Structural Adhesive Film

AF 31

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3. Cure Cycle

A. General Cure Requirements

The cure requirements for 3M™ Scotch-Weld™ Structural Adhesive Film AF 31

are a function of Scotch-Weld AF 31 film adhesive properties, specific application,

equipment available, production limitations and bond properties required. General

cure properties of Scotch-Weld AF 31 film adhesive are as follows:

Tack, Flow, Cure Initiation Temperatures

The tack, flow and cure initiation temperatures for Scotch-Weld film adhesive

AF 31 are a time-temperature relationship and depend upon the rate of heat input.

Normally, Scotch-Weld AF 31 film adhesive will have the following properties:

Tack Temperature:

160°F-180°F (71°C-82°C)

Flow Temperature:

180°F-220°F (82°C-103°C)

Cure Initiation Temp.:

220°F-270°F (104°C-132°C)

B. Cure Pressure

Pressure is required during cure to form the part being bonded and contain any

volatiles given off by the adhesive. Cure pressure may be applied in any manner

which will insure uniform constant pressure throughout the bond area. Pressure

must be uniformly applied before the curing reaction begins and maintained until a

complete cure has been effected. The pressure required to contain volatiles is

dependent on the rate at which bond line temperature is brought to the cure

temperature. The bond line temperature rise rate for Scotch-Weld AF 31 film

adhesive can be varied from 1°F to 300°F/minute. Rise rate (and cure pressure

required) will depend on specific application, cure temperature, bonding equipment,

method of heat application, production limitations and bond properties required.

Figure I, Page 5, depicts typical pressures required for various bond-line temperature

rise rates in platen presses.

C. Cure Temperature

The cure temperature may be varied from 250°F (121°C) to 450°F (232°C),

depending upon the materials bonded, equipment available and bond properties

desired. The desired pressure must be applied before the glue line reaches 160°F

(71°C). The film will soften as temperature is increased to 180-210°F (82-99°C) and

will wet the surface to which it has been applied. A chemical cure will be initiated

between 220-270°F (104-132°C) and a low strength gel formed. Continued heating

chemically converts the adhesive into a high strength, solvent-resistant bond.

Scotch-Weld AF 31 film adhesive will change color only slightly upon application

of heat. Edges of the bond that are exposed to air will change from yellow to rusty

brown.

D. Cure Time

Cure time depends on the cure temperature used, methods of heat application,

production limitations and bond properties required. Since no two bonding

operations are exactly alike, it is suggested that a few simple experiments be

conducted, varying both temperature and cure time to determine optimum

conditions for the particular application. Figure 2, Page 14, is a guide from which an

approximate cure cycle can be taken for various cure times or temperatures.

Product Application

(continued)