Method for processing code for the reinforcement layer of a pneumatic tire

Abstract

A method for processing a single-filament polyethylene terephthalate cord for a reinforcing layer of a pneumatic tire, comprising: (a) an adhesive solution coating step of immersing a single-filament cord in an adhesive solution; (b) a drying step of maintaining a cord coated with an adhesive resin in a drying oven at a temperature of 120 to 180°C; and (c) a heat bonding step of arranging the cord from the drying step in an oven at a temperature of 230 to 260°C for a period of 30 to 90 seconds. During the heat bonding step, a tension of 8 to 12 mN / dtex is applied to the single-filament cord.

Description

Technology Field

[0001] The present invention relates to a method for processing a cord for a reinforcing layer of a pneumatic tire. Background Technology

[0002] Recently, one of the priority tasks in the field of pneumatic tire research is to reduce noise generated by pneumatic tires both inside and outside the cabin.

[0003] This necessity conflicts with the trend of reducing the weight of pneumatic tires to lower rolling resistance. In fact, as is known to those skilled in the art, reducing the weight of pneumatic tires leads to an increase in noise levels during operation, despite the accompanying improvements in rolling resistance.

[0004] As is known to those skilled in the art, reinforcing plies are typically used as reinforcing materials in carcasses, belts, and cap plies. In particular, the cap plies are arranged between the belt and the tread belt.

[0005] For quite some time, some research in the pneumatic tire sector has focused on developing novel reinforcing plies for the cap plies of pneumatic tires to achieve improvements in both rolling resistance and noise generation.

[0006] In particular, a cap-ply was manufactured comprising a reinforcing ply composed of a polyethylene terephthalate (PET) cord having a single filament with a linear density of 500 to 3000 dtex each.

[0007] However, even though cap-plies manufactured using the above-mentioned plies meet requirements related to lighter weight and less noise, they have some significant problems regarding mechanical properties, particularly in relation to high-speed durability.

[0008] The inventors of the present invention have devised a processing method for a single filament cord of a ply for a cap-ply that ensures the required level of high-speed durability in addition to having advantages related to lighter weight and lower levels of noise. Specific details for implementing the invention

[0009] The subject of the present invention is a method for processing a single-filament polyethylene terephthalate cord used in the manufacture of a reinforcing layer of a pneumatic tire; the method comprises: (a) an adhesive solution coating step of immersing the single-filament polyethylene terephthalate cord in an adhesive solution; (b) a drying step of maintaining the single-filament polyethylene terephthalate cord coated with the adhesive solution in a drying oven at a temperature of 120 to 180°C; and (c) a heat bonding step of placing the single-filament polyethylene terephthalate cord in an oven at a temperature of 230 to 260°C for a period of 30 to 90 seconds; and the method is characterized in that a twist tension of 8 to 12 mN / dtex is applied to the single-filament polyethylene terephthalate cord during the heat bonding step.

[0010] Preferably, the thermal bonding step is performed at a temperature of 235 to 250°C.

[0011] Preferably, the thermal bonding step is continued for a period of 40 to 80 seconds.

[0012] Preferably, each of the above codes has a linear density of 1,000 to 2,000 dtex.

[0013] Preferably, each of the above codes has a twist factor of 70 to 180; more preferably, 120 to 160.

[0014] The twist coefficient is given by the formula Tf = a * Nt * T 0.5 It is expressed as, where a=8.513*10 -3And, Nt is the twist level (number of twists per meter) and T is the linear density of the cord (dtex).

[0015] Further subject of the present invention is a cap-ply manufactured using a ply comprising a single-filament cord processed according to the method of the present invention.

[0016] Further subject of the present invention is a pneumatic tire comprising a cap-ply made of a ply containing a single-filament cord processed according to the method of the present invention.

[0017] The following are exemplary, non-limiting embodiments provided purely for illustrative purposes.

[0018] Four cap-plies (A-D) were manufactured. Cap-ply A is a comparative example comprising a reinforcing ply made from a multi-filament cord and represents the currently adopted solution. Cap-plies B and C are comparative examples in that they comprise a reinforcing ply according to the present invention, whereas cap-ply D is a comparative example in that a single-filament cord is applied to a treatment having characteristics different from those described in the appended claims.

[0019] In particular, the reinforcing plies of cap-ply B-C were manufactured using a single-filament cord of PET characterized by a linear density in the range of 1000 to 2000 dtex and a twist coefficient in the range of 70 to 140.

[0020] In contrast, the reinforcing plies of Cap-Ply A were manufactured using double-filament PET cords according to commonly adopted practices. Each PET filament has a linear density of 1100 dtex and a twist factor of 104.

[0021] Each cap-ply was manufactured by inserting a ply between two layers of rubber compound.

[0022] Table I presents the composition of the formulation used to manufacture the cap-ply in phr.

[0023]

[0024]

[0025] Natural rubber is naturally derived cis-1,4-polyisoprene rubber.

[0026] The vulcanization accelerator is TBBS (N-tert-butyl-2-benzothiazyl sulfenamide).

[0027] The cap-ply manufactured in this way was applied to measure elastic modulus and durability.

