JP2009084727A - Rubber-steel cord composite material, production method thereof, and pneumatic tire produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber-steel cord composite material capable of maintaining the cord strength after vulcanization without increasing the diameter of a cord in a cord having a double-twisted structure by improving both the breaking strength and the tenacity density of the single cord, and to provide a method for producing the composite material and a pneumatic tire produced by using the same. <P>SOLUTION: The rubber-steel cord composite material contains a steel cord embedded in a rubber. The steel cord has a double-twisted structure obtained by twisting a plurality of filaments 1 to form a strand having a layer-twisted structure, and twisting a plurality of the strands in the form of a layer-twisted structure formed of a core 11 and at least one layer of sheath 12. The circumscribing circles of the outermost sheath strands 12 of the steel cord are made contact with each other between the adjacent strands, and the covering ratio of rubber around the strand layer positioned immediately inside at least the outermost sheath strand 12 is 50% or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber-steel cord composite, a method for producing the same, and a pneumatic tire using the same (hereinafter, also simply referred to as “composite”, “manufacturing method”, and “tire”). The present invention relates to a rubber-steel cord composite used as a reinforcing material for various rubber articles such as industrial belts, a manufacturing method thereof, and a pneumatic tire using the same.

  In general, a steel radial tire for a construction vehicle is used under a heavy load on rough terrain or the like with severe irregularities. Therefore, the steel cord that is the skeleton member is required to have a very high breaking strength.

  Thus, the basic structure of a steel cord that requires durability against a heavy load is a multiple twist structure obtained by preparing a plurality of strands obtained by twisting a plurality of filaments and further twisting them. .

  In the conventional steel cord, in order to improve the breaking strength, it is necessary to increase the cross-sectional area of the steel cord, but when the amount of steel used is increased, the weight becomes heavier and when applied to a pneumatic tire, Increasing product weight is a problem. On the other hand, to suppress the increase in weight, by adjusting the carbon composition and processing rate of the steel filament, the tensile strength of the filament is increased, and a steel cord with high breaking strength can be obtained without increasing the cross-sectional area. Has been done.

  However, in the case of a cord with a double twist structure, the internal filament is cut in advance with a load lower than the breaking load of the entire steel cord, and the effective sectional area of the filament contributing to the breaking strength is reduced. For this reason, there has been a problem that even if an attempt is made to increase the breaking strength by increasing the tensile strength of the filament, the breaking strength cannot be improved by an amount corresponding to the increase in the tensile strength. The reason why the steel filament is cut first is that the tightening pressure caused by the tightening when a large load close to the breaking strength is applied to the twisted wire is applied to the steel filament bearing the tensile load. This is because it acts from the side, and this is a phenomenon that occurs at the cross contact point between steel filaments where the tightening stress is concentrated.

As a technique related to the improvement of the steel cord, for example, in Patent Document 1, in a steel cord composed of at least one adjacent layer of a metal core strand and a steel element provided around the metal core strand, the metal core strand has a predetermined minimum thickness. A technique for obtaining a high cord breaking strength as well as an effect of suppressing the preceding breaking of the filament by coating with a polymer material is disclosed. In Patent Document 2, a metal core filament and a metal sheath filament are twisted into a layer twist structure to form one strand, and a plurality of strands are formed of a core strand and a sheath strand. A rubber article in which a non-metallic filament is spirally wound around the surface layer of a core strand in a steel cord having a single strand by twisting the twisted structure into a single steel cord. A steel cord for reinforcement is disclosed.
JP-T-2004-522864 Publication (Claims etc.) JP 2005-248374 A (Claims etc.)

  As described above, in the cord with a structure in which there is no coating layer around the core strand and the sheath strand and the core strand are in contact with each other, the internal filament is pre-ruptured before the entire cord breaks, contributing to strength. As a result, the effective cross-sectional area is reduced, resulting in a problem that the breaking strength of the entire cord is lowered. As a prior art for improving the preceding breakage of the inner filament, there is a method of completely covering a coating layer around the core strand as described in Patent Documents 1 and 2 above.

