Surface treatment method for brass-containing metal substrate and surface-treated brass-containing metal substrate

Abstract

To enhance adhesive performance to rubber without using a catalyst metal such as cobalt.SOLUTION: An alkaline aqueous solution is brought into contact with the 1A of the steel cord plated with brass (step 12), a silane-coupling agent aqueous solution is brought into contact with the 1A of the steel cord contacted with the alkaline aqueous solution (step 13), and the 1A of the steel cord contacted with the silane-coupling agent aqueous solution is heated (step 14). The contact step with the silane coupling agent aqueous solution (step 13) and the heating step (step 14) are repeated a plurality of times.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for surface treatment of a brass-containing metal substrate and a surface-treated brass-containing metal substrate. [Background technology]

[0002] Rubber and brass are strongly bonded by copper sulfide, which is produced by reacting (vulcanizing) the sulfur contained in the rubber with the copper contained in the brass. It has been proposed to use cobalt salts to promote the reaction between sulfur and brass. Patent Document 1 describes a method for improving adhesion to a rubber composition by applying a metal-containing silane coupling agent solution, specifically a silane coupling agent solution containing Co (cobalt) or Ni (nickel) as a catalytic metal, to the surface of brass. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2006 / 059579

[0004] However, cobalt is expensive, so using it for surface treatment results in an expensive final product. Also, since cobalt can cause soil and water contamination, there is a demand to reduce its use. DISCLOSURE OF THE INVENTION

[0005] The purpose of this invention is to improve adhesive performance with rubber without using catalytic metals such as cobalt.

[0006] The surface treatment method for a brass-containing metal substrate according to the present invention is a method in which an alkaline aqueous solution is brought into contact with the surface of a substrate having a brass-containing metal surface layer, an aqueous silane coupling agent solution is brought into contact with the surface of the substrate that has been contacted with the alkaline aqueous solution, and the substrate that has been contacted with the aqueous silane coupling agent solution is heated, and is characterized in that the step of contacting with the aqueous silane coupling agent solution and the step of heating the substrate that has been contacted with the aqueous silane coupling agent solution are repeated multiple times.

[0007] The substrate having a brass-containing metal on its surface may be a substrate made of a brass-containing metal (a brass-containing metal substrate), or may be a substrate made of a material that does not contain brass (such as steel) with a brass-containing metal plated on its surface. For example, the substrate may be a plurality of wires (filaments, cords) each having a brass-containing metal plated on its surface. In either case, the brass-containing metal substrate to be surface-treated by this invention has a brass-containing metal on the surface that is exposed to the outside air.

[0008] The silane coupling agent is used in a liquid state dissolved in water. From the viewpoint of water solubility, an amino-based silane coupling agent, such as 3-aminopropyltriethoxysilane, can be preferably used as the silane coupling agent.

[0009] The brass-containing metal substrate to be surface-treated in this invention has a brass-containing metal on its surface, so when it is brought into contact with an alkaline aqueous solution, for example, an aqueous solution of sodium hydroxide, the zinc contained in the brass and the base chemically react to introduce hydroxyl groups onto the surface of the brass-containing metal substrate. When it is brought into contact with an aqueous solution of a silane coupling agent, hydrogen bonds are formed between the silanol groups and the hydroxyl groups on the surface of the brass-containing metal substrate.

[0010] When a substrate that has been in contact with an aqueous solution of a silane coupling agent is heated, a dehydration condensation reaction occurs, forming SiO bonds instead of hydrogen bonds. This gives the substrate surface a surface property that reacts easily with organic materials and firmly adheres (chemically bonds) to them.

[0011] According to this invention, the step of contacting the substrate with an aqueous silane coupling agent solution and the step of heating the substrate that has been contacted with the aqueous silane coupling agent solution are repeated multiple times. Further SiO bonds are formed on (in an upper layer of) the SiO bonds on the surface of the brass-containing metal substrate. SiO bonds (layers, films) corresponding to the number of times the contacting step and heating step are repeated are layered on the surface of the brass-containing metal substrate.

