RELEASE LINER

Many of the unique properties of siUcone oils are associated with the surface effects of dimethylsiloxanes, eg, imparting water repeUency to fabrics, antifoaming agents, release liners for adhesive labels, and a variety of poHshes and waxes (343). Dimethylsilicone oils can spread onto many soHd and Hquid surfaces to form films of molecular dimensions (344,345). This phenomenon is greatly affected by even small changes in the chemical stmcture of siloxane in the siloxane polymer. Increasing the size of the alkyl substituent from methyl to ethyl dramatically reduces the film-forming abiUty of the polymer (346). The phenyl-substituted siUcones are spread onto water or soHd surfaces more slowly than PDMS (347). 

Habitrol (102), co-developed by Lohmarin Therapie Systeme and Ciba-Geigy Ltd., and marketed by Ciba-Geigy, consists of an impermeable backiag laminate with a layer of adhesive and a nonwoven pad to which a nicotine solution is appHed (103). Multiple layers of adhesive on a release liner are then laminated on the patch. The systems come ia 10, 20, and 30 cm sizes corresponding to 7, 14, and 21 mg/day, respectively, deUvered over 24 hours. 

One of the important breakthroughs in the silicone PSA industry has been the development of new release liners based on fluorosilicones [116]. These new materials significantly improve the release characteristics of the silicone PSAs, something that has been difficult to achieve because of the high adhesion silicone PSAs show to low energy substrates, including silicone rubbers and liners. 

Pressure sensitive adhesives can be coated on a substrate such as a polyester or paper backing to make a tape or label, or on a release liner to make a transfer adhesive, or a special substrate to make a graphic film or retro-reflective sheeting product. In some cases, where precision placement of the PSA is required, one may also coat directly on the substrate using techniques such as screen-printing. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

Release coatings are important components of pressure sensitive adhesive (PSA) products such as tapes and labels [1]. Release materials are coated onto the backside of PSA tape backings (often called low adhesion backsizes or LABs in this form) to provide the desired tape roll unwind force. They are also coated onto various substrates to form release liners for PSA products such as labels and transfer tapes. Typically the thickness of the release coating is less than 1 p,m, and often times less than 0.1 jLm. Release coatings can be thought of as the PSA delivery system, providing a controlled unwind or release force and protecting the adhesive from contamination and unintentional contact until it is applied. 

Thermoplastic urethane adhesives may be processed into an adhesive film. I,amination of two substrates can, in theory, be done immediately, but the film is often extruded onto one substrate, covered by a release liner, and allowed to cool. Crystallization follows to create a non-tacky film that may be cut into specific shapes. The release liner is then removed, and the shaped adhesive can be heat-activated on one substrate, using infrared lamps. The second substrate is then nipped under pressure, followed by a cooling press to speed crystallization. Once the backbone has crystallized, the bond should be strong. 

Silicone release liners are used as a nonadhering surface to which adhesive materials, such as, for example, pressure-sensitive adhesives, can be laminated. UV curable release coatings are based on poly(dimethylsiloxane) oligomers functionalized with acrylate or epoxy groups and are mostly coated onto papers or thin films. 

A hydrophilic polyurethane prepolymer was made according to the procedure taught by Braatz. - The prepolymer was mixed with water at a ratio of 10 parts water to one part prepolymer. The emulsion was poured immediately onto a silicone release liner and allowed to cure for 30 min. It was free of voids and had a density roughly the same as water. For the contraction experiments, the gel was immersed in excess distilled and sterile water for 24 h, tlicii cut with a steel-ruled die into circles 40 mm in diameter. 

As seen in Figures 6 and 7, the final system has a tab that aides in commercial system application. This tab is formed from the release liner by the relamination step, which consists of placing a roll of laminate onto the slitter-relaminating equipment. This roll is then guided through rollers where the release liner is removed and slit (sliced) to the correct width. The slitted material is then placed... 

Tape and film are the most common forms of solid epoxy adhesives. Tape and film are terms that are used rather loosely for adhesives in a thin sheet form. The term tape generally refers to an adhesive that is supported on a web of paper or nonwoven fabric, or on an open-weave scrim of glass, cotton, or nylon. Films, on the other hand, are free of supporting material and consist only of the adhesive. Both tape and film products may be accompanied with a release liner depending on the tack or blocking characteristics of the adhesive. 

The final thickness of epoxy tape or film adhesives is on the order of 5 to 15 mils. These adhesives may be soft and tacky, or stiff and dry, depending on their formulation. The soft and tacky products are valuable in products requiring application to contoured or vertical surfaces. If the product is especially tacky, a release liner (e.g., polyethylene film, coated paper) is generally used to keep the film from blocking. The stiff and dry products are generally used for flat surfaces where speed and ease of application are required. 

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