JPH02210068A - Polyvinyl alcohol based synthetic fiber for rubber reinforcing - Google Patents

Abstract

PURPOSE:To obtain the title fiber for rubber reinforcing remarkably improved in fatigue resistance by subjecting a high-strength PVA based synthetic fiber having strength of specific value or above to crosslinking treatment with an organic titanium and then treating the fiber with an adhesive. CONSTITUTION:A high-strength PVA based synthetic fiber having >=15g/d dope strength is treated with a liquid for crosslinking treatment obtained by diluting an organotitanium with water or an organic solvent to give a synthetic fiber containing 0.01-0.1wt.% organic titanium, which is then treated with a normal RFL adhesive to provide the PVA based synthetic fiber for rubber reinforcement causing no lowering of strength of the fiber (or tire cord) also after practical running when the fiber is applied to air tire and having excellent effects.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to polyvinyl alcohol-based synthetic fibers (hereinafter abbreviated as rPVA fibers) for use in rubber reinforcement that have significantly improved fatigue resistance.

(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, etc., which are subjected to a large amount of bending strain, has been 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, by making the PVA polymer have a molecular weight slightly larger than that of conventional PVA fibers,
Industrially, a method for supplying high-strength PVA fibers in large quantities was discovered relatively easily (for example, in Japanese Patent Laid-Open No. 60-12
No. 6311 and No. 60-126312, etc.), and it is expected to be used industrially and commercially as a rubber reinforcing cord. 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. 13, it is significantly improved against mechanical strain input compared to conventional PVA fibers, so its fatigue resistance as a tire cord for rubber reinforcement is sufficient for practical use. It was considered a thing.

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.

(Problems 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,
The cord breaks even during normal driving (rCBUJ:
It was revealed that this system was completely unsuitable for practical use due to tire safety concerns. below,
This point will be explained in more detail.

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 in comparison with the cord strength when new after drum running and actual running. The obtained results are also listed in Table 2. The strength retention rate of the carcass ply cord was measured at the part marked with an x on the tire shown in FIG.

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. On the other hand, the strength of high-strength PVA fibers decreased to 20 to 40%, and in some cases, CBtJ 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 (normally 1°7 kg/cm"), but this is only a controlled condition for tire usage conditions. In the general market, it may be overloaded or used under abnormal conditions such as internal pressure of less than 1.0kg/CIm'', so the code after 50,000 miles of actual driving under controlled conditions. Strong retention rate is 2
Since it was 0 to 40%, it had to be determined that safety in the general market could not be guaranteed at all, and it was determined that the product could not be put to practical use as it was.

As mentioned above, phenomena that cannot be detected by LABO tests such as tire drum tests and so-called tube fatigue tests are caused by PVA.
Since this phenomenon is thought to be unique to fibers, the present inventors further conducted the following tests in order to thoroughly investigate the cause of fatigue as described above. First, a tire size P235 of the fold belt structure shown in Fig. 2 using various fiber materials shown in Table 3 below as belt cord under the conditions shown in the same table.
/75 Prototype of R15 passenger car tire was made. 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. The location where the strength retention rate of the belt cord was measured was the area marked with an x in FIG. 2.

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 in an epoxy resin after actual driving and observed the cross section of the cord cut with a microtome, we found that the filaments near the intersecting plane of the first and second twists were significantly deformed, and more than 10 filaments were found. was found to be agglomerated into bundles. 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 miles running, strong cord retention rate 60
%), the filament aggregation phenomenon described above is observed in some areas, but the extent is extremely small, and it is thought that the strain input is still uniformly distributed to each filament during drum running. In addition, conventional PVA fibers generate CBU after 4,700 km of drum running, but the high-strength PVA fibers have a residual strength of 60% even when running at 20,000 km, and are significantly more resistant to fatigue than conventional PVA fibers. It can be seen that the properties have been improved. However, even with this improved high-strength PVA fiber, the strength of the cord decreases significantly after being run on the ground, a phenomenon that could not have been 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 irregular temperature history from 100° C. to room temperature.

(2) During actual running, the strain input received by the cord constantly changes irregularly, and accordingly, the locations where the filaments rub against each other and the rubbing input 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 and bundling as described above and increase the fatigue resistance of the cord of high-strength PVA fibers, the present invention has been developed as follows. This was done after careful consideration.

