Patent ID: 12214565

DETAILED DESCRIPTION

Configurations of embodiments of the present technology are described in detail below with reference to the accompanying drawings.FIGS.1to3illustrate a pneumatic tire according to an embodiment of the present technology. As illustrated inFIG.1, the pneumatic tire according to the present embodiment includes an annular tread portion1extending in the tire circumferential direction, a pair of sidewall portions2disposed on both sides of the tread portion1, and a pair of bead portions3disposed inward of the sidewall portions2in the tire radial direction. A ring-shaped noise absorber6illustrated inFIG.2is mounted in the cavity4defined by the tread portion1, the sidewall portion2, and the bead portion3. This noise absorber6is disposed in a region of the tire inner surface5corresponding to the tread portion1.

A noise absorber6is bonded along the tire circumferential direction to a region of the tire inner surface5corresponding to the tread portion1, via an adhesive layer7. The noise absorber6is made of a porous material with open cells, and has predetermined noise absorbing properties based on the porous structure. Polyurethane foam is preferably used as the porous material of the noise absorber6. The adhesive layer7is not particularly limited, and for example, an adhesive or double-sided adhesive tape can be used.

In the pneumatic tire described above, as illustrated inFIG.3, a transfer layer8formed by a release agent is present between the tire inner surface5and the adhesive layer7. In other words, the noise absorber6, the adhesive layer7, and the transfer layer8of the release agent are layered in this order from the inner side in the tire radial direction. The green tire is vulcanized using a bladder provided with a coating layer made of a release agent, whereby the transfer layer8is transferred on the tire inner surface5of the vulcanized pneumatic tire. The release agent transferred in this manner is not entirely transferred but is dispersed on the tire inner surface5.

The thickness g of the transfer layer8formed of the release agent illustrated inFIG.3is 0.1 μm to 100 μm at least in the fixation region for the noise absorber6of the tire inner surface5. The thickness g of this transfer layer8formed by the release agent can be detected using an electron microscope. When measuring the thickness g of the transfer layer8formed by the release agent using an electron microscope, the thickness of a plurality of locations (for example, four locations in the tire circumferential direction and three locations in the tire lateral direction) is measured using a sample obtained by cutting out the pneumatic tire along the tire lateral direction. Then, the thickness g (average thickness) of the transfer layer8of the mold release agent is calculated by averaging the measurement values measured at the plurality of locations.

Examples of components that can be compounded in the transfer layer8formed by the release agent include those containing a silicone component as an active ingredient. Examples of the silicone component include organopolysiloxanes, such as, for example, dialkylpolysiloxane, alkyl phenyl polysiloxane, alkyl aralkyl polysiloxane, 3,3,3-trifluoropropylmethylpolysiloxane, and the like. The dialkylpolysiloxane is, for example, dimethylpolysiloxane, diethylpolysiloxane, methyl isopropyl polysiloxane, and methyl dodecyl polysiloxane. Examples of the alkyl phenyl polysiloxane include a methylphenylpolysiloxane, a dimethylsiloxane-methylphenylsiloxane copolymer, and a dimethylsiloxane-diphenylsiloxane copolymer. Examples of the alkyl aralkyl polysiloxane include methyl (phenylethyl) polysiloxane, and methyl (phenylpropyl) polysiloxane. One type or two or more types of these organopolysiloxanes may be used in combination.

By performing vulcanization using a bladder provided with a coating layer formed by a release agent as described above, a thickness of the release agent transferred can be 0.1 μm to 100 μm at least in a fixation region for the noise absorber6. The release agent in such a small amount attached to the tire inner surface5in this manner inhibits the permeation of air from the tire inner surface5so that air retention can be improved, while sufficiently ensuring the adhesion between the tire inner surface5and the noise absorber6. Here, if the thickness of the release agent transferred on the fixation region for the noise absorber6is less than 0.1 μm, improvement in air retention cannot be achieved, and when the thickness is greater than 100 μm, the adhesion of the noise absorber6will be compromised resulting in a failure to achieve sufficient durability.

