JP6912366B2 - How to make a pneumatic tire - Google Patents

Description

The present invention includes a pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, and a tread portion that is connected to each tire radial outer end of the sidewall portion to form a tread surface. The present invention relates to a method for producing a pneumatic tire including a vulcanization step of heating and vulcanizing an unvulcanized raw tire in a mold.

When manufacturing pneumatic tires, which are rubber products, the vulcanization process is the most time-consuming process, and efforts are still being made to shorten the vulcanization process time. On the other hand, if the rubber part is insufficiently vulcanized in the vulcanization process, the air generated by the vulcanization reaction of the rubber remains in the vulcanized rubber, and such residual air causes tire failure at the product stage. May be. Therefore, in a normal tire production site, considering that the temperature of raw unvulcanized tires, which are raw materials, the temperature inside the mold, the atmospheric temperature, etc., vary depending on seasonal factors, the total variation in the vulcanization process. The time required for the vulcanization process is set by adding the extra time in consideration of.

However, setting the margin time is not preferable from the viewpoint of improving the productivity of the tire, and it has been desired to determine the end time of vulcanization for each tire and efficiently execute the vulcanization process.

In Patent Document 1 below, the impedance of a vulcanized sample is measured while the vulcanization process is in progress, and the optimum vulcanization is when the rate of increase in the polymer resistance value Rp of the vulcanized sample suddenly slows down. A method for adjusting the real-time vulcanization of a vulcanized sample as an downtime is described. However, in this method, it is necessary to measure the impedance of the vulcanized sample by sandwiching the vulcanized sample between two electrodes, and since the tire is usually a laminate of composite materials, this method is used. It is difficult to apply it to tires during tire vulcanization.

Japanese Unexamined Patent Publication No. 2003-21459

The present invention has been made in view of the above circumstances, and an object of the present invention is to shorten the vulcanization time and significantly improve productivity by reliably determining the end time point of the vulcanization process for each tire. The purpose is to provide a method for manufacturing tires.

The above object can be achieved by the present invention as described below. That is, the present invention includes a pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, and a tread portion that is connected to each tire radial outer end of the sidewall portion to form a tread surface. A method for producing a pneumatic tire including a vulcanization step of heating and vulcanizing an unvulcanized raw tire provided with the above, wherein the vulcanization step is performed at the latest vulcanization portion of the raw tire. Using the first step of burying the temperature measurement probe, the second step of acquiring a plurality of time series data including a predetermined number of temperature values acquired at intervals of 10 seconds or less by the temperature measurement probe, and the minimum square method. , A coefficient curve is created by approximating a predetermined number of temperature values included in the time series data to a linear formula, calculating the slope of the approximate linear formula for each time series data, and plotting against the vulcanization time. Manufacture of a pneumatic tire having a third step and ending the vulcanization step when a change point appearing in the vulcanization time reaching near the target vulcanization temperature of the coefficient curve is detected. Regarding the method.

The present invention is characterized by a vulcanization step of a pneumatic tire and has at least the first to third steps. First, a pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, and a tread portion connected to each tire radial outer end of the sidewall portion to form a tread surface are not added. A temperature measurement probe is embedded in the slowest part of the vulcanization of the raw vulcanized tire (first stage), and time-series data including a plurality of temperature values acquired at intervals of 10 seconds or less is acquired by the temperature measurement probe (first stage). Second stage). Next, by using the least squares method to approximate a predetermined number of temperature values contained in the time series data to a linear formula, the slope of the approximate linear formula is calculated for each time series data, and plotted against the brewing time. , Create a coefficient curve (third stage). Then, the vulcanization step is terminated when an inflection point appearing at the vulcanization time reaching the vicinity of the target vulcanization temperature on the coefficient curve is detected. Thereby, in the vulcanization process of the pneumatic tire, the vulcanization end point can be easily determined. As a result, it is not necessary to set an extra spare time, and the productivity of the pneumatic tire can be increased. In addition, since it can be confirmed that the vulcanization reaction is surely completed for each pneumatic tire, a quality assurance system can be established. The term "near the target vulcanization temperature" preferably means a range of ± 20 ° C. of the set target vulcanization temperature, and more preferably means a range of ± 10 ° C. of the set target vulcanization temperature. Shall be.

In the method for manufacturing a pneumatic tire, the acquisition interval of the temperature value in the time series data is preferably 1 second or less, and the predetermined number is preferably 10 to 30. This makes it possible to more reliably determine the vulcanization end point of the pneumatic tire, and further increase the productivity of the pneumatic tire.

