RUBBER CEMENT WITH SUPERCONDUCTIVE BLACK FOR ELECTRICAL CONDUCTIVITY OF PNEUMATIC TYRE

FIELD OF THE INVENTION:

The present invention relates to solvent based curable rubber cement formulation for application on tyres with high silica tread compound to effectively discharge static electricity charge generated on the vehicle/tyre to the road. The formulations described in the present invention overcomes the problems associated with non-conductivity of silica based formulations by improving the conductive performance of the tyre. Also disclosed in the instant invention is a process of preparing such a formulation.

BACKGROUND OF THE INVENTION:

Tread cap compound with high silica as filler was developed for passenger car radial for reducing the rolling resistance of the tyre. However, as silica is a poor conductor of electricity compared to the normally used carbon black filler, these tyres had a problem with the conduction of static electric charge generated on the vehicle/tyre to the road.

Generally the components from bead area which is in contact with metal rim upto wing-tip of the tyre have electrical conductivity, but the tread cap component which comes in contact with road doesn't have much electrical conductivity as illustrated in Figure 1.

The accumulation of static electric charge in moving vehicles could have an adverse effect on electronic circuitry and may also pose a safety hazard if a spark discharge occurs during re-fuelling. The charge is generally conducted to the earth through tyres which require that the tyre themselves have a suitable level of conductivity normally described as anti-static. Such levels of conductivity are normally assured by employing tyre compounds containing significant proportions of carbon black as reinforcing filler. However, this could impact the rolling resistance and fuel consumption of the tyre.

To overcome those problems, various techniques of ensuring conductivity of a tire by providing a conductive member having mixed therewith carbon black on a part of a tread structure have conventionally been proposed. For example JP-A-2002-1834 (kokai) proposes forming a conductive thin film containing carbon black on an outer surface of a tread and a side wall by applying a conductive liquid rubber paste composition to an area of from the vicinity of the part corresponding to the ground end of a tread of a green tyre to the part corresponding to a buttress, vulcanizing and molding, thereby covering the entire groove surface of transverse grooves at a tyre shoulder.

EP0819741 discloses a method of forming a continuous coating film by applying a rubber cement obtained by dissolving and uniformly dispersing a rubber composition comprising 100 parts by weight of a diene rubber and from 40 to 100 parts by weight of carbon black having an N2SA of 130 m2/g or more and a DBP absorption of 110 ml/100 g or more in an organic solvent, to an outer surface of a tire tread cap rubber having an intrinsic resistance value of 108 Q.cm or more and a part of at least one member adjacent to the outer surface.

However, the techniques described in the above references are still manifest with disadvantages such as higher dosage of carbon black, thereby the rubber composition generates more hysteresis, less process friendly , environmental friendly and not being able to maintain good electrical conductivity for a long period / in usage .

The present inventors have endeavored to develop a solvent based curable rubber cement formulation that employs effective amounts of super conductive carbon black which affords good conductivity without adversely affecting tyre rolling resistance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an effective rubber cement formulation with super conductive black for grounding the static electricity generated on the vehicle or tyre.

The formulation according to the aspect of the present invention comprises a rubber cement composition, said rubber cement being applied to an outer surface of a tyre from wing-tip ending to center of tread on one side of the tyre (as shown in figure 1) to form a coating film of the rubber cement wherein the formulation comprises 100 parts by weight of a rubber component containing super conductive carbon black from 5 to 20 parts by weight and other ingredients such as antioxidants, activators, curatives and process oil, the ingredients dissolved in an organic solvent. Another object of the present invention is related to the process of preparing the same.

According to an advantageous aspect of the present invention, tire performance such as rolling resistance or wet performance of a tire by silica formulation are maintained, and additionally conductive performance of a tire is improved by the subject composition and the improved performance of the tyre is sustained over a long period of time.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, because various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION OF FIGURES

The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. In the drawings: Figure 1: Illustration of various parts of the tyre and showing less conductive tread cap.