Furthermore, the tire productivity would not be compromised unlike in conventional cases where the tire inner surface is buffed, where a film is applied to the tire inner surface, or where the tire inner surface is cleaned. As a result, the air retention and the adhesion of the noise absorber6can both be achieved without compromising the tire productivity. On the other hand, removal of the release agent adhered to the tire inner surface with the conventional method described above involves additional working time in each step. As a result, tire productivity is lower than that in a case where the noise absorber is fixed in a state in which the release agent is adhered as in the present technology.

In the pneumatic tire described above, the peeling adhesive strength of the adhesive layer7is preferably from 5 N/20 mm to 100 N/20 mm. With the peeling adhesive strength of the adhesive layer7thus appropriately set, the fixing strength of the noise absorber6is suitably maintained and also application of the noise absorber6and removal of the noise absorber6upon tire disposal can be easily performed. Examples of the adhesive that forms the adhesive layer7include acrylic-adhesives, rubber-based adhesives, and silicone-based adhesives, and the adhesive layer7is preferably formed from any of these adhesives. Silicone adhesives are particularly preferable because the adhesion using such adhesives is free of temperature dependency meaning that excellent adhesion with the noise absorber6can be achieved even when the release agent is remaining. Acrylic adhesives have excellent heat resistance and are therefore suitable in high speed regions.

The adhesive layer7is formed by double-sided adhesive tape, and the adhesive layer7is preferably configured to have a total thickness in a range from 10 μm to 150 μm. The adhesive layer7having such a configuration ensures followability with respect to deformation during molding. The adhesive layer7with a total thickness that is less than 10 μm results in a failure to ensure sufficient adhesion to the noise absorber6due to insufficient strength of the double-sided adhesive tape. The adhesive layer7with a total thickness exceeding 150 μm inhibits heat dissipation during high speed traveling and thus is likely to result in deterioration of high-speed durability.

The adhesive layer7is preferably a double-sided adhesive tape including only an adhesive or a double-sided adhesive tape including an adhesive and a nonwoven fabric. The double-sided adhesive tape including only an adhesive (a double-sided adhesive tape without a base member serving as a support that supports the adhesive) will not hinder heat dissipation so that the deterioration of high-speed durability can be suppressed and also features excellent followability with respect to deformation of the tire. The double-sided adhesive tape including an adhesive and a nonwoven fabric (a double-sided adhesive tape having a nonwoven fabric serving as the base member) can achieve both high-speed durability and followability. Here, when the base member is formed from a rigid material such as polyethylene terephthalate (PET), peeling is more likely to occur between the base material and the adhesive or the tire and the adhesive due to deformation of the tire, leading to the dropping of the noise absorber6. In addition, if the strength at break and the breaking elongation of the base member are low, the base member itself may be damaged. A base member formed from acrylic foam has a large thickness which is likely to lead to deterioration of the high-speed durability.

In the pneumatic tire described above, the hardness of the noise absorber6is preferably 80 N to 150 N, the tensile strength of the noise absorber6is preferably not less than 90 kPa, and the breaking elongation of the noise absorber6is preferably 200% or greater. The noise absorber6with such physical properties has superior durability against expansion of the tire during inflation and/or shear strain of the adhesive surface due to rolling on ground. Here, the noise absorber6with the hardness that is less than 80 N is likely to be compressed and deformed by centrifugal force during traveling. The noise absorber6with the hardness exceeding 150 N cannot follow the deformation of the tire during traveling and thus might break.

The center position of the noise absorber6in the width direction is preferably in a range of ±10 mm from the tire equator, and more preferably being in a range of ±5 mm from the tire equator. With the noise absorber6disposed in this manner, tire uniformity would not be compromised.

The volume of the noise absorber6is preferably in a range from 10% to 30% of the cavity volume of the tire. The width of the noise absorber6is more preferably in the range from 30% to 90% of the tire ground contact width. This makes it possible to obtain even higher sound absorbing effect of the noise absorber6. The noise absorber6with a volume that is less than 10% of the cavity volume of the tire fails to appropriately provide the sound absorbing effect. The noise absorber6with a volume exceeding 30% of the inner cavity volume of the tire can only achieve a constant noise reduction effect against the noise due to the cavernous resonance, meaning that higher reduction effect cannot be obtained.

