Method for vulcanizing rubber laminates for tires, and method for manufacturing retreaded tires

Abstract

To provide a method for vulcanizing a rubber laminate for a tire capable of uniformly vulcanizing a rubber laminate for a tire in which an unvulcanized rubber layer and a vulcanized rubber layer are laminated by microwave irradiation.SOLUTION: There is provided a method for vulcanizing a rubber laminate for a tire which vulcanizes a rubber laminate for a tire in which an unvulcanized rubber layer and a vulcanized rubber layer are laminated by irradiating microwaves, wherein the unvulcanized rubber layer contains a diene-based rubber and carbon black, the vulcanized rubber layer contains a diene-based rubber and carbon black and the method comprises a step of changing the frequency of the microwaves irradiating the rubber laminate for a tire during vulcanization within a predetermined frequency range by a frequency change range selected from a range from more than 0 Hz and 1000 Hz or less at each passage of a time interval selected from a range from more than 0 μsec and 100 μsec or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for vulcanizing rubber laminates for tires and a method for manufacturing retreaded tires. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-66924 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in reality, Patent Document 1 terminates the heating by microwave energy before the start of the vulcanization reaction. In this regard, conventionally, when a vulcanization reaction is carried out by irradiating with microwaves, it is extremely difficult to control the vulcanization reaction, and problems such as uneven vulcanization and localized charring have occurred. Due to problems such as uneven vulcanization, microwave-based rubber vulcanization has not yet been fully put into practical use, and the use of microwaves has been limited to, at best, preheating before vulcanization.

[0005] Furthermore, in the manufacture of retreaded tires, there is a method (precure method) in which a pre-cured tread (vulcanized rubber layer) with a tread pattern already formed is attached to a base tire (the base portion of a tire whose primary lifespan has ended) via a cushion rubber (unvulcanized rubber layer), and the cushion rubber is then vulcanized and bonded. In this method, there is a need for technology to efficiently and uniformly vulcanize the cushion rubber to be vulcanized using microwaves.

[0006] Therefore, the present invention aims to provide a method for vulcanizing a tire rubber laminate, which has an unvulcanized rubber layer and a vulcanized rubber layer laminated together, and which enables uniform vulcanization of the tire rubber laminate by microwave irradiation. Furthermore, the present invention aims to provide a method for manufacturing a retreaded tire that can produce a uniformly vulcanized retreaded tire. [Means for solving the problem]

[0007] The inventors focused on the fact that carbon black can be a heating element with excellent microwave absorption properties and conducted extensive research. They discovered that when heating (vulcanizing) a rubber composition containing carbon black by microwave irradiation, uniform vulcanization can be achieved by sweeping the microwave frequency in a predetermined manner. Furthermore, based on this finding, they discovered that when vulcanizing a laminate comprising an unvulcanized rubber layer and a vulcanized rubber layer, efficient and uniform vulcanization can be achieved by shaping the laminate in a predetermined manner, leading to the present invention.

[0008] In other words, the gist of the present invention for achieving the above objective is as follows.

[0009] [1] A method for vulcanizing a tire rubber laminate, wherein the tire rubber laminate, which has an unvulcanized rubber layer and a vulcanized rubber layer laminated together, is vulcanized by irradiating it with microwaves, The aforementioned unvulcanized rubber layer contains diene rubber and carbon black. The vulcanized rubber layer contains diene rubber and carbon black, The penetration depth D of microwaves with wavelength λ (mm) into the vulcanized rubber constituting the vulcanized rubber layer , ,

[0012] , , ,

[0011] (mm) is defined by the following formula: [Number] [In the formula, λ represents the wavelength of the microwave (mm), and ε λ ’ represents the relative permittivity of the vulcanized rubber at the wavelength λ, and ε λ ” represents the relative dielectric loss of the vulcanized rubber at the wavelength λ.], when defined by this formula, the penetration depth D λ select the frequency range of the microwave so as to include the frequency corresponding to the wavelength λ at which D is greater than or equal to the value of the thickness of the vulcanized rubber layer, and during vulcanization, the frequency of the microwave irradiated on the rubber laminate for the tire is selected within the frequency range, at every elapse of a time interval selected from a range of more than 0 μsec and less than or equal to 100 μsec, and the frequency is changed by a frequency change width selected from a range of more than 0 Hz and less than or equal to 1000 Hz. A method for vulcanizing a rubber laminate for a tire, characterized by including this step. According to such a method for vulcanizing a rubber laminate for a tire, it is possible to uniformly vulcanize a rubber laminate for a tire in which an unvulcanized rubber layer and a vulcanized rubber layer are laminated by irradiation with microwaves.

