NIOSH Hazard Review: Carbonless Copy Paper/The Technology of CCP
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
- Methyl cellulose
- Starch or starch derivatives (wheat or corn) or polymer lattices (e.g., butadiene/styrene copolymers or acrylic homopolymers or copolymers)
- Vinyl acetate and water soluble polymers such as carboxymethyl cellulose
- 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.
2.3 Microcapsule Production
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
|CB (coated-back) sheet||
|CFB *coated-front and -back) sheet||
|←Color developing mobile|
|CF (coated-front) sheet||
|←Color developing module|
urea-forrnaldehyde, melamine-forrnaldehyde, polyamide, and polyurethane resins [Asano et al. 1983]. Maggio et al.  stated that urea-formaldehyde capsules are more resistant to pressure than those made of gelatin.
2.4 CCP Production Process
Apol and Thoburn  described the process of CCP manufacturing. The plant they investigated made paper from pulp and then applied the appropriate coatings to the paper to make CCP. The paper itself is usually produced in a continuous sheet from a pulp slurry to form a wet web of paper as it exits on a screen, such as in a Fourdrinier paper machine. Apol and Thoburn  describe a process in which the CF and CB coatings are applied to the wet web. The CF coating can also be applied as the paper exits from the paper machine. As the coating is applied, the paper passes through a dryer and is wound on a roll. The CB coating may be applied in a separate plant area to the paper as it passes through a series of dryers and is rewound on a roll.
The CF and CB coatings are prepared in the coater preparation area. The phenolic resins (1- to 10-μm or 1- to 3-μm size range is preferred [Mathiaparanam 1992]) may be prepared by grinding the resins to specific-size particles, or they may be purchased already prepared. The already prepared resin reduces exposure to phenol among workers who handle the coating preparation and is the preferred option for today's technology.
A typical coating composition for the CF component is shown in Table 2–1. The CF is dried in a high-velocity air oven at 93 °C [Kroschwitz and Howe-Grant 1995]. Miller and Phillips  stated that suitable amounts of the various materials per unit of paper are as follows: chromogenic dyes, 0.03 to 0.075 lb/ream (one ream is 500 sheets of 25- × 38-in. paper totaling 3,300 ft2), with the preferred amount being 0.05 lb/ream; solvent, 1 to 3 lb/ream; polymer, 0.5 to 3 lb/ream.
CF, CB, and CFB coated papers are produced in large rolls weighing up to several tons. These are subsequently cut down by machines to a variety of smaller reel and sheet sizes. This cutting means that the contents of the microcapsules will be ruptured and released. Although many of the sheeting, reeling, and packing operations are automated, some of the paper still needs to be hand-sorted. The workers who hand sort these papers are potentially exposed to the components, particularly the contents of the ruptured capsules that have been cut in previous mechanical operations. Some of these workers sort paper at the rate of 90 kg/hr (or more than 2 tons/week [600,000 sheets]) [AEMCP 1985].
|Table 2–1. CF coating slurry formulation|
|Novolak resin dispersion||12|
CCP is converted into forms for a variety of applications—for example, business forms, invoices, computer paper, and Telex rolls. This process is normally performed by printers with appropriate forms design using conventional printing inks as well as specialized desensitizing inks. The latter are applied to the CF surface to prevent the color former from developing into an image on certain areas of the paper [AEMCP 1985].
CCP may be collated into business form sets that are glued along one edge. The glues (called edge-padding, edge-tipping, or "fanapart" glues) are similar to those used for ordinary paper writing pads. Manifold forms using pressure-sensitive CCP are produced using conventional printing press techniques. For some applications, the production of the multipart form by photocopying or laser printer operations is preferred—especially in short-run for production, emergencies, and experimental or individualized forms. The manifold forms are bound with an adhesive containing gum resins such as abietic acid. More recently, Moore Business Forms, Inc., was granted a patent [McIntyre and Greig 1989] for the use of a repositionable adhesive pad on the CF (such as is found on money wrappers). Bodmer and Peters  and Bodmer and Miller [1985, 1986] noted that CF coating components can accumulate on the heated fuser roll of the copier or the laser printer, which becomes tacky and can lead to poor copy quality. A phenolic polymeric film material, diolefmic alkylated or alkenylated cyclic hydrocarbons (cyclic terpene derivatives such as limonene), and/or an oil-soluble metallic salt (primarily zinc) of a phenol-formaldehyde novolak resin can be used to overcome the fuser roll contamination problem, which may or may not result in slower print speeds.
