JPH0284587A - Polyvinyl alcohol-based synthetic fiber and pneumatic radial tire reinforced with cord therefrom - Google Patents

Abstract

PURPOSE:To obtain the title fiber for rubber reinforcement markedly improved in the fatigue resistance of the reinforcing cords therefrom and causing no decreases in the breaking strength of said cords by crosslinking reaction of the surface of high-strength PVA-based synthetic fiber followed by adhesive treatment. CONSTITUTION:A cord from high-strength PVA-based synthetic fiber >=15g/de in tenacity is put to crosslinking reaction on the fiber surface using a crosslinking agent consisting of an aldehyde, methylol, isocyanate or carboxylic acid, followed by dipping treatment using a RFL adhesive, thus obtaining a cord for rubber reinforcement. This surface crosslinking reaction will markedly improve the fatigue resistance of said PVA fiber as an previous disadvantage; Therefore, when applied to pneumatic tires, this cord will not decrease in breaking strength.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention significantly improves the fatigue resistance of polyvinyl alcohol composite Ffj fibers (hereinafter abbreviated as "PVA fibers") for reinforcing rubber, especially pneumatic tires. It relates to code processing techniques that can be improved.

(Prior Art) Conventionally, PVA fibers have been widely used as rubber reinforcing materials and as industrial fibers. However, this fiber has poor fatigue resistance, and since it has a polymer characteristic of being inherently soluble in water, it has the disadvantage of poor hot water resistance. Therefore, its use as a rubber reinforcing cord for tires that are subjected to a large amount of bending is extremely limited.

However, as seen in JP-A-59-130314 and JP-A-59-100710, it has now become possible to increase the strength of PVA fibers by increasing the molecular weight (for example, average molecular weight of 400,000 or more). However, it is difficult to industrially produce such ultra-high molecular weight PVA polymer, and due to manufacturing difficulties, it is also less expensive than fibers used in general rubber reinforcing cords such as polyester and nylon. It was significantly more expensive and could not be commercially competitive.

From the above background, PVA polymer has been replaced with conventional PVA polymer.
By making the molecular weight slightly larger than the molecular weight of A Va fiber, it is relatively easy to produce high-strength PV in large quantities industrially.
A! A method for supplying li fibers has been discovered (for example, as described in JP-A-60-126311 and JP-A-60-126312, etc.), and the prospect of industrial and commercial use as a rubber reinforcing cord has been achieved. Although the high-strength PVA fibers supplied in this way are not comparable to aramid fibers in terms of strength and elastic modulus, they are significantly stronger than conventional fibers such as nylon and polyester, and are reinforced with rubber. It was considered that the code was sufficiently usable as a commercial code. In addition, the high-strength PVA fiber obtained by this method is
As described in Publication No. 1-108713, it is significantly improved against mechanical strain input compared to conventional PVAI and fibers, so its fatigue resistance is sufficient for practical use as a tire cord for rubber reinforcement. considered to be tolerable.

On the other hand, as conventional means for improving the fiber performance of PVA fibers, Japanese Patent Publications Nos. 47-8186, 48-7887, and 48-
No. 9210, No. 48-32623, No. 48-3262
4, No. 48-9209, No. 52-25602, and No. 53-1368 are known, and improvements have been made in heat and humidity resistance, initial modulus at high temperatures, etc.

However, the above-mentioned Japanese Patent Application Laid-open No. 60-126311 and No. 6
High strength PV obtained by the method described in No. 0-126312 etc.
As shown in Table 1 below, the A fiber has a strength of 15 g/d or more, whereas the filament strength of the conventional improved PVA fiber was only 11 g/d at most.

Therefore, since such high-strength PVA fibers have significantly improved strength and fatigue resistance compared to conventional PVA fibers, they are considered to be extremely promising as fibers for reinforcing rubber.

(Problem to be Solved by the Invention) However, the present inventors
It has been revealed that the high-strength PVA fibers obtained by the methods described in No. 11 and No. 60-126312 have a serious drawback in terms of fatigue resistance. In other words, as it is, the fatigue resistance as a tire cord is completely insufficient,
Cord breakage (hereinafter referred to as rcBUJ: cord breaking up) occurred even during normal actual driving, making it clear that the tire safety upper side sole was not suitable for practical use. This point will be explained in more detail below.

