PROCESS FOR INCORPORATING ANTI-SKID GRANULES INTO TIRES

Abstract: Process for incorporating anti-skid granules into tires and the like, consisting in coating said granules with at least one coating adhesive, or ''primer'', selected from among such primers as Chemosil 211, Megum 3270, Chemosil X 1400 and still other primers having similar properties, in subsequently treating the so-coated granules with at least one covering adhesive, or ''cover-coat'', selected from among covering compositions such as Chemosil 221, Megum 100, Chemosil X 4400 and other similar compositions, in subsequently sieving the granules in order to separate them from one another and eliminating the clots, then in mixing the so-sorted granules into a compound of a raw, either natural or synthetic, rubber, or of a synthetic resin, and then in forming the pattern of the desired tire, and in curing it according to the techniques known from the prior art.

Description: Process for incorporating anti-skid granules into tires The present invention relates to a process for stably incorporating granules of high-hardness materials, substantially granules of ceramic type, into the tread of tires for motor vehicles and the like. It is known that several processes are already used in the art in order to coat with hi gh-fri ct i ona l-coeffi c i ent materials the tires for motor vehicles, in order to endow said tires with a particularly high resistance to skidding on wet, ice- covered or snow-covered roadbeds. The most widely used processes provide for hard bodies, as irregular polyhedral granules, to be incorporated inside a support and e last i c- retent i on matrix, such as natural or synthetic rubber, or a synthetic resin of epoxy type. The granules used are generally constituted by substances selected from among the carbides and/or nitrides and/or oxides of si licon, titanium, tungsten, aluminium, zirconium, boron, magnesium, chrome, mixtures of said substances and sti ll other ceramic or cermet materials, and the like. The techniques of incorporation of the granules provide for a compound of vulcanisable rubber, or epoxy resin, single-component or double-component polyurethane resin, or the like, to be formed; with granules having pre-established size being incorporated into said compound, in the preestabl i shed amount, by weight, before the end moulding and curing or cross linki ng. In some cases, the granules, before being charged to the rubber compound, are coated with a thin layer of an adhesive selected from among those adhesives which show a good compatibi lity and affinity with both the rubber and the granules. It was observed that the incorporation processes carried out according to the various techniques known from the prior art, whether using known adhesives, or not, do not secure the necessary stabi lity of the granules inside their seats, in particular when the so-treated tires undergo heavy stress conditions. In fact, owing to the continuous tensi le and compression stresses the tire undergoes, when it is squeezed against the roadbed and then relaxes, and, above all, when it is submitted to a braking, an acceleration, or when it travels along a road bend, the granules tend to leave their seat and to be thrown towards the outside, thus altering the outer surface of the tire, and consequently causing a dangerous reduction in tire surface grip. Therefore, a purpose of the present invention is to provide a process for incorporating granules of ceramic type into either natural or synthetic rubber, or into synthetic resins of epoxy type, of polyurethane type, and the like, in particular into the tread of tires in general, which is easy and simple to be practiced, and is such as to reduce the possible detaching of granules down to negligible percent values. A further purpose of the present invention is to provide a tire which comprises a tread provided with ceramic granules, by means of a process of incorporation of said ceramic granules, which is capable of giving said granules a reliable and long-lasting stability inside their rubber support under any stress conditions the tire may be submitted to, with the drawbacks and the serious dangers which the detaching of the granules may cause, being thus prevented. The present Applicant was able to observe that if the granules of ceramic type, having a suitable, properly selected average size, are previously coated with a coating constituted by compounds endowed with high covering and adhesive properties, which compounds are already known and used in order to bond various metals to either