Patent Publication Number: US-2021162820-A1

Title: Pneumatic Tire and Method for Manufacturing the Same

Description:
TECHNICAL FIELD 
     The present technology relates to a pneumatic tire including a sensor unit that acquires tire information and a method for manufacturing the same, and particularly to a pneumatic tire and a method for manufacturing the same that can provide enhanced adhesiveness between a tire inner surface and a sensor unit while ensuring air retention properties by bonding the sensor unit to the tire inner surface in a state where a release agent is applied to the tire inner surface. 
     BACKGROUND ART 
     To acquire tire internal information such as internal pressure and temperature, various sensors are installed in a tire cavity (for example, see Japan Patent No. 6272225 and Japan Unexamined Patent Publication No. 2016-505438). 
     On the other hand, in vulcanizing a green tire by using a bladder, the bladder is likely to bond to an inner surface of the green tire, and thus, a release agent is applied to the inner surface of the green tire to prevent bonding of the green tire and the bladder. In such a case, in an attempt to directly bond and fix the sensor unit to the tire inner surface, there is a problem of poor adhesiveness between the tire inner surface to which the release agent is applied and the sensor unit, and of easy peeling of the sensor unit. 
     In contrast, it has been proposed to apply a release agent to an inner surface of a green tire, vulcanize the green tire, and then buff the tire inner surface to remove the release agent (for example, Japan Patent No. 4410753). However, there is a problem in such buffing that reduces a gauge of an innerliner, and thus degrades air retention properties. Additionally, it has been proposed to bond a film to an inner surface of a green tire in advance, apply a release agent to the inner surface of the green tire in a state where the film is bonded to the inner surface, vulcanize the green tire, and then peel the film to remove the release agent (for example, Japan Unexamined Patent Publication No. 2015-107690). However, there is a problem of degradation of air retention properties due to the step of peeling the film after vulcanization. Moreover, it has been proposed to clean a tire inner surface to which a release agent is applied. However, there is a problem in such a technique that cannot sufficiently remove the release agent. 
     SUMMARY 
     The present technology provides a pneumatic tire and a method for manufacturing the same that can provide enhanced adhesiveness between a tire inner surface and a sensor unit while ensuring air retention properties by bonding the sensor unit to the tire inner surface in a state where a release agent is applied to the tire inner surface. 
     A pneumatic tire according to an embodiment of the present technology includes at least one sensor unit fixed to a tire inner surface via an adhesive layer and including a sensor that acquires tire information. An amount of silicon in a release agent detected by fluorescent X-ray analysis at least in a fixing region for the sensor unit is from 0.1 wt % to 10.0 wt %. 
     A method for manufacturing a pneumatic tire according to an embodiment of the present technology is a method for manufacturing a pneumatic tire that includes vulcanizing a green tire by using a bladder including a coating layer made of a release agent, the method including, in fixing a sensor unit to an inner surface of a tread portion of a vulcanized pneumatic tire, setting an amount of silicon in the release agent detected by fluorescent X-ray analysis at least in a fixing region for the sensor unit to from 0.1 wt % to 10.0 wt %, and fixing the sensor unit to the fixing region for the sensor unit via an adhesive layer. 
     Additionally, a method for manufacturing a pneumatic tire according to an embodiment of the present technology includes, in fixing a sensor unit to a tire inner surface, irradiating the tire inner surface with a laser to remove a release agent, setting an amount of silicon in the release agent detected by fluorescent X-ray analysis at least in a fixing region for the sensor unit to from 0.1 wt % to 10.0 wt %, and fixing the sensor unit to the fixing region for the sensor unit via an adhesive layer. 
     In an embodiment of the present technology, an amount of silicon in a release agent detected by fluorescent X-ray analysis at least in a fixing region for a sensor unit is set to from 0.1 wt % to 10.0 wt %, and the sensor unit is fixed to a tire inner surface in a state where a trace amount of the release agent is applied to the tire inner surface. Thus, while the release agent inhibits permeation of air from the tire inner surface and air retention properties improves, the adhesiveness between the tire inner surface and the sensor unit can be ensured sufficiently. 
