JPH0257405A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To reduce noise, rolling resistance, and weight of a tire, by forming a reinforcing carcass ply cord arranged in the radial direction of a tire out of a polyamide monofilament cord having a elliptical section. CONSTITUTION:A tire comprises a tread part, a pair of side parts continued on both sides of the tread part, and a pair of bead parts formed on the inner circumference of the side parts. And the tire is reinforced with a carcass ply arranged carcass ply cords in the radial direction of the tire and a belt layer buried inside the tread surrounding the carcass ply. In the above-stated constitution, the carcass ply cord is formed out of a polyamide monofilament cord having a elliptical section. The occupancy ratio of the cord at a crown center part b/a is instituted to be 20%<b/a<45%. Moreover the section of the cord is instituted: 1.5<b/c<5.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a pneumatic radial tire,
This relates to tire noise reduction, tire rolling resistance reduction, and tire weight reduction.

(Prior technology) In the past, tubeless radial tires had an inner liner rubber layer attached to the inner surface of the tire to prevent air leakage, but this was considered essential to prevent air leakage. .

However, the weight of the inner liner rubber layer is as much as 400 g/piece in a 165 SR13 size radial tire for passenger cars, which has been a major hindrance in efforts to reduce the weight of the tire.

Generally, air leakage is thought to occur when high-pressure air inside the tire passes through the inner liner rubber layer and leaks to the outside of the tire through the carcass ply cord, resulting in a decrease in tire internal pressure.

Therefore, measures have been taken such as increasing the thickness of the inner liner layer, using bromobutyl or chlorobutyl rubber as the inner liner rubber with low air permeability, and further reducing the air permeability of the cord.

Also, US Patent Nos. 3963678 and 3984600
Although monofilaments of polyester fibers are disclosed in publications such as the above, the present inventors have found that although polyester monofilament cords significantly improve air permeability, they have poor fatigue resistance and are not practical for use as tire carcass cords. I found out that I can't provide it.

(Problems to be Solved by the Invention) As mentioned above, as a means to reduce the tire internal pressure (1) Use butyl rubber such as chlorobutyl and bromobutyl as a rubber with extremely low air permeability in the inner liner rubber layer. Method: (2) In order to suppress air permeation in the cord, adhesive is applied to the cord and dried, which is the so-called dipping process, which increases the cord stretch rate at a temperature close to the cord's melting point and close-packs the filament. Methods to make it difficult for air to pass through the inside of the cord by deforming the cord: Although these methods cannot completely prevent a drop in tire internal pressure, chlorobutyl rubber is effective against so-called air permeability. was used for the inner liner, the inner liner gauge at the crown center part was set to about 0.5 mm, and the above (1) Cord tension, which is considered to be difficult for air to permeate, A drop in internal pressure of about 10% was unavoidable.

This means that no matter how much you try to prevent air permeability with an inner liner, it is difficult to completely cover the inner surface of the tire with the inner liner all the way around the tire, especially down to the bead. It is essential to completely prevent it from passing through the interior.

In addition, in recent years, reducing tire noise has become a social demand, and as a result of our intensive study of the noise generation mechanism of tires, the inventors have found that the noise generated during tire running is mainly caused by minute vibrations in the tire sidewall. It was clarified that this was caused by

In general, the tire sidewall of a tire repeatedly undergoes large deformations during rotation, and when the tire touches the ground, the sidewall bulges outward, and when it comes off the ground, the sidewall repeats its normal state, that is, it is relatively indented. . However, the tire sidewall exhibits even more complex behavior and repeatedly undergoes complex three-dimensional deformation. Such multidimensional movement of the sidewall vibrates the air near the tire sidewall, producing noise. As a countermeasure to this problem, it would be sufficient to suppress the deformation of the tire sidewall, but this has the disadvantage that suppressing the sidewall deformation reduces the vibration absorption ability and extremely deteriorates the riding comfort due to the vibration.

(Means for Solving the Problems) Therefore, the inventors of the present invention have solved the above problems and have conducted intensive studies to prevent air leakage from radial tires and reduce tire noise. As a result, the monofilament cord has achieved 100% air permeation through the cord. We succeeded in preventing this problem and also achieved lower tire noise and tire weight. First, when the polyester monofilament described in U.S. Pat. No. 3,963,678, U.S. Pat. However, the present inventors have clarified the fact that fatigue resistance and adhesiveness are poor, and it cannot be put to practical use as a tire cord.

Therefore, it is easy to imagine using a polyamide monofilament to reduce these weaknesses, but it still has poor fatigue resistance.

However, we have found that an elliptical monofilament can ensure a level of fatigue resistance that does not pose any problem in practical use.

It is generally believed that when monofilament is made into a single cord, compressive strain and tensile strain are applied to the cord, resulting in a significant decrease in so-called fatigue resistance. It was found that fatigue resistance was improved.

