The following is the overall detection solution of corrugated paper printing quality:

Appearance inspection:

Dirty inspection: under sufficient illumination, check whether there are stains, oil stains, ink spots and other dirties on the corrugated paper surface at a suitable visual distance (such as 30-50cm). For slight dirt, if the area is small and does not affect the overall appearance, it can be regarded as a secondary defect; However, if the dirt is obvious, large in area or distributed in key graphic parts, it is regarded as a serious defect.

Scratch and indentation detection: check whether there are scratches, indentations and other marks on the corrugated paper surface. Shallow scratches and slight indentations are acceptable to some extent if they do not affect the clarity and integrity of pictures and texts; However, deep scratches and serious indentations may affect the strength and appearance of corrugated paper, which needs to be strictly controlled.

Surface defects:

Flatness detection: put corrugated paper on a horizontal surface or pass through a flatness detection instrument to check whether it is flat or not. The flatness of corrugated paper is very important for subsequent processing and use. Excessive bending or twisting of corrugated paper may lead to problems such as printing pattern deformation and misregister. For the deviation of flatness, the acceptable range should be determined according to the specific use requirements and standards.

Cutting accuracy detection: measure the edge cutting size of corrugated paper and compare it with the design size. The deviation of cutting size should be controlled within a certain range, for example, the error of side length should not exceed 2 mm to ensure that the size of corrugated paper meets the requirements and is convenient for subsequent packaging and assembly. At the same time, check whether the edge is neat, whether there are burrs and jagged edges, and the length of the burrs should not exceed 1 mm.

Color detection:

Color accuracy: the color of printed corrugated paper is compared with the standard color sample by using spectrophotometer or color comparator. Ensure that the hue, saturation and lightness of the color are within the acceptable deviation range, for example, the color difference δ E value should be less than 3. For brand packaging or high-end product packaging with strict color requirements, the control requirements of color difference may be higher.

Color uniformity: measure the color in different parts of corrugated paper to check whether the color is evenly distributed. Especially for large-area monochrome printing or gradient printing, color uniformity is particularly important. The color difference should be controlled within a certain range, such as δ E value less than 1.5, to ensure the overall printing effect.

Text and pattern detection:

Clarity detection: check whether the characters and patterns on corrugated paper are legible through a magnifying glass or a high-resolution camera. The strokes of characters should be complete and sharp, and the lines of patterns should be smooth and fine. For smaller characters, the width and clarity of strokes should meet the requirements of readability; For complex patterns, make sure that the details can be clearly presented. Corresponding definition standards can be formulated, for example, the minimum stroke width of characters is not less than 0.2mm, and the minimum line width of patterns is not less than 0.3 mm.

Integrity detection: check whether the characters and patterns are complete, and there are no problems such as missing, truncation and deformation. Especially for corrugated packaging with specific signs, brand names or important information, the integrity of patterns and characters is very important. For example, each element of the trademark design should be intact, and the text content should be accurate, and there should be no typos or missing words.

Overprinting accuracy detection: for multi-color printed corrugated paper, check the overprinting accuracy between patterns or characters of different colors. Overprinting errors should be controlled within a certain range, for example, the horizontal and vertical overprinting errors should not exceed 0.5 mm. Overprint inspection marks or professional overprint inspection instruments can be used for measurement and evaluation.

Physical performance testing:

Strength testing: the compressive strength, tensile strength and bursting strength of corrugated paper are tested to ensure that corrugated paper can withstand certain pressure and external force during transportation, storage and use. For example, according to the relevant standard test methods, the compressive strength of corrugated paper should meet the weight and stacking requirements of packaged products, and the bursting strength should be able to prevent it from breaking due to external impact during handling and loading and unloading.

Adhesion detection: check the adhesion of printing ink or coating on corrugated paper surface. Tape sticking test or friction test can be used to ensure that the ink or coating will not fall off or wear during normal use. For example, stick it on the printing area with tape, and then quickly tear off the tape to see if the ink falls off; Or use a friction tester to test the friction of the printing surface to check the wear resistance of the ink.

Overall effect evaluation:

Simulated use environment test: put the corrugated paper packaging samples in the simulated transportation, storage and use environment to observe whether the printing quality is affected. For example, under high temperature, high humidity, low temperature and other environmental conditions, check whether the color of corrugated paper fades, whether the pattern is deformed, whether the ink sticks, etc.

Comparison and evaluation with the design draft: compare the printed corrugated paper with the design draft to evaluate whether the printing quality meets the design requirements and expected results as a whole. Besides paying attention to the accuracy and quality of printing, we should also consider the overall aesthetics, readability and functionality of corrugated packaging.

In order to improve the efficiency and accuracy of detection, automatic detection equipment, such as online image detection system and color detection instrument, combined with manual sampling, can be used to comprehensively detect and control the printing quality of corrugated paper.