  However, when the core strand surface layer is completely covered with the polymer in this way, there is a new problem that the cord diameter becomes large due to the thickness of the coating portion and the thickness of the spiral winding of the core strand.

  As a result, although an improvement in strength can be achieved in terms of the breaking strength of the cord alone, a loss occurs from the viewpoint of the strength density obtained by dividing the breaking strength by the circular area of the cord cross section. In the composite of rubber and cord that reinforces a rubber article, the higher the strength density, the more advantageous it is to make a lighter or higher strength product at the stage where the cord is arranged on a flat surface to form a sheet.

  Accordingly, an object of the present invention is to maintain the cord strength after vulcanization by improving both the breaking strength and the strength density of the cord alone without increasing the cord diameter in the cord of the double twist structure. An object of the present invention is to provide a rubber-steel cord composite, a manufacturing method thereof, and a pneumatic tire using the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has made the sheath of the sheath around the strand positioned just inside the outermost layer sheath of the rubber-steel cord composite a predetermined value or more. It has been found that it is possible to maintain the cord strength without increasing the cord diameter by dispersing the tightening pressure of the filament, and such a composite by adjusting the vulcanization pressure during vulcanization to a predetermined level As a result, the present invention has been completed.

That is, the rubber-steel cord composite of the present invention is a rubber-steel cord composite in which a steel cord is embedded in rubber, and the steel cord twists a plurality of filaments into a layer twist structure. In a rubber-steel cord composite having a double twist structure in which a plurality of strands are twisted into a layer twist structure including a core and at least one sheath,
The circumscribed circle of the outermost layer sheath strand of the steel cord is in a state in which adjacent strands are in contact with each other, and at least the rubber covering ratio around the strand layer located immediately inside the outermost layer sheath strand is 50%. It is the above, It is characterized by the above. The circumscribed circle of the outermost sheath strand in the present invention is a substantially circular shape such as a slightly elliptical shape by causing a slight shift between the longitudinal direction of the strand and the longitudinal direction of the cord due to the twist angle of the strand. Including cases.

  In the composite of the present invention, the steel cord has a sheath of two or more layers, and the strand located just inside the outermost sheath sheath strand of the steel cord is around the strand layer located further inside. The rubber coverage is preferably 50% or more.

The method for producing a rubber-steel cord composite according to the present invention is a method for producing a rubber-steel cord composite in which a steel cord is embedded in rubber, and the steel cord comprises a plurality of filaments. In a method for producing a rubber-steel cord composite having a double twist structure in which a plurality of strands twisted into a twist structure are twisted into a layer twist structure composed of a core and at least one sheath,
The steel cord is embedded in unvulcanized rubber and then vulcanized at a vulcanization pressure of 3.0 MPa or more.

  In the production method of the present invention, the vulcanization pressure is preferably 3 MPa to 10 MPa.

  Furthermore, the pneumatic tire of the present invention is characterized by using the rubber-steel cord composite of the present invention as a reinforcing material.

  According to the present invention, with the above-described configuration, it is possible to realize a rubber-steel cord composite having a double twist structure that retains strength after vulcanization without increasing the cord diameter, and a method for manufacturing the same. It was. Therefore, by using such a rubber-steel cord composite of the present invention, a pneumatic tire satisfying light weight and high strength as compared with the prior art can be obtained.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a schematic cross-sectional view of a rubber-steel cord composite according to a preferred embodiment of the present invention. In the illustrated rubber-steel cord composite, a steel cord 10 is embedded in a rubber 20, and the steel cord 10 is composed of seven strands formed by twisting 27 filaments 1 into a layer twist structure, and a core 11. And a double twist structure formed by twisting together a layer twist structure composed of one layer of sheath 12. In the figure, the outer portion of the cord is indicated by a solid line (the same applies to FIGS. 2 to 6).

