JPH1081783A - Antistatic rubber cement and pneumatic tire coated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber cement having high leaving stability and giving an excellent effect to the antistatic effect of a low fuel cost pneumatic tire having a low conductive tread, and to provide a pneumatic tire coated with the rubber cement. SOLUTION: This rubber cement is produced by homogeneously dissolving and dispersing a rubber composition containing 100 pts.wt. of a dienic rubber and 40-100 pts.wt. of carbon black having a nitrogen-adsorbing specific surface area (N2 SA) of >=130m<2> /g and a dibutyl phthalate oil-adsorbing amount (DBP) of >=110ml/100g in an organic solvent. The rubber cement preferably has an intrinsic resistance of <=10<6> Ω.cm after vulcanized. The rubber cement is coated on the outer surface of a tire tread can rubber having an intrinsic resistance of >=10<8> Ω.cm and on an part of at least one member adjacent to the outer surface to obtain the pneumatic tire on which the continuous coating film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an antistatic rubber cement and a pneumatic tire coated with the same.
More specifically, a rubber cement for preventing electrification of a pneumatic tire having a low conductive tread, in which a filler such as silica is incorporated in a large amount to improve fuel efficiency, and a pneumatic tire coated with the rubber cement About.

[0002]

2. Description of the Related Art Tires having excellent fuel efficiency, particularly tires provided with a silica-containing tread, have a high electric resistance value.
Since the conductivity is low, static electricity generated in the vehicle body and tires is hardly dissipated to the ground surface through the tread, so that there has been a problem of radio noise, electric shock, spark and the like.

As a method for solving such a problem, the following methods have been mainly known. One of them is to use a tread rubber mixed with carbon black having excellent conductivity, which is different from carbon black usually used in tires.

Another method is to coat a tread surface with a conductive substance, for example, cement in which conductive carbon black is mixed with a water-based rubber composition at the time of extruding the tread during tire production. (For example, see Japanese Patent Application Laid-Open No. 8-120120). According to this method, even when the product tire after tire vulcanization is mounted on a passenger car and the tread portion is worn, the conductive coating material remains on the sidewalls of many grooves carved as a pattern of the tread portion. Thereby, the static electricity charged on the entire tire can be dissipated to the road surface.

[0005] Still another method is to sandwich a thin conductive rubber sheet from the tread shoulder to the inside of the side instead of using cement as described above (for example, see US Pat. No. 5,518,055).

[0006]

However, each of the above methods has problems in manufacturing and quality as described below, and has not always been sufficiently satisfactory. For example, when several parts by weight of conductive carbon black is added to 100 parts by weight of a rubber component, the specific resistance value of the tread rubber decreases,
Fuel efficiency, which is the original purpose of the tire, deteriorates remarkably,
Further, the carbon black itself has a remarkably low reinforcing property with the polymer, and as a result, there is a problem that the wear resistance of the tire tread is reduced.

Further, the method of coating a water-based cement containing conductive carbon black on the rubber surface of the cap layer has a problem with the standing stability of the cement itself, and may cause phase separation. In order to prevent foaming at the time, various stabilizers are required,
They reduce the durability of the rubber composition on the film after vulcanization and cause mold contamination during vulcanization.
Furthermore, the rubber composition of the cap layer is hydrophobic, and it takes a long time to dry when applying the above-mentioned water-based cement, and also causes uneven coating, resulting in poor durability of the coated film. Furthermore, at the time of vulcanization, the interfacial adhesive strength between the rubber of the cap layer and the rubber coated with the water-based cement decreases,
There is a problem that interfacial peeling occurs during traveling, and the energization path is cut off at the end of traveling, so that an antistatic effect cannot be obtained.

Further, when a conductive rubber sheet having a thickness of 1 mm to 200 μm as disclosed in the above-mentioned US Pat. No. 5,518,055 is inserted from the tread shoulder to the inside of the side, the durability until the end of running is considered. ,
A peeling phenomenon due to a difference in elastic modulus from the cap rubber is likely to occur, and it becomes difficult to stably maintain a low electric resistance value as a tire until the end of traveling. In addition, in particular, with the improvement of the wear resistance of the tread cap by the silica-containing rubber composition, in order to maintain such an effect until the end of traveling, the wear resistance of the conductive rubber sheet or the conductive coating film is the same as that of the tread cap rubber. Similarly, if not improved, abrasion of the conductive rubber sheet or the conductive coating film is promoted by running, only the cap rubber is grounded, and the conduction path is cut off, and as a result, the antistatic effect is not obtained. become.

