Лако-красочные материалы — производство

1. Chemical Cure

Chemical bonding techniques for all acrylic adhesives are similar. First, the activator is applied to one of the surfaces to be joined as a thin film. While the permissible ‘‘ratio’’ of activator to adhesive is quite wide (10:1 to 50:1), too much activator will lower bond strengths. Activators are available in solvents to help assure thin film applications. Second, the adhesive is applied to the mating surface, and the two surfaces are brought together and held until handling strength is reached.

Application of activator to both substrates is recommended where one substrate is porous or where gaps of more than 20 mils are to be filled. Activator and adhesive may be applied to the same surface, but this initiates the bonding action so that the parts must be joined immediately.

Advantages of Activator Curing Aerobic Acrylics

Simple no-mix application Multiple curing methods available

Broad applicability to a wide variety of substrates (metal, plastic, glass, ceramics) with minimal surface preparation

Tolerance for oil-contaminated surfaces Rapid bonding at room temperature Excellent bond flexibility

High peel strength, lap shear strength, and impact resistance

Excellent solvent resistance

Wide latitude in cure rate

Ability to bond heat-sensitive substrates

Low shrinkage during polymerization

Excellent reproducibility and reliability

Good low — and high-temperature properties

Wide formulating flexibility for specific end-use requirements

2. Heat Cure

Many aerobic formulations can be heat cured, but only between two surfaces. Table 1 shows the heat curing properties in an adhesive used to fix surface mount devices onto printed circuit boards compared to a typical epoxy and a typical anaerobic formulation used for the same purpose.

3. Curing by Ultraviolet Light

Aerobic adhesives are easily converted to UV curing formulations. This is not sur­prising as (meth) acrylics are commonly used as the base resin in UV inks and coatings. However, UV products usually have rather poor adhesion to hard, tough surfaces such as metal.

Many UV curing aerobic adhesives show the unique property of having structural properties regardless of the cure mechanism used, as shown below. A more detailed dis­cussion of UV curing aerobic acrylics can be found in Sec. IV.

Figure 1 shows that complete cure using a preapplied activator requires 24-48 hr. UV cure, however, is complete—reaching the same strength level in only seconds.