JP7663801B2 - Sealant composition - 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, 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 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 part of the sealant around the through hole to be chipped, making it impossible to properly seal the through hole. Therefore, the sealant composition that constitutes the sealant is required to exhibit good sealing ability even in low-temperature environments.

Furthermore, with regard to the flow of the above-mentioned sealant material, there is a concern that the sealant material will gradually flow toward the tire center during storage, not only during the above-mentioned driving, but also when the tire with the sealant layer provided is stored for a long period of time. Therefore, there is a demand for suppressing flow (improving storage properties) even when the tire is left stationary for a long period of time under specified conditions.

JP 2006-152110 A

The object of the present invention is to provide a sealant material composition that exhibits good sealing properties even in low-temperature environments, suppresses the flow of the sealant while the vehicle is in motion, and also suppresses the flow of the sealant during storage.

The sealant material composition of the present invention which achieves the above object is a sealant material composition constituting a sealant layer disposed on the inner surface of a pneumatic tire, and is characterized in that, relative to 100 parts by mass of a rubber component, 40 to 450 parts by mass of paraffin oil, 1 to 45 parts by mass of an organic peroxide, 0.1 to 40 parts by mass of a crosslinking agent containing a sulfur component, and more than 0 to less than 1 part by mass of a crosslinking aid are blended, and the sealant material composition has a viscosity V0 _{°C at 0} °C of 2 kPa·s to 15 kPa·s, a viscosity _{V40°C at 40°C} of 1 kPa·s to 14 kPa·s, and a viscosity _V80°C at 80°C of 0.6 kPa·s to 10.8 kPa·s , and a ratio _V0°C /V40 _°C of the viscosity _V0°C to the viscosity _V40°C of 1.0 to 3.0 .

Since the sealant composition of the present invention has the above-mentioned characteristics, it exhibits good sealing properties even in a low-temperature environment, suppresses the flow of the sealant during driving, and also suppresses the flow of the sealant during storage, and these performances can be balanced. In particular, by having a viscosity V _0°C of 2 kPa·s to 15 kPa·s at 0°C, the sealant is prevented from hardening in a low-temperature environment and can maintain appropriate viscosity and flexibility, so that good sealing properties can be ensured even in a low-temperature environment. Furthermore, by having a viscosity V _40°C of 1 kPa·s to 14 kPa·s at 40°C, appropriate elasticity can be obtained under temperature conditions close to the storage state, so that the flow of the sealant during tire storage can be suppressed (storability can be improved). Furthermore, by having a viscosity V _80°C of 0.5 kPa·s to 12 kPa·s at 80°C, appropriate elasticity can be obtained even under high-temperature conditions, so that the flow of the sealant accompanying driving can be effectively suppressed. In particular, since an appropriate viscosity that can achieve a good balance of these performances is maintained regardless of temperature, it is possible to achieve a good balance of sealing properties, storage properties, and flowability in a low-temperature environment. In the present invention, the "viscosity" is a value measured using a rotational rheometer using a sample having a diameter of 25 mm and a thickness of 1.5 mm under conditions of a deformation of 0.1%, a frequency of 1 Hz, and each of the specified temperature conditions (0°C, 40°C, and 80°C).

The sealant composition of the present invention preferably has a ratio V0°C/V40°C of the viscosity _V0° C at _{0 °C} to the viscosity V40°C at _40°C , that is, 5 or less. Also, it is preferable that the ratio _V0°C /V80°C of the viscosity _V0°C at _0°C to the _{viscosity V80°C at 80°C} , that is, 10 or less. Such a small difference in viscosity between different temperature conditions is advantageous in achieving a good balance between sealability, storage properties, and fluidity in a low-temperature environment.

The sealant composition of the present invention preferably contains 50 to 400 parts by mass of paraffin oil per 100 parts by mass of the rubber component. Furthermore, it is preferable that 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 sealant composition, which is advantageous for ensuring good sealing properties in low-temperature environments.

The sealant composition of the present invention preferably contains 1 to 40 parts by mass of an organic peroxide, 0.1 to 40 parts by mass of a crosslinking agent, and more than 0 to less than 1 part by mass of a crosslinking aid, per 100 parts by mass of the rubber component. By crosslinking using a crosslinking agent and an organic peroxide in combination in this way, 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, which is advantageous for achieving a good balance between these performance properties. In addition, such a blending method makes it possible to reduce the temperature dependency of the physical properties of the sealant composition, which is advantageous for achieving a good balance between sealing properties, storage properties, and flowability in low-temperature environments.

