The main factors affecting the compressive strength of cartons are: ① raw material quality; ② moisture; ③ Cabinet-type and corrugated type; ④ printing and opening; ⑤ processing technology.
a. Raw material quality
The Kellicutt formula calculates the compressive strength of the carton based on the ring compressive strength of the corrugated cardboard, which is an indicator of the compressive strength of the carton. The ring crush strength is the bonding strength of the core paper and the face paper or inner paper. The raw material is the main factor affecting the ring crush strength, which is related to the quantitative, tightness and moisture of the raw material. The grades of containerboard and corrugated base paper mainly include A, B, C, D, E, etc. In general, the principle of grade matching should be followed when selecting materials. The grades of containerboard and corrugated base paper should be similar. The weight of paper and corrugated base paper should be kept within the range of 21, so as to ensure the overall quality level of raw materials and the quality of corrugated board. Of course, corrugated cardboard volatilizes by bonding the surface paper, the core paper and the inner paper, so the factors of the adhesive and the core paper should also be considered. Appropriate moisture content, tightness and uniformity of the core paper are conducive to pasting with the face paper and inner paper, and the better adhesion performance of the adhesive and the appropriate thickness of the adhesive layer are conducive to improving the compression resistance of corrugated boxes strength.
b. Moisture
The production environment, storage environment, use environment, weather, climate and other factors of the carton will affect the water content of the carton. In order to ensure the compressive strength of the carton, the influence of the external environment on the water content of the carton should be avoided as much as possible.
The initial moisture content of corrugated base paper will directly affect the quality of corrugated cardboard. If the moisture content is high, the base paper will be soft, but the tensile strength will be relatively reduced; In the production of corrugated cardboard, the moisture content that is expected to obtain the best strength value is generally 6% to 8%. The traditional method of moisture determination is the dry weighing method at 105°C, using an oven and a balance, which is the standard method.
c. Box type and corrugated type
The Cabinet-type refers to the type of box and the size ratio of the same type of box, which have a significant impact on the compressive strength. Some carton boxes are made of double-layer corrugated cardboard, and their compressive strength is significantly higher than that of single-layer boxes of the same specification; under the same conditions, the higher the box body, the worse the stability and the lower the compressive strength.
In people's consciousness, it is often believed that the larger the corrugated shape is, the higher the compressive strength of the carton is, and it is easy to ignore the influence of the corrugated shape on the amount of deformation. The larger the flute type, the greater the compressive strength of the carton and the greater the deformation; the smaller the flute type, the smaller the compressive strength of the carton and the smaller the deformation. If the carton is too large but the corrugation is small, the carton will be easily crushed during the compression test; if the carton is too small but the corrugation is large, the deformation will be too large during the compression test, and the buffering process will be long, which is effective The force value deviates too much from the final force value.
d. Printing and perforation
Printing will cause some damage to corrugated cardboard, which will reduce the compressive strength of the carton. The size of the pressure and the size of the bearing area are the main factors affecting the compressive strength of the carton. If the printing pressure is too large, it is easy to crush the corrugated and reduce the corrugated height. Especially when printing at the crimping line, the entire cardboard will be crushed for forced and clear printing at the creasing line, which will greatly reduce the compressive strength of the carton, so printing here should be avoided as much as possible. When the carton is full or surrounded by printing graphics, in addition to the pressing effect of the embossing roller on the corrugated cardboard, the ink also has an infiltration effect on the paper surface, which in turn reduces the compressive strength of the carton. When the general carton is fully printed, its compressive strength will drop by about 40%.
For products with ventilation requirements, opening holes on the box surface or punching handle holes on the side of the box will reduce the strength of the carton, especially if the opening area is large and it is biased to one side, the impact is more obvious.
e. Processing deviation
According to the test, under the same conditions, the compressive strength of the carton will decrease by 90N-130N and the deformation will increase by about 2mm for every 1mm widening of the transverse pressure line of the carton. If the pressure line is too wide, the force value of the carton will increase slowly during the compression test, the effective force value will be small, and the final deformation will be large. In order to ensure the compressive strength, we should try our best to improve the production process and reduce the impact of each process on the compressive strength of the carton.
In the process of box making, improper crimping, too deep groove, and weak combination will also reduce the compressive strength of the box.
