JPS6237107A - Vulcanizing mold - Google Patents

Abstract

PURPOSE:To prevent unbalance in degree of vulcanization, by providing a heat insulation layer whose thermal conductivity is low and whose thermal expansion coefficient is less than a specific value on the inside of a mold in a vulcanizing mold which has been formed of a material having aluminum for its main ingredient and the thermal expansion coefficient of more than the specific value. CONSTITUTION:The titled mold possesses aluminum for its main ingredient and is formed of a material superior in thermal conductivity whose thermal diffusivity is more than 0.6cm<2>/sec. a heat insulation layer 11 provided on the inside of the mold of a part which has to prevent partial overcure of an article to be vulcanized is composed of a nonthermal-conductive material whose thermal diffusivity is less than 1X10<-2>cm<2>/sec. With this construction, as a side wall part 8 which is located closet to an external heating part and is a thin part of a tire 5 is provided with a heat insulation layer 11 of ceramics whose thermal conductivity is low on a part coming into contact with the inside 1b of the mold, the side wall part 8 can be controlled so as to fall within a range of a predetermined degree of vulcanization, and unbalanced phenomenon in the degree of vulcanization can be eliminated at the time when the other tire part reaches the predetermined degree of vulcanization.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a mold for curing molded articles such as tires, and particularly relates to a mold for curing molded articles such as tires, and in particular, a mold for curing molded articles such as tires. The present invention relates to a technique for preventing local overvulcanization of a vulcanized molded product and eliminating local non-uniformity in the degree of vulcanization.

(Prior art) A platen-based vulcanization mold, which is conventionally used to vulcanize molded products such as tires, consists of a mold that is divided into upper and lower parts. An external heat generating part is provided, and in order to improve the transfer of heat from the heat generating part to the mold, for example, in a tire curing mold, as shown in FIG. A heat generating plate 2 made of iron is attached to the flat surface in contact with the outer surface 1a, and a heat generating portion 3 whose temperature can be controlled by steam, a heater, etc. is provided within the heat generating plate 2.

Therefore, for example, when vulcanizing a tire, as shown in FIG. The thin sidewall part 8 is the heat generating part 3
Since more heat is transferred to the sidewall portion 8 than to the tread portion 6 and bead portion 7 which are located closer to the heat generating portion 3 and have a greater distance from the heat generating portion 3, the tread portion 6 and bead portion 7 are vulcanized by a predetermined amount. During this time, the sidewall portion 8 is significantly over-vulcanized, and as a result, thermal deterioration of the sidewall portion 8 progresses.
There were drawbacks such as early cracking.

For the purpose of preventing the above-mentioned unevenness in the degree of vulcanization caused by the difference in the local wall thickness of the molded product to be vulcanized and the difference in distance from the external heat generating part, for example, Japanese Patent Application Laid-open No. 58-49232 discloses the following methods: As shown in FIG. 3, a tire 5, which is a molded product to be vulcanized,
A technique is disclosed in which a portion 9 having a different thermal conductivity is arranged between a sidewall portion 8, which is a thin wall portion, and an external heat generating portion 3.

(Problems to be solved by the invention) Generally, in order to improve productivity in the vulcanization process of molded products such as tires, it is necessary to adopt a method that can produce high-quality tires in a shorter time. And for this reason,
It is necessary not only to increase the vulcanization temperature, but also to increase the rate of heat transfer to the molded article. In order to satisfy these demands, it has been proposed to use an aluminum alloy, which is a material with better thermal diffusivity than iron-based materials conventionally used for molds.

However, in platen-type vulcanization molds, heat is transferred from the external heat generating part attached to the outside of the mold, which is divided into upper and lower parts as described above. The problem is that the sidewall part of the tire, which is a thin molded part located close to the heat generating part, is relatively excessively vulcanized compared to the tread part, which is a thick part, resulting in a decline in product quality. In order to prevent this, a portion 9 having a different thermal conductivity is disposed between the sidewall portion 8 and the external heat generating portion 3, as described above. Showa 58-4
As described in Japanese Patent No. 9232, the portions 9 having different thermal conductivities are placed on the outer surface 1a of the mold 1 or on the heat generating plate 2.
In the configuration in which the mold is formed in the recess 10 provided in the side surface 2a of the tire 5, thereby lengthening the path for heat to be transmitted from the heat generating part 3 to the thin side wall part 8 of the tire 5, the mold is made of an aluminum alloy with a high thermal diffusion coefficient. In this case, the effect of reducing the amount of heat transferred to the thin sidewall portion 8 cannot be expected much, and as a result, the sidewall portion 8 is over-vulcanized, and the problem of unbalanced degree of vulcanization remains unresolved. I confirmed this fact.

Therefore, an object of the present invention is to solve the above-mentioned problem of imbalance in the degree of vulcanization in a vulcanization mold having excellent thermal conductivity.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention aims to prevent local overvulcanization of the molded product to be vulcanized in a vulcanization mold with excellent thermal conductivity. A heat insulating layer made of a material with a low heat transfer coefficient is provided on the inner surface of the mold in contact with the vulcanization mold, and the vulcanization mold is made of aluminum with a thermal diffusion coefficient of 0.6 cm2/sec or more, which has excellent thermal conductivity. The heat insulating layer provided on the inner surface of the mold in the area where local overvulcanization of the article to be vulcanized is to be prevented is made of a non-thermally conductive material with a thermal diffusion coefficient of IXl0-2 cm27 seconds or less. It is characterized by becoming.

