JP2006088434A - Rubber foamed molded product and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber foamed molded product manufacturing method capable of manufacturing a rubber foamed molded product uniformly and finely foamed over the whole interior thereof in a short time. <P>SOLUTION: The cavity 21 of a mold 2 is filled with unvulcanized rubber composition pieces 4 formed into a size of 1 mm<SP>2</SP>square or below and heated up to the vulcanization temperature region of the unvulcanized rubber composition pieces 4, a supercritical fluid is introduced into the cavity 21, the unvulcanized rubber composition pieces are exposed to a fluid in a supercritical state for 5 min or above in a vulcanization time of a 90% vulcanization point to be impregnated with the fluid. Thereafter, the fluid in the supercritical state is gasified to internally foam the unvulcanized rubber composition pieces to crosslink the unvulcanized rubber composition pieces. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a rubber foam molded article and a rubber foam molded article produced by this method, and more specifically, impregnating a fluid in a supercritical state or a subcritical state inside a raw rubber composition, The present invention relates to a method for producing a rubber foam molded article comprising a step of vaporizing a fluid impregnated under reduced pressure and forming fine bubbles inside a raw rubber composition, and a rubber foam molded article produced by this method.

  As a method for producing a foamed molded article of rubber, a fluid in a supercritical state or a subcritical state is impregnated inside a raw rubber composition, and then the impregnated fluid in a supercritical state or a subcritical state is added. A method is known in which a large number of fine bubbles are formed inside the rubber composition by vaporization.

  And the structure which applies the said method and manufactures the foaming molding of rubber | gum in which the pore and the bubble of the ultrafine structure were disperse | distributed uniformly is proposed (refer patent document 1). In the configuration described in Patent Document 1, the unvulcanized rubber is impregnated with a fluid in a supercritical state or a subcritical state during the kneading step or vulcanizing step of the unvulcanized rubber, and then the pressure is reduced. . This configuration is based on the principle that pores and bubbles are formed on the surface and inside of the unvulcanized rubber when the fluid impregnated inside the raw unvulcanized rubber is vaporized by decompression.

  According to the configuration described in Patent Document 1, it is considered that the surface layer portion of the foamed molded article of rubber to be produced is foamed uniformly and finely, but the deep layer portion is not foamed or foamed. Even if it does, it is thought that it does not become a uniform foaming state. In particular, Patent Document 1 describes that “a tire in which at least a tire surface rubber is foamed is provided” is also suitable for producing a foamed molded article of rubber foamed to a deep layer portion. It is thought that it is not.

  In order to produce a foamed molded article of rubber foamed over the entire interior, it is necessary to impregnate the entire interior of the rubber composition with a fluid in a supercritical state or a subcritical state. For this purpose, it is preferable to impregnate the fluid at a low temperature for a long time. However, if the rubber composition is at a low temperature in the step of impregnating the fluid, the temperature of the surface layer portion rises in a short time in the step of heating the rubber composition in the subsequent crosslinking step, but the deep layer portion is compared with the surface layer portion. Therefore, it takes a long time for the temperature to rise. For this reason, cross-linking proceeds in a short time in the surface layer portion, and the bubbles generated in the surface layer portion are fixed in a state of being uniformly and finely foamed. On the other hand, even if the deep layer portion is foamed uniformly and finely due to reduced pressure, the deep layer portion is likely to become enormous due to the bonding of bubbles before the crosslinking is completed. As a result, the bubble diameters of the bubbles are not uniform between the surface layer portion and the deep layer portion, and the physical characteristics and the like of the manufactured rubber may be deteriorated.

  On the other hand, in order to prevent the temperature distribution inside the rubber composition from becoming non-uniform, if the rubber composition is maintained at a high temperature in the impregnation process of the fluid in the supercritical state or the subcritical state, Crosslinking can proceed before vaporizing the fluid in the critical state. For this reason, there exists a possibility that the foaming state of a rubber composition may deteriorate.

  As another configuration to which the above configuration is applied, a configuration has been proposed in which the specific strength of a foamed molded article of rubber produced by refining bubbles is improved, thereby reducing the weight without reducing the strength ( Patent Document 2). This configuration applies a condition in which the fluid in the supercritical state or the subcritical state does not pass through the liquid region excluding the gas-liquid mixed phase or the subcritical state in the enthalpy-pressure diagram in the decompression step of the above configuration. Is. According to this configuration, the bubble diameter of the bubbles formed inside the rubber foam molded body is about several μm, and a foamed molded body of rubber that is finely foamed can be manufactured.

  However, in the configuration described in Patent Document 2, it takes a long time to impregnate the fluid in the supercritical state or subcritical state inside the raw rubber composition. Specifically, in the example described in Patent Document 2, the impregnation step of the fluid in the supercritical state or the subcritical state requires 2 hours. As described above, the configuration described in Patent Document 2 is considered to require a long time for producing a foamed molded article of rubber and has low productivity.

  As described above, in the conventional method for producing a rubber foam molded body using a fluid in a supercritical state or a subcritical state, a rubber foam molded body that is foamed uniformly and finely over the entire interior in a short time. It was difficult to manufacture.