     In an embodiment of the present technology, preferably, adhesive strength of the adhesive layer ranges from 0.4 N/mm 2  to 100 N/mm 2 . Accordingly, work of installing the sensor unit can be performed easily while maintaining good adhesive strength of the adhesive layer. The adhesive strength (tensile shear adhesive strength) of the adhesive layer complies with any of JIS (Japanese Industrial Standard)-K6850 and JIS-Z0237, and is measured in a standard state (23° C. and RH 50%). 
     In an embodiment of the present technology, preferably, the adhesive layer is made of a cyanoacrylate-based adhesive. Accordingly, working time for installing the sensor unit can be reduced. 
     In an embodiment of the present technology, preferably, the sensor unit is disposed in an inner side of a ground contact edge in a tire width direction. Accordingly, in a case of a sensor that detects an amount of wear of a tread portion, the sensor can accurately acquire tire information. 
     In an embodiment of the present technology, preferably, the sensor unit is bonded directly to the tire inner surface. Accordingly, in a case of a sensor that detects an amount of wear of a tread portion, the sensor can accurately acquire tire information. 
     In an embodiment of the present technology, preferably, a base is inserted between the sensor unit and the adhesive layer. Accordingly, in a case where a material that can follow tire deformation is used as a material for the base, peeling of the sensor unit due to the tire deformation can be prevented. 
     In an embodiment of the present technology, preferably, at a step of forming the coating layer in the bladder, coating time t (hour) and temperature T (° C.) of the coating layer satisfy t≥0.0001T 2 −0.07T+9 and T≤180° C. Accordingly, in the bladder including the coating layer, time for coating the release agent can be reduced, and shortening of a bladder life can be prevented. 
     In an embodiment of the present technology, ground contact edge refers to an end portion in the tire axial direction of a tire mounted on a regular rim and inflated to a regular internal pressure, and placed vertically on a flat surface with a regular load applied to the tire. “Regular rim” refers to a rim defined by a standard for each tire according to a system of standards that includes standards with which tires comply, and is a “standard rim” defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim” defined by the Tire and Rim Association, Inc. (TRA), or a “Measuring Rim” defined by the European Tyre and Rim Technical Organisation (ETRTO). In a system of standards including standards with which tires comply, “regular internal pressure” refers to air pressure defined by each of the standards for each tire and is “maximum air pressure” defined by JATMA, a maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURE” defined by ETRTO. However, “regular internal pressure” is 250 kPa in a case where a tire is a tire for a passenger vehicle. “Regular load” is a load defined by a standard for each tire according to a system of standards that includes standards with which tires comply, and is a “maximum load capacity” defined by JATMA, a maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO. However, “regular load” is a load corresponding to 80% of the load described above in a case where a tire is a tire for a passenger vehicle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a meridian cross-sectional view illustrating an example of a pneumatic tire according to an embodiment of the present technology. 
         FIG. 2  is an enlarged cross-sectional view of a portion of the pneumatic tire of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a modified example of a pneumatic tire according to an embodiment of the present technology. 
         FIG. 4  is a perspective view of another modified example of a pneumatic tire according to an embodiment of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     Configurations of embodiments of the present technology will be described in detail below with reference to the accompanying drawings.  FIGS. 1 and 2  illustrate a pneumatic tire according to an embodiment of the present technology. Note that in  FIG. 1 , CL denotes a tire center line. 
     As illustrated in  FIG. 1 , a pneumatic tire according to an embodiment of the present technology includes a tread portion  1  having an annular shape and extending in the tire circumferential direction, a pair of sidewall portions  2 ,  2  disposed in both sides of the tread portion  1 , and a pair of bead portions  3 ,  3  disposed in inner sides of the sidewall portions  2  in the tire radial direction. 
