In order to increase the overall effect of the packaging, many customers will design a large area of spot color when designing the packaging. If it cannot be well controlled during the printing process, it will greatly reduce the grade of the product, thus affecting the competitiveness of the product in the market. Therefore, strict requirements must be imposed on the quality control of raw materials and the technical quality of operators during printing.

1. The hue of each batch or the same batch is inconsistent

(1) When making the first proof, be sure to make detailed records of the scraper angle and ink ratio.

(2) Pre-printing control, since the spot color ink is generally prepared by yourself, it is necessary to ensure that the ink used is accurate in deviation and ratio, and the ink tray, ink stirring stick, and ink pump must be clean. The remaining ink from the previous use should be added to the new ink in an appropriate amount, and the scraper record and ink viscosity should be adjusted according to the record.

(3) The viscosity of the ink must be controlled during printing. It is recommended to increase the number of manual measurements or prepare an automatic tracking and adjustment instrument for the viscosity.

2. Uneven ink transfer

(1) When mixing colors, the number of inks should be minimized. If two colors can be used, do not use three colors. Inks from different manufacturers cannot be mixed. After mixing, they should be fully stirred and dissolved with appropriate amount of butanone. When adding the solution, add it slowly and stir it evenly to avoid the impact with the solution causing the solubility to deteriorate, destroying the ink structure, and thus causing poor transfer.

(2) Reduce the scraper angle and scraper pressure (more applicable to transition spot colors).

(3) Water marks

Increase the ink viscosity. Because the spot color plate is deeply concave, generally 30-35um, water marks will appear if the ink viscosity is too low. It is recommended to use 22 seconds to 20 seconds at a speed of 120-150m/min (Zahn No. 3 cup)

3. Twill lines of indentation

(1) Reduce the pressure of the indentation roller.

(2) The colloid of the embossing roller is relatively soft. Replace the embossing roller with a good hardness of 75 Shore.

4. Insufficient peel strength and sticking speed

Because the spot color generally accounts for 40%-60% of the entire package, or even more. Therefore, the peel strength of the spot color must be good, which can be controlled from the following aspects.

(1) The surface tension of the substrate must meet the requirements and cannot be less than 38 dynes/cm.

(2) Select ink suitable for the substrate model.

(3) Select a solvent with a lower surface tension to reduce the surface tension of the entire ink system, thereby improving the wettability to the substrate.

(4) Increase the heat and air volume of the oven. If the heat and air volume of the oven are small and the amount of spot color ink is large, it will cause adhesion and insufficient peeling.