Discussion on bar code printing technology of the

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Discussion on bar code printing technology of plastic packaging

bar code technology is an automatic recognition technology produced and developed in the practice of computer application. Since its emergence in the 1960s, it has shown strong vitality and developed extremely rapidly. After more than 30 years of continuous improvement and development, it has been widely used in many fields such as commodity circulation. So far, more than 60000 enterprises in China have been approved to use commodity bar codes, and about 500000 kinds of commodity projects have adopted commercial bar codes. There are thousands of chain stores, storage supermarkets and distribution centers that use product packaging bar code technology for commercial automation management

bar code printing technology is one of the important contents of bar code technology. With the extensive use of bar code technology in food and daily chemical products in China, the plastic packaging manufacturers supporting it must adapt to the development of this situation. According to relevant departments, there are many unqualified barcode printing phenomena in the market at present. Barcodes that fail to meet the quality requirements not only cannot improve the management efficiency, but will cause confusion (large foreign retailers have clear punishment measures for the quality problems of suppliers' barcodes). Therefore, in-depth study of plastic packaging bar code printing technology is very necessary. This paper makes a preliminary discussion on some issues and communicates with peers

I. The main technical indicators of bar code printing

the specific standards of bar codes have been specified in detail in the national standard gb12904-91. The printing technical indicators mainly include three aspects: width tolerance; Appearance (including stains, pores, edge roughness, etc.); Reflectivity and contrast

1. Width tolerance

because bar codes use bars and spaces of different widths to represent information, if the printing error of the width of bars and spaces is not strictly controlled, the width of wide and narrow bars (spaces) may be close to or narrow to almost disappear. This will make the bar code symbol unreadable or cause a large number of errors. Therefore, the width size of bar and space and the sum of bar and width accuracy are the key to ensure that the decoder can receive the correct waveform and complete the decoding correctly

bar code width tolerance mainly includes bar space width tolerance, width tolerance from edge to similar edge, and character width tolerance. It describes the allowable error range of bar and space width in printing. If it is beyond this range, the reading effect will be affected

2. Appearance

(1) whether the surface has defects such as damage, fracture, perforation, coating, etc

(2) whether there are dirt, ink lines, uneven inking and other phenomena on the surface

(3) whether it is too close to other patterns or there is overlapping printing

(4) stain, porosity and edge roughness

in the process of bar code printing, for some reason, sometimes there is ink in the air of bar code symbol or uneven inking in the bar, resulting in pores (deinking). The bar code is allowed to have any number of stains and pores (deinking), but the following conditions should be met:

① its area should not exceed 25% of the circular area with a diameter of 0.8x

② its area does not completely cover the area of a circle with a diameter of 0.4x

where x is the width of the narrowest cell

the requirement of edge roughness is that the elements on all possible scanning tracks can meet the requirements of printing dimensional tolerance

3. reflectance and contrast

contrast (PCS) refers to the ratio of the difference between the reflectance of space and strip to the reflectance of space. Reflectance and contrast (PCS) values shall comply with corresponding regulations

II. Problems that should be paid attention to in the process of bar code printing

according to the above technical requirements of bar code printing, the following is an analysis of the problems that should be paid attention to in the process of printing and processing, involving design, plate making, printing, compounding, packaging and other aspects

(-) design

1. Bar code position design

bar code position should be considered based on the actual position after loading into the physical object (at the same time, the bar code of transparent outer packaging cannot be displayed at the same time with the bar code on a single retail commodity inside), and whether its design is reasonable or not will directly affect the actual reading effect. For bread, candy, bagged food, etc., the barcode position should generally be selected in the following order: bottom, back, side, but not in the position of bending, partition and corner. For cylindrical, three side sealed and back sealed bags, generally choose the back and pay attention to avoiding the heat sealed parts and empty parts; For pillow shaped packaging bags, the actual position after packaging should be determined to avoid being in the corner position. For bar codes on curved surfaces, the surface curvature shall not exceed 30 °

2. Size design

bar code size refers to the size of the left and right blank areas of bar code symbols. Generally, the bar code magnification factor is directly proportional to the size deviation of the ultra light carbon fiber composite material allowed by the bar code printing. The magnification is generally controlled between 0.8-2

in order to ensure the correct reading of the bar code, a certain width of blank area should be left on the left and right of the bar code. The size of the blank area varies according to the type of bar code, which is at least 10 times the minimum bar width. According to gb12904-91 "general commodity bar code", when the magnification factor is 1.0, the minimum width of the left and right blank areas of the bar code is 3.63mm and 2.31mm respectively. In order to obtain the best scanning effect, the size of the left and right blank areas should generally not be less than 5mm wide

in order to ensure that the bar code reading success rate will not be affected due to the height of the bar code, the general bar code symbols shall not be truncated at will. If it is necessary to truncate it, it shall comply with the corresponding technical specifications

