Reinforcing (Two-Step) Resins
Reinforcing or two-step resins are significant in rubber, adding useful properties to a
compound. The properties that reinforcing resins impart are: increased hardness,
lower compound viscosity, higher tensile, shorter elongation, chemical resistance
and higher abrasion resistance. These resins also act as a process aid for stiff, highly
loaded compounds.
Reinforcing resins are generally oil modified with either tall oil or cashew nut oil.
The main purpose of the modifying oil is to make the resin more compatible with the
polymer, but it also makes the resin more flexible after it is cured and acts as a process
aid as well. These resins are cured with hexamethylenetetramine and are available with
or without the hexa already added. Akrochem’s reinforcing (two-step) resins for this
application and others like it are as follows:
WITH HEXA
SP-6600 (P-87)
SP-6600 is a cashew nut oil modified phenol-formaldehyde two-step resin. It exhibits
compatibility in all proportions with NBR. During processing, the resin plasticizes the
stock, making filler loading and milling easier. In the cured state, increases in the resin
content will decrease elongation but will increase tensile strength, flexural strength,
hardness, abrasion resistance and rigidity. SP-6600 has limited compatibility with SBR
and CR. However, within these compatibility limits, it is used to reinforce these rubbers.
SP-6601 (P-55)
SP-6601 is a tall oil modified phenol-formaldehyde two-step resin with hexa. It was
primarily designed for use in SBR compounds. As a rule, phenolic resins have little or no
compatibility with SBR. SP-6601 resin, however, is an exception in that as much as 50 phr
of the resin (by weight) on 100 phr (by weight) of SBR can be used before compatibility
problems are encountered. If compatibility with SBR becomes an issue, try adding NBR
which will serve as a common solvent or flux to help overcome potential issues. This resin
serves as an effective plasticizer during processing and facilitates pigment dispersion.
Increasing the amounts of SP-6601 resin will increase the hardness and abrasion
resistance of SBR vulcanizates.
SP-8855 (P-40) [Product of ASK Chemicals]
SP-8855 is an unmodified phenol-formaldehyde two-step resin containing hexa.
SP-8855 is used as a hardening and reinforcing agent for NBR, NBR-SBR blends,
CSPE and Polybutadiene polymers. It has medium flow, cure and setting properties.