JPH11236403A - Vulcanizing and molding of foamed vulcanized rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vulcanizing and molding method of a highly foamed vulcanized rubber (e.g. a motocross tire tube) by which the productivity at the vulcanizing and molding process is extremely improved while keeping properties of a highly foamed massive rubber product. SOLUTION: A foamable non-vulcanized rubber is pressurized and heated with a mold as the primary vulcanization to provide a previously vulcanized rubber molding product, and the previously vulcanized rubber molding product is vulcanized by a high frequency dielectric heating as the secondary vulcanization in the method for vulcanizing and molding the foamed and vulcanized molding product. In the other aspect, the foamable non-vulcanized rubber is formed into the previously vulcanized rubber molding product by the high frequency dielectric heating, and the previously vulcanized rubber molding product is pressurized and heated by the mold to vulcanize the previously vulcanized rubber molding product as the secondary vulcanization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vulcanization molding method for a thick and highly foamed vulcanized rubber article such as a motocross tire tube. By vulcanizing the unvulcanized rubber, the degree of vulcanization (distribution) of the rubber article after vulcanization molding is uniform from the thick surface layer to the entire thickness of the central part, and the predetermined physical properties (distribution) In addition, the foaming rate (distribution) is made uniform, and accordingly, the prevention of blow near the surface layer, the uniformity of deformation and the riding comfort and durability are excellent, and at the same time, the vulcanization molding of this rubber article has a high efficiency in a short time. The present invention relates to a vulcanization molding method for a thick-walled high-foamed vulcanized rubber article that enables highly vulcanization molding and contributes to greatly improving the productivity throughout this process.

[0002]

2. Description of the Related Art It is known that a tube such as a motocross tire requires no puncture, and as a method of obtaining the no puncture performance, a highly foamed tube is used. Since such a highly foamed tube is thick, the unvulcanized rubber after extrusion before vulcanization becomes thick.

[0003] A conventional general method of vulcanizing and molding this thick, highly foamed unvulcanized rubber only by heat conduction from its surface,
For example, in the mold vulcanization method and the open vulcanization method after the mold vulcanization, the temperature rise in the central part is higher than that in the surface part due to the remarkably small thermal conductivity inherent in rubber from the heated surface part to the center part. As a rule, it is necessary to continue heating for vulcanization molding until the center of the difficult temperature rise reaches a proper degree of vulcanization (a degree of vulcanization exhibiting the most desirable physical properties that can be expected).

In this case, the degree of vulcanization gradually increases from the center of the difficult temperature rise to the surface layer.
The closer part shows a remarkable over-vulcanization state. That is,
The degree of vulcanization is significantly different between the surface layer and the center, and accordingly, uneven distribution of physical properties and foaming ratio occurs in the thickness direction, for example, the surface layer is softened, and the distortion of the surface layer during running is remarkable. As a result, the durability of the portion is deteriorated.

[0005] In the conventional vulcanization molding method of thick-wall high-foamed unvulcanized rubber, it is further added that after the primary mold pre-vulcanization, the vulcanized rubber is already in the form of a foam, so that open heat vulcanization is performed. In sulfur, the thermal conductivity is even lower. As a result, in open heat vulcanization, it takes a long time to reach heat to the center, and the surface layer becomes considerably over-vulcanized.For example, under an air atmosphere, thermal aging of the surface layer considerably progresses There is a problem. Also, in another conventional vulcanization molding method of a thick-wall high-foamed unvulcanized rubber, the vulcanization molding using only the mold vulcanization without performing the above-mentioned open heat vulcanization also involves overvulcanization of the surface layer portion. The problem of deterioration of the state and the resulting performance is a problem, and this tendency becomes more remarkable when vulcanizing the mold at a higher temperature to improve productivity. In order to minimize the performance deterioration as described above, vulcanization molding at a low temperature and for a long time is inevitable, resulting in a problem that productivity is significantly impaired. Has been strongly sought after.

