Problems needing attention in the most popular scr

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In packaging and anti-counterfeiting printing, bar code labels can facilitate users to quickly read general information of goods and have certain anti-counterfeiting functions, which plays a great role in improving commodity sales management and commodity anti-counterfeiting security. Although it can not provide detailed information about commodity production, quality assurance, management, etc., and the anti-counterfeiting effect is not ideal, and it has the trend of being gradually replaced by RFID (radio frequency identification tag), because bar code has many advantages, such as small equipment investment, convenient printing and production, wide range of use and so on, it still occupies a large area of rivers and mountains, especially in the ordinary commodity packaging with low anti-counterfeiting requirements. Bar code printing can adopt a variety of printing methods. Now let's talk about the technical requirements of bar code printing and some problems that should be paid attention to in plate printing

I. the function of bar code and its application in packaging and printing

bar code is an automatic identification information code. Because of its high data collection rate, strong reliability and low cost, it is widely used in many books, stickers, commodities and packaging. Bar code is a computer graphics language composed of lines and number symbols with a certain length and width, which can be read by photoelectric scanning reading device. Bar code is a kind of data input technology and automatic identification technology researched and developed in recent decades. It can reflect many information such as the type of business, manufacturer, weight, amount, date of manufacture and circulation. It plays an important role in the production, sales, storage, inspection and exchange of goods. It is a link between manufacturers, exporters, sellers and customers all over the world

at present, the barcodes seen in the market are all early one-dimensional barcodes. With the development of VLSI technology, aiming at the shortcomings of small information capacity of one-dimensional barcodes and reducing the area of barcodes to improve the ability to resist pollution, two-dimensional barcodes (2-D code for short) have been developed to make the area of barcodes smaller and smaller, and the function of bar code readers has also been greatly improved, making the reading more precise and accurate, The storage space of barcode is increased. In addition, encryption technology can also be used in the two-dimensional bar code, which greatly improves the anti-counterfeiting performance of commodities. According to different structures, two-dimensional bar codes can be divided into stacked and matrix types. In printing, it can not only print black words on white paper, but also print in color. It is not restricted to the printing machine and printing object. The reading of data can be from line to surface or even rotate 360 °, and the fault correction function can be adopted, which can restore and recognize the stained or damaged bar code. The misreading rate is a few 610 million. The two-dimensional bar code also has large storage capacity, strong damage resistance, high security, fax and photocopying, good data concealment Information goes with products

with the development of science and technology, a variety of new barcodes have been developed, such as invisible barcodes (including covert invisible barcodes, invisible ink and photochemical invisible barcodes), metal barcodes, watermark magnetic codes, etc., which have improved the depth and breadth of barcode applications

II. Technical requirements of bar code

the original negative of bar code printing must be registered, compiled and distributed through international or national coding centers. To make the bar code can be correctly recognized by the bar code recognizer, the bar code lines are required to be straight without breaking, the edges of the lines should be smooth and sharp without sawtooth, 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 mainly include: (1) size scaling. The bar code is usually printed directly from the original size, and the enlargement or reduction printing should be carried out according to the technical requirements of the ean organization. It is not allowed to be carried out at will. Generally, it is stipulated that the zoom ratio should be controlled at 80% ~ 200%. The bar code scaling rate has a great impact on the printing qualification rate. When the scaling factor is 100%, the printing qualification rate is 97.3%; When the zoom ratio is 90%, the printing qualification rate is 95.7%; When the zoom ratio is 85%, the printing qualification rate is 25%; When the zoom ratio is less than 80%, the printing qualification rate is only 10%. Therefore, scaling printing is best completed by the provider of bar code film

(2) color matching. Since the barcode reading system stipulates that the general scanner light source is a red light source with a wavelength of 630 ~ 700nm, the red light effect of ink should be considered. When the incident light of the scanner irradiates the bar code surface of different colors, different effects of reflection will occur. Black ink can completely absorb red light, and the reflectivity of the printed matter to the incident light is less than 3%, which is the most safe and ideal bar code color; White ink 2:4 will be used, and it will completely reflect the red light. The reflectivity of its print to the incident light is close to 100%, which is the safest blank color. Therefore, bar codes are generally printed in black and white monochrome. However, in packaging and printing, in order to increase its decoration, other color strips are often selected for empty matching. At this time, we should pay attention to selecting the appropriate matching according to the red light effect of the color, and pay attention to whether there is scratch matching. There are yellow, orange, red and other colors with high reflectivity to red light, and green, purple and other colors with low reflectivity to red light. As long as any color matching that can meet the requirements of bar code for reflectivity, scanning density and its printing contrast P C s value is a reasonable bar code printing color design