JP 11-293022 A JP 2002-322308 A

  In view of the above situation, the problem to be solved by the present invention is to provide a method for producing a foamed rubber foam that is uniformly and finely foamed throughout the interior, and a rubber foam molded article produced by this method, or It is an object of the present invention to provide a method for producing a rubber foam molded article which is foamed over the entire interior in a short time and a rubber foam molded article produced by this method.

  In order to solve such a problem, the invention described in claim 1 includes a step of filling a finely divided unvulcanized rubber composition in a mold, and an unvulcanized rubber filled in the die. A step of heating the composition to a crosslinking temperature region, a step of pressurizing a fluid in a supercritical state or a subcritical state into the mold, and impregnating the unvulcanized rubber composition; And a step of foaming the unvulcanized rubber and a step of crosslinking the unvulcanized rubber.

  Here, as described in claim 2, the particle size of the unvulcanized rubber composition is 1 mm or less, and the time for impregnating the unvulcanized rubber composition with a fluid in a supercritical state or a subcritical state. Is preferably set to a time during which the progress of crosslinking of the unvulcanized rubber composition does not exceed 90%.

  The gist of the invention described in claim 3 is that the inside is formed into a uniform foam cell size by the method for producing a rubber foam molded article described in claim 1 or claim 2. is there.

  According to the first aspect of the present invention, since the finely pulverized unvulcanized rubber composition is used, the ratio of the total surface area to the total volume of the rubber composition filled in the cavity is increased. Moreover, the fluid in a supercritical state also flows into the unvulcanized rubber composition and contacts the surface. For this reason, the contact area between the unvulcanized rubber composition and the fluid in the supercritical state is increased, and the fluid in the supercritical state or the subcritical state is easily impregnated inside the unvulcanized rubber composition. Further, since the unvulcanized rubber composition is finely divided, the penetration depth of the fluid in the supercritical state or the subcritical state may be small. Accordingly, it is possible to shorten the impregnation time of the fluid in the supercritical state, and it is possible to produce a rubber foam molded body foamed over the entire interior in a short time.

  Further, the unvulcanized rubber composition filled in the molding die is heated in advance to the cross-linking temperature region, and then maintained at that temperature. For this reason, in the crosslinking step after foaming, there is no temperature difference between the surface layer portion and the deep layer portion of the unvulcanized rubber composition, and the crosslinking proceeds uniformly. Therefore, a foamed molded article of rubber that is uniformly foamed over the entire interior can be produced without causing a nonuniformity in bubble diameter due to nonuniformity in the progress of crosslinking.

  According to the second aspect of the present invention, when the particle size of the unvulcanized rubber composition is molded to about 1 mm, the impregnation of the fluid in the supercritical state or the subcritical state can be completed in a short time. It is possible to greatly reduce the production time of the rubber foam molding. And since it can be made to foam in the state where bridge | crosslinking of a rubber composition is not completed, a favorable foaming state is obtained.

  According to the third aspect of the present invention, since the foaming is uniform to the inside, the physical characteristics are excellent. For example, the weight can be reduced while maintaining the strength.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following, the method for producing a foamed molded article of rubber according to the present invention may be abbreviated as “the present method”. In addition, the “fluid in the supercritical state” may be referred to as “supercritical fluid”. In the following embodiments, the term “supercritical fluid” includes fluid in a subcritical state.

  FIG. 1 is a schematic diagram showing an example of the configuration of equipment used for carrying out the present method. Hereinafter, the equipment used for carrying out the method may be abbreviated as “present equipment”. The equipment 1 includes a molding die 2 that molds a raw rubber composition into a predetermined shape, and a high-pressure container 3 that can accommodate the molding die 2.

  The molding die 2 includes a fluid supply / discharge path 22 that communicates a cavity 21 formed inside and an external space. The molding die 2 is configured such that fluid can enter and exit the cavity 21 through the fluid supply / discharge path 22 even in a closed state.

  The high-pressure vessel 3 is a vessel capable of maintaining the internal space at a high pressure (for example, about 30 MPa at the maximum). A fluid supply / discharge path 31 that can supply and discharge fluid from the outside to the internal space is provided. The fluid supply / discharge path 31 is connected to a fluid supply mechanism (not shown), and fluid can be supplied to and discharged from the internal space of the high-pressure vessel 3 through the fluid supply / discharge path 31. The internal pressure of the high-pressure vessel 3 can be maintained at a predetermined value by the fluid introduced into the internal space. For example, a configuration including a cylinder that stores fluid and a pump that can feed the fluid at a predetermined pressure is applied to the fluid supply mechanism.

  Examples of the rubber composition to which the present method is applied include styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), natural rubber (NR), nitrile rubber (NBR), chloroprene rubber (CR), Examples include butyl rubber (IIR), ethylene / propylene rubber (EPDM, EPM), fluorine rubber, silicone rubber, urethane rubber, and acrylic rubber.

  And the rubber composition shape | molded by the predetermined dimension shape is used. Specifically, it is preferably formed in a dimensional shape of 1 mm square or less, but may be a size of 3 mm square or less. Hereinafter, a rubber composition molded into a predetermined size and shape is referred to as a “rubber composition piece”.