natural or synthetic rubber, or to several synthetic resins, during the end vulcan sation or crosslinking step, a reliable and long-lasting stabi lity of incorporation of the granules inside the tire tread is obtained, without any danger of expulsion of the same granules from their respective seats. The best results are obtained by preliminari ly coating the ceramic granules with a first layer of a coating adhesive, or "primer", which is constituted by organic polymers in solution with solid matter in dispersion in an organic solvent, and subsequently applying a second layer of coating material, or "cover-coat", constituted by a polymeric solution also dispersed in a solvent. The formulations of the coating compounds known from the prior art, which showed to be the most suitable for stably incorporating ceramic granules inside the treads of tires, are the following: for_t he_fjrst_coatjng_ layer, i.e., the_βrimer : the products known under the trade marks "CHEMOSIL 211" and "CHEMOSIL X 1400", available from HUGHSON Che. Co., U.S.A.; "MEGUM 3270" avai lable from the German Company Chemetall G.m.b.H.; "THIXON P10", or "THIXON P6-1", available from the Company WHITTAKER; and "ANCHOR TP/6", avai lable from the Company ANCHOR Che. Ltd. of London; and, or_t he_secgnd_ layer_ ( the_coyerjng iiϊ§£2 / ϊ • e • r the coyer * ;cgat : the adhesive products known under the trade marks "CHEMOSIL 221", "CHEMOSIL X 4400", "MEGUM 100" or "MEGUM 500", "THIXON 520", "THIXON OSN-2" and "ANCHOR PT/5", available from the same companies as hereinabove cited. In order to achieve the above stated purposes and advantages, the present invention provides a process for stably incorporating granules of ceramic type, such as corundum, carbides, nitrides, borides and oxides of various metals and/or mixtures thereof, into the tread of tires, and the like, which process consists in treating the ceramic granules inside a tumbling barrel, or a similar mixer, with at least one primer selected from among CHEMOSIL 211, CHEMOSIL X 1400, MEGUM 3270, THIXON P10, THIXON P6-1, ANCHOR TP/6 and similar t*pes, so as to form on said granules a first coating layer, with the thickness of said coating layer being preestabli shed as a function of the weight and of the chemical and physical characteristics of the adhesive used, and in subsequently treating the so-coated granules with at least one cover- coat selected from among CHEMOSIL 221, CHEMOSIL X 4400, MEGUM 100, MEGUM 500, THIXON 520, THIXON OSN-2 and ANCHOR TP/5 or the like, so as to form above said first layer a second covering layer, in subsequently sieving the so- treated granules in order to separate them from one another, and to eliminate clots, then in blending the sieved granules with compounds of raw, either natural or synthetic rubber, or of a synthetic resin, containing all of the necessary fillers and sulphur and/or suitable crosslinking agents (the "compound"), and finally in forming with said rubber or resin compound containing said granules, the pattern of the tread, and in curing or crosslinking it according to the traditional methods. Still according to the invention, the thickness of the first primer layer, once dried, should be comprised, according to the type, the weight and the size of the product, at least within the range of from 5 to 40 microns, preferably of from 10 to 20 microns, and the thickness of the covering layer (i.e., the "cover-coat"), should be comprised at least within the range of from 5 to 60 microns, preferably of from 20 to 40 microns. The preferred ratio of the volume of the coated granules to the volume of the rubber compound should be substantially comprised within the range of from 10 to 15J. by volume, in order to reduce, i .e., to cause the elasticity of the rubber to absorb, the high tensi le stresses the granules would be submitted to, in case they were placed too near to one other; this would occur in case the granule ratios by volume were higher than about 20-25J.. In some cases, said first primer layer can be replaced by a layer, having the same thickness, which is constituted by the same material as of the second cover-coat layer, or even by another material, of different type, sti ll selected from among the group consisting of the cover-coat covering materi a Is. The process according to the present invention can be practically embodied in a particularly simple and cheap way, in that neither special equipment pieces, nor particular temperatures are required. In fact, the initial selection of the average size of the ceramic granules, which can be