Tire size 19 using various fiber materials shown in Table 2 below with the number of twists shown in the same table as carcass ply cord.
5/70 SR14 passenger car tires were prototyped, and the cord strength retention rate of the carcass ply was evaluated by comparing with the cord strength when new after drum running and actual running.The obtained results were Also listed in Table 2.

The strong retention rate of the carcass ply cord is measured at the following locations:
The area marked with an x on the tire shown in FIG. 1 was used.

As is clear from Table 2, the strength retention rate of high-strength PVA fibers after drum running was almost the same as that of polyester fibers, but the cord strength retention rate after actual running was 90% or more for polyester fibers. In contrast, the strength of high-strength PVA fibers decreased to 20 to 40%, and in some cases, CBU occurred and the tire was on the verge of puncture.

The above practical driving test was conducted with the test tires mounted on a normal vehicle and at normal internal pressure (usually 1.7 kg/cm2), but this is only a controlled condition for tire usage conditions. In the general market, overloading and sometimes internal pressure 1. Okg/c [112
Because it may be used in the following abnormal conditions,
The fact that the cord strength retention rate was 20-40% after 50,000 km of actual driving under controlled conditions means that we cannot guarantee safety at all in the general market. It was determined that the bottom could not be put to practical use.

As mentioned above, phenomena that cannot be detected in LABO tests such as tire drum tests and so-called tube fatigue tests are thought to be unique to PVA fibers, so the inventors of the present invention conducted a thorough investigation into the causes of fatigue as described above. The following tests were also conducted. First, we tested a tire size P235/100 with the fold belt structure shown in Figure 2 using various fiber materials shown in Table 3 below as belt cords under the conditions shown in the same table.
We made a prototype of a 75 R15 passenger car tire. Regarding these tires, the strength retention rate of the belt cord after actual running was evaluated as described above. The obtained results are also listed in Table 3. In addition, the measurement point for the strong retention rate of the belt cord is the second
This is the part marked with an X in the figure.

As is clear from Table 3 above, even when high-strength PVA fibers are used as belt cords, the strength retention rate of the cords decreases to about 60% compared to when they were new, indicating that fatigue resistance is still a major problem. There was found.

Therefore, an object of the present invention is to provide a rubber reinforcing PVA with significantly improved fatigue resistance that hardly causes a decrease in cord strength even after actual running when applied to pneumatic tires, for example.
The object of the present invention is to provide a technique by which fiber cords can be obtained.

(Means for Solving the Problems) The inventor of the present invention has made the following findings as a result of intensive investigation into the cause of the decrease in the strength of the high-strength PVA fiber cord after the above-mentioned actual running.

First, when we embedded the cord taken out from the tire after actual driving into epoxy resin and observed the cross section of the cord cut with a microtome, we found that the filaments near the intersection of the first and second twists were significantly deformed, and more than 10 filaments was found to be concentrated in Tohoku. Normally, the filament has the role of dispersing the strain applied to the cord between the filament and the cord, so if the filament aggregates and the strain cannot be evenly distributed, the strength of the filament or cord will decrease more quickly. .

Next, in order to further clarify such filament agglomeration phenomenon, the upper twist and lower twist were loosened, and the cord interface where the upper twist and the lower twist were in contact was observed under a microscope. As a result, it was found that the filaments were formed into a film-like shape in units of several to several tens of filaments, as if they had been pressed, and it was impossible to alleviate the strain input, which is thought to be the original role of filaments. I understand. Such a phenomenon of aggregation between filaments was not observed in polyester or aramid fibers, but was a phenomenon observed only in PVA fibers.

On the other hand, drum running (20,000 km running, strong cord retention rate 6)
Although the filament agglomeration phenomenon described above is slightly observed in some parts of the cord with 0%), the extent of the filament aggregation phenomenon is extremely small, and it is considered that the strain input is still uniformly distributed to each filament during drum running. In addition, with conventional PVA fiber, even when running on a drum, the CBU is
However, the high strength PVA fiber has 2
Even after 10,000 km, the residual strength was 60%, indicating that the fatigue resistance was significantly improved compared to conventional PVA fibers. However, even with such improved high-strength PVA fibers, the strength of the cord after actual running is greatly reduced, a phenomenon that could not be predicted based on conventional knowledge.

The inventors of the present invention have found the following differences by closely observing the cord and filament after actual running and after running on a drum. That is, (1) during actual driving, the vehicle repeatedly runs and stops, so it is repeatedly subjected to an irregular temperature history from 100° C. to room temperature.

(2) During actual running, the strain input that the cord receives changes constantly and irregularly, and accordingly, the locations where the filaments rub against each other and the force exerted by the rubbing also change.

