Method for the treatment of cords for the reinforcing layers of pneumatic tires

Abstract

Method for the treatment of single-filament polyethylene terephthalate cords for the reinforcing layers of a pneumatic tyre comprising (a) an adhesive solution coating step, wherein the single filament cord is immersed in an adhesive solution; (b) a drying step, wherein the cord covered in adhesive resin is held within a drying oven at a temperature of between 12 and 180 C.; and (c) a thermobonding step wherein the cord, proceeding from the drying step, is arranged within an oven at a temperature of between 23 and 260 C. for a period of between 30 and 90 seconds. During the thermobonding step, the single filament cord is subjected to a tension of between 8 and 12 mN/dtex.

Claims

1. A method for treatment of single filament cords for reinforcing layers of a pneumatic tire, said method comprising: an adhesive solution coating step, wherein a single-ply cord comprising a single filament is immersed in an adhesive solution; a drying step, wherein the single-ply cord covered in adhesive resin is held in a drying oven at a temperature of between 12 and 180 C.; and a thermobonding step wherein the cord, proceeding from the drying step, is arranged within an oven at a temperature of between 23 and 260 C. for a period of between 30 and 90 seconds, wherein during said thermobonding step a tensile load of between 8 and 12 mN/dtex is applied to the single filament of the single-ply cord.

2. The method of claim 1, wherein said thermobonding step is performed at a temperature of between 235 and 250 C.

3. The method of claim 1, wherein said thermobonding step endures for a period of between 40 and 80 seconds.

4. The method of claim 1, wherein the single filament cord has a linear density of between 1000 and 2000 dtex.

5. The method of claim 1, wherein the single filament cord has a twist factor of between 70 and 180.

6. The method of claim 1, the single filament cord has a twist factor of between 120 and 160.

7. A method for treatment of single filament cords for reinforcing layers of a pneumatic tire, said method comprising: an adhesive solution coating step, wherein a single filament cord is immersed in an adhesive solution; a drying step, wherein the cord covered in adhesive resin is held in a drying oven at a temperature of between 12 and 180 C.; and a thermobonding step wherein the cord, proceeding from the drying step, is arranged within an oven at a temperature of between 23 and 260 C. for a period of between 30 and 90 seconds, wherein during said thermobonding step the single filament cord is subjected to a tension ranging from about 8.9 mN/dtex to about 10.3 mN/dtex.

Description

(1) In Table I the composition in phr is recorded of the compound used for the manufacture of the cap-ply.

(2) TABLE-US-00001 TABLE I Natural rubber 100 Carbon black 40 Sulfur 40 Vulcanization 1.5 accelerator agent

(3) The natural rubber is the cis-1,4-polyisoprene rubber of natural origin.

(4) The vulcanization accelerator is TBBS (N-tert-butyl-2-benzothiazyl sulfenamide).

(5) The cap-plies thus made were subjected to elastic modulus and durability measurements.

(6) The elastic modulus of the cords was measured using a dynamic mechanical analyzer (DMA). The value is calculated based upon the storage modulus measured at a temperature range of between 3 and 160 C., under a preload of 10 N and a frequency of 52 Hz. The elastic modulus is calculated as the ratio between the dynamic force (N) and the dynamic twisting tension (%).

(7) The durability assessment was based upon the fatigue method described below.

(8) The organic material cords submerged in a rubber matrix in such a way as to produce parallel layers of cords. In this way a rubber sample for testing was produced. The rubber sample has a width of 50 mm, a length of 500 mm and a height of 5.5 mm.

(9) The number of cords is 50/50 mm; the distance between the cords is 2.5 mm; the distance between the center of the cords and the surface is 1.5 mm. Subsequently, the rubber sample is suspended from a pulley and a load of 50 Kg/inch (19.7 Kg/cm) is applied in the direction of the axis of the cords, and the twisting tension and compression force are applied cyclically with a frequency of 100 rpm, increasing the number of cycles until a tensile strength degradation of 80% is reached. The durability is then calculated based upon the number of cycles required in order to reach the above condition.

