JP7545029B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a sealant material composition that constitutes a sealant layer of a self-sealing type pneumatic tire that has a sealant layer on the inner surface of the tire.

It has been proposed to provide a sealant layer on the radially inner side of the inner liner layer in the tread portion of a pneumatic tire (see, for example, Patent Document 1). In such a pneumatic tire (a so-called self-sealing type pneumatic tire), when a foreign object such as a nail penetrates the tread portion, the sealant material constituting the sealant layer flows into the through hole, suppressing the decrease in air pressure and making it possible to maintain driving.

In the above-mentioned self-sealing type pneumatic tire, if the viscosity of the sealant is low, the sealant can be expected to improve the sealing performance in that the sealant can easily flow into the through-holes. However, if the sealant flows toward the tire center due to the heat and centrifugal force applied during driving, and as a result, if the through-holes are not in the tire center region, there is a risk that the sealant will be insufficient and sufficient sealing performance will not be obtained. On the other hand, if the viscosity of the sealant is high, the flow of the sealant can be prevented, but the sealant will not easily flow into the through-holes, and there is a risk that the sealing performance will be reduced. Therefore, the sealant composition that constitutes the sealant is required to achieve a good balance between suppressing the flow of the sealant during driving and ensuring good sealing performance.

In addition, the viscosity of a sealant is generally temperature-dependent, and the lower the temperature, the higher the viscosity tends to be. Therefore, in low-temperature environments such as when used in winter or cold regions, the viscosity of the sealant increases, and there is a risk of the sealant losing its sealing ability. Furthermore, depending on the temperature conditions, the sealant may solidify, and when a foreign object such as a nail penetrates the tread portion, the impact may cause a part of the sealant around the through hole to be chipped, making it impossible to properly seal the through hole. Furthermore, when running in a low-temperature environment, the sealant may have difficulty following the deformation of the tire, and may peel off from the inner surface of the tire. Therefore, the sealant composition constituting the sealant is required to exhibit good sealing and adhesive properties even in low-temperature environments.

JP 2006-152110 A

The object of the present invention is to provide a sealant composition that suppresses the flow of the sealant during driving and exhibits good sealing and adhesive properties in low-temperature environments.

The pneumatic tire of the present invention that achieves the above object is a pneumatic tire having a sealant layer on the inner surface of the tire, the sealant layer being composed of an adhesive sealant obtained by vulcanizing a sealant composition, the sealant composition containing, relative to 100 parts by mass of a rubber component, 0.1 to 40 parts by mass of sulfur, more than 0 parts by mass and less than 1 part by mass of a cross-linking aid, and 50 to 400 parts by mass of paraffin oil having a molecular weight of 800 or more as a plasticizer component, the rubber component containing chlorinated butyl rubber and natural rubber, the proportion of the chlorinated butyl rubber in 100% by mass of the rubber component being 10% by mass or more, the adhesive sealant being vulcanized under conditions of a vulcanization temperature of 150°C or more and a vulcanization time of 5 to 60 minutes, and having a maximum stress of 0.05 MPa to 0.1 MPa and a breaking elongation of 800 or more, as measured when a tensile test is performed under conditions of a tensile speed of 5.0 m/s and a temperature of -30°C. % or more, and the maximum value of tan δ measured in the temperature range of 20° C. to 100° C. is 1.0 or less.

In the pneumatic tire of the present invention, since the sealant composition is composed of the above-mentioned blend, the flow of the sealant during driving is suppressed, and good sealing and adhesive properties can be exhibited in a low-temperature environment. Specifically, since the sealant composition contains sulfur (is crosslinked by sulfur), the adhesion to the inner surface of the tire can be increased, and since the blend is as described above, it is possible to obtain a suitable elasticity that does not flow during driving or storage while ensuring sufficient viscosity to obtain good sealing properties, thereby achieving a good balance between these performances. In addition, since the sealant composition of the pneumatic tire of the present invention has the above-mentioned properties, it is easy to follow the deformation of the tire during driving even in a low-temperature environment, and therefore it is possible to exhibit good sealing and adhesive properties in a low-temperature environment.

In the pneumatic tire of the present invention, the sealant composition preferably has a breaking elongation of 800% or more, as measured in a tensile test at a tensile speed of 5.0 m/s and a temperature of −30° C. This improves the physical properties of the sealant composition in a low-temperature environment, which is advantageous for exhibiting good sealing properties and adhesion in a low-temperature environment.

