The Effect of Paper Acidity and Alkali on Printing Quality

The printing process requires that the pH of the paper be neutral. However, due to the differences in the sizing material, filler properties, and pigment composition during the pulping process, the paper may be either acidic or alkaline. For example, Vaseline sizing is used in the papermaking process. There are certain residual chlorine and organic acids in the pulp. If proper treatment is not carried out, the resulting paper will be acidic; the caustic soda (NaOH) is used in the process of sheet production. ) As well as alkaline fillers and colorants, residual alkali liquor in the slurry, etc., without necessary treatment, the resulting paper will be alkaline.

Acid paper will inhibit the drying of the printed ink. The stronger the acidity, the slower the ink will dry. In one example, cigarette packs were printed once for a cigarette factory, the same ink, the same offset press, and two different coated papers. However, the drying speeds were quite different. Afterwards contacted with the coated paper mill. The reason for the slow drying of the coated paper was due to the fact that the paper filler and the compound contained acidic substances, which caused the coated paper to be acidic. The acidity and alkalinity of the paper has a decisive influence on the drying process of the printing process and the printing ink. The acid paper inhibits the printing ink conjunctiva. When the pH of the paper is reduced from 5.5 to 4.4, the ink drying speed is slowed by three times. The paper is acidic, which also affects the color of the printed product.

Alkaline paper is generally mistaken for faster ink drying. In fact, the effect is not obvious, but it is faster. It is by no means a direct relationship. Letterpress, gravure, screen printing, paper acidity only affects the speed of ink drying. Offset printing, the acidity of the paper not only affects the drying of the ink. Because the offset printing fountain solution is not pure, there are surfactants, wetting agents and other acidic substances with cleaning ability. If the pH of the paper is higher than 9 at this time, the alkaline substance of the paper during the printing process will be neutralized with the acidic component of the aqueous solution, affecting the pH of the fountain solution. In addition, the acidic paper will emulsify the ink and cause dinging.

If there is free acid in the paper, the paper will be gradually eroded by acid, reducing the durability of the paper.
In the printing of gold, printing silver, bronzing, the paper will be acid and alkaline chemical reaction with the metal powder, so that imprinting, foil gold foil discoloration, lose the original light and color.

The paper is preferably neutral during the printing process, that is, the pH is about 7, or slightly alkaline. For example, the pH value of coated paper, offset paper, and writing paper, which are commonly used for offset printing, should be neutral. We must close the purchase of good paper, ink, and PS. The pH of the paper can be measured with a pH test paper or with a magnetic flux meter.