JPH0510208B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing rubber foam molded products useful in all fields, including industrial products such as various floats, packings, gaskets, seals, and cushions, and everyday products such as footwear soles. BACKGROUND OF THE INVENTION Rubber foam molded products are important industrial rubber products and are used in a wide range of fields, such as extruded foam products, plate-shaped foam products, molded foam products, and the like. this house,
The required performance of closed-cell foam products used in various floats, packing, gaskets, seals, cushions, footwear sole materials, etc. is increasing, and the demand for precise, complex, and irregularly shaped rubber foam products is increasing. is increasing. These rubber foam molded products are usually closed-cell foams obtained by a high-pressure two-stage foaming method of a rubber composition (hereinafter referred to as a foaming compound) in which a foaming agent is blended with rubber or a mixture of rubber and synthetic resin. has traditionally been the mainstream. An overview of the conventional method for manufacturing rubber foam molded products using this high-pressure two-stage foaming method is as follows. (1) Fill a primary mold with the required precision cavity with the foaming compound by at least 100% of the cavity capacity, (2) Under high pressure (at least 40 kg/cm ² or more per projected area of the cavity) ) to promote crosslinking to such an extent that the decomposed gas of the blowing agent blended in the foaming compound does not escape into the atmosphere, allowing the decomposed gas of the blowing agent to exist in independent bubbles. (This process is usually called primary crosslinking.) (3) Next, the molded product obtained by primary crosslinking is taken out and molded into a product mold (also called secondary mold) having a cavity capacity larger than that of the primary mold. ), and (4) heat under pressure (it is sufficient to have enough pressure to prevent the product mold from opening; the pressure may be lower than during the primary crosslinking), and then heat it in the product mold cavity. Complete foaming and complete crosslinking at the same time. (This process is usually referred to as secondary crosslinking.) (5) After foaming and crosslinking are completed, immediately remove the pressure and take out the foamed product, or remove the foamed product due to its complex and irregular shape. If it is damaged, cool it under pressure,
After solidifying, open the mold and take out the product. However, the above-mentioned high-pressure two-stage foaming method has various problems as described below. (a) It is a two-step manufacturing process in which primary crosslinking and secondary crosslinking are separated, and two types of molds are required, increasing the number of man-hours and mold costs. (b) When obtaining foams with complex and irregular shapes, foams that require dimensional accuracy, or composite foams with different compositions, the product shape, i.e. 2
It is difficult to design the cavity of the primary mold to give the secondary mold an appropriate shape and expansion ratio, and it will become increasingly difficult to develop foamed products that require high performance in the future. (c) In the primary crosslinking process, it is necessary to charge more than 100% of the foamed rubber compound into the cavity, so some protrusion occurs, material loss is unavoidable, and a finishing process is required to remove this protrusion. Become. Furthermore, the cell structure in this protruding portion is destroyed during finishing, reducing the quality of the closed cell foam.
This can cause negative effects such as a decline in product quality and variations. Purpose of the Invention The present invention was made in order to solve the drawbacks of the conventional cross-linking foaming process, which is a two-step high-pressure foaming method and uses two types of molds, in the production of rubber foam molded products as described above. It has physical properties equivalent to or better than closed cell foam obtained by the conventional high-pressure two-stage foaming method, and can produce high-quality foam molded products at low cost by reducing man-hours, mold costs, materials, etc. The object of the present invention is to provide a resource-saving and energy-saving manufacturing method that can be manufactured with high productivity. Structure of the Invention The present invention is a direct molding method using only a product mold, and consists of the following two inventions. First, the first aspect of the present invention is to fill a product mold with a foaming compound in an amount equal to or less than the cavity capacity in advance so as to obtain the necessary foaming ratio, and to fill the surplus space of the cavity with high pressure from the outside. By introducing and filling a gas such as air or nitrogen gas (approx. 10 kg/cm ² ), keeping it airtight and maintaining a pressurized state, crosslinking can be achieved to some extent while suppressing excessive preliminary foaming of the foaming compound due to heating. This is a method in which foaming and crosslinking are completed by allowing the foam to proceed, then releasing the introduced high-pressure gas and continuing heating. In addition, a second invention according to the present invention basically utilizes the technical means of the first invention, but a foaming method is provided in which a small amount of foaming agent is blended into a part of the cavity of a product mold. The same method as in the first invention is carried out by charging two or more types of foaming compounds with different amounts of foaming agents, such as charging a foaming compound with a larger amount of foaming agent than the above compound into other parts of the cavity. By the method of
