected to the cavity 3, that is, the portion forming the joint portion which is the boundary portion between the obtained product portion and the burr, is formed such that the inner surface on the shallow portion 12 side approaches the cavity 3 side. It is formed in a curved surface shape that expands along with the R surface in this example.

As shown in FIG. 1, the depth D1 (the sum of the depths d1 of the grooves formed in the dies 2 and 2) of the deep portion 13 is equal to the depth D2 of the shallow portion 12 (the die). The depth L1 of the deep portion 13 is longer than the shallow portion L2. With such a configuration, the volume of the deep portion 13 is sufficiently larger than the volume of the shallow portion 12, whereby the volume of the sacrificial layer forming portion 11 is also sufficiently large.

In order to manufacture a rubber crosslinked product using the molding die 10 having such a configuration, the cavity 3 is filled with an uncrosslinked rubber in the same manner as in the prior art, and is heated and kept warm in advance. The uncrosslinked rubber is heated and pressurized in the mold 10 to cause a crosslinking reaction, and molding is performed. When the cross-linking reaction is performed in this manner, the increase in the internal pressure is sufficiently mitigated by the sacrificial layer forming portion 11 having a large volume, even when manufacturing a large-capacity thick-walled cast product. Defects due to cracks or cracks during mold release are prevented.

Further, since the volume of the sacrificial layer forming portion 11 can be increased by providing the deep portion 13, the shallow portion 12 directly communicating with the cavity 3 is made sufficiently thin to remove burrs and the like. Finishing of the product can be facilitated. Further, as described above, the sacrifice layer forming portion 11
Is formed from the shallow portion 12 and the deep portion 13 to prevent the product portion from being chipped or cracked, so that the inner surface R on the shallow portion 12 side can be made smaller than before without increasing particularly. The boundary between the product part and the burr can be clarified.

In the above-described embodiment, the sacrificial layer forming portion 11 is formed by forming grooves in both the dies 2 and 2. However, the present invention is not limited to this. Groove is formed only in the sacrifice layer forming portion 11 from now on.
May be formed, and a curved surface (R surface) is formed in the shallow portion 12, but this need not be formed.

A molding die as the product (example) of the present invention shown in FIG. 3 was manufactured in the following shape and dimensions. For comparison, molding dies having the conventional structure shown in FIGS. 2 and 3 were manufactured in the following shapes and dimensions. (Example 1) The volume of the cavity 3 of the molding die 10 was 9
000 cc. Further, the length L2 of the shallow portion 12 in the sacrificial layer forming portion 11 is 10 mm, the depth D2 is 6 mm,
Further, the radius of curvature (R) of the R surface at the boundary with the cavity 3 was 6 mm. The vertical section of the deep portion 13 was a circle having a diameter of 20 mm, and therefore, the depth D1 and the length L1 were set to 20 mm.

Comparative Example 1 Cavity 3 of Mold 1
Was 9000 cc in volume. The length L of the sacrificial layer forming portion 5 is 15 mm, the depth D is 6 mm, and the radius of curvature (R) of the R surface at the boundary with the cavity 3 is 6 mm.
mm. (Comparative Example 2) The volume of the cavity 3 of the molding die 1 was set to 90
00 cc. Further, the length L of the sacrificial layer forming portion 5 is set to 15
mm, the depth D was 8 mm, and the radius of curvature (R) of the R surface at the boundary with the cavity 3 was 8 mm. (Comparative Example 3) The volume of the cavity 3 of the molding die 1 was set to 90
00 cc. Further, the length L of the sacrifice layer forming portion 5 is set to 15
mm, the depth D was 10 mm, and the radius of curvature (R) of the R surface at the boundary with the cavity 3 was 10 mm.

Using the molding dies of Example 1 and Comparative Examples 1 to 3, rubber crosslinked products were produced by injection molding. However, the rubber used EPDM of the same composition. The mold temperature was set to 180 ° C., and the rubber preheating temperature was set to 80 ° C. The presence or absence of defects and cracks in the product part of the obtained rubber crosslinked product was examined, and the results are shown in Table 1 below. "Table 1" Example 1 Comparative example 1 Comparative example 2 Comparative example 3 Defect of product part No Yes Yes No Crack of product part No Yes Yes No Good / bad judgment Good Bad Bad Good

In Example 1, it was confirmed that there were no defects and no cracks in the product part, which was effective in preventing defects. In addition, since R at the boundary between the product portion and the burr was relatively small, this boundary was easy to understand, so that finishing was easy. On the other hand, in Comparative Examples 1 and 2, both defects due to the protrusion of the rubber during molding and cracks in the product portion occurred, resulting in failure. Further, in Comparative Example 3, although neither a defect nor a crack was generated, since the radius at the boundary between the product portion and the burr was large, it took time to finish the product portion.

