EP1039974A2

EP1039974A2 - Rubber-metal composite

Info

Publication number: EP1039974A2
Application number: EP98965765A
Authority: EP
Inventors: Ralf Schelbach; Ilona Lange
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1997-12-13
Filing date: 1998-12-04
Publication date: 2000-10-04
Also published as: WO1999030841A3; US6379752B1; AU2158499A; WO1999030841A2; CA2299195A1; DE19755421A1; ID25470A; HRP20000357A2; CN1281403A; ZA9811396B; PL341709A1; BR9813518A; JP2002512136A; TR200001674T2; CZ20002183A3; JP4054177B2

Abstract

The invention relates to a method for the production of a metal-rubber composite on a metal, characterised in that a) a self-depositing resin is deposited on the metal and hardened; b) a primer is applied to the resin, if desired; c) a binding agent is deposited on the primer or self-depositing resin; d) a natural or synthetic rubber is deposited on the binding agent; e) the rubber is vulcanised at a temperature of 90-220 DEG C. The invention also relates to a composite component which can be obtained according to said method.

Description

"Rubber-metal composite"

The invention relates to a method for producing a rubber-metal composite, the innovation of which is that a layer of a self-depositing resin is applied to the metal before the rubber is vulcanized in a later step. Furthermore, the invention relates to a composite component made of metal and rubber, which contains a hardened layer of a self-separating resin between the metal surface and the rubber. Composite components of this type can be used in many technical fields. Examples include vehicle and mechanical engineering.

The natural requirement for rubber-metal composite components is that the rubber adheres sufficiently firmly to the metal. Sufficiently firm adhesion is given if, in adhesion tests in which the rubber and metal bond is torn apart, the fracture occurs within the rubber compound and not between rubber and metal. However, the corrosion resistance of the rubber-metal composites is a serious problem in many applications. The composites can come into contact with corrosive media such as salt water and must have sufficient corrosion resistance for this. In principle, the entire rubber-metal composite could be painted over after its manufacture. However, lacquers that have to be baked at a temperature at which the rubber is damaged cannot be used for this. However, paints that cannot be burned in do not provide adequate corrosion protection. And even with good corrosion-protecting paints, corrosion problems can occur if the paint cracks or flakes due to mechanical deformation of the composite. Different possibilities are proposed in the prior art to improve the corrosion protection of rubber-metal composites. DE-A-27 48 686 describes a method for increasing the corrosion resistance of a rubber-metal structure, in which an epoxy resin-based powder coating is applied to the metal surface before being connected to the rubber. This coating has the disadvantage that it softens at the temperatures of the rubber vulcanization. Since vulcanization is usually carried out under pressure, there is a risk that the rubber will shift on the softened surface. The same danger exists with a later load at a temperature that occurs above the softening point of the powder coating (from about 50 ° C). Such temperatures can easily be reached, for example, in a motor vehicle parked in the sun.

EP-A-54 861 proposes to coat the metal with a cataphoretic dip coating before the rubber is applied. On the one hand, this is complex in terms of plant technology, since chemical pretreatment of the metal surface, such as phosphating, including rinsing, has to be carried out before the cataphoretic dip coating. There are therefore several upstream process steps and thus several treatment baths required. In addition, the cataphoretic dip painting requires a lot of energy and therefore has economic disadvantages.

The object of the invention is to provide a new method for producing a rubber-metal composite. The metal should be coated with a protective coating known to have good anti-corrosion properties before the rubber is applied. This protective coating should be able to be applied in a technically simple and thus economical manner and should not soften under the conditions of the vulcanization of the rubber. In a first aspect, the invention accordingly relates to a method for producing a rubber-metal composite on a metal, characterized in that a) a self-depositing resin is deposited and cured on the metal, b) if desired, a primer is applied to the resin, c ) a binder is applied to the primer or to the self-separating resin, d) a natural or synthetic rubber is applied to the binder and e) the rubber is vulcanized at a temperature in the range from 90 to 220 ° C.

Metals whose ions lead to the coagulation and deposition of the self-depositing resin are suitable as the metal substrate. Cast iron, steel or other iron-containing substrates are currently considered for this. Accordingly, the method is preferably carried out using iron-containing substrates. However, it can also be carried out on zinc or galvanized steel if suitable baths of self-separating resins are selected and / or suitable pre-rinses are used. Other metal substrates are also suitable, provided that self-depositing resins are available for this.

