Vulcanization method and vulcanized rubber composition

Abstract

To provide a vulcanization method capable of vulcanizing a rubber composition in a uniform manner by radiation with a microwave.SOLUTION: A vulcanization method for vulcanizing a rubber composition containing a diene rubber and a carbon black is provided. A microwave is applied while controlling an average temperature rise speed (°C / minute) in a temperature range of T(α)-T(β)(°C) to 0.2 times to 0.8 times an average temperature rise speed (°C / minute) in a temperature range of 30 to T(α)(°C), where in a temperature-dielectric loss curve of the rubber composition in a temperature range of 30-200°C at a frequency of the microwave being used, T(α)(°C)is a temperature when the value of the dielectric loss (ε") is ε"(α) as calculated by formula (1), and T(β)(°C) is a temperature when the value of the dielectric loss (ε") is ε"(β) as calculated by formula (2).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a vulcanization method and a vulcanized rubber composition. [Background technology]

[0002] It is known to use microwave energy in the manufacture of rubber products for tires. For example, Patent Document 1 discloses that the total heating time can be shortened by using microwave energy for at least a part of the heat energy required in the manufacture of pneumatic tires. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-66924 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in fact, in Patent Document 1, heating by microwave energy is terminated before the start of the vulcanization reaction. In this regard, when the vulcanization reaction was conventionally performed by irradiating microwaves, there were problems such as extremely difficult control of the vulcanization reaction, uneven vulcanization, and localized scorching. Due to such problems of uneven vulcanization, rubber vulcanization using microwaves has not yet been fully put to practical use, and the use of microwaves has at best been limited to preheating before vulcanization.

[0005] Therefore, an object of the present invention is to provide a vulcanization method capable of uniformly vulcanizing a rubber composition by irradiating it with microwaves, and to provide a vulcanized rubber composition vulcanized by the above vulcanization method. [Means for solving the problem]

[0006] As a result of extensive research to achieve the above object, the inventors first discovered that when a rubber composition containing carbon black is heated (vulcanized) by microwave irradiation, the higher the temperature, the more easily microwaves are specifically absorbed.

[0007] Due to this tendency, when a certain temperature is reached in a part of the rubber composition, the amount of microwave absorption increases and the rubber composition becomes more susceptible to heating, which results in an increasingly large non-uniformity in the vulcanization, which was predicted to cause the above-mentioned conventional problems.

[0008] As a result of further investigations, the present inventors have surprisingly found that when a rubber composition containing carbon black is heated (vulcanized) by microwave irradiation, the dielectric loss (ε″) and dielectric tangent (tan δ) increase significantly within at least a part of the temperature range exceeding 30° C. This phenomenon is considered to be specific to carbon black among fillers, and is also considered to be related to the aggregation of carbon black.

[0009] The inventors have also found that uniform vulcanization can be achieved by irradiating microwaves while appropriately controlling the heating rate within the above-mentioned temperature range, which has led to the invention.

[0010] That is, the gist and configuration of the present invention to achieve the above object is as follows.

[0011] The vulcanization method of the present invention is a method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, comprising the steps of: In a temperature-dielectric loss curve of the rubber composition in a temperature range of 30 to 200° C. at a microwave frequency used, the value of dielectric loss (ε″) satisfies the following formula (1): ε″(α)=ε″ min +(ε″ max -ε″ min ) × α (1) (In the formula, ε″ min is the minimum value of dielectric loss, ε″max is the maximum value of the dielectric loss, and α is an arbitrary constant satisfying 0.01<α<0.30), the temperature at which ε″(α) is calculated is defined as T(α) [°C], and the value of the dielectric loss (ε″) is calculated using the following formula (2): ε″(β)=ε″ min +(ε″ max -ε″ min ) × β (2) (where β is an arbitrary constant satisfying 0.70<β<0.99) the temperature at which ε″(β) is calculated is T(β) [°C], The method is characterized in that microwaves are irradiated while controlling the average heating rate [°C / min] in the temperature range of T(α) to T(β) [°C] to be within the range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(α) [°C]. According to the vulcanization method of the present invention, it is possible to uniformly vulcanize the rubber composition by irradiating it with microwaves.