In the sealant composition of the present invention, it is preferable that the crosslinking agent contains a sulfur component. This increases the reactivity of the rubber component (e.g., butyl rubber) with the crosslinking agent (sulfur) or organic peroxide, improving the processability of the sealant composition.

In the sealant composition of the present invention, the amount of crosslinking aid is preferably 50% to 400% by mass of the amount of crosslinking agent. This provides a good balance between the crosslinking agent and the crosslinking aid, suppresses thermal deterioration, and enables good sealing properties to be maintained for a long period of time.

In the sealant material composition of the present invention, the crosslinking aid is preferably a thiazole compound or a thiuram compound. This makes it possible to increase the vulcanization speed and improve productivity. At the same time, it is possible to suppress thermal degradation more than other crosslinking aids, and it is also possible to maintain good sealing properties for a long period of time.

In the sealant composition of the present invention, the rubber component preferably contains butyl rubber, and the amount of butyl rubber per 100% by mass of the rubber component is preferably 10% by mass or more. Furthermore, it is preferable that the butyl rubber contains chlorinated butyl rubber, and the amount of chlorinated butyl rubber per 100% by mass of the rubber component is 5% by mass or more. By using such a composition, it is possible to improve adhesion to the inner surface of a tire.

In a pneumatic tire having a sealant layer made of the sealant material composition of the present invention described above, the excellent physical properties of the sealant material composition described above enable the tire to exhibit good sealing properties while suppressing the flow of the sealant that occurs during driving, and in particular, good sealing properties can be ensured even in low temperature environments.

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 toroidal basic 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 mounted 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 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 attaching it to the inner surface of the vulcanized pneumatic tire afterwards. For example, the sealant layer 10 can be formed by attaching a sealant material made of the sealant material composition described later in a sheet shape to the entire circumference of the inner surface of the tire, or by attaching a sealant material made of the sealant material composition described later in a string or strip shape to the inner surface of the tire in a spiral shape. In addition, by heating the sealant material composition at this time, the variation in the performance of the sealant material composition can be suppressed. The heating conditions are preferably a temperature of 140°C to 180°C, more preferably 160°C to 180°C, and a heating time of preferably 5 minutes to 30 minutes, more preferably 10 minutes to 20 minutes. According to this method for manufacturing a pneumatic tire, a pneumatic tire that has good sealing properties when punctured and is less likely to cause sealant flow can be efficiently manufactured.

The present invention primarily relates to the sealant material composition used in the sealant layer 10 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 material composition of the present invention has a viscosity V _{0° C.} at 0° C. of 2 kPa·s to 15 kPa·s, preferably 3 kPa·s to 10 kPa·s. The viscosity V _{40° C.} at 40° C. is 1 kPa·s to 14 kPa·s, preferably 2 kPa·s to 8 kPa·s. The viscosity V _{80° C.} at 80° C. is 0.5 kPa·s to 12 kPa·s, preferably 1 kPa·s to 6 kPa·s. When used in the sealant layer 10 of a pneumatic tire, the sealant material composition having such properties exhibits good sealing properties even in a low-temperature environment, suppresses the flow of the sealant during driving, and also suppresses the flow of the sealant during storage, thereby achieving a good balance between these performance properties. In particular, the fact that the physical properties (viscosity) are appropriate at different temperatures means that the effect of temperature on the physical properties of the sealant is small, and an appropriate viscosity that can exhibit these performance properties in a balanced manner is maintained regardless of temperature, so that a high level of balance can be achieved between sealing properties, storage properties, and fluidity in low-temperature environments.

In this case, if the viscosity V0 _°C at 0°C is less than 2 kPa·s, the fluidity is deteriorated, and if the viscosity V0 _°C at 0°C exceeds 15 kPa·s, the sealing property in a low temperature environment is deteriorated. If the viscosity V40 _{°C at 40} °C is less than 1 kPa·s, the flow of the sealant during storage cannot be sufficiently suppressed, and the storage property is deteriorated. If the viscosity V40 _{°C at 40} °C exceeds 14 kPa·s, the sealing property is deteriorated. If the viscosity V80 _{°C at 80°} C is less than 0.5 kPa·s, the fluidity of the sealant during driving is deteriorated, and if the viscosity _V80°C at 80°C exceeds 12 kPa·s, the sealing property is deteriorated.