In the pneumatic tire of the present invention, it is preferable that 1 to 40 parts by mass of an organic peroxide is blended with 100 parts by mass of the rubber component constituting the sealant composition. By containing an organic peroxide in this manner and carrying out crosslinking by the combined use of sulfur and the organic peroxide described above, it is advantageous to obtain a suitable elasticity that does not flow during driving or storage while ensuring sufficient viscosity to obtain good sealing properties, thereby achieving a good balance between these performance properties.

As described above, the pneumatic tire of the present invention contains 10% by mass or more of butyl rubber relative to 100% by mass of the rubber component constituting the sealant composition . Furthermore, the butyl rubber contains chlorinated butyl rubber, and the content of the chlorinated butyl rubber relative to 100% by mass of the rubber component is 10% by mass or more . By using such a blending method, the adhesion to the inner surface of the tire can be improved.

In the pneumatic tire of the present invention, the plasticizer component contained in the sealant material composition is a liquid polymer. In particular, this liquid polymer is paraffin oil. Furthermore, the molecular weight of the paraffin oil is 800 or more. This makes it possible to reduce the temperature dependency of the physical properties of the adhesive sealant material, which is advantageous for ensuring good sealing properties in low-temperature environments. In addition, this is advantageous for preventing the plasticizer component from migrating into the tire and suppressing its effect on tire performance.

In the pneumatic tire of the present invention having a sealant layer composed of an adhesive sealant obtained by vulcanizing the above -mentioned sealant composition, the excellent physical properties of the above-mentioned sealant composition enable the tire to exhibit good sealing and adhesion even in low temperature environments while suppressing the flow of the sealant that occurs during driving.

At this time, the adhesive sealant is vulcanized under the conditions of a vulcanization temperature of 150° C. or more and a vulcanization time of 5 to 60 minutes. By carrying out vulcanization under these conditions, it is possible to suppress the remaining unreacted sulfur in the adhesive sealant, which is advantageous for maintaining the performance of the adhesive sealant well over a long period of time.

In the present invention, "maximum stress" refers to the maximum stress measured at yield or breakage in a tensile test conducted in accordance with JIS-K6251 using a No. 7 dumbbell-shaped test piece at a tensile speed of 5.0 m/s and a temperature of -30°C. "Break elongation" refers to the elongation measured at breakage in a tensile test conducted in accordance with JIS-K6251 using a No. 7 dumbbell-shaped test piece at a tensile speed of 5.0 m/s and a temperature of -30°C. "tan δ" refers to a value measured in accordance with JIS K6394 using a viscoelasticity spectrometer in the temperature range of 20°C to 100°C, with an elongation deformation strain rate of 10% ± 2% and a vibration frequency of 20 Hz.

1 is a meridian cross-sectional view showing an example of a pneumatic tire of the present invention.

The configuration of the present invention will be described in detail below with reference to the attached drawings.

As shown in FIG. 1, the pneumatic tire of the present invention (self-sealing type pneumatic tire) has a tread portion 1 that extends in the tire circumferential direction to form a ring, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the tire radial inner side of the sidewall portions 2. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction to form a ring, thereby forming the basic toroidal structure of the pneumatic tire. In addition, other tire components in the meridian cross section also extend in the tire circumferential direction to form a ring, unless otherwise specified.

In the example shown in FIG. 1, a carcass layer 4 is fitted between a pair of left and right bead portions 3. The carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction, and is folded from the inside to the outside of the vehicle around the bead cores 5 and bead fillers 6 arranged in each bead portion 3. The bead fillers 6 are arranged on the outer periphery of the bead cores 5, and are enclosed by the main body and folded portions of the carcass layer.

A plurality of belt layers 7 (two layers in FIG. 1) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Of these belt layers 7, the layer with the smallest belt width is called the smallest belt layer 7a, and the layer with the largest belt width is called the largest belt layer 7b. Each belt layer 7 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to, for example, a range of 10° to 40°. A belt reinforcing layer 8 is provided on the outer periphery of the belt layer 7 in the tread portion 1. In the illustrated example, two belt reinforcing layers 8 are provided: a full cover layer that covers the entire width of the belt layer 7, and an edge cover layer that is arranged further outward from the full cover layer and covers only the ends of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction, and the angle of the organic fiber cords with respect to the tire circumferential direction is set to, for example, 0° to 5°.