     A carcass layer  4  is mounted between the pair of bead portions  3 ,  3 . The carcass layer  4  includes a plurality of reinforcing cords extending in the tire radial direction and is folded back around a bead core  5  disposed in each of the bead portions  3  from a tire inner side to a tire outer side. A bead filler  6  having a triangular cross-sectional shape and formed of a rubber composition is disposed on an outer circumference of the bead core  5 . Then, an innerliner  9  is disposed in a region between the pair of bead portions  3 ,  3  in the tire inner surface. The innerliner  9  forms a tire inner surface Ts. 
     On the other hand, a plurality of belt layers  7  are embedded in an outer circumferential side of the carcass layer  4  in the tread portion  1 . The belt layers  7  include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and are disposed with the reinforcing cords intersecting each other between the layers. In the belt layers  7 , an inclination angle of the reinforcing cords with respect to the tire circumferential direction is set within the range of from 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers  7 . To improve high-speed durability, at least one belt cover layer  8  formed by arranging reinforcing cords at an angle of, for example, not greater than 5° with respect to the tire circumferential direction is disposed in the outer circumferential side of the belt layers  7 . Organic fiber cords such as nylon, and aramid are preferably used as the reinforcing cords of the belt cover layer  8 . 
     Note that the tire internal structure described above represents a typical example for a pneumatic tire, but is not limited to this. 
     In the pneumatic tire described above, at least one sensor unit  20  is fixed in a region corresponding to the tread portion  1  of the tire inner surface Ts. As illustrated in  FIG. 2 , the sensor unit  20  is bonded to the tire inner surface Ts via an adhesive layer  10 . 
     The adhesive layer  10  can include a liquid adhesive or a double sided adhesive tape. Examples of the adhesive include a reaction curable adhesive including an epoxy resin or a urethane resin. Particularly, the adhesive layer  10  may include a cyanoacrylate-based adhesive (instantaneous adhesive) to reduce working time for installing the sensor unit  20  in the tire inner surface Ts. 
     The sensor unit  20  includes a housing  21  and an electronic component  22 . The housing  21  has a hollow structure, and accommodates the electronic component  22  inside. The electronic component  22  includes a sensor  23  that acquires tire information, a transmitter, a receiver, a control circuit, a battery, and the like as appropriate. Examples of the tire information acquired by the sensor  23  include internal temperature and internal pressure of the pneumatic tire, and an amount of wear of the tread portion  1 . For example, a temperature sensor or a pressure sensor is used to measure internal temperature or internal pressure. In a case where an amount of wear of the tread portion  1  is detected, a piezoelectric sensor that comes into contact with the tire inner surface Ts can be used as the sensor  23 , and the piezoelectric sensor detects an output voltage corresponding to deformation of a tire during traveling, and detects an amount of wear of the tread portion  1  based on the output voltage. Moreover, an acceleration sensor or a magnetic sensor can also be used. Additionally, the sensor unit  20  is configured to transmit the tire information acquired by the sensor  23  to an outside of the tire. Note that the internal structure of the sensor unit  20  illustrated in  FIG. 2  is an example of the sensor unit, and is not limited to this. 
     In the pneumatic tire described above, a release agent layer  11  including a release agent applied in a process of manufacturing a pneumatic tire is present between the tire inner surface Ts and the adhesive layer  10 . That is, the sensor unit  20 , the adhesive layer  10 , and the release agent layer  11  are layered in order from the inner side in the tire radial direction. An amount of silicon in the release agent layer  11  is from 0.1 wt % to 10.0 wt % at least in a fixing region S for the sensor unit  20  of the tire inner surface Ts. In an embodiment of the present technology, in defining an amount of the release agent in an inner surface of the tread portion  1 , an amount of silicon that is a main component of a typical release agent is used as an indicator. The amount of silicon can be detected by using fluorescent X-ray analysis, and the fluorescent X-ray analysis typically includes an FP method (Fundamental Parameter method) and a calibration curve method. In an embodiment of the present technology, the FP method is employed. In measuring the amount of the release agent (silicon), a fluorescent X-ray analyzer is used to measure amounts of the release agent at a total of five locations including a center point of the fixing region S for the sensor unit  20 , two locations in both sides in the tire circumferential direction with the center point as the center, and two locations in both sides in the tire width direction with the center point as the center, and the amounts of the release agent at the five locations are averaged to calculate the amount of the release agent. Additionally, fluorescent X-ray particles have intrinsic energy proportional to an atomic number, and an element can be identified by measuring the intrinsic energy. Specifically, silicon has intrinsic energy of 1.74±0.05 keV. Note that the number of fluorescent X-ray particles (X-ray intensity) of the release agent (silicon) ranges from 0.1 cps/μA to 1.5 cps/μA. 
