How Carbonless (NCR) Paper Actually Works: CB, CFB & CF Chemistry

Direct answer: Carbonless paper works by breaking microscopic capsules of colorless dye under the pressure of a pen or an impact printer. The released dye lands on an acidic clay-and-resin coating on the sheet below, and the reaction between the two turns the dye dark. There is no carbon and no ink transfer. The image is manufactured on the receiving sheet at the moment of contact.

The two coatings

Carbonless copy paper (CCP), often called NCR paper after the National Cash Register Company that patented it in 1953, is ordinary bond paper carrying one or two functional coatings (Wikipedia).

The capsule layer (CB side). The back of the top sheet carries microcapsules 3 to 6 micrometers in diameter, applied at several million per square centimeter. Each holds a colorless solution of 2% to 6% dye precursor dissolved in a high-boiling-point organic solvent (NIOSH Hazard Review: Carbonless Copy Paper, §2.1–2.2).

The precursor is a leuco dye. Leuco means colorless. The most common one, and the first used commercially, is crystal violet lactone (CVL); N-benzoylleucomethylene blue is another (NIOSH §2.2; Wikipedia).

Mixed into that layer are inert spacer particles called stilts, deliberately larger than the capsules. Materials include floc, uncooked arrowroot, and wheat starch. They hold sheets a hair apart so ordinary handling and press work do not crush capsules before the customer writes (NIOSH §2.1).

The developer layer (CF side). The receiving surface carries an acidic developer, usually a phenolic resin in the US and Japan, more often reactive clay in Europe (NIOSH §2.2). A published CF slurry runs 64 parts kaolin clay, 12 parts styrene-butadiene latex, 12 parts novolak resin dispersion, 6 parts colloidal silica, 3 parts calcium carbonate, and 3 parts hydroxyethyl starch, dried at 93 °C (NIOSH Table 2-1).

The chemistry is a proton transfer. The developer is acidic, so on contact the dye’s lactone ring opens, the molecule becomes conjugated, and it absorbs visible light. Colorless becomes blue or black (NIOSH §2.2).

CB, CFB, and CF: the three ply types

Multi-part sets are built from three sheet grades (Nekoosa/Appvion Carbonless Sheet Training; SEF Inc.):

A fourth grade, SC (self-contained), carries capsules and developer in one layer on the same face, so any plain sheet on top will still produce an image (Koehler Paper).

How a 3-part set transfers down the stack

Reading down a 3-part stack, the coatings alternate cleanly: Ply 1 White (CB) carries microcapsules on its underside; Ply 2 Canary (CFB) carries reactive clay developer on top and microcapsules on its underside; and Ply 3 Pink (CF) carries reactive clay developer on its top face only with uncoated bond on the back.

Add a fourth ply by adding one more CFB sheet in the middle—so a 4-part set runs White (CB), Canary (CFB), Pink (CFB), and Goldenrod (CF).

Why the sequence matters

Every interface needs a capsule face pointing down at a developer face pointing up. Break that pairing anywhere and the chain stops there.

Two failure modes follow. Reordering the plies: put the CF sheet in the middle and everything below it is dead, because a CF back is uncoated bond. This is why converters say never to change the order of a pre-collated set (Relyco). Printing on the wrong side: reams ship with the print side marked on the label, and running a sheet upside down puts toner on the coating instead of the bond face (Nekoosa/Appvion).

Pre-collated stock ships in two orders. Reverse sequence takes a single color and a single pass. Straight takes two passes and back printing. Normally an even number of equipment passes needs straight, an odd number needs reverse (Nekoosa/Appvion).

Turning the reaction off on purpose

Desensitizing ink is a clear ink printed onto the CF surface. It caps the developer so no image forms in that zone, while leaving the area writable after the set is separated (NIOSH §2.7; Iowa DHS Forms Handbook). Coverage has a ceiling: as a general rule no more than 60% of the offset blanket area should carry it (SEF Inc. glossary).

Blockouts mask the area visually instead. The two standard patterns are the solid masking blockout and the dense random-line “Chinese” blockout (NIOSH §2.7), and they should print in the same color the carbonless image will appear in (Iowa DHS Handbook).

Design consequence: keep the transfer zone clean

Because the developer must be chemically available the instant the dye arrives, heavy ink over a write-in area interferes with the reaction. Keep screen density at or below 50% anywhere customers write (SEF Inc.). Government forms guidance is more conservative still, recommending a 10% to 15% screen where the form gets subsequent processing (Iowa DHS Handbook).

FAQ

Is carbonless paper the same as carbon paper? No. Carbon paper transfers pigment from a coated interleaf. Carbonless carries no pigment until pressure triggers a reaction between a colorless dye and an acidic developer (Wikipedia).

What does NCR stand for? It is read as “no carbon required,” but it began as the initials of the National Cash Register Company, which applied for the patent on June 30, 1953 (Wikipedia).

What are the CB, CFB, and CF sheets? CB is coated back and is always the top sheet. CFB is coated front and back and makes up every middle sheet. CF is coated front and is always the bottom sheet (Nekoosa/Appvion).

Why is the copy blue on some forms and black on others? Image color is a property of the leuco dye system in the CB coating, not of the ink used to print the form (NIOSH §2.2).

Can you laser print on carbonless paper? Yes, with grades qualified for it. Digital carbonless is a standard product category, run one sheet at a time then assembled into sets (Nekoosa).

What is self-contained carbonless paper? SC paper carries capsules and developer in one layer on the same face, so the reaction happens within that layer and any plain sheet can go on top (Koehler).

Why don’t the capsules break during shipping? Inert spacer particles called stilts, larger than the capsules, are coated into the CB layer specifically to prevent premature rupture during manufacturing, converting, and handling (NIOSH §2.1).

Can I block out a section so it does not copy through? Yes. Clear desensitizing ink on the CF surface deactivates the developer in that zone, and printed blockouts mask it. The two are often combined (Iowa DHS Handbook).

Sources

• NIOSH Hazard Review: Carbonless Copy Paper, “The Technology of CCP” — https://en.wikisource.org/wiki/NIOSH_Hazard_Review:_Carbonless_Copy_Paper/The_Technology_of_CCP
• Nekoosa / Appvion, Carbonless Sheet Training —
• Nekoosa, NCR PAPER* Superior Carbonless — https://nekoosa.com/products/ncr-paper-superior-carbonless
• Koehler Paper, How carbonless paper works — https://www.koehlerpaper.com/en/products/Carbonless-paper/functionality-of-carbonless-paper.php
• SEF Inc., Understanding Carbonless Paper — https://www.seforms.com/resources/knowledge_base/carbonless.html
• SEF Inc., Glossary of Terms — https://www.seforms.com/resources/glossary.html
• Iowa Dept. of Human Services, Forms Analysis and Design Handbook — https://hhs.iowa.gov/media/6488/download?inline
• Midtown Printing, Printing Basics glossary — https://midtownprinting.com/pages/printing-basics
• Relyco, How to Print Multi-Part Carbonless Forms in a Laser Printer — https://www.relyco.com/blogs/relyco/how-to-print-multipart-carbonless-forms-laser-printer
• Carbonless On Demand, Sequential Numbering on Carbonless Forms — https://www.carbonlessondemand.com/cgi-bin/shop/Sequential-Numbering.html
• Wikipedia, Carbonless copy paper — https://en.wikipedia.org/wiki/Carbonless_copy_paper