JPH06344510A - Vulcanization molding of thick-walled unvulcanized rubber composite - Google Patents

Abstract

PURPOSE:To provide a vulcanization molding method for a thick-walled unvulcanized rubber composite capable of greatly enhancing the productivity of a vulcanization molding process while maintaining the properties of a thick- walled rubber product. CONSTITUTION:A thick-walled composite wherein two or more kinds of unvulcanized rubbers are integrally bonded each other is preheated by high frequency dielectric heating to be subjected to vulcanization molding. In this case, a small amt. of conductive carbon black is preliminarily added to and compounded with the component compsn. of the unvulcanized rubber low in the value of a loss coefficient represented by the product epsilon.tandelta of a specific dielectric constant (epsilon) and a dielectric loss angle (tandelta) among the respective unvulcanized rubbers and the difference between the loss coefficient between the respective unvulcanized rubbers is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick-walled composite in which a plurality of unvulcanized rubbers are joined and integrated with each other, and is preferably preheated by high-frequency dielectric heating for subsequent vulcanization and then vulcanization-molded. The method is particularly suitable for thick-walled composites having a large difference in the value of the loss coefficient represented by the product ε · tan δ of the relative permittivity ε and the dielectric loss angle tan δ between each unvulcanized rubber, After the vulcanization molding, the rubber product will exhibit the desired sufficient performance, and at the same time, it will enable the vulcanization molding with high efficiency at high temperature and in a short time, which will contribute to the significant improvement in the productivity in the whole process. The present invention relates to a vulcanization molding method for a vulcanized rubber composite.

[0002]

2. Description of the Related Art In the conventional general method of vulcanizing and molding a thick-walled composite material by relying only on heat conduction from its surface portion, a remarkably low thermal conductivity peculiar to rubber increases from the surface to be heated to the inside. Because of this, the temperature rise will be significantly delayed compared to the surface part, but as a convention, this difficult temperature rising part will be vulcanized until the proper vulcanization degree (vulcanization degree showing the most desirable physical properties that can be expected) is reached. It was necessary to continue heating.

In this case, the degree of vulcanization gradually increases from the difficult-to-heat-up portion to the surface portion, so that a portion closer to the surface portion shows a significantly over-vulcanized state, and deterioration of the physical properties of the rubber results in deterioration of product performance. However, the vulcanization molding at low temperature for a long time is unavoidable in order to minimize this deterioration of performance, which causes a problem that productivity is significantly impaired.Therefore, simultaneous improvement of these is strongly demanded. Came.

The simplest means for this improvement is to reach a substantially uniform temperature throughout the thick composite in a preheating chamber in which the ambient temperature is higher than room temperature but significantly lower than the vulcanization temperature. The method of heating was adopted. However, this method needs to be kept low because the vulcanization of the surface part of the thick-walled composite will proceed too much if the set temperature of heating is raised too high, and as a result, the difficult temperature rising part is raised to a predetermined temperature level. It takes a long time and the degree of heating is low, and in the end, the improvement of productivity over the entire vulcanization molding process is unavoidable, and in addition, the problem of overvulcanization cannot be solved.

[0005]

Therefore, high-frequency dielectric heating, especially microwave heating, has been attempted as an even more effective method. However, even with this method, only in the case of a thick body having a single compounded rubber composition or in a thick-walled composite, when the compounded composition between each unvulcanized rubber is similar, There is a disadvantage that the practically usable rubber product is significantly limited, that is, the difficult temperature rising portion can be heated to the desired temperature in a short time by making the microwave electric field uniform.

[0006] In this respect, for example, a thick-walled composite body for a solid tire suitable for use in a forklift truck,
When each unvulcanized rubber is compounded and designed to meet different required characteristics, and there is a significant difference in compounded composition between each unvulcanized rubber, microwaves with high heating efficiency When heating is applied, the temperature of the difficult-to-heat-up portion is substantially lower than that of unvulcanized rubber with a high loss coefficient value, for example, the result of the surface portion is significantly lower, which is not suitable for subsequent vulcanization molding. It is nothing but a cause.