An inner liner layer 9 is provided on the inner surface of the tire along the carcass layer 4. This inner liner layer 9 is a layer that prevents the air filled in the tire from permeating to the outside of the tire. The inner liner layer 9 is composed of, for example, a rubber composition mainly made of butyl rubber that has air permeation prevention properties. Alternatively, it can be composed of a resin layer with a thermoplastic resin as a matrix. In the case of a resin layer, an elastomer component may be dispersed in a thermoplastic resin matrix.

As shown in FIG. 1, a sealant layer 10 is provided on the radially inner side of the inner liner layer 9 in the tread portion 1. In particular, the sealant layer 10 is provided on the inner surface of the tire corresponding to the ground contact area of the tread portion 1, that is, the area where a foreign object such as a nail may be stuck during driving. In particular, it is preferable to provide the sealant layer 10 in an area wider than the width of the minimum belt layer 7a. The sealant material composition of the present invention is used for this sealant layer 10. The sealant layer 10 is attached to the inner surface of a pneumatic tire having the above-mentioned basic structure. For example, when a foreign object such as a nail is stuck in the tread portion 1, the adhesive sealant material constituting the sealant layer 10 flows into the through hole and seals the through hole, thereby suppressing the decrease in air pressure and enabling driving to be continued.

The sealant layer 10 has a thickness of, for example, 0.5 mm to 5.0 mm. With a thickness of this order, it is possible to suppress the flow of the sealant during driving while ensuring good sealing properties. In addition, the sealant layer 10 is easy to process when applied to the inner surface of the tire. If the thickness of the sealant layer 10 is less than 0.5 mm, it becomes difficult to ensure sufficient sealing properties. If the thickness of the sealant layer 10 exceeds 5.0 mm, the tire weight increases and the rolling resistance deteriorates. Note that the thickness of the sealant layer 10 is the average thickness.

The sealant layer 10 can be formed by later attaching it to the inner surface of a vulcanized pneumatic tire. For example, an adhesive sealant material obtained by vulcanizing a sealant material composition described below can be attached to the inner surface of the tire to form the sealant layer 10. When attaching the adhesive sealant material, an adhesive sealant material molded in a sheet shape can be attached to the entire circumference of the inner surface of the tire, or an adhesive sealant material molded in a string or band shape can be attached in a spiral shape to the inner surface of the tire.

The vulcanization conditions for vulcanizing the sealant composition described below to obtain the above-mentioned adhesive sealant are not particularly limited, but considering the composition and physical properties of the sealant composition described below, the vulcanization temperature is preferably 150°C or higher, more preferably 160°C to 180°C, and the vulcanization time is preferably 5 minutes to 60 minutes, more preferably 10 minutes to 30 minutes. By vulcanizing under these conditions, it is possible to suppress the remaining unreacted sulfur in the adhesive sealant, which is advantageous for maintaining good performance of the adhesive sealant over a long period of time.

The present invention is primarily concerned with the sealant composition that constitutes the sealant layer 10 (adhesive sealant) of the self-sealing type pneumatic tire described above, so the basic structure of the pneumatic tire and the structure of the sealant layer 10 are not limited to the above examples.

The sealant composition of the present invention has a maximum stress of 0.2 MPa or less, preferably 0.05 MPa to 0.1 MPa, measured when a tensile test is performed at a tensile speed of 5.0 m/s and at a temperature of -30°C. It also has a breaking elongation of 600% or more, preferably 800% or more, more preferably 1000% to 2000%, measured when a tensile test is performed at a tensile speed of 5.0 m/s and at a temperature of -30°C. It also has a maximum tan δ of 1.0 or less, preferably 0.2 to 0.8, measured in a temperature range of 20°C to 100°C.