As described above, it is important that the viscosities of the sealant composition of the present invention at different temperatures are in the appropriate ranges described above. In particular, the ratio V _{0 °C} /V 40 °C of the viscosity V _{0 °} C at 0 _°C to the viscosity V 40 °C _{at 40 °C} is preferably 5 or less, more preferably 1.0 to 3.0. Since the difference between the viscosity at low temperature (0 °C) and the viscosity at moderate temperature conditions (40 °C) is small, it is possible to achieve a good balance between the sealability and storage properties in a low temperature environment. In this case, if the ratio V _{0 °C} /V _{40 °C} exceeds 5, the difference in viscosity due to temperature conditions increases, making it difficult to achieve a good balance between the sealability and storage properties in a low temperature environment.

Similarly, in the sealant composition of the present invention, the ratio V0 _{°C/V80°C of the viscosity at 0} °C _V0° C to the viscosity at _80° C _V80°C is preferably 10 or less, more preferably 1.0 to 5.0. Since the difference between the viscosity at low temperature (0°C) and the viscosity at high temperature (80°C) is small, it is possible to achieve a good balance between the sealing property in a low temperature environment and the fluidity during driving. In this case, if the ratio V0 _°C / _V80°C exceeds 10, the difference in viscosity due to temperature conditions increases, making it difficult to achieve a good balance between the sealing property in a low temperature environment and the fluidity during driving.

The specific composition of the sealant material composition used in the present invention is not particularly limited as long as it has the above-mentioned physical properties. However, in order to reliably obtain the above-mentioned physical properties, it is preferable to adopt, for example, the composition described below.

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, more preferably 20% by mass to 90% by mass, and even more preferably 30% 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, the adhesion to the inner surface of the tire cannot be sufficiently ensured. In particular, within the above-mentioned range, the viscosity at 0°C tends to decrease as the blending amount of the butyl-based rubber increases, and the viscosity at 0°C tends to increase as the blending amount of the butyl-based rubber decreases. Therefore, setting the proportion of the butyl-based rubber to the above-mentioned more preferable range (20% by mass to 90% by mass) or the more preferable range (30% by mass to 90% by mass) is effective in setting the viscosity (particularly the viscosity at 0°C) to the appropriate range specified in the present invention.

In the sealant composition of the present invention, it is preferable to include a halogenated butyl rubber as the butyl-based rubber. Examples of the halogenated butyl rubber include chlorinated butyl rubber and brominated butyl rubber, and chlorinated butyl rubber is particularly suitable. When using chlorinated butyl rubber, the ratio of the chlorinated butyl rubber to 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass to 85% by mass, and even more preferably 30% by mass to 70% by mass. By including a halogenated butyl rubber (chlorinated butyl rubber), the reactivity of the rubber component with a crosslinking agent or an 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 ratio of the chlorinated butyl rubber is less than 5% by mass, the reactivity of the rubber component with a crosslinking agent or an organic peroxide described below is not sufficiently improved, and the desired effect cannot be sufficiently obtained. In particular, within the above-mentioned range, the chlorinated butyl rubber has a tendency that the viscosity at 0°C decreases as the blending amount increases and that the viscosity at 0°C increases as the blending amount decreases. Therefore, setting the proportion of the chlorinated butyl rubber within the above-mentioned more preferable range (10% by mass to 85% by mass) or even more preferable range (30% by mass to 70% by mass) is effective for setting the viscosity (particularly the viscosity at 0°C) within the appropriate range specified in the present invention.

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 material composition of the present invention, it is preferable to mix a crosslinking agent and an organic peroxide. In addition, the "crosslinking agent" in the present invention is a crosslinking agent other than an organic peroxide, and examples thereof include sulfur, zinc oxide, cyclic sulfide, resin (resin vulcanization), and amine (amine vulcanization). Here, an example of the resin (resin vulcanization) is phenol formaldehyde resin. Also, an example of the amine (amine vulcanization) is phenylhydroxylamine. As the crosslinking agent, it is preferable to use one that contains a sulfur component (e.g., sulfur). By mixing the crosslinking agent and the organic peroxide in combination in this way, it is possible to achieve an appropriate crosslinking to ensure sealing properties and prevent the flow of the sealant at the same time.