The major axis and minor axis C of the so-called filament cord cross-sectional shape
It is preferable that the ratio b/c (Fig. 1) is l,5 < b/c < 5. If b/c is 1.5 or less, it will be close to a perfect circle, improving fatigue resistance and adhesion. Unfavorable from this point of view. Also b
When /c is 5 or more, fatigue resistance and adhesion are improved, but even if the number of filament cords is increased, there is a limit to the number of filament cords, which causes the disadvantage that the tire carcass strength is insufficient. This is not preferred in practice since the number of sheets has to be increased. For these reasons, 1.5
b/c < 5 is preferred, but preferably 2 < b
/c<4 is more preferable in terms of fatigue resistance and strength design.

By applying a monofilament polyamide coat having such an elliptical shape to the chassis brazing of a pneumatic radial tire, it becomes possible to reduce tire noise, reduce rolling resistance, and reduce tire weight, which are the objectives of the present invention.

In other words, the gauge at the center of the tire crown is usually 0.
．． If a 5 mm inner liner is attached to the inner surface of the tire, it is not possible to reduce the tire weight, so it is possible to significantly reduce the inner liner rubber gauge by taking advantage of the fact that the air permeability of the tire cord can be greatly improved with monofilament. It was investigated. However, even if the inner liner gauge was simply made thinner, the air permeability of the rubber itself would be poor, and the inner liner would crack due to strain. Therefore, when 30 parts or more of mica, 5 parts or more of P, E resin, or 40 parts or more of all butyl or chlorobutyl were added to the inner liner rubber, air permeability was prevented even in thin gauges.
It has also been found that it is possible to improve fatigue resistance against cracks, etc. Making the inner liner thinner like this is effective for lower tire weight ranges even when using normal tire cords, but as mentioned above, normal tire cords inherently allow air to pass through easily, so using an inner liner is not recommended. Even if the tires are improved to have a thinner gauge, it is difficult to maintain the same low tire air pressure level as in the past, so the inner liner with a single gauge can only be effective when used in conjunction with monofilament.

In this way, the combination of monofilament and inner liner rubber can increase the inner liner gauge to 0.4 mm.
Only by doing the following will it be possible to manually manufacture the tire that is the object of the present invention.

Furthermore, it is preferable to set the inner liner gauge to 0.2 mm or less from the viewpoint of reducing tire weight. For example, the inner liner gauge of the conventional 0.51 is 0.15n+
m, it is possible to reduce the weight of a 165 SR13 size tire by more than 5% (350 g) of the total tire weight, and furthermore, it is possible to obtain a tire that can significantly improve the drop in tire internal pressure compared to conventional tires.

In addition, the tire performance of the present invention is significantly improved in rolling resistance and noise reduction/reduction performance, but the former rolling resistance is only 2% compared to conventional tires if the inner liner is made thinner.
It is improved only to a certain degree. However, by combining it with a monofilament cord, an improvement of about 10% is possible. On the other hand, simply using a monofilament cord as the carcass ply cord does not necessarily improve the rolling resistance in all cases, and it is closely related to the number of monofilament cords. In other words, the rolling resistance is improved as the number of strokes (cord occupation rate) is smaller, and the inventors also found that the rolling resistance improvement effect can be obtained when b/a shown in Fig. 1 is 45% or less. This is a fact revealed by. According to studies by the inventors, when the cord occupancy rate b/a is about 30%, the rolling resistance is improved by about 10% compared to conventional tires.
The smaller the code occupancy rate, the greater the effect.
If the cord occupancy rate is less than 20%, it is not preferable because the tire safety factor will drop significantly due to an insufficient number of cords. In addition, it is generally preferable that the tire safety factor, which is defined by the cord strength x number of strokes, is a certain value or more, but when the monofilament cord used in the present invention is used, the value defined by the conventional cord strength x the number of strokes is lower. It has become clear that it does not matter if there is less, and as a result, it is possible to significantly reduce the amount of code used.

The reason for this is thought to be that the use of monofilament cord improves the rigidity of the tire side part. For example, when a plunger is applied to the sidewall part, the plunger energy is the same as that of a conventional twisted cord (cord strength x number of strokes). The improvement is about 20% for the monofilament cord carcass compared to when used in the monofilament cord carcass. That is, due to the improved rigidity of the sidewall portion, when the plunger is pushed into the sidewall, the concave portion expands and the stress is uniformly and widely dispersed. Therefore, in a tire using a monofilament cord, it is possible to reduce the strength of the cord or the number of cord strikes by about 20% compared to the conventional tire safety factor, thereby making it possible to significantly reduce rolling resistance.