[0012] Tests have confirmed that treated brass-containing metal substrates that have undergone the contact and heating processes multiple times have improved adhesion to rubber compositions. By repeating the contact and heating processes multiple times, SiO bonds are formed uniformly and in multiple layers (multiple stages) on the surface of the treated brass-containing metal substrate, which is thought to contribute to improved adhesion.

[0013] In one embodiment, the concentration of the silane coupling agent aqueous solution is 0.01 to 1.00 mass%, preferably 0.10 to 0.50 mass%. Tests have confirmed that an excessively high concentration of the silane coupling agent aqueous solution reduces adhesion to the rubber composition. When a high-concentration silane coupling agent aqueous solution is used, the condensation reaction between silanol groups proceeds more rapidly than the condensation reaction with the surface of the brass-containing metal substrate during the heating process, which is thought to reduce reactivity with the brass-containing metal substrate. Furthermore, the use of a high-concentration silane coupling agent aqueous solution may result in an uneven SiO bond layer, which is also thought to be a factor in reducing adhesion. Conversely, if the concentration of the silane coupling agent aqueous solution is too low, the number of hydrogen bonds between silanol groups and hydroxyl groups formed on the surface of the brass-containing metal substrate may decrease, reducing adhesion. To compensate for this, the contact time (immersion time) in the silane coupling agent aqueous solution may be excessive. By setting the concentration of the silane coupling agent aqueous solution to 0.01 to 1.00 mass%, preferably 0.10 to 0.50 mass%, it is believed that even if the contact process with the silane coupling agent aqueous solution is for a relatively short period of time, it is possible to ensure sufficient bonding between silanol groups and hydroxyl groups on the surface of the brass-containing metal substrate, and furthermore, the number of SiO bonds after the heating process.

[0014] The present invention also provides a surface-treated brass-containing metal substrate manufactured by the above-mentioned surface treatment method, and a bonding method for vulcanization bonding the surface-treated brass-containing metal substrate to a rubber composition. The surface-treated brass-containing metal substrate according to the present invention is characterized in that it comprises a brass-containing metal on a surface layer, SiO bonds are formed on the surface of the brass-containing metal, and further SiO is bonded to the SiO bonds on the surface of the brass-containing metal substrate. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing a surface treatment process for a brass-plated steel cord. [Figure 2] FIG. 1 is an enlarged cross-sectional view of a brass-plated filament with multiple SiO bonds. [Figure 3] The surface of a brass-plated filament (steel cord) with multiple SiO bonds is shown schematically by chemical formula. [Example]

[0016] Figure 1 is a block diagram showing the surface treatment process for a steel cord (brass-plated steel cord) 1A, in which the surface of a steel cord made from high-strength carbon filaments is plated with brass. Figure 2 is an enlarged cross-sectional view of a surface-treated brass-plated filament with multiple SiO bonds on its outermost surface. Figure 3 is a schematic chemical formula showing the surface appearance of a surface-treated brass-plated filament (steel cord) with multiple SiO bonds.

[0017] Brass-plated steel cord 1A (hereinafter simply referred to as steel cord 1A) is made by twisting two pairs of 0.25 mm diameter high-carbon steel wires (filaments) electroplated with brass into another pair of brass-plated filaments; steel cord 1A with this configuration is called a "2+2 configuration." The brass can have a copper / zinc composition ratio of 63 / 37. The structure of steel cord 1A and the brass composition ratio can be designed as appropriate.

[0018] A long steel cord 1A is wound around a payout bobbin (not shown), and is paid out from the payout bobbin at a constant speed.

[0019] The steel cord 1A unwound from the unwinding bobbin is first subjected to a degreasing treatment 11 using an organic solvent. Oil, particularly water-insoluble oil, that adheres to the steel cord 1A during processing (manufacturing, forming) of the steel cord 1A is removed in the degreasing treatment 11. For the degreasing treatment, hydrocarbon, ketone, alcohol, ester, or ether organic solvents can be used depending on the composition of the oil adhering to the steel cord 1A. Of course, if no oil is adhering to the steel cord 1A, the degreasing treatment 11 can be omitted.