The amount of the crosslinking agent is preferably 0.1 to 40 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the rubber component. The amount of the organic peroxide is preferably 1 to 40 parts by mass, more preferably 1.0 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the rubber component. If the amount of the crosslinking agent is less than 0.1 parts by mass, the composition is essentially equivalent to the composition not containing the crosslinking agent, and appropriate crosslinking cannot be performed. If the amount of the crosslinking agent is more than 40 parts by mass, the crosslinking of the sealant composition proceeds too much, resulting in a decrease in sealing properties. If the amount of the organic peroxide is less than 1 part by mass, the amount of organic peroxide is too small, and crosslinking cannot be performed sufficiently, and desired physical properties cannot be obtained. If the amount of the organic peroxide is more than 40 parts by mass, the crosslinking of the sealant composition proceeds too much, resulting in a decrease in sealing properties.

Within the above-mentioned range, the crosslinking agent has a tendency that the viscosity at 0°C increases as the amount is increased and decreases as the amount is decreased. Therefore, setting the amount of the crosslinking agent to the above-mentioned more preferred range (0.5 parts by mass to 20 parts by mass) or even more preferred range (1 part by mass to 10 parts by mass) is effective for setting the viscosity (particularly the viscosity at 0°C) to the appropriate range specified in the present invention. Also, within the above-mentioned range, the organic peroxide has a tendency that the viscosity at 23°C decreases as the amount is increased and increases as the amount is decreased. Therefore, setting the amount of the organic peroxide to the above-mentioned more preferred range (1.0 parts by mass to 20 parts by mass) or even more preferred range (5 parts by mass to 15 parts by mass) is effective for setting the viscosity (particularly the viscosity at 0°C) to the appropriate range specified in the present invention.

When using a crosslinking agent and an organic peroxide in combination in this way, the mass ratio A/B of the amount of crosslinking agent 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 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 Corporation'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.

It is preferable to compound a crosslinking aid in the sealant composition of the present invention. The crosslinking aid is a compound that acts as a crosslinking reaction catalyst when compounded with a crosslinking agent containing a sulfur component. By compounding a crosslinking agent and a crosslinking aid, the vulcanization speed can be increased, and the productivity of the sealant composition can be improved. The compounding 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 above-mentioned rubber component. By suppressing the compounding amount of the crosslinking aid in this way, it is possible to suppress the deterioration (thermal deterioration) of the sealant composition while promoting the crosslinking reaction as a catalyst. If the compounding 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 compounded 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 and a crosslinking assistant in combination, the amount of the crosslinking agent is preferably 50% to 400% by mass, more preferably 100% to 200% by mass, of the amount of the crosslinking assistant described above. By appropriately mixing the crosslinking agent with the crosslinking assistant in this way, the crosslinking assistant can effectively function as a catalyst, which is advantageous for ensuring both sealing properties and preventing the sealant from flowing. If the amount of the crosslinking agent is less than 50% by mass of the amount of the crosslinking assistant, the flowability decreases. If the amount of the crosslinking agent 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 by the crosslinking agent, 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 preferably contains a liquid polymer. By adding a liquid polymer in this way, the viscosity of the sealant composition can be increased and the sealing properties can be improved. The amount of liquid polymer is preferably 50 to 400 parts by mass, more preferably 70 to 200 parts by mass, and even more preferably 80 to 200 parts by mass, per 100 parts by mass of the rubber component described above. If the amount of liquid polymer is less than 50 parts by mass, the effect of increasing the viscosity of the sealant composition may not be sufficiently obtained. If the amount of liquid polymer is more than 400 parts by mass, the flow of the sealant cannot be sufficiently prevented. Furthermore, within the above-mentioned range, the greater the amount of liquid polymer blended, the lower the viscosity at 0°C tends to be, and the smaller the amount blended, the higher the viscosity at 0°C tends to be. Therefore, setting the blend amount of liquid polymer blended within the above-mentioned more preferred range (70 parts by mass to 200 parts by mass) or even more preferred range (80 parts by mass to 200 parts by mass) is effective for setting the viscosity (particularly the viscosity at 0°C) within the appropriate range specified in the present invention.

