2 The Technology of CCP
2.1 How CCP Works
A three-part business form (Figure 2–1) illustrates the concept of how CCP works. The first sheet in this three-part example is a coated-back (CB) sheet, the second is a coated-front and -back (CFB) sheet, and the third is a coated-front (CF) sheet. The bottom surfaces of the top and the second sheet are coated with a layer of microcapsules that have a diameter of 3 to 6 μm. The coating includes inert spacer particles ("stilts," such as floc, uncooked arrowroot, and/or wheat starch particles) that are larger than the microcapsules and are added to protect the microcapsules from premature rupture. The microcapsules (filled with a colorless solution of 2% to 6% dye dissolved in a high-boiling-point-organic solvent) rupture under pressures encountered in normal handwriting or impact printing. For example, in a three-part form, the released dye solution is transferred from the bottom surfaces of the first and second sheets to the top surfaces of the second and third sheets, respectively, where it reacts with the clay or resin coating to form an image. The capsules and reactive coating can be coated onto the same paper surface. In this case, the product is called self-contained CCP.
2.2 CCP Production
The principles of the CCP production process are similar throughout the industry, but many components are variable and complex. During CCP production, an acid-sensitive dye precursor such as crystal violet lactone (CVL) or N-benzoylleucomethylene blue (N-BLMB) is microencapsulated with a high-boiling-point solvent or oil within a cross-linked gelatin or in synthetic mononuclear microcapsules, including polyamides, polyesters, or polyurethanes. From the origination of NCR paper until 1970, the main solvent for the dyes was poly-chlorinated biphenyls (PCBs [Arochlor]). Examples of solvents that have replaced PCBs are hydrogenated terphenyls, diarylethanes, alkyl-naphthalenes, cyclohexane, and dibutyl-phthalate (more detailed information about solvent composition, technical requirements, and admixtures is given later in this section). These materials are often diluted with odorless kerosene [Calnan 1979].
CCP production consumes thousands of tons of microcapsules annually. During CCP manufacturing, microcapsules are coated onto the back of the top sheet (referred to as a CB sheet) at a density of several million per cm2 with a binder or suitable adhesive [Certin and Zissu 1983]. Since paper is the usual support, the binders or adhesives are principally paper-coating agents such as the following [Murray 1991; Mathiaparanam 1992]:
- Gum arabic
- Hydroxymethyl cellulose
- Casein
- Methyl cellulose
- Dextrin
- Starch or starch derivatives (wheat or corn) or polymer lattices (e.g., butadiene/styrene copolymers or acrylic homopolymers or copolymers)