  In addition, the type of fluid applied to the present method is not particularly limited, but carbon dioxide and nitrogen that can easily be brought into a supercritical state can be suitably applied.

  Below, the implementation procedure of this invention using this installation 1 is demonstrated.

  First, the molding die 2 and the high-pressure vessel 3 are preheated to a predetermined temperature. The preheating temperature varies depending on the type and composition of the rubber composition to be applied, but is preferably the crosslinking temperature of the rubber composition to be applied or a temperature in the vicinity thereof. For example, it is preferable that the temperature is 150 ° C. or its vicinity for EPDM, 140 ° C. or its vicinity for NR, and 150 ° C. or its vicinity for NBR.

  Next, the raw rubber composition piece 4 is filled into the cavity 21 of the molding die 2. The amount of the rubber composition piece 4 filled in the cavity 21 is the expansion ratio of the foamed molded article to be produced (here, the apparent volume increase rate of the rubber composition piece 4 due to foaming is the same hereinafter). It may be determined according to. For example, in order to produce a foamed molded article having a foaming ratio of 200%, it is sufficient to fill a rubber composition piece in an amount that is a half of the volume of the cavity 21, and the foaming ratio is 400%. In order to produce a foamed molded article, it is sufficient to fill a rubber composition piece in an amount that is a quarter of the volume of the cavity 21. The rubber composition piece 4 filled in the cavity 21 is heated to the predetermined temperature by the preheated molding die 2 and thereafter maintained at this temperature.

  When the rubber composition pieces 4 are fused and integrated to make it difficult to fill the cavity 21, for example, talc is applied to the surface of the rubber composition piece 4 so that the rubber composition piece 4 What is necessary is just to prevent mutual fusion | melting.

  Then, the molding die 2 filled with the rubber composition piece 4 is accommodated in the high-pressure vessel 3, and the supercritical fluid is filled into the internal space of the high-pressure vessel 3 through the fluid supply / discharge path 31. The supercritical fluid filled in the internal space of the pressure vessel 3 enters the cavity 21 through the fluid supply / discharge path 22 of the molding die 2, and the rubber composition piece 4 filled in the cavity 21 is supercritical. Exposed to fluid. The temperature of the supercritical fluid at this time is preferably the crosslinking temperature of the rubber composition piece 4 filled in the cavity 21 or a temperature in the vicinity thereof. Moreover, the pressure of the supercritical fluid is preferably in the range of 7 to 30 MPa, more preferably about 15 to 20 MPa.

  Thereafter, when this state is maintained, the supercritical fluid penetrates into the rubber composition piece 4. In order to produce a foamed molded article foamed over the entire interior, it is necessary to impregnate the supercritical fluid throughout the entire interior of the rubber composition piece 4 filled in the cavity 21. The required impregnation time depends on the type and size of the rubber composition piece 4, the progress of crosslinking, or the temperature and pressure of the supercritical fluid. This is because (1) a rubber composition (rubber composition piece) generally having a polar group in the molecule has low supercritical fluid permeability, and (2) rubber is added due to the addition of carbon black or the progress of crosslinking. This is because, as the internal viscosity of the composition piece increases, the resistance to penetration increases. For this reason, it sets according to conditions.

In this method, the time is preferably within 90% vulcanization point. Here, “90% vulcanization point” refers to t _c (90) defined in JIS K6300-2: 2001. Within this range, at the stage of foaming, the rubber composition piece is not completely cross-linked, so the rubber composition piece is fused and a good foamed state is obtained.

  The specific impregnation time is preferably about 8 minutes in the case of EPDM formed in a 3 mm square, for example. In the case of EPDM formed into 1 mm square or pulverized to 0.5 mm diameter, about 5 minutes is preferable. If it is NR formed in the magnitude | size of 3 mm square or less, about 5 minutes are preferable. If it is NBR formed in 3 mm square or less, about 10 minutes are preferable. As described above, if a rubber composition molded in a size of 3 mm square or less is used in advance, the impregnation time of the supercritical fluid may be 10 minutes or less, so that the impregnation time is significantly reduced compared to the conventional method. can do.

  After maintaining the state for a predetermined time, the internal pressure of the high-pressure vessel 3 is reduced to a predetermined pressure (for example, atmospheric pressure). When the pressure inside the high-pressure vessel 3 is reduced, the supercritical fluid that has penetrated into the rubber composition piece 4 is vaporized, and the rubber composition piece 4 is foamed. If the pressure difference between before and after depressurization is small, the phase separation of the supercritical fluid impregnated inside the rubber composition piece 4 will proceed slowly, causing bubbles to coalesce or bubbles to collect with the filler as the core. As a result, bubbles tend to become large. On the other hand, if the pressure difference between before and after decompression is large, the phase separation of the supercritical fluid impregnated in the rubber composition piece 4 proceeds rapidly, and the supercritical fluid is vaporized all at once in a short time. Is formed, the bubble diameter of the bubbles is reduced. Therefore, the bubble diameter of the bubbles formed can be controlled by adjusting the pressure difference between before and after decompression.