This is a method of integrally molding a low-density foamed portion and a firm, relatively high-density foamed portion at the same time. Functions, Effects, and Modes of the Invention The method of the present invention is similar in principle to the conventional high-pressure two-stage foaming method. That is, they are the same in that the crosslinking process is carried out in two stages: primary crosslinking and secondary crosslinking. However, the method is completely different from the conventional high-pressure two-stage foaming method. In other words, by omitting the use of a conventional primary mold, filling the product mold directly with the foaming compound, and introducing and filling the product mold with a high-pressure gas, we can suppress excessive preliminary foaming of the foaming compound due to heating. Crosslinking is allowed to proceed to a certain extent, then the gas is released, and heating is continued to complete foaming and crosslinking, and the two-step crosslinking is performed in a series of steps. Therefore, compared to the conventional high-pressure two-stage foaming method, the number of man-hours is reduced, and workability and productivity can be greatly improved. In addition, since a primary mold is not required, mold costs can be greatly reduced, and unlike conventional methods, protruding parts do not occur during the primary crosslinking process, and the finishing process of the primary crosslinked product is no longer necessary. It is also possible to prevent bubbles from breaking in the protruding portion. Furthermore, it is possible to easily produce closed-cell foams with complex irregular shapes, which have been difficult to obtain using conventional high-pressure two-stage foaming methods. In addition, in the method of the present invention, crosslinking is allowed to proceed to a certain extent while suppressing excessive preliminary foaming of the foaming compound due to heating (primary heating) under a pressurized state by a gas body, and then the gas pressure is released. Since foaming and crosslinking are completed by subsequent heating (secondary heating), it is preferable to set the temperature of the second heating higher than that of the first heating. In addition, the second invention according to the present invention is to foam and crosslink two or more foaming compounds containing different amounts of foaming agents by the above-mentioned method, and to form a low-foaming part and a high-foaming part, and thus to improve density and hardness. , parts with different physical properties such as heat resistance are integrally molded at the same time. Conventionally, floats for automobile carburetors, for example, often had complex irregular cross-sections due to the required performance. Moreover, it is required to have parts that require light weight and parts that require strength at the same time.
For this reason, some floats had movable metal arms firmly attached to the float body, others had magnets embedded in them. However, these metal parts have to be attached to the primary cross-linked structure, which poses a problem in that extra attachment work is required. On the other hand, it is conceivable that the above-mentioned parts requiring strength are made of a rubber foam with a low expansion ratio and high hardness, and are integrally molded with a lightweight part with a high expansion ratio. However, when this is carried out using the conventional high-pressure two-stage foaming method, each primary crosslinked product is molded separately.
After cooling and solidifying this and taking it out, it is necessary to perform secondary crosslinking in a product mold. Therefore, once cooled,
Even if the solidified primary crosslinked product is subjected to secondary crosslinking, the fusion and adhesion between the low expansion ratio part and the high expansion ratio part will not be sufficient, and the boundary will easily break, and two primary molds will be required, making it difficult to manufacture. There are also problems in terms of workability, productivity, and cost, as the number of steps increases and becomes complicated. However, in the second invention according to the present invention, it is sufficient to use only one product mold, and furthermore,
The primary crosslinked product that has been primary crosslinked by heating is cooled,
Since the secondary crosslinking treatment is performed as it is without being solidified, the effect of sufficiently high fusion and adhesion between the low expansion ratio portion and the high expansion ratio portion can be obtained. Furthermore, only one mold is needed for the product, and the two-step crosslinking is performed in a series of single steps.