The cooperation of these physical properties allows the sealant composition of the present invention to easily follow the deformation of the tire during driving even in a low-temperature environment, and therefore it can exhibit good sealing and adhesive properties in a low-temperature environment. Specifically, the maximum stress when a tensile test is performed at high speed (tensile speed 5.0 m/s) in a low-temperature environment (-30°C) is sufficiently small, so that the sealant composition can improve sealing properties. In addition, the elongation rate when a tensile test is performed at high speed (tensile speed 5.0 m/s) in a low-temperature environment (-30°C) is sufficiently large, so that the sealant composition can be prevented from peeling off from the inner surface of the tire even when driving in a low-temperature environment. Furthermore, the maximum value of tan δ measured in the temperature range of 20°C to 100°C is within the above-mentioned range, so that the flowability can be improved.

At this time, if the above-mentioned maximum stress exceeds 0.2 MPa, the sealability in a low-temperature environment cannot be sufficiently ensured. If the above-mentioned breaking elongation is less than 600%, the adhesiveness in a low-temperature environment cannot be sufficiently ensured. If the above-mentioned breaking elongation is 600% or more, peeling of the sealant material can be prevented, but if the above-mentioned breaking elongation is set to a high range of 800% or more, the sealability in a low-temperature environment can be further improved. If the maximum value of tan δ in the above-mentioned temperature range exceeds 1.0, the fluidity decreases. If the above-mentioned relationship is satisfied, the tan δ at each temperature in the above-mentioned temperature range is not particularly limited. However, the tan δ at 20°C, which is the lower limit of the temperature range, is preferably 0.2 to 0.8, more preferably 0.4 to 0.6. Furthermore, the tan δ at 100°C, which is the upper limit of the temperature range, is preferably 0.2 to 0.8, more preferably 0.4 to 0.6.

The sealant composition of the present invention has the above-mentioned physical properties and is composed of the following composition.

In the sealant material composition of the present invention, the rubber component may contain a butyl-based rubber. The proportion of the butyl-based rubber in the rubber component is preferably 10% by mass or more, and more preferably 20% by mass to 90% by mass. By containing the butyl-based rubber in this way, good adhesion to the inner surface of the tire can be ensured. If the proportion of the butyl-based rubber is less than 10% by mass, sufficient adhesion to the inner surface of the tire cannot be ensured.

In the sealant composition of the present invention, it is preferable to include halogenated butyl rubber as the butyl-based rubber. Examples of halogenated butyl rubber include chlorinated butyl rubber and brominated butyl rubber, and chlorinated butyl rubber is particularly suitable. When chlorinated butyl rubber is used, the proportion of chlorinated butyl rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass to 85% by mass. By including halogenated butyl rubber (chlorinated butyl rubber), the reactivity of the rubber component with the crosslinking agent and organic peroxide described below is increased, which is advantageous for ensuring the sealing property and suppressing the flow of the sealant. In addition, the processability of the sealant composition can be improved. If the proportion of chlorinated butyl rubber is less than 5% by mass, the reactivity of the rubber component with the crosslinking agent and organic peroxide described below is not sufficiently improved, and the desired effect cannot be sufficiently obtained.

In the sealant composition of the present invention, the entire amount of the butyl-based rubber does not need to be halogenated butyl rubber (chlorinated butyl rubber), and non-halogenated butyl rubber can also be used in combination. Examples of non-halogenated butyl rubber include unmodified butyl rubbers that are commonly used in sealant compositions, such as BUTYL-065 manufactured by JSR Corporation and BUTYL-301 manufactured by LANXESS Corporation. When halogenated butyl rubber and non-halogenated butyl rubber are used in combination, the amount of non-halogenated butyl rubber is preferably less than 20% by mass, more preferably less than 10% by mass, based on 100% by mass of the rubber component.

In the sealant composition of the present invention, it is preferable to use two or more types of rubber in combination as the butyl-based rubber. That is, it is preferable to use chlorinated butyl rubber in combination with other halogenated butyl rubber (e.g., brominated butyl rubber) or non-halogenated butyl rubber. Since the three types of chlorinated butyl rubber, other halogenated butyl rubber (brominated butyl rubber), and non-halogenated butyl rubber have different vulcanization rates, when at least two types are used in combination, the physical properties (viscosity, elasticity, etc.) of the sealant composition after vulcanization are not uniform due to the difference in vulcanization rate. That is, due to the distribution (variation in concentration) of rubbers with different vulcanization rates in the sealant composition, relatively hard parts and relatively soft parts are mixed in the sealant layer after vulcanization. As a result, the flowability is suppressed in the relatively hard parts, and the sealing property is exhibited in the relatively soft parts, which is advantageous for achieving a good balance between these performances.