In the method for manufacturing a pneumatic tire, it is preferable that the temperature measuring probe is a platinum resistance temperature detector. If the sensitivity of the temperature measurement probe is poor, the detection of the vulcanization end point based on the time when the heat generated by the vulcanization reaction is detected near the target vulcanization temperature, and the plotted vulcanization temperature curve first near the target vulcanization temperature. It may be difficult to detect the vulcanization end point based on the upwardly convex inflection point that appears in. On the other hand, since the platinum resistance temperature detector is extremely sensitive to temperature changes, it is possible to reliably determine the vulcanization end point, and thus the productivity of pneumatic tires can be further increased.

In the method for manufacturing a pneumatic tire, it is preferable that the slowest vulcanization portion is the shoulder portion of the tread portion. This makes it possible to more reliably determine the vulcanization end point of the pneumatic tire, and further increase the productivity of the pneumatic tire.

In the method for producing a pneumatic tire, the target vulcanization temperature is preferably 120 to 200 ° C.

A tire meridian cross-sectional view showing an example of a tire according to the present invention. Cross-sectional view conceptually showing a mold used for vulcanizing tires An example of a coefficient curve and a vulcanization temperature curve in one embodiment of the present invention.

Embodiments of the present invention will be described with reference to the drawings. The raw tire 9 shown in FIG. 1 is connected to a pair of bead portions 1, a sidewall portion 2 extending outward in the tire radial direction from each of the bead portions 1, and each tire radial outer end of the sidewall portion 2. It is a pneumatic tire provided with a tread portion 3 constituting a tread surface. An annular bead core 1a is arranged in the bead portion 1.

The carcass layer 4 reaches the bead portion 1 from the tread portion 3 through the sidewall portion 2, and the end portion thereof is folded back via the bead core 1a. The carcass layer 4 is composed of at least one carcass ply. The carcass ply is formed by covering a carcass cord extending at an angle of approximately 90 ° with respect to the tire circumferential direction with a topping rubber.

The belt layer 5 is attached to the outside of the carcass layer 4 at the tread portion 3, and is covered from the outside by the tread rubber 6. The belt layer 5 is composed of a plurality of belt plies (two in the present embodiment). Each belt ply is formed by covering a belt cord extending in an inclined direction with respect to the tire circumferential direction with a topping rubber, and the belt cords are laminated so as to intersect each other in opposite directions between the plies.

The tread rubber 6 may be composed of only one layer, or may be composed of a so-called cap base structure having a base tread on the inner side in the tire radial direction and a cap tread located on the outer peripheral side thereof.

The raw tire 9 shown in FIG. 1 is a raw tire in an unvulcanized state, and is shaped into the shape of a product tire in a vulcanization step described later (see FIG. 2), and various treads are formed on the tread surface thereof. A pattern is formed.

In the vulcanization molding of the raw tire 9, the mold 10 as shown in FIG. 2 is used. The raw tire 9 is set in the mold 10 in an unvulcanized state, and the vulcanization step is performed by applying heat and pressure to the raw tire 9 in the mold 10.

The mold 10 includes a tread mold portion 11 in contact with the tread surface of the raw tire 9, a lower mold portion 12 in contact with the tire outer surface facing downward, and an upper mold portion 13 in contact with the tire outer surface facing upward. These are configured to be displaceable between the mold tightening state and the mold open state by an opening / closing mechanism (not shown) installed around them, and the structure of such an opening / closing mechanism is well known. The tread mold portion 11 is further divided into a plurality of parts in the circumferential direction, and is movable in the radial direction of the raw tire 9 arranged in the mold 10. Further, the mold 10 is provided with a platen plate (not shown) having a heat source such as an electric heater or a steam jacket, whereby each mold portion is heated.

A central mechanism 14 is provided coaxially with the tire in the central portion of the mold 10, and a tread mold portion 11, a lower mold portion 12, and an upper mold portion 13 are installed around the central mechanism 14. The central mechanism 14 has a rubber bag-shaped bladder 15 and a center post 16 extending in the tire axial direction, and the center post 16 is provided with an upper clamp 17 and a lower clamp 18 for gripping the end portion of the bladder 15. ing.

In the central mechanism 14, a medium supply path 21 for supplying the heating medium into the bladder 15 is extended vertically, and an ejection port 22 is formed at the upper end of the medium supply path 21. A heating medium supplied from the heating medium supply source 23 and a supply pipe 24 through which the pressure medium supplied from the pressure medium supply source 26 flows are connected to the medium supply path 21. The heating medium is supplied according to the opening / closing operation of the valve 25, and the pressurizing medium is supplied according to the opening / closing operation of the valve 28.