     Examples of a component that can be compounded in the release agent layer  11  include a component containing a silicone component as an active ingredient. Examples of the silicone component include organopolysiloxanes, for example, dialkylpolysiloxane, alkylphenylpolysiloxane, alkylaralkylpolysiloxane, and 3,3,3-trifluoropropylmethylpolysiloxane. Dialkylpolysiloxane is, for example, dimethylpolysiloxane, diethylpolysiloxane, methylisopropyl polysiloxane, or methyldodecylpolysiloxane. Alkylphenylpolysiloxane is, for example, methylphenylpolysiloxane, a dimethylsiloxane-methylphenylsiloxane copolymer, or a dimethylsiloxane-diphenylsiloxane copolymer. Alkylaralkylpolysiloxane is, for example, methyl (phenylethyl) polysiloxane or methyl (phenylpropyl) polysiloxane. One type or two or more types of these organopolysiloxanes may be used in combination. 
     In the pneumatic tire described above, the amount of silicon in the release agent detected by fluorescent X-ray analysis at least in the fixing region S for the sensor unit  20  is set to from 0.1 wt % to 10.0 wt %, and the sensor unit  20  is fixed in a state where a trace amount of the release agent is applied to the tire inner surface Ts. Thus, while the release agent inhibits permeation of air from the tire inner surface Ts and air retention properties improve, the adhesiveness between the tire inner surface Ts and the sensor unit  20  can be ensured sufficiently. Here, when the amount of silicon in the release agent in the fixing region S for the sensor unit  20  is less than 0.1 wt %, improvement of air retention properties cannot be obtained, and when the amount is more than 10.0 wt %, the adhesiveness of the sensor unit  20  degrades, and sufficient durability cannot be obtained. 
     In  FIG. 1  and  FIG. 2 , the sensor unit  20  is disposed in an inner side of the ground contact edge in the tire width direction. In the case of the sensor  23  that detects an amount of wear of the tread portion  1 , the sensor unit  20  is disposed in this way, and thus the sensor  23  can accurately acquire the tire information. 
     Additionally, the sensor unit  20  is bonded directly to the tire inner surface Ts. In the case of the sensor  23  that detects an amount of wear of the tread portion  1 , the sensor unit  20  is bonded directly to the tire inner surface Ts in this way, and thus the sensor  23  can accurately acquire the tire information. 
     In the pneumatic tire described above, the adhesive strength of the adhesive layer  10  preferably ranges from 0.4 N/mm 2  to 100 N/mm 2 . Particularly, the adhesive strength preferably ranges from 5.0 N/mm 2  to 80 N/mm 2 . The adhesive strength of the adhesive layer  10  is appropriately set in this way, and thus work of installing the sensor unit  20  can be performed easily while maintaining good adhesive strength of the adhesive layer  10 . Here, when the adhesive strength of the adhesive layer  10  is less than 0.4 N/mm 2 , the adhesiveness between the tire inner surface Ts and the sensor unit  20  degrades, and the sensor unit  20  easily peels. On the other hand, when the adhesive strength of the adhesive layer  10  is more than 100 N/mm 2 , replacement work in replacing the sensor unit  20  cannot be performed easily. 
       FIG. 3  illustrates a modified example of a pneumatic tire according to an embodiment of the present technology. As illustrated in  FIG. 3 , a base  24  that holds a sensor unit  20  is inserted between the sensor unit  20  and an adhesive layer  10 . The base  24  functions as a cushioning material to prevent the sensor unit  20  from peeling due to tire deformation. As a material for the base  24 , natural rubber (NR), chloroprene rubber (Cr), butyl rubber (IIR), ethylene-propylene-diene rubber (EPDM), urethane rubber, nitrile rubber (NBR), a thermoplastic elastomer, and a thermosetting elastomer can be exemplified. In a case where the base  24  is made of any of these materials, the base  24  is less likely to be damaged by tire deformation. Particularly, the base  24  may be made of rubber having tensile elongation at break of 80% or more. Additionally, the base  24  is preferably in a solid state, and is more preferably porous. In a case where the base  24  is porous, the base  24  has an excellent cushioning effect and is advantageous against peeling of the sensor unit  20  due to tire deformation. The base  24  is made of any of the above-described materials, and thus the base  24  can follow tire deformation, and can prevent peeling of the sensor unit  20  due to tire deformation. Note that, in the embodiment illustrated in  FIG. 3 , the example in which the base  24  is formed in a U shape in a cross-sectional view in the tire width direction is described, but the shape of the base  24  is not particularly limited. In  FIG. 3 , a fixing region S for the sensor unit  20  corresponds to a fixing region for the base  24  that holds the sensor unit  20 . 
