JP2007118622A - Composite body of steel code and rubber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite body of a code and rubber capable of realizing sure adhesion on an interface between the code and the rubber by synchronizing a vulcanizing reaction and an adhering reaction. <P>SOLUTION: A composite body of a steel code and rubber comprises one or more steel wires plated with brass on its periphery. An adhesion layer is formed on an interface between the steel code and the rubber, and a zinc thickening layer with the thickness of 3 nm is formed on a brass plated side of the adhesion layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite of a steel cord and rubber, for example, a composite of a steel cord and rubber applied to a belt or carcass of a radial tire represented by a tire for a truck / bus, a tire for a passenger car and a tire for a light truck. About the body.

Conventionally, in radial tires, steel cords made by twisting a plurality of brass-plated steel wires and bonded to rubber are applied to belts and carcass plies to function as tire reinforcements. I am letting. In order to make full use of this function, it is important that the steel cord and rubber are firmly bonded. From the viewpoint of maintaining excellent adhesion between the two, the surface of the wire plated with brass A method of precisely adjusting the structure (see Patent Document 1) and further optimizing the types and amounts of rubber adhesion promoters, crosslinking agents, and vulcanization accelerators have been adopted.
JP-A-6-49783

  Here, the vulcanization reaction and the adhesion reaction are both competing and complementary, and the synchronization of both reactions is an important control guide for adhesion of the steel cord and the rubber composite.

  However, since the adhesion reaction can only be evaluated through a rubber and cord destructive test, it is always influenced by the properties of the vulcanized rubber. For example, if the strength of the crosslinked rubber is small, even if the degree of completion of adhesion is low, the appearance of the rubber after peeling will increase, and the phenomenon that the adhesiveness has improved may occur. There is no guarantee that the two composites with 100% rubber will have essentially the same adhesion. Moreover, even if a difference occurs between the two when the corrosive gas component enters from the outside, it is possible to determine whether the difference has occurred due to the deterioration characteristics of the rubber or whether the difference has occurred due to deterioration of the adhesive interface. Absent.

  Accordingly, the present invention is intended to provide a cord and rubber composite that realizes reliable adhesion at the interface between the cord and rubber by synchronizing the vulcanization reaction and the adhesion reaction.

  The inventor has moved away from the conventional method of individually optimizing the composition of the brass plating on the cord surface and the rubber composition, and has widely changed the completeness of the adhesion of the steel cord and the rubber composite to break the conventional vulcanized adhesive. Adhesion at the interface by directly evaluating the adhesiveness of the composite cord / rubber interface based on a measure independent of rubber vulcanization, that is, based on the adhesion reaction, rather than evaluation by testing. We found a way to increase the degree of completeness, and created a measure to improve the durability of the composite, especially.

  That is, in order to solve the above-mentioned problem, for a composite of a cord in which wires drawn under various conditions are twisted together and a rubber in which the type and amount of the adhesion promoter and vulcanizing agent are changed, the cord and the rubber Directly observe the structure of the interface of the composite as it is, that is, create it by a processing technique such as cutting the interface of the composite with a heavy atom ion beam such as gallium ion (Foucused Ion Beam: FIB). , By using analytical means to qualitatively and quantitatively analyze the composite specimen directly with a transmission electron microscope, the new interface structure generated as a result of the adhesion reaction at the stage where rubber vulcanization is completed, We succeeded in improving the perfection of adhesion by controlling it to form. Specifically, when the zinc-concentrated zinc-based layer produced due to the diffusion of Cu from the plating surface has a certain thickness and covers the entire interface uniformly, the degree of perfection of adhesion increases, especially It was newly found that the durability adhesion is improved.

The gist of the present invention is as follows.
(1) A composite of a steel cord and rubber composed of one or a plurality of steel wires with brass plating on the peripheral surface, and having an adhesive layer at the interface between the steel cord and rubber, the adhesive layer A composite of a steel cord and rubber having a zinc-concentrated layer having a thickness of 3 nm or more on the brass plating side.