Suitable materials for the heat insulating layer made of such materials with low thermal conductivity include, for example, ceramics, graphite, Teflon resin, polyester sulfine resin, polycarbonate resin, polyimide resin, heat-resistant plastics, etc. After molding into a predetermined shape using a vulcanized product, if necessary, in order to improve the mold release properties of tires, etc. after vulcanization, metals, resin materials, etc. with high mold release effects are added to the surface that comes into contact with the vulcanized molded product. It is preferable to cover it by plating, coating, etc.

In carrying out the present invention, it is assumed that the thermal diffusion coefficient of the heat insulating layer is I
If it is higher than Xlo-2C/sec, the difference with the thermal diffusion coefficient of the mold becomes too small, and this is not desirable in terms of design. According to the present invention, the thermal diffusion coefficient of the heat insulating layer is set to 1 x 1010-2C/sec.
It should be less than seconds.

Incidentally, the thermal diffusion coefficient αrcm2/sec is determined by the following formula.

λ α= □ Cp-ρ In the above formula, λ: Thermal conductivity [cal/sec・cm-deg:]Cp
: Specific heat (cat/g-deg) ρ: Specific gravity [
g/cm3] α: Thermal diffusion coefficient [Cm2/sec] (Function) According to the present invention, for example, even though the tire curing mold is made of an aluminum alloy with a high thermal diffusion coefficient, external heat generation does not occur. The sidewall part 8, which is the thin wall part of the tire and closest to the sidewall part, is provided with a heat insulating layer made of a material with low thermal conductivity that is in contact with the sidewall part 8, so that the other parts of the tire reach a predetermined degree of vulcanization. At the point when the degree of vulcanization is reached, the degree of vulcanization can be suppressed within a predetermined range, and the phenomenon of unbalanced degree of vulcanization can be eliminated.

By coating the surface of the heat insulating layer that comes into contact with the tire with a metal, resin, etc. that has a high mold release effect, it has a high affinity with rubber.
In addition, materials such as ceramics, which are difficult to release from the tire during vulcanization but have guaranteed heat resistance and strength, can also be used for the heat insulating layer.

(Example) FIG. 1 shows a longitudinal section of about half of the lower die of a tire vulcanization mold according to the present invention.

In the illustrated example, a heat insulating layer 11 made of ceramics with low thermal conductivity is provided on the inner surface 1b of the tire vulcanizing mold 1 made of aluminum alloy at a portion where the tire sidewall portion 8 contacts. The part of the surface in contact with 5 is coated with Teflon (sealant coating) to improve the releasability from the rubber during vulcanization.

Examples with various insulation layers and surface coatings are shown in Table 1. Table 1 shows the results of tests conducted under various conditions for Examples 1 to 4 according to the present invention and Comparative Examples 1 to 4 in order to confirm the effects of the present invention. "Aluminum" in the table means JISAjl! Casting Type 7 A (A
C? This is an abbreviation for A).

(Effects of the Invention) As is clear from Table 1, by providing a heat insulating layer on the tire side of the aluminum mold according to the present invention, the maximum temperature reached at the tire side part during vulcanization was increased by 5% compared to Comparative Example 1. ~6℃
The temperature can be lowered by 4 to 5°C compared to Comparative Example 3, thereby preventing local overvulcanization and reducing local unevenness in the degree of vulcanization.

In addition, as shown in Example 2 of the present invention, by using a material such as Teflon resin as the heat insulating layer that has excellent mold release properties from rubber during tire vulcanization, surface treatment for improving the surface mold release properties can be omitted. be able to. Further, as shown in Example 3, the material used for the heat insulating layer may be polyester sulfine resin or the like which has excellent heat resistance. As shown in Example 4 (= If ceramic is used for the heat insulating layer and no surface treatment is performed, the mold releasability during tire vulcanization is poor, but in order to improve the mold release property, metal plating is applied to the surface of the heat insulating layer The mold releasability can be improved by applying mold release improving resin coating, etc. Therefore, any material can be selected as long as it can guarantee heat resistance and strength as the heat insulating layer.

Furthermore, it is possible to freely set the thickness of the heat insulating layer and the material of the heat insulating layer to have different thermal diffusion coefficients, and by combining these, it is possible to freely design the mold that provides the optimal vulcanization conditions for the tire. can.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical sectional view of a tire vulcanizing mold according to the present invention, and FIGS. 2 and 3 are partial vertical sectional views of a conventional tire vulcanizing mold. 1... Mold 2... Heat generating plate 3.
...Heating part 4...Vulcanizing bladder 5...
Tire 6...Tread part 7...Bead part End...Sidewall part 11...Insulating layer

Claims (1)

[Claims] 1. In a vulcanization mold made of a material mainly composed of aluminum with excellent thermal conductivity and having a thermal expansion coefficient of 0.6 cm^2/sec or more, a molded product to be vulcanized A heat insulating layer made of a material with a low thermal conductivity and a thermal expansion coefficient of 1 x 10^-^2 cm^2/sec or less is provided on the inner surface of the mold that is in contact with the part where local overvulcanization is to be prevented. A vulcanization mold featuring: 2. The vulcanizing mold according to claim 1, wherein the surface of the heat insulating layer that comes into contact with the molded product to be vulcanized is coated with a metal or resin material having good mold releasability.