(10) The cap-plies (A-D) above were used to make four tires (Pa-Pd) which differ from one another only insofar as the different cap-ply used.

(11) The Pa-Pd pneumatic tire were subjected to rolling resistance, noise and weight measurements.

(12) The rolling resistance was measured according to the ASTM D5992 standard.

(13) The noise measurement was performed within a semi-anechoic chamber with the dimensions: 8 m (Length)6 m (Width)3.5 m (Height), ISO 3744 certified (Sound Power Test).

(14) The pneumatic tire was loaded by means of a pneumatic tire-carrier on a drum coated with a resin shell that simulates the asphalt used for external BPN (British Pendulum Number) approval tests. The measuring equipment was composed of 11 microphones spaced angularly in the same manner in order to evaluate the noise directivity. An algorithm (developed by the Applicant) makes it possible to calculate the predicted external BPN value (r.sup.2=0.9) at 80 Km/h.

(15) Table II reports the technical characteristics of the cords and of the method by which they are made, of the respective cap-plies and of the respective pneumatic tire. In order to more clearly show the advantages of the invention, in Table II a few values are indexed to the relative value of the comparative example (cap-ply A), and some of the pneumatic tire characteristics are indicated as a variation of the respective value of the pneumatic tire Pa taken as a reference (Ref.).

(16) TABLE-US-00002 TABLE II A B C D Linear density of the yarn (dtex) 1100 1670 1440 1670 Cord twist level (tpm) 260 390 410 390 Cord twist level (tpm) 260 Twist factor 104 136 132 136 Thickness of the rubber coating (indexed) 100 100 100 100 EPDM (cord/dm) 100 100 100 100 Twisting tension during the 19.6 15.7 14.7 10.2 thermobonding step (N) Twisting tension during the 8.92 9.40 10.22 6.11 thermobonding step (mN/dtex) Thermobonding step temperature ( C.) 240 240 240 240 Thermobonding step duration (seconds) 60 60 60 60 Modulus at 60 C. (N/%) 26.7 17.3 17 11.1 Modulus at 160 C. (N/%) 16.4 11.9 10.7 7.1 Durability (indexed)** 100 110 105 110 High-speed durability (indexed) 100 99 98 80 Rolling resistance of the pneumatic tire Ref. 2% 2% 2% Pneumatic tire noise (dB) Ref. 0.7 0.6 0.7 Pneumatic tire weight (g/pneumatic tire) Ref. 62 76 62

(17) These measurements confirmed that the pneumatic tire Pb-Pd: (i) have 2% lower rolling resistance compared to that of the pneumatic tire Pa; (ii) produce 0.4-0.7 dB lower noise than that produced by the pneumatic tire Pa; (iii) have less weight than the pneumatic tire Pa.

(18) Furthermore, the values reported in Table II demonstrate how the method of the present invention, in addition to satisfying the demands in terms of weight and noise, ensure durability values that are comparable with those of the classic plies included in cap-ply A. In fact, the values in relation to cap-plies B and C, wherein the plies thereof were made according to the present invention, have high-speed durability values that are significantly higher than those of cap-ply D, wherein the plies thereof were made using a method that differs from the method according to the present invention. In particular, the cords of the ply in relation to cap-ply D, during the thermobonding step, were subjected to a lower twisting tension than that indicated as an essential feature in claim 1.

(19) To summarize, the method, the object of the present invention, has the great advantage of producing plies that are capable of ensuring a decrease in weight and a decrease in the noise of the related pneumatic tire without, for this reason, compromising the high-speed durability.

(20) Method for the treatment of single-filament cords for the reinforcing layers of a pneumatic tire comprising (a) an adhesive solution coating step, wherein the single filament cord is immersed in an adhesive solution; (b) a drying step, wherein the cord covered in adhesive resin is held within a drying oven at a temperature of between 12 and 180 C.; and (c) a thermobonding step wherein the cord, proceeding from the drying step, is arranged within an oven at a temperature of between 23 and 260 C. for a period of between 30 and 90 seconds. During the thermobonding step, the single filament cord is subjected to a tension of between 8 and 12 mN/dtex.