JPS6032613A - Manufacture of rubber foamed and molded item - Google Patents

Abstract

PURPOSE:To obtain a high quality foamed and molded item with good productivity, by feeding a foamable compound in an amount up to the volume of a cavity, and filling the remaining space with a high pressure gas to keep a pressurized state so that excessive preceding foaming may be suppressed. CONSTITUTION:A foamable compound 2 is fed into a cavity 1 of a split mold so that a required expansion rate will be obtained, a rubber packing 4 is fitted in a packing groove 6, and while a high pressure air (about 10kg/cm<2>) is injected from introduction pipes 5, the mold is heated with the mold closed by a press. While excessive preceding foaming of the foamable compound is suppressed, the crosslinking is allowed to proceed to a certain extent, then the high pressure air is released, and the temperature is elevated with the mold closed by the press to complete the foaming and crosslinking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing rubber foam molded products that are useful in all fields, including industrial products such as various floats, packings, gaskets, seals, and cushions, and everyday products such as footwear sole materials. It is.

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. Among these, the performance requirements for products used as closed-cell foams for molded foam products, such as various floats, Harakin, gaskets, seals, cushions, and footwear sole materials, are increasing, and precise, complex, and irregularly shaped rubber foams are required. Demand for products is increasing.

Conventionally, these rubber foam molded products are 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. It has dominated since then.

An overview of the conventional method for manufacturing rubber foam molded products using this high-pressure two-stage foaming method is as follows.

1) Apply the foaming compound to the primary mold with the required precision cavity, at least 10% of the cavity volume.
2) Heating under high pressure (at least 40 to more pressure per projected area of the cavity) to proceed with crosslinking to the extent that the decomposed gas of the blowing agent blended in the foaming compound does not escape into the atmosphere. , the decomposition gas of the blowing agent is made to exist in independent bubbles.

(This step is usually referred to as primary crosslinking.) 8) Next, 1
The molded product obtained by the secondary crosslinking is taken out and placed in a product mold (also referred to as a secondary mold) having a cavity capacity larger than that of the primary mold, and 4) under pressure (to the extent that the product mold does not open). It is sufficient to apply a pressure of 1,000 ml, and the pressure may be lower than that during the primary crosslinking) to complete the crosslinking at the same time without foaming and filling the cavity of the product mold.

(This process is usually referred to as secondary crosslinking.) 6) After foaming and crosslinking are completed, immediately remove the pressure and take out the foamed product, or the foamed product may be damaged when it pops out due to its complex and irregular shape. If the mold is used, the product is cooled and solidified while being pressurized, then the mold is opened and the product is removed.

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, it is necessary to make sure that the product shape, that is, the secondary mold, has an appropriate shape and expansion ratio. It is difficult to design the primary mold cavity, and it will become increasingly difficult to respond to the development of foamed products that require high functionality in the future.

c) In the primary crosslinking process, it is necessary to introduce more than 100 inches of foamed rubber bound into the cavity, so some protrusion will occur, material loss is unavoidable, and a finishing process is required to remove this protrusion. . Furthermore, the cell structure of this protruding part is destroyed during finishing processing, resulting in a decrease in the quality of the closed cell foam, resulting in a decrease in product quality.
This can cause negative effects such as variations.

Purpose of the Invention The present invention was made in order to solve the drawbacks of the conventional high-pressure two-stage foaming process, which involves two steps 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. Our goal is to provide a resource-saving and energy-saving manufacturing method.

Structure of the Invention The present invention is a direct molding method using only a product mold,
This invention 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 created at this time with high pressure from the outside. By introducing a gas such as air or nitrogen gas of about 10 to 9, filling it, keeping it airtight and maintaining it in a pressurized state, crosslinking can proceed to a certain extent while suppressing excessive preliminary foaming of the foaming compound due to heating. Then, the introduced high-pressure gas is released, and heating is continued to complete foaming and crosslinking.

Moreover, the second invention according to the present invention basically comprises the above-mentioned first invention.
However, a foaming compound containing a small amount of foaming agent is placed in a part of the cavity of the product mold, and a larger amount of foaming agent than the above compound is mixed in the other part of the cavity. By charging two or more types of foaming compounds with different blending amounts of foaming agents, for example, by charging a foaming compound, by the same method as in the first invention,
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. but,
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, and directly charging the product mold with the foaming compound, and introducing and filling it with a high-pressure gas, crosslinking can be achieved while suppressing excessive preliminary foaming of the foaming compound due to heating. Let it progress to some extent,
Thereafter, the gas is released and heating is continued to complete foaming and crosslinking, and the two-stage 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.
Workability and productivity can be greatly improved.

