Bar code printing knowledge

Bar codes are also called line codes and barcodes. It is a general merchandise packaging label and can be said to be the identity of a product. Through it can reflect a lot of information, play an important role in the production of goods, sales, storage and inspection and communication information. Barcodes are widely used in trademarks, packaging, books, and other products to become a link for communication. Therefore, it is of great importance to understand and master some of the knowledge of bar code printing and use and to improve the printing quality of bar codes. 

First, the structure of the bar code and the principle of recognition

The bar code is composed of a set of unequal widths, black and white parallel lines combined according to a specific format and spacing, usually printed on merchandise or printed matter, can replace various textual information, and can be read at any time through the optical renewal device. data. The EAN barcode system consists of a bar code that conforms to itself, a bar code recognition device, an interface, and a computer to complete the input and output of product information. There are two kinds of coincidences for barcode reading. Bar code symbols are rectangular line patterns. The information read by an optical scanner mainly reads and recognizes these barcode symbols. Digital symbols are numbers and letters outside the line, including 0 to 9 digits, A to Z letters, which can be directly recognized by the naked eye, generally from 8 to 16 digits, with different codes and different digits. The arrangement, width, and number of lines of the bar code are stipulated by each manufacturer and determine the meaning of the code. Generally, there are marks at the beginning and end of reading on both ends, and some are printed on the underside of the line, which can be directly identified or interpreted by an optical character reader, and thus can also count, count, and manage products. 

The reading performance of the barcode system, that is to say whether the barcode system can be used normally depends on the reading ability of the system and the printing quality of the barcode. Bar code, as a kind of coded information, is a specific language that people and computers communicate with each other. The black and white lines in the bar code are consistent with each other. The thick black line represents 1 in the computer, and the thin black line represents 0. Through logic conversion, it can be represented as 0 to 9 Arabic numerals and arrays. Therefore, a reading device must be provided. Use it to read. The reading system mainly includes a scanner and a decoder. The scanner is a part that directly contacts the bar code reading signal. It consists of a light emitter, a photo detector, and an optical lens. It can read the information abbreviated by the bar code at an extremely fast speed. During scanning, when the light beam emitted from the light emitter shines on the bar code, the photo detector responds according to the light intensity of the light beam reflected from the bar code when the scanning light spot is swept to the white paper surface or is in two black lines. When there is a gap between them, the reflected light is strong and the detector outputs a large current; when scanning into a black line, the reflected light is weak, the detector outputs a small current, and the response is made according to the width or width of the black line for different lengths of time. As the light and dark changes in the bar code are converted into current signals of different sizes, they are amplified and sent to the decoder. The signal is translated into data by the decoder, local inspection and display, and connected to the keyboard and sent to the computer for data processing. Therefore, the bar code printing quality is related to the ability to read normally. The ink is uniform and uniform, the layout is not dirty, the lines are clear without breaking, and it is the basic quality requirement for bar code printing. 

Second, the bar code printing and its problems should be noted

There are two kinds of bar code printing methods. First, printing equipment is used for batch printing and compounding, which is a commercial bar code label production. In this way, barcodes and patterns are generally printed together. The second is computer-controlled printing of bar code labels and bar code files. The former applies to a large number of barcodes with the same specifications and the same content, and is designed and printed at the same time as the packaging graphic. The latter can be controlled by computers, real-time printing as required, with greater flexibility. The barcode printing equipment includes inkjet printers, thermal printers, thermal transfer printers, impact printers, and laser printers. In order to ensure that the printed bar code meets the design specifications, the plate making process should be considered according to the printing process and the characteristics of the substrate. For example, in the flexographic printing process, the line width may be appropriately reduced in making a plate to compensate for the extended deviation in printing. For the printed heat-shrinkable packaging material, the position of the barcode after shrinking the film should be considered, and the vertical and horizontal shrinkage factors should be calculated in advance so that the adjustment can be made during the plate making. 

In order to facilitate normal reading, attention should be paid to the color matching of barcodes. Bar code reading system, set the scanner light source is generally a red light source with a wavelength of 630 ~ 700nm, it should consider the red effect of ink. The scanner's incident light shines on the surface of the bar code of different materials and colors, and the reflected effect is also different. Black ink can be completely absorbed by red light. The reflectance of incident light on printed materials is generally below 3%. Therefore, most bar codes are designed to be printed in black ink colors. The white ink is completely reflective to red light, and its reflectance of incident light is close to 100%. Therefore, it is the ideal blank color. For the above reasons, most of the bar codes on printed products are printed on white paper. However, some packaging products, starting from the decorative effect, there are other colors to choose, so you should pay attention to match the nature of the color. Usually, red, yellow, orange, red, and brown are the colors with high red reflectivity. The black, green, purple, and cyan colors have low reflectance to red light. Reasonably designing the bar code printing color should fully consider the factors such as the reflectivity of the red light. Under the transparent film packaging, it is appropriate to directly print the barcode. It should be printed with white ink, yellow or orange red as the substrate, and then printed with a dark bar code, such as black, dark green, dark blue, etc., which is easy to read and use. 