2.6 Other Forms and Variations of CCP Technology
Forms sometimes combine CCP with carbon paper to become a "two-write" system [Mead Corporation 1992]. The Branch Safety Council for Offices and Administrations  also reported on another type of CCP that is pressure sensitive and is called "mechanical" paper. The CB sheet is coated with zinc chloride and covered by a thin layer of wax. Pressure created on the top side of the form causes the zinc chloride to break through the wax and adhere to the sheet below that is coated with an absorbing layer of color generators, polyvinyl acetate, and clay. The Mead Corporation was granted a patent that incorporated a micro-encapsulated, photosensitive material that cured to a stable image when heat-activated in the presence of a developer such as an organic peroxide [Sanders 1984]. The Mead Corporation was also granted a patent on a novel system that uses a self-contained imaging sheet to produce images on plain paper using a photosensitive, photocurable, image-forming agent and a developer material on the surface of the paper support [Feldman et al. 1994].
The NCR Corporation (formerly the National Cash Register Company) was granted a patent [Marinelli 1985] for the addition of an aqueous wax emulsion to the CB coating to act as a barrier between the reactants in the CB coating and in the CF coating in multiple-copy printing operations. The technology prevents precolor formation caused by reactants seeping into the CF and can withstand on-press CF coating (presumably with desensitizing inks). Formulations included the use of JonwaxTM 120 (an emulsion of polyethylene and paraffin wax), Jonwax 26 (a wax emulsion of polythene wax), and Jonwax 22 (a water-based wax compound). The wax emulsion also replaces some of the microcapsules on the substrate. (JonwaxTM is a registered trademark of S.C. Johnson and Son, Inc., of Racine, Wisconsin.) According to Graves and Tardiff , this process was never commercialized.
2.7 Desensitizing Inks
Frequently, information entered on the top form must be unreadable on certain sections of the form or forms beneath. If the areas on the forms beneath are not needed for other data, two types of obscuring methods can be used. The most common is the "masking" blockout, which entails the printing of a solid block of blue ink over the appropriate areas. The second type of blockout method calls for printing a dense pattern of random lines and blotches suggestive of Chinese characters ("Chinese blockout"). Both methods use the same color ink as the carbonless image color. When the blocked-out areas must remain clear to allow data entry on lower plies, the manufacturer must print a special clear "desensitizing" ink on that area. This desensitizing ink deactivates the carbonless imaging system by not allowing the CF side to react with the color former encapsulated on the CB surface [Mead Corporation 1993]. Desensitizing inks may contain a variety of solvents such as white spirits, kerosene, toluene, alcohols, glycols, ketones, and plasticizers such as dibutyl phthalate, etc. [AEMCP 1985]. Desensitizing inks are sold to industrial printers much like other printing inks [Graves and Tardiff 1999].
Chang  described a patented method of desensitizing CCP when the color developer is a combination of acid clay, phenolic novolac resin, and metal salt of an organic carboxylic acid coated with 10 to 35 parts N-vinylpyrrolidone and about 65 to 90 parts of a free-radical, co-polymerizable compound of a photoinitiator having at least one terminal ethylenic group per molecule. The paper is then subjected to ultraviolet radiation.
Some CCP originates from printing shops that may use different manufacturing sources of CCP in the same manifold. Thus it is extremely difficult to trace the origin of a particular paper. For example, the CF sheet could come from one manufacturer and the remainder of the form from another supplier or manufacturer. In addition, the printer can apply the desensitizing inks to the form [Danish Branch Safety Council for Offices and Administration 1988].
2.8 Summary of Chemical Components of CCP
This section lists the known components of CCP classified as to the microcapsule, color developer, CF coating, etc. The compilation was taken from the scientific literature, patent applications, and manufacturers' submissions.