Figure 2: Depiction of parts of the tyre painted with rubber cement composition of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein.

As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual components, substituents, and ranges are for illustration only; they do not exclude other defined values or other values within defined ranges for the components and substituents.

As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.

"Optional" or "Optionally" means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it need not occur.

The terms "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

When the term "about" is used in describing a value or an endpoint of a range, the disclosure should be understood to include both the specific value or end-point referred to.

As used herein the terms "comprises", "comprising", "includes", "including", "containing", "characterized by", "having" or any other variation thereof, are intended to cover a non-exclusive inclusion.

The term "on", when used in the context of a coating applied on a surface or substrate, includes both coatings applied directly or indirectly to the surface or substrate.

The present invention relates to a solvent curable rubber cement composition comprising natural rubber or synthetic rubber (SBR), super conductive black with or without N-330 carbon black, PF resin and other ingredients such as antioxidants, activators, curatives and process oil.

The objective of the present invention is to develop a solvent based curable rubber cement formulation that employs effective amounts of extra conductive carbon black which affords good conductivity without adversely affecting tyre rolling resistance.

Accordingly, the present invention provides for a solvent based curable rubber cement
with high electrical conductivity which can be applied on tyre having high silica tread compound so that the conduction of static electric charge occurs from wing-tip to the road contact area of tread.

An important aspect of the present invention is the utilization of effective quantities of one or more super conductive carbon blacks to impart conductivity to the composition and especially the tire tread composition which is further described herein below. A superconductive carbon black can be defined as carbon black having BET-surface area of at least 500, generally at least 600, desirably at least 750 or 900, and preferably at least 1,000 and even 1,200 square meters per gram. It is noted that super conductive carbon black generally exists as particles with porous structure. Preferably, the present invention employs superconductive black and N-330 carbon black.

The amount of super conductive carbon black is preferably incorporated in the amount of about 5-50 parts by weight per 100 parts by weight of rubber, more preferably from about 10 to about 20 parts by weight for every 100 parts by weight of all rubber compounds and most preferably from about 5 parts to about 15 parts by weight for every 100 parts by weight of all rubber utilized within the rubber cement composition.

A rubber compound with superconductive black (Iodine adsorption range 1025-1625mg/g) was mixed in laboratory with different dosages and in combination with commonly used N-330 (Iodine adsorption range 77-87mg/g) carbon black grade.

The rubber compound broadly comprises the following formulation with the ranges of each component as tabulated below.

Table 1 - Rubber compound formulation

The above mixed rubber compound is made into cement in the proportion given as in the table 2 by continuously stirring rubber compound pieces in a suitable organic solvent.

Solvents preferably used and described herein inert aprotic solvents, e.g. Toluene, paraffinic hexanes, heptanes, octanes, decanes, cyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane or 1,4-dimethylcyclohexane and the like. These solvents can be used individually or in combination. Preference is given to hexane.

Table 2 - Conductive cement formulation

According to one advantageous aspect of the present invention, the rubber cement formulation is preferably based on natural rubber which affords good tack and better stability of cement film on green tyre. Synthetic rubber imparts better fatigue properties to the rubber compound and better compatibility with tread rubber on which the cement is applied as the tread rubber generally contains more synthetic rubber.

The present invention employs naphthenic oil that helps in the flexibility of the film and renders the mixing easier. Naphthenic oil is employed instead of aromatic oil which is low in PAH [Polycyclic aromatic Hydrocarbon] and hence is environmental friendly and compliant to environmental regulations.

The amount of naphthenic oil or TDAE oil is preferably incorporated in the amount of about 1-20 parts by weight per 100 parts by weight of rubber, more preferably from about 3 to about 15 parts by weight for every 100 parts by weight of all rubber compounds and most preferably from about 3 parts to about 10 parts by weight for every 100 parts by weight of all rubber utilized within the rubber cement composition.