Further, in the central mechanism 14, a medium discharge path 31 for discharging a high-temperature and high-pressure fluid in which a heating medium and a pressure medium in the bladder 15 are mixed is extended vertically at the upper end of the medium discharge path 31. A collection port 32 is formed. A discharge pipe 34 through which a high-temperature and high-pressure fluid flows is connected to the medium discharge passage 31, and a blow valve 33 for operating the opening / closing of the discharge pipe 34 is provided in the discharge pipe 34. The pump 35 may use a method of forcibly circulating the high-temperature and high-pressure fluid so that the high-temperature and high-pressure fluid passing through the medium discharge path 31 is resupplied to the inside of the bladder 15 via the medium supply path 21.

Hereinafter, the vulcanization step in the production method of the present invention will be specifically described.

First, as shown in FIG. 2, the raw tire 9 is set in the mold 10, and the raw tire 9 is shaped to be close to the inner surface shape of the mold 10 by the expanded bladder 15. As a result, the raw tire 9 is held by the bladder 15 and addressed to each of the tread mold portion 11, the lower mold portion 12, and the upper mold portion 13. At this point, the temperature measuring probe is embedded in the slowest part of the vulcanization of the raw tire 9 (first stage). The slowest vulcanization portion means a portion where vulcanization of the tire is most difficult to proceed, and usually means a shoulder portion of the tread portion 3. In particular, among the shoulder portions, the position where the thickness of the tread portion 3 is maximized, which is measured along the normal of the inner surface of the tread portion 3 after vulcanization, is preferably the slowest vulcanization portion. In any case, in the present invention, in order to measure the vulcanization temperature in the slowest vulcanization portion, the temperature measuring probe is embedded in the slowest vulcanization portion of the raw tire 9. As an embedding method, for example, when a temperature measuring probe is arranged at a position corresponding to the shoulder portion of the tread mold portion 11 and the tread mold portion 11 moves in the radial direction of the raw tire 9 and the raw tire 9 is addressed. It is conceivable to design the temperature measuring probe so that it is embedded while being pushed into the raw tire 9. With the temperature measuring probe embedded in the raw tire 9 in this way, the temperature of the raw tire is measured at the time of the vulcanization process, and at the end of the vulcanization process, when the tire is removed from the mold 10 including the tread mold portion 11. The temperature measuring probe may be extracted from the slowest part of the vulcanization at the same time.

In the present invention, as a temperature measuring probe used when measuring the vulcanization temperature, a resistance temperature measuring resistor utilizing the property that the electric resistance of a metal changes with respect to a temperature change can be used. Examples of such metals include platinum, nickel, and copper, but in the present invention, the resistance value change (sensitivity) to a temperature change is large, and as a result, the platinum temperature measurement is extremely sensitive to a temperature change. Resistors can be used particularly preferably.

Subsequently, outside heating is performed by heating the mold 10 to heat the tire 9 from the tire outer surface side, and inside heating is performed by supplying a high-temperature heating medium to the bladder 15 in the mold 10 to heat the tire 9 from the tire inner surface side. The raw tire 9 is vulcanized by heating the tire. The mold 10 is preheated by the steam jacket or the like described above, whereby the outside heating is performed. The inner heating is performed by supplying the heating medium into the bladder 15 through the medium supply path 21 after shaping the tire 9. After supplying the heating medium for a predetermined time, the pressurizing medium is subsequently supplied into the bladder 15 to pressurize the tire 9 at a high pressure. As the heating medium, for example, steam or high-temperature water is used, and as the pressure medium, for example, an inert gas such as nitrogen gas or steam is used.

The temperature measurement probe acquires time-series data including a plurality of temperature values acquired at intervals of 10 seconds or less (second stage). For the acquisition of such time-series data, a high-precision digital data logger generally distributed in the market (temperature resolution of about 0.001 ° C., accuracy of about ± 0.005 ° C., minimum temperature value acquisition interval of 1 second) can be used. .. In the second stage, when the data acquisition interval of the time series data of the temperature of the raw tire during vulcanization is short, it is preferable because the final vulcanization end point can be determined more accurately. Specifically, the acquisition interval of the temperature value in the time series data is preferably 5 seconds or less, and preferably 1 second or less. On the other hand, if the data acquisition interval of the time-series data of the temperature of the raw tire during vulcanization is too short, the noise may become large and it may be difficult to accurately determine the vulcanization end point. Therefore, the acquisition interval of the temperature value in the time series data is preferably 0.5 seconds or more.