  In the composite of the present invention, a circumscribed circle of the outermost sheath strand 12 of the steel cord 10 is in a state of being in contact with each other between adjacent strands, and at least a strand layer positioned immediately inside the outermost sheath strand 12; In the illustrated example, it is important that the rubber coverage around the entire core strand 11 is 50% or more.

  Thereby, the tightening pressure of the sheath strand peculiar when the tensile load of the double twisted cord is borne can be dispersed by the action of the rubber coated around the inner strand. By dispersing the stress concentration on the outermost filament of the strand, the preceding breakage of the filament can be suppressed, so that it is possible to suppress the decrease in the cord break strength. Here, as described above, even if the rubber coverage is increased, if the cord diameter is increased, the increase in strength density is offset and reduced, but in the present invention, the circumscribed circle of the outermost sheath strand 12 is reduced. Since the cord diameter is not increased in the state where the adjacent strands are in contact with each other, the strength density can be improved while suppressing a decrease in the cord breaking strength. That is, as in the conventional cord 100 shown in FIG. 3, the nylon filament 103 is arranged around the core 101, and the rubber covering portion 104 is provided in this portion, thereby increasing the rubber coverage according to the present invention. In this case, a gap is inevitably generated between the adjacent sheath strands 102 as the cord diameter increases, but the present invention does not include such a case. The same applies to the case where the core strand diameter is intentionally increased with the cord as shown in FIG. 4 or the number of sheath strands is reduced. If the circumscribed circle of the outermost layer sheath strand is in a non-contact state between adjacent sheath strands, the ratio of steel in the cord cross-sectional area is reduced, so that the cord breaking strength becomes insufficient.

  In the composite of the present invention, when the steel cord has a sheath of two or more layers, the rubber is also provided around the strand layer positioned further inside the strand positioned just inside the outermost sheath strand. By making the state covered with a rubber covering ratio of 50% or more, the preceding breakage of the filament at that portion is suppressed, and therefore the cord breakage strength can be further improved.

  In the present invention, if any of the strand layer located immediately inside the outermost sheath strand or the strand layer located further inside thereof has a rubber coverage of less than 50% in the periphery thereof, The dispersion effect of the clamping pressure is reduced, and a sufficient effect cannot be obtained. The higher the rubber coverage, the more effective.

  If the composite of the present invention satisfies the conditions regarding the rubber coverage in the cord of the double twist structure, the specific cord structure, the filament diameter to be used, the cord diameter, the twist pitch, etc. It does not restrict | limit in particular, It is possible to select suitably as desired. For example, in the example shown in FIG. 1, the spiral filament 2 is disposed around the sheath 12, but this need not be present.

  The composite of the present invention can be easily obtained by embedding a steel cord having the above-mentioned double twist structure in an unvulcanized rubber and then vulcanizing at a vulcanization pressure of 3.0 MPa or more. When this vulcanization pressure is lower than 3.0 MPa, it is not possible to obtain a rubber coverage that exhibits a sufficient effect. This vulcanization pressure is preferably in the range of 3 MPa to 10 MPa.

  The pneumatic tire according to the present invention is obtained by applying the composite according to the present invention as a reinforcing material to, for example, a carcass cord, a belt cord, and the like. It can be. The tire of the present invention is not particularly limited except that the composite of the present invention is used as a reinforcing material, and can be appropriately configured according to a conventional method.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Example 1>
A rubber-steel cord composite having a 7 × (3 + 9 + 15) +1 double twist structure as shown in FIG. 1 was produced according to the conditions shown in Table 1 below. As shown, the composite of Example 1 has a rubber coating around the core strand.

