Pressure sensitive adhesive bonding

This group includes heat-sealing adhesives and high-frequency (HF) sensitive heat-seal coats these are coating adhesives that are heat-activated during bonding. Contact adhesives and pressure-sensitive adhesives bond by the same principle but without the action of heat. 

Adhesives. Acryhc emulsion and solution polymers form the basis of a variety of adhesive types. The principal use is in pressure-sensitive adhesives, where a film of a very low T (<—20 " C) acrylic polymer or copolymer is used on the adherent side of tapes, decals, and labels. Acrylics provide a good balance of tack and bond strength with exceptional color stabiUty and resistance to aging (201,202). AcryUcs also find use in numerous types of constmction adhesive formulations and as film-to-film laminating adhesives (qv). 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

Silicones are probably best known for their application as sealants and as release materials for pressure sensitive adhesives [107]. The silicone polymer combines an inorganic backbone made from silicon-oxygen bonds with organic substitution on the silicon atom. This repeating unit, shown below is called a siloxane. 

NR adhesives can be divided in two types wet bonding and dry bonding. Wet bonding adhesives are applied on substrates in a fluid state, the bond being formed by drying. The dry bonding NR adhesives are pressure-sensitive adhesives because the bond is created under pressure. 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

A method of evaluating the adhesive bond to a plastic coating substrate is a tape test. Pressure-sensitive adhesive tape is applied to an area of the adhesive coating, which is... 

Pressure-sensitive adhesives Pressure-sensitive adhesions are actually viscous polymer melts at room temperature. The polymers must be applied at temperatures above their Tg to permit rapid flow. The adhesive is made to flow by application of pressure. When the pressure is removed, the viscosity of the polymer is sufficient to hold and adhere to the surface. Many tapes are of this type where the back is smooth and coated with a nonpolar coating so as not to bond with the sticky surface. The two adhering surfaces can be separated, but only with some difficulty. 

Way back in 1968 Dr. Silver was working for 3M on pressure-sensitive adhesives. These are glues that bond instantly to a surface but can be removed without destroying that surface. Today we are very familiar with such products peel-off stickers are everywhere. In 1968, however, they were virtually unknown. Scientists did realize that certain polymers, like natural rubber, could be peeled off under the right conditions, but they were not ideal. So Silver went to work. He investigated various synthetic polymers and eventually came up with one that was a weak adhesive and could be pulled off a surface. The difficulty was that it would not always pull off cleanly, and Silver lost interest. 

Film Adhesive. A further type which is of importance commercially is the film adhesive which exists usually as pre-formed shapes on suitable substrate materials (often, siliconized release paper). When being applied, such adhesives are activated by heat or pressure and so converted into a semi-fluid condition, when they can wet the surface to be bonded. The pressure-sensitive adhesives are an example of this type—the application of finger pressure alone being sufficient to form the bond. 

One of the most popular uses of radiant curing is the advancement (viscosity increase) or crosslinking of pressure-sensitive adhesives. These applications have been satisfied mostly with acrylate-based adhesive systems. With epoxy-based adhesives, the main applications are electrical and electronic components, the bonding of large aerospace structures such as composites, and the bonding of transparent substrates such as glass and plastic. 

Test Method for Impact Strength of Adhesive Bonds Test Method for Tensile Properties of Adhesive Bonds Test Methods for Pressure Sensitive Adhesive Coated Tapes Used for Electrical and Electronic Applications... 

Bonding techniques, involving adhesives, are also common. An in-depth study of PVC adhesion is available, together with the recommendation for a solvent borne pressure sensitive adhesive (229). A report is also available on solvent based pressure sensitive adhesives suitable for PVC surfaces (226). 

Adhesion and Bonding " "Adhesive Compositions," Vol. 1 (1985). "Pressure Sensitive Adhesives and Products," Vol. 3 (1988) in J. I. Kroschwitz, ed., Encyclopedia of Polymer Science and Engineering John Wiley Sons, Inc., New York. 

The primary mode of bonding for a pressure-sensitive adhesive is not chemical or mechanical but rather a polar attraction to the substrate. This always requires pressure to achieve sufficient wet-out onto the surface thereby providing adequate adhesion. The four main varieties of pressure-sensitive adhesives are derived from rubber-based, acrylic, modified acrylic and silicone formulations. Release liners are used to carry the sticky label and enable it to be printed. The release liners are normally paper, treated with a very thin silicone coating to allow the label to be peeled away easily without tearing. Some transfer of the silicone into the adhesive is inevitable. 

National legislation on adhesives includes German BfR Recommendation XXVIII (Components of adhesives) and US FDA Title 21 Part 175 on adhesives. Part 175.105 deals with adhesives overall and Part 175.125 deals with pressure-sensitive adhesives. In addition, FDA Part 177.1390 permits the use of certain high temperature laminates that may be safely used for food contact at temperatures up to 275 °F, given that only the specified adhesives are used to bond the layers that make up the laminate. Part 177.1395 permits certain laminates that may be safely used at temperatures between 120 °F and 250 °F. However, it does not specify permitted adhesives. 

If polymer A has a butadiene rubber block, it will not find application in pressure-sensitive adhesives. It is not readily tackified, it is not readily melt processable, and it will not close a box. However, if dissolved in solvent, compounded with filler and certain resins, it will make the world s best construction mastic, very capable of bonding drywall to wood, etc. If one wants to maximize the solids content in this mastic (use less solvent), and if one wants to design the SBS molecule to be soluble in more environmentally friendly solvents, then in what direction should one head If not A , then where in the region does one strike the balance for a highly extended but tough mastic that allows the solvents of choice while achieving maximum solids and a viscosity low enough to squeeze from a tube ... 

Furthermore, polymer layers applied to the respective substrates are known that show their own adhesiveness due to the addition of tackifying components (e.g., resins). With the application of adequate surface pressure, these systems known as pressure-sensitive adhesives (Section 5.6) result in a bonded joint. 

The peeling off of a hook fitted with a pressure sensitive adhesive and attached to a ceramic or glass surface can be regarded as a typical example for the creep behavior of an adhesive layer. In particular, thermoplastic adhesives that, to a great extent, also include pressure-sensitive adhesives (Section 5.6) tend to creep under high strain. A reason for this behavior is the time-related failure of individual bonds between the polymer molecules due to the strain imposed from outside. The application of adhesives with a higher crosslink ratio can reduce the adhesive layers tendency to creep. 

Pressure-sensitive adhesives are the essential components of adhesive tapes and labels. They are polymers with permanent tack, usually applied on substrates (plastic/metal films, siliconized papers). To enhance their tack, compounds with high inherent tack are added, for example, resins, plasticizers. Pressure-sensitive adhesives reach their adhesion on the material to be bonded by contact pressure, from which the term pressure-sensitive adhesive (PSA) derives. Apart from electron radiation, also UV-radiation curing described in Section 4.3.2 is applied in adhesive tape manufacturing. The monomer molecules to be polymerized are applied, in liquid form, to the substrates to be coated by rolling and are continuously cured to a polymer layer within seconds under a UV-radiation source. Depending on their composition, predetermined adhesion values can be adjusted. The adhesive tapes can be subsumed under the systems shown in Figure 5.4 ... 

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