How to check and control the printing quality of barcodes

With the vigorous development of the socialist market economy, bar codes are playing an increasingly important role in the sale and circulation of goods. In particular, the rapid development of computers and network technologies, bar codes are providing more and more convenience for the sale and management of goods. Fast, so grasping the type, application and quality control of barcodes is urgent and important for printing companies and manufacturers. The author summarizes some experiences and opinions on how to check and control the printing quality of barcodes.

First, the application of the bar code and printing method

As we all know, bar codes have been applied to almost all product packaging, some even directly printed on the product. The product packaging methods vary widely. There are paper products, plastic packaging, metal packaging, etc. The product shape and surface materials are also different, so the way of printing bar codes is also different. In fact, all printing methods can print barcodes, such as offset printing, letterpress/flexographic printing, gravure printing, screen printing, and inkjet printing. For bar code printing, different printing methods have different control methods, but the inspection methods are the same.

Second, the basic quality requirements of bar codes;

1. Exterior:

The bar code symbol is neat and clean, with no obvious dirt, wrinkles, damage or perforation.

• The numbers, letters, and special symbols in the bar code symbol are printed in a clear, unambiguous manner.

Bar code symbols have no significant deinking, smearing, or broken lines; the edges of the bar are neat, with no significant bending deformation.

• The ink color of the bar code symbol is uniform and there is no significant difference.

2. skills requirement:

In accordance with the bar code national standards adopted by the sample, for these technical requirements, the national bar code standard has detailed quantitative indicators. The specific items include:

Bar (empty) reflectivity, print contrast (PCS value / Print Contrast Signal):

PCS = (Rl-Rd)/Rl, where Rl represents the reflectivity of the bar code symbol, and Rd represents the reflectivity of the bar code symbol. In fact, most barcode readers (like QUICKCHECK 400, XAMINER 6500, etc.) can automatically calculate PCS values. If you want to calculate by yourself, you need to measure the reflectance of the null and bar separately with the bar code reading pen (demonstration equipment and operation method), and then substitute the above formula to obtain the PCS value. The PCS value needs to meet the technical specifications specified in the national standard GB12904-1998. . In principle, the color of the selection bar and the blank should be appropriate, and the bar and the empty reflection density value should be pulled as far as possible. The PCS value will not be a problem. So the main requirement of this item is to choose the right color at design time and control the color in the printing process.

• Bar (empty) size error, can be measured with a length measuring accuracy of more than 0.01mm. However, this is also a test project in the main design process. In the actual process if the bar or empty size is wrong, the bar code will not be readable. The national standard has strict regulations on the deviations of the original film and printed material. If necessary, relevant standards can be found. Now, special software has been used to generate bar codes automatically, like the MBC software of the Mac, so now the size of the bar and the space is not very common.

• The size of the Quiet Zone is quite common because it is sometimes easy for designers to ignore this requirement when space is limited. The measurement method is relatively simple, and a length measuring instrument with an accuracy of 0.5 mm can be used.

· The bar height refers to the bar height, which should not be less than the integer value of the standard bar high size. This item is more flexible, so the amount is relatively simple, but this item cannot be directly measured by the bar code reader. , so be careful when designing.

· Numbers and letters should use OCR B character set (GB/T12508). These human-readable characters or letters should be printed on the bottom of the bar code and correspond to the corresponding bar code character. Its size should comply with national standards and be in accordance with the bar code. The same magnification is enlarged or reduced. This item is also not directly measured by a bar code reader, so care must be taken when designing.

·Check codes can be checked according to the calculation method specified by the state.

• The correctness of the decoding, ie, the readability of the bar code, is very important and must be judged by means of a bar code reader.

• The magnification factor is the ratio of the length dimension of the bar code symbol to the standard size. The general magnification factor is 0.80-2.00, as long as a pair of standard bar code film is known.

• Printed thickness refers to the difference in thickness between bars and spaces in the bar code symbol. The difference must be less than 0.1 mm. In other words, the printing must be as even and smooth as possible, as long as the accuracy is 0.01 mm.

· The printing position should be visually measured according to the provisions of GB/T14257. The above technical specifications require the consideration of factors and inspection items in the design of the barcode.

Third, the common quality problems of bar code printing

Several of the items listed below are the most common quality problems in the printing process. The main reason for judging these problems is to rely on barcode readers. At present, there are many kinds of such instruments in foreign countries, and there are many functions, such as QUICK-CHECK 400 and XAMINER 6500 in the United States. Take the XAMINER 6500 as an example to explain how to check and control quality issues in bar code printing.