[0010] [2] The method for vulcanizing a rubber laminate for a tire according to [1], wherein the frequency range of the microwave is in a band of 30 GHz or less. In this case, since the carbon black contained in the vulcanized rubber is difficult to absorb microwaves (easy to transmit), the influence on the irradiation of microwaves on the vulcanized rubber becomes smaller.

[0011] [3] The method for vulcanizing a rubber laminate for a tire according to [1], wherein the frequency range of the microwave is in a band of 3 GHz or less. In this case, since the carbon black contained in the vulcanized rubber is difficult to absorb microwaves (easy to transmit), the influence on the irradiation of microwaves on the vulcanized rubber becomes smaller.

[0012] [4] The vulcanization method of the rubber laminate for tires according to any one of [1] to [3], wherein the carbon black content in the vulcanized rubber layer is 15 parts by mass or more with respect to 100 parts by mass of the diene rubber. In this case, durability and the like of the tire rubber can be enhanced.

[0013] [5] The vulcanization method of the rubber laminate for tires according to any one of [1] to [4], wherein the carbon black content in the vulcanized rubber layer is 60 parts by mass or less with respect to 100 parts by mass of the diene rubber. In this case, microwaves can penetrate through the vulcanized rubber layer having a certain thickness without being absorbed and reach deep into the layer in a wide band.

[0014] [6] The carbon black in the unvulcanized rubber layer contains carbon black A having a nitrogen adsorption specific surface area of 50 m 2 / g or more and 130 m 2 / g or less, and is the vulcanization method of the rubber laminate for tires according to any one of [1] to [5]. In this case, the vulcanization can be more effectively made uniform.

[0015] [7] The vulcanization method of the rubber laminate for tires according to any one of [1] to [6], wherein the carbon black content in the unvulcanized rubber layer is 20 parts by mass or more with respect to 100 parts by mass of the diene rubber. In this case, the effect of uniform vulcanization can be more surely enjoyed.

[0016] [8] The vulcanization method of the rubber laminate for tires according to any one of [1] to [7], wherein the time interval is constant each time. In this case, the vulcanization can be more effectively made uniform.

[0017] [9] The vulcanization method of the rubber laminate for tires according to any one of [1] to [8], wherein the frequency change width is constant each time. In this case, the vulcanization can be more effectively made uniform.

[0018]

[10] A method for manufacturing a retreaded tire, comprising the steps of attaching a pre-cured tread, which is a vulcanized rubber layer, to a base tire via a cushion rubber, which is an unvulcanized rubber layer, and vulcanizing and bonding the cushion rubber, A method for manufacturing a retreaded tire, characterized in that the above step uses a method for vulcanizing a rubber laminate for tires described in any of [1] to [9]. According to this method of manufacturing retread tires, it is possible to obtain uniformly vulcanized retread tires. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a method for vulcanizing a tire rubber laminate, in which an unvulcanized rubber layer and a vulcanized rubber layer are laminated, and to uniformly vulcanize the tire rubber laminate by microwave irradiation. Furthermore, according to the present invention, it is possible to provide a method for manufacturing retreaded tires that can obtain uniformly vulcanized retreaded tires. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram illustrating an example of a sweep pattern of microwave frequencies irradiated onto a rubber laminate for tires, according to the present invention. [Modes for carrying out the invention]

[0021] The present invention will be described in detail below based on its embodiments.

[0022] (Vulcanization method for rubber laminates used in tires) The vulcanization method of the rubber laminate for tires according to an embodiment of the present invention (hereinafter sometimes referred to as "the vulcanization method of the present embodiment") is a method of vulcanizing a rubber laminate for tires by irradiating microwaves. The rubber laminate for tires used in the vulcanization method of the present embodiment is formed by laminating an unvulcanized rubber layer and a vulcanized rubber layer. The unvulcanized rubber layer contains a diene rubber and carbon black, and the vulcanized rubber layer contains a diene rubber and carbon black. In the vulcanization method of the present embodiment, first, the penetration depth D λ (mm) of microwaves with a wavelength λ (mm) into the vulcanized rubber constituting the vulcanized rubber layer is calculated by the following formula: [Equation] [where λ represents the wavelength (mm) of the microwaves, ε λ ’ represents the relative permittivity of the vulcanized rubber at the wavelength λ of the microwaves, and ε λ ” represents the relative dielectric loss of the vulcanized rubber at the wavelength λ of the microwaves.]. When defined by this formula, the frequency range of the microwaves is selected so as to include the frequency corresponding to the wavelength λ at which the penetration depth D λ is equal to or greater than the value of the thickness of the vulcanized rubber layer. During vulcanization, the frequency of the microwaves irradiated onto the rubber laminate for tires is changed by a frequency change width selected from the range of more than 0 Hz and less than or equal to 1000 Hz at every elapse of a time interval selected from the range of more than 0 μsec and less than or equal to 100 μsec within the frequency range selected as described above. This is a characteristic of the present invention. The vulcanization method of the present embodiment is based on the technical idea of selectively and uniformly vulcanizing the unvulcanized rubber layer of the above-mentioned rubber laminate for tires while maintaining the quality of other members (such as the vulcanized rubber layer).