[0006] The simplest means of this improvement is to use a thick-wall highly foamed unvulcanized rubber as a whole in a preheating chamber in which the atmosphere is higher than room temperature but significantly lower than the vulcanization temperature.
The method of heating until reaching a substantially uniform temperature was adopted.
However, in this method, if the set temperature of the heating is too high, the vulcanization of the surface layer portion of the thick-walled high-foamed unvulcanized rubber proceeds excessively, so that it is necessary to keep the temperature low. It takes a long time to raise the temperature of the core to a predetermined temperature level, and the degree of heating is low. As a result, it is inevitable that the productivity improvement over the entire vulcanization molding process will be insufficient. The sulfur problem was not solved.

In addition, a vulcanization molding method including high-frequency dielectric heating of a thick unvulcanized rubber article such as a tire before vulcanization molding greatly improves the productivity and appropriately vulcanizes the rubber throughout the rubber article. By the present inventors that it is possible to obtain a rubber article having the desired rubber properties satisfying the required performance under the degree.
It has been proposed in JP-A-5-301231, JP-A-6-344510, JP-A-8-335496, and the like. However, it differs from a rubber article using ordinary rubber which does not foam as described above in that the rubber component, compounding agent, etc. are significantly different, and that foaming is newly required. A vulcanization molding method using high-frequency dielectric heating to obtain a foamed vulcanized rubber article is not known. For example, in a vulcanization method in which only high-frequency dielectric heating is applied to such a thick-walled highly foamed unvulcanized rubber, the resulting rubber article lacks uniformity in the degree of vulcanization over the entire thickness, and the obtained rubber article has inferior shape stability. It cannot be a usable rubber article.

[0008]

Accordingly, a vulcanization molding method for applying high-frequency dielectric heating, in particular, microwave heating and mold vulcanization in combination to a thick-walled highly foamed unvulcanized rubber article allows the product to be entirely covered. Thick, highly foamed vulcanized rubber that can exhibit the desired rubber properties that meet the required performance under the appropriate degree of vulcanization of the rubber and can greatly improve the productivity throughout the vulcanization molding process It is an object of the present invention to provide a vulcanization molding method.

[0009]

The inventor of the present invention has focused on the characteristics of thick and highly foamed unvulcanized rubber and thick and highly foamed prevulcanized rubber, and the characteristics of various vulcanization molding methods such as high-frequency dielectric vulcanization. As a result of intensive studies, they have found that the above objects can be achieved by the following means, and have completed the present invention.

That is, (1) In the vulcanization molding method of the foamed vulcanized rubber of the present invention, as the primary vulcanization, the foamed unvulcanized rubber after extruding is pre-vulcanized by pressing and heating in a mold. A molded product is obtained, and then, as a secondary vulcanization, the pre-vulcanized rubber molded product is vulcanized by high-frequency dielectric heating.

(2) In the vulcanization molding method for foamed vulcanized rubber according to the present invention, as a primary vulcanization, a foamed unvulcanized rubber after extrusion is subjected to high frequency dielectric heating to obtain a pre-vulcanized rubber body. The secondary vulcanization is characterized in that the pre-vulcanized rubber body is vulcanized by heating under pressure in a mold.

(3) The vulcanization molding method for foamed vulcanized rubber according to the present invention is characterized in that in the above item (1) or (2), the foamed vulcanized rubber has a foaming ratio of 50 to 1200%. And

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings.

FIGS. 2 and 3 show an example of a method of vulcanizing and molding an annular thick-walled high-vulcanized rubber 10 which becomes a motocross tire tube after vulcanization as an example of a thick-wall high-vulcanized rubber article.

As shown in the vulcanization molding method (II) in FIG. 2, the vulcanization molding method according to one embodiment of the present invention is a highly vulcanized unvulcanized rubber after extrusion into a mold 12 as primary vulcanization. 10 and vulcanization under pressure to obtain a pre-vulcanized rubber molded body 10, which is then subjected to secondary vulcanization.
Vulcanization is performed by high-frequency dielectric heating using a high-frequency dielectric heating apparatus.

