How to Meet Customer's Requirements for Compression Strength (I)

The most important function of the carton is that it has good protection for the goods, and the overall compressive strength of the carton is a comprehensive manifestation of the carton protection performance. The importance of the compressive strength to the carton is self-evident. In recent years, with the rapid development of the packaging industry in China, many factories have gradually recognized the carton from the merits of the development of the carton to the stage of testing and analyzing the physical properties of the carton using various instruments. Many manufacturers also have The compressive instrument tests the compressive strength of the carton. Not only that, many customers, especially foreign large multinational companies, have also undergone profound changes in their understanding of carton boxes, that is, they are concerned with the compressive strength of carton boxes and gradually change their compressive strength, and regard compressive strength as the most important indicator of quality acceptance.

As a result, how to provide customers with cartons that meet the compressive strength requirements has become the focus of many carton plants. Especially in the past two years, the price of base paper remained high, and the profit margin of the carton shrunk. The manufacture of cardboard boxes with the lowest cost of paper and the ability to meet customers' pressure requirements has become the common goal of many cartons.

Focusing on the factors that affect the compressive strength of the carton, the method of calculating the compressive strength of the carton, the configuration method of the compressive strength of the paper, and the testing methods of the compressive strength, the compressive strength of the carton is comprehensively discussed and analyzed. . Some places will inevitably be guilty of conspiring, but hope to provide useful reference for the majority of their peers.

Factors affecting the compressive strength of carton

There are many factors that affect the compressive strength of the carton, which can be roughly summed up as the side pressure strength, structure size, processing technology, moisture, and stacking mode after packing. Due to the interactive effects of various factors, we often cause some deviations in our prediction of the compressive strength. Carton factories often also have inadequate knowledge of these factors and improper handling of the design, printing, and post-processing processes, resulting in huge cost and customer complaints. Therefore, it is very necessary to clarify the influence of these factors.

Corrugated board side pressure strength

The side pressure strength, also called the vertical compressive strength, is to apply pressure to the corrugated cardboard samples in the vertical direction. The maximum force the cardboard can withstand during the pressure application is the side pressure strength of the carton. The compressive strength of the carton is mainly determined by the cardboard side pressure strength, while the side pressure strength is related to the lateral crushing strength of the layers of the base paper constituting the corrugated cardboard, the combination of the cardboard type and the adhesive strength of the paperboard.

The side pressure strength of the corrugated board is mainly related to the transverse crushing strength of the base paper of each layer. In general, the base paper with higher grammage, better quality and tightness of papermaking materials, has a higher lateral compressive strength. However, it is not necessarily higher than the base paper with low basis weight. Taking boxboard as an example, the index of horizontal compression of imported leather can reach 12N·m/g or more, and the linerboard produced by some small paper mills in the Mainland is only 8 N·m/g, a difference of 30 percentage points. In other words, the imported ox card with a grammage of 175 g / m2 has a crush strength of 260 g / m2. Therefore, the quality of carton protection is not judged by the weight of carton paper.

The structural design of corrugated paperboard is very scientific. The corrugated corrugated shape of the corrugated cardboard is like a small arched door that is connected in a row, supporting each other to form a triangular structure, strong and powerful, and can withstand the plane Certain pressure, flexibility, strong buffer, can play a role in earthquake protection and protection of goods. Corrugated shapes are generally classified into U-shaped, V-shaped, and UV-shaped, depending on the radius of the arc. U-shaped peak top arc radius is larger, arc-shaped, such as B楞, C楞; V-shaped peak radius is small, and sharp, such as A楞; UV type in between the two, such as AB楞. According to experiments, the V-shaped rake is less skewed in the initial stage of compression, but it quickly breaks when it exceeds the highest point, and the U-shaped rake absorbs higher energy. When the pressure is eliminated, it can still be restored to its original state, but it is flexible. The compressive strength is not high. In addition, the V-shaped crucible saves corrugated paper and has less adhesive consumption, but it is prone to high and low defects during processing, and the corrugating roll wears quickly. UV-shaped crucibles are a combination of U-shaped and V-shaped features, which are currently widely used.

Corrugated board type and its combination, in terms of single-hole cardboard, the general A-carton compressive strength is highest, but vulnerable to damage; B pit strength is poor, but good stability; C pit anti-pressure and stability Centered. A-type corrugated has good shock-proof cushioning, and the vertical compressive strength is also higher; B-type corrugated has a sharper peak end, a narrower bonding surface, and a small corrugation height, which can save corrugated base paper and its flat compressive force The capacity exceeds the A-type corrugated type, and the B-type corrugated file has a large number of corrugations per unit length, and has more supporting points with the noodle paper, so that it is not easily deformed and has a relatively flat surface. When printing, it has strong compressive ability and good printing effect. C-type corrugated sheet has both the characteristics of A-type and B-type corrugated type. Its shockproof performance is similar to that of Type A, and the flat pressure resistance is close to Type B corrugated. E-type corrugated type is the finest type of corrugated medium, with the largest number of corrugated irons per unit length, able to withstand large plane pressures, and can be used for offset printing, and can print high-quality graphics on the packaging surface. Cardboard and cardboard are about the same strength.

Table 1 Three Types of Comparison Table Corrugated Type Plane Pressure Vertical Pressure Parallel Pressure
A 3 1 3
B 1 3 1
C 2 2 2
Note: 1. Plane pressure refers to the pressure perpendicular to the plane of the corrugated board.

2. Vertical pressure refers to the pressure in the direction of the corrugation, and parallel pressure refers to the pressure in the direction perpendicular to the corrugation.
3. "1" represents the strongest.

According to the different characteristics of the above-mentioned different types of corrugated medium, single corrugated cardboard boxes are suitable for type A and type C; double corrugated cardboard boxes are used with type A and B, and types B and C are the best combination; type B, which is close to the surface, can resist The impact of a strong role; close to the inner layer with A-type or C-type elastic foot, strong buffer; mining useful AB type or BC-type combination, so that the physical properties of the carton to play two advantages. In the packaging should use C-type 楞, E-type corrugated cardboard instead of cardboard, used for small packages. In recent years, foreign countries have also developed F楞, G楞, etc., which are smaller than E楞. At the same time, they also developed K特 and other large-scale corrugations.

In addition, the paper board adhesive strength and pit stiffness also have a certain impact on the cardboard side pressure strength. The better the pit shape, the better the adhesion and the higher the edge pressure strength. The strength of paperboards with defects such as pits, smashing, and degumming will be weakened to varying degrees.

Carton length, width, height and ratio

A lot of data analysis shows that there is a certain relationship between the compressive strength of the carton and the perimeter of the carton, the height of the carton and the aspect ratio of the carton. The longer the carton perimeter, the higher the compressive strength, and there is a certain conversion relationship between the carton perimeter and the compressive strength.

n When the box height is 10 cm to 35 cm, the compressive strength decreases slightly with increasing height;

n When the box height is in the range of 35 cm to 65 cm, its compressive strength is almost constant;
n When the box height is greater than 65 cm, the compressive strength decreases as the height increases.
The main reason is that the height increases and its instability increases accordingly.

In general, the aspect ratio of the carton is in the range of 1 to 1.8, and the effect of the aspect ratio on the compressive strength is only ±5%. When the aspect ratio RL=1.2 to 1.5, the carton has the highest pressure resistance value. When the ratio of length to width of the carton is 2:1, the compressive strength is reduced by about 20%. Therefore, the length-to-width ratio when designing the carton should not exceed 2, otherwise it would cause waste of cost.