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 have found that by crosslinking the filaments, it is possible to prevent the filaments from coagulating and abrading each other, thereby substantially preventing a decrease in the strength of the high-strength PVA fiber cord during actual running, and improving fatigue resistance. We investigated various crosslinking agents for PVA fibers having OH groups.

For example, it is well known that PVA fibers crosslinked using formaldehyde or boric acid have improved heat resistance. However, such crosslinking has problems such as a decrease in strength and a high possibility of becoming brittle against compressive strain due to bending. In fact, when compressive strain was applied to PVA fibers crosslinked using boric acid, the fatigue resistance was poor.

Therefore, the present inventors conducted extensive studies based on the idea that fatigue resistance would be improved if a preferable crosslinking agent was found, and found that organic titanium is an excellent crosslinking agent. When titanium reacts with the OH groups of PVA fibers, it forms a crosslink as shown in the following formula. However, such a reaction
Due to the strong bonding force, it is difficult to control the reaction, and the PV
A: Significantly reduces the strength of the fibers.

Therefore, the present inventors used Ti as a crosslinking agent with an organic substance added thereto, based on the idea that a crosslink with less loss of strength could be formed by indirectly bonding the OH groups of PVA fibers with Ti. However, they succeeded in improving the fatigue resistance of PVA fibers and completed the present invention.

That is, the present invention relates to a PVA fiber cord for rubber reinforcement in which PVA fibers having a yarn strength of 15 g/d or more are cross-linked using organic titanium and then treated with an adhesive.

As the organic titanium in the present invention, Ti (OR)
Alkoxide represented by 4, Ti(OR)4-11(
OCOR').

Acylate expressed as Ti(OR)a-, An or T
A chelate represented by i(OH)4-a +An or the like can be considered. Generally, these compounds are easily hydrolyzed and cannot be used in the presence of water, but if an OH group is added to a chelate, which is said to be relatively stable in water, it becomes soluble in water without being hydrolyzed.

Specifically, Ti (0-isocsHt) is used for alcocyto.
n, Ti (0-ncJ*) a, Ti (OCHzCH
(CH3)C4HQ) a, Ti(0-C+Jzs)a
etc., and the acylate is Ti (0-nC
JJ 5 (OCOCIg H3S), Ti (0-icd
h) (OCOC+tHffs)s, and further titanium chelates include Ti(0-icJt)z(QC
(CH3)CHCOCH3)z, Ti(Oll)z
(OCH(CH3)COOH) z, etc. can be considered. In particular, Ti(OH)z (OCI((CH3)COO
H)! Since it is stable and soluble in water, it has great expectations from an industrial and industrial perspective.

These crosslinking agents are used as processing agents diluted in water or other organic solvents. Two types of crosslinking are possible, surface crosslinking and internal crosslinking, depending on whether the treatment agent is attached only to the filament surface or permeates into the inside of the filament.

Both of these forms have a fatigue improving effect, but surface crosslinking is particularly effective against frictional fatigue, whereas internal crosslinking is effective under friction and compressive strain.

Surface crosslinking can be carried out by attaching a treatment agent to the surface of the yarn or raw cord and then subjecting it to heat treatment to cause a crosslinking reaction.

Internal crosslinking is achieved by swelling the raw yarn or raw cord with water or other organic solvent, allowing the crosslinking agent to penetrate into the inside of the filament, washing away the excess crosslinking agent, and performing a dry heat treatment to carry out the crosslinking reaction. It can be tightened. Alternatively, the crosslinking reaction may be carried out by adding a crosslinking agent to the spinning stock solution and applying heat after spinning.

Each crosslinking method will be explained in more detail.

First, in the surface crosslinking method, a crosslinking agent is dissolved in water and an organic solvent to a concentration of 0.5% by weight or more and 2% by weight or less. Next, the PVA fibers are immersed in the above treatment liquid and then subjected to dry heat treatment. The treatment temperature is preferably 150"C or more and 240"C or less. The PVA fibers to be subjected to crosslinking treatment may be either raw yarn or raw cord, but it is preferable to apply an oil agent and twist the fibers after treatment.

Next is the internal crosslinking method, in which a crosslinking agent is first added.
The yarn or raw cord is immersed in a solution diluted with water or an organic solvent to a concentration of 5% by weight or more and 5% by weight or less. At this time, the amorphous portion of the pvA fiber is swollen by applying temperature, so that the crosslinking agent penetrates into the inside of the filament. The temperature is preferably 50"C or more and 80°C or less, and the immersion time is preferably 10 minutes or more and 40 minutes or less. Thereafter, after washing away excess crosslinking agent adhering to the surface, a dry heat treatment is performed.