<Comparative Example 1>
A rubber-steel cord composite having a double twist structure of 7 × (3 + 9 + 15) +1 as shown in FIG. 3 was produced according to the conditions shown in Table 1 below. As shown in the figure, in the composite of Comparative Example 1, nylon wrapping 103 is applied around the core strand, and this portion is covered with rubber 104. The composite of Comparative Example 1 was manufactured by securing a gap in the steel cord in advance by lapping nylon monofilament 103 and filling the gap with rubber during vulcanization.

<Conventional example 1>
A rubber-steel cord composite having a double twist structure of 7 × (3 + 9 + 15) +1 as shown in FIG. 4 was produced according to the conditions shown in Table 1 below. As shown in the figure, the composite of Conventional Example 1 has no rubber coating around the core strand.

<Example 2>
A rubber-steel cord composite having a double twist structure of (3 + 7) + 6 × (3 + 7) + 12 × (3 + 7) as shown in FIG. 2 was produced according to the conditions shown in Table 1 below. As shown, the composite of Example 2 has a rubber coating around the core strand.

<Comparative example 2>
A rubber-steel cord composite having a double twist structure of (3 + 7) + 6 × (3 + 7) + 12 × (3 + 7) as shown in FIG. 5 was produced according to the conditions shown in Table 1 below. As shown in the drawing, in the composite of Comparative Example 2, nylon wrapping 203, 303 is applied around the core strand, and rubber 204, 304 is coated on this portion. The composite of Comparative Example 2 was manufactured by lapping nylon monofilaments 203 and 303 to secure a gap in the steel cord in advance and filling the gap with rubber during vulcanization.

<Conventional example 2>
A rubber-steel cord composite having a double twist structure of (3 + 7) + 6 × (3 + 7) + 12 × (3 + 7) as shown in FIG. 6 was produced according to the conditions shown in Table 1 below. As shown in the figure, the composite of Conventional Example 2 has no rubber coating around the core strand.

  For each of the above composites, the tensile strength at break of one cord was measured and indicated by the comparative index shown below. Further, the strength density obtained by dividing the breaking strength by the circular area of the cord cross-section calculated from the cord diameter excluding the spiral filament was obtained, and similarly displayed as a comparative index. Note that Example 1 and Comparative Example 1 were based on Conventional Example 1, and Example 2 and Comparative Example 2 were based on Conventional Example 2. The results are also shown in Table 1 below.

<Measurement of tensile breaking strength (breaking force test)>
Specifically, the breaking force test is a tensile test based on JIS G3510 and JIS Z2241, and in this tensile test, the maximum tensile load until the cord breaks is obtained, and the breaking strength of each composite is calculated. did.

(Break strength comparison index) = Cord break strength (N) of the index calculation target / break strength (N) of conventional cord × 100
(Strength density comparison index) = strength density of cords for index calculation / strength density of conventional code × 100

<Rubber coverage>
The rubber coverage of each composite was measured as follows. First, each composite was unwound and a strand layer for measuring rubber coverage was provided on the outermost surface of the cord. The side part of the whole strand layer was photographed, and the ratio of the rubber covered area to the sample area in the photograph of this sample was defined as the rubber coverage.

  As shown in Table 1, although Comparative Examples 1 and 2 have improved breaking strengths compared to Conventional Examples 1 and 2, respectively, the cord diameter has increased, so the strength density improvement has decreased. . On the other hand, in Examples 1 and 2, since the increase in the cord diameter was eliminated, it was confirmed that the strength density compared with the comparative example was improved.

Further, the rubber-steel cord composites described above were applied to the reinforcing material constituting the skeleton of the tire, and comparison was made in a treat (sheet-like member) state as an intermediate material (see FIG. 7, reference numerals in the figure) 30 indicates a rubber-steel cord composite, and 31 indicates rubber). Assuming that the cord interval x and the upper and lower gauges t ₁ and t ₂ of the coating rubber are the same, the effect of applying each composite was calculated. As a guide for weight reduction, the treat thickness T was compared, and the thinner the weight, the lighter the weight. Further, as a measure for increasing the strength, the treat strength per unit width was compared, and the higher the treat strength, the higher the strength. The results are shown in Table 2 below using an index with the conventional example being 100.

