Discussion on the requirements of bar code printing for printing technology
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The original negative of the printed bar code must be registered and registered by the International or National Code Center. In order for the barcode to be correctly recognized by the barcode reader, the barcode is required to be straight and cannot be broken. The edge of the line should be smooth and sharp, and the sawtooth should not appear. The distance between the lines is in line with the standard, the line blackness is sufficient, and the contrast is large. The technical requirements for barcodes are mainly:
1, size and zoom
The bar code is usually printed directly from the original large size, and the printing to be enlarged or reduced is not subject to the technical requirements of the EAN organization. It is generally stipulated that the zoom ratio should be controlled at 80% to 200%. The barcode scaling rate has a great influence on the printing pass rate. When the zoom ratio is 100%, the printing pass rate is 97.3%; when the zoom ratio is 90%, the print pass rate is 95.7%; when the zoom ratio is 85%, the print pass rate is It is 25%; when the zoom ratio is less than 80%, the printing pass rate is only 10%. Therefore, the scaled printing is preferably done by the supply mechanism of the barcode film.
2, color matching
Since the bar code reading system stipulates that the general scanner light source is a red light source having a wavelength of 630 to 700 nm, the red light effect of the ink color should be considered.
The incident light from the scanner is illuminated on the surface of the bar of different colors, and different effects are reflected. Black ink can completely absorb red light, and the reflectivity of printed matter to incident light is below 3%, which is the safest and ideal bar code color; white ink will completely reflect red light, and the reflectivity of printed matter to incident light is close to 100. % is the safest blank color, so barcodes are usually printed in black and white. However, in packaging printing, in order to increase the decorativeness, it is often preferred to choose other colors and strips. At this time, it is necessary to pay attention to the appropriate matching according to the red light effect of the color. For red light, the reflectance is high, such as yellow, orange, and red. For red light, the reflectance is low, such as green or purple. Any color matching that satisfies the bar code's requirements for reflectivity, sweep density, and its printed contrast PCS value is a reasonable bar code printing color design.
3， requirements for substrates
In terms of optical characteristics, in order to ensure a 45° angle incidence and a 15° reflection of the scanning light source, the substrate is required to have good light dispersion characteristics. In terms of materials, paper substrates generally have a white color on the white base of the paper itself, and have certain requirements on the whiteness, opacity and gloss of the paper. The whiteness requirement is to make the paper surface have better reflection ability; the opacity is required to prevent the incident light from passing through the back side of the paper to reduce the light signal, resulting in a decrease in reflectance; the lower gloss is required to reduce the incident light. Specular reflection effect. For transparent or translucent printed carriers, the same color as the contents of the package (especially liquid contents) should be disabled as a strip color to avoid darkening the color of the contents, bringing the empty color closer to the strip and lowering the PCS value.
This problem is often overlooked in practical applications: printing white open space, dark blue or dark green barcodes on blue or green liquid transparent packaging, blue and green contents will make the white open space pale blue or light green; in black The transparent packaging of the watermelon seeds prints a bar code of white open space and black bars, and the black contents will make the white open space light gray. At this time, the concentration of the white base printing ink should be deepened so that the color of the contents does not pass through the base color, or the color matching is changed to avoid the above phenomenon. When the color of the packaging decoration design conflicts with the color of the barcode design, the color of the packaging design should be modified according to the barcode design. When the carrier leaks light, the following measures should be taken: a color code with the same color, large enough area, and sufficient ink to be printed is specially printed; if the barcode is printed on the plastic film seal and the back part has a decorative part, it should be sealed. The two layers are sandwiched by an opaque interlayer to ensure that the backside decor color does not affect the barcode PCS value. When a reflective material such as aluminum foil is used as the carrier, the color of the body or the base color of a layer of white, yellow and orange is covered with an empty color, and the bar code is printed in black, dark blue, dark green or dark brown; or the reflective material body For the strip color, the bar code is printed in white, yellow, orange, and red, which is called reverse white printing. The principle of reverse white printing is still based on this color design to meet the specified strip and space reflectivity, reflection density and PCS corresponding values. For the dimensional stability requirements of the printing material, materials with good weather resistance, stable size, good coloration, moderate ink expansion, low 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 substrates for bar code marks. The corrugated cardboard used in large packaging is not flat enough and the ink permeability is different, which may cause large printing errors. Therefore, in addition to the large-rate EAN, UPC and ITF codes, it is generally not directly used as a substrate. Instead, it uses a paste-and-print label. A non-polar group polypropylene film having poor coloring power and a woven tape having poor dimensional stability cannot be used as a substrate for a bar code mark.
4, the requirements of the ink
When the ink color is matched, the color shift of the ink should be considered. The color shift of the ink has a great influence on the accuracy of the barcode. In theory, as long as the ink is used according to the color ratio, the bar code can be satisfied. However, due to the defect of the hue of the printing ink, the color cast phenomenon may occur. For example, the blue ink may cause red light due to the wrong absorption of red light. The reflectivity increases, reducing the PCS value of the barcode. Therefore, the ink color should be strictly controlled to make the ink density uniform, the hue is saturated, and the purity is high. It is better to determine whether the reflectance of an ink under red light meets the requirements before printing the magnetic barcode.
The glare and gloss of metallic inks such as gold can cause specular reflection and cannot be used for bar code printing. Since the bar code printing is solid printing, the reflection density that can be achieved by printing 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 printing product increases as the thickness of the ink increases, and when the thickness of the ink reaches a certain value, The density is saturated, so pay special attention to the ink concentration and the thickness of the ink layer. Different printing processes, the thickness of the ink layer is quite different, offset printing is 2 ~ 4μm, embossing is 8μm, flexo printing is 10μm, gravure printing is 12μm, and screen printing can reach 30μm.
According to the test, the printed density of the printed materials obtained above can reach 0.3 or more, and the black, cyan, blue, green and other colors can all absorb red light. Therefore, the bar code color and reflection are printed by using the above several printing processes. The rate can meet the requirements. The viscosity of the ink for bar code printing should not be too large, and attention should be paid to the amount of ink supplied and the 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, so that the precision is reduced; the ink supply is small, the lines are not full or even broken; the printing pressure is too large, the ink shear stress When the volume is increased, the fluidity is also increased. On the one hand, the ink is spread. On the other hand, the embossing area between the plate cylinder and the impression cylinder is widened, and the bar code is widened. These will affect the accuracy of bar code printing, so it is necessary to adjust the control of ink supply, printing pressure, printing speed and other factors according to different printing methods, rheology of different inks and ink absorption performance of printing materials.