Pressure-sensitive backing

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Hydrocarbon resin is a broad term that is usually used to describe a low molecular weight thermoplastic polymer synthesized via the thermal or catalytic polymerization of coal-tar fractions, cracked petroleum distillates, terpenes, or pure olefinic monomers. These resins are used extensively as modifiers in the hot melt and pressure sensitive adhesive industries. They are also used in numerous other appHcations such as sealants, printing inks, paints, plastics, road marking, carpet backing, flooring, and oil field appHcations. They are rarely used alone. 

Carbonless Copy Paper. In carbonless copy paper, also referred to as pressure-sensitive record sheet, an acid-sensitive dye precursor, such as crystal violet lactone or /V-hen2oy11eucomethy1ene blue, is microencapsulated with a high boiling solvent or oil within a cross-linked gelatin (76,83,84) or in synthetic mononuclear microcapsules. Microcapsules that have a starch binder are coated onto the back of the top sheet. This is referred to as a coated-back (CB) sheet. The sheet intended to receive the image is treated on the front (coated-front (CF)) with an acid. When the top sheet is mechanically impacted, the dye capsules mpture and the dye solution is transferred to the receiving sheet where the acid developer activates the dye. 

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. 

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. 

Pressure-sensitive tapes Unlike the more recently developed petrolatum tapes which rely on both the petroleum and backing films, the pressure-sensitive tapes offer protection which depends almost entirely upon the prevention of ingress of moisture to the metal surface by the tape itself. 

In addition to the petrolatum tapes and those based on a laminate of p.e. or p.v.c. with an elastomeric sealant or pressure-sensitive adhesive layer, recent developments have centred around self-adhesive bituminous laminates. These tapes are commonly constructed with a p.v.c. backing, whose thickness ranges from 0 08 to 0 75 mm and a bituminous adhesive compound layer to provide a total tape thickness of up to 2 mm. In order to maintain conformability without compromising impact values, tapes may also be manufactured with a fabric reinforcement within the bituminous layer. 

Pressure-sensitive recording materials are obtained by dissolving a triphenylmethane leuco dye in a solvent composed of paraffin oils. The microcapsules are formed from a water-soluble106 or water-dispersible material.107,108 Leuco dyes dissolved in sunflower oil are microencapsulated in a solution containing a melamine-HCHO precondensate and coated on the back side of a paper sheet. Contact of the microcapsule-coated sheet with an acid-coated receptor sheet allows the color formation to occur. 

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. 

Fig. 5.6 shows the heat flux produced in zone II and the heat flux transferred back from zone III to zone II as a function of pressure, n is approximately equal to Am, both of which increase with increasing pressure according to Am p0.7s nd n p0.65 ii is evident from Eq. (5.2) that the pressure sensitivity of n is approximately equal to that of the burning rate. The pressure sensitivity of the HMX burning rate ( p0.66j ig ther gas-phase reaction.P7]... 

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. 

Self-Adhesive or Pressure-Sensitive Labels. It is preferable to call these pressure-sensitive labels, as both the pregummed and heat-sensitive labels are self-adhesive (i.e., the adhesive is already there). They consist of a suitable label facing material (usually paper or polymer), the reverse side of which is coated with a permanently tacky adhesive that is in contact with a backing paper (occasionally plastic) that protects it prior to use. The backing paper is coated with a special release coating that permits the label to be removed easily. Labels may be provided on roll or sheet form both can have the label laid on that is, the unprinted area has been cut and removed. 

D 2686 Specification for Polytetrafluoroethylene Backed Pressure Sensitive Electrical... 

Pressure-sensitive adhesives are used for labelling applications. They are permanently tacky and adhere to the surface of the desired substrate under pressure. A paper or plastic film label is coated with a pressure-sensitive adhesive and applied to a backing layer - usually siliconised paper from which the label can be removed easily. The labels are then printed and sent... 

A variety of standard and specialized applicators exist for pressure-sensitive labeling. Standard portable head applicators provide top, side, and bottom labeling. These applicators use one of several basic methods available for application of automatic pressure-sensitive labels. In a tamp-blow method of application, the label is dispensed from the backing web and held in position by vacuum on a tamp pad. The tamp pad is indexed 0.8-1.5 cm away from the product, and then the label is applied to the product by a gentle blast of air. Tamp-blow applications are used for a large array of packages that have irregular, curved, or recessed surfaces. 

Batteries are typically produced with deep drawn metal cans on which a pressure sensitive adhesive label is applied for product identification, branding and safety information. Customers began complaining of batteries becoming jammed in various types of equipment. Devices returned to the manufacturer showed that the pressure sensitive labels had peeled back, resulting in adhesion between the overturned label and the device. Further examination of batteries on store shelves for more than a year also indicated peeling labels in a low frequency of batteries. These labels consisted of laminates of paper and polyester. The labels are normally flat and stiff and when applied over a battery, the labels will return to the flat condition if the adhesive fails. This results in peel-back at the edges of the label. 

The backing material and release liner can be fabricated from a variety of materials including polyvinylchloride, polyethylene, polypropylene, ethylene-vinyl acetate and aluminium foil. The most important property of these materials is that they are impervious to both drug and formulation excipients. The most useful backing materials conform with the skin and provide a balanced resistance to transepidermal water loss, which will allow some hydration of the stratum corneum, yet maintain a healthy subpatch environment. The release liners are usually films or coated papers and must separate easily from the adhesive layer without lifting off any of the pressure-sensitive adhesive. Silicone release coatings are used with acrylate and rubber-based adhesive systems, and fluorocarbon coatings with silicone adhesives. 

Pressure sensitive or self-adhesive—applied by the application of pressure. Paper is pre-coated with a permanently tacky adhesive which is attached to a separate backing paper (which has an easy release coating on it). 

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