       FIG. 4  illustrates another modified example of a pneumatic tire according to an embodiment of the present technology. As illustrated in  FIG. 4 , a sensor unit  20  is bonded to a smooth surface M of a tire inner surface Ts via an adhesive layer  10 . The smooth surface M is formed in a central portion in the tire width direction in performing vulcanization molding by using a bladder. The smooth surface M is an annular flat surface extending in the tire circumferential direction. In a case where the sensor unit  20  is disposed on the smooth surface M of the tire inner surface Ts, the adhesiveness between the tire inner surface Ts and the sensor unit  20  can be enhanced effectively. Note that in  FIG. 4 , a fixing region S for the sensor unit  20  corresponds to a fixing region for a base  24  that holds the sensor unit  20 . 
     Next, a method for manufacturing a pneumatic tire according to an embodiment of the present technology will be described. In vulcanizing a green tire, a bladder is coated (preferably baked) with a release agent in advance, and a coating layer made of the release agent is formed in an outer surface of the bladder. The step of forming the coating layer in the outer surface of the bladder is performed, while, for example, after application of the release agent, the bladder is stored at 150° C. for 1 hour, at 90° C. for 4 hours, or at ambient temperature for 8 hours. Additionally, the step of forming the coating layer in the outer surface of the bladder is performed once or more and three times or less. The green tire is vulcanized by using the bladder in which the coating layer is formed in this way. Then, in the vulcanized tire, the sensor unit  20  is fixed to the fixing region S for the sensor unit  20  in the tire inner surface Ts of the tread portion  1  via the adhesive layer  10 . In a case where vulcanization is performed by using the bladder including the coating layer made of the release agent in this way, the release agent layer  11  is formed in the tire inner surface Ts of the vulcanized pneumatic tire. In the release agent layer  11 , the release agent is not transferred entirely in the tire inner surface Ts, but is scattered in the tire inner surface Ts. 
     Instead of performing vulcanization by using the bladder including the coating layer made of the release agent as described above, the step of vulcanizing the green tire can also include applying the release agent to an inner surface of the green tire, vulcanizing the green tire by using a regular bladder, and then irradiating the tire inner surface Ts of the vulcanized tire with a laser to remove the release agent applied to the tire inner surface Ts. 
     As described above, vulcanization is performed by using the bladder including the coating layer made of the release agent, or vulcanization is performed by using a regular bladder and the tire inner surface Ts of the vulcanized tire is irradiated with a laser to remove the release agent, and thus the amount of silicon in the release agent detected by fluorescent X-ray analysis at least in the fixing region S for the sensor unit  20  can be set to from 0.1 wt % to 10.0 wt %. In a case where a trace amount of the release agent is applied to the tire inner surface Ts in this way, while the release agent inhibits permeation of air from the tire inner surface Ts and air retention properties improves, the adhesiveness between the tire inner surface Ts and the sensor unit  20  can be ensured sufficiently. 
     Particularly, at the step of forming the coating layer in the outer surface of the bladder, coating time t (hours) and temperature T (° C.) of the coating layer preferably satisfy t≥0.0001T 2 −0.07T+9 and T≤180° C. Additionally, preferably, the relationship between the coating time t and the temperature T described above is satisfied, and the coating time t ranges from 1 to 8 hours. Further, more preferably, the temperature T is 90° C. and the coating time t is 4 hours, and most preferably, the temperature T is 150° C. and the coating time t is 1 hour. Satisfying such conditions, in the bladder including the coating layer, time for coating the release agent can be reduced and shortening of a bladder life can be prevented. Here, as the temperature T (° C.) is higher, the coating layer can be formed in shorter time but the bladder is more likely to deteriorate, and a bladder life is shortened. 