After the second step, a predetermined number of temperature values included in the time series data are approximated to a linear formula using the least squares method, and the slope value of the approximate linear formula is calculated for each time series data to obtain the brewing time. By plotting against it, a coefficient curve is created (third stage). FIG. 3 shows an example of a coefficient curve and a vulcanization temperature curve in one embodiment of the present invention. In FIG. 3, the horizontal axis represents the time (seconds) when the vulcanization start point is the time when the mold 10 is completed, the vertical axis represents the temperature (° C.) of the raw tire, A is the vulcanization temperature curve, and B. Shows a coefficient curve. In the present embodiment, the temperature value acquisition interval is 1 second, and the temperature value included in one time series data is 20 ((predetermined number) = 20). Specifically, 20 temperature values acquired at 1-second intervals are grouped as one time-series data, the slope of this time-series data is calculated using the minimum square method, and the brewing time is calculated for each time-series data. On the other hand, the slope calculated in time series is plotted. In FIG. 3, the slope calculated based on each time series data is plotted as points with respect to the vulcanization time.

When approximating linearly using the least squares method, the predetermined number of temperature values to be used is preferably 10 to 30 which is continuous in time series, and more preferably 15 to 25. If the predetermined number is 5 or less, the noise of the coefficient curve becomes large and it may be difficult to detect the inflection point. If the predetermined number exceeds 30, the size of the inflection point becomes small and the detection is also performed. May be difficult.

In the present embodiment, when the target vulcanization temperature is set to 150 ° C., an inflection point P is observed around the vulcanization temperature curve exceeding 140 ° C. The vulcanization step is terminated when the inflection point P is detected. In the present invention, the target vulcanization temperature is preferably 120 to 200 ° C, more preferably 140 to 180 ° C.

After the vulcanization step is completed, the temperature measuring probe arranged in the mold 10 is pulled out from the vulcanized tire while the mold 10 is in the open state. As a result, it is possible to identify the vulcanization end point for each tire and manufacture a pneumatic tire while shortening the vulcanization time.

The present invention is not limited to the above-described embodiment, and various improvements and changes can be made without departing from the spirit of the present invention.

Example 1, Comparative Example 1
In order to specifically show the configuration and effect of the present invention, a sample tire (tire size: 275 / 70R22.5) was vulcanized using the vulcanization die 10 shown in FIG. At that time, a platinum resistance temperature detector (“thin tube resistance temperature detector” manufactured by Yamazato Sangyo Co., Ltd.) connected to a high-precision digital data logger (Fluke, trade name “1586A”) was placed in the mold 10. , Arranged at a position corresponding to the shoulder portion of the pneumatic tire.

The target vulcanization temperature was set to 150 ° C., and the sample tire was heated and vulcanized so as to have the vulcanization temperature curve shown in FIG. In Comparative Example 1, the vulcanization step was completed at the inflection start point time of 57 minutes (= 3420 seconds) at the inflection point P, and in Example 1, the vulcanization step was added at the inflection end time of 59 minutes (= 3540 seconds) at the inflection point P. The vulcanization process was completed.

When the obtained sample tire was disassembled, in Comparative Example 1, bubbles of 1 to 2 mm called blister remained in the rubber portion near the tip of the probe. On the other hand, in Example 1, no blister remained in the rubber portion near the tip of the probe, and it was found that the vulcanization reaction was surely completed.

Claims (6)

A pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, and a tread portion connected to each tire radial outer end of the sidewall portion to form a tread surface are not added. A method for producing a pneumatic tire, which includes a vulcanization step of heating and vulcanizing a raw vulcanized tire in a mold.
The brewing step is a time series including a first step of embedding a temperature measuring probe in the slowest part of brewing of the raw tire and a predetermined number of temperature values acquired by the temperature measuring probe at intervals of 10 seconds or less. Using the second step of acquiring a plurality of data and the least squares method, a predetermined number of temperature values included in the time series data are approximated to a linear formula, and the slope of the approximate linear formula is calculated for each time series data. With a third step of creating a coefficient curve by plotting against the brewing time,
A method for manufacturing a pneumatic tire, which comprises ending the vulcanization step when an inflection point appearing at a vulcanization time reaching a vicinity of a target vulcanization temperature on the coefficient curve is detected. The method for manufacturing a pneumatic tire according to claim 1, wherein the acquisition interval of the temperature value in the time series data is 1 second or less. The method for manufacturing a pneumatic tire according to claim 1 or 2, wherein the predetermined number is 10 to 30. The method for manufacturing a pneumatic tire according to any one of claims 1 to 3, wherein the temperature measuring probe is a platinum resistance temperature detector. The method for manufacturing a pneumatic tire according to any one of claims 1 to 4, wherein the slowest vulcanization portion is a shoulder portion of the tread portion. The method for producing a pneumatic tire according to any one of claims 1 to 5, wherein the target vulcanization temperature is 120 to 200 ° C.

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