[0012] In the vulcanization method of the present invention, the average temperature rise rate in the temperature range of T(α) to T(β) [° C.] is preferably 20° C. / min or less, which can further improve the vulcanization uniformity of the rubber composition.

[0013] Another vulcanization method of the present invention is a method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, comprising the steps of: In a temperature-dielectric tangent curve of the rubber composition in a temperature range of 30 to 200° C. at a microwave frequency used, the value of the dielectric tangent (tan δ) satisfies the following formula (3): tan δ(γ)=tan δ min +(tan δ max -tan δ min ) × γ (3) (In the formula, tanδ min is the minimum value of the dielectric tangent, and tan δ maxis the maximum value of the dielectric tangent, and γ is an arbitrary constant satisfying 0.01<γ<0.30), the temperature at which tan δ(γ) is calculated is defined as T(γ) [°C], and the value of the dielectric tangent (tan δ) is calculated using the following formula (4): tan δ(σ)=tan δ min +(tan δ max -tan δ min ) × σ (4) (wherein σ is an arbitrary constant satisfying 0.70<σ<0.99) the temperature at which tan δ(σ) is calculated is T(σ) [°C], The method is characterized in that microwaves are irradiated while controlling the average heating rate [°C / min] in the temperature range of T(γ) to T(σ) [°C] to be within the range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(γ) [°C]. According to the vulcanization method of the present invention, it is possible to uniformly vulcanize the rubber composition by irradiating it with microwaves.

[0014] In the vulcanization method of the present invention, the average temperature rise rate in the temperature range of T(γ) to T(σ) (° C.) is preferably 20° C. / min or less. In this case, the vulcanization uniformity of the rubber composition can be further improved.

[0015] In the above-mentioned vulcanization method, from the viewpoint of more reliably enjoying the effect of uniform vulcanization, the content of carbon black in the rubber composition is preferably 10 parts by mass or more per 100 parts by mass of the diene rubber.

[0016] The vulcanized rubber composition of the present invention is characterized by being vulcanized by the above-mentioned vulcanization method. Effect of the Invention

[0017] According to the present invention, there is provided a vulcanization method capable of uniformly vulcanizing a rubber composition by irradiating with microwaves. Also, according to the present invention, there is provided a vulcanized rubber composition vulcanized by the above vulcanization method. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram showing a temperature-dielectric loss (ε″) curve for an example rubber composition. [Diagram 2] FIG. 2 is a schematic diagram showing a temperature-dielectric tangent (tan δ) curve for an example rubber composition. [Diagram 3] FIG. 2 is a plot diagram of measurement results of temperature vs. dielectric loss (ε″) for rubber compositions of the examples. [Figure 4] FIG. 3 is a plot diagram of measurement results of temperature vs. dielectric tangent (tan δ) for rubber compositions of the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be described in detail below with reference to the embodiments.

[0020] <Vulcanization method of the first embodiment> The vulcanization method of the first embodiment of the present invention is a vulcanization method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, In a temperature-dielectric loss curve of the rubber composition in a temperature range of 30 to 200° C. at a microwave frequency used, the value of dielectric loss (ε″) satisfies the following formula (1): ε″(α)=ε″ min +(ε″ max -ε″ min ) × α (1) (In the formula, ε″ min is the minimum value of dielectric loss, ε″ max is the maximum value of the dielectric loss, and α is an arbitrary constant satisfying 0.01<α<0.30), the temperature at which ε″(α) is calculated is defined as T(α) [°C], and the value of the dielectric loss (ε″) is calculated using the following formula (2): ε″(β)=ε″ min +(ε″ max -ε″ min ) × β (2) (where β is an arbitrary constant satisfying 0.70<β<0.99) the temperature at which ε″(β) is calculated is T(β) [°C], The method is characterized in that microwaves are irradiated while controlling the average heating rate [°C / min] in the temperature range of T(α) to T(β) [°C] to be within the range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(α) [°C].