[0023] In this specification, "microwaves" shall refer to electromagnetic waves with a frequency of 300 MHz to 300 GHz. Also, in this specification, the "unvulcanized rubber layer" shall refer to a layered member made from a rubber composition and not subjected to vulcanization treatment, and the "vulcanized rubber layer" shall refer to a layered member made from a rubber composition and already subjected to vulcanization treatment.

[0024] Figure 1 is a schematic diagram showing an example of a sweep pattern of the microwave frequency irradiated onto a rubber laminate for tires, according to the vulcanization method of this embodiment. In the sweep pattern shown in Figure 1, the frequency of the microwave irradiated onto the rubber laminate for tires is increased by a constant frequency change (F) at regular intervals (T).

[0025] The inventors believe that the mechanism by which the vulcanization method of this embodiment enables the uniform vulcanization of rubber laminates for tires, particularly the unvulcanized rubber layer, is as follows. Normally, when a rubber composition containing carbon black is irradiated with microwaves, interference occurs between the microwaves directly irradiated onto the rubber composition and the microwaves that are reflected at least once within the microwave generator before being irradiated onto the rubber composition. In this regard, for example, if the microwave frequency is constant, areas in the rubber composition where interference is likely to occur and areas where it is not will be fixedly unevenly distributed, which may result in some parts being overheated and others underheated. This situation is particularly pronounced at temperatures above 120°C where the crosslinking reaction occurs, and is thought to result in non-uniform vulcanization. In contrast, in the vulcanization method of this embodiment, the frequency of the irradiated microwaves is swept in a predetermined manner, so that localized concentration of energy absorption in the rubber composition can be effectively avoided, and as a result, uniform heating (vulcanization) can be achieved.

[0026] Therefore, in the vulcanization method of this embodiment, it is not essential to move or rotate the object to be heated within the device (as in a turntable-type microwave oven) in order to avoid uneven heating.

[0027] On the other hand, microwaves gradually attenuate as they are absorbed by dielectrics and converted into thermal energy. Therefore, the distance they can penetrate (penetration depth) into the target dielectric (such as vulcanized rubber) is limited. Specifically, the penetration depth D of microwaves with wavelength λ (mm) into the vulcanized rubber constituting the vulcanized rubber layer is... λ (mm) is calculated using the following formula:

number

[0028] Furthermore, the penetration depth can be adjusted, for example, by adjusting the frequency range of the selected microwaves or by adjusting the compound (composition) of the vulcanized rubber to control the dielectric constant (ε). λ ') and relative dielectric loss (ε λ This can be done by changing the value of "". For example, regarding a blend consisting of 60 parts by mass of natural rubber, 40 parts by mass of butadiene rubber, and 50 parts by mass of HAF-grade carbon black, the penetration depth D at 5.8 GHz (approximately 52 mm wavelength) 52 This is the penetration depth D at 3.1 mm, 2.45 GHz (approximately wavelength 122 mm). 122 This is the penetration depth D at 4.9 mm, 900 MHz (approximately wavelength 333 mm). 333 The result is 22.1 mm. On the other hand, for example, with a composition of 100 parts by mass of styrene-butadiene rubber and 40 parts by mass of ISAF-grade carbon black, the penetration depth D at 5.8 GHz (≒wavelength 52 mm) is... 52 This is the penetration depth D at 6.3 mm, 2.45 GHz (approximately wavelength 122 mm). 122 This is the penetration depth D at 13.2 mm, 900 MHz (approximately wavelength 333 mm). 333 This will be 28.8mm.