(3) On the other hand, the cord during drum running is constantly exposed to high temperatures of 100° C. or higher, and the rubbing force between the filaments is easily alleviated by the softening of the filaments themselves.

The above findings indicate that the filaments of the cord after running on a drum have a so-called bias cut surface due to the misalignment between the filaments concentrating in one place in the filament, whereas the filament surface of the cord after running on the drum has a large number of cut surfaces. This can also be explained by the fact that rubbing scratches between the filaments can be seen in some places, and even when looking only at the bias cut surface, there are several rubbing scars in the bias cut.

Based on the knowledge that it is sufficient to prevent filament aggregation in order to reduce the filament input due to filament aggregation Tohoku and increase the fatigue resistance of high-strength PVA fiber cords as explained above, the present invention has been developed based on the following considerations. This was done under the

In other words, since PVA fibers originally have hydrogen bonds within their molecules, the hydrogen bonds have an affinity for water molecules even in the presence of a small amount of water, and this has the disadvantage that PVA fibers themselves tend to aggregate. It is thought that it has become. Furthermore, it is thought that so-called water molecules penetrate into the amorphous portion of the PVA fiber and cause the amorphous portion of the PVA fiber to swell, resulting in, for example, a decrease in the glass transition point.

In the above-mentioned high-strength PVA fiber, high strength is achieved by making the amorphous part denser and highly oriented as a means of achieving high strength. Although it has been reported that the vapor pressure resistance is also improved, it is clear from the above results that it is still impossible to improve the fatigue resistance of the cord after actual running with this alone.

Therefore, the present inventors found that it is possible to prevent the agglomeration and wear of the filaments by further densifying the amorphous structure or creating a so-called skin-core structure. As a result of further intensive studies based on the idea that it is possible to substantially prevent a decrease in strength and impart fatigue resistance, the present invention has been achieved.

That is, the present invention subjects the surface of PVA fibers having a yarn strength of 15 g/d or more to a crosslinking reaction, and then using adhesive-treated PVA fibers and cords made by twisting these fibers to form carcass and/or belts. This relates to a pneumatic radial tire used as a reinforcing cord.

The crosslinking reaction in the present invention can provide an effect of improving fatigue resistance by either intramolecular crosslinking or intermolecular crosslinking of PVA molecules. As a crosslinking agent that causes such a crosslinking reaction, organic compounds such as aldehydes, methylols, incyanates, carboxylic acids, epoxies, or organic peroxides, and inorganic compounds such as phosphoric acids, hydrochloric acid, silica, and titanium are used. be done. However, no effect was observed with boric acid.

Specifically, the aldehydes include formaldehyde, nonylaldehyde, benzaldehyde, chloroacecoolaldehyde, acetaldehyde, acrolein, crotonaldehyde, glyoxa/peterepthaldialdehyde, furfural, hexahydrobenzaldehyde, p
- tolualdehyde, α-naphthaldehyde, 4-phenylbenzaldehyde, 9-anthraldehyde, 0-chlorobenzaldehyde, p-chlorobenzaldehyde,
2.4-Dichlorobenzaldehyde, n-butyraldehyde, isovaleraldehyde, pentaldehyde, phenylacetaldehyde, 3°5.5-)! Examples include J methylhexal.

Examples of methylols include acrylonitrile, N-methylol acrylamide, and N-methylol melamine.

Examples of carboxylic acids include monocarboxylic acids such as formic acid and acetic acid, and dicarboxylic acids such as adipic acid and terephthalic acid. In the case of dicarboxylic acids, intermolecular or intramolecular crosslinks represented by the following formula can occur between so-called PVA molecules.

Examples of incyanates include blocked incyanates such as 4,4-diphenylmethane diisocyanate (MDI: Prominate Tolidine diisocyanate (TODI), xylene diisocyanate,
Examples include 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, and dicyclohexylmethane diisocyanate (hydrogenated MDI), and as epoxy compounds, there are epoxy compounds having a difunctional or more functional epoxy group.

Dicumyl peroxide, 2゜5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2.5-dimethylhexane-2゜5-di(beroxyl benzoate), 2.5-dicumyl peroxide as organic peroxides. dimethyl-2,5-
Examples include di(tert-butylperoxy)hexane-3.

By applying heat, the organic peroxide can be converted to the following formula, R-0-0
Radical 0. is generated according to -R-R-0. .0-R, and then hydrogen is abstracted to form a crosslinking reaction.