[0021] In this specification, the term "microwave" refers to electromagnetic waves with a frequency of 300 MHz to 300 GHz. The frequency of the microwaves used is not particularly limited and can be appropriately selected depending on the purpose.

[0022] Examples of microwave generators used during microwave irradiation include a general 2.45 GHz magnetron oscillator, a fixed frequency microwave generator using a semiconductor oscillator, and a variable frequency microwave generator (VFM) using a semiconductor oscillator. If a variable frequency microwave generator is used, vulcanization of rubber-metal part composites can also be achieved.

[0023] More specifically, in the vulcanization method of the present embodiment, first, a temperature-dielectric loss curve is obtained for the rubber composition to be vulcanized in the temperature range of 30 to 200°C at the frequency of the microwave used. The measurement of the dielectric loss at each temperature can be performed, for example, using a network analyzer. In addition, in creating the curve, it is preferable to use another rubber composition having the same composition as the rubber composition to be vulcanized as the pseudo rubber composition, and it is more preferable to use another rubber composition having the same composition and shape as the rubber composition to be vulcanized.

[0024] In addition, the dielectric loss of the rubber composition at each temperature is usually measured while the rubber composition is heated. Since the degree of aggregation and / or the degree of vulcanization of carbon black may change depending on the temperature rise behavior, it is extremely difficult to uniquely determine the dielectric loss value of the rubber composition at each temperature. In light of this, when measuring the dielectric loss using a pseudo rubber composition, it is preferable to raise the temperature at a stable gradient so that the temperature does not stagnate for a long period of time or rise suddenly.

[0025] For reference, a temperature-dielectric loss curve for an example rubber composition is shown in FIG. 1. In the vulcanization method of the present embodiment, the minimum value of dielectric loss (ε″ min ) and maximum value (ε″ max ) and the dielectric loss value is "ε" min +(ε″ max -ε″ min ) × α”, that is, the temperature (T(α)) when the dielectric loss value is “ε″(α) min +(ε″ max -ε″ min )×β”, that is, the temperature (T(β)) at which ε″(β) is satisfied. Here, α is an arbitrary constant greater than 0.01 and less than 0.30, and β is an arbitrary constant greater than 0.70 and less than 0.99. Note that T(α) is a temperature greater than 30° C. and higher than the temperature at which the dielectric loss value is minimum, and T(β) is a temperature less than 200° C. and lower than the temperature at which the dielectric loss value is maximum.

[0026] In the vulcanization method of the present embodiment, when the rubber composition is actually irradiated with microwaves to be vulcanized, the average heating rate in the temperature range of T(α) to T(β) (hereinafter sometimes referred to as the "second temperature range") is controlled to be within a range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C to T(α) (hereinafter sometimes referred to as the "first temperature range"). In this way, the vulcanization method of the present embodiment is based on measuring the dielectric properties of the rubber composition to be vulcanized in advance, and irradiating the rubber composition with microwaves while appropriately monitoring the temperature of the rubber composition based on the measurement results. In the vulcanization method of the present embodiment, the average heating rate of the rubber composition in a predetermined temperature range is relatively small when irradiating the rubber composition with microwaves, so that the rubber composition can be uniformly vulcanized.

[0027] The average temperature rise rate can be calculated using the time required to reach the end temperature from the starting temperature.

[0028] The average rate of temperature rise can be controlled, for example, by finely adjusting the amount of microwave irradiation, or by switching microwave irradiation on and off.

[0029] Furthermore, when controlling the average rate of temperature rise within a specified temperature range, the rate can be controlled by focusing on the time it takes for the temperature range to reach from the starting temperature to the end temperature, or more precisely, the temperature range can be divided (e.g., divided every 10°C) and the rate can be controlled by focusing on the time it takes for each divided temperature range to reach from the starting temperature to the end temperature.

[0030] As described above, α and β are arbitrary constants, and therefore each value can be appropriately selected from a predetermined range. In a preferred example, the value of α can be selected within the range of 0.05<α<0.20, and the value of β can be selected within the range of 0.80<β<0.95. In a further example, the value of α can be selected as 0.10, and the value of β can be selected as 0.90.