[0029] In the vulcanization method of this embodiment, a variable frequency microwave generator (VFM), particularly a variable frequency microwave generator using a semiconductor oscillator or amplifier, can be used.

[0030] In the vulcanization method of this embodiment, the time interval (T) is the time between timings in which the frequency is changed, or in other words, the time for which microwaves of a constant frequency are irradiated. The time interval (T) is selected from a range of greater than 0 μsec and less than or equal to 100 μsec. If the time interval (T) exceeds 100 μsec, there is a risk that the concentration of heat on some parts of the rubber composition cannot be sufficiently suppressed. Furthermore, the lower limit of the time interval (T) is greater than 0 μsec and can be adjusted as appropriate depending on the specifications of the equipment used. In particular, from the viewpoint of microwave irradiation efficiency, a time interval (T) of 1 μsec or more is preferable. From a similar viewpoint, the time interval (T) is preferably selected from a range of 3 to 50 μsec, more preferably from a range of 5 to 30 μsec, and even more preferably from a range of 10 to 25 μsec.

[0031] In light of the mechanism described above, the time interval (T) may be constant each time, as shown in Figure 1, or it may vary each time. However, in the vulcanization method of this embodiment, it is preferable that the time interval (T) is constant each time from the viewpoint of more effectively achieving uniform vulcanization.

[0032] Furthermore, the frequency variation range (F) is selected from a range of over 0 Hz and up to 1000 Hz. If the frequency does not change at all (the frequency variation range (F) is 0 Hz), heat will concentrate on certain parts of the rubber composition. Also, if the frequency variation range (F) exceeds 1000 Hz, the stability of microwave irradiation will deteriorate, which may adversely affect uniform vulcanization. From a similar viewpoint, the frequency variation range (F) is preferably selected from a range of 10 to 500 Hz, more preferably from a range of 50 to 350 Hz, and even more preferably from a range of 100 to 260 Hz.

[0033] In view of the mechanism described above, the frequency variation range (F) may be constant each time, as shown in Figure 1, or it may vary each time. However, in the vulcanization method of this embodiment, it is preferable that the frequency variation range (F) is constant each time from the viewpoint of more effectively achieving uniform vulcanization.

[0034] Furthermore, in view of the mechanism described above, the way in which the frequency is changed by the frequency change range (F) may be an increase each time, or a decrease each time, or the increase or decrease may differ each time, as shown in Figure 1. However, in the vulcanization method of this embodiment, it is preferable to increase the frequency by the frequency change range (F) each time.

[0035] Note that variable frequency microwave generators typically have upper and lower limits on the variable frequency specified in their specifications. Therefore, when using such a variable frequency microwave generator and repeatedly increasing the frequency, the frequency may reach or approach the upper limit of the variable frequency. In this case, you should first switch the frequency to or near the lower limit of the variable frequency, and then resume increasing the frequency each time. The same procedure should be followed when repeatedly decreasing the frequency.

[0036] In the vulcanization method of this embodiment, the selected microwave frequency range (usable frequency band) is a predetermined frequency (i.e., penetration depth D λThe frequency range is not particularly limited as long as it includes a frequency corresponding to a wavelength λ that is greater than or equal to the thickness of the vulcanized rubber layer. For example, it can be appropriately selected based on the specifications of the microwave generator used (especially the type of oscillator or amplifier). In vulcanized rubber of various formulations, microwave absorption depends on the wavelength of the microwave, so it is preferable to select an appropriate frequency range. In particular, the microwave frequency range selected in the vulcanization method of this embodiment is preferably in the band of 30 GHz or less, and more preferably in the band of 3 GHz or less. In this case, the carbon black contained in the vulcanized rubber becomes less likely to absorb microwaves (more likely to transmit them), so the effect of microwave irradiation on the vulcanized rubber becomes smaller. Also, since microwave absorption depends on the temperature of the rubber, by changing the frequency to the optimal frequency midway through while irradiating with microwaves, the contained carbon black becomes less likely to absorb microwaves (more likely to transmit them), so the effect of microwave irradiation on the vulcanized rubber becomes smaller.

[0037] In the vulcanization method of this embodiment, although not particularly limited, the duration of the operation of irradiating with microwaves while sweeping the frequency in a predetermined manner is preferably 100 seconds or more, more preferably 200 seconds or more, and even more preferably 300 seconds or more. In this case, the degree of vulcanization of the rubber composition can be increased more sufficiently.