As the phosphoric acid, metaphosphoric acid, birophosphoric acid, orthophosphoric acid, triphosphoric acid or tetraphosphoric acid can be used.

Among the above-mentioned crosslinking agents, epoxies and isocyanates are suitable for surface crosslinking because they easily react with the application of heat. On the other hand, since it is preferable to react aldehydes, methylols, inorganic acids, and organic acids in a swelling bath, it is preferable that these crosslinking agents penetrate into the interior of the m-fibers to uniformly crosslink them.

Preferred inorganic acids include hydrochloric acid and phosphoric acid, and preferred organic acids include carboxylic acids such as formic acid and acetic acid. It is believed that these acids react with the 10H group of PVA to form an ester bond or ether bond according to the following formula: l-OHHO→→l-0→+H20.

The PVA fibers are crosslinked by the crosslinking treatment using the above crosslinking agent, but at least only the filament surface layer is crosslinked.

Further, the crosslinking treatment may be carried out on either the raw yarn or the raw cord. For example, to give a specific example of crosslinking treatment on the raw yarn, after the crosslinking treatment is sufficiently air-dried, the yarn is twisted in the usual manner. It was twisted at 1500 d/2.31 x 31 (twice/foCm) to form a sagging fabric, then immersed in a normal resorcin-formalin/latex (hereinafter abbreviated as rRFLJ) solution as an adhesive treatment, and heated at 150°C x 120°C.
xo per second, 1g/d (dip tension), 200℃
x 30 seconds x 1 g/d and 205°C x 30 seconds x 0.
6 g/d in dry, hot, and normal zones, followed by coating with a rubber sheet and subsequent vulcanization (for example, at 150° C. for 30 minutes) in a conventional manner.

In this case, the components of the RFL liquid are not particularly defined.

Furthermore, when crosslinking raw cord, high strength PVAw and fiber-reinforced rubber can be obtained by the same process as above after sagging.

It should be noted that the effect of the crosslinking treatment remains the same whether it is at the yarn production stage or at the raw cord stage.

Although the strength of the cord slightly decreases due to the crosslinking treatment, it is preferable to suppress the decrease in strength due to the crosslinking treatment to 10% or less. On the other hand, depending on the crosslinking reaction conditions, the reaction may proceed even if the tension heat treatment is applied after the RFL liquid is attached, and the strength of the dip cord may decrease, so it is preferable to thoroughly wash the cord after the crosslinking reaction.

(Function) It has generally been said that when fibers are subjected to treatments such as crosslinking, the filaments harden and their movement is restricted by mechanical strain, resulting in a decrease in fatigue resistance. Currently, there are no reports of improved performance.

In fact, all conventional crosslinking treatments for PVA fibers have been concerned with improving heat and humidity resistance and dyeability.

However, in the present invention, it has been discovered for the first time that crosslinking treatment of PVA fibers has the effect of improving fatigue resistance as reinforcing fibers for rubber. This fact breaks down the conventional concept that fatigue resistance decreases as the filament hardens, and was the result of the inventors' detailed study of the fatigue behavior of PVA fibers as described above. , P
VA l! It was discovered that surface hardening is effective as a means to improve the fatigue resistance of fibers.

The fatigue resistance improvement effect of the crosslinking treatment in the present invention is also effective for conventional PVA fibers with relatively low strength of about 118/d, but such PVA fibers have extremely poor fatigue resistance, so nylon and The fatigue resistance level does not reach the fatigue resistance level of general-purpose rubber reinforcing fibers such as polyester fibers, and thus
It is only when applied to high-strength PVAIa materials described in No. 710 etc. that the benefits of high strength and improved fatigue resistance can be obtained.
It is extremely useful compared to conventional rubber reinforcing fibers such as nylon and polyester fibers.

(Example) Next, the present invention will be explained with reference to Examples and Comparative Examples.

Comparative Example 1 JP-A-59-130314 and JP-A-59-10071
High-strength PVA fibers obtained by the method described in Publication No. 0 were twisted to 1500 d/2.31 x 31 times/10 c
A twisted cord of m length was immersed in a normal RFL dip solution for 150 t x 120 seconds at xO, 1 g/d.

Tension heat treatment was performed at 200° C. for 30 seconds at 1 g/d and at 205° C. for 30 seconds at 0.6 g/d in dry, hot, and normal zones. This code was used as a control for the following examples and comparative examples.