ADHESIVES FOR BINDING THE VARIOUS COATINGS TO THE PAPER
polymer lattices (e.g., butadiene/ styrene copolymers or acrylic homopolymers or copolymers)
starch or starch derivatives (wheat or corn)
water-soluble polymers (e.g., carboxymethyl cellulose, polyvinyl acetate and polyvinyl alcohol)
COLOR DEVELOPERS FOR DYE-FORMERS ON CF AND OTHER ASSOCIATED AGENTS
Active clays (examples)
acid-treated montmorillonite clay
aluminum sulfate and phosphate
calcium stearate activated kaolin
silica or silica gel
zinc chloride and nitrate
Phenolic resins (examples)
bis-Phenol A as an admixture
polyphenylphenol as a trace contaminant
para-tertiary phenol resin
Aromatic carboxylic acids (examples)
diphenic acid and metal salt compounds
thereof (zinc, aluminum, and calcium)
substituted salicylic acids
Organic acids (examples)
Addition product with phenol for color developers on the CF
oleﬁns (e.g., limonene, alpha-terpinene, diyinylbenzene, various isomers of diisopropenylbenzene, terpenes, and 4-vinyl-1-cyclohexene)
Polyvalent metal salt (magnesium, aluminum, and zinc) of carboxylated terpenephenol resin
Inorganic dispersing agents (examples)
organic dispersing agents such as carboxylic
acid types (polyacrylic acid), polymaleic
acid types (styrene-maleic anhydride
copolymer), di-tertiary acetylene glycol, and sulfonic acid types (naphthalene-sulphonic acid salts) used in conjunction with coatings of acid clays on the CF
UV absorbers (examples)
2-(2-hydroxyphenyl) benzotriazoles used in the active clay formulation
Inorganic pigment on the CF
chalk (calcium carbonate)
Organic pigment on the CF
Defoamer used to augment coating (example)
sulfonated castor oil
AGENTS CONNECTED WITH THE COATINGS ON THE CB
Dyes or color formers (examples)
alpha- and beta-unsaturated aryl ketones
basic mono azo dyes
chromogenic azaphthalide compounds
ﬂuoran derivatives (3-dialkylamino-7-dialkylamylﬂuoran)
Dyes or color formers (examples—continued)
leucobenzoyl methylene blue
phthalides led by CVL
phthalide leuco dyes
polysryl carbinols and 8' methoxy benzoindolinospiropyrans
rhodamine beta lactams
para-toluene sulfonate of Michler's hydrol
triphenylmethanes (gentian violet and
xanthine structure types
Solvents for solubilizing the color formers in the CB coating (examples)
aromatic ethers (e.g., benzylphenyl ether)
benzyl butyl phthlate
benzylated xylene and other chlorinated or hydrogenated condensed aromatic hydrocarbons, paraffin oils or kerosene and diisopropylr1aphthalene
butyl diphenyl (butyl biphenyl)
sec-butylbiphenyls and di-sec-butyl-biphenyls
cotton seed oil
diethylated, di-propylated, or di-butylated biphenyl, biphenyl oxide, or biphenyl
hydocarbon oil (e.g., parafﬁn, kerosene, or odorless [refined] kerosene)
linear alkyl benzenes (C10 to C13-LABs)
mixtures of solvents (e.g., MIPB and hydrogenated terphenyl)
mono-ethylated, mono-propylated or mono-butylated biphenyl, biphenyl oxide, or biphenyl methane
naphthalene or terphenyl (e.g., isopropyl, isobutyl, sec- or tert-butyl)
partially hydrogenated terphenyls
polyhalogenated paraffin (e.g., chloroparaffin)
polyhalogenated diphenyl (e.g., monochlorodiphenyl or trichloro-diphenyl)
Santosol 100 (consists of ethyl-DPMs, benzyl-ethyl-DPMs, and dibenzyl-ethyl-DPMs)
Santosol 150 (contains dimethyl-DPMs, benzyl-dimethyl-DPMs, and dibenzyl-dimethyl-DPMs)
alcohols (e.g., partially hydrolyzed polyvinyl alcohol or lignosulfonate)
aliphatic diisocyanates dissolved in diisopropylnaphthalene, hydrogenated terphenyl, alkylated biphenyl, or diphenyl-alkanes (such as chloroparaffin) or a mixture of these solvents and diamines
amines (e.g., ethylenediamine, hexamethyl-enediamine, or triethylenetetramine) and alcohols (e.g., partially hydrolyzed polyvinyl alcohol or lignosulfonate)
Japan wax, beeswax, paraffin wax, candelilla wax, rice wax, carnauba wax or other synthetic waxes and a solvent such as n-tridecane
multifunctional acid chlorides
polyamide and polyurethane resins
polyisocyanates and cross-linking agents (amines)
solvent such as n-tridecane
Cross-linking agents in the manufacture of capsules
aid on CB in reducing premature microcapsule breakage (e.g., floc, uncooked arrowroot, wheat starch particles, starch, talc)
2.9 Brand Names or Trademarks for CCP
Brand names or trademarks for CCP were obtained from the following sources: Calnan , CHIP , Levy and Hanoa , Olsen and Mørck , Paper Europe , and Dady . The brand names or trademarks are listed as follows:
Baron Self Copy
Carbonless Copy Paper
Double EC Copy
Idem Recycled Sheets
Idem Superior CB60 NTC
Kores Direct Copy
Moore Clean Print (MCP)
Nashua Carbonless Paper
Pressure Sensitive Paper
Scotchmark Carbonless Paper
Transfer Receptive Paper
- "Actinic radiation," including the entire electromagnetic spectrum.