The rubber compound mixtures can comprise other auxiliaries, such as known reaction accelerators, antioxidants, light stabilizers, antiozonants, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, retarders, metal oxides and activators.

The PF resin incorporated in the rubber compound mixture is preferably incorporated in the amount of about 1-5 parts by weight per 100 parts by weight of rubber, more preferably from about 3 to about 5 parts by weight for every 100 parts by weight of all rubber compounds and most preferably from about 1.5 parts to about 3.5 parts by weight for every 100 parts by weight of all rubber utilized within the rubber cement composition.

Other alternative resins include but is not limited to Koresin (tradename), Cumarone Indene resin and the like.

In accordance to one of the alternate embodiments of the present invention the component N-330 carbon black is present in the rubber compound mixture in an amount of upto 50 weight percent, or in some cases upto 40 weight percent, or in some cases 30 weight percent with the weight percent being considered based on the total weight of rubber. Alternatively, N-330 could be replaced with N-100 or N-200 series of carbon black.

The solvent curable rubber cement compositions of the present invention can be utilized for any tire application wherein it is desirable to discharge static electricity charge or accumulation, both with regard to the tire and to the vehicle. Suitable tire applications include passenger vehicles, off-the-road vehicles, agricultural vehicles, light trucks, trucks and buses, and high performance vehicles. Another advantage is that the conductivity is maintained due to presence of cured layer of conductive cement on the sides of the tread grooves.

The invention is further illustrated in the Examples section which follows. This section is set forth to aid in an understanding of the invention but is not intended to, and should not be construed to, limit in any way the invention as set forth in the claims which follow thereafter.

EXAMPLE 1

This illustrates embodiments of the rubber compound composition of the present invention. Formulation 1 tabulated in Table 4 is an embodiment of rubber compound composition of one of the rubber cements of the present invention. The formulation is in accordance with the representative composition of rubber compound in Table 3.

STEP 1:

The rubber compound mixture was prepared in a two-roll mill which is a machinery traditionally used for mixing rubber compounds. The invention employs a two step mixing in two roll mill (1) master batch mixing of ingredients as per the formulation except sulphur & TBBS (2) Master batch from previous step mixed with sulphur & TBBS. The rubber compound was then sheeted out in 5mm at the end of second step in two roll mill.

Table 3 - Representative Composition for Rubber Compound

STEP 2:

The mixed rubber compound obtained from Step 1 is made into a cement by continuously stirring rubber compound pieces in hexane solvent. The weight percentage of the rubber compound in the cement is about 10-15%.

STEP 3:

Tyre application - The prepared rubber cement composition was painted on un-vulcanized tyre before curing. The painted area included a 3 inch wide brush stroke from side wall ending to centre of tread width on one side of tyre as depicted in Figure
2.

Number of brush strokes : One Number of painted strips per tyre: Two

STEP 4:

The electrical resistance of the tyre was tested. The tyre mounted on a rim was vertically loaded on a copper plate resting on an insulated bed plate and electrical resistance between the central portion of a rim and the copper plate was measured at six portions on the circumference of the tyre using a resistance measuring instrument with a maximum capacity of 1000V. The resistance of the tyre was found to be 3.7 x 107Q. The tyre after running on the field for 100 kms demonstrated a resistance of 1 x
io8a

TABLE - 4 Cement compound formulations

TABLE - 5 - Evaluation of physical properties of rubber compounds of cement & cement solutions

Inferences drawn:

As illustrated in Table 5 above the composition of the present invention demonstrates the appropriate modulus (not high) and elongation at break (not being low). Therefore, illustrated composition of the instant invention displays good flexibility and stability of the coating without breakage.

The storage modulus is in line with that of tread compound over which the coating is applied- Therefore, there is better compatibility of the coated film.

Fatigue to failure life - Higher the better for durability - Cement 4 and 5 demonstrate excellent durability.

Cement 4 and 5 also establish excellent electrical conductivity values.