As a method of subjecting a tire before vulcanization molding to microwave heating, Japanese Patent Publication No. 57-42501 discloses that the tread rubber of the tire is subjected to microwave heating in advance and then assembled and molded. However, during this assembly molding to vulcanization molding, due to heat conduction to other joining members that are not subjected to preheating, the temperature decreases significantly near the joining surface of the other joining members of the tread rubber, Further, if it is attempted to heat a plurality of rubber members at the same time in order to avoid this, a large number of microwave heating devices corresponding to the number of the members are required, which is a great practical disadvantage.

Therefore, high-frequency dielectric heating, in particular microwave heating, is applied to a thick-walled composite containing unvulcanized rubbers having a plurality of types of compounding compositions which are largely different from each other, and the temperature of the difficult-to-heat-up portion of the thick-walled composite is increased. By vulcanization and molding after raising the temperature to a desired temperature above the surface, the product exhibits the desired rubber physical properties satisfying the required performance under the appropriate degree of vulcanization of the rubber throughout the product. It is an object of the present invention to propose a vulcanization molding method for a thick unvulcanized rubber composite which is capable of significantly improving the productivity over the entire vulcanization molding process.

[0009]

The above object can be achieved by paying attention to the loss coefficient ε · tan δ represented by the product of the relative permittivity ε of each unvulcanized rubber and the dielectric loss angle tan δ. That is, the present invention has been completed. That is, the method for vulcanizing and molding the thick unvulcanized rubber composite of the present invention is to vulcanize and mold a thick composite in which a plurality of types of unvulcanized rubbers are joined and integrated with each other by heating them in advance by high-frequency dielectric heating. Of each unvulcanized rubber,
A small amount of conductive carbon black is added and blended in advance to the component composition of the unvulcanized rubber having a small loss coefficient value represented by the product ε · tan δ of the relative permittivity (ε) and the dielectric loss angle (tan δ). Thus, the difference in the loss coefficient between the unvulcanized rubbers is reduced.

The present invention will be described in more detail below with reference to FIGS. 2 and 3. 2 (a), (b) and FIG. 3 (a),
(B) shows an annular thick composite 1 that becomes a solid tire after vulcanization molding as an example of the thick unvulcanized rubber composite. FIG. 2 shows two kinds of unvulcanized rubber, and FIG. 3 shows three kinds of unvulcanized rubber. An example in which unvulcanized rubbers are joined and integrated with each other is shown. 2 (a) and 3
(A) shows the state of the thick composite body 1 when viewed obliquely from above, and FIG. 2 (b) and FIG. 3 (b) show cross sections taken along the line A-A, respectively, where B is the temperature rise that is difficult to heat up. Represents a part.

2 and 3, the annular thick composite body 1 is shown.
Is the innermost unvulcanized rubber 1-1 in the radial direction and the outermost unvulcanized rubber 1-2 whose compounding composition is significantly different from this rubber. In the example shown in FIG. In the middle of the above, unvulcanized rubbers 1-3, which also have different compounding compositions from any rubber, are joined and integrated with each other.

Prior to vulcanization molding after heating the above-mentioned thick composite 1 by high frequency dielectric heating in advance, loss coefficient ε · tan δ of unvulcanized rubber 1-1, 1-2, 1-3.
Unvulcanized rubber having a small value of, for example, the innermost unvulcanized rubber 1
-1, and an intermediate unvulcanized rubber 1-3, in which a small amount of conductive carbon black is added and blended in advance in the component composition,
This reduces the difference in loss coefficient among the unvulcanized rubbers 1-1, 1-2 and 1-3.

Here, a small amount of a small amount of conductive carbon black means an amount within a range capable of maintaining desired proper rubber physical properties in a product solid tire, preferably 20 parts by weight with respect to 100 parts by weight of rubber. Within On the other hand, however, as exemplified below, it is nothing but the application of conductive carbon black, which has the property of sufficiently contributing to the reduction of the difference in the above-mentioned loss factors, even with a small amount of additive compounding.