     EXAMPLES 
     Tires according to Comparative Examples 1 to 5 and Examples 1 to 7 were manufactured. The tires each have a tire size of 275/40R21 and include at least one sensor unit fixed to a tire inner surface via an adhesive layer and including a sensor that acquires tire information. A method for removing a release agent, application of the release agent to the tire inner surface, use of a bladder including a coating layer made of the release agent during vulcanization, and an amount of the release agent (silicon) in the tire inner surface are set as indicated in Table 1. 
     As for Comparative Example 1, the release agent was applied to the tire inner surface, and work of removing the release agent was not performed. Additionally, as for Comparative Examples 2 to 4, the release agent was applied to the tire inner surface, and work of removing the release agent was performed after the end of the vulcanization step. Specifically, in Comparative Example 2, the release agent in the tire inner surface was removed by buffing, and in Comparative Example 3, a film bonded to the tire inner surface in advance was peeled to remove the release agent from the tire inner surface, and in Comparative Example 4, the tire inner surface was cleaned to remove the release agent from the tire inner surface. 
     Note that in Table 1, an amount (wt %) of the release agent (silicon) in the tire inner surface was obtained by using an energy dispersive fluorescent X-ray analyzer (EDX-720, available from Shimadzu Corporation) to measure amounts of the release agent (silicon) at a total of five locations including a center point of the fixing region for the sensor unit in each test tire obtained after the end of the manufacturing step, two locations in both sides in the tire circumferential direction with the center point as the center, and two locations in both sides in the tire width direction with the center point as the center, and averaging the measurement values. Measurement conditions include a voltage of 50 kV, a current of 100 μA, integration time of 50 seconds, and a collimator of φ10 mm in a vacuum state. 
     The test tires were evaluated for the adhesiveness of the sensor unit and air retention properties by a test method described below. The results of the evaluation are also indicated in Table 1. Further, the tires according to Examples 1 to 3 and 5 to 7 and Comparative Example 5 were evaluated for bladder life, and the results of the evaluation are also indicated in Table 1. 
     Adhesiveness of Sensor Unit 
     Adhesiveness of the sensor unit as used here indicates evaluation of peeling in an adhering surface between the tire inner surface and the sensor unit. Each of the test tires was mounted on a wheel having a rim size of 21×9.5J, and a running test was performed by using a drum testing machine at a running speed of 80 km/h, an air pressure of 120 kPa, a load of 8.5 kN, and a running distance of 6480 km. After the test was performed, presence of falling off or peeling of the sensor unit was visually observed. The case where there is no falling off and no peeling of the sensor unit is indicated by “excellent,” the case where less than ⅛ of all the sensor unit peeled is indicated by “good,” the case where ⅛ or more and less than ¼ of all the sensor unit peeled is indicated by “fair,” and the case where ¼ or more of all the sensor unit peeled is indicated by “poor.” 
     Air Retention Properties 
     Each of the test tires was mounted on a wheel having a rim size of 21×9.5J, and left for 24 hours at an air pressure of 270 kPa and a temperature of 21° C. Then, an initial air pressure of 250 kPa was set, and air pressure was measured for 42 days. An inclination of an air leakage amount from the 15th day to the 42nd day was determined. The evaluation results are expressed as index values by using reciprocals of measurement values, with Comparative Example 1 being assigned as the reference 100. The larger index values mean excellent air retention properties. 
     Bladder Life 
     Vulcanization was performed by using a bladder including a coating layer made of a release agent, and the number of green tires that enabled vulcanization in a state where an amount of the release agent (silicon) transferred to a tire inner surface was within the range specified in an embodiment of the present technology was measured. Evaluation results are expressed as index values, with Example 1 being assigned as the reference 100. The larger index values mean a more excellent bladder life. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1-1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Method for removing release 
                 — 
                 Buffing 
                 Peeling of 
                 Cleaning 
               