[0020] The steel cord 1A then undergoes a hydroxylation treatment, in which the steel cord 1A is passed through a solution tank containing an alkaline aqueous solution.

[0021] By immersing the steel cord 1A in an alkaline aqueous solution, if any water-soluble oil is present on the steel cord 1A, the water-soluble oil is saponified and removed. As described above, the steel cord 1A is plated with brass, and therefore copper (or copper oxide) and zinc (or zinc oxide) contained in the brass plating are present on its surface. When the brass plating comes into contact with an alkaline aqueous solution, a chemical reaction occurs between the zinc in the brass and the base in the alkaline aqueous solution, introducing hydroxyl groups (-OH) onto the surface of the steel cord 1A.

[0022] If the alkaline concentration of the alkaline aqueous solution is too low, the reaction rate between zinc and the base will be slow and the introduction of hydroxyl groups may be insufficient, so an alkaline concentration of pH 11 or higher, preferably pH 12 or higher, is required. Conversely, if the alkaline concentration is too high, the chemical reaction may become uneven, the copper in the brass may discolor, and cleaning may take a long time, so an alkaline concentration of pH 13.5 or lower is preferable. When the alkaline aqueous solution is a sodium hydroxide aqueous solution, the concentration of sodium hydroxide is, for example, about 1% by mass.

[0023] Typically, the steel cord 1A is immersed in the alkaline aqueous solution for about one minute.

[0024] After the hydroxylation treatment 12, the steel cord 1A is washed with water and then subjected to a silane coupling treatment, in which the steel cord 1A is passed through a solution tank containing an aqueous solution of a silane coupling agent.

[0025] For example, an aqueous solution of an amino-based silane coupling agent is used, in which an amino-based silane coupling agent containing an amino group (-NH2) as a functional group is dissolved in water. The silane coupling agent contains a hydrolyzable group (e.g., an alkoxyl group (RO-)), which hydrolyzes to form a silanol group (Si-OH) when dissolved in water. When a steel cord 1A with hydroxyl groups introduced onto its surface is immersed in an aqueous solution of the silane coupling agent, the silanol groups form hydrogen bonds with the hydroxyl groups on the surface of the steel cord 1A, and the silane coupling agent adheres to the surface of the steel cord 1A.

[0026] A low concentration of the silane coupling agent aqueous solution facilitates the formation of a uniform coating (SiO bonds, as described below); however, if the concentration is too low, the number of hydrogen bonds between silanol groups and hydroxyl groups decreases, making it difficult to achieve adhesion to rubber. Furthermore, if the concentration is less than 0.01% by mass, a longer immersion time is required. On the other hand, if the concentration is too high, the condensation reaction between silanol groups proceeds more rapidly than the condensation reaction with the surface of the steel cord 1A, as described below, resulting in the formation of a non-uniform coating, which may impair adhesion to rubber. For this reason, the concentration of the silane coupling agent in the silane coupling agent aqueous solution is set to approximately 0.01 to 1% by mass. Although details will be described later, a concentration of 0.1 to 0.5% by mass is even more preferable. When a highly concentrated silane coupling agent aqueous solution is used in the silane coupling treatment 13, the higher the concentration, the lower the adhesion (pull-out strength) between the steel cord and rubber, as will be explained in the test results described below.

[0027] After the silane coupling treatment 13, the steel cord 1A is subjected to a heat treatment 14. In the heat treatment, the steel cord 1A is passed through a heating furnace. A dehydration condensation reaction occurs between the silanol groups derived from the silane coupling agent and the hydroxyl groups on the surface of the steel cord 1A, forming SiO bonds on the surface of the steel cord 1A (brass), which are chemically strongly bonded (fixed) to the surface of the steel cord 1A. The heating temperature in the heating furnace is, for example, about 110°C, and the heating time is set to a time appropriate for the dehydration condensation reaction, for example, about 5 minutes.