  As shown in Table 2 above, it was confirmed that in the treat materials using the composites of Examples 1 and 2, high strength was achieved while maintaining light weight.

  As described above, in a composite of a steel cord and rubber having a double twist structure, the cord coverage is increased by setting the rubber coverage at least around the strand layer immediately inside the outermost sheath strand to 50% or more. It is clear that the breaking strength of the single cord can be improved while suppressing (strong density loss). When this composite is used for a rubber article such as a tire, an increase in the cord diameter is suppressed, so that more cords can be arranged in the same plane, and the thickness and volume of the reinforcing layer can be reduced. A reduction effect can also be obtained. Thereby, the strength improvement and weight reduction of a rubber article can be made compatible. Furthermore, by using this as a skeleton member, it is possible to provide a lightweight and highly durable tire product.

It is a schematic sectional drawing which shows the rubber-steel cord composite body of 7 * (3 + 9 + 15) +1 structure based on one embodiment of this invention. It is a schematic sectional drawing which shows the rubber-steel cord composite body of the (3 + 7) + 6 * (3 + 7) + 12 * (3 + 7) structure concerning other embodiment of this invention. 6 is a schematic cross-sectional view showing a rubber-steel cord composite having a 7 × (3 + 9 + 15) +1 structure according to Comparative Example 1. FIG. It is a schematic sectional drawing which shows the rubber-steel cord composite body of 7 * (3 + 9 + 15) +1 structure concerning the prior art example 1. FIG. 6 is a schematic cross-sectional view showing a rubber-steel cord composite having a (3 + 7) + 6 × (3 + 7) + 12 × (3 + 7) structure according to Comparative Example 2. FIG. It is a schematic sectional drawing which shows the rubber-steel cord composite body of the (3 + 7) + 6 * (3 + 7) + 12 * (3 + 7) structure concerning the prior art example 2. It is sectional drawing which shows a part of treat material used in the Example.

DESCRIPTION OF SYMBOLS 1 Filament 2 Spiral filament 10,100 Steel cord 11,101 Core 12 Sheath (outermost layer sheath strand)
20 Rubber 30 Rubber-steel cord composite 31 Rubber 102 Sheath strand 103, 203, 303 Nylon filament (nylon wrapping)
104,204,304 Rubber coating (rubber)

Claims (5)

A rubber-steel cord composite in which a steel cord is embedded in rubber, wherein the steel cord includes a plurality of strands formed by twisting a plurality of filaments in a layer twist structure, a core, and at least one layer In a rubber-steel cord composite having a double twist structure formed by twisting a layer twist structure formed of a sheath of
The circumscribed circle of the outermost layer sheath strand of the steel cord is in a state in which adjacent strands are in contact with each other, and at least the rubber covering ratio around the strand layer located immediately inside the outermost layer sheath strand is 50%. A rubber-steel cord composite characterized by the above.   The steel cord has a sheath of two or more layers, and the rubber coverage around the strand layer located further inside the strand positioned just inside the outermost sheath strand of the steel cord is 50% or more The rubber-steel cord composite according to claim 1. A method for producing a rubber-steel cord composite in which a steel cord is embedded in rubber, the steel cord comprising a plurality of strands formed by twisting a plurality of filaments in a layer twist structure, a core, In a method for producing a rubber-steel cord composite having a double twist structure formed by twisting a layer twist structure comprising at least one layer of a sheath,
A method for producing a rubber-steel cord composite, wherein the steel cord is embedded in unvulcanized rubber and then vulcanized at a vulcanization pressure of 3.0 MPa or more.   The method for producing a rubber-steel cord composite according to claim 3, wherein the vulcanization pressure is 3 MPa to 10 MPa.   A pneumatic tire using the rubber-steel cord composite according to claim 1 as a reinforcing material.