Further, such improvement in the rigidity of the sidewall portion is also recognized to have a significant effect on reducing tire noise. Tire noise is the vibration of a small area of the tire sidewall, and is not the deformation strain of the entire tire sidewall, so it is possible to reduce the noise without impairing the tire vibration riding comfort. In other words, monofilament cord has high bending rigidity, which prevents slight deformation of the tire sidewall, and as a result, prevents membrane deformation of the tire sidewall, which is a source of noise generation, making it possible to significantly reduce noise. be.

(Example) Next, the present invention will be explained by examples.

The radial tires used in Examples and Comparative Examples were subjected to the following measurements.

(1) Number of driving cuts Cut the tire crown center part in the tire circumferential direction,
After puffing the cross section, the number of carcass ply cord strikes per inch length was measured.

The unit is wood/inch.

(2) Cord occupancy rate The diameter of the cord (in the case of an elliptical cord, the major axis and minor axis) was measured from the cross section created in (1), and the major axis was defined as b and the minor axis as a. In addition, the cord occupation rate was calculated by dividing the number of cords driven per inch length x major diameter by inches (see Figure 1).

1 cord occupancy (%) (3) The inner liner gauge was measured from the cross section created with the inner liner gauge (1).

(4) Tire internal pressure reduction rate index After filling the tire with an internal pressure of 1.9 atm and leaving the tire in a room at 25 ± 1'C for 24 hours, the internal pressure was adjusted to 1.9 atm again, and the tire was filled with an internal pressure of 1.9 atm for 60 days. Leave it indoors at ±1°C.
After 60 days, the internal pressure of the tire was measured. The internal pressure of conventional tires decreased by approximately 0.2 atm over a two-month period, but this internal pressure decrease was taken as 100 and indexed; (5) Rolling resistance index Internal pressure of 1.70 kg/c on a drum with an outer diameter of 1708 mm.
A test tire adjusted to JIS 100% was installed.
After applying the load, the drum was pre-run for 30 minutes at 80 km/hr, the air pressure was readjusted and the drum rotation speed was increased to a speed of 200 km/hr, and then the drum was allowed to coast, and the speed was increased from 185 km/hr to 20 km/hr. It was calculated from the moment of inertia until the drum rotation speed decreased to km/hr.

Tire rolling resistance formula Medium■ D Ni drum inertia moment ■ L: Tire moment of inertia l? D Nidram radius Rt: Tire radius The rolling resistance value at 50 km/l+r determined by the above formula was determined as a representative value. Note that the measurement was carried out in a room whose environment was controlled at 24±2°C. The indexing was expressed as test tire index=100+100X.

As a result, the smaller the rolling resistance value, the larger the index.
Therefore, fuel efficiency is improved.

(6) Noise After a preliminary run of 20 km at a speed of 60 to 80 km/hr with an internal tire pressure of 1.7 kg/cm2 and a load at full capacity, the internal tire pressure was increased to 1.7 kg/cn+'' again. Adjust and test vehicle speed 40.60.80.100 km
/ hr and 7.5 mi from the vehicle center line! The microphone noise level was measured. Incidentally, the vehicle started coasting 50 m in front of the microphone, and continued coasting for an additional 50 m or more after passing the microphone. Two microphones were installed at a height of 1.2 m above the ground with a width of 50 cm, and the microphones were oriented perpendicular to the tire running direction and parallel to the road surface. Also, the speed is test speed ±2 km/h
The speed was calculated from the passing time of a total of 10 m section centered on the microphone position, and the noise level was recorded after confirming that it was within the permissible range of vehicle speed.

Further, it is desirable that the background noise is 10 dB (A) or less of the passing noise. The measurement was performed using the average value obtained twice for each speed condition, and the difference in the read noise level was 2.5 d.
(A) In the case of above, the test was repeated two more times and the average of the four tests was adopted. The measurement value was obtained by averaging the noise level read by the microphone and the noise level from the tape playback, and the recording format was in accordance with JASO 7319.

(7) Strong cord Tire A carcass ply cord with a length of about 35 cm centered on the crown center was collected from the tire, and JI was conducted with a distance of 25 cm between chunks centered on the crown center.
The strength at break was measured by pulling at room temperature in accordance with S L 1017, and the value obtained by dividing the strength at break by the torque denier before twisting was defined as the strength S (g/d). The denier before twisting was used as the tote denier, but this was done to avoid complication since the cord would expand and contract slightly during the cord treatment process and tire vulcanization process.

The tires are 165 SR13 size and the carcass ply is regular polyester (PET) 1500d/2,4
A twisted cord with a twist of 0x40T/10cm and a 4000 d monofilament cord whose main component is nylon 66 were trial-produced by changing the number of twists as appropriate. Also, the belt is 2
The cord structure consists of two steel belt layers with a diameter of 0.2
A 3 mm 1×5 structure was used. The above nylon monofilament carcass ply is made using the following dip liquid adhesive:
Lucine 1, 306 formalin (37%) 1.900 caustic soda 0.
036 VP Latex (41%) 5.800 SBR Latex (40%) 23.942 After coating, adhesive tension heat treatment was performed under the conditions shown in Table 1 below.

