The ability to crystallize differentiates Neoprene from other elastomer-based adhesives. The value of crystallization is the cohesive strength of the adhesive film formed from Neoprene, which is considerable greater than it would be if formed from an amorphous polymer. The “quick grab” for which Neoprene-based adhesives are noted is the result of this crystallization. Rapid development of bond strength is of immeasurable benefit to the end user who can use accelerated assembly techniques without the need for jigging, clamping, etc.
Not all types of Neoprene crystallize at the same rate; Denka™ Neoprene AD crystallizes very rapidly, while other grades, such as Denka™ Neoprene WHV, crystallize more slowly. Neoprene WRT is highly resistant to crystallization, which enables the adhesive compounder to obtain the desired crystallization rate by blending different types of Neoprene.
Some of the many end uses for Neoprene adhesives are listed in the table. Liquid dispersion adhesives are included for completeness.
|Grades||Solution Viscosity||Crystallization||Features||Data Sheet|
|AD 20||35–53||Rapid||Fast crystallizing|
|AD 40||95-130||Rapid||Fast crystallizing- high viscosity|
Solution Viscosity: mPa-s 5% raw polymer in toluene, 25℃
Denka™ Neoprene AD
Neoprene AD is the most commonly used grade of Neoprene for adhesive applications. It crystallizes rapidly, and the speed and extent of it crystallization results in quick grab and high uncured adhesive strength. Neoprene AD can be exposed to temperatures as high as 70 oC for several weeks without an appreciable change in color or hardness.
Denka™ Neoprene WHV
In contrast to Neoprene AD, Neoprene WHV is a relatively slow crystallizing type. The polymer is useful in blends with Neoprene AD to increase the solution viscosity of ordinary cements. When use as a minor component in such blends, Neoprene WHV will not have a significant effect on tack or bond development rate.
Other Neoprene Types
Denka™ Neoprene W is another relatively slow crystallizing type, with a low-to-intermediate viscosity. It may be used to extend the tack range of Neoprene AD with some decrease in cohesive strength and aggressive bond development. Neoprene WRT is essentially non-crystallizing and is used to formulate adhesives requiring improved extended tack range or a soft, flexible glue line.
Denka™ Neoprene GNA and GRT are less stable during storage than the Neoprene W types. They are more reactive with isocyanates and curatives and can be used in formulations that are intended for two-part adhesives or as curable compositions.
Denka™ Neoprene WB provides high gel content without adversely affecting the rheology of the adhesive. It provides good hot bond strength and is particularly suitable in applications where hot creep resistance is desirable. However, it has essentially no tack, so Neoprene WB must be blended with other Neoprene types in contact adhesives.