[0031] As is clear from the above, in the vulcanization method of this embodiment, the ratio of the average temperature rise rate in the second temperature range (T(α)-T(β)) to the first temperature range (30°C-T(α)) needs to be within the range of 0.2-0.8. If the ratio is less than 0.2, an excessive amount of time is required for vulcanization, and production efficiency may deteriorate. If the ratio exceeds 0.8, vulcanization uniformity may deteriorate. From the same viewpoint, the ratio is preferably 0.3 or more and 0.7 or less.

[0032] In the vulcanization method of the present embodiment, the average temperature rise rate in the second temperature range (T(α) to T(β)) is preferably 20° C. / min or less, which can further improve the vulcanization uniformity of the rubber composition.

[0033] On the other hand, the average rate of temperature rise in the temperature range equal to or higher than T(β) (third temperature range) is not particularly limited, but can be, for example, approximately the same as the average rate of temperature rise in the first temperature range.

[0034] In the vulcanization method of this embodiment, the maximum temperature reached when actually vulcanizing the rubber composition (so-called vulcanization temperature) is not particularly limited and can be appropriately selected depending on the purpose, but is usually T(β) or higher, preferably 140°C or higher, and preferably 190°C or lower, and more preferably 160°C or lower.

[0035] <Vulcanization method of the second embodiment> Next, a vulcanization method according to a second embodiment of the present invention is a vulcanization method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, In a temperature-dielectric tangent curve of the rubber composition in a temperature range of 30 to 200° C. at a microwave frequency used, the value of the dielectric tangent (tan δ) satisfies the following formula (3): tan δ(γ)=tan δ min +(tan δ max -tan δ min ) × γ (3) (In the formula, tanδmin is the minimum value of the dielectric tangent, and tan δ max is the maximum value of the dielectric tangent, and γ is an arbitrary constant satisfying 0.01<γ<0.30), the temperature at which tan δ(γ) is calculated is defined as T(γ) [°C], and the value of the dielectric tangent (tan δ) is calculated using the following formula (4): tan δ(σ)=tan δ min +(tan δ max -tan δ min ) × σ (4) (wherein σ is an arbitrary constant satisfying 0.70<σ<0.99) the temperature at which tan δ(σ) is calculated is T(σ) [°C], The method is characterized in that microwaves are irradiated while controlling the average heating rate [°C / min] in the temperature range of T(γ) to T(σ) [°C] to be within the range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(γ) [°C].

[0036] The dielectric tangent (tan δ) is a value calculated by ε″ / ε' (ε″ is the dielectric loss and ε' is the dielectric constant).

[0037] More specifically, in the vulcanization method of the present embodiment, first, a temperature-dielectric loss tangent curve is obtained for the rubber composition to be vulcanized in the temperature range of 30 to 200 ° C. at the frequency of the microwave used. The measurement of the dielectric loss tangent at each temperature can be performed, for example, using a network analyzer. In addition, in creating the curve, it is preferable to use another rubber composition having the same composition as the rubber composition to be vulcanized as the pseudo rubber composition, and it is more preferable to use another rubber composition having the same composition and shape as the rubber composition to be vulcanized.

[0038] In addition, the dielectric loss tangent of the rubber composition at each temperature is usually measured while the rubber composition is heated. Since the degree of aggregation and / or the degree of vulcanization of carbon black may change depending on the temperature rise behavior, it is extremely difficult to uniquely determine the value of the dielectric loss tangent of the rubber composition at each temperature. In light of this, when measuring the dielectric loss tangent using the pseudo rubber composition, it is preferable to raise the temperature at a stable gradient so that the temperature does not stagnate for a long period of time or rise suddenly.