When the volume of the cavity is 3000 cc,
A molding die having the same size and shape of the sacrifice layer forming portion as in the first embodiment was manufactured to be a second embodiment. Similarly, the volume of the cavity is set to 3000 cc,
A molding die having the same shape as in Comparative Example 1 was used in Comparative Example 4,
The cavity was 3000 cc, and the size and shape of the sacrifice layer forming portion were the same as those in Comparative Example 2. A molding die prepared in Comparative Example 5 was used. The cavity volume was 3000 cc, and the size and shape of the sacrifice layer forming portion were changed. A molding die manufactured in the same manner as in Comparative Example 3 was used as Comparative Example 6.

In each of Example 2 and Comparative Examples 4 to 6, a rubber crosslinked product was molded under the same conditions as those in Example 1 and Comparative Examples 1 to 3, and the product portion of the obtained rubber crosslinked product was obtained. The presence or absence of defects and cracks was examined. The results are shown in Table 2 below. "Table 2" Example 2 Comparative Example 4 Comparative Example 5 Comparative Example 6 Defects in product part None None None None Crack in product part None None None None Judgment of good or not Good Good Good Good In all cases, good products were obtained. This is presumably because when the product volume was small, the pressure applied to the crack surface of the mold was small, and thus no breakage or crack was formed in the product portion.

[0031]

As described above, in the rubber mold for rubber crosslinked product according to the first aspect of the present invention, the sacrificial layer forming portion is formed from a shallow portion and a deep portion, and the deep portion is deeper than the shallow portion. Therefore, the shallow portion directly communicating with the cavity can be made sufficiently thin to facilitate the finishing of the product such as deburring, thereby enabling the finishing work to be sped up. Further, since the deep portion is provided, the volume of the entire sacrifice layer forming portion can be sufficiently secured, so that, for example, even when a large-capacity product is manufactured, the internal pressure of the molding die during cross-linking can be sufficiently increased. This can be alleviated, thereby preventing defects such as defects or cracks in the product portion.

In the method for producing a crosslinked rubber product according to the third aspect, the use of the molding die can facilitate the finishing such as deburring of the product after the crosslinking reaction, and can provide a large-capacity product. Even in the case of manufacturing a product, it is possible to prevent the product portion from being broken or cracked due to an increase in the internal pressure of the molding die.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing an embodiment of a mold for molding a rubber crosslinked product of the present invention.

FIG. 2 is a sectional view of a main part showing an example of a conventional mold for molding a rubber crosslinked product.

FIG. 3 is an enlarged sectional view of a main part of the mold for molding a rubber crosslinked product shown in FIG. 2;

[Explanation of symbols]

2 mold, 3 cavity, 4 parting surface, 1
0 ‥ Mold for rubber crosslinked product molding, 11 ‥ Sacrifice layer forming part, 1
2 ‥ shallow, 13 ‥ deep

Claims (4)

[Claims] 1. A mold for molding a rubber crosslinked product having a hollow sacrificial layer forming portion communicating with a cavity on a crack surface of a mold, wherein the sacrificial layer forming portion directly communicates with the cavity. A mold for molding a rubber crosslinked product, comprising: a shallow portion; and a deep portion communicating with the cavity through the shallow portion, wherein the deep portion is deeper than the shallow portion. 2. The rubber according to claim 1, wherein a shallow inner surface at a boundary portion between the cavity and the shallow portion is formed in a curved shape so as to expand toward the cavity. Mold for molding crosslinked products. 3. A method for producing a rubber cross-linked product in which a cavity of a rubber cross-linked product is filled with an uncross-linked rubber and subjected to a cross-linking reaction to obtain a rubber cross-linked product. A hollow sacrificial layer forming portion communicating with the cavity has a cracked surface, and the sacrificial layer forming portion has a shallow portion directly communicating with the cavity and a deep portion communicating with the cavity through the shallow portion. And a mold having a greater depth than the depth of the shallow portion. 4. The rubber according to claim 3, wherein an inner surface on a shallow portion side at a boundary portion between the cavity and the shallow portion is formed into a curved surface so as to expand toward the cavity side. How to make crosslinked products.