               
                 agent 
                   
                   
                 film 
               
               
                 Application of release agent to 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
               
               
                 tire inner surface 
               
               
                 Use of bladder including 
                 No 
                 No 
                 No 
                 No 
               
               
                 coating layer made of release 
               
               
                 agent during vulcanization 
               
               
                 Amount of release agent 
                   45.0 
                  0 
                  0 
                   15.0 
               
               
                 (silicon) in tire inner surface 
               
               
                 (wt %) 
               
               
                 Coating time t (upper stage) 
                 — 
                 — 
                 — 
                 — 
               
               
                 and temperature T (lower 
               
               
                 stage) of coating layer 
               
               
                 Adhesiveness of sensor unit 
                 Poor 
                 Excellent 
                 Excellent 
                 Fair 
               
               
                 Air retention properties 
                 100 
                 89 
                 96 
                 100 
               
               
                 Bladder life 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1-2 
               
               
                   
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Method for removing release 
                 — 
                 — 
                 — 
                 Laser 
               
               
                 agent 
                   
                   
                   
                 irradiation 
               
               
                 Application of release agent to 
                 No 
                 No 
                 No 
                 Yes 
               
               
                 tire inner surface 
               
               
                 Use of bladder including 
                 Yes 
                 Yes 
                 Yes 
                 No 
               
               
                 coating layer made of release 
               
               
                 agent during vulcanization 
               
               
                 Amount of release agent 
                    0.1 
                    2.0 
                   10.0 
                   10.0 
               
               
                 (silicon) in tire inner surface 
               
               
                 (wt %) 
               
               
                 Coating time t (upper stage) 
                 2 h 
                 5 h 
                 8 h 
                 — 
               
               
                 and temperature T (lower 
                 23° C. 
                 23° C. 
                 23° C. 
               
               
                 stage) of coating layer 
               
               
                 Adhesiveness of sensor unit 
                 Excellent 
                 Excellent 
                 Good 
                 Good 
               
               
                 Air retention properties 
                  98 
                  99 
                 100 
                 100 
               
               
                 Bladder life 
                 100 
                 100 
                 102 
                 — 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1-3 
               
               
                   
                   
               
               
                   
                 Comparative 
                   
                   
                   
               
               
                   
                 Example 5 
                 Example 5 
                 Example 6 
                 Example 7 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Method for removing release 
                 — 
                 — 
                 — 
                 — 
               
               
                 agent 
               
               
                 Application of release agent to 
                 No 
                 No 
                 No 
                 No 
               
               
                 tire inner surface 
               
               
                 Use of bladder including 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
               
               
                 coating layer made of release 
               
               
                 agent during vulcanization 
               
               
                 Amount of release agent 
                   11.0 
                   10.0 
                   10.0 
                   10.0 
               
               
                 (silicon) in tire inner surface 
               
               
                 (wt %) 
               
               
                 Coating time t (upper stage) 
                 9 h 
                 4 h 
                 1 h 
                 30 min 
               
               
                 and temperature T (lower 
                 23° C. 
                 90° C. 
                 150° C. 
                 170° C. 
               
               
                 stage) of coating layer 
               
               
                 Adhesiveness of sensor unit 
                 Fair 
                 Good 
                 Good 
                 Good 
               
               
                 Air retention properties 
                 100 
                 100 
                 100 
                 100 
               
               
                 Bladder life 
                 101 
                 103 
                 105 
                 101 
               
               
                   
               
            
           
         
       
     
     As can be seen from Table 1, as compared with Comparative Example 1, in the pneumatic tires according to Examples 1 to 7, the adhesiveness of the sensor unit was enhanced while maintaining air retention properties. Particularly, in Examples 3 and 5 to 7, bladder life was enhanced. 
     On the other hand, in Comparative Example 2, since the tire inner surface was buffed, a gauge of an innerliner became thin, and thus air retention properties degraded. In Comparative Example 3, since the film was bonded to the tire inner surface and was peeled after vulcanization, air retention properties degraded. In Comparative Example 4, although the tire inner surface was cleaned, the release agent in the tire inner surface could not completely be removed, and a relatively large amount of the release agent remained in the tire inner surface. Thus, the adhesiveness of the sensor unit decreased. In Comparative Example 5, a large amount of the release agent (silicon) in the tire inner surface was set, and thus an effect of enhancing the adhesiveness of the sensor unit was insufficient.