The original negatives printed with bar codes must be registered and issued by the International or National Coding Center. In order for the barcode to be correctly recognized by the barcode recognizer, the barcode must be straight and not broken, the edges of the lines should be smooth and sharp, and there should be no jaggies. The distance between the lines should meet the standard, the blackness of the lines should be sufficient, and the contrast should be large. The technical requirements for bar codes are:
(1) Size scaling. The bar code is usually printed directly from the original, and the enlargement or reduction of printing should be in accordance with the technical requirements of the EAN organization. It cannot be arbitrarily carried out. Generally, the zoom magnification should be controlled at 80% to 200%. The barcode zoom rate has a great influence on the printing pass rate. When the zoom magnification rate is 100%, the printing pass rate is 97.3%; when the zoom magnification rate is 90%, the printing pass rate is 95.7%; when the zoom magnification rate is 85%, the printing pass rate 25%; when the zoom ratio is less than 80%, the printing pass rate is only 10%. Therefore, zoom printing is best done by the provider of the bar code film.
(2) Color matching. As the barcode reading system stipulates that the general scanner light source is a red light source with a wavelength of 630 to 700 nm, the red light effect of the ink color should be considered.
The incident light of the scanner illuminates the surface of barcodes of different colors, and different reflections will occur. Black ink can completely absorb red light, and the reflectivity of the printed product to the incident light is below 3%, which is the most safe and ideal bar code color; white ink will completely reflect the red light, and the reflectivity of the printed product to the incident light is close to 100 % Is the safest blank color, so bar codes are generally printed in black and white. However, in packaging and printing, in order to increase its decorativeness, other colors are often used to match the empty space. At this time, it is necessary to pay attention to the appropriate combination of colors according to the red light effect. Yellow, orange, red and other colors have high reflectance to red light, and green and purple have low reflectance to red light. As long as it can meet any color matching of bar code requirements for reflectivity, scanning density and PCS value of printing contrast, it is a reasonable bar code printing color design.
(3) Requirements for substrates. In terms of optical characteristics, in order to ensure that the scanning light source is incident at 45 ° and reflected at 15 °, the substrate needs to have good light dispersion characteristics. In terms of materials, paper substrates generally use the white base of the paper itself as empty white, and have certain requirements for the whiteness, opacity, and gloss of the paper. The whiteness requirement is to make the paper surface have better reflectivity; the opacity is required to prevent the incident light from passing through the back of the paper and the light signal is reduced, resulting in a decrease in reflectivity; the lower gloss is required to reduce the incident light Specular reflection effect. For transparent or translucent print carriers, the same color as their packaging content (especially liquid content) should be prohibited as a bar color to avoid the content color deepening the empty color, making the empty color closer to the bar color, and reducing the PCS value.
In practical applications, this problem is often ignored: for example, when printing a white space, dark blue or dark green barcode on a blue or green liquid transparent packaging, the blue and green content will make the white space appear light blue or light green; in black Barcodes of white spaces and black bars are printed on the transparent packaging of watermelon seeds. The black content will make the white spaces light gray. At this time, the concentration of the printing ink on the white base should be deepened so that the color of the content will not leak out from the base color, or the color combination should be changed to avoid the above phenomenon. When the packaging decoration color conflicts with the bar code design color, the bar code design shall prevail and the packaging decoration design color shall be modified. When the carrier leaks light, the following measures should be taken: develop a base color with the same color as the empty color, large enough area, and sufficient ink to specifically print the barcode; if the barcode is printed on the plastic film seal and there is a decorative part on the back, it should be sealed An opaque interlayer is sandwiched between the two layers to ensure that the color of the back decoration does not affect the PCS value of the barcode. When using reflective materials such as aluminum foil as a carrier, you can roughen the body color or cover a layer of white, yellow, orange and red as the basic color, and use black, dark blue, dark green, and dark brown as the bar code; you can also reflect the material body. The bar code is printed with white, yellow, orange, and red as the empty color, which is called reverse white printing. The principle of reverse printing is still based on this color design to meet the corresponding values ​​of the reflectivity, reflection density and PCS of the specified bar and space. For the requirements of dimensional stability of printing materials, materials with good weather resistance, stable dimensions, good coloring, moderate ink expansion, small permeability, moderate smoothness and smoothness should be selected. Coated paper, offset paper, whiteboard paper in paper, biaxially oriented polypropylene film in plastic, aluminum foil in metal, and tinplate are all good printing materials for bar code signs. Corrugated cardboard, which is often used in large packaging, may cause large printing errors due to insufficient surface smoothness and uneven ink permeability. Therefore, except for EAN, UPC and ITF codes with large magnification, they are generally not directly used as substrates Instead, it uses the method of affixing printed labels. Non-polar group polypropylene film with poor coloring power and woven tape with poor dimensional stability cannot be used as the substrate for bar code marking.
(4) Requirements for ink. When matching ink colors, the color shift of the ink should be considered. The color deviation of the ink greatly affects the accuracy of the barcode. In theory, as long as the ink is used according to the color ratio, the barcode requirements can be met, but due to the imperfect hue of the printing ink, the color cast phenomenon will occur, such as the blue ink due to the wrong absorption of red light, will cause the red light The reflectivity of the barcode increases, reducing the PCS value of the barcode. Therefore, the color of the ink should be strictly controlled to make the ink density uniform, hue saturated, and high purity. It is best to determine whether the reflectivity of a certain ink under red light meets the requirements before printing the magnetic barcode.
The reflectivity and glossiness of metallic inks (such as gold) can cause specular reflection effects and cannot be used for bar code printing. Since the barcode printing is solid printing, the reflection density that can be achieved is related to the optical characteristics of the ink and the thickness of the ink layer. During the printing process, the reflection density of the printed product increases with the increase of the ink thickness. When the ink thickness reaches a certain value , The density will reach saturation, so pay special attention to the ink concentration and ink layer thickness. Different printing processes have large differences in the thickness of the ink layer, offset printing is 2 ~ 4μm, relief printing 8μm, flexographic printing 10μm, gravure printing 12μm, screen printing can reach 30μm.
According to the test, it can be calculated that the solid reflection density of the printed products obtained by the above printing types can reach more than 0.3, and the black, cyan, blue, green and other colors can all absorb red light. The rate can meet the requirements. The ink viscosity for bar code printing should not be too large, and pay attention to the ink supply and printing pressure during printing. The ink supply is large, the substrate can not be completely absorbed in a short time, and will spread on the surface of the substrate, which will reduce the accuracy; the ink supply is small, the lines are not full or even broken; the printing pressure is too large, the ink shear stress Increased, the fluidity will also increase, on the one hand will cause the spread of ink, on the other hand, the platen cylinder and the platen between the impression area becomes wider, will also cause the bar code bar code wider. These will affect the accuracy of barcode printing, so according to different printing methods, different ink rheology and ink absorption performance of the printing material, adjust and control ink supply, printing pressure, printing speed and other factors.
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