(2) The above (1), wherein when the optimum vulcanization time of the rubber composition at the temperature at which the composite is vulcanized is represented by T _0.9 , the degree of vulcanization of the rubber is 0.8 × T _{0.9 to} 1.5 × T _0.9. Composite of steel cord and rubber described in 1.

(3) The composite of the steel cord and rubber according to (1) or (2) above, wherein the zinc thickened layer has an average thickness of 9 nm or more.

(4) The zinc-enriched layer includes the steel cord and rubber according to any one of the above (1) to (3), wherein the zinc content is 50 to 95 at% relative to the total amount of copper and zinc in the layer. Complex.

(5) The steel cord and rubber composite according to any one of (1) to (4), wherein the adhesive layer has a thickness of 30 nm to 300 nm.

(6) The composite of the steel cord and rubber according to any one of (1) to (5), wherein the amount of ZnO in the steel wire brass plating is 30 to 60 mg / mm ² .

Here, the degree of vulcanization of the rubber is obtained when a vulcanization curve is measured using a rheometer for the vulcanization characteristics of the rubber composition, as shown in FIG. 1 showing the relationship between the vulcanization time and the torque by the rheometer. Of vulcanization time. That is, the degree of vulcanization is displayed by multiplying a time T _0.9 showing a torque 0.9 times the maximum torque Fmax. In FIG. 1 by a coefficient, and this T _0.9 stage is an indication that the crosslinking reaction has been completed and is optimal. It means vulcanization and exhibits the most excellent physical properties.

  According to the present invention, a zinc-concentrated layer that realizes stable adhesion after initial bonding is formed at the interface between the cord and the rubber, thereby preventing deterioration of the adhesion at the interface between the cord and the rubber. A composite of steel cord and rubber excellent in adhesion can be provided.

  The steel cord (hereinafter collectively referred to as a cord including the case of a single wire) and rubber are bonded to copper (Cu) during brass plating on the surface of the steel cord and sulfur (S) in the rubber composition. Is an interfacial reaction that forms CuxS at these interfaces. Since sulfur is also used in the crosslinking reaction of rubber, the quality of adhesion is determined depending on the result of competing sulfur consumption in both reactions. On the other hand, since rubber and CuxS are directly bonded via a chemical bond or a three-dimensional interlock, the interfacial reaction and the crosslinking reaction are not reactions that can proceed completely independently. This is why some synchronization with the vulcanization reaction is required. In other words, when considering the adhesion between the steel cord and the rubber, it means that it is desirable that the CuxS lamination growth and the crosslinking reaction proceed while being synchronized. Initial adhesion should be achieved from this point of view.

On the other hand, in composite products, after vulcanization / adhesion is completed, active molecules such as water and oxygen enter the cord and rubber interface for a long period of time, and the adhesion between the two usually follows the process of deterioration. In particular, since tires are in a harsh environment where they are exposed to dynamic inputs and high temperatures, it is extremely important to suppress the progress of deterioration.
Therefore, durable adhesion is the key to improving product life.

  Recent advances in electron microscopes, especially analytical electron microscopes and their specimen preparation techniques, have made significant progress, enabling the fine structure of the plated surface to be processed and observed on the order of nm. As a result of directly observing the structure of the interface of the steel cord and the rubber composite based on the progress of such technology and elucidating the relationship between the form of the interface and the degree of adhesion completion, the present invention has been led.

  FIG. 2A shows a scanning electron micrograph of a typical example of the interface structure with a high degree of perfection, and FIG. In other words, an adhesive layer made of CuxS and rubber is formed at the interface between the plated surface of the cord and the rubber along with the vulcanization treatment. It is important to have a zinc concentrated layer on the plated side of the adhesive layer. It is.