In addition, since there is no need for a primary mold, mold costs can be significantly reduced, and there is no protruding part during the primary crosslinking process, which is required in the conventional method, and there is no need for the finishing process of the primary crosslinked product. This also prevents bubble collapse 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 some extent while suppressing excessive preliminary foaming of the foaming compound due to heating (primary heating) under a pressurized state by a gas body,
After that, the gas pressure is released and heating is continued (secondary heating) to complete foaming and crosslinking, so it is preferable to set the temperature of the second heating higher than that of the first heating.

In addition, the second aspect of the present invention is to foam and crosslink two or more types of foaming compounds containing different amounts of foaming agents by the above-mentioned method, thereby forming a low-foaming portion and a high-foaming portion, so that the density,
Parts with different physical properties such as hardness and 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 was required to have parts that required light weight and parts that required strength at the same time, and for this reason, there were models with a movable metal arm firmly attached to the main body, or models with embedded magnets. . 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 done using the conventional high-pressure two-stage foaming method, it is necessary to mold each secondary crosslinked product separately, cool it, solidify it, take it out, and then perform secondary crosslinking in a product mold. . Therefore, even if the primary crosslinked product that has been cooled and solidified is secondarily crosslinked, the low expansion ratio part and the high expansion ratio part are not sufficiently fused and adhered to each other, and the boundary between them tends to break easily. There are also problems in terms of workability, productivity, and cost, as the number of manufacturing steps increases and becomes complicated.

However, in the second aspect of the present invention, it is sufficient to use only one product mold, and moreover, the primary crosslinked product that has been primarily crosslinked by heating is not cooled and solidified.
Since it is directly subjected to the secondary cross-cutting treatment, it is possible to obtain the effect that the fusion and adhesion between the low expansion ratio part and the high expansion ratio part are sufficiently high. 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 for the foaming compounds of the low foaming part and the high foaming part to be composed of the same composition except for changing the blended amount of the foaming agent, from the viewpoint of fusion adhesion, but this is not necessarily the case. They may be composed of different compositions as long as they do not differ significantly in terms of physical properties, etc.

Although the above description 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 the raw rubber, all the rubbers used in the production of rubber foams can be used, for example, in addition to natural rubber, synthetic rubbers such as chloroprene rubber, nitrile rubber, 8BJ high styrene rubber, butyl rubber, etc. -r A d: alone or Various raw material rubbers can be used, such as copolymers or blend polymers of rubber and synthetic resins. In addition, the synthetic resins blended into raw rubber include phenolic resin,
Various resins such as PVC and styrene are known. Further, as the blowing agent, conventionally well-known inorganic (11) 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 foaming compound: NBR 80 parts Stearic acid 1 part Carbon black 30 parts Blowing agent (DPT) 6 parts Z
n0 5 parts Urea-based foaming aid 2 parts Sulfur 30 parts The mixture of 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, and weighed. and put it into a mold. For example, as shown in Figure 1 (longitudinal sectional view) and Figure 2 (plan view of the parting surface), a flat type (length: 5 cm, width:
8 cm, thickness: (1 crn rectangular cavity), density 0.25'43
In order to obtain a fuel gauge fleet of 40 crn3, a foaming compound 2 of IOf may be charged into a product mold cavity 1 of 40 crn3. A packing groove 6 is provided on the parting surface around the cavity 1 of the split mold 3, and a rubber packing 4 is fitted into the groove 6 so that the cavity space is kept airtight. High pressure air (9~q-8
'/, I) is heated while the mold is clamped with a pressure press.

Heating was carried out for 18 minutes at approximately 130°C (to steam pressure 2), then the high pressure air was released and the temperature was increased to approximately 165°C (steam pressure 6.5 KV/l) with the press still clamped.
Heat 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.

A foaming compound similar to that in Example 1 was extruded using a stomach tube shape (21a, 21b) as shown in FIG. 3, cut to the required length and weight, and weighed. Into the mold shown in FIG. 5 (plan view of the parting surface), the main body portion 21a and the arm portion 21b are filled 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 6I is provided on the parting surface around the cavity 11, and a rubber packing 41 is fitted into the groove 61. .

The mold is clamped using a pressure press, and N2 gas (ct
, s ''94) for 30 minutes at about 130 °C (steam pressure 2~), then N2 gas was released, and the pressure press temperature was increased to about 170 °C while the mold was still clamped.
(vapour pressure 7 to 60%) and continue heating for 30 minutes to complete foaming and crosslinking.

