GB2041285A

GB2041285A - Bonded Plastics Workpieces

Info

Publication number: GB2041285A
Application number: GB8003414A
Authority: GB
Original assignee: Carl Freudenberg KG
Current assignee: Carl Freudenberg KG
Priority date: 1979-02-10
Filing date: 1980-02-01
Publication date: 1980-09-10
Also published as: BR8000540A; LU81855A1; DE2905127C2; IT1164068B; BE880121A; ES486140A1; NL7908683A; ATA68680A; GB2041285B; DE2905127A1; JPH0245574B2; FR2448426B1; MX154005A; IT7950940A0; NL184669C; JPS55107413A; DK56480A; AT379161B; IE800240L; IE49160B1

Abstract

A bonded workpiece is produced by moulding a resin material in a mould and in contact with a cross- linkable elastomeric material, either or each material containing a compound or group which reacts with the other material, under the conditions of the process, thereby bonding the materials together at their mutual boundary. The mouldable resin may be e.g. an epoxy resin containing a polyamine hardener while the elastomer is e.g. an acrylonitrile-butadiene copolymer containing precipitated silica. Both materials may be injected jointly into a mould in liquid or other form, or one may be injected onto a preform of the other. Alternatively completely reacted moulds of both may be compacted in a mould for reaction.

Description

SPECIFICATION Producing Bonded Workpieces German Offenlegungsschrift No. 2616309 (BPA 15164/77) discloses a process for bonding various plastics and a reactive elastomeric material or a resin, by injecting molten plastics material directly onto a formed mould or blank of the reactive material which is incompletely reacted. The heat transferred from the molten plastics to the reactive material causes completion of the reaction in the latter, and the materials adhere to each other; after the subsequent cooling and hardening or solidification, a bonded workpiece is produced. It is thought that the bond which is obtained between the two materials is probably due to the activation of adhesive properties.

This known process has not yet been conducted on a large commercial scale. A problem with the process is that the temperature of the mould has to be chosen carefully with regard to the particular materials involved. A temperature gradient must prevail within the mould, in order to ensure that the reactive material, at its boundary with the injected nonreactive material, has hardened to a lesser extent than elsewhere. Depending on the size of the parts involved, it can prove difficult or impossible to meet this requirement. It has proved especially difficult to produce bonded workpieces having high strength by this method. It would be desirable to produce bonded workpieces of the type described in which the bond between the two materials was not the weakest point of the workpiece.

According to the present invention, a process for producing a bonded workpiece comprises moulding a mouldable resin material in a mould and in contact with a cross-linkable elastomeric material, in which either or each material contains a compound or group which reacts with the other material, under the conditions of the process, thereby bonding the materials together at their mutual boundary.

In one embodiment of the process of this invention, the cross-linkabfe elastomeric material is an acrylic ester copolymer which contains epoxide groups. In a second embodiment, either or each of the elastomeric material and the resin material contains, in admixture therewith, a compound which, at the temperature at which the resin material is plastic and thus can be moulded, reacts with the other material, e.g. by polyaddition.

By causing reaction between constituents of the two materials, good bonding strengths can be achieved. This result can be obtained by the simple mixing of known substances by known methods. In large-scale operation, all or part of the necessary materials can be obtained directly from a manufacturer and the introduction of the novel process into mass production need not be dependent on heavy economic investment.

Preferred elastomeric materials are acrylonitrile-butadiene copolymers and acrylic ester copolymers. In order to obtain a strong bond with a thermosetting resin, for example an epoxy resin, it is advantageous to include a plasticiser having polyfunctional terminal groups, for example a polyester polyhydric alcohol, into the elastomeric material. It is often also advantageous to include a filler, e.g. precipitated silica, in the elastomeric material to achieve bonding with the resin.

Accordingly the process of the invention can be conducted most simply by employing commercially available mouldable materials comprising an epoxy resin and a suitably made-up elastomeric compound which are brought together in a mould. The way in which the materials are introduced into the mould is not critical. For example, both components may be injected in liquid or other convenient form into the mould jointly, or one component may be injected into the mould onto a preformed mould of the other material. Both these methods require injection moulding apparatus and it is therefore more economic to make incompletely reacted moulds of the two components and compact them in a mould in which they are reacted, i.e. in which the process of the invention is conducted.