In the sealant composition of the present invention, other diene rubbers than butyl rubber can also be blended as the rubber component. As the other diene rubbers, rubbers commonly used in sealant compositions, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR), can be used. These other diene rubbers can be used alone or as any blend.

In the sealant composition of the present invention, sulfur is always blended as a crosslinking agent. The blending amount of sulfur is 0.1 to 40 parts by mass, preferably 0.5 to 20 parts by mass, per 100 parts by mass of the rubber component described above. This allows the adhesive sealant to be crosslinked by the sulfur, improving adhesion to tires. If the blending amount of sulfur is less than 0.1 parts by mass, it is essentially the same as not containing a crosslinking agent, and appropriate crosslinking cannot be performed. If the blending amount of sulfur exceeds 40 parts by mass, crosslinking of the sealant composition proceeds too much, resulting in a decrease in sealing properties. Note that even if a crosslinking agent other than sulfur (e.g., quinone dioxime, zinc oxide, etc.) is used, sufficient adhesion to tires cannot be ensured.

In the sealant composition of the present invention, it is preferable to compound an organic peroxide together with the above-mentioned crosslinking agent (sulfur). By compounding sulfur and an organic peroxide in combination in this way, suitable crosslinking can be achieved to ensure both sealing properties and prevention of sealant flow. The amount of organic peroxide compounded is preferably 1 to 40 parts by mass, more preferably 1.0 to 20 parts by mass, per 100 parts by mass of the above-mentioned rubber component. If the amount of organic peroxide compounded is less than 1 part by mass, the amount of organic peroxide is too small to sufficiently crosslink, and the desired physical properties cannot be obtained. If the amount of organic peroxide compounded exceeds 40 parts by mass, crosslinking of the sealant proceeds too much, reducing the sealant properties.

When sulfur and organic peroxide are used in combination in this way, the mass ratio A/B of the amount of sulfur A to the amount of organic peroxide B is preferably 5/1 to 1/200, more preferably 1/10 to 1/20. By using such a mixing ratio, it is possible to achieve a better balance between ensuring sealing properties and preventing the sealant material from flowing.

Examples of organic peroxides include dicumyl peroxide, t-butylcumyl peroxide, benzoyl peroxide, dibenzoyl peroxide, butyl hydroperoxide, p-chlorobenzoyl peroxide, and 1,1,3,3-tetramethylbutyl hydroperoxide. In particular, organic peroxides with a one-minute half-life temperature of 100°C to 200°C are preferred, and among the specific examples mentioned above, dicumyl peroxide and t-butylcumyl peroxide are particularly preferred. In the present invention, the "one-minute half-life temperature" generally refers to the value listed in NOF Corp.'s "Organic Peroxide Catalog, 10th Edition." If no value is listed, the value determined from thermal decomposition in an organic solvent using the same method as that listed in the catalog is used.

The sealant composition of the present invention is necessarily formulated with a crosslinking aid together with the crosslinking agent (sulfur). The crosslinking aid is a compound that acts as a crosslinking reaction catalyst when formulated with a crosslinking agent containing a sulfur component. By formulating a crosslinking agent (sulfur) and a crosslinking aid, the vulcanization speed can be increased, and the productivity of the sealant can be improved. The amount of the crosslinking aid is preferably more than 0 parts by mass and less than 1 part by mass, more preferably 0.1 parts by mass to 0.9 parts by mass, relative to 100 parts by mass of the rubber component. By suppressing the amount of the crosslinking aid in this way, it is possible to promote the crosslinking reaction as a catalyst while suppressing deterioration (thermal deterioration) of the sealant. If the amount of the crosslinking aid is 1 part by mass or more, the effect of suppressing thermal deterioration cannot be sufficiently obtained. In addition, since the crosslinking aid acts as a crosslinking reaction catalyst when formulated with a crosslinking agent containing a sulfur component as described above, even if it is coexisted with an organic peroxide instead of the sulfur component, it does not act as a crosslinking reaction catalyst, and a large amount of the crosslinking aid must be used, which promotes thermal deterioration.