  When the supercritical fluid is vaporized and fine bubbles are formed inside the rubber composition piece 4, the rubber composition piece 4 expands due to the internal pressure of the bubbles, and the apparent volume increases. And by this apparent volume increase, the cavity 21 is filled with the expanded rubber composition piece 4 without a gap, and the rubber composition piece has a shape along the cavity. Then, the rubber composition pieces 4 are fused and integrated. Since the total volume of bubbles that can be formed inside the foamed molded article to be produced is determined according to the total amount (total volume) of the rubber composition pieces 4 filled in the cavities 21, the adjustment of the filling amount of the rubber composition pieces 4 is adjusted. Can control the bubble diameter of the bubbles. That is, when it is desired to increase the bubble diameter of the bubbles, the total amount of the rubber composition pieces 4 filled in the cavity 21 is reduced. When the bubble diameter of the bubbles is desired to be reduced, the total amount of the rubber composition pieces 4 to be filled is set. Increase it.

  Thereafter, this temperature (that is, the crosslinking temperature or a temperature in the vicinity thereof) is maintained for a predetermined time, and the crosslinking of the integrated rubber composition piece 4 is advanced. Since the temperature of the integrated rubber composition piece 4 is uniform throughout the interior, the crosslinking proceeds uniformly throughout the interior. As a result, the bubble diameter is not uniform due to the non-uniform speed of crosslinking, and the bubbles are enlarged due to the cross-linking of the surface layer first and the loss of the fluid in the deep layer. And the bubble diameter of the bubbles is uniform between the surface layer and the inside.

  Thus, according to this method, the supercritical fluid is impregnated in the entire rubber composition in a short time by using the rubber composition (rubber composition piece) formed in a predetermined size and shape in advance. be able to. For this reason, it is possible to produce a foamed molded article of rubber foamed to the inside in a short time. Moreover, since crosslinking can be made to proceed uniformly throughout the rubber composition, the bubble diameter of the foamed molded article of rubber obtained is uniform throughout the foamed molded article. Therefore, it is possible to produce a foamed molded article that is uniformly and finely foamed to the inside in a short time.

  In the supercritical fluid impregnation step, the rubber composition piece 4 is heated to the cross-linking temperature or a temperature in the vicinity thereof. However, since this step is completed in a short time, the cross-linking proceeds almost in the foaming step. Not. For this reason, impregnation of supercritical fluid and uniform and fine foaming are not hindered.

  Next, examples and comparative examples of the present invention will be described. Table 1 shown below is a table showing the conditions and evaluations of Examples and Comparative Examples of the present invention. There are three types of rubber used here: EPDM, NR, and NBR. Then, a rubber foam molding is produced by changing the size and shape of the rubber composition to be filled in the molding die, the temperature and pressure in the supercritical fluid impregnation step and the crosslinking step, and the time of each step, and foaming. The condition was evaluated.

  The common conditions not shown in Table 1 are as follows. For the evaluation, equipment having the configuration shown in FIG. 1 is used. The molding die includes a main body in which a cavity is formed, and a lid body that is screwed to the main body at three positions to close the cavity. The cavity is formed in a cylindrical shape having an inner diameter of 60 mm and a height of 30 mm. Then, after filling the raw rubber composition piece into the cavity, when the lid is screwed to the main body, a gap of about 0.5 mm is formed between the joint surface of the main body and the lid using the spacer. I did it. This gap functions as a fluid supply / discharge path of the molding die, and fluid can enter and exit the cavity. The high-pressure container is formed in a cylindrical shape having an inner diameter of 130 mm and an inner height of 100 mm, and can accommodate the molding die 2. Carbon dioxide was used as a fluid to be impregnated into the rubber composition piece. Hereinafter, carbon dioxide in a supercritical state is referred to as “supercritical carbon dioxide”.

  Each rubber composition piece to be filled in the cavity is cut or frozen and pulverized to form a predetermined size and shape. A small amount of talc was applied to the surface of the rubber composition pieces so that the rubber composition pieces were not fused together when the rubber composition pieces were filled into the cavities.

  Further, “foaming ratio” in Table 1 indicates an increase rate of the apparent volume of the rubber composition piece due to foaming. In this example and comparative example, the foaming ratio was set in advance, and the cavity was filled with an amount of rubber composition pieces sufficient to achieve the foaming ratio set by the foamed molded article to be manufactured. That is, the filling amount of the rubber composition piece is one half of the volume of the cavity if the foaming is twice, and one half of the volume of the cavity if the foaming ratio is 1.2 times. did.

  The conditions and evaluation of each example and comparative example are described below.

  Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3 use EPDM as the rubber composition. Specifically, esprene is 100 parts by weight, zinc oxide is 5 parts by weight, stearic acid is 1 part by weight, FEF carbon is 45 parts by weight, process oil is 10 parts by weight, and vulcanization accelerator CZ is 1. 5 parts by weight, vulcanization accelerator EZ is 1.5 parts by weight, vulcanization accelerator TET is 1 part by weight, and sulfur is 1.5 parts by weight. Of the properties of this rubber composition piece, the Mooney viscosity at 120 ° C. is 45, and the 90% vulcanization point at 150 ° C. is 10 minutes 30 seconds.