[0039] For reference, a temperature-dielectric dissipation factor curve for an example of a rubber composition is shown in FIG. 2. In the vulcanization method of the present embodiment, the minimum value of the dielectric dissipation factor (tanδ) in the temperature-dielectric dissipation factor curve shown in FIG. min ) and maximum value (tan δ max ) and the dielectric tangent value is calculated as "tanδ min +(tan δ max -tan δ min ) × γ", that is, the temperature (T(γ)) when tan δ(γ) is satisfied, and the value of the dielectric tangent is "tan δ min +(tan δ max -tan δ min )×σ”, i.e., the temperature (T(σ)) at which tan δ(σ) is satisfied. Here, γ is an arbitrary constant greater than 0.01 and less than 0.30, and σ is an arbitrary constant greater than 0.70 and less than 0.99. Furthermore, T(γ) is a temperature greater than 30°C and higher than the temperature at which the dielectric loss value is minimum, and T(σ) is a temperature less than 200°C and lower than the temperature at which the dielectric loss value is maximum.

[0040] In the vulcanization method of the present embodiment, when the rubber composition is actually irradiated with microwaves to be vulcanized, the average heating rate in the temperature range of T(γ) to T(σ) (hereinafter sometimes referred to as the "second temperature range") is controlled to be within a range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C to T(γ) (hereinafter sometimes referred to as the "first temperature range"). In this way, the vulcanization method of the present embodiment, like the first embodiment, is based on measuring the dielectric properties of the rubber composition to be vulcanized in advance, and irradiating the rubber composition with microwaves while appropriately monitoring the temperature of the rubber composition based on the measurement results. In the vulcanization method of the present embodiment, like the first embodiment, the average heating rate of the rubber composition in a predetermined temperature range is relatively small when irradiating the rubber composition with microwaves, so that the rubber composition can be uniformly vulcanized.

[0041] As described above, since γ and σ are arbitrary constants, their respective values ​​can be appropriately selected from within a predetermined range. In a preferred example, however, the value of γ can be selected within the range of 0.05<γ<0.20, and the value of σ can be selected within the range of 0.80<σ<0.95. In a further example, the value of γ can be selected as 0.10, and the value of σ can be selected as 0.90.

[0042] As is clear from the above, in the vulcanization method of this embodiment, the ratio of the average temperature rise rate in the second temperature range (T(γ) to T(σ)) to the first temperature range (30° C. to T(γ)) needs to be within the range of 0.2 to 0.8. If the ratio is less than 0.2, an excessive amount of time is required for vulcanization, and production efficiency may deteriorate. If the ratio exceeds 0.8, vulcanization uniformity may deteriorate. From the same viewpoint, the ratio is preferably 0.3 or more and 0.7 or less.

[0043] In the vulcanization method of the present embodiment, the average temperature rise rate in the second temperature range (T(γ) to T(σ)) is preferably 20° C. / min or less, which can further improve the vulcanization uniformity of the rubber composition.

[0044] On the other hand, the average rate of temperature rise in the temperature range equal to or higher than T(σ) (third temperature range) is not particularly limited, but can be, for example, approximately the same as the average rate of temperature rise in the first temperature range.

[0045] In the vulcanization method of this embodiment, the maximum temperature reached when actually vulcanizing the rubber composition (so-called vulcanization temperature) is not particularly limited and can be appropriately selected depending on the purpose, but is usually T(σ) or more, preferably 140°C or more, and preferably 190°C or less, and more preferably 160°C or less.

[0046] (Rubber composition to be vulcanized) Hereinafter, the rubber composition (the rubber composition to be vulcanized) used in the present invention will be described in common to the above-mentioned vulcanization methods. The rubber composition to be vulcanized contains at least a diene rubber and carbon black. In addition, the rubber composition to be vulcanized may further contain a vulcanizing agent and other components as necessary.

[0047] Examples of diene rubbers include natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, and acrylonitrile-butadiene rubber (NBR). These diene rubbers may be used alone or in combination of two or more. Among these, from the viewpoint of more reliably enjoying the effect of uniform vulcanization by the vulcanization method of the present invention, it is preferable to use at least one of natural rubber, butadiene rubber, isoprene rubber, and styrene-butadiene rubber as the diene rubber.

[0048] Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more. Among these, it is preferable to use HAF, ISAF, or SAF grade carbon black.