Furthermore, when the conditions regarding the zinc-concentrated layer for improving the durable adhesiveness were investigated, the relationship between the half-life index of the durable adhesive and the thickness of the zinc-concentrated layer is shown in FIG. It was found that it is extremely important to set the thickness to 3 nm or more. That is, when the thickness of the zinc-concentrated layer is less than 3 nm, a sudden decrease in durable adhesion is caused. Such a thin portion is undesirable even if it is partially present.
The half-life index for durable adhesion is that the sample under test (the sample used for the initial adhesion evaluation) is subjected to deterioration treatment at a humidity of 90% and a temperature of 75 ° C, and the rubber coating rate reaches 50% in the CRA test. It is a numerical value obtained by converting the number of days required to decrease into a relative index using the number of days required for the case of Comparative Example 1 under the same treatment as a control.

That is, in order to significantly improve the adhesion durability, it is important to sufficiently complete the adhesion by T _0.9, which is a standard for completing the rubber vulcanization treatment, specifically the vulcanization reaction. That is, it is important that a bonding layer composed of CuxS and rubber is generated and that a zinc-concentrated layer is newly formed uniformly and thickly on the plating side of the bonding layer.
However, the conventional evaluation of adhesion by the peel test of rubber and steel cord only determines whether or not the apparent rubber attachment is 100%, and the adhesion is completed in a true sense. Does not mean that In other words, even if the adhesion was not completed microscopically, it could be regarded as complete if 100% rubber could be secured macroscopically. This is because “100% or more” adhesion cannot be evaluated. Durability adhesion is governed by the degree of completion of the initial bond, but the true perfection cannot be evaluated. It was just something.

  The bond between the rubber and the brass component of the plating is mainly handled by CuxS. However, the subsequent deterioration due to active molecules, particularly the deterioration due to water and oxygen, is a dezincification reaction from the brass plating. Therefore, the presence of the zinc concentrated layer here makes it possible to avoid the breakage between the plating and the adhesive layer. That is, the stability of the zinc-concentrated layer between the plating and adhesion layers dominates the durable adhesion.

  However, for the formation of a zinc-enriched layer, simply oxidizing the plating surface of the cord and concentrating the zinc oxide on the plating surface layer, on the other hand, hinders the diffusion of Cu, resulting in a slow adhesion reaction. . In some cases, it may not be bonded. It is important to ensure the stability of the newly formed zinc-enriched layer with respect to water and oxygen while further diffusing Cu.

  Now, the composition of the zinc concentrated layer as a new interface is mainly composed of zinc. Specifically, the zinc content with respect to the total amount of copper and zinc in the zinc concentrated layer is 50 to 95 at%. Since the zinc oxide on the plating surface layer remains, it is no exaggeration to say that it is a zinc oxide layer. Since this zinc oxide is already electrochemically stable, it is important how the layer can ensure a uniform and constant thickness. This is because it is important how to suppress the formation of local cells at the interface of the composite. Preferably, in the degree of vulcanization at which the vulcanization reaction is completed, the entire surface of the cord is uniformly coated, that is, zinc. It is important that the adhesion reaction is completed so that there is no portion where the concentrated layer does not exist.

  Specifically, if the uniformity at the nm level is ensured, that is, if a zinc-concentrated layer having a thickness of 3 nm or more is evenly provided on the plated surface of the cord, the formation of the local battery can be suppressed. That is, if the zinc-concentrated layer has a thickness of less than 3 nm, when an active element enters from the outside of the cord, a local battery is formed because the stability of the portion is inferior, and rapid deterioration proceeds. Because. Further, it preferably has a thickness of 9 nm or more and 12 nm or more.

In addition, in the stage of the optimal vulcanization degree, that is, the temperature at which the composite is vulcanized, if the zinc concentrated layer is not completed at the stage of vulcanization time T _0.9 , the vulcanization time may be extended. Although possible, it cannot compensate for differences in bond completion. Also, extending the vulcanization time is not desirable for the rubber properties as well as for the productivity. From the viewpoint of the physical properties of the rubber, an appropriate vulcanization time for a realistic tire or the like is set. Therefore, if the degree of completion of adhesion within the appropriate vulcanization time is low, the durability adhesion is naturally inferior.

