The back of the first sheet is coated with micro-encapsulated dye. The top of the middle sheet is coated with a clay that quickly reacts with the dye to form a permanent mark. The back of the middle sheet is also coated with the dye. The lowermost sheet is coated on the top surface with the clay with no coating applied to the back side.
When someone writes on the sheets, the pressure from the point of the writing instrument causes the micro-capsules to break and spill their dye. Since the capsules are so small, the print obtained is very accurate.
Carbonless copy paper was also available in a self-contained version that had both the ink and the clay on the same side of the paper.
The first dye used commercially in this application was crystal violet lactone, which is still widely used today. Other dyes and supporting chemicals used are PTSMH (p-toluene sulfinate of Michler's hydrol), TMA (trimellitic anhydride), phenol-formaldehyde resins, azo dyes, DIPN (diisopropyl naphtalenes), formaldehyde isocyanates, hydrocarbon-based solvents, polycyclic aromatic hydrocarbons, polyoxypropylene diamine, epoxy resins, aliphatic isocyanates, Bisphenol A, diethylene triamine, and others. The dyes in carbonless copy papers may cause contact dermatitis in sensitive persons.
Until the 1970s when the use of polychlorinated biphenyls (PCBs) was banned due to health and environmental concerns, PCBs were used as a transfer agent in carbonless copy paper. PCBs are readily transferred to human skin during handling of such papers, and it is difficult to achieve decontamination by ordinary washing with soap and water.
In Japan, carbonless copy paper is treated as a PCB-contaminated waste.
Exposure to certain types of carbonless copy paper or its components has resulted, under some conditions, in mild to moderate symptoms of skin irritation and irritation of the mucosal membranes of the eyes and upper respiratory tract. In most cases, good industrial hygiene and work practices should be adequate to reduce or eliminate symptoms. These include adequate ventilation, humidity, and temperature controls; proper housekeeping; minimal hand-to-mouth and hand-to-eye contact; and periodic cleansing of hands.
The University of Florida has found that chronic exposure to carbonless copy paper can be hazardous to a person's health. In addition, scientists found higher rates of sick leave and illness compliants at the office using large amounts of carbonless copypaper.
Environemtal Health Perspectives 2007 by Maritta S. Jaakkola; Jouni J.K. Jaakkola. Office Work Exposures and Adult-Onset Asthma This study provides new evidence that exposures to paper dust and CCP in office work are related to increased risk of adult-onset asthma. Reduction of these exposures could prevent asthma in office workers. Clinicians seeing asthma patients should be aware of this link to office exposures. http://www.medscape.com/viewarticle/561114
6. http://news.ufl.edu/1997/05/22/carbonls/ U. of FLA News
7. http://www.businessweek.com/2000/00_50/b3711180.htm Business Weeks Expose'
8. http://www.businessweek.com/2000/00_50/b3711181.htm A Paper Trail