The liquid polymer is preferably capable of co-crosslinking with the rubber component (butyl rubber) in the sealant composition, and examples thereof include paraffin oil, polybutene oil, polyisoprene oil, polybutadiene oil, polyisobutene oil, aromatic oil, polypropylene glycol, etc. From the viewpoint of suppressing the temperature dependency of the physical properties of the sealant composition to a low temperature 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 at each of the above-mentioned temperatures to an appropriate range. Specifically, within the above-mentioned range, the viscosity at 0°C tends to decrease as the blending amount of paraffin oil increases, and the viscosity at 0°C tends to increase as the blending amount of paraffin oil decreases. Therefore, adopting paraffin oil as the liquid polymer is effective in setting the viscosity (particularly the viscosity at 0°C) to an appropriate range specified in the present invention. In addition, 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 polymer with such a high molecular weight, it is possible to prevent oil from migrating from the sealant layer on the inner surface of the tire to the tire body and affecting the tire.

The sealant composition having the above-mentioned composition contains at least butyl-based rubber, which gives the rubber component a moderately high viscosity, while the crosslinking agent and organic peroxide are used in combination to crosslink the rubber component, which ensures sufficient viscosity to obtain good sealing properties and moderate elasticity that does not flow during driving, thereby achieving a good balance between these performances. Furthermore, the above-mentioned rubber component (amount of butyl-based rubber or chlorinated butyl rubber), the amount of crosslinking agent and organic peroxide, and the effect on viscosity due to the amount of liquid polymer (the above-mentioned viscosity tendency) work together to adjust the viscosity at low temperature (0°C), medium temperature condition (40°C), and high temperature (80°C) to the appropriate range specified in the present invention. In particular, when an appropriate amount of paraffin oil is added as the liquid polymer, the viscosity at low temperature (0°C), medium temperature condition (40°C), and high temperature (80°C) can be efficiently adjusted to the appropriate range specified in the present invention. Therefore, it can be suitably used for the sealant layer 10 (sealant material) of self-sealing type pneumatic tires, and while fully demonstrating the basic performance of a sealant material (combining flow suppression during driving with good sealing properties), it also exhibits good sealing properties even in low temperature environments, and can effectively suppress the flow of the sealant material during storage.

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.

In a pneumatic tire having a tire size of 255/40R20 and the basic structure shown in FIG. 1 , which has a sealant layer made of a sealant on the tire radially inside of the inner liner layer in the tread portion, tires of Comparative Examples 1 to 3 and Examples 1 to 34 were manufactured in which the formulation and physical properties of the sealant material composition constituting the sealant layer were set as shown in Tables 1 to 4 (Note that Examples 5 to 7 which do not contain a crosslinking aid and do not satisfy the viscosity conditions are reference examples) .

The viscosity was measured by creating samples of 25 mm diameter and 1.5 mm thickness using the sealant composition used in each tire, and measuring the viscosity using a rotational rheometer at a deformation of 0.1%, a frequency of 1 Hz, and at the specified temperature conditions (0°C, 40°C, 80°C).

These test tires were evaluated for their sealing ability in low temperature environments ("Sealability (-20°C)" in the table), storage properties, and fluidity during driving using the following test methods, and the results are shown in Tables 1 and 2.

Sealing property in low temperature environment Each test tire was cooled for 24 hours under a temperature condition of -20°C, then assembled to a wheel with a rim size of 20x9J and mounted on a test vehicle, and a nail with a diameter of 4.0 mm was driven into the tread portion under conditions of an initial air pressure of 250 kPa, a load of 8.5 kN, and a temperature of -20°C. The nail was then removed and the tire was left to stand in a -20°C environment for 1 hour, after which the air pressure was measured. The evaluation results were shown on a 5-point scale as follows. A score of "2" or more in the evaluation result indicates sufficient sealing property, and a higher score indicates a better sealing property.
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

Storage properties: Test tires were stored in a constant temperature room at 70°C for 70 days, and the flow state of the sealant after storage was examined. The evaluation results were obtained by drawing 20 x 40 squares of 5 mm grid lines on the surface of the sealant layer before storage, and counting the number of squares whose shape was distorted after storage. If no flow of the sealant was observed (the number of distorted squares was 0), it was indicated with "○", if the number of distorted squares was less than 1/4 of the total, it was indicated with "△", and if the number of distorted squares was 1/4 or more of the total, it was indicated with "X".