In a procedure of this type, multi-layer presses can be used, if desired, in mass production. It is desirable that the moulds are used at a uniform temperature between 150 and 1 900C. The exact temperature depends on the nature of the materials; a temperature of 1 800C may be particularly suitable for the production of seals or gaskets in which vulcanisation is a part of the reaction.

The addition of the components necessary to achieve polyaddition need not result, at the required amounts, in any impairment of the mechanical properties of the product. The desired components can be selected from a large number of materials, allowing the selection of materials to avoid particular incompatibility.

For example, it is possible to use plasticisers containing hydroxyl groups, e.g. polybutanediols having functional hydroxyl groups, and/or fillers/stiffening materials such as precipitated silica, in the elastomeric compound. Polymers containing epoxide groups and based on ethyl or butyl acrylate, which are cross-linked by amines, can also be used. Such compounds can react, without the addition of further reactive compounds, with a hardenable mouldable material to give a bond of great strength and stability, even under the effect of substances causing swelling. In this respect, the bonds obtained by the process of the invention differ fundamentally from those obtained in the process of German Offenlegungschrift No. 2616309 which are essentially due to the activation of adhesive properties.

The process of the invention is particularly suitable for the production of shaft sealing or packing rings. These usually comprise a stiffening ring of metal onto which a rubber-elastic part with a sealing lip is vulcanised. It has been repeatedly attempted to replace the stiffening ring by a plastics member but these attempts have failed owing to low mechanical strength and cost. The process of this invention may provide a solution to this problem.

The hardening of epoxy resins, i.e. their conversion to thermosetting resins, takes place by the addition of carboxylic acids and anhydrides, carboxylic acids or polyamines (see Kunstoffhandbuch, Vol. Xl, Karl Hanser Verlag, Munich, 1971). Liquid or pasty epoxides of low molecular weight may be used as starting materials. To prepare moulding compositions, normally solid epoxide resins of higher molecular weight or liquid epoxide resins of low molecular weight which have been converted into the B state using suitable hardeners, are used. Suitable hardeners are polyamines such as methylenediamine or m-phenylenediamine and boron trifluoride complexes of amines.It will often be convenient to use commercially available precompounded, pourable moulding compositions including suitable mineral fillers such as sand or glass fibres, lubricants (for improving workability) and compounds assisting removal of the composition from a mould.

The elastomeric material can be based on a natural or synthetic rubber. Suitable compositions of this type may inc!ude fillers, plasticisers or other additives which are conventionally used in the compounding of elastomer materials. In order to cause polyaddition, the material may include reactive groups or added compounds with reactive groups such as primary or secondary amines or carboxyl, thio, hydroxyl or epoxy groups. Hydroxyl, primary amino and epoxy groups are preferred for the formation of strong bonds between the elastomeric material and the resin. It will often be desirable to provide suitable reactive groups in each material, for reaction with the other. This can be achieved without substantial modification of the materials or substantial effect on the product.

The following Examples 1 to 5 illustrate the invention; Example A is comparative.

Example 1(General Procedure) A blank of an uncross-linked elastomeric material is placed in a heated press mould at a temperature of 1 800C. The mould is closed and a pre-plasticised epoxide resin composition injected into the remaining hollow space until material issues at a flash passage provided. After a reaction time of 5 minutes, which is dependent on the compositions used, the epoxide resin has hardened, the elastomeric material is vulcanised and polyaddition between constituents of the two materials has occurred. The finished moulding can be removed from the tool.