Third, the bar code printing process requirements

1 ink request. 
The color matching of the ink should fully consider the color cast of the ink, and the color cast of the ink has a great influence on the accuracy of the barcode. Theoretically speaking, as long as the ink is used according to the color matching ratio, the requirements for barcode printing can be satisfied. However, due to defects in the printing ink that have a coloring phase, the color cast occurs. Therefore, the color of the ink should be accurately controlled so that the ink density is uniform, the hue is saturated, and the purity is high. It is preferable to determine whether the reflectance of a certain ink under red light meets the requirements before printing the barcode. The reflective and glossy properties of gold ink can cause specular reflection effects that affect scanner readability and therefore cannot be used to print bar codes. In addition, the concentration of the ink and the thickness of the ink layer should also be suitable for the bar code printing requirements. Since the bar code printing is a solid printing, the reflection density that can be achieved by the total printing is related to the optical characteristics of the ink and the ink layer thickness. During the printing process, the printed reflection density increases with the increase of the thickness of the ink. When the thickness of the ink reaches a certain value, the density reaches saturation. The general ink saturation density requirements are: ink ink 1.8 to 2.0; cyan ink 1.45 to 1.70; magenta ink 1.25 to 1.50; yellow ink 0.90 to 1.05; other spot inks are 0.8 or more. Due to the difference in the printing process, the thickness of the printed ink layer is also different, generally offset printing is 2 ~ 4μm; embossed printing is 2μm; flexographic printing is 10μm; gravure printing is 12μm; screen printing is 30μm. 

2  The requirements for the substrate. 

Since the scanning light source is incident at an angle of 45° and the collection angle of the reflected light is 15° due to the barcode reading, when the reflected light exceeds the range of 15°, the reflected light signal cannot be collected, which is equivalent to the black effect. Therefore, in order to satisfy the characteristics of bar code scanning, substrates are required to have good light scattering properties and specular reflection cannot occur. Therefore, the paper's whiteness, opacity, and glossiness have a certain influence on the reading of bar codes. In addition, consideration should also be given to materials that have good weatherability, dimensional stability after stress, good colorability, low ink permeability, moderate smoothness, and good finish. 

3 print quality requirements. 

The bar code symbol is the source of information for scanning and reading. In order to ensure correct reading, the printed bar code should be neat and clear, the symbol should not be obviously incomplete, and there should be no dirty ink in the blank space. In order to ensure the correct reading of the barcode, the maximum diameter of the defects and stains on the barcode should be less than or equal to 0.4 times the standard width of the narrowest line code. The line and space in the printed bar code should have obvious contrast signals. The reflectance of the blank should be as large as possible, and the reflectance of the bar should be as small as possible. The larger the PCS value (color contrast), the contrast signal of the bar code. The bigger the reading performance, the better. 

4  printing position requirements. 

The position of bar code symbol shall be determined in accordance with the principles of non-deformation, easy reading and plate making. That is, it is required to be set on the right side of the main display surface of the package or on the plane where the main display surface is connected, and on the back side of the main display surface of the package. Taking into account the printing process characteristics, the bar code direction should be made to correspond with the printing direction, so that the printing distortion can only be expressed in the bar code longitudinal position, so as not to affect the accurate reading. Due to the difference in packaging methods and characteristics, the bar code printing position is also different. General box packaging bar code printed on the right side of the bottom of the box; canned and bottled packaging bar code is best printed on one side of the label below, but the bar code symbol surface curvature can not exceed 30 °; barrel-shaped packaging bar code is best printed in the barrel Side, if the side can not be printed, the bar code can be printed on the lid, but the depth of the lid can not exceed 13mm; bag-shaped package with a bottom and the bottom is larger, the bar code can be printed on the bottom or printed on the back of the lower center; The bar code is usually printed on the bottom left corner of the back cover or the cover, and the direction of the bar is parallel to the spine.

综 In summary, bar code, as a data input technology and automatic identification technology, is widely used in the packaging of goods. It plays an important role in the production, sales, storage and inspection of communication information. Therefore, correctly understanding and understanding the bar code knowledge and printing the bar code is an important part of packaging and printing.