On the other hand, a conventional vulcanization molding method (I) is shown in FIG. That is, as primary vulcanization,
The extruded highly foamable unvulcanized rubber 10 is set in the mold 12 and, after pressure vulcanization, a pre-vulcanized rubber molded body is obtained.
As the secondary vulcanization, this pre-vulcanized rubber molded body 10 is placed in a vulcanization chamber 14 and subjected to open vulcanization. In addition to the low thermal conductivity of rubber, in the stage of open vulcanization, the thermal conductivity further decreases because the vulcanized rubber is a high foam, and it takes a longer time to raise the temperature to the center, The part is considerably overvulcanized. Due to overvulcanization, the surface layer is softened, distortion during running becomes large, and durability is inferior. This is because the degree of vulcanization of the surface layer is remarkably increased with respect to the center of the thick material as shown by the ○-○ line in FIGS. It is easily understood. Further, if the open vulcanization is performed in an air atmosphere, desired characteristics such as heat aging of the surface layer cannot be obtained.

[0017] In the vulcanization molding method (II) of the present invention in which high frequency dielectric vulcanization is used instead of the open vulcanization of the above-mentioned conventional method after the mold preliminary vulcanization, the vulcanized rubber obtained by the mold vulcanization has low thermal conductivity. Despite being a high-foam, high-frequency dielectric heating raises the temperature of the center of the thick material in a short time, and vulcanization occurs uniformly over the surface layer, and becomes harder as it approaches the surface layer. Become. This is shown in FIG.
As can be seen from the line, almost uniform degree of vulcanization was obtained from the center to the surface layer, and the compressive strain increased toward the surface layer. in this way,
According to the vulcanization molding method of the present invention, the problems of the conventional method such as overvulcanization of the surface layer, reduction in productivity, deterioration in physical properties, and the like can be simultaneously solved.

In the vulcanization molding method according to another embodiment of the present invention, as shown in the vulcanization molding method (III) in FIG. Using a heating device, a pre-vulcanized rubber body 10 is obtained by high-frequency dielectric heating, and then, as secondary vulcanization, the pre-vulcanized rubber body 10 is set in a mold 12 and heated by pressurizing and heating. Perform sulfuric acid.

On the other hand, in the conventional method using only the mold vulcanization without performing the above-mentioned open vulcanization, it takes a considerably long time to raise the temperature to the center of the thick material, Becomes overvulcanized. This is because the degree of vulcanization of the surface layer is larger than the center of the thick material and is softer, that is, lower compression strain, as shown by the ○-○ lines in FIGS. 5A and 5B. It can be understood.

In the vulcanization molding method of the present invention, in which high-frequency dielectric heating is performed on a thick material and a highly foamable unvulcanized rubber before vulcanizing the mold, the temperature of the central portion of the thick material is increased in a short time, and the surface portion is heated. Vulcanization occurs uniformly and becomes hard. This is because, as shown by the □-□ lines in FIGS. 5A and 5B, the uniformity of the degree of vulcanization is substantially maintained from the center to the surface layer, and furthermore, the reduction of the compression strain is suppressed and the uniformity is excellent. I understand. Such a vulcanization molding method simultaneously solves many problems of the conventional method, similarly to the vulcanization molding method of the above aspect of the present invention.

As described above, the thick foamed foamed rubber article obtained by the vulcanization molding method shown in various aspects of the present invention, for example, the highly foamed tube of a motocross tire, maintains the hardness of the surface layer portion of the tube, Rather, the center is soft and well-balanced. For this reason, the deformation of the tube during traveling is not limited to the surface layer portion, but deforms to the center portion. Since the blow near the surface layer is prevented and the deformation is made uniform, the ride comfort is not lumpy.

As the high-frequency dielectric heating used in the present invention, for example, microwave heating is preferably used.

The microwave power loss P consumed by the object to be heated is given by the following equation.

[0024]

P = (1 / 1.8) fv ² × ε · tan δ × 10 ^-10 (W / m ³ ) (where f represents the oscillation frequency (Hz), and v represents the magnitude of the electric field (V / m Here, in the right side of the above equation, it is reasonable to fix the oscillation frequency f so as to be optimal for the thick-walled high-foam rubber article to be heated. Varies depending on the loss coefficient ε · tan δ of the heated portion, but must be kept within a predetermined limit in order to avoid the possibility of generating an excessively heated portion.