This drying is done at 100″C or less, and the heat treatment is at 150°C.
The temperature is 240°C or higher.

On the other hand, in the method of adding a crosslinking agent to the spinning dope, PVA is first dissolved in a solvent such as DMSO to a concentration of 5 to 50% by weight.

Furthermore, organic titanium was dissolved in a solvent to this spinning stock solution.
The final Ti content of PVA is 0% by weight.
．． 01 to 0.1% by weight.

Thereafter, this spinning stock solution is subjected to a spinning process, and the spinning process may be a dry method, a wet method, or a combination of both. PV passed through coagulation bath after spinning
A fiber is stretched in a methanol bath and further heated to 160℃~2
The crosslinking reaction can be carried out while stretching at a high temperature of 40°C.

After that, a raw cord can be obtained by applying an oil agent and twisting the yarn.

By treating the cord thus obtained with an ordinary RFL adhesive, it can be used as a rubber reinforcing cord.

Incidentally, the Ti content of the cord thus obtained was 0.
The amount is preferably 0.01 to 0.1% by weight. The reason for this is
If it is less than 0.01% by weight, the effect of improving fatigue properties is not so great.
On the other hand, if it exceeds 0.1% by weight, the improvement effect will be saturated, and there is a risk that strength and adhesion will decrease.

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

-1 to 4'' 12 Here, an example will be shown in which crosslinking was performed by adding a crosslinking agent to the spinning dope.

First, completely saponified type with a degree of polymerization of 3500 (degree of saponification 99.
A 20% by weight DMSO solution of PVA (5% or more) was prepared, and a crosslinking agent mixed with 50% by weight and 4% by solvent was added to this solution, so that the content of Ti was 0.05% by weight per 100% PVA. Adjusted to. As a crosslinking agent, among the organic titanium crosslinking agents shown in Table 4 below, Ti (O4socJ
t) a diluted with i-propatool, ■Ti
(0-nc41 (J4 diluted with n-butanol, ■Ti(0-icJy)t (QC(CHs)CI
ICOCR8) z diluted with i-proper tool, ■Ti(Off)z (OCR(CHs)COO
H) x was diluted with water in Examples 1.2, 3., respectively.
It was set as 4.

After spinning the spinning dope thus obtained, wet-dry spinning was performed in a methyl alcohol coagulation solution. The obtained coagulated thread was washed with methanol to remove solvents such as DMSO, and then stretched three times in a methanol bath. Thereafter, the dried coagulated yarn was heated to 230° C., stretched five times, and simultaneously subjected to a crosslinking reaction.

An oil agent was applied to the PvAMII fibrillar yarn obtained in this manner, and the cord was twisted into gold thread to obtain a raw cord having a diameter of 1500 d/2 and a twist count of 31×31.

These raw cords were then subjected to RFL adhesive treatment as shown in Table 5 below.

The second treatment is dry heat treatment under tension.
°C x 120 seconds x 0.1 g/d, hot zone 20
0” CX 40 seconds x 1 g/d and norm zone 200
°C x 40 seconds x 0.5 g/d.

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

Furthermore, the Ti content in the fibers of such cords was quantified.

The cord strength measurement method, the fatigue test, and the determination of Ti content were carried out as follows.

The breaking strength was measured by pulling at room temperature in accordance with JIS L 1017.

There is a so-called belt bending test method, which is a test method in which PVA fiber cords are compressed in the direction perpendicular to the cord by agglomeration and abrasion at the interface between the first and second twists, and this test method is called the cord fatigue test. It was adopted as The shape of the test sample was a plate with a width of 50 cm, a thickness of ICl11, and a length of 50 cm.
After vulcanizing at 150°C for 30 minutes under a pressure of 100 kg/cm'', the
Bending fatigue was applied 00,000 times, and then the strength of the test cord was measured according to the above-mentioned cord strength measurement method.

After incinerating 1 g of the sample, the ash was treated with hot concentrated sulfuric acid to dissolve white smoke. Next, this solution was diluted, and Tf was quantified by the ICP-Ag3 method. The equipment used for the measurement was Hitachi's Superscan 306, and the standard solution was a commercially available 11000pp.
The solution was diluted and prepared.

The test results obtained are shown in Table 6 below.

