1. Field
Curable compositions such as adhesive compositions for bonding polymeric substrates to hydroxylated surfaces are disclosed. In particular, adhesive compositions suitable for use in polymer-to-glass, for example elastomer-to-glass such as rubber-to-glass, bonding applications are provided. One aspect of the invention provides novel compounds suitable for use in adhesive compositions suitable for rubber to glass bonding applications.
2. Brief Description of Related Technology
Reinforced composite materials play a critical role in the manufacture of high-performance products that need to be lightweight, yet strong enough to take harsh loading and operating conditions. Popular reinforcing materials included wood, glass, metals, quartz and carbon fibres. Composites reinforced with such materials may find utility in the manufacture of a number of structural materials such as aerospace components and racing car bodies.
Per unit weight glass represents one of the strongest structural materials around, and, for example, is stronger than steel on a weight per weight basis. Furthermore, glass exhibits improved stress and strain resistance compared to many other common reinforcement media. For example, glass cord may be utilised to exploit the unique properties of glass fibres to impart strength and dimensional stability to polymeric products.
Glass fibre reinforced composite materials consist of high strength glass fibres embedded in a matrix. For example, Glass Fibre Reinforced Concrete comprises glass fibres embedded in cement-based matrix and may find utility in buildings and other structural edifices. Similarly, Glass Reinforced Plastic comprises glass fibres embedded in a plastic material. Glass Reinforced Plastics are immensely versatile materials which combine to provide lightweight materials with high strength performance. Glass reinforced plastics find utility in a number of different areas from structural engineering to telecommunications.
Elastomer to glass bonding provides an attractive means by which the structural strength of glass can be combined with the elastomeric properties of the elastomer/rubber. Reinforcing fibres such as glass fibres have been used as a reinforcing material for rubber articles such as in rubber belts, tyres and hoses. In particular, glass fibres have been employed to reinforce automotive timing belts, where there is a need for synchronous transfer of power from crankshaft to overhead camshaft without loss of inertia.
In general, rubber articles are repeatedly subjected to a flexing stress resulting in flex fatigue. This can lead to reduced performance, a peel-off between the reinforcing fibre and a rubber matrix and a wearing of the reinforcing fibre. Accordingly, adhesives for rubber to glass bonding should be capable of enduring such stresses.
Traditionally, such glass cord composites are manufactured by coating individual filaments of glass yarn with specialised coatings, such as resorcinol formaldehyde latex (RFL) formulations. Conventional rubber to metal bonding products are then employed to bond the RFL latex to the rubber via a vulcanisation step.
Traditional rubber to metal bonding technology, incorporates a two-step system, where in a first step a primer is applied and thereafter in a second step an adhesive is applied. The primer ordinarily consists of solutions or suspensions of chlorinated rubber and phenolic resins containing reactive groups, and also pigments such as titanium dioxide, zinc oxide, carbon black, etc. The primer is generally applied as a thin layer onto a treated (cleaned) surface of a metallic component such as treated steel component for example a component that has been grit blasted or chemically treated. The adhesive ordinarily consists of a large range of rubber materials and cross-linkers. These include, but are not restricted to, chlorinated and bromochlorinated rubbers, aromatic nitrosobenzene compounds and bismaleimide as cross-linkers, xylene, perchloroethylene and ethylbenzene as solvents, and also some lead or zinc salts. The adhesive layer is generally the link between the primed metal and the rubber.
Generally, it is desirable that bonding to the target substrate is achieved during a vulcanisation step like compression moulding, transfer moulding, injection moulding and autoclave heating, for example with steam or hot air. For example, semi-solid rubber can be injected into a mould. The semi-solid rubber is then cross-linked into a fully cured rubber and the bond with the substrate is formed at the same time.
Certain requirements of the curing system are desirable. This includes, ease of processing, stability (for example avoiding sedimentation), ease of application, fast drying (to allow handling without fouling), good wetting properties, and good curing strengths. Curing should be achieved independently of the type of elastomer (rubber) employed and also independently of the type of substrate. It will be appreciated that some rubbers are blended materials and accordingly it is desirable that good curing is achieved with such blended materials. Suitably consistent curing is achieved under various process parameters. Durability is also desirable.
Notwithstanding the state of the art it would be desirable to provide compounds and compositions to bond polymeric substrates (for example elastomers) to hydroxylated substrates such as glass.