A person skilled in the art will be able to practice the present invention in view of the description presented in this document, which is to be taken as a whole. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, one of skill in the art will appreciate that certain changes and modifications may be practiced within the scope of the appended claims.

Numerous details and examples have been set forth in order to provide a more thorough understanding of the invention. While the invention has been disclosed in its preferred form, the specific embodiments and examples thereof as disclosed and illustrated herein are not to be considered in a limiting sense. It should be readily apparent to those skilled in the art in view of the present description that the invention can be modified in numerous ways. The inventor regards the subject matter of the invention to include all combinations and sub-combinations of the various elements, features, functions and/or properties disclosed herein.

We claim:

1. A rubber compound mixture composition comprising

(a) 100 parts by weight of natural rubber or synthetic rubber

(b) 5-15 parts by weight of super conductive black per 100 parts by weight of said rubber,

(c) 16-20 parts by weight of auxiliary agent per 100 parts by weight of said rubber.

2. A rubber compound mixture as claimed in claim 1, wherein the conventional carbon black is selected from the group comprising N-330, N-100 and N-200 series of carbon black.

3. A rubber compound mixture as claimed in claim 1, wherein the auxiliary agent is an antioxidant.

4. A rubber compound mixture as claimed in claim 3, wherein the antioxidant is 6PPD, IPPD or TMQ.

5. A rubber compound mixture as claimed in claim 4, wherein the antioxidant is employed in the range of about 1.0 - 3.0 parts by weight per 100 parts by weight of said
rubber.

6. A rubber compound mixture as claimed in claim 1, comprising a resin selected from the group comprising PF resin, Koresin and Cumarone Indene resin.

7. A rubber compound mixture as claimed in claim 6, wherein the resin is employed in the range of about 1.5 - 3.5 parts by weight per 100 parts by weight of said rubber.

8. A rubber compound mixture as claimed in claim 1, comprising the auxiliary agent is stearic acid employed in the range of about 0.3 - 1.0 parts by weight per 100 parts by weight of said rubber.

9. A rubber compound mixture as claimed in claim 1, comprising the auxiliary agent is zinc oxide employed in the range of about 3.0-5.0 parts by weight per 100 parts by weight of said rubber.

10. A rubber compound mixture as claimed in claim 1, comprising the auxiliary agent is naphthalene oil or TDAE oil employed in the range of about 3.0 - 6.0 parts by weight per 100 parts by weight of said rubber.

11. A rubber compound mixture as claimed in claim 1, comprising sulphur in the range of about 1.5-2.5 parts by weight per 100 parts by weight of said rubber.

12. A rubber compound mixture as claimed in claim 1, comprising TBBS in the range of about 0.8 - 1.3 parts by weight per 100 parts by weight of said rubber.

13. A rubber cement mixture comprising a rubber compound as claimed in claims 1-12 made into a cement in an organic solvent.

14. A rubber cement mixture as claimed in claim 13, wherein the solvent is hexane.

15.A rubber cement mixture as claimed in claim 13, wherein the weight percentage of the rubber compound is 10-15%.

16. A rubber cement mixture as claimed in claim 13, wherein the weight percentage of the solvent is 85-90%.

17. A rubber cement mixture as claimed in claims 13-17 having a resistance of 3.7 x 107Q.

18. A method of applying the rubber cement composition as claimed in claims 13-16, wherein the composition is applied from wing-tip ending to centre of tread on one side of the tyre.

19. A process for preparing a rubber compound mixture comprising the following steps:

(a) Mixing the ingredients as per the formulation of claim 1 excluding the
components sulphur and TBBS ;

(b) The resultant mixture of step (a) is mixed with sulphur and TBBS;

(c) The rubber compound obtained from step (b) is sheeted out in a roll-mill.

20. The process as claimed in claim 19, wherein the rubber compound mixture is made into a cement by stirring the rubber compound in an organic solvent.