(Example 1-1)
In Example 1-1, a rubber composition piece cut to 3 mm square was used. The expansion ratio was set to 2 times. For this reason, the cavity was filled with an amount of a rubber composition corresponding to one half of the cavity volume. The impregnation time of supercritical carbon dioxide was 8 minutes, and the temperature of supercritical carbon dioxide at this time was 150 ° C. and the pressure was 15 MPa. Thereafter, the pressure was reduced to atmospheric pressure to cause foaming, and the crosslinking was advanced by maintaining the temperature at 150 ° C. for 15 minutes under atmospheric pressure.

  The foamed molded article of rubber produced by applying this condition had a bubble diameter of bubbles formed in the range of 30 to 60 μm, and foamed uniformly throughout the entire interior. Therefore, this condition can be said to be a suitable condition for producing a foamed molded article that is foamed uniformly and finely throughout the interior. And when using the rubber composition piece shape | molded to 3 square mm, it can be said that the impregnation time of a supercritical carbon dioxide may be about 8 minutes.

(Example 1-2)
Example 1-2 is an example in which a rubber composition piece smaller in size than the rubber composition piece used in Example 1-1 was used and the impregnation time of supercritical carbon dioxide was shortened. In Example 1-2, a rubber composition piece formed by cutting into a 1 mm square was used. The impregnation time of supercritical carbon dioxide was 5 minutes. The other conditions were the same as those in Example 1-1.

  The foamed molded article of rubber produced by applying such conditions had a bubble diameter of bubbles formed in the range of 30 to 60 μm, and foamed uniformly throughout the entire interior. Therefore, it can be said that this condition is suitable for producing a foamed molded article that is foamed uniformly and finely throughout the entire interior. When a rubber composition piece molded into a 1 mm square is used, the impregnation time of supercritical carbon dioxide may be about 5 minutes. In order to shorten the impregnation time of supercritical fluid, the size of the rubber composition piece is reduced. It can be said that reducing the size is effective.

(Example 1-3)
In Example 1-3, after impregnating the rubber composition piece with supercritical carbon dioxide, the pressure difference between before and after decompression is adjusted to adjust the pressure difference between the foamed foams of rubber. It is an Example which controls a diameter. In Example 1-2, the pressure was reduced from 15 MPa to atmospheric pressure, whereas in this example, the pressure was reduced from 15 MPa to 5 MPa. And it bridge | crosslinked under the pressure of 5 MPa. The other conditions are the same as in Example 1-2.

  The foamed molded article of rubber produced under such conditions has a bubble diameter of bubbles formed in the range of 60 to 90 μm. Compared with Example 1-1 which pressure-reduced from 15 MPa to atmospheric pressure, the bubble diameter of the bubble is large as a whole. The reason why the difference in pressure difference before and after decompression affects the bubble diameter of the bubbles formed is as described above. Thus, it can be said that adjustment of the reduced pressure width during foaming is effective as a means for controlling the bubble diameter of bubbles. Moreover, this condition can be said to be a condition suitable for producing a foamed molded product that is foamed uniformly and finely throughout the interior.

(Example 1-4)
Example 1-4 is an example using a rubber composition piece having a size smaller than that of Example 1-2. In this example, a 0.5 mm diameter rubber composition piece formed by freeze pulverization was used. The other conditions are the same as in Example 1-2.

  The foamed molded article of rubber produced by applying these conditions had a bubble diameter of bubbles formed in the range of 30 to 50 μm, and foamed uniformly throughout the entire interior. Therefore, it can be said that these conditions and the production method are conditions suitable for producing a foamed molded article of rubber that is uniformly and finely foamed throughout the interior. In addition, compared with Example 1-2, although the bubble diameter of a bubble is small as a whole, this is considered to be based on the following reasons. The rubber composition is easily affected by the pressure difference as the size is reduced, and the same effect as when the pressure difference is substantially increased can be obtained. As described above, when the pressure difference between before and after depressurization increases, the bubble diameter of the formed bubbles becomes smaller. Therefore, it is formed as compared with Example 1-2 using a large rubber composition piece. It is thought that the bubble diameter of bubbles becomes small.

(Example 1-5)
Example 1-5 is an example in which the bubble diameter of the formed bubbles is controlled by adjusting the expansion ratio. In this example, a rubber composition piece having an amount of foaming of 1.2 times was filled in a cavity of a molding die. The other conditions are the same as in Example 1-2.

  The foamed molded article of rubber produced under these conditions had a bubble diameter of bubbles formed in the range of 20 to 50 μm, and foamed uniformly throughout the entire interior. Therefore, this condition can be said to be a condition suitable for production of a foamed molded article of rubber that is uniformly and finely foamed throughout the interior. And compared with Example 1-2, the bubble diameter of the bubble formed has shifted to the side which becomes small entirely. This is because, as described above, the volume occupied by the bubbles in the foamed molded article depends on the amount of the rubber composition pieces filled in the cavity, so increase the filling amount (decrease the setting of the foaming ratio). ), The bubble diameter of bubbles is considered to be small. Thus, it was confirmed that the adjustment of the expansion ratio is effective as a means for controlling the bubble diameter of the formed bubbles.

