Corrugated board strength - the impact of raw materials

The strength of corrugated board is an important technical indicator for quality inspection of packaging containers. The level of these indicators reflects the quality of raw materials on the one hand and the quality of the processing technology on the other. The production process shows that to improve the strength of corrugated board, it is not enough to rely on purchased raw materials. Quality control of the production process is also an important part of improving the strength of corrugated board. Therefore, correctly understanding and understanding the relevant factors that affect the strength of corrugated board is of great significance for better production and product quality improvement. Therefore, in the event of problems, we should carefully observe and analyze the problems. We must adopt a variety of modern statistical analysis techniques to identify the causes of the disease to solve the problems and achieve very good results.

Effect of Raw Materials (Corrugated Paper, Adhesive) on Corrugated Board Strength

1. Relationship between base paper technical index and corrugated board strength

● Quantitative Quantification, also known as grammage, refers to the weight per square meter of paper, expressed in q/m`. The quantitative calculation formula is: the weight of the sample/area of ​​the sample. Quantitative is an important index to measure the physical properties of paper. In general, the paper has a high basis weight, and its tensile strength, ring pressure strength, tear strength, stiffness and thickness are relatively high, and high-quality paper is used to make corrugated paper. Cardboard, its compressive strength is relatively higher. Therefore, to produce high-strength corrugated paperboard, the selection of high-quantitative paper materials is often one of the basic requirements of customers.

● tightness

It refers to the weight per cubic centimeter of paper, expressed in g/Cm3. Its calculation formula is:

The tightness of the paper reflects the degree of densification of its fibrous tissue structure. Boxboard and corrugated paper have high tightness values, and their burst strength, ring pressure strength, puncture resistance, and tensile properties are relatively good. Then, the overall strength of cardboard is relatively high. However, if the tightness is too large, the paper material will be easily brittle, especially for whiteboard paper. If the tightness value is significantly larger than the standard, the folding endurance performance will be reduced. Therefore, the use of white paper for the surface layer of corrugated cardboard, should not use high tightness of the white paper, so as not to affect the folding degree of the cardboard flap.

● Ring pressure strength

The standard sample length (longitudinal) 152 ± 0.2mm, width 12.7 ± 0.1mm, take 10 pieces to be tested, 5 of which are tested outwards outwards, and the other 5 pieces are tested outwardly into the annular tray, after which By formula conversion, the ring pressure strength of the base paper can be obtained. In general, cardboard made from paper with good crush strength is relatively high in strength. The formula for calculating the crush strength is: RF/152. In the formula, R denotes the ring crush strength in kN/m; F denotes the force value read in crushing the sample, unit N; and 152 denotes the length of the sample in mm. The standard value of the ring pressure index in the national standard is an important index to measure the compressive performance of the base paper. It refers to the ratio of the ring pressure strength and the basis weight of the base paper and the unit is N·m/g. The calculation formula for this indicator is: Rd=1000R/W. In the formula, Rd denotes the ring pressure index, R denotes the ring pressure strength, and W denotes the basis weight of the sample, and the unit is g/m2. The ring pressure index of the base paper affects the overall strength of the paperboard to a great extent, and especially affects the compressive strength of the paperboard.

●Sizing degree

Paper, cardboard in the production, the application of a certain amount of rosin gum and other water-resistant colloidal material, the paper surface to increase water resistance, this production and processing technology known as sizing. The degree of sizing is a measure of the quality of the glue. According to the national standard, the ink scribe method and the surface absorption weight method can be used for detection. The factory can also check the degree of squeegee on the paper with the "drip method". The practice is: a little water on the paper surface, if the speed of water droplets infiltration, indicating that the degree of sizing is not good; if the water droplets are not prone to seepage phenomenon, water droplets floating on the paper, indicating the degree of sizing is good. The base paper for making corrugated paperboard requires a good degree of sizing, so that it is not easy to absorb moisture, the moisture content of the paperboard is stable, and the strength of the paperboard can be better guaranteed.

● moisture content

The so-called moisture content refers to the content of water in paper or paperboard. The calculation formula for the test in percentage is:

The moisture content has a great influence on the strength of the cardboard box, so this is also the main reason why the moisture content has become one of the three important defect inspection items for the board. When the moisture content of the board is high, its resistance to puncture compressive strength and burst strength will be relatively reduced. Corrugated paper has a certain degree of pressure resistance, tensile resistance, puncture resistance, and folding endurance. If the moisture content is too high, the paper will appear soft, poor in stiffness, and poor in pressure and adhesion. If the moisture is significantly lower than the lower limit of the standard value, the cracking phenomenon will occur easily when pressing. If the moisture content of corrugated paper and liner board is greatly different, the corrugated board machined by one-sided machine is likely to be curled, and blistering and degumming are likely to occur when the next process is combined to make the strength of the board significantly lower.

● folding degree

As a kind of packing container, the cardboard needs to be frequently opened for the swing cover, which requires the paper material to have a certain folding-resistant ability. The paper's transverse folding resistance measures the 135° reciprocating folding test of a 150mm x 15mm sample under a certain tension, speed, and angle condition. When the paper is broken, it is the inspection of the folding endurance. frequency. The pulp properties of the boxboard and folded paper, the moisture content of the paper, the tightness, the fiber length and the fastness of the binding force, and the influence of factors such as the storage time and temperature of the base paper largely determine the resistance of the base paper. Discounts. Therefore, to improve the folding-resistant performance of the board, it is an important part to ensure the quality of raw materials.

2. solution

Corrugated paper and starch paste are two raw materials for corrugated board production. The quality of the base paper, especially the corrugating medium, directly affects the strength of the paperboard. The reason analysis and solution are shown in Table 1.

In addition, some companies have such a misunderstanding: The thicker the surface, the more paper can increase the cardboard bearing pressure and compressive strength. In actual fact, the actual operation as long as the face paper is not visible after the tannin traces of corrugated marks should try to use low-weight paper core paper, paper, tile paper is best to use good strength, high ring pressure strength grass pulp or wood pulp paper. Do not use medium-strength or strong-strength corrugated paper, as it is mostly a mixture of pulp and recycled pulp. It has fast water absorption, low ring pressure strength, and good toughness but low stiffness. Practice has proved that reducing the weight of the paper inside, increasing the corrugated paper, the weight of the core paper, and improving the price/performance ratio, the competitive advantage is enhanced.

(to be continued)