Self-adhesive Silicone Rubbers

Self-adhesive silicone rubbers do not require a primer and, therefore, the plastic substrate can be injection moulded on the same machine as the silicone rubber. 

Self-adbesive silicone rubbers for injection moulding are restricted to LR mainly. The most peculiar property of these rubbers is the fact that the mould does not have to be treated with a special release agent (which is expensive and complicated to use) when working with these silicone rubbers. 

However, at the same time it is possible to achieve sufficient bonding to steel without having problems with the self-adhesive silicone sticking to the mould, as is the case with conventional bonding agents for rubber to metal components. 

Most recently self-adhesive HTVs have been developed. However, they require special release agents or a specially structured mould suface. They are mainly intended for bonding silicone rubber to steel. 

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The bonding is achieved by different methods. The hard component can contain undercuts where the rubber is anchored during its vulcanisation, a primer on the hard component or even using self-adhesive silicone rubber will give sufficient anchorage. 

Section 11.5. will explain the three alternatives for bonding, where mechanical anchorage (undercuts) or self-adhesive silicone rubber allow for two colour injection moulding. 

In such cases the processor basically has the choice between undercuts, primers or primerless self-adhesive silicone rubber. 

Filler-free formulations of two-component silicone rubbers crosslinkable by condensation or addition are utilized, with or without added solvent, for the coating of papers and plastic foil, optionally as an aqueous emulsion, e.g. for strippable paper for self-adhesive labels or packaging foil for bitumen. Vulcanization is carried out at high temperature (100 to 180°C), to attain as short hardening times as possible. 

Fig. 15. Assembly of a gel cassette for casting IPGs, (a) Glass base plate (3 mm thick) (b) Gel Bond PAG foil (c) U-gasket (in general silicone or rubber, often glued to the glass cover plate usually 0.5 mm thick) (d) Template 3 mm thick glass plate with pieces of self-adhesive Dymo tape (250 p.m thick) for moulding of gel slots (e) paper clips as temporary, additional spacers. (From Gorg et al., 1978. Reproduced with permission of the publisher.)...

Nontacky self-adhesive rubbers (fusible rubbers) are obtained if small amounts of boron ( 1 boron atom per 300 silicon atoms) are incorporated into the polymer chain. They may be obtained by condensing dialkylpolysiloxanes end-blocked with silanol groups with boric acid or by reacting ethoxyl end-blocked polymers with boron triacetate. 

The top-coats are responsible for the durability and resistance to water and chemical impacts from the environment. Mainly acrylic and fiuori-nated polymers are used for top-coats on various base coats (PVC, PUR, PTFE, silicone rubber, etc.) to enhance resistance to soiling and ageing. Certain additives for UV protection can be added. Due to its self-cleaning non-adhesive surface the top-coat is often hard and brittle. On PVC coatings the top-coat gives not only protection against environmental infiuences but also a barrier against emission of plasticizer out of the PVC. 

Self-Adhesive Liquid Silicone Rubbers (LSRs) for the Injection Molding of Rigid Flexible Combinations... 

Self-Adhesive liquid Silicone Rubbers for the Injection Molding 673... 

Roth, J. Albrecht, V. Nitschke, M. Bellmann, C. Simon, F. Zschoche, S. Michel, S. Luhmann, C. Grundke, K. Voit, B., Self Functionalization of Silicone Rubber for Permanent Adhesion Improvement. Langmuir 2008,24, 12603-12611. 

The recently developed self-adhesive HTV silicone rubbers are addition curing, one component materials which remain processable for several weeks at room temperature. Self-adhesive liquid silicone rubbers are always delivered as two components. This is due to the fact that once components A and B are mixed the processing time is approximately 3-10 days at room temperature. 

At the moment self-adhesive LR cannot be used in medical device technology as no testing according to protocols like ISO 10993-1 [14] or USP Class VI [15] has been carried out. Medical devices should be using post-cured silicone rubbers only. One of the latest developments is a self-adhesive liquid silicone rubber which is compliant to BgW and FDA, as post cured. It adheres to PBT and PA only. 

Self-adhesive HTV silicone rubber is formulated in a similar way to self-adhesive LR. The ready-to-use formulation contains all adhesion promoters. However, other than LR, which is two component and addition curing only, self-adhesive HTV can be purchased both, as peroxide and addition curing. Because of fundamental differences in curing speed between self-adhesive peroxide cured HTV and addition cured HTV the applications differ quite substantially. 

Furthermore, HTV silicone rubbers exhibit better mechanical properties than LR. As a consequence applications might differ for the self-adhesive versions of these two family of products, apart from much better adhesion to steel in case of self-adhesive HCR. 

In this case self-adhesive HTV is used as a substitute to the primer. As it is chemically different from primers, which are not silicone rubbers, it is considered in this section. 

The sealing against water leakage between the panels and the supporting structure consists of a self-adhesive rubber strip and silicon-rubber caulking. 

Silicone rubbers are unique because of their low- and high-temperature stability (the temperature range for general applications is —55°C to 250°C), retention of elasticity at low temperature, and excellent electrical properties. They are extremely inert and have found several biomedical applications. Nontacky self-adhesive rubbers are made as follows. One first obtains an OH group at chain ends through hydrolysis, for which even the moisture in the atmosphere may be sufficient ... 

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