When using a crosslinking agent (sulfur) and a crosslinking assistant in combination, the amount of the crosslinking agent (sulfur) is preferably 50% to 400% by mass, more preferably 100% to 200% by mass, of the amount of the crosslinking assistant. By blending the crosslinking agent (sulfur) and the crosslinking assistant in this manner in a well-balanced manner, the crosslinking assistant can effectively function as a catalyst, which is advantageous for ensuring both sealing properties and preventing the sealant material from flowing. If the amount of the crosslinking agent (sulfur) is less than 50% by mass of the amount of the crosslinking assistant, the flowability decreases. If the amount of the crosslinking agent (sulfur) is more than 400% by mass of the amount of the crosslinking assistant, the deterioration resistance decreases.

Examples of crosslinking assistants include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based, aldehyde-ammonia-based, imidazoline-based, and xanthogenic acid-based compounds (vulcanization accelerators). Among these, thiazole-based, thiuram-based, guanidine-based, and dithiocarbamate-based vulcanization accelerators can be preferably used. Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole and dibenzothiazyl disulfide. Examples of thiuram-based vulcanization accelerators include tetramethylthiuram monosulfide and tetramethylthiuram disulfide. Examples of guanidine-based vulcanization accelerators include diphenylguanidine and diorthotolylguanidine. Examples of dithiocarbamate-based vulcanization accelerators include sodium dimethyldithiocarbamate and sodium diethyldithiocarbamate. In particular, in the present invention, it is preferable to use a thiazole-based or thiuram-based vulcanization accelerator, which can suppress variation in the performance of the resulting sealant composition.

For example, a compound that actually functions as a crosslinking agent, such as quinone dioxime, may be conveniently referred to as a crosslinking assistant. However, the crosslinking assistant in the present invention is a compound that functions as a catalyst for the crosslinking reaction caused by the crosslinking agent (sulfur) as described above, so quinone dioxime does not fall under the category of crosslinking assistant in the present invention.

The sealant composition of the present invention necessarily contains a plasticizer component (e.g., a liquid polymer). By containing a plasticizer component in this way, the viscosity of the adhesive sealant can be increased, improving the sealing properties. The amount of the plasticizer component is 50 to 400 parts by mass, preferably 70 to 200 parts by mass, per 100 parts by mass of the rubber component. If the amount of the plasticizer component is less than 50 parts by mass, the effect of increasing the viscosity of the adhesive sealant may not be sufficiently obtained. If the amount of the plasticizer component exceeds 400 parts by mass, the flow of the sealant cannot be sufficiently prevented.

As the plasticizer component, a liquid polymer can be exemplified as described above, but a liquid polymer that can be co-crosslinked with the rubber component (butyl rubber) in the sealant material composition is particularly preferred. Examples of such liquid polymers include paraffin oil, polybutene oil, polyisoprene oil, polybutadiene oil, polyisobutene oil, aromatic oil, polypropylene glycol, etc. From the viewpoint of keeping the temperature dependency of the physical properties of the sealant material composition low and ensuring good sealing properties in a low-temperature environment, paraffin oil, polybutene oil, polyisoprene oil, polybutadiene oil, aromatic oil, and polypropylene glycol are preferred, and paraffin oil is particularly preferred. The use of paraffin oil is advantageous in setting the viscosity in a low-temperature environment to an appropriate range. The molecular weight of the liquid polymer is preferably 800 or more, more preferably 1000 or more, and even more preferably 1200 to 3000. By using a sealant with such a high molecular weight, it is possible to prevent plasticizer components (oil components) from migrating from the sealant layer on the inner surface of the tire to the tire body and affecting the tire.

The sealant composition of the present invention suppresses the flow of the sealant during driving by combining the above-mentioned physical properties and formulation, and exhibits good sealing and adhesive properties in low-temperature environments. Therefore, the sealant composition of the present invention can be suitably used for the sealant layer 10 (adhesive sealant) of a self-sealing type pneumatic tire. A tire having a sealant layer 10 composed of an adhesive sealant obtained by vulcanizing the sealant composition of the present invention has excellent performance based on the cooperation of the above-mentioned physical properties and formulation, and the sealant layer 10 (adhesive sealant) is less likely to flow, the sealant layer 10 (adhesive sealant) is less likely to peel off in low-temperature environments, and excellent sealing properties are exhibited, so that a through hole caused by a puncture can be reliably sealed even in low-temperature environments.