[0028] After the heat treatment 14, the steel cord 1A is again subjected to the silane coupling treatment 13. The silane coupling treatment 13 and the heat treatment 14 are repeated about 2 to 10 times, preferably about 3 to 5 times.

[0029] The steel cord, which has SiO2 chemically bonded to its surface in multiple stages (multilayers) through multiple silane coupling treatments 13 and heat treatments 14, is wound around a winding bobbin (not shown). The steel cord in its final state wound around the winding bobbin is hereinafter referred to as the "surface-treated steel cord 1B."

[0030] 2 and 3, for example, by repeating the silane coupling treatment 13 and the heat treatment 14 three times, thin SiO bonds (layers, coatings) 3a to 3c are laminated in three stages (three layers) on the outermost surface layer of the filament 1, which is plated with brass 2 and constitutes the surface-treated steel cord 1B. As described above, SiO bonds are formed on the surface of the steel cord 1A (brass-plated 2) by a dehydration condensation reaction between silanol groups derived from the silane coupling agent and hydroxyl groups on the surface of the steel cord 1A, thereby chemically and firmly bonding (fixing) the silane coupling agent to the surface of the steel cord 1A. Each time the silane coupling treatment 13 and the heat treatment 14 are performed, the SiO bonds are accumulated. The surface-treated steel cord 1B will have SiO bonds (layers, coatings) 3a to 3c in numbers corresponding to the number of times the silane coupling treatment 13 and the heat treatment 14 are repeated.

[0031] Each of the SiO bonds (layers, films) 3a to 3c is very thin, and their interfaces are often unclear. However, as will be explained below, for example, the adhesion between the steel cord and rubber is completely different between a surface-treated steel cord produced by a single silane coupling treatment 13 and heat treatment 14 using a high-concentration aqueous solution of a silane coupling agent and a surface-treated steel cord produced by repeating the silane coupling treatment 13 and heat treatment 14 multiple times (for example, three times) using a low-concentration aqueous solution of a silane coupling agent.

[0032] Table 1 shows the results of the adhesion evaluation test of the rubber and steel cord composite samples (eight types: Examples 1 to 2 and Comparative Examples 1 to 6).

[0033] [Table 1]

[0034] The rubber and steel cord composite samples were prepared by embedding one end of a specified length of steel cord (10 cm) in a rubber composition and vulcanizing and bonding them by pressing at a temperature of 160°C for 10 minutes. In the adhesion evaluation test, a pull-out tester was used to measure the load required to pull the steel cord out of the rubber (pull-out strength). In addition, the percentage of rubber coverage (rubber coverage rate) adhering to the surface of the steel cord pulled out of the rubber was visually measured.

[0035] Additionally, the adhesion evaluation tests included tests on initial adhesion, water-resistant adhesion, and heat-resistant adhesion. Water-resistant adhesion was measured by immersing the prepared composite sample in water heated to 80°C for seven days, followed by the above-mentioned adhesion evaluation test (known as a water fatigue resistance test). Heat-resistant adhesion was measured by leaving the composite sample in an oven at 80°C for seven days, followed by the above-mentioned adhesion evaluation test (known as a heat fatigue resistance test). Initial adhesion was measured by conducting an adhesion evaluation test on the prepared composite sample immediately after sample preparation (without a long delay), without immersing it in water or heating it as described above.

[0036] All eight composite samples used a common steel cord, which was a 2+2 structure steel cord using high-strength carbon steel filaments with a diameter of 0.25 mm and plated with brass (copper / zinc ratio 63 / 37) to a thickness of 0.3 μm.

[0037] The steel cords constituting the composite samples were prepared without applying oil, and therefore were not subjected to degreasing treatment 11. Hydroxidation treatment 12 was performed on five types of samples: Example 1, Example 2, Comparative Example 4, Comparative Example 5, and Comparative Example 6, but was not performed on three types: Comparative Examples 1, 2, and 3. In hydroxidation treatment 12, the steel cords were immersed in a 1% by mass aqueous solution of sodium hydroxide for one minute.