The test tire was mounted on a wheel with a rim size of 20x9J and mounted on a drum test machine, and the tire was driven for 1 hour under the conditions of an air pressure of 220kPa, a load of 8.5kN, and a running speed of 80km/h, and the flow state of the sealant after the run was examined. The evaluation results were obtained by drawing 20x40 squares of 5mm grid lines on the surface of the sealant layer before the run, and counting the number of squares whose shape was distorted after the run. If no flow of the sealant was observed (the number of distorted squares was 0), it was indicated by "○", if the number of distorted squares was less than 1/4 of the total, it was indicated by "△", and if the number of distorted squares was 1/4 or more of the total, it was indicated by "X".

The types of raw materials used in Tables 1 to 4 are shown below.
Butyl rubber 1: Chlorinated butyl rubber, CHLOROBUTYL1066 manufactured by JSR Corporation
Butyl rubber 2: Brominated butyl rubber, BROMOBUTYL2222 manufactured by JSR Corporation
Natural rubber: Natural rubber manufactured by SRI TRANG Organic peroxide: Dibenzoyl peroxide, Niper NS manufactured by NOF Corporation (1 minute half-life temperature: 133°C)
Crosslinking agent 1: sulfur, small lump sulfur manufactured by Hosoi Chemical Industry Co., Ltd. Crosslinking agent 2: cyclic sulfide, Valnoc R manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking agent 3: quinone dioxime, Valnoc GM manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking aid 1: Thiazole-based vulcanization accelerator, Noccela MZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking aid 2: Thiuram-based vulcanization accelerator, Noccela DM-PO manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Liquid polymer 1: Paraffin oil, Kaneda Hicol K-350 (molecular weight: 850)
Liquid polymer 2: Paraffin oil, Idemitsu Kosan Diana Process PW-380 (molecular weight: 1400)
Liquid polymer 3: Polybutene oil, JXTG Nippon Oil & Energy Corporation's Nippon Oil Polybutene HV-15 (molecular weight: 1300)

As is clear from Tables 1 to 4, the pneumatic tires of Examples 1 to 34 exhibited good sealing properties in low-temperature environments, storage properties, and fluidity during driving, achieving a good balance between these performance properties. On the other hand, Comparative Example 1 had poor sealing properties because the viscosity at 0°C was too high. Comparative Example 2 had poor storage properties because the viscosity at 40°C was too high. Comparative Example 3 had poor viscosity at 80°C, resulting in poor sealant fluidity.

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 (9)

A sealant material composition constituting a sealant layer disposed on the inner surface of a pneumatic tire, the sealant material composition comprising 40 to 450 parts by mass of paraffin oil, 1 to 45 parts by mass of an organic peroxide, 0.1 to 40 parts by mass of a crosslinking agent containing a sulfur component, and more than 0 to less than 1 part by mass of a crosslinking aid, relative to 100 parts by mass of a rubber component, the sealant material composition having a viscosity _V0°C of 2 kPa·s to 15 kPa·s, a viscosity _V40°C of 1 kPa·s to 14 kPa·s, and a viscosity V80 _°C of 0.6 kPa·s to 10.8 kPa·s at _{80 °C} , and a ratio V0 _°C /V40 °C of the viscosity V0°C to the viscosity _V40°C of 1.0 to 3.0 . 2. The sealant material composition according to claim 1, wherein the ratio V0 _°C /V80°C of the viscosity at 0°C to the viscosity at _{80°C , V80°C} , is 10 or less. 3. The sealant material composition according to claim 1, wherein the paraffin oil is blended in an amount of 50 to 400 parts by mass with respect to 100 parts by mass of the rubber component. The sealant composition according to any one of claims 1 to 3 , characterized in that the paraffin oil has a molecular weight of 800 or more. 5. The sealant composition according to claim 1 , wherein the amount of the crosslinking auxiliary is 50% by mass to 400% by mass of the amount of the crosslinking agent. 6. The sealant composition according to claim 1 , wherein the crosslinking aid is a thiazole compound or a thiuram compound. 7. The sealant material composition according to claim 1 , wherein the rubber component contains butyl rubber, and the amount of the butyl rubber is 10% by mass or more relative to 100% by mass of the rubber component. 8. The sealant material composition according to claim 7 , wherein the butyl rubber comprises a chlorinated butyl rubber, and the amount of the chlorinated butyl rubber is 5% by mass or more relative to 100% by mass of the rubber component. A pneumatic tire comprising a sealant layer made of the sealant material composition according to any one of claims 1 to 8 .

Images