(3) requirements for substrate. In terms of optical characteristics, in order to ensure the 45 ° incidence and 15 ° reflection of the scanning light source, the substrate is required to have good astigmatism characteristics. In terms of materials, paper substrates are generally empty white on the white substrate of the paper itself, which has certain requirements for the whiteness, opacity and gloss of the paper. The whiteness requirement is to make the paper surface have better reflection ability; The requirement of opacity is to prevent the incident light from passing through the back of the paper to reduce the optical signal, resulting in reduced reflectivity; The requirement of low gloss is to reduce the specular reflection effect of incident light. For transparent or translucent printing carriers, the same color as its packaging contents (especially liquid contents) should be banned as the strip color, so as to avoid the color of the contents deepening the color of the empty space, making the empty color close to the strip color and reducing the P C s value

in practical application, this problem is often ignored: for example, if white space, dark blue or dark green bar codes are printed on the transparent package of blue or green liquid, the contents of blue and green will make the white space light blue or light green; Print the bar code of white space and black bar on the transparent package of black watermelon seeds, and the black content will make the white space light gray. At this time, the concentration of the printing ink on the white substrate should be deepened so that the color of the content will not be revealed from the primary color, or the color matching should be changed to avoid the above phenomenon. When there is a conflict between the packaging design color and the barcode design color, the barcode design shall prevail and the packaging design color shall be modified. When the carrier leaks light and transmits color, the following measures should be taken: develop a base color with the same color as the empty color, large enough area and thick enough ink to specially print bar codes; If the bar code is printed on the plastic film seal and there is decoration on the back, an opaque interlayer should be sandwiched between the two layers of the seal to ensure that the decoration color on the back does not affect the P C s value of the bar code. When using reflective materials such as aluminum foil as the carrier, you can roughen the body color or cover a layer of white, yellow and orange red as the blank color, and print the bar code with black, dark blue, dark green and dark brown as the bar color; It can also print bar codes with white, yellow, orange and red as blank colors, which is called anti white printing. The principle of anti white printing is still based on the fact that this color design can meet the specified reflectivity, reflection density and the corresponding value of P C s. For the requirements of dimensional stability of printing materials, materials with good weather resistance, stable size after stress, good coloring, moderate ink expansion, small permeability, moderate smoothness and smoothness should be selected. Coated paper, offset paper and whiteboard in paper, biaxially oriented polypropylene film in plastic, aluminum foil and tinplate in metal are all substrates with good bar code marks. The corrugated board often used in large packaging may cause large printing errors due to its uneven surface and different ink permeability. Therefore, in addition to the large magnification ean, UPC and ITF codes, it is generally not directly used as a substrate, but by pasting and printing labels. The coloring Industrial Park focuses on the construction of five platforms: public testing services, raw material trading and distribution, entrepreneurship incubation services, industrial training services, and public information services for the plastic industry. Polypropylene films with poor force and non-polar groups and woven tapes with poor dimensional stability cannot be used as substrates for bar code marks

(4) requirements for ink. In the ink color matching, we should consider the color deviation of the ink. The color deviation of ink has a great influence on the accuracy of bar code. Theoretically, as long as the ink is used according to the color ratio, the bar code requirements can be met. However, due to the defect of printing ink with impure hue, color deviation will occur. For example, due to the wrong absorption of red light by blue ink, the reflectivity under red light will increase and the P C s value of bar code will be reduced. Therefore, the ink color should be strictly controlled to make the ink density uniform, hue saturated and high purity. It is best to determine whether the reflectivity of some ink under red light meets the requirements before printing magnetic bar code

the reflectance and gloss of metal inks (such as gold) will cause specular reflection effect, so they cannot be used for bar code printing. As bar code printing is field printing, the reflection density it can achieve 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 matter increases with the increase of the ink thickness. When the ink thickness reaches a certain value, the density will reach saturation. Therefore, special attention should be paid to the ink concentration and the thickness of the ink layer. The thickness of ink layer varies greatly with different printing processes. Offset printing is 2 ~ 4 μ m. Embossing 8 μ m. Flexo 10 μ m. Gravure 12 μ m. Printing can reach 30 μ m 。

according to the test, the field reflection density of the prints obtained from the above printing types can reach more than 0.3. In addition, black, blue, green and other colors can absorb all red light, so the reflectivity of bar code colors printed by the above printing processes can meet the requirements. The viscosity of the ink used for bar code printing should not be too large, and attention should be paid to the ink supply and printing pressure during printing. The ink supply is large, and the substrate cannot be fully absorbed in a short time, which will spread on the surface of the substrate, reducing the accuracy; The ink supply is small, and the lines are not full or even broken; If the printing pressure is too high, the shear stress of the ink will increase, and the fluidity will also increase. On the one hand, it will cause the ink to spread. On the other hand, the embossing area between the plate cylinder and the embossing cylinder will become wider, which will also cause the bar code to become wider. These will affect the accuracy of bar code printing, so we should adjust and control the ink supply, printing pressure, printing speed and other factors according to different printing methods, the rheology of different inks and the ink absorption performance of printing materials

III. quality requirements for bar code printing

bar code symbols are read by computers, which requires them to have high printing quality. The main influencing factors include printing methods (including contact printing and non-contact printing), printing equipment (including inkjet printing, lithography printing, thermal stress printing, printing printing printing, etc.), printing location (including on-site printing and off-site printing), etc. There are many devices that can complete barcode on-site printing, and most of them use computing

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