[0049] The content of carbon black in the rubber composition is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of more reliably enjoying the effect of uniform vulcanization by the vulcanization method of the present invention, it is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, per 100 parts by mass of diene rubber. In addition, from the viewpoint of maintaining the controllability of the average temperature rise rate in the vulcanization method of the present embodiment and from the viewpoint of maintaining the mechanical properties of the obtained vulcanized rubber composition, the content of carbon black in the rubber composition is preferably 120 parts by mass or less, more preferably 70 parts by mass or less, per 100 parts by mass of diene rubber.

[0050] The rubber composition preferably contains a vulcanizing agent. Examples of the vulcanizing agent include sulfur-based vulcanizing agents such as sulfur and morpholine disulfide; organic peroxides such as benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; and the like. Examples of the vulcanizing agent include hexamethylene bisthiosulfate disodium salt dihydrate, 1,3-bis(citraconimidomethyl)benzene, 4,4'-diphenylmethane bismaleimide, and m-phenylene bismaleimide. These vulcanizing agents may be used alone or in combination of two or more. Among these, it is more preferable to use a sulfur-based vulcanizing agent from the viewpoint of more reliably enjoying the effect of uniform vulcanization by the vulcanization method of the present invention.

[0051] The content of the vulcanizing agent in the rubber composition is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the diene rubber.

[0052] Other components include fillers other than carbon black (such as silica), vulcanization aids such as stearic acid, vulcanization accelerators, vulcanization acceleration aids such as zinc oxide, antioxidants, softeners, plasticizers, processability improvers, and the like, and these can be contained in appropriate amounts.

[0053] The rubber composition to be vulcanized can be obtained by blending and kneading the above-mentioned components in a conventional manner using a kneading machine such as a roll, an internal mixer, or a Banbury rotor.

[0054] The shape of the rubber composition to be vulcanized is not particularly limited. For example, the rubber composition to be vulcanized can be a pre-molded product obtained by molding in advance, and even if the pre-molded product has a complex shape that has been prone to uneven heating in the past, it can be vulcanized uniformly, and thus a desired vulcanized molded product can be obtained.

[0055] <Vulcanized rubber composition> The vulcanized rubber composition according to one embodiment of the present invention is characterized in that it is vulcanized by the above-mentioned vulcanization method. By vulcanizing the vulcanized rubber composition by the above-mentioned vulcanization method, the vulcanization is uniformed, and the vulcanized rubber composition can have high strength. EXAMPLES

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0057] <Preparation of Rubber Composition> The ingredients according to the compounding recipe shown in Table 1 were kneaded in a conventional manner to prepare a rubber composition.

[0058] [Table 1]

[0059] *1 Isoprene rubber: JSR Corporation, IR2200 *2 Carbon black: Tokai Carbon Co., Ltd., Seast 7HM, ISAF grade *3 Anti-aging agent: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *4 Other chemicals: Quintone 1105, manufactured by Zeon Corporation *5 Vulcanization accelerator: N-cyclohexyl-2-benzothiazolyl sulfenamide (Noccela CZ), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0060] <Measurement of dielectric loss (ε″) and dielectric tangent (tan δ)> The dielectric loss (ε″) and dielectric tangent (tan δ) of the above rubber composition were measured by the coaxial cable method using a vector network (Agilent Technologies, Inc., “E5071C”) at an applied frequency of 2.45 GHz in the temperature range of 30 to 160°C. The measurement was performed while raising the temperature of the rubber composition. First, measurements were performed multiple times under the above conditions, and then, based on the measurement results, plots were created showing the correlation between the dielectric loss (ε″) and temperature, and the dielectric tangent (tan δ) and temperature. The plots of these measurement results are shown in Figures 3 and 4, respectively. The dielectric loss (ε″) and dielectric tangent (tan δ) corresponding to temperature based on the above plots are shown in Table 2 below. It is assumed that in the temperature range of 160 to 200° C., the dielectric loss (ε″) and dielectric tangent (tan δ) do not reach their maximum values.