[0038] In the vulcanization method of this embodiment, although not particularly limited, the temperature of the tire rubber laminate, especially the unvulcanized rubber layer, may be monitored when irradiating with microwaves while sweeping the frequency in a predetermined manner. By monitoring the temperature of the tire rubber laminate, especially the unvulcanized rubber layer, more reliable and uniform vulcanization can be achieved. Furthermore, in the vulcanization method of this embodiment, the heating rate of the tire rubber laminate, especially the unvulcanized rubber layer, may be controlled when irradiating with microwaves. In this case, the heating rate can be controlled, for example, by fine-tuning the microwave irradiation output (W). The heating rate control method is not particularly limited, but can be PID control. Alternatively, the heating rate can be controlled by switching the microwave irradiation on and off. The heating rate can be selected, for example, from a range of 0.05°C / second to 0.5°C / second.

[0039] In the vulcanization method of this embodiment, the maximum temperature reached when actually vulcanizing the rubber laminate for tires (the so-called vulcanization temperature) is not particularly limited and can be appropriately selected depending on the purpose, but it is generally preferable to set it to 140°C or higher, preferably 190°C or lower, and more preferably 160°C or lower.

[0040] The vulcanization method of this embodiment may be carried out with the rubber laminate for the tire to be vulcanized placed on any member (for example, a base tire).

[0041] <Rubber laminates for tires to be vulcanized> The rubber laminate for tires to be vulcanized, used in the vulcanization method of this embodiment, comprises at least an unvulcanized rubber layer and a vulcanized rubber layer. The unvulcanized rubber layer may be a single layer or two or more layers. Similarly, the vulcanized rubber layer may be a single layer or two or more layers. Furthermore, the rubber laminate for the tire to be vulcanized may include other layered members (e.g., a base tire) in addition to the unvulcanized rubber layer and the vulcanized rubber layer. In this case, the unvulcanized rubber layer can be positioned to be in contact with or closer to the other members. The other members may also include metal parts (e.g., steel cords). Furthermore, it is preferable that the rubber laminate for the tire to be vulcanized has an unvulcanized rubber layer and a vulcanized rubber layer in contact with each other.

[0042] -Unvulcanized rubber layer- The unvulcanized rubber layer, which is part of the rubber laminate for tires, contains at least diene-based rubber and carbon black. Furthermore, the unvulcanized rubber layer may optionally contain vulcanizing agents, other components, etc.

[0043] 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 individually 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.

[0044] Examples of carbon black contained in the unvulcanized rubber layer include GPF, FEF, HAF, ISAF, and SAF grades. These carbon blacks may be used individually or in combination of two or more types. Furthermore, the carbon black in the unvulcanized rubber layer has a nitrogen adsorption specific surface area of ​​50 m². 2 / g or more 130m 2It is preferable to include carbon black A with a nitrogen adsorption specific surface area of ​​70 m² or less. In this case, the uniformity of vulcanization can be achieved more effectively. Examples of carbon black A include HAF, ISAF, and SAF grades of carbon black. These carbon black A may be used individually or in combination of two or more types. Furthermore, from the viewpoint of achieving uniform vulcanization more effectively, the carbon black A has a nitrogen adsorption specific surface area of ​​70 m². 2 / g or more 120m 2 It is preferable that the nitrogen adsorption specific surface area is less than or equal to / g. Examples of carbon black A having such nitrogen adsorption specific surface area include HAF and ISAF grade carbon blacks. The specific surface area for nitrogen adsorption of carbon black shall be measured in accordance with JIS K 6217-2.

[0045] The carbon black content in the unvulcanized rubber layer is not particularly limited and can be appropriately selected depending on the purpose. However, from the viewpoint of more reliably enjoying the effect of uniform vulcanization by the vulcanization method of this embodiment, it is preferable that the carbon black content be 20 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of diene rubber. Furthermore, from the viewpoint of maintaining the mechanical properties desired for the tire, the carbon black content in the unvulcanized rubber layer is preferably 120 parts by mass or less, and more preferably 70 parts by mass or less, per 100 parts by mass of diene rubber.

[0046] The unvulcanized rubber layer preferably contains a vulcanizing agent. Examples of vulcanizing agents 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 others. Other examples of vulcanizing agents 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 individually or in combination of two or more.

[0047] The content of the vulcanizing agent in the unvulcanized rubber layer 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 diene rubber.

[0048] Other components include fillers other than carbon black (such as silica), vulcanization aids such as stearic acid, vulcanization accelerators, vulcanization accelerators such as zinc oxide, antioxidants, softeners, plasticizers, and processability improvers, and these can be included in appropriate amounts.