The self-separating resins which can be used for the purposes of this invention are also referred to in the art as autophoresis resins or autophoresis lacquers or autophoretic lacquers. The term "Autophoretic ^R Coating Chemicals" is used in Anglo-Saxon language. The abbreviation "ACC *" is often used for this in this language area. The principle of autophoretic paint deposition is that an acidic aqueous emulsion of an organic polymer is provided. If a metal surface is brought into contact with such an emulsion, metal ions are released from the surface by the action of the acid. These combine with the polymer particles and lead to their coagulation. Since this process takes place directly on the metal surface, the coagulated polymer separates as a coating on the metal surface. If the metal surface is completely covered with polymer, the process comes to a standstill. The layer thicknesses obtained are generally in the range from about 15 to about 30 μm. After the coating has been completed, the metal parts are removed from the treatment bath and excess treatment emulsion is rinsed off with water. Reactive rinsing is often carried out, which improves the adhesion of the autophoretic paint to the metal and improves corrosion protection. For example, solutions of chromic acid and / or chromates are suitable. The resin is then cured by heating to a temperature in the range from 140 to 250 ° C., preferably 150 to 180 ° C.

The self-depositing resins which can be used in the process according to the invention are known as such in the prior art for coating metal parts. Their corrosion protection effect has been sufficiently tested. Examples of self-separating resins, such as can be used in the process according to the invention, are listed in WO 93/15154. Examples include urethane resins, epoxy resins, polyester resins and resins based on different acrylates. Specific examples of acrylate resins are those that contain one or more of the following monomers: methyl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-

Hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl acrylate,

Glycidyl methacrylate, acrylamide, methacrylamide, acrylic acid and methacrylic acid, as well as acrylic alkyd resins. These acrylates can exist as copolymers with ethylene, styrene, vinyl chloride, vinylidene chloride and vinyl acetate.

Epoxy-based resins, which can also be used in the process according to the invention, are described, for example, in WO 97/07163. In addition to pure epoxy resins, epoxy-acrylate-based resins are also suitable. In addition to the self-depositing resin and acid, the emulsions often contain oxidizing agents and / or fluoride ions. This improves the deposition process. Examples of such process variants which can be used in the course of the process sequence according to the invention are: EP-A-32 297, EP-A-374 772, WO 93/15154 and WO 93/16813.

As is customary in the coating of metal parts for corrosion protection, it is also preferred in the method according to the invention to carry out an intermediate rinsing with an aqueous solution of chromic acid or chromates between the deposition of the self-separating resin and the curing.

The self-separating resin is cured at a temperature in the range from 140 to 250, in particular from 150 to 180 ° C.

If desired, a so-called primer can now be applied to the self-separating resin. However, this sub-step is not absolutely necessary for the success of the method according to the invention. Primers are usually dispersions of organic polymers in organic solvents. For example, phenolic resins, chlorinated rubber and epoxy resins can be used, which can also be used in combination with one another. Phenolic resins are preferably combined either with chlorinated rubber or with epoxy resins. In addition, the primers can contain metal oxides and / or fillers as additives. After application, the primers are dried at a temperature in the range between about 20 and about 100 ° C. The dry layer layer is usually about 7 to about 10 microns. Instead of dispersions in organic solvents, aqueous primer dispersions can also be used. In a further process step, a binder is applied to the primer layer or, if the primer has been dispensed with, to the hardened self-depositing resin. Like the primers, such binders are known in the prior art for the production of rubber-metal composites. The basis of the technically customary binders is generally a mixture of halogenated polymers such as chlorinated rubber and crosslinkers. Fillers may also be present. The bond between the rubber and the binder is improved if the binder additionally contains nitroso-substituted aromatics. A technically common example of this is p-dinitrosobenzene. The binders are usually in the form of dispersions containing solvents. They are dried at 20 to 100 ° C, with a layer of about 10 to about 15 microns is set. Water-based binders are also available and can be used in the sequence of processes according to the invention.

In a subsequent sub-step, a natural or synthetic rubber is applied to the binder. This can be selected, for example, from natural rubber, styrene-butadiene rubber, ethylene, propylene, diene rubber and nitrile-butadiene rubber. All types of rubber that can be cross-linked by hot vulcanization are suitable. Examples are the rubbers NR; IR, IIR, NBR, HNBR, CR, ACM, CSM, AEM, SBR and EPDM. Preferred rubbers are: NR, TR and NBR.

The rubber is vulcanized at a temperature in the range of 90 to 220 ° C, preferably in the range of 120 to 190 ° C. The rubber mass is preferably pressed against the substrate during the vulcanization step. Here, pressures in the range from about 50 to about 200 bar are exerted. In general, the vulcanization time depends on the type of rubber used and the size of the components. It can therefore fluctuate within wide limits and can range, for example, from about 5 to about 120 minutes. For example, vulcanization can take place at a temperature in the range between 150 and 180 ° C Duration of 10 minutes at a pressure of about 100 bar. It is often advisable to first vulcanize at a lower temperature for a certain period of time and then to vulcanize at an elevated temperature. For example, the preliminary vulcanization can be carried out for a period of time in the range from approximately 5 to approximately 15 minutes at a temperature between approximately 90 and approximately 120 ° C., and the vulcanization for a period of time in the range of approximately 10 to approximately 20 minutes at a temperature in the range between approximately 160 and about 190 ° C.