The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

Sealant compositions (Comparative Examples 1 to 9, Examples 1 to 4) were prepared with the compositions shown in Table 1. Specifically, the rubber component and carbon black were mixed in a 1.7 L Banbury mixer for 10 minutes, then the plasticizer component (liquid polymer) was added, and finally the crosslinker (sulfur) and organic peroxide were added and mixed for another 10 minutes to prepare each sealant composition. The sealant compositions were vulcanized under the conditions shown in Table 1 to obtain adhesive sealants.

Table 1 also lists the breaking elongation (unit: %), maximum stress (unit: MPa), and tan δ of the sealant composition. Specifically, the breaking elongation is the elongation rate at break of the sealant composition, and was measured by conducting a tensile test using a No. 7 dumbbell-shaped test piece at a tensile speed of 5.0 m/s and a temperature of -30°C in accordance with JIS-K6251. The maximum stress is the maximum value of the stress measured at the time of yield or when break is reached, and was measured by conducting a tensile test using a No. 7 dumbbell-shaped test piece at a tensile speed of 5.0 m/s and a temperature of -30°C in accordance with JIS-K6251. Tan δ was measured in accordance with JIS K6394 using a viscoelasticity spectrometer at an elongation deformation strain rate of 10% ± 2% and a vibration frequency of 20 Hz, with "tan δ (maximum value)" being the maximum value measured in the temperature range of 20°C to 100°C, "tan δ (20°C)" being the value measured at a temperature condition of 20°C, and "tan δ (100°C)" being the value measured at a temperature condition of 100°C.

The sealant compositions were evaluated for sealing ability, fluidity during driving, and adhesion using the following test methods, and the results are shown in Table 1.

Sealing property Each adhesive sealant material was attached to the inner side in the tire radial direction of the inner liner layer in the tread part of a pneumatic tire (tire size: 255/40R20) having the basic structure shown in Figure 1 to produce a test tire. Then, each test tire was cooled for 24 hours under a temperature condition of -20 ° C., and then assembled to a wheel with a rim size of 20 x 9J and mounted on a test vehicle. Under conditions of an initial air pressure of 250 kPa, a load of 8.5 kN, and a temperature of -20 ° C., a nail with a diameter of 4.0 mm was driven into the tread part, and the tire was left standing in an environment of -20 ° C. for 1 hour with the nail removed, and then the air pressure was measured. The evaluation results were shown on the following 5-point scale. Note that if the evaluation result score is "3" or more, sufficient sealing property is exhibited, and the higher the score, the better the sealing property is exhibited.
5: Air pressure after standing is 240 kPa or more and 250 kPa or less 4: Air pressure after standing is 230 kPa or more and less than 240 kPa 3: Air pressure after standing is 215 kPa or more and less than 230 kPa 2: Air pressure after standing is 200 kPa or more and less than 215 kPa 1: Air pressure after standing is less than 200 kPa

Fluidity during running Each adhesive sealant was attached to the inner radial side of the inner liner layer in the tread of a pneumatic tire (tire size: 255/40R20) having the basic structure shown in Figure 1 to produce a test tire. The test tire was then mounted on a wheel with a rim size of 20x9J and mounted on a drum test machine, and run for 1 hour under the conditions of an air pressure of 220 kPa, a load of 8.5 kN, and a running speed of 100 km/h, and the flow state of the adhesive sealant after running was examined. The evaluation results were obtained by drawing 20x40 squares of 5 mm grid lines on the surface of the sealant layer before running, and counting the number of squares whose shape was distorted after running. If no flow of the adhesive sealant was observed at all (the number of distorted squares was 0), it was indicated as "good", if the number of distorted squares was less than 1/4 of the total, it was indicated as "passable", and if the number of distorted squares was 1/4 or more of the total, it was indicated as "not good".