As illustrated inFIG.2, the noise absorber6preferably has a missing portion9in at least one position in the tire circumferential direction. The missing portion9is a portion where the noise absorber6is not present on the tire circumference. With the missing portion9provided in the noise absorber6, expansion of the tire during inflation and/or shearing strain of the adhesion surface due to rolling on ground can be tolerated for a long period of time, and the shearing strain on the adhesion surface of the noise absorber6can be effectively relaxed. Such a missing portion9may be provided at one location or at three to five locations on the tire circumference. That is, when the missing portions9are provided at two positions on the tire circumference, tire uniformity due to mass unbalance significantly deteriorates, and when the missing positions9are provided at six or more positions on the circumference, production cost significantly increases.

Note that in cases where the missing portion9is provided at two or more locations on the tire circumference, the noise absorbers6are intermittently provided in the tire circumferential direction. However, even in such cases, for example, the plurality of noise absorbers6may be connected to each other using other laminates such as the adhesive layer7formed by double-sided adhesive tape, so that the noise absorbers6can be handled as an integral member to be easily attached to the tire inner surface5.

Next, a method of manufacturing the pneumatic tire according to an embodiment of the present technology will be described. When vulcanizing a green tire, a release agent is coated (preferably baked) on the bladder in advance to form a coating layer formed by the release agent on the outer surface of the bladder. The step of forming the coating layer on the outer surface of the bladder is implemented, for example, under storage, after the coating of the release agent, with a condition of an hour at 150° C., four hours at 90° C., or eight hours at ambient temperature. Furthermore, the step of forming the coating layer on the outer surface of the bladder is performed once, twice, or three times. The green tire is vulcanized using the bladder with the coating layer thus formed. Then, in the vulcanized tire, the noise absorber6is fixed to the fixation region for the noise absorber6on the tire inner surface5of the tread portion1along the tire circumferential direction via the adhesive layer7.

By performing vulcanization using a bladder provided with a coating layer formed by a release agent as described above, a thickness of the release agent transferred can be 0.1 μm to 100 μm at least in a fixation region for the noise absorber6. The release agent in such a small amount attached to the tire inner surface5in this manner inhibits the permeation of air from the tire inner surface5so that air retention can be improved, while sufficiently ensuring the adhesion between the tire inner surface5and the noise absorber6. Furthermore, the tire productivity would not be compromised unlike in conventional cases where the tire inner surface is buffed, where a film is applied to the tire inner surface, or where the tire inner surface is cleaned. As a result, the air retention and the adhesion of the noise absorber6can both be achieved without compromising the tire productivity.

In particular, the coating layer is preferably formed on the outer surface of the bladder with a coating time t (hour) and a temperature T (° C.) of the coating layer satisfying t≥−0.0571 T+9.14 and 10° C.≤T≤180° C. Furthermore, it is more preferable to set the temperature T to 90° C. and to set the coating time t to 4 hours, and it is even more preferable to set the temperature T to 150° C. and to set the coating time t to 1 hour. By satisfying these conditions, the time for coating the release agent in a bladder provided with the coating layer can be reduced, without shortening the bladder life. Here, higher temperatures T (° C.) allow the coating layer to be formed in a shorter period of time, but may cause deterioration of the bladder resulting in a shorter bladder life.

EXAMPLES

Tires according to Comparative Examples 1 to 5 and Examples 1 to 3 were manufactured based on a pneumatic tire having a tire size of 275/35ZR20, and having a noise absorber fixed to the inner surface of a tread portion via the adhesive layer, along the tire circumferential direction. A method of removing the release agent, the coating of the tire inner surface by the release agent, use of a bladder provided with a coating layer formed by the release agent at the time of vulcanization, and the thickness (μm) of the release agent on the tire inner surface are set as in Table 1.

In Comparative Example 1, the release agent was coated on the tire inner surface, and the release agent was not removed. In Comparative Examples 2 to 4, the release agent was applied to the tire inner surface, and the release agent was removed after the completion of the vulcanization step. Specifically, the release agent on the tire inner surface was removed by buffing in Comparative Example 2, by peeling off the film adhered to the tire inner surface in Comparative Example 3, and by washing the tire inner surface in Comparative Example 4.