Thereafter, the steam in the pressure press is switched to cooling water, and the product is cooled with water for 15 minutes to solidify the product.The pressure press is then released, the mold is opened, and the product is taken out.

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 footwear sole having a complicated pattern on the bottom surface.

Composition of foaming compound: NRl 00 parts Calcium carbonate 50 parts* N1pol-200730 parts Process oil 15 parts Zn
0 5 parts Sulfur 3 parts Stearic acid 1 part Blowing agent (DPT) 5 parts Accelerator (
DM) 0.6 parts Urea-based foaming aid 5 parts Magnesium carbonate 50 parts*) Styrene (85%)-butadiene (+s%) copolymer, manufactured by Nippon Zeon Co., Ltd. A blend of the above composition was mixed and rolled, A slab shape 22,
As shown in Fig. 6 (longitudinal sectional view) and Fig. 7 (half-view of the parting surface), the cavity 1206) is filled to the required cavity capacity or less, and the packing groove 62 provided on the parting surface around the cavity 1206 is airtight. Fit the rubber gasket 42 for use, clamp the mold with a pressure press, and heat it for 10 minutes at about 125°C (vapor pressure 1.4~) while pressurizing N2 gas (9, 8~) from the introduction pipe 52.
Next, release the N2 gas and continue to hold the mold clamp for 1
Heat at 50°C (steam pressure 4~) for 10 minutes 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.

Below is a blank space (16) As shown in the above example, 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 the valve of the pressurized gas introduction pipe Only one operation is needed, and only one mold insertion and mold removal is required, and no extrusion occurs. There is no need for a finishing process for the primary cross-linked material. It also prevents bubbles from bursting at the extrusion area. Furthermore, it is possible to avoid the conventional high pressure two-stage process. It was possible to easily produce closed-cell foams with complex irregular shapes, which were difficult to obtain using the foaming method.

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. Department.

On the other hand, Example 1 except that the amount of blowing agent was 3 parts.
Using a foaming compound having the same composition as shown in Figure 3, it was extruded into a rod shape as shown at 21b in Figure 3, and cut to the required length and weight to form an arm part.

The float body portion 21a and the arm portion 21b were placed in the mold shown in FIGS. 4 and 5, and a float for an automobile carburetor was simultaneously molded in exactly the same manner as in Example 2. A product was obtained in which a strong arm portion (density nO-90'/, 3) was firmly attached to a highly foamed float body (density 0.29 V3).

[Brief explanation of the drawing]

Fig. 1 is a longitudinal 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. 3 is the foaming used in Examples 2 and 4. ° A partial perspective view of the foamed compound molded product before crosslinking, Figure 4 is a vertical sectional view of the mold used in Examples 2 and 4, and Figure 5 is a plane showing the parting surface of the mold shown in Figure 4. 6 is a longitudinal sectional view of the mold used in Example 3, and FIG. 7 is a plan view showing the parting surface of the mold shown in FIG. 6. 1, II, +2...Mold cavity, 2.21a. 21b, 22... Foaming compound, 5.51.
52...Introduction pipe. (19) Figure 1 Figure 2 Bottom 3 Lower F, 4 Figure 5

Claims (1)

[Claims] 1. In the production of rubber foam molded products, rubber or a mixture of rubber and synthetic resin is added in advance to the mold cavity for molding the product in an amount less than the mold cavity capacity so as to achieve the required foaming ratio. A rubber-based composition containing a foaming agent is charged into the mold cavity, and a high-pressure gas is introduced from the outside into the excess space of the mold cavity, which is then filled and heated while maintaining a pressurized state. A method for producing a rubber foam molded product, characterized by allowing crosslinking to proceed to some extent while suppressing foaming of the composition, then releasing a high-pressure gas, and further heating to complete foaming and crosslinking. 2. In the production of rubber foam molded products, two or more rubber-based compositions containing different amounts of blowing agents in rubber or a mixture of rubber and synthetic resin are placed in the mold cavity for product molding in advance for the necessary foaming. Charge the mold cavity in an amount that is less than the capacity of the mold cavity so that the magnification is the same, and introduce a high-pressure gas from the outside into the excess space of the mold cavity that is created at this time, fill it and heat it while keeping it in a pressurized state. , the rubber-based composition is allowed to undergo crosslinking to some extent while suppressing foaming, releases the high-pressure gas, and continues heating to complete foaming and crosslinking, forming a low-density foamed portion and a firm relatively high-density portion. A method for producing a rubber foam molded product, characterized by simultaneously integrally molding a foamed part of.