It has excellent workability and productivity, and is also advantageous in terms of cost. It is most preferable from the viewpoint of fusion and adhesion that the foaming compounds of the low-foaming part and the high-foaming part are composed of the same composition except for changing the amount of the foaming agent, but this is not necessarily the case. They may be composed of different compositions as long as they differ widely in terms of physical properties, etc. Although the above explanation focuses on one product, it is also possible to provide a product mold with a plurality of cavities and simultaneously manufacture a plurality of products in one process. As raw rubber, all the rubber used for manufacturing rubber foam can be used, for example, in addition to natural rubber,
Synthetic rubbers such as chloroprene rubber, nitrile rubber, SBR, high styrene rubber, and butyl rubber can be used alone or in combination, and various raw material rubbers such as copolymers or blend polymers of rubber and synthetic resins can also be used. In addition, synthetic resins blended into raw rubber include phenol resin, PVC,
Various resins such as styrene are known. Further, as the blowing agent, conventionally well-known inorganic blowing agents and organic blowing agents can be used. EXAMPLES The present invention will be specifically explained with reference to Examples below. Note that the number of parts indicates parts by weight. Example 1 In this example, an example of a float for an automobile fuel gauge is shown. Composition of the foaming compound: NBR 80 parts PVC 20 parts phenolic resin 60 parts carbon black 30 parts ZnO 5 parts stearic acid 1 part vulcanization accelerator (DM 1.5 parts CZ 0.5 parts) 2 parts blowing agent (DPT) 6 parts urea Foaming aid: 2 parts Sulfur: 30 parts The above composition is kneaded, rolled or extruded to form a slab, cut into a desired shape and weight that is less than the cavity capacity of the product mold, weighed and molded. Prepare it. For example, as shown in Figure 1 (longitudinal sectional view) and Figure 2 (plan view of the parting surface), the flat type (cuboid cavity with length: 5 cm, width: 8 cm, and thickness: 1 cm) has a density of 0.25 g/ In order to obtain a float for a fuel gauge of cm ³ , 10 g of foaming compound 2 should be charged into a product mold cavity 1 of 40 cm ³ .
A packing groove 6 is provided on the parting surface around the capit 1 of the split mold 3 so that the airtightness of the capit y space is maintained, and a rubber packing 4 is fitted into the groove 6. While pressurizing high-pressure air (9 to 9.8 Kg/cm ³ ) from the introduction pipe 5, the mold is heated while being clamped with a pressure press. Heating was carried out for 18 minutes at approximately 130°C (vapor pressure 2Kg/cm ³ ), then the high pressure was released, and the temperature was lowered to approximately 165°C (vapor pressure) with the pressure press still clamped.
6.5Kg/cm ³ ) and heated for 30 minutes to complete foaming and crosslinking. Then, while keeping the mold clamped, the steam in the pressure press is switched to cooling water and cooled for 10 minutes to solidify the product, then the pressure press and mold are opened and the product is taken out. Example 2 In this example, an example of a float for an automobile carburetor is shown. The same foaming compound as in Example 1 was extruded using rod shapes 21a and 21b as shown in Fig. 3, cut to the required length and weight, and weighed. Flowate body portion 21a and arm portion 21b are charged into the mold shown in the plan view of the parting surface to a required cavity capacity or less. In the above product mold as well, similarly to the mold used in Example 1, a packing groove 61 is provided on the parting surface around the cap 11, and a rubber packing 41 is fitted into the groove 61. The mold was clamped with a pressure press, heated at approximately 130°C (vapor pressure 2Kg/cm ³ ) for 30 minutes while introducing N ₂ gas (9.8Kg/cm ³ ) from the introduction pipe 51, and then the N ₂ gas was released. Then, while keeping the mold clamped, the pressure press temperature was raised to about 170°C (vapor pressure 7Kg/cm ³ ), and heating was continued for 30 minutes to complete foaming and crosslinking. After that, switch the steam of the pressure press to cooling water,
Cool in water for 15 minutes to solidify the product, then release the pressure press, open the mold, and remove the product. We were able to simultaneously mold a product in which the arm part was firmly fused to the float body. Example 3 This example shows an example of a cover bottom having a complicated pattern on the bottom surface. Composition of the foaming compound: NR 100 parts ^* Nipol-2007 30 parts ZnO 5 parts Stearic acid 1 part Accelerator (DM) 0.6 parts Magnesium carbonate 50 parts Calcium carbonate 50 parts Process oil 15 parts Sulfur Yellow 3 parts Blowing agent (DPT) 5 Part Urea-based foaming aid 5 parts *) Styrene (85%)-butadiene (15%) copolymer, manufactured by Nippon Zeon Co., Ltd. The above composition was kneaded and rolled to form a slab 2.