Note that in Table 1, the thickness (μm) of the release agent on the tire inner surface was determined by measuring the thickness of the mold release agent at four locations in the tire circumferential direction and three locations in the tire lateral direction of each of the test tires after the fabrication step was completed, and by averaging the resultant measurement values.

Adhesion of the noise absorber, air retention, and tire productivity were evaluated for these test tires according to the following test methods. Table 1 also shows the result of the evaluation.

Adhesion of Noise Absorber:

The adhesion of the noise absorber referred to here is an evaluation of the peeling of the adhesive surface between the tire inner surface and the noise absorber. The test tires were assembled on wheels having a rim size of 20×9.5 J, and subjected to a running test on a drum testing machine at testing conditions of speed of 80 km/h, air pressure of 160 kPa, load of 8.5 kN, and traveling distance of 6,480 km, after which whether the noise absorber has dropped or peeled was visually confirmed. Here, “Excellent” indicates a case where there is no dropping or peeling of the noise absorber, “Good” indicates a case where the peeling of the noise absorber was less than ⅛ of the entire noise absorber; “Fair” indicates a case where the peeling of the noise absorber was no less than ⅛ or no greater than ¼ of the entire noise absorber, and “Poor” indicates a case where the noise absorber peeling was no less than ¼ of the entire noise absorber.

Air Retention:

Each of the test tires was assembled on wheels having a rim size of 20×9.5J, left for 24 hours under conditions of an air pressure of 270 kPa and a temperature of 21° C., and then the air pressure was measured for 42 days with the initial air pressure set to 250 kPa to obtain the inclination of the air leakage rate in a period between the day 15 to the day 42. The evaluation results are expressed as index values using the reciprocal of the measurement values, with the value of Comparative Example 1 being defined as 100. Larger index values indicate superior air retention. Note that the conventional level of air retention is maintained as long as the index value is equal to or greater than 98.

Tire Productivity:

For each test tire, the fabrication time (minutes) required to fabricate one tire was measured. The evaluation results are expressed as index values using the reciprocal of the measurement values, with the value of Comparative Example 1 being defined as 100. Larger index values indicate superior tire productivity.

TABLE 1ComparativeComparativeComparativeComparativeExample 1Example 2Example 3Example 4Removal method of mold—BuffingFilm peelingCleaningrelease agentApplication of release agentYesYesYesYesto tire inner surfaceUse of a bladder providedNoNoNoNowith a coating layer formedby a release agent invulcanizationThickness of release agent30000150on tire inner surface (μm)Adhesion of Noise absorber:PoorExcellentExcellentFairAir Retention1008996100Tire productivity100959595ComparativeExample 1Example 2Example 3Example 5Removal method of mold————release agentApplication of release agentNoNoNoNoto tire inner surfaceUse of a bladder providedYesYesYesYeswith a coating layer formedby a release agent invulcanizationThickness of release agent0.110100110on tire inner surface (μm)Adhesion of Noise absorber:ExcellentExcellentGoodFairAir Retention9899100100Tire productivity100100100100

As can be seen from Table 1, compared to Comparative Example 1, the pneumatic tires of Examples 1 to 3 have improved adhesion of the noise absorber while maintaining air retention and without compromising the tire productivity.

On the other hand, in Comparative Example 2 where the tire inner surface was buffed, the tire productivity was compromised, and the air retention was also compromised due to the reduction of the gauge of the innerliner. In Comparative Example 3, the film was adhered to the tire inner surface and the film was peeled off after vulcanization, resulting in deterioration of tire productivity. In Comparative Example 4, although the tire inner surface was cleaned, the release agent on the tire inner surface was not completely removed. In fact, there was a relatively large amount of release agent on the tire inner surface, resulting in lower adhesion of the noise absorber. In Comparative Example 5, the thickness of the release agent on the tire inner surface was set to be large, resulting in insufficient improvement effect for the adhesion of the noise absorber.