Adhesion Each adhesive sealant was attached to the inner side of the inner liner layer in the tread of a pneumatic tire (tire size: 255/40R20) having the basic structure shown in FIG. 1 to produce a test tire. Then, each test tire was assembled to a wheel with a rim size of 20×9J and mounted on a drum test machine, and after running 100,000 km under the conditions of an air pressure of 250 kPa, a load of 5.0 kN, a speed of 80 km/h, and a temperature of −20° C., the peeling state of the adhesive sealant at the splice of the adhesive sealant was visually confirmed. The evaluation results were as follows: "good" when no peeling occurred, "passable" when the area where peeling occurred was less than 1/3 of the width of the sealant layer from the tire width direction end of the splice, and "unacceptable" when the area where peeling occurred was 1/3 or more of the width of the sealant layer from the tire width direction end of the splice.

The types of raw materials used in Table 1 are shown below.
Chlorinated butyl rubber: CHLOROBUTYL1066 manufactured by JSR Corporation
Natural rubber: Natural rubber manufactured by SRI TRANG Co., Ltd. Carbon black: Seast KH manufactured by Tokai Carbon Co., Ltd.
Sulfur: small lump sulfur manufactured by Hosoi Chemical Industry Co., Ltd. Quinone dioxime: Valnoc GM manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking aid: Thiuram-based vulcanization accelerator, Noccela TT-P manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Organic peroxide: dibenzoyl peroxide, Niper NS manufactured by Nippon Oil & Fats Co., Ltd. (1-minute half-life temperature: 133°C)
Liquid polymer 1: Aromatic oil, Diana Process Oil AH-58 (molecular weight: 1000) manufactured by Idemitsu Kosan Co., Ltd.
Liquid polymer 2: Paraffin oil, Kaneda Hicol K-350 (molecular weight: 850)
Liquid polymer 3: Polybutene oil, JXTG Nippon Oil & Energy Corporation's Nippon Oil Polybutene HV-15 (molecular weight: 1300)

As is clear from Table 1, when the sealant compositions of Examples 1 to 4 were used as a sealant layer in a self-sealing pneumatic tire, they exhibited good sealing properties in a low-temperature environment and were able to suppress the flow of the sealant during driving. They also ensured good adhesion to the tire. On the other hand, Comparative Examples 1 to 4 did not contain sulfur and did not satisfy the tan δ condition, so they were unable to suppress the flow. Comparative Example 5 did not satisfy the tan δ condition, so they were unable to suppress the flow. Comparative Examples 7 and 8 were formulated with quinone dioxime instead of sulfur and did not satisfy the maximum stress value condition, so they were unable to exhibit good sealing properties in a low-temperature environment. Comparative Example 9 was formulated with quinone dioxime instead of sulfur and did not satisfy the breaking elongation and maximum stress value conditions, so they were unable to exhibit good sealing properties in a low-temperature environment and were unable to ensure adhesion.

Reference Signs List 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 9 inner liner layer 10 sealant layer CL tire equator

Claims (4)

A pneumatic tire having a sealant layer on an inner surface of the tire, the sealant layer being composed of an adhesive sealant material obtained by vulcanizing a sealant material composition, the sealant material composition containing, relative to 100 parts by mass of a rubber component, 0.1 to 40 parts by mass of sulfur, more than 0 part by mass and less than 1 part by mass of a cross-linking aid, and 50 to 400 parts by mass of paraffin oil having a molecular weight of 800 or more as a plasticizer component, the rubber component containing chlorinated butyl rubber and natural rubber, and a proportion of the chlorinated butyl rubber in 100% by mass of the rubber component being 10% by mass or more,
The adhesive sealant is vulcanized under conditions of a vulcanization temperature of 150°C or higher and a vulcanization time of 5 to 60 minutes, and the pneumatic tire is characterized in that, when a tensile test is conducted under conditions of a tensile speed of 5.0 m/s and a temperature of -30°C, the maximum stress measured is 0.05 MPa to 0.1 MPa , the breaking elongation is 800 % or higher, and the maximum value of tan δ measured in a temperature range of 20°C to 100°C is 1.0 or less. 2. The pneumatic tire according to claim 1, wherein the sealant composition has a breaking elongation of 800% or more when measured in a tensile test at a tensile speed of 5.0 m/s and a temperature of -30°C. 3. The pneumatic tire according to claim 1, wherein 1 to 40 parts by mass of an organic peroxide is blended with 100 parts by mass of the rubber component constituting the sealant material composition . 4. The pneumatic tire according to claim 3, wherein a mass ratio A/B of the blending amount A of the sulfur to the blending amount B of the organic peroxide is 5/1 to 1/200.

Images