Silicone, Acrylic, or Rubber PSA?

Pressure sensitive adhesives are characterized by instantaneous adhesion on application of only light pressure. Pressure sensitive adhesives are available as coatable liquids (generally water emulsions or solvent solutions) as free unsupported films called transfer tapes, and as pre-applied coatings on various substrates. This latter category includes tapes, labels, protective films, and the like.

The more obvious examples of pressure sensitive adhesives are tape (duct tape, office tape, etc.) laminating resins, medical bandages, and double backed tape for mounting bumper strips, etc. The pressure sensitive adhesive (PSA) sector is among the fastest growing in the adhesives market.

A fair number of polymers show pressure sensitive characteristics. They are usually based on elastomers or thermoplastic resins. By far, the largest PSA polymer families are INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (1) acrylic, INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (2) silicone, and INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (3) synthetic elastomers headed by styrene block copolymers. Within each family there are thousands of possible variations of the base polymer, available adhesive forms, and formulation components that are available. Given this and the greater variety of applications that are possible, the selection of the correct PSA can be a daunting experience.

This article is designed to assist the end-user in choosing the correct PSA for the application. The three main polymer families will be considered. Various factors relating to the PSA base polymer and requirements of the application will be considered. PSA application and performance parameters associated with each of these families will be discussed.

Generic PSA Characteristics and Requirements

Pressure sensitive adhesives are unlike other adhesives in that they are permanently tacky. When in the dry state, they are aggressive and bond instantaneously at room temperature and will adhere to a variety of dissimilar materials with only the need for slight pressure. Often the pressure is applied by hand, but it can also be applied by rollers, presses, or other mechanical devices.

In addition to being tacky, pressure sensitive adhesive compositions are also inherently soft materials. Thus, a balance of adhesive properties (tack and peel strength) and cohesive strength (shear and tensile strength) must be made depending on the specific application. This balance will depend on the viscoelastic nature of the adhesive as well as the additives used in the adhesive formulation.

The primary mode of bonding for a pressure sensitive adhesive is not chemical or mechanical but rather a polar attraction to the substrate, and this always requires that the adhesive make intimate contact with the substrate and achieve sufficient wet-out to provide adequate adhesion. The adhesion or tack must be sufficient to adhere with no more than finger pressure and provide an instantaneous bond that is suitable for the application. The cohesion or internal strength of the adhesive film must be sufficiently high to resist the creep and shear stresses in the application. If the PSA is applied as an unsupported film, the cohesive strength of the film must be great enough to allow application without tearing or separation. Cohesive strength is also important if the PSA is to allow separation of the substrate and possible rebonding (as in the case of some food packaging, POST-IT Notes, etc.).

Importance of the Base Polymer in PSAs

Pressure sensitive adhesives normally are composed of a rubber based elastomer or acrylic combined with a liquid or solid resin tackifier components and a series of additives, such as plasticizers, fillers, and antioxidants, designed