That is, for the conductive carbon black, for example, Ketjen EC, Ketjen 600JD (Lion Co., Ltd.), Vulcan XC-72, Vulcan SC, Vulcan C (CABOT Co., USA), Printex XE2.
A conductive furnace black such as (DEGUSSA, Germany) or a conductive acetylene black such as Denka Black (Denka Co., Ltd.) is suitable, and carbon black other than these is also suitable as long as it has the above-mentioned characteristics. If applicable.

Thus, each unvulcanized rubber 1-1, 1-2, 1
-3 is made into the thick-walled composite body 1 in which the difference in the loss coefficient is reduced in advance, and then this is subjected to high-frequency heating to be pre-heated, so that the thick-walled composite body 1 has a whole area from the difficult temperature rising portion to the surface portion. The vulcanization molding is performed after raising the temperature of each part to a desired temperature. For preheating the thick unvulcanized rubber composite, microwave irradiation is preferable among high frequencies. The degree of heating is actually determined by the loss coefficient of the unvulcanized rubber, as will be described later.

Although the thick-walled composite 1 which is made into a solid tire by vulcanization molding has been described above as an example, it can be applied to other thick-walled rubber tires in general and thick-walled composites in other thick-walled rubber articles. it can.

[0017]

In general, the thick-walled composite 1 is a rubber product after vulcanization molding, for example, as a tire, it is necessary for each part to correspond to different required performances. Therefore, a plurality of types of unvulcanized rubbers 1-1 and 1-2 are required. 1
-3 has a greatly different compounding design, and thus the unvulcanized rubber compositions are generally greatly different from each other. Also,
Similar differences often occur to meet demands from manufacturing considerations.

If the compounding compositions of the unvulcanized rubbers 1-1, 1-2, and 1-3 are greatly different, the loss coefficient ε · tan δ in the high frequency electric field is also large among the unvulcanized rubbers. It is customary for differences to occur. Therefore, when the thick composite body 1 in which these rubbers are bonded and integrated to each other is irradiated with a high frequency wave, in particular, by being irradiated with microwaves, the power loss of the microwave has a large loss coefficient in the thick composite body 1. As a result of selectively concentrating on the vulcanized rubber portion, the unvulcanized rubber portion is heated mainly and becomes extremely hot as compared with other portions.

These are unvulcanized rubbers 1-1, 1-2, 1-
The microwave power loss P consumed in 3 is

## EQU1 ## P = (1 / 1.8) fv ² × ε · tan δ × 10 ^-10 (W / m ³ ) where f: oscillation frequency (Hz), v: electric field magnitude (V / m), In the right side of the above equation, it is rational to fix the oscillation frequency f to be optimum for the thick composite body 1 as the object to be heated. If the thick composite 1 has a large difference in the value of the loss coefficient between the unvulcanized rubbers, it is necessary to suppress the loss within a predetermined limit in order to avoid grazing caused by an excessively heated portion. The microwave power loss consumed by the vulcanized rubbers 1-1, 1-2, and 1-3, that is, the amount of heat generated is the loss factor ε.
This is because it is proportional to tan δ.

As described above, for example, each unvulcanized rubber 1-1 (loss factor 0.2) and 1-2 (loss factor 1 immediately after subjecting the conventional thick composite body 1 to microwave heating are used. ．
05) An example of measuring the temperature of the surface portion of 1-3 (loss factor 0.1) and the inside is as shown in FIGS.
It is clear from the fact that the internal temperature of the unvulcanized rubber 1-2 having the largest value of the loss coefficient shows a remarkably higher temperature than the other unvulcanized rubbers 1-1 and 1-3.

Therefore, the object which enables the conventional microwave heating described at the beginning is a thick body having a single compounded rubber composition or similar thicknesses in which the compounded compositions between unvulcanized rubbers are similar to each other. The reason for being limited to the meat complex is the above reason.