[0049] The rubber composition constituting the unvulcanized rubber layer can be obtained, for example, by mixing the above-mentioned components in accordance with conventional methods using a kneader such as a roll, internal mixer, or Banbury rotor.

[0050] The thickness of the unvulcanized rubber layer is not particularly limited and can be, for example, 0.5 mm to 4 mm.

[0051] Furthermore, metal parts (for example, steel cords) may be included in the unvulcanized rubber layer. In the vulcanization method of this embodiment, as described above, the sweeping pattern of the irradiated microwave frequency is optimized, so it is expected that problems such as arcing in metal parts will be suppressed.

[0052] -Vulcanized rubber layer- The vulcanized rubber layer, which is part of the rubber laminate for tires, is a layer that has already undergone vulcanization treatment and contains at least diene rubber and carbon black. The vulcanization treatment described above is not particularly limited. Furthermore, the vulcanized rubber layer may contain vulcanizing agents, other components, etc., as needed.

[0053] Specific examples and preferred embodiments of diene rubber, carbon black, vulcanizing agent, and other components are the same as those contained in the unvulcanized rubber layer.

[0054] The carbon black content in the vulcanized rubber layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of improving durability as tire rubber, it is preferable to have 15 parts by mass or more per 100 parts by mass of diene rubber. Furthermore, it is preferable that the carbon black content in the vulcanized rubber layer be 60 parts by mass or less per 100 parts by mass of diene rubber. In this case, microwaves can penetrate even vulcanized rubber layers of a certain thickness without being absorbed over a wide bandwidth and reach deep into the layer. Moreover, adverse effects such as heat generation in the vulcanized rubber layer during the vulcanization of the tire rubber laminate can be reduced.

[0055] The thickness of the vulcanized rubber layer is not particularly limited and can be, for example, 10 mm to 50 mm. Furthermore, the vulcanized rubber layer may have a textured surface (e.g., a tread pattern) formed on one of its surfaces.

[0056] Furthermore, metal parts (for example, steel cords) may be included in the vulcanized rubber layer. In the vulcanization method of this embodiment, as described above, the sweeping pattern of the irradiated microwave frequency is optimized, so it is expected that problems such as arcing in metal parts will be suppressed.

[0057] (How to manufacture retreaded tires) A method for manufacturing a retreaded tire according to one embodiment of the present invention (hereinafter sometimes referred to as "the manufacturing method of this embodiment") is a method for manufacturing a retreaded tire that includes the step of attaching a pre-cure tread, which is a vulcanized rubber layer, to a base tire via a cushion rubber, which is an unvulcanized rubber layer, and then vulcanizing and bonding the cushion rubber, characterized in that the vulcanization method for tire rubber laminates described above is used in the above step. Specifically, in the manufacturing method of this embodiment, the member including the cushion rubber and the pre-cure tread corresponds to the tire rubber laminate in the vulcanization method of this embodiment. According to this manufacturing method, it is possible to obtain uniformly vulcanized retread tires. [Examples]

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0059] A 3.0 mm thick vulcanized rubber layer sample was prepared by mixing and vulcanizing according to the conventional method using the formulation shown in Table 1. Dielectric loss (ε″) and dielectric loss tangent (tanδ) of this vulcanized rubber layer sample were measured using a vector network (Agilent Technologies, Inc., "E5071C") in the microwave frequency range of 0.3 GHz to 6.5 GHz (i.e., wavelength λ in the range of approximately 46 mm to 1000 mm) by the coaxial cable method. Table 1 shows the relative permittivity ε″ at microwave frequencies of 5.8 GHz (≈ wavelength 52 mm), 2.45 GHz (≈ wavelength 122 mm), and 900 MHz (≈ wavelength 333 mm). λ 'and relative dielectric loss ε λ It indicates ".

[0060] [Table 1]

[0061] *1 Carbon Black (HAF): Manufactured by Tokai Carbon Co., Ltd., Seast 3H, HAF grade (Nitrogen adsorption specific surface area: 82m²) 2 / g) *2 Anti-aging agent: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *3 Wax: Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Sunnock *4 Vulcanization accelerator: N-cyclohexyl-2-benzothiazolyl sulfenamide (Noxellar CZ), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0062] Meanwhile, an unvulcanized rubber layer with a thickness of 1 mm was prepared by kneading according to the conventional method using the formulation shown in Table 2. Next, this unvulcanized rubber layer was sandwiched between the two vulcanized rubber layers described above to prepare a laminated sample with dimensions of 80 mm x 80 mm. This laminated sample was vulcanized by irradiating it with microwaves according to the following procedure.

