1. Requirements for ink
The color matching of ink should fully consider the color deviation of ink, which also has a great influence on the accuracy of bar code. Theoretically, as long as the ink is used according to the color ratio, it can meet the requirements of bar code printing. However, due to the defect of impure coloring phase of printing ink, color deviation occurs. Therefore, we should accurately control the color of the ink, so that the ink density is uniform, hue saturation, high purity, it is best to determine whether the reflectivity of an ink under red light meets the requirements before printing bar code. The reflectance and gloss of gold ink can cause the specular reflection effect and affect the scanner's reading, so it can't be used to print bar code. In addition, the ink concentration and the thickness of the ink layer should also meet the requirements of bar code printing. Because bar code printing is field printing, the reflection density achieved by printing is related to the optical characteristics of the ink and the thickness of the ink layer. In the printing process, the reflection density increases with the increase of ink thickness. When the ink thickness reaches a certain value, the density will reach saturation. General ink saturation density requirements are: black ink 1.8 ~ 2.0; cyan ink 1.45 ~ 1.70; magenta ink 1.25 ~ 1.50; yellow ink 0.90 ~ 1.05; other spot color ink 0.8 or more. Due to the difference of printing technology, the thickness of ink layer is also different. Generally, it is 2-4 μ m for offset printing, 8 μ m for convex printing, 10 μ m for flexo printing, 12 μ m for gravure printing and 30 μ m for silk screen printing.
2. Requirements for substrate
When the bar code is read, the scanning light source is incident at an angle of 45 ° and the collection angle of the reflected light is 15 °, when the reflected light exceeds 15 ° range, the reflected light signal cannot be collected, which is equivalent to the black effect. Therefore, in order to meet the bar code scanning characteristics, the substrate is required to have good light scattering characteristics, and can not appear specular reflection. Therefore, the white matter, opacity and glossiness of the paper have a certain impact on the bar code reading. In addition, we should also consider the selection of good weather resistance, dimensional stability after stress, good coloring, ink permeability, smoothness and finish moderate material.
3. Printing quality requirements
Bar code symbol is the information source of scanning and reading. In order to ensure correct reading, the printed bar code should be neat and clear, the bar code should have no obvious incomplete, and the blank space should have no dirty ink. In order to ensure the correct reading of the bar code, the maximum diameter of the defects and stains on the bar code should be less than or equal to 0.4 times of the standard width of the narrowest bar code. There should be obvious contrast signal between the line and blank in the printed bar code, the reflectivity of the blank should be as large as possible, and the reflectivity of the line should be as small as possible. The larger the PCs value (color contrast), the larger the contrast signal of the bar code, and the better the readability.
4. Requirements for printing position
The location of bar code symbol should be determined in accordance with the principle of no deformation, easy to read and plate making. That is to say, it is required to be set on the right side of the main display surface of the commodity package, or on the plane connected with the main display surface, and on the back of the main display surface of the commodity package. Considering the characteristics of the printing process, the direction of the bar code should correspond to the direction of the printing, so that the printing deformation can only be displayed in the vertical position of the bar code, so as not to affect the accurate reading. Due to the differences of packaging methods and characteristics, the printing position of bar code is also different. Generally, the barcode of box packaging should be printed on the right side of the lower part of the box; the barcode of canned and bottled packaging should be printed on the lower side of the label, but the surface curvature of the barcode symbol should not exceed 30 °; the barcode of barrel packaging should be printed on the side of the barrel, if the side can not be printed, the barcode can be printed on the cover, but the depth of the cover should not exceed 13mm; the bag packaging has a bottom and a large bottom, which can be printed The bar code is printed on the bottom or the lower center of the back; the book bar code is usually printed on the bottom left corner of the back cover or cover, and the direction of the line is parallel to the spine of the book. To sum up, as a kind of data input technology and automatic identification technology, bar code is widely used in commodity packaging. It plays an important role in the production, sales, storage, inspection and information communication of commodities. Therefore, the correct understanding and understanding of bar code knowledge and printing bar code is an important part of packaging and printing.