Therefore, among the unvulcanized rubbers 1-1, 1-2, and 1-3 whose compounding compositions greatly differ from each other, an unvulcanized rubber composition having a small loss coefficient, for example, unvulcanized rubber 1-1. ,
By adding a small amount of conductive carbon black having the above-mentioned characteristics to 1-3, and blending them, the values of these loss coefficients can be increased.

This is because the unvulcanized rubber 1-1 (loss factor of 0.
By adding 1.5 to 8.0 parts by weight of the above-mentioned various conductive carbon blacks to 2) and 1-3 (loss factor 0.1), both of these loss factors increase to 1.00. This is a finding based on the finding of this.

Further, various thicknesses of unvulcanized rubber 1-1 and 1-3 whose loss coefficient value is 1.00 and unvulcanized rubber 1-2 (loss coefficient 1.05) which is the same as the conventional example. To meat complex 1,
The measured temperature immediately after the microwave heating is performed under the same irradiation condition as that of the conventional example is shown in FIG.
As shown in FIGS. 4A and 4B, these are all shown in FIG.
It is shown that the low temperature, which is particularly exhibited in the difficult temperature rising portion B or the vicinity thereof in (a) and (b), is remarkably increased until it is higher than the surface portion. 4 to
FIG. 6 shows the temperature measured at each point on the line passing through the difficult temperature rising portion B by dividing the cross-section of the annular thick composite body 1 shown in FIGS. 2 (b) and 3 (b) into upper and lower parts in the figure. The temperature distribution graph which plotted is shown.

Here, it is generally said that the penetration depth of microwaves into a dielectric material such as unvulcanized rubber having a single composition is inversely proportional to the oscillation frequency f, but this is illustrated in FIGS. 5 and 6. Such a temperature increase phenomenon is caused by, for example, the shape of a thick body,
Microwave frequency f that allows microwaves to overlap in the vicinity of the difficult temperature rising portion B depending on the size, rubber composition, etc.
Can be obtained by selecting appropriately. In the examples shown in FIGS. 5 and 6, the frequency f is set to 915 MHz. By the way, when the frequency f is set to 2450 MHz, the temperature of the difficult temperature rising portion B is significantly lower than that of the surface portion. It was

Further, by appropriately combining the above-described action with the amount or type of the conductive carbon black added, the temperature distribution of the thick composite body 1 from the difficult temperature rising portion B to the surface portion can be improved. Can be formed into a desired form.

Thus, the unvulcanized rubber 1 of the thick-walled composite 1
By reducing the difference in loss coefficient among 1, 1-2, and 1-3, when the thick composite 1 is subjected to high-frequency dielectric heating, particularly microwave heating, the difficult-to-heat-up portion B and its vicinity Can be raised to the desired temperature above the surface temperature.

In this case, in addition to the optimum microwave frequency f, the output power or the heated object is heated depending on the compounding composition, shape, size and the like of each unvulcanized rubber of the thick composite body 1 which is the object to be heated. It goes without saying that preheating is performed by setting various conditions such as the magnitude v of the electric field around the body and the irradiation time, and the thick-walled composite body 1 thus prepared is preferably followed by a mold according to a customary manner. When the vulcanization molding used is performed, a rubber product in which the degree of vulcanization in each part of the thick-walled composite 1 is appropriately maintained can be obtained in a short time at high temperature.

As a result, the rubber product after the vulcanization molding of the thick composite body 1 has no excess or deficiency of vulcanization in each part, and the addition of a small amount of conductive carbon black is sufficient, so that the required performance can be exhibited. Rubber properties can be retained. At the same time, high-efficiency vulcanization molding under high-temperature and short-time conditions is possible, which contributes to a significant improvement in productivity over the entire process. Further, it is possible to further increase the high frequency output power of microwaves and the like, and it is possible to shorten the irradiation time.