[0063] In Examples 1-4, a variable-frequency microwave generator (manufactured by LAMBDA Technology, product name "VariWave®") was used to heat (vulcanize) the laminated sample by irradiating it with microwaves while changing (increasing) the microwave frequency by a certain frequency change range shown in Table 2 at regular time intervals shown in Table 2. At that time, the laminated sample was sandwiched in a plastic mold, the initial vulcanization pressure was set to 0.5 MPa, and the microwave irradiation output was PID controlled so that the temperature of the sheet-like sample, as measured by an infrared thermometer, rose from approximately 30°C at a heating rate of 0.2°C / second. Once it reached 140°C, it was held at that temperature for 30 minutes. The variable frequency microwave generator used has a variable frequency range of 5.8 to 6.6 GHz according to its specifications. Therefore, in the above embodiment, the microwave frequency range of 5.8 to 6.6 GHz was selected, and the microwave frequency was increased each time until it reached 6.6 GHz, at which point it was switched to 5.8 GHz, and then the frequency increase was resumed. As can be seen from Table 1, the above frequency range corresponds to the penetration depth D λ It includes a frequency (5.8 GHz) corresponding to a wavelength λ (52 mm) that is greater than or equal to the thickness value of the vulcanized rubber (3.0 mm).

[0064] <Measurement of peel strength> Tensile tests were performed on each laminate sample in accordance with JIS K 6854-3, and the peel strength (N / inch) until the sample broke was measured. The results are shown in Table 2. A higher measured value indicates stronger adhesive strength.

[0065] <Destruction form> For each laminated sample, if no fracture was observed at the interfaces of each layer or in the intermediate layers vulcanized by microwave irradiation, but the vulcanized rubber layers on both sides were fractured, it was evaluated as "rubber fracture." If fracture occurred at the interfaces of each layer of the laminated sample or in the intermediate layers vulcanized by microwave irradiation, it was evaluated as "adhesive fracture." The results are shown in Table 2.

[0066] <Adhesion Evaluation> If the failure mode described above was "rubber failure," the adhesion evaluation was marked as ○. If the failure was "adhesive failure" at the rubber interface, the adhesion evaluation was marked as ×. The results are shown in Table 2.

[0067] [Table 2]

[0068] Table 2 shows that strong adhesion was observed between the layers of the laminates in Examples 1-4, suggesting that the vulcanization of the intermediate layer (unvulcanized rubber layer) was uniform. In other words, it can be seen that even with layers of a certain thickness or less, uniform vulcanization can be achieved by irradiating a rubber composition containing diene-based rubber and carbon black with microwaves while sweeping the frequency in a predetermined manner. Therefore, it is believed that the vulcanization method for tire rubber laminates of the present invention can uniformly vulcanize at least the unvulcanized rubber layer.

[0069] Next, focusing solely on the unvulcanized rubber layer, we evaluated the comparison of vulcanization uniformity based on different vulcanization methods.

[0070] A rubber composition was prepared by mixing the compounds shown in Table 3 according to a conventional method. This rubber composition was prepared as a sheet sample with dimensions of 80 mm × 80 mm × 2 mm thickness and vulcanized by microwave irradiation according to the following procedure.

[0071] In Examples 5-8, a variable-frequency microwave generator (manufactured by LAMBDA Technology, product name "VariWave®") was used to heat (vulcanize) a sheet-like sample by irradiating it with microwaves while changing (increasing) the microwave frequency by a certain frequency change range shown in Table 3 at regular time intervals shown in Table 3. At that time, the sheet-like sample was sandwiched in a plastic mold, the initial vulcanization pressure was set to 0.5 MPa, and the microwave irradiation output was PID controlled so that the temperature of the sheet-like sample, as measured by an infrared thermometer, rose from approximately 30°C at a heating rate of 0.2°C / second. Once it reached 140°C, it was held at that temperature for 30 minutes. The variable-frequency microwave generator used has a variable frequency range of 5.8 to 6.6 GHz according to its specifications. Therefore, each time the microwave frequency was increased and reached 6.6 GHz, it was switched to 5.8 GHz, and then the frequency increase was resumed.