Accordingly, an object of the present invention is to provide a fuel-efficient pneumatic tire having a low conductivity tread in which a filler such as silica is blended in a large amount, has an excellent antistatic effect, and has a high storage stability. An object of the present invention is to provide a rubber cement having properties and a pneumatic tire coated with the rubber cement.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, a rubber cement in which a rubber composition containing a specific carbon black is dissolved and uniformly dispersed in an organic solvent, The present inventors have found that the object can be achieved by applying a predetermined portion of a fuel-efficient pneumatic tire having a low-conductive tread to form a continuous film, thereby completing the present invention.

That is, the present invention provides a diene rubber 100
The nitrogen adsorption specific surface area (N ₂ SA) is 130 parts by weight.
m ² / g or more and dibutyl phthalate oil absorption (DB
A rubber cement characterized in that a rubber composition containing 40 to 100 parts by weight of carbon black having P) of 110 ml / 100 g or more is dissolved and uniformly dispersed in an organic solvent.

The specific resistance value of the rubber cement after sulfur curing is preferably 10 ⁶ Ω · cm or less.

Further, the present invention provides the rubber cement according to the present invention, wherein the rubber cement has an outer surface of a tire tread cap rubber having a specific resistance of 10 ⁸ Ω · cm or more and a part of at least one member adjacent to the outer surface. A pneumatic tire characterized by being applied to form a continuous film.

The member adjacent to the outer surface of the cap is preferably a wing or a sidewall.

The thickness of the continuous coating after vulcanization is preferably 20 to 60 μm.

The pneumatic tire of the present invention has an electric resistance of the tire, that is, an electric resistance between the rim and the ground surface of 10 ⁷ Ω.
It is preferable to be as follows.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The diene rubber used in the rubber cement of the present invention is styrene butadiene rubber (SBR),
It is preferred from the viewpoint of durability that at least one of butadiene rubber (BR) and natural rubber (NR) is included.

The rubber cement of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of at least 130 m ² / g and a dibutyl phthalate oil absorption (DBP) of 110 ml / 10 g.
Use 0 g or more of carbon black. In the rubber cement of the present invention, by using the carbon black having such a small particle size and a high structure, the durability of the coating film forming the current path can be improved, and the antistatic effect can be exerted until the end of running of the tire. To do. Where N ₂ SA
Is ASTM D3037-89 and DBP is AST
These values are obtained in accordance with MD2414-90, respectively.

When the compounding amount of the carbon black is less than 40 parts by weight based on 100 parts by weight of the diene rubber, the reinforcing property is not sufficient. On the other hand, when the amount exceeds 100 parts by weight, when the softening agent is small, it becomes hard after vulcanization. Overheating, cracking, etc., and when the amount of the softening agent is large, abrasion resistance decreases. As the compounding agent other than carbon black, compounding agents usually used in rubber products, for example, vulcanizing agents, vulcanization accelerators, vulcanization accelerating assistants, softeners, antioxidants, etc. It is appropriately blended.

In the rubber cement of the present invention, the rubber cement is obtained based on an organic solvent instead of using water as a solvent. The organic solvent is a good solvent capable of dissolving the above-mentioned polymer, preferably one having a boiling point not exceeding 100 ° C., for example, hexane, petroleum ether, heptane, tetrahydrofuran (TH
F), cyclohexane and the like, and preferably hexane. Such a rubber cement can be obtained by dissolving a rubber composition kneaded with a Banbury or a roll in an organic solvent and uniformly dispersing the same. When the rubber cement thus obtained is dried and cured with sulfur, its specific resistance value is 1
It is preferably at most ⁶ Ω · cm. If this value is exceeded, the antistatic effect cannot be said to be sufficient.

Next, the pneumatic tire of the present invention will be specifically described. In the pneumatic tire of the present invention, the rubber cement has an outer surface of a tire tread cap rubber having a specific resistance of 10 ⁸ Ω · cm or more, and a part of at least one member adjacent to the outer surface, It is uniformly applied by a brush, a spray or the like to form a continuous film. Such adjacent members are preferably wings (mini side)
Or a sidewall. In addition, on the outer surface,
It also includes the tire contact portion on the side of the lug groove.

