Surface Preparation for 3M™ VHB™ Tape Applications

Most substrates are best prepared by cleaning with a 50:50 mixture of isopropyl alcohol (IPA) and water* prior to applying 3M™ VHB™ Tapes. There are exceptions!

Exceptions to this general procedure that may require additional surface preparation include:
 

• Heavy Oils: A degreaser or solvent-based cleaner may be required to remove heavy oil or grease from a surface and should be followed by cleaning with IPA/water.
   
• Abrasion: Abrading a surface, followed by cleaning with IPA/water, can remove heavy dirt or oxidation and can increase surface area to improve adhesion.
   
• Adhesion Promoters: Priming a surface can significantly improve initial and ultimate adhesion to many materials such as plastics and paints.
   
• Porous Surfaces: Most porous and fibered materials such as wood, particleboard, concrete etc. need to be sealed to provide a unified surface.
   
• Unique Materials: Special surface preparation may be needed for glass and glass-like materials, copper and copper containing metals and plastics or rubber that contain components that migrate (e.g. plasticizers).

On surfaces with a light oily film, or other light contamination, the 50:50 IPA/water solution is usually adequate. Where heavy oils or grease are present, a "degreasing" solvent such as 3M™ Prep Solvent 70, 3M™ Citrus Base Cleaner, mineral spirits, naphtha or similar solvents are suggested to cut the oil. This should always be followed with an IPA/water cleaning to help ensure that any residue or film is completely removed.

Abrading a surface can serve several functions:
 

• Remove heavy levels of dirt or oxide from metals or paints (e.g. galvanized steel).
   
• Create additional surface area that can increase adhesion.
   
• Smooth a surface to obtain more flatness, allowing improved contact area.

Abrasion often helps adhesion to paints and plastics. When abrading, it is important for tapes to have a finely abraded surface. Very small scratches in the surface, generated with circular motion rather than straight-line motion, are most desirable. A surface with many micro-scratches in it can have up to 40% additional available surface area, translating to higher ultimate strength and greater initial adhesion. Scotch-Brite® Hand Pads (such as 7447 Maroon or Heavy Duty Green) are good for achieving the right level of abrasion. Tools such as a power palm sander will assist on large jobs. Avoid grinding a surface with coarse abrasive materials, since they may create too rough of a texture for the adhesive to adequately flow into the surface. Always clean the surface with the IPA/water solution or additional methods previously described, and be certain that all loose particles are removed prior to bonding. Exceptions to these abrading guidelines are 3M™ VHB™ Tapes 4932 and 4952, as they typically perform best on smooth glossy surfaces and abrasion may reduce the bond strength.

Priming a surface can significantly improve initial and ultimate adhesion to many materials such as plastics and paints because of their low surface energy or the additives they may contain. A primer creates a new surface for 3M™ VHB™ Tape to adhere to and can also create a layer that may impede the migration of additives that may be present in a material. It is important for the user to determine the suitability of the 3M™ VHB™ Tape, the adhesion promoter and the application process.

Rough, porous or fibered materials such as wood, particleboard, cement, etc., have an open surface and require sealing to provide a unified surface for tape bonding. Common sealing materials would include paint, varnish or other hard surface coatings. Fast drying 3M™ Rubber and Vinyl Spray 80 can also be used to unify the surface and improve the tape bond.

Glass, stone, ceramic or other siliceous materials are hydrophilic (water-loving) by nature. Normally, the hydrophilic nature makes pressure sensitive adhesive bond durability susceptible to change under high humidity or exposure to moisture. In basic terms, water vapor can undercut the tape bond and interfere with the normal adhesion forces. Silane coupling agents, added to the IPA/water cleaning solution, can help reduce the “water-loving” tendency of these surfaces and enhance the tape bond in high moisture environments.

Copper, brass, and bronze are prone to oxidation even after the 3M™ VHB™ Tape is applied. To prevent a weakening of the bond, a lacquer or varnish should be applied to these surfaces. Be sure to test the tape bond to the sealer on a metal surface to verify good adhesion.

Flexible PVC (vinyl) contains plasticizers that can migrate into the tape and affect adhesion. There are several 3M™ VHB™ Tapes that are formulated to be resistant to plasticizer migration, or 3M™ Scotch-Weld™ Plastic Adhesive 2262, thinned, can serve as a barrier to migration. Rubber materials (e.g. EPDM, neoprene) can have low surface energy and may also contain plasticizers and oils. These require the use of an adhesion promoter for stable bond strength. Test for compatibility with flexible PVC and rubber materials by aging bonded samples for a week at 150°F (66°C) and check for softening of the adhesive, discoloration or reduction in bond strength.

*Note: These cleaner solutions contain greater than 250 g/l of volatile organic compounds (VOC). Please consult your local Air Quality Regulations to be sure the cleaner is compliant. When using solvents, be sure to follow the manufacturer’s precautions and directions for use when handling such materials.

The table below offers suggested primers and alternative methods that commonly require primers, adhesion promoters or other surface treatments for successful use with 3M™ VHB™ Tapes. This list is not intended to be fully comprehensive but may be useful for many applications. It is very important for the user to determine the suitability of the 3M™ VHB™ Tape, primer and application process and compliance with local Air Quality Regulations.

• 3M™ Primer 94, 3M™ Adhesion Promoter 111 and 3M™ Silane Glass Treatment AP 115 are available through distributors that carry 3M™ VHB™ Tapes.
• 3M™ Scotch-Weld™ Plastic Adhesive 2262 must be thinned in acetone or MEK* in a 1:5 or 1:10 ratio (e.g., 1 part Scotch-Weld™ plastic adhesive 2262 to 5 parts acetone or MEK). The product is available premixed in either acetone or MEK from: PRC DeSoto at (317) 290-1600.
• 3M™ Scotch-Weld™ Plastic Adhesive 2262T, thinned in 10:1 MEK solution or 3M™ Scotch- Grip™ Plastic Adhesive 2262TA, thinned in 10:1 acetone solution.* When diluted in acetone at this ratio, this material contains 196 g/l VOC.*
• Diluted 3M™ Scotch-Weld™ Plastic Adhesive 1099 must be thinned in acetone* in a 1:3 ratio (e.g., 1 part Scotch-Weld™ plastic adhesive 1099 to 3 parts acetone). This thinned material contains zero VOC’s when diluted in these ratios.
• 3M™ Adhesion Promoter N-200J is available from PRC DeSoto at (317) 290-1600.
• Silane Coupling Agent is also available premixed in a 91:9 IPA/water solution or as a concentrate. A 0.5 wt. % level of silane* adhesion promoter diluted in a 91:9 IPA/water cleaning solution has been found to be sufficient.
  Suggested Sources for Silane Coupling Agents:
  Custom-Pak Products, Inc. (262) 251-6180 available premixed in IPA/water
  Lancaster Synthesis, Inc. (603) 889-3306 available 100% concentrated

*Note: Be sure to read and follow silane and solvent manufacturer’s precautions and directions for use for proper handling and storage information.