1. According to the function of the bar code, its main quality characteristic is its readability, readability is the ability to decode with a special bar code reader. In the ordinary printing process, the common problem is that the bar code is not readable, and the reasons come from many aspects. Normally, the barcode cannot be decoded because some characteristics of the barcode do not meet the specified requirements. In general, bar code readers have two modes of analysis, one of which is the ANSI (American National Standards Association) mode: This mode will bar code PCS value, ECMIN value (minimum edge contrast), DECODABLE (decoding), SC value ( Contrast, DECODABILITY, DEFECT, and so on are classified into Levels A, B, C, D, E, and F. If we set the level to be C (most customers use this level), The bar code reader will automatically calculate the average value of each measurement result or several measurement results (according to the instrument settings) to obtain the level of this bar code. If C or more like A and B are all readable. On the contrary, if one of the values ​​is lower than the C level, the total measurement will not pass. If the PCS value or ECMIN value or SC value is lower than C, it indicates that: 1 and/or empty colors are not matched; 2 colors are printed too shallow, such as water, small ink, and low pressure; 3 under color printing Too deep as water, heavy ink, heavy pressure, etc.; 4 parts printed too shallow like water, debris, etc. This kind of print quality problem is very easy to appear, especially because it is more difficult to predict such problems during design. Most of the barcodes are placed on the back or bottom, and in order to pursue the overall mounting effect, barcodes are always printed on the background or blanked out of a blank area. However, in order to save costs, the colors that are already on the screen are always selected, which makes it very easy to influence the PCS value of the bar code due to other colors. This requires experienced technicians to reduce this problem by appropriately adjusting the film or typesetting method.

If the DECODABLE value is lower than C, there is a problem with the encoding, such as a checksum error. However, if the DECODABILITY value is lower than C, it cannot be decoded. This is a comprehensive assessment. For example, the left and right blank areas are not enough. This problem is very common. Because some packaging formats are limited, this point is often overlooked, and some bar code readers can also decode, but the risk is too high, and some instruments will not be able to decode it. Check this method is very simple, as long as the two sides of the bar code covered with white paper, scan with a bar code reader can find whether the space is enough; bar code near other patterns or text, because the bar code reader may use these as bars or empty Processing can not be decoded. The design should pay attention to this issue; PCS or ECMIN value or SC value is lower than C; or defect level is lower than C; coding error; bar code size error, and so on. If the defect is lower than the C level, there are debris on the bar code, such as ink, ghosting, etc.

2. The dimensional error of the bar or space, ie, partial or thin. XAMINER also has a traditional pattern analysis (TRANDITIONA): check the size deviation of the bar and space, the most common in the printing process is due to the large amount of ink or pressure caused by partial fat, or in the film copy or copy caused by the bar The width changes. In many cases, the same factors as the previous PCS value failures are the same. For example, the amount of ink in the bar code is difficult to control due to the influence of other colors on the layout. Therefore, the designer should consider this factor in selecting the color and the layout of the production personnel. Generally divided into five levels: too narrow, narrow, normal, fat, too fat, too narrow and too fat will result in unreadable bar codes. The author once printed a kind of packing box whose bar code was printed with black bar code on the dark violet background. It was no problem from the viewpoint of color selection, but the dark violet was a four-color net superimposition, and black naturally influenced deep violet and black bar codes. It's easy to become fat. After a few failures, we narrow down the bar code and finally solve the thorny problem.

3. The encoding is wrong. It means that the bar code reader's digits or letters or symbols are different from those in the code. When measuring the bar code, it is necessary to carefully check whether the number read by the instrument is the same as the number on the bar code itself.

4. Deinking. It refers to the printing defect of the bar symbol in the bar code symbol, and its reflectance is similar to the empty reflectance. In fact, the PCS value is too low. If possible, use a bar code with a high color contrast ratio.

5. Stain. It refers to the printing defect in the hollow or blank area of ​​the bar code symbol, and its reflectance is similar to that of the bar. As for the appearance of common problems, due to the different bar code printing, the problems and causes presented are also different, and the technical personnel of the enterprise must look for different solutions according to different actual conditions.

The above inspection and control methods are based on the company's barcode readers or related instruments, but some companies may not have the relevant equipment to check, and some simple identification methods can be used: 1 copy the barcode from the design company to ensure that the decoding is very good, As a standard for checking the bar/void size during production, it is easier to compare because the film is transparent. If it does not match, you need to use a 0.01mm measuring tool to check. 2 For appearance defects, place the bar code under the standard light source and check the position of the sample 400 mm away. If it is obvious, there is a problem. 3 Ensure that the left and right blank areas are sufficient. 4 Ensure that the printing color is uniform and there are no printing problems such as dirty prints. 5 Be careful when the bar code is printed on a reflective film that is very strong like a laser film, aluminized film, etc., or when the background color is similar to red.