comprised within the range of from 0.8 mm to 3.5-4 mm, is carried out in relationship with the type of use the tires are designed for. The granules are charged to a tumbling drum and are treated with a primer (a high-performance coating adhesive), e.g., with Chemosil 211, in such mutual propo¬ rtions as to form on the outer surface of the granu¬ les a first coating Layer having a thickness comprised within the range of from 10 to 20 microns (as referred to the dry coating), and the coated granules are subse¬ quently treated, still inside the tumbling drum, with a covei—coat, e.g. Chemosil 221, in such a way as to form on said first layer a second coating Layer having a thickness comprised within the range of from 20 to 40 mi¬ crons (still referred to the dry coating). A drying is then carried out at a temperature of about 50-60°C, pre¬ ferably with hot air, and the granules are then submit¬ ted to a sieving, also this step be ng preferably car- ried out in a hot air stream, in order to complete the evaporation of the solvent, and to prevent the granules from forming clots, in order to sort the same granules, to separate them from one another, and to eliminate any possible clots and fragmented granules generated by the action of the treatment inside the tumbling drum. A compound of raw, either na ural or synthetic, rubber, or of suitable resins is then prepared, and the sieved granules are mixed inside an open mixer, preferably of the calendei—pass type, or the like, with the rubber already containing all of the necessary fillers and the necessary amount of sulphur and/or of suitable crosslinking agents. The ratio of the granules to the rubber by volume is mantained comprised within the range of from 5 to 15%. Finally, with said rubber compound containing the coated granules, the pattern of the desired tread is formed, and is cured in a known way. The SUBSTITUTESHEET present Applicant was able to observe that by means of the coating method according to the present invention, a bonding of the granules to the rubber can be obtained, which is so highly efficacious, even in corri spondence of the edges or sides of the tread, that, after the application of strong and long-lasting stresses to the tire, a loss of granules is observed, which is practically negligible, i.e., is of about 7-9% of total granules, after a run¬ ning test correspond ng to a covered distance of 1,000 Km. and without any variation of said rate also after an additional run of 1,000 Km. At the end of the test, the present Applicant was also able to observe that, by force¬ dly removing some granules from the surface of the tire, the part of rubber which enclosed the granule was torn, with said rubber part remaining bonded to the same granu¬ le, instead of being detached from it. The present Applicant was moreover able to observe that the shape of the granules is of considerable importance for the purposes of the efficac ousness and of the Life of the same granules inside the tire. In fact, when the granule is of long shape, for example, is of either cylind r ical or prismatic shape, or has a* flat shape, e.g., a "noodles" - or "tile" - or "flake"- like shape, or the like, it tends to arrange itself in a radial orientation when the compound which contains it is charged to the mould; in other terms, preferably presenting the edge of the noodle or tile, or either of the bases, on the outer surface of the finished tire obtained, with this particular orientation being favoured by the presence of the blades, or of the other vertical elements installed inside the same mould in order to SUBSTITUTE SHEET accomplish the tread pattern. In such a way, the granule offers a much higher resistance to the removal by friction and to the detachment, and furthermore shows a much more regular and progressive wear, practically corresponding to the progressive wear of the same tread. The granules of ceramic type obtained by extrusion, drawing or suitable processes and subsequent sintering; with it being possible the shape, width or diameter, and length thereof to be varied as desired and according to the use requirements; have shown to be particularly usefu I. Finally, it is obvious that to the invention, as hereinabove disclosed according to a preferred form of practical embodiment thereof, modifications and variants can be supplied as regards the types and the average size of the ceramic granules used, as well as regards the types of covering substances, and the thicknesses of these Latter, without departing from the scope of protection of the same invention.

