Printed matter gives people an obvious feeling, that is, its color, brightness and authenticity. In addition to the structure of the pattern and the printing level, it is almost expressed by color. And because there are many printing plants that print a fixed product every month, the color of the ink is required to be consistent, otherwise it will lead to inconsistent color of the printed matter and so on. Therefore, the inspection of ink color is very important.

There are two main methods to detect ink color:

One is instrument inspection method; The color difference meter, spectrophotometer and other instruments are used for measurement.

A conventional inspection method, which is to compare and judge the ink coated on the base material.

The conventional inspection method is a method of parallel observation and comparison of standard (standard) and test (test) samples by human eyes. This method is relatively simple, but it can not be expressed in numbers.

The three stimulus values can be obtained by instrumental measurement, and the values of main wavelength, purity and brightness in CIE system or hue, chroma and brightness in Munsell system can be calculated, which can also be expressed by color difference data;

Next, let's introduce the instrument inspection method:

(1) Tools and materials

a. Small ink adjusting knife;

b. Doctor blade;

c. Scraping paper (or printed with black cross track, 11cm long and 6.5cm wide).

d. Color difference meter (such as CS-200, CS-210, CS-220)

(2) Inspection method:

a. Take a small amount of standard sample and sample with a small ink adjusting knife, place them on the glass plate respectively, and mix them evenly. Then take a small amount of standard sample with a small ink adjusting knife and apply it to the upper left of the sample scraping paper, and then take a small amount of sample and apply it to the upper right. The two should be adjacent and not connected.

b. Use the doctor blade to scrape the ink into a thin layer on the sample paper from top to bottom. After scraping to 3 ~ 5cm, gradually lay the doctor blade flat (i.e. the angle with the paper becomes smaller) and reduce the pressure at the same time, so that the ink can be coated into a thicker ink layer on the paper.

c. After the ink layer is solidified, the color information of the sample and the standard sample is measured with a color difference meter, so as to obtain the difference between them.

(3) Precautions:

a. Scraping is one of the important basic skills of ink manufacturers and inspectors. Thin and high fluidity ink is easier to scrape, while thick (thick) and high viscosity ink is not easy to scrape. For example, the ink with poor ink property, excessively thick, short and rough ink, and the scraped shape is irregular (this phenomenon often occurs in engraving intaglio ink), which is very ugly.

b. When the blade of the scraper is sharp, the ink layer scraped on the paper is relatively thin, on the contrary, the ink layer scraped is relatively thick.

c. When scraping thin ink, the angle of the knife can be smaller to ensure that the ink layer is thicker. When scraping thick ink, the angle of the knife should be larger to make the ink left on the paper thinner.

d. The quality of paper has a great influence on scraping. Generally, securities paper with uniform fiber and flat surface or high-grade Daolin paper is more suitable. The color of the paper shall be neutral white, without fluorescence and watermark.

Internationally, the background color generally refers to the color printed on the paper with a thin layer of ink. The complexion refers to the color reflected by the thick layer of ink;

e. Solvent based inks can also be scraped by this method, but they can also be scraped by wire rod scraping method.

f. Lithographic ink and relief ink focus on the surface color and background color; Screen printing ink and intaglio printing ink focus on the color of face and ink.

g. In order to inspect the color more accurately, we can use the printability test holder (such as IGT printability test machine and ri-1 printability test machine) to compare and judge after printing.