In a second aspect, the invention relates to a composite component made of metal and rubber, which contains a hardened layer of a self-separating resin between the metal surface and the rubber. In this case, there is preferably at least one binder layer between the layer of a self-depositing resin and the rubber, if desired both a primer and a binder layer. The self-separating resins, rubbers (= rubber), primers and binders that come into question for this have been described in more detail above.

The composite components according to the invention and obtainable by the method according to the invention have the advantage that the good corrosion-protecting layer of the self-separating resin lies between metal and rubber. The composite components are often designed in such a way that the entire metal surface is not covered with rubber. The metal surface, which is not covered with rubber, lies however under the continuous layer of the self-separating resin and is thereby protected against corrosion. The layer of self-depositing resin covers the entire metal surface regardless of whether the rubber follows or not. This avoids a point of corrosion attack where the rubber coating begins. The sequence of processes according to the invention can, for example, be embedded in the following treatment sequence:

1. Alkaline cleaning

2. Rinse

3. Rinse with deionized water

4. Separation of the self-separating resin

5. Rinse

6. Rinsing with a reactive sink (can be avoided in particular if self-separating resins based on epoxy are used)

7. Drying

8. If necessary, apply and dry the primer

9. Application and drying of the binder

10. Application and vulcanization of the rubber.

embodiments

The dry adhesion of the rubber-metal composite was checked using a peel test in accordance with DIN 53531, Part 1. Unblasted ASTM-B bodies, ST 37, were used as test specimens. After coating with the self-separating resin, the organic-based binder Chemosil ^R 411 was applied by dipping or the water-based binder XW 7484 by brushing in a first test series without reactive rinsing of the self-depositing resin and without using a primer. The natural rubber NR 11426 and the synthetic nitrile butadiene rubber NBR 60041 were used as rubber. The rubber was cured at 160 ° C under a pressure of 100 bar for 10 to 30 minutes. The adhesive values were determined in daN / mm using a tear machine and the tear pattern was then assessed.

The results are shown in Table 1 compared to a standard treatment (without ACC coating: sheet metal + primer + binder + rubber). They show that adhesive values similar to those of standard methods can be achieved with the rubber-metal composite according to the invention. However, it is known that the standard processes do not provide the corrosion protection effect which is achieved by coating with the self-separating resin.

Table 1: Rubber-metal composite on epoxy-based self-separating resins (mean values of 3 measurements each)

M = separation between metal and adhesive 3) Sheet (blasted) with primer XW 1 180

CP = separation between ACC layer and binder

Table 2 shows adhesion values and crack patterns when using the autophoretic 703 acrylate-based self-separating resin, Henkel Surface Technologies. After the self-separating resin had been separated, a reactive rinse was used

Chromic acid-containing solutions of different concentrations performed and the resin cured as shown in Table 2. Various binders were used with or without intermediate application of a primer. Binders and primers are commercial products from Henkel KGaA in Düsseldorf. Test methods, comparative tests, rubber types used and vulcanization conditions as above.

Table 2: Rubber-metal composites on acrylate-based self-separating resin (mean values from 3 measurements each); Products and evaluation: cf. Table 1; Comparative examples: blasted sheet

Continuation of table 2

Claims

claims

1. A process for producing a rubber-metal composite on a metal, characterized in that a) a self-separating resin is deposited on the metal and cured, b) if desired, a primer is applied to the resin, c) on the primer or on the self-separating resin applies a binder, d) a natural or synthetic rubber is applied to the binder and e) vulcanizes the rubber at a temperature in the range from 90 to 220 ° C.

2. The method according to claim 1, characterized in that the self-separating resin in sub-step a) is selected from resins based on acrylate, acrylate-alkyd resin, epoxy-based and epoxy-acrylate-based.

3. The method according to one or both of claims 1 and 2, characterized in that an intermediate rinsing with an aqueous solution of chromate or chromic acid takes place in sub-step a) between the deposition of the self-separating resin and the curing.

4. The method according to one or more of claims 1 to 3, characterized in that the self-depositing resin is cured at a temperature in the range from 140 to 250 ° C.

5. The method according to one or more of claims 1 to 4, characterized in that in the optional sub-step b) a primer based on phenolic resins, chlorinated rubber or epoxy resins is applied.

6. The method according to one or more of claims 1 to 5, characterized in that in step c) a binder based on a mixture of halogenated polymers and crosslinkers is applied.

7. The method according to claim 6, characterized in that the binder contains nitroso-substituted aromatics.

8. The method according to one or more of claims 1 to 7, characterized in that the natural or synthetic rubber in sub-step d) is selected from natural rubber, styrene-butadiene rubber, ethylene, propylene, diene rubber and nitrile-butadiene Rubber.

9. The method according to one or more of claims 1 to 8, characterized in that a pressure in the range from 50 to 200 bar is exerted on the rubber during the vulcanization in substep e).

10. Composite component made of metal and rubber, which contains a hardened layer of a self-separating resin between the metal surface and the rubber.