[0038] For the silane coupling treatment 13, the steel cord was immersed in a 0.1 to 2 mass % aqueous aminosilane solution at room temperature for 3 minutes. For the heat treatment 14 after the silane coupling treatment, the cord was heated in a heating furnace for 5 minutes. For Example 1, the silane coupling treatment 13 and the heat treatment 14 were repeated three times, and for Example 2, they were repeated five times. For Comparative Examples 1 and 2, the silane coupling treatment 13 and the heat treatment 14 were not performed even once. For Comparative Examples 3 to 6, the silane coupling treatment 13 and the heat treatment 14 were performed only once.

[0039] The same rubber composition was used for the remaining seven types of composite samples except for Comparative Example 1. For Comparative Example 1, a rubber composition containing cobalt neodecanoate was used.

[0040] Only the initial adhesion test was conducted for Comparative Examples 3 to 6. This is because a relatively small value was measured for the pull-out strength in the initial adhesion test, and therefore the tests for water-resistant adhesion and heat-resistant adhesion were not conducted and were omitted.

[0041] First, comparing Comparative Example 3 and Comparative Example 4, the only difference is the presence or absence of hydroxylation treatment 12. Comparative Example 3 is a sample using a steel cord that was subjected to silane coupling treatment 13 (and further heat treatment 14, the same applies below) without hydroxylation treatment 12, while Comparative Example 4 is a sample using a steel cord that was subjected to both hydroxylation treatment 12 and silane coupling treatment 13. Comparative Example 4 has a higher pull-out strength, and it can be seen that the combination of hydroxylation treatment 12 and silane coupling treatment 13 significantly improves the pull-out strength. It is thought that the introduction of hydroxyl groups to the surface of the steel cord by performing hydroxylation treatment 12 before silane coupling treatment 13 strengthens the bond. Comparative Example 3 and Comparative Example 4 had the same rubber coverage.

[0042] Comparing Comparative Examples 4, 5, and 6, these differ in the concentration of the aqueous silane coupling agent solution used in the silane coupling treatment 13. The higher the concentration of the aqueous silane coupling agent solution was (Comparative Example 4 < Comparative Example 5 < Comparative Example 6), the lower the pull-out strength. It can be seen that the higher the concentration of the aqueous silane coupling agent solution, the weaker the adhesive reaction. In particular, when the concentration of the aqueous silane coupling agent solution was set to 2 mass% (Comparative Example 6), the rubber coverage rate was drastically reduced.

[0043] Comparing Comparative Example 2 and Comparative Example 3, Comparative Example 2 is a sample in which neither the hydroxylation treatment 12 nor the silane coupling treatment 13 was performed on the steel cord, and Comparative Example 3 is a sample in which only the silane coupling treatment 13 was performed on the steel cord without the hydroxylation treatment 12. The pull-out strength of Comparative Example 2 is higher than that of Comparative Example 3, and it can be seen that when only the silane coupling treatment 13 is performed without the hydroxylation treatment 12, the adhesive performance is reduced compared to when neither the hydroxylation treatment 12 nor the silane coupling treatment 13 is performed. It can be said that the silane coupling treatment 13 improves adhesiveness when combined with the hydroxylation treatment 12.

[0044] Comparing Comparative Example 1 and Comparative Example 2, Comparative Example 1 is the same as Comparative Example 2 in that neither the hydroxylation treatment 12 nor the silane coupling treatment 13 is performed, but differs in that the rubber composition contains cobalt neodecanoate. It can be seen that by including cobalt in the rubber composition, the sample of Comparative Example 1 has a significantly improved pull-out strength (293 N) in the initial adhesion test compared to the pull-out strength (227 N) of the sample of Comparative Example 2. The rubber coverage rate in the initial adhesion test is also higher in Comparative Example 1 than in Comparative Example 2.