(Example 1-6)
Example 1-6 is also an example in which the bubble diameter of the formed bubbles is controlled by adjusting the expansion ratio, and is an example to be compared with Example 1-4. In this example, a rubber composition piece having an amount of foaming of 1.2 times was filled in a cavity of a molding die. The other conditions are the same as in Example 1-4.

  The foamed molded article of rubber produced by applying these conditions had a bubble diameter of bubbles formed in the range of 20 to 50 μm, and foamed uniformly throughout the entire interior. Therefore, this condition can be said to be a condition suitable for producing a foamed molded article of rubber that is uniformly and finely foamed throughout the interior. And compared with Example 1-4, the bubble diameter of the bubble formed has shifted to the side which becomes small entirely. The reason for this is considered to be the same as the reason described in Example 1-5. Therefore, it was confirmed that the adjustment of the foaming ratio was effective as a means for controlling the bubble diameter of the bubbles formed inside the foamed molded article of rubber.

(Comparative Example 1-1)
Comparative Example 1-1 is an example of a conventional method using a large-sized rubber composition molded integrally instead of a rubber composition (rubber composition piece) molded into a predetermined size and shape. In this example, a disk-shaped rubber composition having a diameter of 60 mm and a thickness of 15 mm was used. The other conditions are the same as in Example 1-2 or Example 1-4.

  The foamed molded article produced by applying these conditions foamed in the range of a depth of about 1 to 2 mm from the surface, but no foaming was observed in a portion deeper than this range. Therefore, this condition is unsuitable for producing a foamed molded article of rubber that is uniformly and finely foamed throughout the interior. This is probably because the impregnation time was short and the supercritical carbon dioxide did not penetrate into the deep layer. Therefore, when considered in comparison with Example 1-2 or Example 1-4, in order to impregnate supercritical carbon dioxide over the entire interior of the rubber composition piece in 5 minutes, the side of the rubber composition is 1 mm square. It can be said that it is preferable to form and use the following.

(Comparative Example 1-2)
In Comparative Example 1-2, in the case where the integrally molded rubber composition used in Comparative Example 1-1 is applied, the impregnation time of supercritical carbon dioxide is increased so that the supercritical carbon dioxide is a rubber composition. This is an example in which the entire interior is impregnated. Specifically, the impregnation time of supercritical carbon dioxide was 120 minutes, the temperature of supercritical carbon dioxide at that time was 50 ° C., and the pressure was 15 MPa. Then, the pressure was reduced to atmospheric pressure to foam, heated to 150 ° C., and crosslinked at 150 ° C. for 15 minutes under atmospheric pressure.

  In the foamed molded article produced by applying these conditions, the bubble diameter of bubbles formed increased from the surface layer portion toward the deep layer portion, and the bubble diameter of the bubbles increased to about 1 mm in the deep layer portion. Therefore, it can be said that this condition is inappropriate as a condition for producing a foamed molded article of rubber that is uniformly and finely foamed throughout the entire interior.

  The reason is considered to be as follows. When the rubber composition is impregnated with supercritical carbon dioxide at a low temperature, and then the rubber composition is heated in the cross-linking step, the temperature of the surface layer portion is increased in a short time, and the cross-linking is completed in a short time. It is fixed almost as it is. On the other hand, in the deep layer portion, the temperature rise is relatively slow compared to the surface layer portion due to the time difference required for heat transfer, so that the progress of the crosslinking is also slowed, and the bubbles become enormous due to the bonding of bubbles between them. Therefore, in the deep layer portion, the bubble diameter is larger than that of the surface layer portion. Thus, in the case of using an integral huge rubber composition, even if the supercritical carbon dioxide impregnation time is ensured for a long time, a foamed molded product of rubber that is foamed uniformly and finely throughout the inside is manufactured. It can be said that it is difficult to do.

(Comparative Example 1-3)
Comparative Example 1-3 is an example in which the impregnation time of supercritical carbon dioxide was shortened to 5 minutes using a rubber composition piece molded into 3 mm square. This “5 minutes” is a suitable time for a rubber composition piece of 1 mm square or 0.5 mm diameter. Accordingly, the same conditions as in Example 1-2 or Example 1-4 are applied except that a 3 mm square rubber composition piece is used.

  The rubber foam molded body produced by applying these conditions had an unfoamed portion inside. This is probably because time was short and the entire inside of the rubber composition piece was not impregnated with supercritical carbon dioxide. Moreover, the bubble diameter of the bubble formed is 30-200 micrometers, and the dispersion | variation in the bubble diameter of the bubble became large. Therefore, this condition is unsuitable for the production of a foamed molded article of rubber that is foamed uniformly and finely throughout the interior. Thus, when using the rubber composition piece shape | molded by 3 mm square, it is preferable that the impregnation time of a supercritical carbon dioxide is about 8 minutes, and it can be said that it is insufficient in 5 minutes.