Example 2 In accordance with the procedure of Example 1, a blank having the following composition was placed in the moulding tool: parts Acrylonitrile(AN)-butadiene copolymer containing 28% AN 100 Precipitated silica 30 Calcined chalk 50 Stearic acid 2 Ether thioether plasticiser (Vulkanol OT; Bayer AG) 10 Zinc oxide 5 Tetramethylthiuram disulphide 2.5 2-(2-benzothiazyl)cyclohexylsul- phenamide 3 Sulphur 0.7 A second blank, of an epoxide resin moulding material, was put on top of the blank placed in the tool. This second blank consisted of a resin of Thgher molecular weight based on epichlorhydrin and bisphenol-A with a polyamine as hardening constituent and mineral fillers and glass fibres as reinforcing constituents.The tool was closed and heated to a temperature of 1 800C. Owing to the pressure exerted on the two blanks, they were strongly pressed together in the region of the boundary layer. In the course of the following reaction of the materials of the two parts, polyaddition in the region of the boundary layer occurred, the silanol groups of the precipitated silica and the epoxy groups of the moulding material reacting with the aminic hardening constituent. The two materials were strongly bonded together in the region of the boundary layers. Even after length storage in a swelling medium, for example heated oil, the bond obtained could not be forcibly broken in the region of the boundary layer.

Example 3 Under the conditions of Example 1, there was used a blank of an uncross-linked elastomeric material based on butyl acrylate and containing a cross-linking constituent having epoxide groups, the composition being as follows:~ parts Elastomer 100 Carbon black with a specific surface area of 80 m2/g (HAF carbon black) 40 Stearic Acid 2 Aminic cross-linking agent 1 The moulding composition from which the second part was formed as in Example 2. The adhesion between the two materials after cooling was sufficiently strong that, in a rending test, a fracture occurred within the cross-linked elastomeric material. The bond at the boundary layer was the result of polyaddition reaction between the elastomer containing epoxide groups and the aminic hardening constituent which is contained in the moulding composition.

Example A (Comparative) Under the conditions of Example 1, an elastomer mix of the following composition was used for comparison in corresponding manner: parts Acrylonitrile-butadiene copolymer containing 28% AN 100 Carbon black with a specific surface area of 40 m2/g 70 Zinc Oxide 5 Stearic acid 2 Plasticiser (dioctyl phthalate) 20 Tetramethylthiuram disulphide 2.5 2-(2-Benzothiazyl) cyclohexylsulphenamide 3 Sulphur 0.7 The composition was treated further under the conditions of Example 1. Only poor bonding between the two adjoining parts in the region of the boundary surface was achieved owing to the absence of mutually reactive constituents in the joined materials. In a bending test, a fracture was produced in the region of the boundary surface.

Example 4 Example 2 was repeated except that a polyester polyhydric alcohol was added, in equal weight, as plasticiser. Similar results were achieved.

Example 5 Example 2 was repeated except that a polybutadiene having hydroxyl terminal groups was used in place of the given plasticiser. The strength of the final bond, the result of polyaddition between the silanol groups of the precipitated silica and hydroxyl groups of the polybutadiene oil on the one hand, and the epoxide groups of the moulding material on the other hand, corresponded to that of the product of Example 2.

Claims

1. A process for producing a bonded workpiece, which comprises moulding a mouldable resin material in a mould and in contact with a cross-linkable elastomeric material, in which either or each material contains a compound or group which reacts with the other material, under the conditions of the process, thereby bonding the materials together at their mutual boundary.

2. A process according to claim 1 in which the elastomeric material is an acrylic ester copolymer containing epoxide groups.

3. A process according to claim 1 in which either or each material contains, in admixture therewith, a compound which, at the temperature at which the resin material can be moulded, reacts with the other material.

4. A process according to claim 3 in which the elastomeric material is an acrylonitrile-butadiene copolymer or an acrylic ester copolymer.

5. A process according to claim 3 or claim 4 in which the elastomeric material contains a plasticiser having polyfunctional terminal groups.

6. A process according to claim 5 in which the plasticiser is a polyester polyhydric alcohol or a polybutadiene oil having hydroxyl groups.

7. A process according to any of claims 3 to 6 in which the elastomeric material contains a filler.

8. A process according to claim 7 in which the filler is precipitated silica.

9. A process according to any of claims 3 to 8 in which the resin material is a thermosetting epoxide resin.

10. A process according to claim 9 in which the epoxide resin is fibre-reinforced.

11. A process according to claim 1 substantially as described in any of Examples 1 to 5.