3. color design

a certain contrast must be guaranteed when designing colors. Different colors have different reflectivity to light. Black does not reflect visible light of various wavelengths, but white can reflect light of various wavelengths. Therefore, black bar and white space are the best design

at the same time, the influence of composite aluminum foil or aluminized film on hue should be considered. Aluminum foil belongs to specular reflection. For the code reader, the reflected light cannot be collected, and the reflectivity is the smallest. It can be used as a bar color. The blank color must be white, yellow, orange or red printed on the aluminum foil. This is called anti white printing. Some plastic packages do not print the background color (empty color) but only the bar color when printing bar codes, and use the color of the content itself as the empty color. This method should not be used, such as chili sauce packaging bags. If you use soy sauce as the empty color, the reflectivity is low, forming insufficient contrast, and affecting reading

the plastic film has a certain gloss. For the bar code printed in the composite, its gloss will change the reflectivity of the strip and space, causing the contrast change. Therefore, this factor should be considered in the color design, leaving a certain margin for the contrast

(II) plate making

in addition to the basic requirements, the following two points should be paid attention to when making bar code plate:

1 The original film with extremely high production accuracy shall be selected and adapted to the gravure printing process (the strip width correction of the film shall be adapted to the gravure printing process)

2. The wires at the positions are relatively deep and dense. If the tested wire and cable samples do not produce breakdown, it is a qualified product. This is because the ink amount is less if the line is shallow, which cannot ensure sufficient hiding power. Some light is transmitted and the reflectivity is reduced. If the line is too thin, it is easy to deform, and the edge of the printed strip is not neat, which is easy to cause difficulty in reading

(III) printing

bar code printing has higher requirements than ordinary plastic packaging printing. The following problems should be paid attention to in the printing process:

1 When bar codes and other patterns are printed at the same time, sometimes technical means such as ink thinning and scraper position adjustment need to be used to adjust the hue. At this time, priority should be given to the reading of bar codes. If you can't give consideration to both, you must remake the plate

2. The ink fastness and wear resistance of plastic film should be paid enough attention, especially for surface printing packaging. If the ink fastness and wear resistance are not good, it may cause ink falling off, bar code incomplete and other faults in the process of commodity circulation, resulting in unreadability

polyethylene and polypropylene are non-polar materials, which should be paid special attention

3. Ink should maintain a certain viscosity, viscosity should not be too small. If the viscosity is small, the ink has low covering power and low reflectivity. In particular, the contents are dark products, such as western specific requirements: melon seeds, pickles, soy sauce, Western sauce, etc. if the hiding power of the empty is low, the color of the contents will deepen the empty color, making the empty color close to the tan color, resulting in a reduction in contrast. Therefore, the viscosity of white ink (or other bottom color ink) should be increased to ensure sufficient hiding power

4. Choose high-quality ink to avoid ink deterioration. The ink should have a high transfer rate to ensure the density of the ink. In addition, the ink should also have sufficient high-temperature stability to prevent the color change of bar code in the process of compounding and post-processing

5. Strictly control the printing tension, drying temperature and other process conditions, and try to avoid the shrinkage change of size

(IV) compound

two points should be paid attention to in the process of compound

1. stretch. During the compounding process, if the temperature of the drying oven is too high or the tension is too large, the film stretching phenomenon will occur, resulting in the deformation of the bar code. Therefore, the temperature and various tensions of the drying oven must be strictly controlled to avoid stretching

2. if adhesive is added in the compounding process, the film must be prevented from wrinkling at the AC agent coating. Although the wrinkles can be adjusted and removed in front of the compounding head, because the adhesive contains solvent ethyl acetate, the ink in the bar code part may be dissolved and broken under the extrusion of the coating roller and the rubber pressing roller, thus affecting the reading effect

(V) packaging method

inflatable packaging is the same as ordinary packaging, and its appearance is relatively flat, so it has no other impact on bar code printing and reading, while certain attention should be paid to vacuum packaging and heat shrinkable packaging

1. Vacuum packaging, because the contents of the package are mostly in irregular shape, the packaging bag is tightly attached to the surface of the contents after vacuumizing, showing an irregular three-dimensional shape, and the surface is uneven, so that the barcode is deformed and cannot be read. Therefore, the inner bag of vacuum packaging should not be directly printed with barcode, but an outer bag can be added to print barcode and other graphics

2. Heat shrinkable packaging: for the heat shrinkable packaging film used in beverages and fruit milk bottles, when printing bar codes, we should first consider the position of the bar code after the film shrinks; Second, calculate the vertical and horizontal shrinkage times, and adjust the size of the bar code in advance during plate making; Third, we should choose high-quality heat shrinkable films with uniform shrinkage. At the same time, ensure that the strip space is on the same plane after thermal shrinkage of the film

III. common faults and solutions in bar code plastic gravure printing

the common faults introduced below are minor defects for packaging and printing other than bar codes if the fault is not serious. However, for bar code printing, even a slight defect will directly affect the reading effect, and measures must be taken to avoid it. Therefore, in a sense, it can be said that bar code printing is more stringent than other parts of the printing requirements

1. Knife line

when deciding whether to buy it, the so-called knife line refers to that the ink of the part without pattern lines on the layout is not scraped clean and transferred to the printed matter, and linear pollution occurs in the place where ink is not allowed (producing an ugly Silk Road). Generally speaking, this kind of failure will occur after printing for a period of time and a certain number of prints. Printing ink, printing plate roller and scraper are the three main factors that affect the printing knife line. Environmental printing conditions also have a certain impact on the printing knife line



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