Here, it is generally considered that the penetration depth of microwaves into a dielectric such as rubber to be heated, which has a single compounding composition, is inversely proportional to the oscillation frequency f.
For example, it can be obtained by appropriately selecting a microwave frequency f that allows the microwaves to overlap in the vicinity of the center of the difficult temperature rise according to the shape, size, rubber compounding composition, and the like of the thick body.

The microwave oscillation frequencies f which can be used industrially are 2450 MHz and 915 MHz, but the penetration depth of the microwave is three times deeper at 915 MHz than at 2450 MHz. In the example of the present invention, since the thickness of the highly foamed vulcanized rubber article is 5 cm or more, the frequency is preferably 915 MHz, but is not limited thereto.

Based on the new finding that when a highly foamable rubber body having a thickness of 5 cm or more is heated by a 915 MHz microwave as in the example of the present invention, the central portion is heated from the surface layer. Thus, the present invention has been completed. This characteristic is a heating characteristic opposite to that of heating by heat conduction from the surface layer, as in a conventional heat molding method (for example, a mold vulcanization method or an open vulcanization method after mold vulcanization). In the present invention, by combining high-frequency dielectric vulcanization and mold vulcanization, the obtained thick-walled and highly foamed vulcanized rubber article has a uniform temperature distribution over the entire thickness, that is, a uniform degree of vulcanization, and a surface layer. The riding comfort is improved because the part has a distribution that is harder than the inside.

As the rubber component of the foamed vulcanized rubber used in the present invention, for example, butyl rubber, natural rubber, styrene-
Butadiene rubber, butadiene rubber and the like can be mentioned, but butyl rubber is preferred from the viewpoint of the gas retaining effect.

Examples of the foaming agent for the foamed vulcanized rubber used in the present invention include dinitrosopentamethylenetetraamine (DPT), azodicarbonamide (ADCA),
Dinitrosopentastyrenetetramine, benzenesulfonylhydrazide derivative, oxybisbenzenesulfonylhydrazide (OBSH), ammonium bicarbonate that generates carbon dioxide, sodium bicarbonate, ammonium carbonate, nitrososulfonylazo compound that generates nitrogen,
N, N′-dimethyl-N, N′-dinitrosophthalamide, toluenesulfonylhydrazide, P-toluenesulfonylsemicarbazide, P, P′-oxy-bis (benzenesulfonylsemicarbazide) and the like. These may be used alone or in combination of two or more.

Among these foaming agents, dinitrosopentamethylenetetraamine (DPT) and azodicarbonamide (ADCA) are preferable, and azodicarbonamide (ADCA) is particularly preferable.

Examples of the foaming auxiliary include urea, zinc stearate, zinc benzenesulfinate, zinc white, and the like, which are usually used in the production of foamed products. These may be used alone or in combination of two or more. Among these, urea, zinc stearate, zinc benzenesulfinate and the like are preferable.

The rubber composition of the foamed vulcanized rubber used in the present invention may contain a reinforcing filler, a softening agent, an antioxidant, a vulcanizing agent, a vulcanization accelerator and the like in addition to the rubber component and the foaming agent. Compounding agents used in the rubber industry can be appropriately compounded.

The rubber composition is obtained by kneading using a kneading machine such as a roll, an internal mixer, a Banbury mixer, and the like, and this is vulcanized by the vulcanization molding method of the present invention into a desired material such as a motocross tire tube. Such a thick, highly foamed vulcanized rubber article is obtained.

The foaming rate of the foamed vulcanized rubber in the present invention is 5
0-2000% is preferable, and further 100-1000%
Is more preferred. When the foaming ratio is less than 50%, the tire becomes a weight and a non-foamed solid tire or a tire close thereto,
If it exceeds 2000%, it is not preferable in terms of puncture.

The foaming ratio Vs is represented by the following equation.