Example 1 A twisted cord obtained in the same manner as in Comparative Example 1 was used as H2S0420.
%, Na25O, 10% and formalin (formaldehyde 37% aqueous solution) in a bath of 37% by weight aqueous solution.
℃ for 30 minutes at a bath ratio of 50:l. Next, it was washed with water for 1 minute, air-dried for 24 hours, and then dried in a dry state for 48 hours. Thereafter, the same RFL dip treatment as in Comparative Example 1 was performed.

Example 2 A twisted cord obtained in the same manner as in Comparative Example 1 was
%, Na, 30.10% and terephthaldehyde 4
The sample was subjected to the same immersion treatment as in Example 1 using a wt% ethanol solution, and then to the same RFL dip treatment.

Example 3 A twisted cord obtained in the same manner as in Comparative Example 1 was immersed in a bath of an aqueous solution of 5% acrylonitrile, 8% Na2SO4 and 0.5% NaOH at 60° C. for 60 minutes at a bath ratio of 50:1. Next, it was thoroughly washed with water, air-dried, and subjected to the same RFL dip treatment as in Comparative Example 1.

Example 4 A twisted cord obtained in the same manner as in Comparative Example 1 was mixed with 5% N-methylolacrylamide, 0.5% NH, CI, and Na
NaO8,2
An alkali treatment was performed at 60° C. for 60 minutes using an aqueous solution containing 0%, Na, and 30.3%. Thereafter, it was thoroughly air-dried and then subjected to the same RFL dip treatment as in Comparative Example 1.

Comparative Example 2 A twisted cord obtained in the same manner as Comparative Example 1 was mixed with 3.5% boric acid.
The sample was immersed in an aqueous solution bath at 100° C. for 5 minutes at a bath ratio of 50:1, then dried, and then subjected to the same RFL dip treatment as in Comparative Example 1.

Example 5 A twisted cord obtained in the same manner as in Comparative Example 1 was treated with H2SO45,
7%, (NH2)2C014, 3% by weight aqueous solution at 60°C for 30 minutes at a bath ratio of 50:1, thoroughly rinsed with water, dried at 100°C for 30 minutes, and then dried at 100°C for 30 minutes.
Heat treatment was performed at 0° C. for 3 minutes. Thereafter, the same RFL dip treatment as in Comparative Example 1 was performed.

Example 6 MDI blocked with caprolactam as blocked isocyanate (trade name: t, Bromine manufactured by Tayaku@)
XC-929), the twisted cord obtained in the same manner as in Comparative Example 1 was placed in a bath of an aqueous solution having an MD of 11.7% at a bath ratio of 50:
1, and then treated at 150°C for 2 minutes and then at 200°C for 1 minute. After that, RFL similar to Comparative Example 1
Deep treatment was applied.

Example 7.8 A twisted cord obtained similarly to Comparative Example 1 was dissolved in a THF solution of 1% adipic acid chloride (Example 7) or phthalic acid chloride (Example 8) and 0.5% triethylamine at room temperature for 15 minutes. After soaking for a time, washing with methyl alcohol, and air drying, the same RFL dip treatment as in Comparative Example 1 was performed.

Examples 9 and 10 A twisted cord obtained in the same manner as in Comparative Example 1 was treated with terephthalic acid diglycidyl ester (Example 9) or 0-phthalic acid diglycidyl ester (Example 10) (trade name: Nagase Sangyo, Epoxy IEX 711) . [EX 721)6.
5%, and DMP: 30. After 5 minutes of immersion in 0.2% acetone solution, 2 minutes at 150°C, then 1 minute at 200°C.
A heat treatment was performed for 1 minute, and then an RFL dip treatment similar to that of the comparative example was performed.

Example 11 A twisted cord obtained in the same manner as in Comparative Example 1 was mixed with 10% dicumyl peroxide (trade name: Permil D manufactured by NOF ■).
immersed in a bath of acetone solution for 15 minutes and heated at 200 °C for 3
A heat treatment was performed for a minute, and then an RFL dip treatment similar to that in Comparative Example 1 was performed.

The strength of each RFL dip-treated cord (hereinafter abbreviated as "dip cord") treated as described above and the strength of the cord after the fatigue test were measured, and the strength retention rate in comparison with the dip cord was determined.

The cord strength measurement method and fatigue test were conducted as follows.