Claims: C_l_a_j_m_s 1. Process for stably incorporating into tires, and namely into their tread, anti-skid granules of ceramic type, such as corundum, carbides, nitrides, borides and oxides of various metals and/or mixtures thereof, characterized in that it consists in treating said granules of ceramic type inside a tumbling barrel, or a simi lar mixer, with at least one coating material, or "primer", constituted by a polymeric solution dispersed in a solvent, so as to form on said granules a first coating layer of a thickness pre-established as a function of the weight and of the chemical and physical characteristics of the material used, and in subsequently treating the so coated granules with at least one covering layer, i.e., a "cover-coat" also constituted by a polymeric solution dispersed in a solvent, so as to form above said first layer a second covering layer, in carrying out a drying of the coated granules at a temperature of about 50-60°C, and in subsequently sieving the so-treated granules in order to separate them from one another, and to eliminate clots, then in blending the sieved granules with compounds of raw, either natural or synthetic rubber, or of a synthetic resin, containing all of the necessary fi llers and sulphur and/or suitable crosslinking agents (compound), and finally in forming with said rubber or resin compound containing said granules, the pattern of the tread, and in curing it according to the traditional methods. 2. Process according to claim 1, characterized in that said "primer" is constituted by organic polymers in solution with solid matter in dispersion in an organic solvent. 3. Process according to claim 2, characterized in that said "primer" is constituted by a product selected from among CHEMOSIL 211, CHEMOSIL X 1400, MEGUM 3270, THIXON P/10, THIXON P6-1, ANCHOR TP/6. 4. Process according to claim 1, characterized in that said cover-coat is constituted by a product selected from among CHEMOSIL 221, CHEMOSIL X 4400, MEGUM 100, MEGUM 500, THIXON 520, THIXON 0SN-2 and ANCHOR TP/5. 5. Process according to claim 1, characterized in that said first coating layer is made from a covering composition selected from among CHEMOSIL 221, CHEMOSIL X 4400, MEGUM 100, MEGUM 500, THIXON 520, THIXON OSN-2 and ANCHOR TP/5. 6. Process according to claim 1, characterized in that it provides for the thickness of said first primer layer to be comprised within the range of from 5 to 40 microns, preferably of from 10 to 20 microns, as referred to the dry coating, and for the thickness of said second covering layer (i.e., the "cover-coat"), to be comprised within the range of from 5 to 60 microns, preferably of from 20 to 40 microns, with said thicknesses of the layers being selected according to the weight and the characteristics of the products used. 7. Process according to claim 1, characterized in that the volume of the granules incorporated into the rubber compound is comprised within the range of from about 5 to 15% of the total volume. 8. Process according to claim 1, characterized in that said drying is carried out with heated air, and that said sieving is carried out in a hot air stream. 9. Process according to claim 1, characterized in that the mixing of the coated granules with said raw rubber compound is preferably carried out inside an open mixer of calender-pass type. 10. Process according to claim 1, characterized in that said granules of ceramic type have a long, cylindrical or prismatic shape, or a "noodles"-, "tile"- or "flake"-like shape, and are obtained by extrusion, drawing or compression in general and subsequent sintering, in order to be able to arrange themselves in a radial orientation inside the compound-containing mould, thanks to the presence of the blades and/or of other vertical elements provided inside the same mould in order to accomplish the tread pattern. 11. Process according to claim 1, characterized in that the loss of granules is reduced to a percentage of the total of the incorporated granules, which is comprised within the range of from 7% to 9%, after at least 1,000 km of distance covered by the tire. 12. Product constituted by natural or synthetic rubber contained ceramic granules incorporated into it, according to claim 1, character zed in that it is particularly suitable for forming the tread of tires or the like, endowed with high anti-skid properties on a wet, ice-covered or beaten-snow-covered roadbed. 13. Tire for vehicle wheels provided with a tread containing incorporated anti-skid granules of ceramic type, such as corundum, carbides, nitrides and oxides of various metals, or their mixtures, characterized in that said granules are coated with a double coating layer, in order to bond said material to said tread, with both of said coating layers being each accomplished by means of a polymeric solution dispersed in a solvent.

Inventors: VERZOCCHI ENRICO, VERZOCCHI, ENRICO
Applicants: KERATEK SRL, KERATEK S.R.L.
Application year: 1989
Main classification: C08K9
IPC codes: B60C11, C08K3, C08K9, C08L21, C09C1, C09C3