[0036]

Vs = ｛(ρ _o -ρ _g ) / (ρ _l -ρ _g ) -1｝ × 100 (%) (1) (where, ρ _l is the density (g / cm ³ ), ρ _o is the density (g / cm ³ ) of the solid phase rubber portion of the foamed rubber, and ρ _g is the density (g / cm ³ ) of the gas portion in the bubbles of the foamed rubber.) The density ρ _g of the gas part of
Since it is almost zero and extremely small with respect to the density ρ _o of the solid phase rubber part, the equation (1) is

[0037]

Vs = (ρ _o / ρ _l −1) × 100 (%) (2)

[0038]

EXAMPLE An example of microwave heating common to Examples 1 and 2 described later will be described with reference to FIGS.

The microwave heating device shown in FIG. 2 is applied to the pre-vulcanized rubber molded body 10 using a mold, and the microwave heating device shown in FIG. It is a schematic structure figure showing the device which performs heating.
These devices include a microwave generator 16, a microwave waveguide 18, an applicator 20 for applying microwave irradiation to the rubber molded body 10, a stirrer (rotary wing) 22 for reflecting and stirring the microwave in the applicator, and preferably. The rotary support 24 is made of a synthetic resin such as polypropylene that transmits microwaves.

The foaming rate was determined by cutting a block-shaped sample from a thick-walled highly foamed vulcanized rubber and measuring its density ρ ₁ (g / cm ³ ), while measuring the density ρ ₀ of the non-foamed rubber, It was determined using 2). (Example 1) As in the vulcanization molding method II of FIG. 2, after foaming unvulcanized rubber is pre-vulcanized in a mold, the obtained pre-vulcanized rubber molded body is subjected to microwave heating to obtain a motocross tire tube. Is an experimental example of obtaining a highly foamed vulcanized rubber for use.

The composition of the foamable unvulcanized rubber is as shown in Table 1. This unvulcanized rubber was subjected to mold vulcanization under vulcanization conditions of 145 ° × 80 minutes. 915 MHz
X1KW x 85min conditions, more specifically 915MHz x 1K
When irradiation with W was performed for 5 minutes, and then irradiation for 1 minute and stop for 9 minutes were repeated, microwave heating was performed. As a result, the tube material diameter was 5 cm, the annular tube outer diameter was 30 cm, and the volume was 154.
A 1 cm ³ unvulcanized rubber becomes a motocross tire tube having a foaming ratio of 800% and a tube material diameter of 10 cm.

The center and the middle (2.
The results of measuring the degree of vulcanization of each part of the surface (5 cm) and the surface (5.0 cm) are shown by the □-□ lines in FIG. 4A. It can be seen that this tube has excellent uniformity of vulcanization degree from the center to the surface layer. Further, the compressive strain was measured, and the result is shown by the line □-□ in FIG. 4B, but the surface layer has a harder distribution than the inside. (Comparative Example 1) Experimental example of obtaining a foamed vulcanized rubber in the same manner as in Example 1 except that open vulcanization was performed instead of microwave vulcanization as in the conventional vulcanization molding method (I) of FIG. It is.

Mold vulcanization was carried out in the same manner as in Example 1, and the obtained molded product was subjected to open vulcanization under vulcanization conditions of 145 ° C. × 80 minutes. Thus, a motocross tire tube having a tube material diameter of 10 cm is obtained.

As in Example 1, the result of measuring the degree of vulcanization of each part of the tube is shown by the line −- ○ in FIG. 4A.
It is apparent that the degree of vulcanization of this tube is greatly increased from the center to the surface layer, that is, the degree of vulcanization is not uniform. The compressive strain is shown by the line − in FIG. 4B, and the surface portion has a soft distribution corresponding to the degree of vulcanization of the surface portion. (Example 2) As in the vulcanization molding method III in FIG. 3, the foamable unvulcanized rubber was pre-vulcanized by microwave heating, and the obtained pre-vulcanized rubber body was subjected to mold vulcanization. This is an experimental example of obtaining a highly foamed vulcanized rubber for a motocross tire tube.