[0061] [Table 2]

[0062] According to the vulcanization method of the first embodiment, a temperature-dielectric loss (ε″) curve was created from the above measurement results. min(minimum dielectric loss) is the value at 30℃, and ε″ max The maximum dielectric loss was measured at 160°C. Furthermore, when 0.01 was selected as the value of α in formula (1), ε″(α), i.e., ε″(0.01), was 2.00, and T(α), i.e., T(0.01) was 40°C. Similarly, when 0.30 was selected as the value of α in formula (1), ε″(α), i.e., ε″(0.30) was 7.92, and T(α), i.e., T(0.30) was 114°C. Furthermore, when 0.70 was selected as the value of β in formula (2), ε″(β), i.e., ε″(0.70), was 16.08, and T(β), i.e., T(0.70), was 134°C. Similarly, when 0.99 was selected as the value of β in formula (2), ε″(β), i.e., ε″(0.99), was 22.00, and T(β), i.e., T(0.99), was 158°C.

[0063] Therefore, when this rubber composition is irradiated with microwaves to vulcanize it, uniform vulcanization is possible by irradiating microwaves while controlling the average heating rate in the temperature range of more than 40°C or more than 114°C and less than 134°C or less than 158°C to within a range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C or more and 40°C or less or 114°C or less.

[0064] In short, when this rubber composition is irradiated with microwaves to vulcanize it, any temperature within the range of 40°C to 114°C is selected as T(α) and any temperature within the range of 134°C to 158°C is selected as T(β), and microwaves are irradiated while controlling the average heating rate in the temperature range of T(α) to T(β) to be within the range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C to T(α), thereby enabling uniform vulcanization.

[0065] Similarly, when a temperature-dielectric tangent (tan δ) curve was created from the above measurement results according to the vulcanization method of the second embodiment, tan δ min (Minimum value of dielectric tangent) is the value at 30℃, and tanδ maxThe maximum dielectric tangent was the value at 160°C. Furthermore, when 0.01 was selected as the value of γ in formula (3), tan δ(γ), i.e., tan δ(0.01), was 0.159, and T(γ), i.e., T(0.01) was 35° C. Similarly, when 0.30 was selected as the value of γ in formula (3), tan δ(γ), i.e., tan δ(0.30) was 0.528, and T(γ), i.e., T(0.30) was 113° C. Furthermore, when 0.70 was selected as the value of σ in formula (4), tan δ(σ), i.e., tan δ(0.70), was 1.038, and T(σ), i.e., T(0.70), was 135° C. Similarly, when 0.99 was selected as the value of σ in formula (4), tan δ(σ), i.e., tan δ(0.99), was 1.407, and T(σ), i.e., T(0.99), was 158° C.

[0066] Therefore, when this rubber composition is irradiated with microwaves to vulcanize it, uniform vulcanization is possible by irradiating microwaves while controlling the average heating rate in the temperature range of more than 35°C or more than 113°C and less than 135°C or less than 158°C to within a range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C or more and 35°C or less or 113°C or less.

[0067] In short, when this rubber composition is irradiated with microwaves to vulcanize it, any temperature within the range of 35°C to 113°C is selected as T(γ) and any temperature within the range of 135°C to 158°C is selected as T(σ), and microwaves are irradiated while controlling the average heating rate in the temperature range of T(γ) to T(σ) to be within the range of 0.2 to 0.8 times the average heating rate in the temperature range of 30°C to T(γ), thereby enabling uniform vulcanization.

[0068] <Vulcanization of rubber composition> The rubber composition was cut into a sheet sample measuring 80 mm × 80 mm × 2 mm thick, and vacuum dried at room temperature for 24 hours. The sheet sample was then sandwiched between Teflon (registered trademark) molds, pressurized at a pressure of 0.4 MPa, and heated (vulcanized) by microwave irradiation under the heating conditions shown in Table 3.

