New Development of Instant Inspection Technology for Packaging and Printing Products

With the rapid development of China’s market economy, people’s lives are gradually moving towards a well-to-do society. People are increasingly demanding the quality of social life products. At the same time, the requirements for the packaging of products and printed matter for decoration are also increasing. Because the current market's credit system is not standardized, under the influence of the “what all money looks at” erroneous trend of thought, the phenomenon of counterfeit and shoddy products in China is very embarrassing, especially for brand products. Therefore, the exquisite characteristics of the product packaging print not only affect the success and failure of the product sales in the market, but the stability of its quality performance will also affect the authenticity of the product. The slight print defect in quality, especially the difference of “brand spot color”, will affect the judgment of the customer on the authenticity of the product, which may often lead to the product's slow sales in the market, and then cause the printer to lose the trust of the user and suffer. Huge economic loss.

In addition, the printing bar code is indispensable for the logistics network system, and the printed label of the pharmaceutical product records the information related to human life. Any errors or problems in the bar code of the packaging web print may cause major social problems. . In order to increase the market competitiveness of printing companies, it is necessary not only to increase the level and efficiency of production and management, but also to improve the stability of the quality and quality of production. It can not only reduce the loss of waste products, save production costs, but also protect the brand effect of high-quality products of enterprises, so the quality of products is the basic conditions for enterprises to survive.

Of course, there are many factors to improve and maintain the high quality level of printed products. How to monitor quality in a timely manner in the production process and make adjustments in a timely manner is of great significance for stabilizing the quality of printed products.

In the past, most of the quality inspections in print production were manual sampling and visual inspection by the leader or quality control personnel. There was an over-reliance on the individual responsibility and proficiency of the operators and the disadvantages of large errors, while the advanced printing products were automatically detected. The system can improve the inspection accuracy of producers, timely feedback the causes of defects, and make effective and timely control, which is one of the effective ways to improve the quality of printing products and printing efficiency.

At present, with the development of printing press manufacturing technology and digital electronic technology, the immediate supervision and control technology for the quality of printed products in the production site is also developing very rapidly. Traditionally, for the inspection of the quality of printed products, In order to unify standard management, in order to unify standard management, various types of quality control bar/signal strip are used for offline visual inspection; later, in order to implement data management, density meters and spectrophotometers are used. Manual or automatic detection. Now, with the development of digital image ingestion technology and processing technology, the entire image of the print product has begun to be detected, and a closed-loop control system can be used for immediate adjustment. In industrially developed regions such as Europe and the United States, most printer manufacturers have standardized image detection systems. The use of computers for automatic detection of defects in printed matter after print has the characteristics of high speed and objective test results. However, the application of digital image processing technology to the quality inspection of printed materials will undoubtedly have a broader development prospect.

This article gives a brief introduction to the development of the real-time inspection technology used in the printing production process.

First, the control strip detection technology

1, visual inspection of traditional detection methods

Visual inspection is performed on the control strip in the control strip, and then the printing conditions are adjusted manually.

2, manual detection of the density meter

Using density detection and control of ink, it can measure data such as color density, superimposition, dot gain, etc., but it requires manual data recording and is cumbersome.

3, manual detection of spectrophotometer

For color measurement, spectrophotometers are further developed than densitometers, more accurate and unique, especially for spot colors used in packaging, because traditional densitometers use color filter sampling, only Can take four sections in the spectrum (corresponding to C, M, Y, K four colors), while the spectrophotometer is full spectrum sampling, so you can measure the spot color. It can also directly detect the printed image and obtain the color difference information between the proofs and standard proofs. Therefore, it is an effective tool for printing production personnel to control the print quality. Such measuring instruments include GretagMacbeth's SpectroEye spectrocolorimeters.

4. Automatic scanning detection of spectrophotometer

Tests are performed on the press's central automatic console, such as the CPC-24 in Heidelberg, which has automatic detection and recording functions.

The detection aperture of general inspection instruments is relatively large (4mm or more), and the area of ​​the control strip is also required to be compared. Generally, the width is about 10mm. In China, since the white edge of the trailing edge of the sheetfed offset paper is relatively narrow, most factories cannot install the control bar, so that the data quality and standardized quality management cannot be implemented until the printing production cycle. A small number of factories with more standardized management in order to strengthen quality management and ensure the quality level of printed matter, had to increase the width of the white edge of the paper to increase the cost of paper and paper, resulting in a substantial increase in the cost of the factory. Now, X-Rite has been able to supply small aperture automatic measurement instruments - ATS Publication (Automatic Scanning Spectrophotometer for magazines), measuring the width of the strip as long as 2mm, which makes most of the single sheet and roll of paper The prints can be placed under the original dimensions without additional production costs.

ATS Publication has many features. Such as: measuring the ink's color, density, color and print measurement records. They can fix quality parameters, establish accurate targets and tolerances based on user samples, pre-operating data or vendor standards, and can save them for rapid and accurate setting before reprinting, providing real-time color quality control during print runs. data. The easy-to-read graphical interface alerts the operator when the color quality deviates from the preset tolerances.

