Page 300 - Handbook of Adhesives and Sealants

Primers and Adhesion Promoters 265

meric resin is forced into the mold, and it contacts and wets the sur-
face of the hub. As the elastomer cures in the mold, a strong adhesive
bond forms between the metal and elastomer by virtue of the primer.
Primers are applied as intermediate layers between the insert ad-
herend and elastomeric resin under conditions where the adherend
and resin are incompatible or where a chemical reaction is required
for strong adhesion. The primer is able, by its chemical formulation,
to react with both adherend surface and the elastomer. A very strong
bond is formed between the curing elastomer compound and the pri-
mer system during cure of the rubber. In these cases, the primer may
be considered an adhesive. Although, more accurately, it is a surface
primer, and the unvulcanized rubber provides the adhesion. The pri-
mer provides a protected surface that is easy to wet; but more impor-
tantly, it provides a reactive surface that is chemically compatible with
the elastomer.
Often solutions of unvulcanized rubber in polymeric resin are used
for the primer. For example, a typical primer formulation may include
chlorinated rubber, phenolic resin, and solvent. However, several wa-
ter borne elastomer bonding agents have been developed and are com-
mercially available. The resin component provides cohesive strength
and enhances adhesion to the metal. The rubber component provides
toughness to the system and assists in reducing residual bond-line
stress. Proprietary primers for elastomer-to-insert bonding include
Chemlok, Ty Ply, Thixon, and Cilbond brand names. Table 7.4 gives
details of several proprietary products.
The most common elastomers to be bonded in this way include ni-
trile, neoprene, urethane, natural rubber, SBR, and butyl rubber. Less

TABLE 7.4 Proprietary Primers for Bonding Unvulcanized Elastomers to Metal
Inserts 20
Product Manufacturer Suitable to bond Type product
Chemlok 205 Hughson Chemicals NBR Metal primer
Ty Ply UP CR
Ty Ply T NBR, ACM, OT
Thixon P5 Dayton Coatings and NBR, CR, CO Metal primer
Thixon P6 Chemicals NBR
Thixon P7 NBR
Thixon P9 NBR, CR
Cilbond 10 Compounding Ingredients NBR Metal primer
Limited (UK)
Cilbond 17 NBR ACM
NBR-Nitrile rubber
CR-Neoprene
ACM-Polyacrylate rubber
OT-Polysulfide rubber
CO-Epichlorohydrin rubber