[0045] In the water-resistant adhesion test and heat-resistant adhesion test, comparable values ​​were measured for both pull-out strength and rubber coverage in Comparative Example 1 and Comparative Example 2. It is clear that cobalt is effective in improving initial adhesion.

[0046] Referring to Example 1, the sample of Example 1 shows test results for a sample prepared using the above-described surface-treated steel cord 1B, i.e., a surface-treated steel cord 1B obtained by subjecting a steel cord 1A to a hydroxylation treatment 12, a silane coupling treatment 13 using a relatively low-concentration (specifically, 0.1% by mass) aqueous solution of a silane coupling agent, and a heat treatment 14, with the silane coupling treatment 13 and heat treatment 14 being repeated three times. Comparing Example 1 with Comparative Example 1, the pull-out strength and rubber coverage measured in the initial adhesion test were almost equivalent between Example 1 and Comparative Example 1. On the other hand, the pull-out strength and rubber coverage measured in the water-resistant adhesion test and the heat-resistant adhesion test were significantly higher for the sample of Example 1 than for the sample of Comparative Example 1. That is, it can be seen that the sample of Example 1 has the same initial adhesion as the sample of Comparative Example 1 and is less susceptible to deterioration than the sample of Comparative Example 1. Furthermore, the pull-out strength of the sample of Example 1 in the water-resistant adhesion test and the heat-resistant adhesion test was greater than the pull-out strength in the initial adhesion test. It is believed that the surface-treated steel cord 1B and the rubber composition bond more firmly with the passage of time.

[0047] Example 2 differs from Example 1 in that the silane coupling treatment 13 and the heat treatment 14 were repeated five times. The sample of Example 2 measured better values ​​for rubber coverage than the sample of Example 1 in all of the initial adhesion test, water-resistant adhesion test, and heat-resistant adhesion test. The pull-out strength also measured better values ​​than the sample of Example 1 in the initial adhesion test and water-resistant adhesion test. [Explanation of symbols]

[0048] 1A Steel Cord 1B surface treated steel cord 1 filament 2 Brass (brass plated) 3a~3c SiO bond 11 Degreasing process 12 Hydroxidation treatment 13 Silane coupling treatment 14 Heat treatment

Claims

1. A method for forming SiO bonds on a surface of a substrate by bringing an alkaline aqueous solution into contact with the surface of a substrate having a brass-containing metal on a surface layer, bringing an aqueous silane coupling agent solution into contact with the surface of the substrate that has been contacted with the alkaline aqueous solution, and heating the substrate that has been contacted with the aqueous silane coupling agent solution, comprising: The step of contacting the substrate with the aqueous silane coupling agent solution and the step of heating the substrate that has been contacted with the aqueous silane coupling agent solution are repeated multiple times. A method for treating the surface of a brass-containing metal substrate.

2. The concentration of the silane coupling agent aqueous solution is 0.01 to 1.00% by mass, preferably 0.10 to 0.50% by mass. The method for treating the surface of a brass-containing metal substrate according to claim 1 .

3. 2. The method for treating the surface of a brass-containing metal substrate according to claim 1, wherein the alkaline aqueous solution is an aqueous sodium hydroxide solution.

4. 2. The method for treating the surface of a brass-containing metal substrate according to claim 1, wherein the silane coupling agent is an amino-based silane coupling agent.

5. 2. The method for treating the surface of a brass-containing metal substrate according to claim 1, wherein the substrate is a filament whose surface is plated with a brass-containing metal.

6. The substrate includes a plurality of filaments each having a brass-containing metal plated on its surface. The method for treating the surface of a brass-containing metal substrate according to claim 1 .

7. A rubber composition is vulcanization-bonded to a treated brass-containing metal substrate that has been treated by the method for surface treatment of a brass-containing metal substrate according to any one of claims 1 to 6. Adhesion method.

8. The surface is made of brass-containing metal, SiO bonds are formed on the surface of the brass-containing metal, and SiO is further bonded to the SiO bonds on the surface of the brass-containing metal base material. Surface-treated brass-containing metal substrate.

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