Carbonless Paper（NCR paper） is divided into upper page Paper or CB Paper (Coated Back Paper), middle page paper or CFB paper (Coated Front & Back Paper) and lower page paper or CF paper (Coated Front paper).

The front of the upper page (CB paper) is not coated, and the back is coated with CB paint; The front of the middle page paper (CFB paper) is coated with CF paint, and the back is coated with CB paint; The front of the next page (CF paper) is coated with CF paint, and the back is not coated.

Carbon-free carbon paper coatings include CB coatings and CF coatings. Among them, CB coating on CFB paper is not exactly the same as CB coating on paper, the main difference is that the amount of microcapsules is different. The CF paint of CFB paper and the CF paint of the next paper generally use the same CF paint, which is mainly to prevent confusion in the production process and facilitate production management. CB coating is mainly composed of hair color agent microcapsule, spacer, adhesive, additive and water. CF coatings are mainly composed of pigments, color developing agents, adhesives, additives and water.

Next, the common components of CB and CF coatings will be analyzed in detail to provide theoretical guidance and problem-solving ideas for carbon-free carbon paper manufacturers.

1. CB coating commonly used components and performance requirements

CB coating is mainly composed of hair color agent microcapsules, spacers, adhesives, additives and water.

1.1microcapsule

Microcapsules are the most important components of CB coatings, and the quality and dosage of microcapsules have the greatest relationship with the color rendering of carbon-free carbon paper.
The solid content of microcapsules is generally 40% ~ 50%, which is mainly composed of colorless dye oil, wall material and emulsifier. The quality of microcapsules mainly affects the color rendering effect, light resistance and pollution of carbon-free carbon paper. The particle size of microcapsules is generally controlled below 10μm, and the microcapsules with 5μm to 6μm particle size should account for the majority, the microcapsules with large particle size are easy to break, the pollution of the paper is large, and the normal use of the paper will be affected seriously, but the particle size is not good, the microcapsules with small particle size are strong, and the color effect will be reduced. In CB coatings, the amount of microcapsules accounts for about 50% to 60% of the total paint (absolute dry ratio).

1.2 Spacer
Spacers are used in CB coatings to prevent the microcapsules from breaking prematurely due to external forces during dosing and coating. At present, wheat starch is the most commonly used spacer in CB coatings. Spacer The main quality index is the size of the particle size, the general requirements of the particle size in the range of 15 ~ 25μm spacer should account for 60 ~ 80%, the particle size can not be greater than 40μm. The amount of spacer is generally 30% to 50% of the amount of microcapsules (absolute dry ratio), the larger the size of microcapsules or the weaker the strength of microcapsules, the more spacer dosage is required.

1. 3 Adhesive

There are generally two kinds of adhesives used in CB coatings, one is carboxylic styrene butadiene latex, one is modified starch, and a few manufacturers use polyvinyl alcohol (PVA) with modified starch. Among them, the amount of carboxylated styrene butadiene latex is generally 3% to 4% (for paint, dry ratio), and the amount of modified starch is generally 10% to 12% (for paint, dry ratio).
1. 4 Additives
The additives used in CB coatings include dispersant, sodium carboxymethyl cellulose (CMC) and preservatives. The dispersant is sodium polyacrylate, the amount is generally 0.2% ~ 0.3% (for paint, dry ratio), and the amount of sodium carboxymethyl cellulose (CMC) is generally 0.5% ~ 1.5% (for paint, dry ratio), which can be adjusted according to the requirements of paint viscosity. The amount of preservatives is generally 0.5% (for starch, dry ratio).

2. Common components of CF coatings and their performance requirements
CF coatings are mainly composed of pigments, color developing agents, adhesives, additives and water.
2. 1 Paint
The purpose of using coating pigments for carbon-free carbon paper is to fill and cover the uneven surface of the base paper, improve the whiteness and opacity of the paper, improve the smoothness and gloss of the paper, so that the surface of the paper has a uniform and good ink absorption, and finally obtain a good printing effect.
The main pigments used in CF paint are kaolin and calcium carbonate.

2.1.1 Kaolin clay

The kaolin used in CF coating is generally hexagonal flake, of which the kaolin content of particle size less than 2μm should reach 70%(quantity ratio). The amount of kaolin generally accounts for 50% to 70% of the total amount of pigments.

2.1.2 calcium titanate

The calcium carbonate used in CF coating is generally light calcium carbonate, with a particle size of 0.1 ~ 1μm, and calcium carbonate can improve the opacity of the paper
Degree, whiteness and ink absorption. The amount of calcium carbonate generally accounts for 30% to 50% of the total pigment.

2.2 Color developing agent
The color developing agent used in CF coating is mainly phenolic resin, and a small amount of zinc salicylate is added to match the use of zinc salicylate mainly to improve the color developing speed of carbon-free paper, especially at low temperature. The amount of color developing agent generally accounts for 11% to 13% of the total paint (absolute dry ratio), and the addition ratio of phenolic resin and zinc salicylate is generally 10:1 (absolute dry ratio), the addition of zinc salicylate can not be too much, otherwise it will increase the pollution of the paper.
2. 3 Adhesive
There are generally two kinds of adhesives used in CF paint, one is carboxylic styrene butadiene latex, and the other is modified starch. Among them, the amount of carboxylated styrene butadiene latex is generally 4% to 5% (for paint, dry ratio), and the amount of modified starch is generally 12% to 14% (for paint, dry ratio).

2. 4 Additives
The additives used in CF coating include dispersant, sodium carboxymethyl cellulose, foam suppressor, lubricant, preservative and caustic soda. In addition, when producing colored paper, the colors added in the paint include red powder, yellow powder, turquoise blue and green pigments, and the corresponding production of carbon-free carbon paper colors are red, yellow, blue and green.
The dispersant is sodium polyacrylate, and the dosage is generally 0.2% ~ 0.3% (for pigment, absolute dry ratio); The amount of sodium carboxymethyl cellulose (CMC) is generally 1.0% to 1.5% (for pigments, dry ratio), adjusted according to the requirements of paint viscosity; The dosage of foam suppressant is generally 0.02% ~ 0.05% (for pigment, dry ratio); The lubricant is calcium stearate, and the amount is generally 1.0% ~ 1.5% (for pigment, dry ratio); The amount of preservatives is generally 0.5% (starch, dry ratio); Caustic soda is mainly used to regulate the pH value of paint.

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