  As described above, when EPDM is applied as a rubber composition, the impregnation time of supercritical carbon dioxide is about 8 minutes for a rubber composition piece molded to 3 mm square, and for a rubber composition piece molded to 1 mm square or less. It can be said that about 5 minutes is preferable. Moreover, it can be said that adjustment of the pressure difference before pressure reduction and after pressure reduction, and adjustment of a foaming ratio are effective for control of the bubble diameter of the bubble formed. Therefore, it can be said that this method is effective as a method for producing a foamed molded product of rubber which is foamed uniformly and finely throughout the entire portion in a short time. On the other hand, in the case of applying an integral huge rubber composition as in the prior art, if the impregnation time of supercritical carbon dioxide is shortened, foaming does not occur over the entire interior, and the impregnation time is increased to extend over the entire interior. When impregnated, the bubble diameter is not uniform.

  The following Example 2-1, Example 2-2, and Comparative Example 2-1 are examples in which NR is applied as a rubber composition. The composition of the rubber composition is 100 parts by weight of natural rubber, 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 60 parts by weight of FEF carbon black, 10 parts by weight of process oil, and a vulcanization accelerator. 64 is 1 part by weight and sulfur is 1.8 parts by weight. Among the properties of this rubber composition, the Mooney viscosity at 120 ° C. is 30, and the 90% vulcanization point at 150 ° C. is 9 minutes.

(Example 2-1)
In Example 2-1, a rubber composition piece cut to 3 mm square was used. The expansion ratio was set to 2 times. For this reason, the cavity was filled with an amount of a rubber composition corresponding to one half of the cavity volume. The impregnation time of supercritical carbon dioxide was 5 minutes, and the pressure of supercritical carbon dioxide at this time was 20 MPa, and the temperature was 140 ° C. Thereafter, the pressure was reduced to atmospheric pressure, and crosslinking was performed while maintaining the temperature at 140 ° C. for 12 minutes under atmospheric pressure.

  The foamed molded product of rubber produced by applying these conditions had a bubble diameter of bubbles formed in the range of 40 to 100 μm, and foamed uniformly and finely throughout the interior. Therefore, this condition can be said to be a suitable condition for producing a foamed molded product of rubber that is uniformly and finely foamed throughout the interior.

(Example 2-2)
Example 2-2 is an example in which a rubber composition piece having a size smaller than that of the rubber composition piece applied in Example 2-1 was used. A rubber composition piece having a diameter of 0.5 mm formed by freeze pulverization was used. Using. Except for the size of the rubber composition piece and the molding method, the same conditions as in Example 2-1 are applied.

  The foamed molded product of rubber produced by applying these conditions had a bubble diameter of bubbles formed in the range of 40 to 90 μm, and foamed uniformly and finely throughout the interior. Therefore, it can be said that this condition is suitable for producing a foamed molded product of rubber that is uniformly and finely foamed throughout the interior. In addition, it is thought that it is based on the reason similar to Example 1-4 that the bubble diameter of the bubble is small compared with Example 2-1.

(Comparative Example 2-1)
Comparative Example 2-1 is an example of a conventional method using a large-sized rubber composition molded integrally instead of a rubber composition (rubber composition piece) molded into a predetermined size and shape. In this example, a rubber composition formed into a disk shape having a diameter of 60 mm and a thickness of 15 mm was used. The other conditions are the same as those in Example 2-1 or Example 2-2.

  The foamed molded article produced by applying these conditions foamed in the range of a depth of 1 to 2 mm from the surface, but did not foam in a deeper part. Thus, it can be said that this condition is unsuitable for the production of a foamed molded product that is foamed uniformly and finely throughout the entire interior. This is presumably because supercritical carbon dioxide was not impregnated into the deep layer portion of the rubber composition for the same reason as in Comparative Example 1-1.

  As described above, according to Examples 2-1 and 2-2 and Comparative Example 2-1, when NR is applied to a rubber composition, a rubber composition piece molded to 3 mm square or less is used, and supercritical dioxide is used. It can be said that the carbon impregnation time is preferably 5 minutes. On the other hand, when applying an integrally molded rubber composition, if the impregnation time of supercritical carbon dioxide is shortened, foaming does not occur over the entire interior, and foaming is performed uniformly and finely throughout the interior. The manufacture of the body is difficult. Therefore, it can be said that this method is effective as a method for producing a foamed molded product of rubber which is foamed uniformly and finely throughout the entire portion in a short time.

  Example 3-1, Example 3-2, and Comparative Example 3-1 are examples to which NBR is applied. The composition of the rubber composition is 100 parts by weight of medium / high nitrile NBR, 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 45 parts by weight of FEF carbon, 10 parts by weight of process oil, and a vulcanization accelerator. DM is 1.5 parts by weight, vulcanization accelerator TS is 0.5 parts by weight, and sulfur is 1.2 parts by weight. Among the properties of this rubber composition piece, the Mooney viscosity at 120 ° C. is 42, and the 90% vulcanization point at 150 ° C. is 13 minutes.

(Example 3-1)
In Example 3-1, a rubber composition piece cut to 3 mm square was used. The expansion ratio was doubled, and for this reason, the cavity was filled with an amount of a rubber composition piece corresponding to a half of the cavity volume. The impregnation time of supercritical carbon dioxide was 10 minutes, and the temperature of supercritical carbon dioxide at this time was 150 ° C. and the pressure was 15 MPa. Thereafter, crosslinking was carried out while maintaining the temperature at 150 ° C. for 15 minutes under atmospheric pressure.