[0028] The elastic modulus of the cord was measured using a dynamic mechanical analyzer (DMA). The above value is calculated based on the storage modulus measured at a preload of 10 N and a frequency of 52 Hz in a temperature range of 30 to 160°C. The elastic modulus is calculated as the ratio between dynamic force (N) and dynamic twist tension (%).

[0029] Durability evaluation was based on the fatigue method described below.

[0030] Organic material cords were immersed in a rubber matrix in such a manner that parallel cord layers were formed. In this way, rubber samples for testing were prepared. The rubber samples have a width of 50 mm, a length of 500 mm, and a height of 5.5 mm.

[0031] The number of cords is 50 / 50 mm; the distance between cords is 2.5 mm; and the distance between the center of the cord and the surface is 1.5 mm. Subsequently, a rubber sample is suspended from a pulley and a load of 50 kg / inch (19.7 kg / cm) is applied axially to the cord, and twist tension and compressive force are periodically applied using a frequency of 100 rpm, increasing the number of cycles until the reduction in tensile strength reaches 80%. Then, the durability is calculated based on the number of cycles required to reach the above conditions.

[0032] Using the above cap-plies (A - D), four different tires (Pa - Pd) were manufactured that differ from each other only in that different cap-plies were used.

[0033] Pa-Pd pneumatic tires were applied to measure rolling resistance, noise, and weight.

[0034] Rolling resistance was measured according to the ASTM D5992 standard.

[0035] Noise measurements were performed in a semi-anechoic chamber certified by ISO 3744 (Sound Power Test) with dimensions of 8 m (length) x 6 m (width) x 3.5 m (height).

[0036] Pneumatic tires were loaded onto drums coated with a resin shell mimicking the asphalt used in external BPN (British Skid Resistance Value) approval tests, using a pneumatic tire carrier. The measuring equipment consisted of 11 micro-meters spaced at an angle in the same manner to evaluate noise directionality. The algorithm (developed by the applicant) predicted the external BPN value (r) at 80 km / h 2 It makes it possible to calculate =0.9).

[0037] Table II describes the code and its manufacturing method, as well as the technical features of the corresponding cap-ply and the corresponding pneumatic tire. To more clearly demonstrate the advantages of the present invention, several values ​​in Table II have been indexed based on the values ​​of the comparative example (cap-ply A), and some of the pneumatic tire features have been indicated as variations in the corresponding values ​​of the pneumatic tire Pa, which are represented as reference values ​​(Ref.).

[0038] Table II

[0039]

[0040] Through these measurements, it was confirmed that pneumatic tires Pb - Pd have (i) rolling resistance 2% lower than that of pneumatic tire Pa; (ii) noise 0.4 - 0.7 dB lower than that produced by pneumatic tire Pa; and (iii) have a lighter weight than pneumatic tire Pa.

[0041] Furthermore, the values ​​listed in Table II demonstrate how the method of the present invention, in addition to meeting requirements in terms of weight and noise, guarantees durability values ​​comparable to those of a typical ply included in cap-ply A. In fact, the values ​​associated with cap-ply B and C, which include ply manufactured according to the present invention, have much higher high-speed durability values ​​than the high-speed durability values ​​of cap-ply D, which includes ply manufactured using a method different from the method according to the present invention. In particular, a lower twist tension than that presented as an essential feature in Claim 1 was applied to the cord of the ply associated with cap-ply D during the thermal bonding step.

[0042] In summary, the method of the present invention has the significant advantage of ensuring weight and noise reduction of the relevant pneumatic tire and, for this reason, manufacturing a ply that does not compromise high-speed durability.

Claims

Claim 1 A method for processing a single-filament polyethylene terephthalate cord used in the manufacture of a reinforcing layer of a pneumatic tire; the method comprises (a) an adhesive solution coating step of immersing the single-filament polyethylene terephthalate cord in an adhesive solution; (b) a drying step of maintaining the single-filament polyethylene terephthalate cord coated with the adhesive solution in a drying oven at a temperature of 120 to 180°C; and (c) a heat bonding step of placing the single-filament polyethylene terephthalate cord in an oven at a temperature of 230 to 260°C for a period of 30 to 90 seconds; and the method is characterized in that a tension of 8 to 12 mN / dtex is applied to the single-filament polyethylene terephthalate cord during the heat bonding step. Claim 2 A method according to claim 1, characterized in that the thermal bonding step is performed at a temperature of 235 to 250°C. Claim 3 A method according to claim 1 or 2, characterized in that the thermal bonding step is sustained for a period of 40 to 80 seconds. Claim 4 A method according to claim 1 or 2, characterized in that the single filament polyethylene terephthalate cord has a linear density of 1,000 to 2,000 dtex. Claim 5 A method according to claim 1 or 2, characterized in that the single filament polyethylene terephthalate cord has a twist coefficient of 70 to 180. Claim 6 A method according to claim 1 or 2, characterized in that the single filament polyethylene terephthalate cord has a twist coefficient of 120 to 160. Claim 7 A cap-ply manufactured from a ply comprising a single filament polyethylene terephthalate cord processed using the method according to claim 1 or 2. Claim 8 A pneumatic tire comprising a cap-ply according to paragraph 7.

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