  Incidentally, the rubber with the optimum degree of vulcanization has the maximum tensile strength. Even if the degree of vulcanization is lower or higher than this, the tensile strength is lowered, so that the fracture characteristics of the product such as tire belt durability are inferior.

  Furthermore, when the zinc concentrated layer is completed at the level of vulcanization of the composite, the greater the amount of zinc oxide in the zinc concentrated layer, the higher the adhesion stability. desirable.

Here, the normal code production conditions, but the amount of zinc oxide in the raw cord (before vulcanization code) is 10~29mg / mm ^2, using a wire adjusting this amount of zinc oxide in the 30-60 mg / mm ² It is preferable. That is, if it is less than 30 mg / mm ² , the stability as zinc oxide is relatively low, and the above-described effects are small. On the other hand, if it exceeds 60 mg / mm ² , the surface layer becomes too brittle and cannot be drawn.

  In order to adjust the zinc oxide amount of the wire, it is effective to control the liquid temperature at the time of wire drawing and the area reduction rate of the final pass.

  Further, the thickness of the adhesive layer not including the zinc concentrated layer is preferably 30 nm or more and 300 nm or less. This is because if the thickness is less than 30 nm, not only the intended zinc-concentrated layer is not formed, but also the bonding between the plating and the adhesive layer is insufficient, while if it exceeds 300 nm, the strength of the adhesive layer itself is required and dynamic bonding is required. This is because durability is insufficient.

  Here, in order to form a zinc-concentrated layer with a predetermined thickness at the interface between the steel cord and the rubber, in the steel cord, if the plating composition is the same, the zinc oxide on the surface of the wire is increased, and the surface lubricating film is formed. It is effective to select wire drawing conditions that can be eliminated, and it is suitable to employ, for example, a sintered diamond die for the final few passes. On the other hand, in rubber, an appropriate amount of a compounding agent capable of dissolving the lubricating film on the wire surface in the vulcanization stage, for example, a resoncin chemical, is used.

  In order to suppress deterioration of the adhesive layer due to water resistance and oxygen resistance, steel cords are cords used for tire tires for passenger cars such as 1 × N and 1 + N (N: 1 to 6) and 2 + N. However, when active molecules act even in large tires, it is also desirable to apply to layered and double-burning cords.

  Hereinafter, specific examples of the present invention will be described in detail in comparison with a composite of a cord made of brass plating wire and a practical compound rubber that is actually used. In addition, this invention is not restrict | limited to a following example.

  When a composite is produced by combining steel cords and rubbers having the specifications shown in Table 1, a composite having a zinc-concentrated layer shown in Table 1 is obtained at 165 ° C. by using various treatments prior to the vulcanization treatment. It was produced under the condition of 8 minutes, that is, the optimum degree of vulcanization.

The composite thus obtained was examined for initial adhesion and durability adhesion. The results are also shown in Table 1.
Here, initial adhesiveness refers to the rubber adhesion specified in JIS G 3510 (1992) for composites that are vulcanized and bonded under conditions generally corresponding to vulcanization temperature and time during the manufacture of passenger car tires. The cord / rubber adhesion test was performed in accordance with the test method. The result is shown by the rubber coverage after peeling.

  Durability adhesion is the time it takes the specimen subjected to initial adhesion to undergo degradation treatment under the conditions of 90% humidity and 75 ° C, and the rubber coverage is reduced to 50% in the CRA test. Is expressed as a relative index when the measured value of Comparative Example 1 is 100. It shows that it is excellent in durable adhesiveness, so that this figure is large.

  The amount of phosphorus in the cord surface layer shown in Table 1 is a numerical value obtained by quantifying the amount of P on the brass plating surface of the cord in atomic% using X-ray photoelectron spectroscopy (XPS).