[0030]

EXAMPLES First, Examples 1 and 2 and Comparative Examples 1 and 2 which will be described later.
An example of microwave heating common to the above will be described with reference to FIG. FIG. 1 schematically shows an apparatus for applying microwave heating to the thick composite 1, 2 is a microwave generator, 3 is a microwave waveguide, and 4 is an application for applying microwave to the thick composite 1. 5 is a stirrer (rotary blade) that reflects and stirs the microwaves in the applicator, and 6 is a rotary support base preferably made of a synthetic resin such as polypropylene that transmits microwaves.

[Example 1] The annular thick composite body 1 which becomes a solid tire after vulcanization molding has a total thickness t along the line AA of 10 cm according to FIGS. 2 (a) and 2 (b). The inner unvulcanized rubber 1-1 is a rubber in which short fibers are evenly dispersed and mixed in a normal rubber, the thickness t / 2 is 5 cm, and the loss coefficient thereof is 0.2. 1-2 had the composition shown in Table 1, the thickness t / 2 was 5 cm, and the loss coefficient thereof was 1.05. The difficult temperature rising portion in this example is located on the center circumferential line B of the joint surface between the rubbers 1-1 and 1-2.
The volume was about 17500 cm ³ .

[0032]

[Table 1]

Using the above thick composite 1 as Comparative Example 1, the thick composite 1 of (A) to (D) was prepared by adding the following conductive carbon black to the innermost unvulcanized rubber 1-1. ,
Each unvulcanized rubber 1-1 was provided with subscripts a to d and prepared as Example 1. (A) 1-1a; 1.5 parts by weight of Ketjen EC, (B) 1-1b; 1.5 parts by weight of Printex XE2, (C) 1-1c; 6 parts by weight of Vulcan XC-72. Addition, (D) 1-1d; 8 parts by weight of acetylene black was added, and the loss factors of (A) to (D) above were adjusted to 1.00.

Microwave heating was applied to each of Example 1 (A) to (D) and Comparative Example 1 separately by the apparatus illustrated in FIG. The frequency f of the microwave is 915 MH
z, output power was 3 kW, and irradiation time was about 10 minutes.

After the microwave heating, the temperature of each part of each thick composite body 1 was continuously measured.
(A), (A) to (D) of Example 1 are shown in FIG.
It shows in (d). 5 (a) corresponds to (A), FIG. 5 (b) corresponds to (B), FIG. 5 (c) corresponds to (C), and FIG. 5 (d) corresponds to (D). In each figure, the horizontal axis represents the thickness t (cm). As is clear from FIGS. 4 (a) and 5, each thick composite body 1 of Example 1 has a temperature in the vicinity of the difficult temperature rising portion B higher than that of the surface portion, and has a preferable temperature distribution for subsequent vulcanization molding. The temperature distribution of Comparative Example 1 is significantly improved.

After each thick composite body 1 was vulcanized and molded into a solid tire by a mold, the vulcanization degree of each portion of each solid tire was measured in the vicinity of the temperature measurement position in FIGS. 4 to 6, When expressed by an index in which the proper vulcanization degree is 100 described at the beginning, Comparative Example 1 has a distribution in the range of 100 to 440, while (A) to Example 1 of Example 1
(D) falls within the range of 100 to 170, and no change is found in the basic physical properties of rubber, and product performance is secured.

It was impossible to attempt low-temperature vulcanization molding of Comparative Example 1 so that it would fall within the range of the vulcanization degree shown in each Example 1. [Example 2] A thick-walled composite body 1 which similarly becomes a solid tire
Is the total thickness t along the line AA according to FIGS. 3 (a) and 3 (b).
Is 10 cm, the innermost unvulcanized rubber 1-1 is a short fiber mixed rubber having the same loss coefficient of 0.2 as in Example 1, and the thickness t /
2 is 5 cm, and the outermost unvulcanized rubber 1-2 has the same composition as in Example 1 shown in Table 1 with a loss factor of 1.05 and a thickness of t / 4 of 2.5 cm. Sulfur rubber 1-3 is shown in Table 1.
The loss factor is 0.1 and the thickness t is
/ 4 is 2.5 cm. In this example as well, the difficult-to-heat-up portion is located almost on the center line B of the joint surface between the innermost unvulcanized rubber 1-1 and the intermediate unvulcanized rubber 1-3, and the volume is about 1750.
It was set to 0 cm ³ .