The composition of the foamable unvulcanized rubber is as shown in Table 1, and the unvulcanized rubber was 915 MHz × 1 KW ×
When microwave heating is performed under the conditions of 5 minutes, and the obtained foam is subjected to mold vulcanization under the vulcanization conditions of 160 ° C. × 40 minutes,
As compared with Example 1, a motocross tire tube having a foaming ratio of 580% and a shape corresponding to the foaming ratio (tube material diameter: 9 cm) is obtained.

As in Example 1, the results of measuring the degree of vulcanization of each part of the tube are shown by the lines □-□ in FIG. 5A.
It can be seen that this tube has excellent uniformity of vulcanization degree from the center to the surface layer. As a result, the distribution of the compressive strain is also excellent in uniformity as shown by the line □-□ in FIG. 5B. (Comparative Example 2) This is an experimental example in which a foamed vulcanized rubber is obtained in the same manner as in Example 2 except that microwave vulcanization is not used (a heat molding method using only mold vulcanization).

According to this method, a motocross tire tube having the same shape as in Example 2 and a foaming ratio of 580% is obtained.

As in Example 2, the results of measuring the degree of vulcanization of each part of this tube are shown by the circles in FIG. 5A.
It can be seen that this tube has poor uniformity of the degree of vulcanization from the center to the surface. The distribution of the compressive strain is also inferior to the uniformity as shown by the ○-○ line in FIG. 5B.

[0049]

[Table 1]

In terms of an index with the appropriate degree of vulcanization being 100 as described at the beginning, Comparative Examples 1 and 2 have a distribution ranging from 100 to 440, whereas Examples 1 and 2 have a distribution of 100. And the obtained highly foamed vulcanized rubber molded product has desired excellent performance.

Incidentally, it was impossible to perform low-temperature vulcanization molding on Comparative Examples 1 and 2 so as to fall within the range of the degree of vulcanization shown in each of Examples 1 and 2.

[0052]

According to the present invention, by combining mold vulcanization and high-frequency dielectric heating, especially microwave heating, the product after vulcanization molding has adequate rubber properties that can sufficiently meet the required performance. The present invention can provide a vulcanization molding method for a thick, highly foamed vulcanized rubber article that can greatly improve productivity throughout the vulcanization molding step.

[Brief description of the drawings]

FIG. 1 shows an example of a conventional vulcanization molding method.

FIG. 2 shows a vulcanization molding method according to Example 1 of the present invention.

FIG. 3 shows a vulcanization molding method according to Example 2 of the present invention.

FIG. 4A shows the degree of vulcanization from the center to the surface layer of the highly foamed vulcanized rubber obtained by the vulcanization molding method of the present invention and the conventional vulcanization molding method. B shows the compression strain from the center to the surface layer of the highly foamed vulcanized rubber.

FIG. 5A shows the degree of vulcanization from the center to the surface layer of a highly foamed vulcanized rubber obtained by each of the other vulcanization molding methods of the present invention and another conventional vulcanization molding method. B shows the compression strain from the center to the surface layer of the highly foamed vulcanized rubber.

[Explanation of symbols]

10 Highly foamable unvulcanized rubber, pre-vulcanized rubber molded product or highly foamed vulcanized rubber

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // B29C 35/12 B29C 67/22 B29K 105: 04 105: 24

Claims (3)

[Claims] 1. A vulcanization molding method for a foamed vulcanized rubber, wherein as a primary vulcanization, a foamed unvulcanized rubber after extrusion is heated under pressure in a mold to obtain a pre-vulcanized rubber molded body. And vulcanizing the pre-vulcanized rubber molded article by high-frequency dielectric heating as secondary vulcanization. 2. A vulcanization molding method of a foamed vulcanized rubber, wherein a pre-vulcanized rubber body is obtained as a primary vulcanization by extruding an extrudable foamable unvulcanized rubber by high-frequency dielectric heating. A vulcanization molding method for foamed vulcanized rubber, comprising vulcanizing the pre-vulcanized rubber body by pressurizing and heating in a mold as the next vulcanization. 3. The foamed vulcanized rubber has a foaming ratio of 50 to 20.
The vulcanization molding method for a foamed vulcanized rubber according to claim 1 or 2, wherein the content is 00%.