The thickness of the continuous coating after vulcanization is preferably 20 to 60 μm in consideration of durability up to the end of running.
It is. If the thickness exceeds 60 μm, a peeling phenomenon due to a difference in elastic modulus from the tread cap rubber tends to occur, and it becomes difficult to stably maintain a low electric resistance value as a tire until the end of running. On the other hand, if it is less than 20 μm, the formation of the energization path is not sufficient.

An example of the electric resistance value of the pneumatic tire of the present invention, that is, the electric resistance value from the rim to the ground surface will be specifically described with reference to FIG. When the rubber cement 5 is applied from the tread cap 1 to the wing (mini side) 2 of the pneumatic tire shown in FIG. 1, even if the specific resistance value of the cap rubber is as high as 10 ¹¹ Ω · cm,
The specific resistance of the rubber cement is 10 ⁵ Ω · cm, the specific resistance of the mini side is 10 ⁶ Ω · cm, the specific resistance of the sidewall is 10 ⁶ Ω · cm, and the specific resistance of the rubber chafer is 10 ^5. When the resistance is Ω · cm, an energization path is formed between the ground surface, the cement on the cap, the mini-side, the side wall, the rubber chafer, the rim, and the rim via the conductive film formed by coating, and the specific resistance value of the cap rubber is formed. Irrespective of this, a low electric resistance value can be maintained as a tire. Incidentally, even in a pneumatic tire having no mini-side, a similar energization path is formed between the cap and the sidewall, and the same effect is obtained. In the pneumatic tire of the present invention, it is preferable that the electric resistance between the rim and the ground based on the current path formed in this way be 10 ⁷ Ω or less, in order to prevent charging properly.

[0024]

The present invention will be specifically described below based on examples and comparative examples. Tread cap rubbers for pneumatic tires and various rubber cements A to C were respectively prepared according to the compounding recipes shown in Tables 1 to 3 below.

(Table 1) Cap rubber styrene butadiene rubber ^* 196 (parts by weight) Butadiene rubber ^{* 2} 30 SiO ₂ ^* 360 Carbon black (N234) ^{* 4} 20 Silane coupling agent ^* 56 ZnO 3 Stearic acid 2 Aroma Oil 10 Vulcanization accelerator (CBS) ^{* 6} 1.5 Vulcanization accelerator (DPG) ^{* 7} 2 Sulfur 1.5 * 1 SBR1712 manufactured by Nippon Synthetic Rubber Co., Ltd. * 2 96% cis bond * 3 Nipsil VN3 * 4 N ₂ SA: 126 m ² / g DBP: 125 ml / 100 g * 5 Si69 manufactured by DEGUSSA * 6 N-cyclohexyl-2-benzothiazylsulfenamide * 7 diphenylguanidine

(Table 2) Organic Cement (A) Organic Cement (B) Natural Rubber 40 (parts by weight) 40 Styrene butadiene rubber ^{* 8} 60 60 Carbon black (N134) ^* 960-Carbon black (N330) ^* 10-65 Aroma oil 15 15 ZnO 2 2 Antioxidant ^{* 11 11} Vulcanization accelerator (DPG) 0.2 0.2 Vulcanization accelerator (NS) ^{* 12} 0.8 0.8 Sulfur 1.5 1.5 Hexane 500 500 * 8 NBR SA manufactured by Nippon Synthetic Rubber Co., Ltd. * 9 N ₂ SA: 146 m ² / g DBP: 127 ml / 100 g * 10 N ₂ SA: 83 m ² / g DBP: 102 ml / 100 g * 11 N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine * 12 N-tert- Butyl-2-benzothiazolylsulfenamide

(Table 3) Water-based cement (C) Natural rubber Lux 100 ^{* 13} carbon black dispersion 100 ^{* 14} * 13 Carbon containing carbon black having a rubber content of about 60% by weight and a pH of about 11 * 14 20% by weight Black dispersion water

Each of the obtained rubber cements A to C was applied to two types of pneumatic tires of size 185 / 70R14 at locations shown in FIGS. 2A and 2B, respectively. The gauge of the conductive layer in the new tire after vulcanization formed by coating is as shown in Table 4 below.

The resistance value (electric resistance value) of these tires
Was determined as follows. That is, GERMAN AS
SOCIATION OF RUBBER INDUS
The measurement was performed as shown in FIG. 3 using a high resistance meter of model HP4339A manufactured by Hewlett Packard Co. based on TRY WdK 110 sheet 3. In the figure, 11 is a tire, 12 is a steel plate, 13 is an insulating plate, and 14 is the high resistance meter, which was measured by applying a current of 1000 V between the steel plate 12 on the insulating plate 13 and the rim of the tire 11.