Using this thick-walled composite 1 as Comparative Example 2,
The following conductive carbon black was added and blended to the innermost unvulcanized rubber 1-1 and the intermediate unvulcanized rubber 1-3 (E),
(F) was prepared as Example 2. The subscripts e and f are the same as those in the first embodiment. (E) 1-1e; 1.5 parts by weight of Printex XE2 added; 1-3e; 5.0 parts by weight of Printex XE2; (F) 1-1f; 6.0 parts by weight of Vulcan XC-72 Addition, 1-3f; 5.0 parts by weight of Printex XE2 was added, and the loss factors of the innermost and middle unvulcanized rubbers of (E) and (F) were adjusted to 1.00.

Microwave heating was applied to Examples (E) and (F) and Comparative Example 2 separately by the apparatus illustrated in FIG. The microwave frequency f was 915 MHz, the output power was 3 KW, and the irradiation time was about 10 minutes.

After the microwave heating, the temperature of each part of each thick composite body 1 was continuously measured.
(B), (E) and (F) of Example 2 are shown in FIG.
It shows in (b). Note that FIG. 6A is shown in FIG. 6E and FIG.
Corresponds to (F), and the horizontal axis of each figure indicates the thickness t. Figure 4
(B) As is apparent from FIG. 6, in Example 2 also, each thick-walled composite body 1 has a temperature in the vicinity of the difficult temperature rising portion B higher than that in the surface portion, and shows a preferable temperature distribution for subsequent vulcanization molding. Compared to the temperature distribution of Comparative Example 2, it is significantly improved.

After each thick composite body 1 was vulcanized and molded into a solid tire by using a mold, the vulcanization degree of each portion was measured in the vicinity of the temperature measurement position shown in FIGS. 4 to 6, and the result was obtained. Is expressed by an index with an appropriate degree of vulcanization being 100, Comparative Example 2 also has a distribution in the range of 100 to 550, while (E) and (F) of Example 2 are 100.
Within the range of up to 180, no change is found in the basic physical properties of the rubber, and product performance is secured.

Further, even if an attempt was made to perform low temperature vulcanization molding on the solid tire of Comparative Example 2 so that it would fall within the range of the vulcanization degree of each Example 2, it was still impossible.

[0043]

According to the present invention, high temperature dielectric heating, particularly microwave heating, is applied to a thick-walled composite containing unvulcanized rubber having a plurality of types of compounding compositions which are greatly different from each other, thereby making it difficult to raise the temperature. It enables preheating to raise the temperature of the part to a higher temperature than that of the surface part, which allows the product after vulcanization molding to have appropriate rubber physical properties that can sufficiently meet the required performance. At the same time, it is possible to provide a vulcanization molding method for a thick unvulcanized rubber composite that can significantly improve the productivity over the entire vulcanization molding process.

[Brief description of drawings]

FIG. 1 shows an example of a microwave heating apparatus of the present invention.

FIG. 2 shows an example of a thick composite.

FIG. 3 shows an example of another thick composite.

FIG. 4 shows a temperature distribution of a conventional thick composite by high frequency heating.

FIG. 5 shows the temperature distribution of a thick composite according to the present invention.

FIG. 6 shows the temperature distribution of another thick composite according to the present invention.

[Explanation of symbols]

 1 Thick Composite 1-1 Unvulcanized Rubber 1-2 Unvulcanized Rubber

Claims (1)

[Claims] 1. A relative permittivity of each unvulcanized rubber when a thick composite in which a plurality of unvulcanized rubbers are joined and integrated with each other is preheated by high-frequency dielectric heating and then vulcanized and molded. (Ε) and dielectric loss angle (tan δ), which is a product of ε · tan δ and has a small loss coefficient represented by ε · tan δ. A method for vulcanizing and molding a thick unvulcanized rubber composite, which comprises reducing the difference in loss coefficient between vulcanized rubbers.