Application of RK Scraper in Spreader paper whiteness performance test

This article mainly excerpts Gao Haiming, Shi Licai, Hu Qingyun, Sui Xiaofei, Zang Yonghua's "Influence of Base Paper Whiteness and Pigment Proportion on Coated Paper Whiteness" to illustrate the role of RK scraping rod in the author's experiment.

Whiteness is one of the important optical indicators of coated paper. High-whiteness paper can truly and objectively reflect all the colors of the printed color screen, improve the contrast of text and ink, make the printed matter bright in color, rich in layers, and sharp in contrast, achieving the effect of both pictures and text

This experiment mainly discusses the influence of different whiteness base papers on the whiteness of coated paper and the influence of pigment ratio on the whiteness of coated paper. In the study of the interaction between base paper and coating

In terms of the effect on the whiteness of coated paper, mainly by changing the ratio of GCC and kaolin in the coating, and then performing a single coating, the effect of coatings with different ratios of calcium carbonate and kaolin on the whiteness and gloss of coated paper was analyzed. Impact.

1.1 Experimental raw materials

Pulp: natural kraft softwood pulp (brightness 22%ISO); bleached softwood pulp; bleached hardwood pulp BCTMP; the pulp is all obtained from a paper mill in Tianjin. Coating components: kaolin (powder), more than 93% of particle size ≤ 2 μm, provided by Maoming Petrochemical Mining Co., Ltd.; ground calcium carbonate (GCC, dispersion liquid), more than 95% of particle size ≤ 2 μm, obtained from Yanzhou Dongsheng Fine Chemical Co., Ltd.; carboxylated styrene-butadiene latex (Styronal302G, average particle size 0.15μm, glass transition temperature 10℃, provided by BASF Shanghai Company) as adhesive; dispersant, sodium polyacrylate, obtained from a paper mill in Fuyang; CMC , taken from a paper mill in Fuyang; optical brightener (OBA, liquid, 4S type), provided by BASF Shanghai.

1.2 Experimental equipment

High-speed disperser, QJ‑90 multifunctional agitator, RKPrintCoatInstruments Steel Wire Drawdown Rod, DHG‑9D53A electric blast dryer, hand paper machine (RK‑ZA‑KWT, produced by PTI Austria), ELREPHO Spectrophotometer (produced by Swedish L&W company), laboratory multi-purpose calender, wet paper press, XGP series portable specular gloss meter.

1.3 Experimental method

1.3.1 Natural color paste bleaching

Bleaching the original color paste to different whiteness (22%~80%ISO), specifically refer to the method introduced in literature [14‑18].

1.3.2 Manufacture and processing of base paper (hand-sheet) When studying the influence of different whiteness of base paper on the whiteness of coated paper, pulps with different whiteness are made into base paper. When studying the interaction between base paper and coating, the base paper consisted of 40% bleached softwood pulp, 50% bleached hardwood pulp and 10% BCTMP. Use a PFI mill to beat the pulp to (35±2)°SR, and then decompose the slurry with a concentration of 1.5% using a standard decomposer with a rotation speed of 15000r. According to the Tappi standard T272sp-2002, use the RK-ZA-KWT hand paper machine to make the sheets, and the paper weight is (80±2) g·m-2.

1.3.3 Coating preparation

Pigment dispersion: Kaolin is dispersed at 4500r·min‑1 for 30min with a high-speed disperser, the solid content of the dispersion is 68%, and the amount of dispersant is 0.3 parts (per 100 parts of pigment). CMC gelatinization: prepare CMC into a 10% mass percent aqueous solution, put it in a constant temperature Water Bath at 70°C for 30 minutes, stir it with a stirrer at a constant speed during the gelatinization process, and add the water lost by evaporation after the gelatinization is completed and cooled ,spare. Finally, add kaolin pre-dispersion, calcium carbonate, carboxylated styrene-butadiene latex, CMC, OBA and dedistilled water into the dispersion tank according to a certain ratio (solid content 60%), stir evenly and adjust the pH value of the coating to 8.0~ with NaOH solution 8.5, get the final paint.

Coating formula: GCC/kaolin ratios are 0/100, 20/80, 40/60, 60/40, 0/20, 100/0; carboxylated styrene-butadiene latex 15 parts, CMC 0.8 parts, OBA 0.8 parts ( Only the ratio of GCC and kaolin in the paint formulation is changed, the others are fixed).

1.3.4 Coating, drying and calendering

Use a Bar Coater to coat the handsheet on one side at one time, and dry it in an electric Forced Air Drying Oven (95°C) for 30 seconds after coating. Using laboratory calender

Under the conditions of a pressure of 3 MPa and a temperature of 80℃., soft roll calendering was performed on the coated paper. After the sample is calendered, it is placed at (23±1)°C and (50±2)% constant temperature and humidity for 24 hours.