Solvents & Cross-Linking Agents
Adirondack Specialty Adhesives produces a complete line of tapes and adhesives for splicing coated abrasive belts. We manufacture and distribute a family of urethane adhesives that are used with cross-linking agents to achieve optimum properties and end results. These cross-linking agents are either solvent based or 100% reactive liquid isocyanates containing prepolymers or adducts which react with the hydroxy functionality in the adhesive. In either case, the reaction product is a polyurethane polymer. In addition, isocyanate terminated materials react with moisture to form urea linkages.

We distribute a variety of cross-linking agents which have been specifically designed for use with urethane adhesives. Adirondack urethane adhesives are manufactured from toluene diisocyanate (TDI) based linear polyester polyurethane and develop thermoset characteristics when used in conjunction with these isocyanate cross-linking agents. The amount and type of cross-linking agent to be used with any given adhesive will vary based on the specific desired properties of the cured adhesive.

Cross-linking agents will upgrade the performance properties of the adhesive and are essential to urethane adhesives. These coreactants offer special properties such as non-darkening joint color, differing cure rates, increased tensile strength, bond strength and softening point, improved moisture/grinding aid/solvent resistance, and decreased elongation. The pot life of mixed adhesive will vary depending on the amount and type of cross-linking agent used and the ambient relative humidity.

The urethane adhesives react with the isocyanate terminated prepolymer at normal room temperatures of 77°F. In most cases, the “green strength” of the adhesive will allow for subsequent slitting and handling almost immediately after pressing with heat (refer to specific product data sheets for additional information). Full (80-90%) cure is obtained after 48 to 72 hours and is sufficient for many end use applications. The cure rate is significantly inhibited if the storage and shipping temperatures of the finished belt are below 70°F.

Isocyanate cross-linking agents are moisture sensitive; therefore, adequate precautions must be taken to avoid moisture contamination of these prepolymers. Sources of moisture can be grains of water (humidity) in the air, condensation on surfaces below the dew point, water content of solvents, etc. Only urethane grade solvents should be used to dilute the adhesive and coreactant. Do not pre-dilute these products.

Avoid contamination of the isocyanate cross-linking agents with alcohols, monoglycols, monoamines, and other chemicals containing active hydrogens. The products can react preferentially with these active chemicals instead of the second component of the system, leaving the adhesive partly or fully uncured.

The solvents used in the adhesives and cross-linking agents have varying levels of toxicity and are readily absorbed through the skin. Care should be taken to prevent skin contact and to prevent operator exposure to vapor concentrations that exceed established OSHA Time Weighted and Average exposure limits.

The isocyanate coreactants are prepolymers made from isocyanate monomers. They typically contain residual amounts of free monomer which may be hazardous. Good ventilation and handling procedures must be maintained in mixing rooms and other work areas to ensure that the OSHA Permissible Exposure Limits for the isocyanate monomer are not exceeded.

Cross-Linking Agent Color % Solids Specific Gravity Solvent % NCO Viscosity (CPS)
Desmodur RE Yellowish-Green 27 1.0 Ethyl Acetate 9.3 3
Desmodur RFE Yellowish-Green 27 1.0 Ethyl Acetate 7.2 3
L-75 Pale Yellow 75 1.2 Ethyl Acetate 13.0 2000
VK-18 Dark Brown 100 1.2 None 31.5 180
Adhesive Color % Solids Specific Gravity Solvent Viscosity (CPS)
Bostik 7070 Amber 20 0.93 Ethyl Acetate/Acetone 6000
ADK 75A Amber 21 0.93 Ethyl Acetate/Acetone 5000
ADK 7514A Amber 14 0.92 Ethyl Acetate/Acetone 500
ADK 77A Amber 21 0.86 MEK 3000