  The foamed molded article of rubber produced by applying these conditions had a bubble diameter of the formed bubbles in the range of 30 to 100 μm, and foamed uniformly and finely throughout the entire interior. Therefore, this condition can be said to be a condition suitable for producing a foamed molded product of rubber that is uniformly and finely foamed throughout the interior.

(Example 3-2)
Example 3-2 is an example in which a rubber composition piece having a smaller size than that of Example 3-1 was applied. In this example, a rubber composition piece having a diameter of 0.5 mm formed by freeze pulverization was used. Except for the molding method and dimensions of the rubber composition pieces, the same conditions as in Example 3-1 were applied.

  The foamed molded article of rubber produced by applying these conditions had a bubble diameter of bubbles formed in the range of 30 to 90 μm, and foamed uniformly and finely throughout the entire interior. Therefore, this condition can be said to be a suitable condition for producing a foamed molded product of rubber that is uniformly and finely foamed throughout the interior.

(Comparative Example 3-1)
Comparative Example 3-1 is an example in which a rubber composition piece formed in 3 mm square was applied and the impregnation time of supercritical carbon dioxide was shortened to 8 minutes. Except for this impregnation time, the same conditions as in Example 3-1 apply. This “8 minutes” is a suitable impregnation time for EPDM molded into 3 mm square (see Example 1-1).

  The rubber foam molded body produced by applying these conditions had the rubber composition pieces fused together to form an integral molded body, but there was an unfoamed portion inside. This is presumably because the impregnation time was insufficient and the supercritical carbon dioxide was not impregnated throughout the rubber composition piece. Therefore, this condition can be said to be an unsuitable condition for the production of a foamed molded product of uniformly and finely foamed rubber.

  As mentioned above, when applying NBR as a rubber composition from Examples 3-1 and 3-2 and Comparative Example 3-1, when using a rubber composition piece molded to 3 mm square or less, supercritical carbon dioxide The impregnation time may be about 10 minutes, and it can be said that a foamed molded article that is foamed uniformly and finely over the entire interior can be produced in a short time. In addition, when using the rubber composition piece shape | molded by 3 square mm, the impregnation time of a supercritical carbon dioxide is preferable about 10 minutes, and it can be said that 8 minutes is insufficient.

  In summary, the impregnation time of the supercritical fluid depends on the composition of the rubber composition piece and the progress of the crosslinking, and further on the pressure and temperature of the fluid. A good foamed state can be obtained with an impregnation time of about 5 minutes below the corner. With NR, a good foamed state can be obtained with an impregnation time of about 5 minutes at 3 mm square or less. NBR has a longer impregnation time than EPDM, but a good foamed state can be obtained by impregnation at 3 mm square for about 10 minutes. As described above, even when the time required for the crosslinking step is included, it is possible to produce a foamed molded article of rubber in about 20 minutes. Therefore, the impregnation time can be greatly shortened as compared with the case where the conventional impregnation time is 120 minutes. And the foaming molding of the rubber | gum which foamed uniformly and finely over the whole inside can be manufactured, shortening impregnation time.

  Although the embodiments and examples of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments or examples, and various modifications can be made without departing from the spirit of the present invention. Needless to say. In the above-described embodiments and examples, the configuration using a supercritical fluid (supercritical carbon dioxide) has been described, but naturally, a fluid in a subcritical state can also be used.

  Also, the equipment applied to the implementation of this method is not limited to the configuration shown in FIG. For example, a configuration in which a fluid in a supercritical state or a subcritical state is directly supplied to and discharged from a fluid supply mechanism without using a high-pressure vessel may be used.

  When the expansion ratio is increased, it is considered that even a rubber composition piece molded to a size of 3 mm square or more can be applied. In addition, a rubber composition that has a low viscosity and can be easily impregnated with a supercritical fluid, or a rubber composition that slowly progresses in crosslinking, may be applicable even if it is molded to a size of 3 mm square or more.

It is the figure which showed typically the example of the structure of the equipment used for the manufacturing method of the foaming molding of rubber | gum which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Equipment applied to implementation of this invention 2 Molding die 3 High pressure vessel 4 Rubber composition piece 21 Cavity 22 Fluid supply / discharge path 31 Fluid supply / discharge path

Claims (3)

  A step of filling the pulverized unvulcanized rubber composition in a mold, a step of heating the unvulcanized rubber composition filled in the die to a crosslinking temperature region, and a step of Pressurizing and injecting a fluid in a critical state or subcritical state and impregnating the unvulcanized rubber composition; depressurizing the mold to foam the unvulcanized rubber; and A method for producing a rubber foam molded article, comprising the step of crosslinking vulcanized rubber.   The particle size of the unvulcanized rubber composition is 1 mm or less, and the time for impregnating the unvulcanized rubber composition with a fluid in a supercritical state or a subcritical state is determined by crosslinking the unvulcanized rubber composition. 2. The method for producing a rubber foam molded article according to claim 1, wherein the progress of is not longer than 90%.   3. A rubber foam molded article, the inside of which is formed into a uniform foam cell size by the method for producing a rubber foam molded article according to claim 1 or 2.

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