[0072] In Comparative Examples 1-4, a magnetron oscillator (Milestone General Co., Ltd.'s microwave synthesis reactor, "flexiWAVE") was used to heat (vulcanize) a sheet-like sample by irradiation with microwaves at a fixed frequency (2.45 GHz). The initial vulcanization pressure and temperature control were the same as in the above examples.

[0073] <Evaluation of vulcanization uniformity> For each sheet-like sample after vulcanization, the hardness was measured at 36 points at 1 cm intervals using a digital hardness tester RH 101a from Polymer Instruments Co., Ltd. The percentage (%) of all measurement points (36 points) where the hardness was equal to or greater than the predetermined value shown below was then calculated. Carbon black content: 30 parts... Hardness: 44 Carbon black content: 35%... Hardness: 48 Carbon black content: 40 parts... Hardness: 53 Carbon black content 50 parts... Hardness 60 The results are shown in Table 1 as "vulcanization uniformity." A higher percentage indicates higher vulcanization uniformity. Note that "hardness above a specified value" is based on the results of a toluene immersion test of sheet-like samples, where if the hardness was above the specified value, the material did not dissolve in toluene due to crosslinking.

[0074] [Table 3]

[0075] *5 Isoprene rubber: Manufactured by JSR Corporation, IR2200

[0076] Table 3 shows that in the example, by irradiating the rubber composition with microwaves while sweeping the frequency in a predetermined manner, the resulting vulcanized product exhibits higher vulcanization uniformity than the comparative example. [Industrial applicability]

[0077] According to the present invention, it is possible to provide a method for vulcanizing a tire rubber laminate, in which an unvulcanized rubber layer and a vulcanized rubber layer are laminated, and to uniformly vulcanize the tire rubber laminate by microwave irradiation. Furthermore, according to the present invention, it is possible to provide a method for manufacturing retreaded tires that can obtain uniformly vulcanized retreaded tires.

Claims

1. A method for vulcanizing a tire rubber laminate, comprising laminating an unvulcanized rubber layer and a vulcanized rubber layer, by irradiating the laminate with microwaves, The aforementioned unvulcanized rubber layer contains diene rubber and carbon black. The vulcanized rubber layer contains diene rubber and carbon black, The penetration depth D of microwaves with wavelength λ (mm) into the vulcanized rubber constituting the vulcanized rubber layer. λ (mm) is given by the following formula: [Math 1] [In the formula, λ represents the wavelength of microwaves (mm), and ε λ ' represents the relative permittivity of vulcanized rubber at wavelength λ, and ε λ When defined as "[where λ represents the relative dielectric loss of vulcanized rubber at wavelength λ]", the penetration depth D λ A method for vulcanizing a tire rubber laminate, characterized by selecting a microwave frequency range that includes a frequency corresponding to a wavelength λ which is greater than or equal to the thickness of the vulcanized rubber layer, and during vulcanization, changing the frequency of the microwaves irradiated onto the tire rubber laminate by a frequency change width selected from a range of greater than 0 Hz and less than or equal to 100 Hz at each time interval selected from a range of greater than 0 μsec and less than or equal to 100 μsec within the frequency range.

2. The method for vulcanizing a rubber laminate for tires according to claim 1, wherein the frequency range of the microwaves is in the band of 30 GHz or less.

3. The method for vulcanizing a rubber laminate for tires according to claim 1, wherein the frequency range of the microwaves is in the band of 3 GHz or less.

4. A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, wherein the carbon black content in the vulcanized rubber layer is 15 parts by mass or more per 100 parts by mass of the diene rubber.

5. A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, wherein the carbon black content in the vulcanized rubber layer is 60 parts by mass or less per 100 parts by mass of the diene rubber.

6. The carbon black in the unvulcanized rubber layer has a nitrogen adsorption specific surface area of ​​50 m². ２ / g or more 130m ２ A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, comprising carbon black A in a quantity of 1 / g or less.

7. A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, wherein the carbon black content in the unvulcanized rubber layer is 20 parts by mass or more per 100 parts by mass of the diene rubber.

8. A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, wherein the time interval is constant each time.

9. A method for vulcanizing a rubber laminate for tires according to any one of claims 1 to 3, wherein the frequency change range is constant each time.

10. A method for manufacturing a retreaded tire, comprising the steps of attaching a pre-cured tread, which is a vulcanized rubber layer, to a base tire via a cushion rubber, which is an unvulcanized rubber layer, and then vulcanizing and bonding the cushion rubber, A method for manufacturing a retreaded tire, characterized in that the vulcanization method for a tire rubber laminate described in any one of claims 1 to 3 is used in the above step.

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