2, as shown in FIG. 6 (longitudinal cross-sectional view) and FIG. 7 (plan view of the parting surface), the cavity is filled to less than the required cavity capacity, and the packing groove 62 provided on the parting surface around the cavity 12 is airtightly filled. Insert the rubber gasket 42, clamp the mold with a pressure press, and heat it at about 125°C (steam pressure 1.4Kg/cm ² ) for 10 minutes while injecting N ₂ gas (9.8Kg/cm ² ) from the introduction pipe 52.
Heating for 1 minute, then releasing the N ₂ gas, and heating at 150℃ (vapor pressure 4Kg/cm ² ) for 10 minutes while keeping the mold clamped.
Heat for a minute to complete foaming and crosslinking, release the pressure press, open the mold and take out the product. The physical properties of the foams obtained in Examples 1 to 3 above are shown in Tables 1 and 2 below.

【table】

[Table] As shown in the above examples, compared to the conventional high-pressure two-stage foaming method, the method of the present invention does not require any particular change in the composition of the foaming compound, and only requires pulving of the pressurized gas introduction pipe. In addition, only one mold insertion and mold removal is required, and no protrusion occurs.
It eliminates the need for a primary crosslinking process, prevents bubble collapse in protruding areas, and facilitates the production of complex, irregularly shaped, closed-cell foams that are difficult to obtain using conventional high-pressure two-stage foaming methods. Ta. Example 4 A foaming compound having the same composition as that shown in Example 1 was extruded into a rod shape 21a as shown in FIG.
It was cut into weight pieces to make the float body. On the other hand, a third foaming compound was prepared using the same foaming compound as shown in Example 1 except that the amount of foaming agent was changed to 3 parts.
It was extruded into a rod shape as shown by 21b in the figure, and cut to the required length and weight to form an arm portion. The float main body part 21a and the arm part 21b
was charged into the mold shown in FIGS. 4 and 5, and a float for an automobile capretor was simultaneously molded in exactly the same manner as in Example 2. Highly foamed float body (density 0.29g/cm ³ ) and solid arm part (density 0.90
A product was obtained in which the weight ratio (g/cm ³ ) was firmly fixed.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the mold used in Example 1, FIG. 2 is a plan view showing the parting surface of the mold shown in FIG. 1, and FIG.
A partial perspective view of a foamed compound molded product before crosslinking,
Fig. 4 is a vertical cross-sectional view of the mold used in Examples 2 and 4, Fig. 5 is a plan view showing the parting surface of the mold shown in Fig. 4, and Fig. 6 is the mold used in Example 3. FIG. 7 is a plan view showing the parting surface of the mold shown in FIG. 6. 1, 11, 12... Mold cavity, 2, 21
a, 21b, 22... Foaming compound, 5, 5
1,52...Introduction pipe.

Claims (1)

[Scope of Claims] 1. In the production of rubber foam molded products, rubber or a mixture of rubber and synthetic resin is foamed in an amount less than the capacity of the mold cavity in advance to obtain the required foaming ratio in the mold cavity for molding the product. The rubber composition containing the agent is charged, and a high-pressure gas is introduced from the outside into the excess space of the mold cavity that is created at that time.
Fill the rubber composition and heat it while keeping it in a pressurized state to allow crosslinking to proceed to some extent while suppressing foaming of the rubber composition, then release the high pressure gas and continue heating to complete foaming and crosslinking. A manufacturing method for characteristic rubber foam molded products. 2. In the production of rubber foam molded products, two or more rubber compositions containing different amounts of blowing agents in rubber or a mixture of rubber and synthetic resin are added to the mold cavity for molding the product at the required expansion ratio. A high-pressure gas is introduced from the outside into the excess space of the mold cavity that is created at this time, filling it and heating it while maintaining the pressurized state. Crosslinking is allowed to proceed to some extent while suppressing foaming of the rubber composition, and then a high-pressure gas is released, and heating is continued to complete foaming and crosslinking, forming a low-density foamed portion and a firm relatively high-density foamed portion. A method for manufacturing a rubber foam molded product, characterized by integrally molding a foamed part and a foamed part at the same time.