First, the structure of the bar code and reading principle
The bar code is a set of symbols with different widths and widths and black and white parallel lines combined according to a specific format and spacing. Usually printed on goods or printed matter, it can replace various types of text information and can be read at any time through a photoelectric readout device. data. The EAN barcode system consists of a bar code symbol itself, a barcode reading device, an interface, and a computer, which completes the input and output of commodity information. There are two kinds of barcode reading symbols, bar code symbol for the rectangular line graphics, optical scanners to read the main information is to read and identify these bar code 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 bits to 16 bits, with different code systems and different numbers of 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 for people and computers to communicate with each other. Black and white line thickness in the bar code symbol, thick black lines in the computer as 1, thin black lines 0, through the logic conversion, can be expressed as 0-9 Arabic numerals and arrays, so there must be a reading device Use it together 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, and scans the light spot to the white paper surface or the two black lines. When there is a gap between the two, 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 according to the width of the black line, a response of different lengths of time is made, along with the bar code The light and dark changes into current signals of different sizes, which 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 attention to the problem
There are two kinds of bar code printing methods. First, the use of printing equipment for bulk printing and copying, is a commercial bar code label production, this way generally bar code and pattern together imposition printing. 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. Bar code printing devices include inkjet printers, thermal printers, thermal transfer printers, impact dot matrix printers, and laser printers. In order to ensure that the printed bar code meets the 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, it is considered that the line width can be appropriately reduced when making a plate, so as to compensate for the expanded 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 is completely absorbed by red light, and the reflectance of incident light on printed materials is generally below 3%. Therefore, most bar codes are designed to be printed with black ink. 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. Transparent film packaging is not suitable for direct printing of bar codes. It should be printed with white ink or yellow, 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 requirements
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 the printing can reach 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. General ink saturation density requirements: black ink 1.8 ~ 2.0; cyan ink 1.45 ~ 1.70; magenta ink 1.25 ~ 1.50; yellow ink 0.90 ~ 1.05; other special The color ink is 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 ~ 4Î¼m; embossing printing is 8Î¼m; flexographic printing is 10Î¼m; gravure printing is 12Î¼m; screen printing is 30Î¼m.
2. The requirements for the substrate.
Since the scanning light source is incident at an angle of 45Â° and the collection angle of the reflected light is 15Â° due to the barcode reading, when the reflected light exceeds the range of 15Â°, 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 white quality, opacity, and gloss of the paper have a certain influence on the reading of the barcode. 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 lines and spaces 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 line 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. Print 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 Â°; 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. In summary, barcodes are used as a kind of data input technology and automatic identification technology. They are widely used in the packaging of goods. They play an important role in the production, sales, storage, inspection and communication of goods. Therefore, correctly understanding and understanding the bar code knowledge and printing the bar code is an important part of packaging and printing.
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