[0069] The hardness of the vulcanized sheet sample was measured at 49 points at 1 cm intervals using a Digital Hardness Tester RH 101a manufactured by Kobunshi Keiki Co., Ltd. The percentage of all measurement points (49 points) with a hardness of 60 or more was calculated. The results are shown in Table 3 as "vulcanization uniformity." A higher percentage indicates higher vulcanization uniformity. The "hardness of 60 or more" is based on the result that a sheet sample with a hardness of 60 or more did not elute into toluene due to crosslinking in a toluene immersion test.

[0070] In addition, the difference between the maximum and minimum values ​​among all the measurement points (49 points) was calculated. The results are shown in Table 3 as "vulcanization variation."

[0071] [Table 3]

[0072] From Table 3, it can be seen that in the examples, microwave irradiation was performed while controlling the temperature rise conditions, so that the vulcanizate obtained had high vulcanization uniformity and small vulcanization variation. [Industrial Applicability]

[0073] According to the present invention, there is provided a vulcanization method capable of uniformly vulcanizing a rubber composition by irradiating with microwaves. Also, according to the present invention, there is provided a vulcanized rubber composition vulcanized by the above vulcanization method.

Claims

1. A vulcanization method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, comprising the steps of: In a temperature-dielectric loss curve of the rubber composition in a temperature range of 30 to 200° C. at a microwave frequency used, the value of dielectric loss (ε″) satisfies the following formula (1): e″(a)=e″ ｍｉｎ +(e″ ｍａｘ -e″ ｍｉｎ )×a ・・・(1) (In the formula, ε″ ｍｉｎ is the minimum value of dielectric loss, ε″ ｍａｘ is the maximum value of the dielectric loss, and α is an arbitrary constant satisfying 0.01<α<0.30), the temperature at which ε″(α) is calculated is defined as T(α) [° C.], and the value of the dielectric loss (ε″) is expressed by the following formula (2): e″(b)=e″ ｍｉｎ +(e″ ｍａｘ -e″ ｍｉｎ )×β・・・(2) (where β is an arbitrary constant satisfying 0.70<β<0.99) the temperature at which ε″(β) is calculated is T(β) [° C.], A vulcanization method comprising irradiating microwaves while controlling an average heating rate [°C / min] in the temperature range of T(α) to T(β) [°C] to be within a range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(α) [°C].

2. The vulcanization method according to claim 1, wherein the average temperature rise rate in the temperature range of T(α) to T(β) [°C] is 20°C / min or less.

3. A vulcanization method for vulcanizing a rubber composition containing a diene rubber and carbon black by irradiating the rubber composition with microwaves, comprising the steps of: In the temperature-dielectric tangent curve of the rubber composition in the temperature range of 30 to 200° C. at the frequency of the microwave used, the value of the dielectric tangent (tan δ) is expressed by the following formula (3): tan (c) = tan ｍｉｎ + (tand) ｍａｘ -tand ｍｉｎ )×γ・・・(3) (In the formula, tanδ ｍｉｎ is the minimum value of the dielectric tangent, and tan δ ｍａｘ is the maximum value of the dielectric tangent, and γ is an arbitrary constant satisfying 0.01<γ<0.30), the temperature at which tan δ(γ) is calculated is defined as T(γ) [°C], and the value of the dielectric tangent (tan δ) is expressed by the following formula (4): tan (s) = tan ｍｉｎ + (tand) ｍａｘ -tand ｍｉｎ )×σ・・・(4) (wherein σ is an arbitrary constant satisfying 0.70<σ<0.99) is used, the temperature at which tan δ(σ) is calculated is defined as T(σ) [°C], A vulcanization method comprising irradiating microwaves while controlling an average heating rate [°C / min] in the temperature range of T(γ) to T(σ) [°C] to be within a range of 0.2 to 0.8 times the average heating rate [°C / min] in the temperature range of 30 to T(γ) [°C].

4. The vulcanization method according to claim 3, wherein the average heating rate in the temperature range of T(γ) to T(σ) (°C) is 20°C / min or less.

5. The vulcanization method according to any one of claims 1 to 4, wherein the content of carbon black in the rubber composition is 10 parts by mass or more based on 100 parts by mass of the diene rubber.

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