Application Prospect of BCTMP in High-grade Coated Printing Paper

BCTMP is the English abbreviation of Bleached ChemithermomechanicalPulp. At present, many papermaking and scientific research workers at home and abroad are actively exploring their applications in various types of paper. The application of BCTMP has far-reaching social benefits, and it is particularly important for China, where the relative lack of wood resources. In the past, people have been controversial about the use of high-throughput mechanical pulp in printing/writing papers, mainly because the paper produced from mechanical pulps tends to yellow easily, and lignin is considered to cause a decrease in durability. However, recent studies have shown that the main cause of degradation of paper aging is the acidity of paper, not lignin. In terms of mechanical properties, lignin-containing papers made under alkaline conditions are as good as lignin-free papers, but light-induced yellowing is still a problem, and light-induced yellowing is associated with wood in the pulp. Concerning the content of the pigments, when the amount is between 10% and 25%, yellowing is not obvious in most cases and it is acceptable. The degree of yellowing in the coated paper will be even smaller.

In the past, BCTMP in China was mainly used in newsprint paper, light offset paper, whiteboard paper and white paperboard, but it was less widely used in high-grade coated printing paper. However, with the increasingly fierce competition in the market, coated printing paper manufacturers face enormous cost pressures. In the past two years, some papermaking enterprises in China have also begun to add 0-30% BCTMP pulp to coated paper, thus opening up the application of BCTMP in high-grade coated printing paper.

1 Introduction of Coated Printing Paper in Developed Countries in Europe and America

Europe is the main production area of ​​BCTMP, and it is also an advocate of using BCTMP. The study of BCTMP has a long history of application. It has also been applied successfully in coated printing papers. See Table 1 for the classification of European coated paper. The United States is the world’s largest consumer of coated paper, accounting for 30% of the world’s coated paper consumption. Its demand trends affect the global coated paper market. In 2003, 11.5 million tons of coated printing paper was consumed, including mechanical pulp. The coated paper accounted for more than half, and the coated paper containing mechanical pulp was mainly low-weight coated paper. Some experts predict that with the increase in the brightness of mechanical pulp, the market share of coated paper containing mechanical pulp will further increase.

2 Status of China's coated printing paper

China’s coated paper production in 2004 was about 3 million tons, of which 2.5 million tons were coated paper, and CGW coated paper with a basis weight of 80~150g/m2 was relatively scarce in the Chinese paper consumption market, and the paper was in the market. Demand will increase year by year.

3 BCTMP application practice in high-grade coated paper

3.1 Selection of BCTMP pulp

The BCTMP slurry has different physical properties due to its different types, materials, and manufacturers. First of all, it is necessary to clearly use the purpose of the slurry, and to select the type of slurry and determine the amount of use in combination with the characteristics of its own equipment. For example, in order to increase the thickness, HB type (high-thickness) can be used. To reduce costs, HT type (high-strength) BCTMP can be selected as much as possible to replace more chemical pulp.

3.2 Considerations for Applying BCTMP

At present, BCTMP has two types of broad-leaved pulp and softwood pulp. In high-grade coated printing paper, it mainly consists of broad-leaved wood pulp. Its BCTMP fibers are short and thick, and the content of fine fibers is relatively large, and the fibers contain more negative Charges, these characteristics determine its problems in production applications.

3.2.1 Water Filtration Problems

Due to the high content of fine fiber in BCTMP, when making high-quantity paper, the thicker pulp layer makes it difficult to filter water. Therefore, it is advisable to treat the slurry separately during the beating or to use a microparticle retention system.

3.2.2 paper strength

When a small amount of BCTMP is added, the strength does not change much, but it also slightly increases. When the amount exceeds 15%, the strength decreases significantly, especially the folding endurance. Therefore, it is necessary to properly increase the ratio of softwood pulp.

3.2.3 Smoothness

Because the BCTMP fiber is short and thick, the paper-making surface is less smooth. Therefore, in order to influence the coating quality, it is necessary to increase the pressure of the squeezing and calendering rollers, and the ash content of the formed paper can be appropriately increased under the precondition of ensuring the strength of the paper.

3.2.4 Coating performance

Due to the addition of excessive amount of BCTMP, the fiber is easily pulled out during surface sizing or blade coating, which causes difficulties in the operation of the coater. Therefore, special attention must be paid to the fiber bundle content of BCTMP. Select a BCTMP with a low fiber bundle content in the slurry. Adding a dry strength agent or increasing the penetration of the surface sizing liquid on the paper increases the bond strength in the base paper.

4 Application Prospects of BCTMP

Because BCTMP has many advantages such as low cost, high bulkiness, high paper opacity, and good coating properties on paper fillers, many papermakers are actively studying to expand their application range and dosage. With the application of the paper-folding paper machine and stacking paper machine, the reduction of the difference between the two sides of the paper and the improvement of the coating method, it is believed that the paste has a broad application prospect in high-blocking coated printing paper.