Corrugated cardboard box inspection

Basic testing items

1. Appearance quality

Qualified cardboard boxes require clear printing patterns and handwriting, without any broken or missing lines; The pattern color is consistent, bright and bright, and the printing position error is small. The error of the large cardboard box is within 7mm, and the error of the small cardboard box is within 4mm. The surface quality should be intact without damage, stains, and there should be no leaks around the box. After each box cover is closed, there should be no gaps. For the shape of the cardboard box, the tolerance between the inner diameter of the box and the design dimensions should be maintained within ± 5mm for the large box and ± 3mm for the small box, and the overall dimensions should be basically the same. The corrugated cardboard box shake cover should be folded back and forth at 180 degrees for more than 5 times. The total length of cracks in the surface and inner layers of Class I and II cardboard boxes, as well as the inner layer of Class III cardboard boxes, should not exceed 70mm. In addition, it is also required that the box joints be standardized, with neat edges and no overlapping corners.

2. Moisture content

The so-called moisture content refers to the amount of moisture in corrugated paper or cardboard, expressed as a percentage. Moisture content has a significant impact on the strength of the cardboard box and is one of the three major defect inspection items for cardboard boxes. 

Corrugated base paper has certain pressure resistance, tensile strength, puncture resistance, and folding resistance. If the moisture content is too high, the paper appears soft, has poor stiffness, and the quality of corrugation and bonding is also poor. If the moisture content is too low, the paper becomes too brittle, prone to cracking during corrugation, and has poor folding resistance. If there is a significant difference in moisture content between corrugated paper and cardboard, the corrugated cardboard produced by single-sided machine processing is prone to curling, blistering, and delamination during lamination. If the formed cardboard box absorbs moisture and becomes damp during storage, it will significantly reduce the strength of the cardboard box and affect its use. 

The moisture content standard for corrugated cardboard boxes is (12 ± 4)%. The most accurate method for measuring the moisture content of cardboard boxes is the drying method, which involves taking several samples from different parts of the cardboard or box, weighing about 50g of the sample with a balance, tearing it into pieces, and placing it in an oven to dry to a constant weight to determine its moisture content.

The formula for calculating moisture content is:

Moisture content=(original weight of sample - weight of sample after drying) ÷ original weight of sample × 100%

3. Board thickness

The thickness of corrugated cardboard refers to the vertical distance between the top and bottom of corrugated cardboard under a certain pressure, measured in millimeters. It is one of the inspection items for appearance defects of cardboard boxes and directly affects the edge compression strength, puncture strength, and compressive strength of cardboard. There are many reasons that affect the thickness of cardboard. If the thickness of corrugated cardboard is too thin, its edge compression strength, puncture strength, and compressive strength will correspondingly decrease. The thickness of corrugated cardboard varies depending on its corrugated shape. 

The laboratory usually uses a corrugated cardboard thickness gauge to measure the thickness of the cardboard. The thickness gauge has a circular anvil and a cylindrical measuring head, and the measurement results can be read through a display. The pressure applied by the measuring head is 20kPa ± 0.5kPa, and the diameter of the measuring surface is approximately 35.6mm.