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 Vinyl acetate and water soluble polymers such as carboxymethyl cellulose Polyvinylacetate Gelatin Polyacrylates Polystyrene Polyvinyl alcohol 

The paper employed comprises not only normal paper made from cellulose ﬁbers, but also paper in which cellulose fibers are replaced (partially or completely) by synthetic polymers [Bedekovic and Fletcher 1986]. (Please refer to Section 2.8 for a listing of brand names and trademarks of CCP.)

The sheet intended to receive the image, the CF sheet, is treated on the front with a clay or resin that is alkaline on the surface but acidic inside, or with an alternative reactive coating [Calnan 1979]. In Europe, the color developer system is typically based on clays, whereas phenolic resins are most commonly used in the United States and Japan [Murray 1991]. The coating is spread in a mixture, dried, and adhered with a styrene-butadiene-latex or one of the binders listed above. When the top sheet is mechanically impacted, the dye capsules rupture and the dye solution is transferred to the receiving sheet, where the acid developer activates the dye as a result of a change in pH or oxidation.

Three processes can be used to microencapsulize the dyes for the size requirements of CCP: complex coacervation, interfacial polymerization, or in situ polymerization [Kroschwitz and Howe-Grant 1979, 1995; Sliwka 1975]. The complex coacervation process produces a shell material of gelatin and gum arabic (treated with glutaraldehyde); the chemical class is a protein-polysaccharide complex. Interfacial polymerization produces a shell of polyurea or polyamide and is chemically classed as a cross-linked polymer. The in situ process results in a shell material of aminoplasts and is also considered to be in the cross-linked polymer chemical class. Microcapsules have a wide range of geometries and structures. These range from a continuous core shell that surrounds the core material to a multinuclear capsule in which a number of cells of core material are distributed uniformly throughout the matrix of shell material and a continuous core capsule with two different shells. Examples of other synthetic resins used for the microencapsulation process are

Figure 2-1. Three-part carbonless copy paper system.