Example 12.13 A twisted cord obtained in the same manner as in Comparative Row 1 was immersed in an aqueous solution of hydrochloric acid or formic acid adjusted to pH 3 for 30 minutes at 60°C.
After removing excess acid by washing with water, a tension treatment was performed. The conditions were: 150°C x 120 seconds x tension 0.1g/d, then 200°C x 40 seconds x 1g/d, then 200°C x 4
It was set as xO for 0 seconds and 5 g/d.

Thereafter, the same RFL dip treatment as in Comparative Example 1 was performed, and a cord test was conducted.

The cord strength measurement method and fatigue test were conducted as follows.

(1) Cord strength measurement method After removing the attached rubber with scissors from the belt bending sample and the cord taken out from the tire, the cord was pulled at room temperature with a distance between chucks IQ cm according to JIS L1017, and the strength at break was measured. The value obtained by dividing the strength by the total denier number before twisting was defined as the strength S (g/d). For the total denier, we used the denier before twisting, but this is complicated because the cord expands and contracts slightly during the cord processing process and tire vulcanization process, and the cord taken out from the tire has some rubber adhesion. This is to avoid.

(2) Cord fatigue test There is a so-called belt bending test method, which is a test method in which PVA fiber cords undergo compression in the direction perpendicular to the cord due to agglomeration and abrasion at the interface between the first and second twists. It was adopted as a test. The shape of the test sample was a plate with a width of 50 cm, a thickness of 1 cm, and a length of 50 cm.The test cord and steel cord were placed in this plate and vulcanized at 150°C for 30 minutes under a pressure of 100 kg/cm2. Rear pulley diameter 50mmφ, load 100kg
The test cord was subjected to bending fatigue 100,000 times, and then the strength of the test cord was measured according to the above-mentioned cord strength measuring method.

The test results obtained are shown in Table 4 below.

As is clear from the test results shown in Table 4, Examples 1 to I
The dip cord strength of O was almost the same as that of the control, and the fatigue resistance was significantly improved.

Furthermore, in Examples 11 to 13, both the dip cord strength and fatigue resistance were improved.

On the other hand, in Comparative Example 2, the above improvement effect was not observed.

Comparative Examples 3 to 4, Examples 14 to 21 Next, as an application of the above various cords to tires, a 185/70R13 size tire using such cords for the belt and polyester cord for the carcass ply,
A 195/70SR14 size tire was prototyped using the cord for the carcass ply and a steel cord for the belt.

These prototype tires were subjected to the following drum running test and field running test.

(1) BF drum running test Prototype tires were placed indoors at 25°C ± 2°C at an internal pressure of 3.0 kg/
cm2, the tire was left for 24 hours, the air pressure was readjusted, a load twice the JIS load was applied to the tire, and the tire was run for 20,000 km at a speed of 60 kg/hour on a drum with a diameter of 3 m. Thereafter, the cord was removed from the tire, and the strength of the cord was measured in accordance with JIS L1017 as described above.

(2) Practical driving test After assembling the prototype tire with the specified rim, it was installed on a general passenger and driven for general driving.The 195/70 SR14 size prototype tire for carcass ply study was driven approximately 50,000 km in the field.
In addition, the cord strength of the 185/70 R13 belt cord trial tire after traveling 32,000 km was measured in accordance with JIS L1017 as described above.

The test results obtained are shown in Table 5.

Incidentally, the twist count α of the cord in the same table was determined by the following formula.

a = N As is clear from the test results shown in the table, Examples 14-
Cord strength retention after running was improved in No. 18 as compared to Comparative Example 3, and in Examples 19 to 21 as compared with Comparative Example 4.

(Effect of the invention) As explained above, in the PVA fiber of the present invention,
Since the surface of the high-strength PVAI #1 fiber is subjected to a cross-linking reaction, for example, when this is applied to a pneumatic tire, there is an effect that the cord strength hardly decreases even after actual running. As a result, the durability of the pneumatic radial tire of the present invention reinforced with such cords can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of the tire showing the locations where the strength retention rate of the carcass ply cord is measured, and FIG. 2 is a partial sectional view of the tire showing the locations where the strength retention rate of the belt cords is measured.

Claims (1)

[Scope of Claims] 1. A polyvinyl alcohol synthetic fiber having a yarn strength of 15 g/d or more, which is characterized in that at least the surface thereof is subjected to a crosslinking reaction and then treated with an adhesive. 2. A pneumatic radial tire characterized in that a cord made by twisting the polyvinyl alcohol synthetic fibers according to claim 1 is used as a reinforcing cord for a carcass and/or a belt.