For comparison, Comparative Example 1 shows the test results using conventional PVA fiber, and Comparative Example 2 shows the test results using high-strength PVA fiber.
The test results using VA fibers but without crosslinking treatment are also listed in Table 6.

From Table 6, the following was confirmed.

First, Comparative Example 1 is an example using conventional PVA fiber, but in this case, the cord strength was low and the fatigue resistance was also poor (it broke in the belt bending test).

Comparative Example 2 uses high-strength PVA fibers and uses D as the spinning solvent.
Since MSO was used, the fatigue resistance was considerably improved compared to Comparative Example 1.

Examples 1 to 4 are all examples in which different crosslinking agents were added to the spinning stock solution, and the crosslinking reaction was carried out by stretching and heat treatment after spinning, but in these cases, the cord strength was high in all of the crosslinking agents. , fatigue resistance were all significantly improved compared to Comparative Example 2.

5 to 12 to 3 Next, examples will be shown in which all of the crosslinking agents (1) to (4) shown in Table 4 were diluted in various solvents and swelling crosslinking was performed.

High strength PVA fiber cord is disclosed in Japanese Patent Application Laid-Open No. 61-108711.
Yarn strength 17.5 g/
The high-strength PVA filament of d is spliced to 1,500 denier, and this is twisted 31 times/10cm to create two
The book was further twisted with 31 twists/10 cII.

This high-strength PVA fiber cord was immersed in a solution in which crosslinking agents (1) to (4) were dissolved in respective solvents to give a concentration of 2%.

The temperature was maintained at 60°C, and after immersion for 30 minutes, excess crosslinking agent adhering to the surface was washed away. Then,
A crosslinking reaction was carried out by dry heat treatment under tension. The drying conditions are: processing temperature 150°C x exposure time 120 seconds x tension 0.1g/d + 200°C x 120 seconds x 0.5g/d
It was set as d.

The cord was then subjected to the RFL adhesive treatment described above.

Each RFL dip-treated cord thus obtained was subjected to the same test as above. The obtained results are summarized in Section 7 below.
Shown in the table.

Examples 5 to 12 shown in Table 7 are all examples in which raw cord fibers were swollen and a crosslinking reaction was performed with a specific crosslinking agent, but in all of these cases, excellent fatigue resistance improvement effects were achieved. Admitted. Furthermore, from these Examples, it was found that the use of polar solvents caused greater swelling of the fibers and had a greater effect on improving fatigue resistance.

On the other hand, Comparative Example 3 is an example in which Ti (SO4) z was used as a crosslinking agent, but in this case, a significant decrease in strength was observed.

13-20. - 4 Here, we will show an example in which crosslinking was carried out by attaching a crosslinking agent only to the surface of high-strength PVA fibers.

First, crosslinking agents (1) to (2) were diluted with their respective solvents to a concentration of 1.5%. Next, the high-strength PVA fiber cord was dip-treated with the solution and heat-treated under tension to carry out a crosslinking reaction. The tension heat treatment conditions were 200° C. x 120 seconds x 0.5 g/d.

Thereafter, the RFL adhesive treatment was performed as described above, and then the same test as above was conducted.

The results are shown in Table 8 below.

Examples 13 to 20 obtained and shown in Table 8 are all examples in which the crosslinking reaction was carried out only on the surface of the filament using a specific crosslinking agent, and in all of these cases, the effect of improving fatigue resistance was observed. .

On the other hand, Comparative Example 4 is an example in which Ti (S04) z was used as a crosslinking agent, but in this case, a decrease in cord strength was observed.

In addition, from such fatigue tests, it was also found that the above-mentioned internal crosslinking was more effective than crosslinking only on the filament surface.

(Effects of the Invention) As explained above, in the PVA fiber for rubber reinforcement of the present invention, by subjecting the high-strength PVA fiber to crosslinking treatment with organic titanium, for example, when this is applied to a pneumatic tire, it can be used in practical applications. The effect is that the strength of the cord hardly decreases even after running. As a result, the durability of rubber products including tires 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)

[Claims] 1. A polyvinyl alcohol synthetic fiber for rubber reinforcement, characterized in that the polyvinyl alcohol synthetic fiber has a fiber strength of 15 g/d or more and is crosslinked with organic titanium and then treated with an adhesive. fiber. 2. The polyvinyl alcohol synthetic fiber for rubber reinforcement according to claim 1, wherein the crosslinked polyvinyl alcohol synthetic fiber has a titanium content of 0.01 to 0.1% by weight.