Exploring how high-temperature dry waste materials are produced under a qualified paper bag

2. Adhesive deposition

Many of the chemicals used in paper coating, printing, and paper processing can become stickies when recycled paper is reused. These stickies often deposit on the surface of the equipment, sticking to the web, sticking carpets, sticking cylinders, and creating paper. The machine breaks the paper and the runnability drops. Newsprint, corrugated paper and toilet paper have the most serious problems with viscose.

In addition to the stickiness of the paper machine, the wax-based hot melt adhesive in the OCC material also forms a lot of dark spots on the surface of the liner board, making the paperboard an external product.

Stickies in waste paper come mainly from hot-melts, pressure-sensitive adhesives, waxes, inks, and coating latices. The most common It is polyvinyl acetate (PVAc), ethylene vinyl acetate copolymer (EVA), and poly 2-ethylhexyl acrylate (PEHA).

During the deposition of stickies, other components of the slurry, such as fibers, fillers, and some chemicals, are often co-settled with the stickies, causing changes in the color and appearance of the deposits. Therefore, to solve the problem of sticky material deposition, we must first comprehensively and accurately analyze the composition of the sediment and understand the characteristics of the sticky material; at the same time, we must collect relevant data of the papermaking production process, and finally determine the most important control of the deposition of stickies. The best solution.
The basic strategy for controlling stickies deposition is mechanical removal plus chemical treatment. First, the primary stickies should be removed from the waste paper by strengthening the waste paper sorting, strengthening the pulp screening and purification process. In practice, high-density shredding and screening should be used, low-concentration centrifugation and purification, and addition of vibrating screen to remove; use of thermal disperser, optimized deinking flotation.

Next, chemical treatment is performed on the native adhesive that has not been mechanically removed to prevent the aggregation of the rubber particles from becoming large. Chemical treatment also helps to reduce secondary stickies.

The chemical treatment has four methods of adsorption, dispersion, fixation, and passivation, which prevent deposition of stickies by changing the stickiness of the stickies and avoiding the accumulation of stickies. Experience shows that if various factors such as effects and costs are comprehensively considered, the filler (bentonite) and the fixing agent are the best chemicals for controlling the deposition of stickies. Of course, it is best to have the cooperation of retention aids.

Deposition of stickies and stickies has become a growing problem in the use of waste paper. For this reason, Ciba Specialty Chemicals has established three paper machine deposits and paper disease analysis centers in Europe, the Americas, and Shanghai, China, using advanced technologies. The instrument analyzes and identifies various deposits and paper diseases sent by paper mills. In addition to helping paper mills determine the composition and possible sources of sediments, it also analyzes a large number of results and summarizes the deposition rules of stickies. Provides the basis for solving the problem of sticky material deposition.

3. Low paper strength

After repeated use of waste paper, the length of the fiber becomes shorter, the toughness becomes worse, and the paper strength also decreases. Intensity problems are common in corrugated paper. Corrugated paper is a product with low value and low profitability. Many companies use ordinary long wire paper machines to make paper, and do not carry out internal sizing and surface sizing. At present, there are several methods to improve the strength of corrugated base paper: (1) internal sizing of rosin; (2) surface sizing of starch; (3) adding cationic starch in wet end; (4) using raw starch to strengthen the wet end; (5) wet The Department uses dry strength synthetic resin.

Experience has shown that the first few methods have certain limitations in improving the two most important strength indicators of corrugated base paper, the flat compressive strength and the cyclical compressive strength.

Dry strength synthetic resins are mainly acrylamide products, which are anionic, cationic, amphoteric and modified. The dry strength of synthetic resin has obvious enhancement effect on corrugated paper, but its use cost is relatively high. If the level of corrugated base paper can be improved through effective enhancement, higher input costs are still acceptable.

4. Paper whiteness is low

Residual ink and impurities in waste paper are the main factors that affect paper whiteness. Although deinking and bleaching of waste paper are performed when producing some paper grades, it is impossible to remove all the inks whether it is deinking by washing method or deinking by flotation method, and the removal rate of the ink is usually 80% to 90%. A very small amount of residual ink can significantly reduce the whiteness of the pulp.

The ink and colored impurities in waste paper can absorb a large amount of visible light, making the paper become dark and yellow. In the production of coated white paperboard, the recovered pulp is usually subjected to a whitening treatment. Blue and violet dyes are used to balance the yellow hue of the pulp, to increase the visual whiteness of the paper and make the paper appear whiter; on the other hand, the use of a disulfonic or tetrasulfonic acid type optical brightener in the wet part can improve the paper's The total reflection of light further increases the whiteness and brightness of the paper.

In a word, the methods to make up for the loss of whiteness of waste pulp mainly include:

(1) Improve the deinking efficiency; (2) Bleach the deinking pulp, if necessary, perform the first oxidative bleaching and then the second reductive bleaching; (3) Improve the efficiency of the slag remover; (4) Use fluorescent brighteners and Toning dyes improve the whiteness and hue of paper sheets.

China is a country with scarce forest resources. Vigorously developing waste paper pulping and secondary fiber papermaking technology is an important part of the strategy for sustainable development.

With the continuous increase in the recovery and use of waste paper, the continuous increase in the speed of paper machines, and the rapid development of the printing and packaging industry, the four major problems in the recycling of waste paper are becoming increasingly serious. Solving these problems cannot be achieved by one method alone, but rather by a comprehensive approach. In the future, new reinforcing agents should be developed and the efficiency of existing enhancers and retention aids should be improved. Pulp screening and purification equipment and processes should be designed or improved to further develop enzyme technology. (Text / Liu Jun Ti Dejun)