Where control strips are used for quality inspection and control, most are generally offline.

Second, the image detection technology

1, artificial visual inspection

One of the most traditional methods of detection is offline, and the other uses a strobe light for visual inspection on a web gravure printer or flexo printer.

2, offline automatic detection

Tests are carried out on the central automatic console of the printing press. Most of them are used on sheet-fed and web offset presses, such as the CPC-2 control technology console in Heidelberg. Heidelberg's newly developed CPC24 system, known as the "E-Eye", is a new image and color management system for use on the CP2000 offset press. It basically abandons the traditional use of color control strips to measure the color of prints with the "eye". Instead of analyzing the color difference between printed sheets and proofs, an automated color measurement and control system was used. Its technical characteristics mainly include: measuring the entire printed sheet image; real colorimetric analysis by spectrophotometry technology, basically no need for color control strips.

3, automatic detection in the machine

The general image detection system can stably shoot the instant printing effect at the same position when the printing press runs at a high speed, and presents it on the display. The image to be observed is then enlarged according to different needs and longitudinally automatically traced and scanned. This system allows operators to instantly detect defects in prints when the press is operating at high speeds, correct errors, and reduce waste. However, skilled professionals are required. This makes it impossible to perform a comprehensive inspection and record the inspection results, and the manual visual inspection method is difficult to adapt to high-speed, large-volume print inspections. This method is generally used on gravure and flexo presses. The effect is not the same after using the digital detection system.

Digital printing quality inspection system works

The detection system used in automatic print quality inspection equipment is to first take a standard image using a high-definition, high-speed digital camera lens, set a certain standard on this basis, and then shoot the detected image, and then compare the two. The CCD linear sensor converts the change in the light quantity of each pixel into an electronic signal. After the comparison, if the detected image is different from the standard image, the system considers the detected image to be a defective product. The various errors that occur in the printing process are different from the standard image and the detected image. For example, overprint errors, smudges, and ink color defects are included in the errors. The working principle of automatic detection equipment is shown in Figure 1.

At present, BOBST in Switzerland, PROIMACE in the United States, DAC in Japan, and TOKIMEC can provide full automatic print quality inspection equipment.

Taking the PRINT-CAPVer4 series printing defect inspection device of TOKIMEC (Japan Eastcom America) as an example, it is a state-of-the-art printed matter inspection device comprising a high-precision camera, image processing technology, and Windows 95/98-based environment software. The digital printing defect inspection apparatus is composed of a main body, a 3-line CCD camera, lighting, an encoder, and a labeling machine. The inspection method is to read an image as a reference image, compare the pixel data of the image taken by the 3-line CCD camera with the reference image at the same address, detect the defect, display the defect image, store the defect data, and use The attached browsing software analyzes the shortcomings of the saved data and labels them at the end. After the inspection is completed, the system can perform defect history printing, defect image printing, and use the network to confirm the defect information.

The 3-line CCD sensor has high resolution and spectral gradation. The three parallel pixels cover the RGB filter respectively. When capturing a color picture, the complete color picture is composed of multiple rows of pixels. The detection system uses a 3-line CCD high-speed scanning camera to monitor the printed matter at any time, decomposes the printed print image into red, green and blue colors, and performs high-precision, high-speed data processing on the decomposed individual color components. Very fine print defects can be checked. Using a 3-line CCD sensor, there is no color blind zone in the horizontal direction, and the knife wire can be effectively detected; phase compensation is required in the longitudinal direction, and then each line of data read is stored in a memory and converted into a two-dimensional image.

The advanced image recognition technology adopts pixel-to-pixel inspection, area-to-area inspection, and special tool inspection board to realize high-speed and high-precision inspection. The high alignment accuracy can reduce the false detection caused by the expansion and contraction of printed materials; the concise and clear inspection screen is more conducive to the detection of defects, and is automatically classified according to heavy defects, medium defects, and light defects, and the inspection of various types of defects. Conditions can be set by the user. The digital printing inspection device can also find ways to eradicate the defective product, reduce the defective product rate, and then reduce the penalties for non-compliance and the cost of reprinting, as well as save raw materials and labor costs, thus greatly improving production efficiency.

PRINT-CAP is designed to adapt to various operating conditions such as online and offline. Because the number of cameras can be arbitrarily selected, it can better meet the user's inspection accuracy requirements. The digital inspection device can be widely used in various printing machines such as intaglio printing, sheet-fed offset printing, form printing, label printing, aniline printing, etc. It can also be used in various machines such as sub-dispenser, rewinder, laminator, coater, etc. . The device can not only check the printed matter, but also check the unpatterned film, film, and paper.

This on-line digital print image quality inspection system can produce remarkable results for high-quality packaging printing production such as high-grade cigarette packs and wine bags.


Author (Gong Renxuan)

Source: Shanghai Packaging