The specific resistance of the cement (conductive layer) after sulfur hardening was determined as follows. That is, a disk-shaped sample was prepared, radius: r = 2.5 cm, thickness: t
The electric resistance value R at a portion of = 0.2 cm was measured using an insulation resistance test box manufactured by Advance Corporation shown in FIG. 4, and the specific resistance value ρ was calculated by the following equation. ρ = (a / t) R (where a is the cross-sectional area (= π × r ² ) and t is the thickness), where A is the main electrode, B is the counter electrode, C indicates the guard electrode, t indicates the thickness of the sample, and when new, 10,0.
The electric resistance values after running at 00 km and after running at 40,000 km are shown in Table 4 below.

(Table 4) In Comparative Examples 2 to 4, after traveling 10,000 km, on the tire circumference,
The variation of the value was extremely large depending on the measurement point, and the resistance value width of the four points measured on the circumference was displayed.

As can be seen from the above Table 4, the effect of lowering the electric resistance value of any rubber cement was observed when the rubber cement was new.

In Comparative Examples 2 and 3, a low electric resistance was maintained after running 10,000 km, although there was some variation regardless of the presence or absence of the mini-side of the tire. However, after traveling 40,000 km, the variation range of the electric resistance value on the circumference of the tire became large, and in some parts, it increased to 10 ¹⁰ Ω. This is because the energization path that existed around the entire circumference of the tire at the beginning of traveling,
At a certain grounding section, it was cut off, indicating that the rubber cement application effect had disappeared. That is, it shows that such a tire cannot maintain a constant low electric resistance value until the end of traveling.

In Comparative Example 4, Comparative Examples 2 and 3
The interruption of the current path is observed earlier than due to the loss of the gauge, but due to a decrease in interfacial adhesion between the water-based cement (C) and the tread cap.

On the other hand, in Example 1 and Example 2, regardless of the presence or absence of the mini side, 40,000 km
The electric resistance value of 10 ⁶ Ω was maintained even after running. This indicates that the energization path of the rubber cement is well maintained even at the end of traveling.

[0036]

As described above, the organic solvent-containing antistatic rubber cement of the present invention comprises:
When applied to a predetermined location of a fuel-efficient pneumatic tire having a low-conductivity silica-containing tread, the tire has an excellent antistatic effect until the end of traveling and has high standing stability. Therefore, the pneumatic tire of the present invention in which such a rubber cement is applied to a predetermined location has an excellent effect as an antistatic tire.

[Brief description of the drawings]

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

FIG. 2 is a partial cross-sectional view of the pneumatic tire showing an application position of rubber cement.

FIG. 3 is a schematic view of a tire electric resistance measuring device used in Examples.

FIG. 4 is an explanatory diagram showing a method of measuring an electric resistance value R of a sample rubber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tread cap 2 Wing (mini side) 3 Side wall 4 Rubber chefer 5 Rubber cement 11 Tire 12 Steel plate 13 Insulation plate 14 High resistance meter

Claims (7)

[Claims] 1. A nitrogen adsorption specific surface area (N ₂ SA) of at least 130 m ² / g and a dibutyl phthalate oil absorption (DBP) of 110 ml / 1 based on 100 parts by weight of a diene rubber.
A rubber cement characterized in that a rubber composition containing 40 to 100 parts by weight of carbon black of at least 00 g is dissolved and uniformly dispersed in an organic solvent. 2. The specific resistance value after curing with sulfur is 10 ⁶ Ω · c.
The rubber cement according to claim 1, which is not more than m. 3. An outer surface of a tire tread cap rubber having a specific resistance of 10 ⁸ Ω · cm or more, and a part of at least one member adjacent to the outer surface, wherein the rubber cement according to claim 1 or 2 is used. A pneumatic tire, wherein the pneumatic tire is applied to a tire to form a continuous film. 4. The pneumatic tire according to claim 3, wherein the member adjacent to the outer surface of the cap is a wing. 5. The pneumatic tire according to claim 3, wherein the member adjacent to the outer surface of the cap is a sidewall. 6. The thickness of the continuous coating after vulcanization is 20 to 6
The pneumatic tire according to any one of claims 3 to 5, which has a thickness of 0 µm. 7. The pneumatic tire according to claim 3, wherein an electric resistance value of the tire is 10 ⁷ Ω or less.