  In addition, the thickness of each layer at the interface of the composite was prepared by preparing five FIB-processed specimens for TEM observation per sample, and viewing the 1 μm field of the wire cross section as shown in FIG. Analysis was performed, and the results were obtained from the line analysis results as shown in FIG.

  First, Comparative Example 1 is an example of a general composite in which a practical belt rubber for a passenger car tire and a practical cord are combined. On the other hand, Invention Example 1 is an example of a composite in which a wire having a surface phosphoric acid amount reduced by diamond die drawing is applied to a cord and combined with a rubber compounded with a cobalt salt as an adhesion promoter. In Invention Example 1, since the average thickness of the zinc concentrated layer is remarkably increased and there is no portion where the thickness of the zinc concentrated layer is 3 nm or less, the durability adhesion is 1.4 times that of Comparative Example 1. Improved.

  Inventive examples 2 and 3 are examples in which the number of diamond dies is increased to further reduce the surface lubricating film and the amount of surface zinc oxide is increased, and the durability adhesion can be improved to 150% and 170%. It was.

  Comparative Examples 2, 3, 4 and 5 and Invention Examples 4, 5, 6, 7 and 8 employ a rubber composition in which resorcin is further blended in addition to a Co salt as an adhesion promoter in the rubber composition. Is an example in which the brass plating composition was changed using a wire drawn with a diamond die. In general, it is known that high-Cu brass plating improves initial adhesion but is inferior in durability. Certainly, in Comparative Examples 2, 3, and 4, the average thickness of the zinc concentrated layer is slightly increased, but the zinc concentrated layer portion of less than 3 nm is present, and the amount of zinc oxide on the wire surface is decreased. Adhesive properties corresponding to that.

  On the other hand, in Invention Examples 4, 5, 6, 7 and 8, the partial ratio of 3 nm or less is zero with the average thickness of the zinc concentrated layer, and the durability adhesion is greatly improved. Here, it is generally said that the low Cu concentration brass plating composition is slow in initial adhesiveness and is not suitable for practical use, but it is preferable to reduce the lubricating film by using diamond die drawing, and the average thickness of the zinc concentrated layer is preferable. As a result of the success in eliminating the zinc-concentrated layer of 3 nm or less, the durable adhesiveness was greatly improved, and it became possible to put it into practical use.

It is a figure which shows the relationship between vulcanization time and the torque by a rheometer. It is the scanning electron micrograph of the interface of the composite_body | complex excellent in durable adhesiveness, and its explanatory drawing. It is a figure which shows the relationship between durable adhesiveness and the thickness of a zinc concentration layer. It is a figure which shows an example of a line analysis result.

Claims (6)

  A steel cord / rubber composite composed of one or more steel wires with brass plating on the peripheral surface, and having an adhesive layer at the interface between the steel cord and rubber, and brass plating of the adhesive layer A steel cord / rubber composite comprising a zinc concentrated layer having a thickness of 3 nm or more on the side. When the complex was displayed between optimum vulcanization of a rubber composition at a temperature which is vulcanized at T _0.9, steel according to claim 1 rubber vulcanization degree is 0.8 × T _0.9 ~1.5 × T _0.9 A composite of cord and rubber.   The composite of steel cord and rubber according to claim 1 or 2, wherein the zinc thickened layer has an average thickness of 9 nm or more.   The composite of steel cord and rubber according to any one of claims 1 to 3, wherein the zinc-enriched layer has a zinc content of 50 to 95 at% with respect to the total amount of copper and zinc in the layer.   The steel cord / rubber composite according to any one of claims 1 to 4, wherein the adhesive layer has a thickness of 30 nm to 300 nm. The composite of steel cord and rubber according to any one of claims 1 to 5, wherein the amount of ZnO in the steel wire brass plating is 30 to 60 mg / mm ² .