Table 1: Minus stretch (0
-3%) is preferable. In addition, polyester cord was treated under normal processing conditions, dry zone: 140'
C1Ig/d, 120 seconds, hot zone = 245°C1
Ig/d, 45 seconds, norm zone: 250°C10,5
g/d, 45 seconds of treatment temperature, tension, and exposure time.

Each cord was made into a sudare weave in a conventional manner, subjected to dip treatment under the above conditions, coated with rubber, and used as a carcass ply as a conventional rubberized cloth for tires. The properties of the raw cord and the dimpled cord are shown in Table 2 below.

The important thing in the tension heat treatment of seven filament cords is to keep the stretch in the cord tension heat treatment process on the contraction side, and the tire molding and vulcanization conditions, etc., which have a large pulling tension, are exactly the same as current ones. I made a prototype. The measurement test results for these test tires are shown in Table 3 below.

From Table 3 above, the following was confirmed.

A single carcass ply of the above-mentioned PET 1500d/2 as usual was used. Also, the driving rate of the crown center portion is 14 tires/inch, which is exactly the same as that of ordinary tires on the market. The gauge of the inner liner rubber of this tire is 0.5 mm, and the tire weight is 6.
It was 5 kg. Tires on the market were used as control tires.

Comparison ■Also, the same as Comparative Example 1 except that the inner liner gauge was set to 0.15 mm (Chiku).The tire weight was reduced by 350g by making the inner liner thinner, but since the gauge was made thinner, air permeation sex was significantly inferior.

Kita Atsura Unii When the inner liner rubber of Comparative Examples 3 to 5 was used as an inner liner rubber that can prevent air permeability, the air permeability was improved compared to Comparative Example 2, but the internal pressure decreased less than the control tire. It was big.

Example 1 - The procedure was the same as Comparative Example 3 except that the above-mentioned nylon monofilament coat was used as a carcass ply and the number of strokes was 7 per inch, but since a monofilament cord was used, it was possible to prevent a decrease in internal pressure, and it was also possible to prevent rolling. The corrosion resistance and noise level have also been significantly improved.

Flame installation 1 The same as Example 1 except that the rubber quality of the anti-sender inner liner was changed, but the effect was the same as Example 1.

Implementation ±↓ From Example 1, set the inner liner gauge to a thickness of 0 or 2.
When it was set to 5 mm, the tire weight increased compared to Example 1,
Although the rolling resistance index is slightly lower, it is still a significant improvement over the control.

When the inner liner gauge was further increased to 17 from Example 4, the tire weight became the same as the control.

1 and 19i The rolling resistance was slightly worse because the number of strokes was increased compared to Example 1, but the rolling resistance was significantly higher than that of the control.
The noise level and air reduction rate have also been improved.

Since the number of shots was increased compared to Example 1, the rolling resistance was equal to or inferior to the control.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce noise, reduce rolling resistance, and further reduce weight of a pneumatic radial tire.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a monofilament cord of a carcass ply.

Claims (1)

[Claims] 1. A tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions formed on the inner periphery of the side portions, and a carcass in the radial direction of the tire. In a radial tire reinforced with a carcass ply formed by arranging ply cords and a belt layer surrounding the carcass ply and buried inside the tread portion, the carcass ply cord is a polyamide monofilament cord having an elliptical shape. A pneumatic radial tire with certain characteristics. 2. A tire comprising a tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions formed on the inner periphery of the side portions, and having carcass ply cords arranged in the radial direction of the tire. radial tire reinforced with a carcass ply of The carcass ply cord is made of a polyamide monofilament cord having an elliptical shape, and the driving occupancy rate b/a of the monofilament cord at the crown center portion (where a is the first
As shown in the figure, the distance from the cord end to the cord end when cut circumferentially at the tire crown center (b is the length of the cord cross section in the longitudinal direction) is 20%<b/a<45%. The pneumatic radial tire according to claim 1. 3. The inner liner rubber contains 30 parts by weight or more of mica or 5 parts by weight of PE resin based on 100 parts by weight of a rubber composition consisting of 40 to 100 parts by weight of butyl rubber or halogenated butyl rubber and 0 to 60 parts by weight of diene rubber. The pneumatic radial tire according to claim 1 or 2, wherein the pneumatic radial tire contains at least 1 part. 4. The pneumatic radial tire according to any one of claims 1 to 3, wherein a gauge of the inner liner rubber at the tire crown center portion is 0.2 mm or less. 5. The cross section of the carcass ply monofilament cord has a ratio b/c of the major axis (b) to the minor axis (c) of 1.
．． Claims 1 to 4 characterized in that 5<b/c<5.
A pneumatic radial tie according to any one of the above.