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Correctly understand the physical strength of base paper

with the rapid development of China's packaging industry, people's understanding of corrugated boxes has gradually progressed from judging the quality of cartons only by hand feeling to using various professional instruments to detect various physical performance indicators. The performance of corrugated boxes is mainly determined by the layers of base paper that make up the corrugated board. Therefore, the physical strength of base paper has become the focus of corrugated packaging enterprises

this paper will briefly describe the physical properties of the base paper in combination with the papermaking process of the base paper, so that the packaging industry colleagues can have a comprehensive and in-depth understanding of the physical properties of the base paper


effect of fiber structure of base paper on the strength of corrugated board

the fiber structure of base paper is different, and the bursting strength and edge compression strength of corrugated board produced will also be different. The fiber structure of base paper is mainly the proportion of raw pulp and recycled pulp, wood pulp fiber and straw pulp fiber in base paper production

kraft paperboard made of whole wood pulp is mostly produced by mixing softwood and hardwood pulp or mixing slow-growing Forest Pulp and fast-growing forest pulp. The physical properties of the base paper vary with the proportion of wood pulp

the difference in the ratio of surface pulp to bottom pulp of kraft linerboard will directly affect the bursting value of the base paper. Some manufacturers reduce the amount of flour paste in order to save costs, such as 175g/m2 dried Kraft linerboard (class a paper). Generally, the quantity of flour paste should be g, but it is found that some are only G in the test, so the bursting value and ring pressure strength will be low

in corrugated base paper or ordinary noodle box board, the content of wood pulp fiber will also affect the ring crush strength of the base paper


the relationship between the tightness of the base paper and the strength of corrugated paperboard

whether it is carton paper or corrugated base paper, its tightness is also an important aspect that affects the strength of corrugated paperboard. Calculation formula of tightness: tightness (g/cm3) = quantitative (g) ÷ [thickness (CM) × 10000cm2] (Note: the thickness is measured with a thickness gauge, which can refer to GB standard). From the formula, it can be seen that the tightness of the base paper is the weight of the base paper in the unit volume. The higher the weight, the greater the fiber density of the paper. From the actual production and testing, the higher the bursting strength is. The higher the tightness, the higher the stiffness of the corrugated base paper. When processed into corrugated board, the corrugated shape is well formed and the flat pressing strength is also high (that is, the better the hand hardness, from now on to 2020). It has been proved in practice that the higher the tightness of the paper, the higher the ring pressing strength is, so it has little effect on the edge pressing strength of the paperboard

the squeezing effect of the base paper in the production process. The tightness will affect the firmness between the fibers, and then affect the ring compression strength and tensile strength of the base paper, and ultimately affect the compressive strength of the carton. Due to the insufficient tightness of the paper, it will also affect the moisture absorption of the carton, making the carton absorb excessive moisture in the use or storage process and reducing the compressive strength of the carton itself


the relationship between the sizing degree and moisture of the base paper and the strength of corrugated board

the sizing degree and moisture of the base paper have a great influence on the strength of corrugated board. Whether it is carton board or corrugated base paper, the higher the sizing degree, the smaller the change of water content. On the contrary, the greater the change of moisture content

when the sizing degree is too high, the base paper fiber will become brittle. Although it has a good performance on the flat compression strength of corrugated board, it will affect its bursting strength and impact strength. In particular, the folding resistance of paperboard will be poor, and indentation fracture will occur after the paperboard is packed. The base paper with too low sizing degree is easy to absorb the moisture in the air, making the water content of the base paper high. The base paper fiber expands after absorbing water, and the paper becomes soft. Its bursting strength and ring pressure strength will be reduced, which will affect the relevant physical properties of corrugated board


base paper ring pressure

the ring pressure test of base paper is divided into longitudinal ring pressure strength and transverse ring pressure strength. One thing to pay attention to in the ring pressure test sampling is that the longitudinal ring pressure strength sampling needs to be consistent with the width direction of the paper, and the transverse ring pressure strength sampling needs to be consistent with the length direction of the paper. During the test process, we will find that although the arrangement of fibers in the long paper machine tends to be disordered, The horizontal hoop compression strength is always lower than the longitudinal hoop compression strength, and as a 0201 corrugated box, the horizontal hoop compression strength is consistent with the stress direction of the corrugated box

the long paper machine increases the number of fibers in the transverse annular pressure test while disorderly arranging the fibers, so as to enhance the transverse annular pressure strength of the base paper. At the same time, due to the disorderly arrangement of the fibers, it enhances the firmness between the fibers, thus ensuring the stability of the compressive strength of corrugated boxes, and reducing the drop of the anti pressure value between individual boxes


bursting strength of base paper

bursting strength of base paper refers to the uniformly increased maximum pressure that the paper or paper can bear on the unit area perpendicular to the surface of the sample

in papermaking, the proportion of fibers in the pulp tank has a great impact on the bursting strength. The more the proportion of coniferous wood pulp is, the greater the proportion of long fibers is, and the higher the bursting strength is. On the contrary, if the waste paper recycled for many times is used more, it will be popular with customers after being put into the market, and the burst resistance will be lower

there is a saying in the paper industry: "three points for paper making, seven points for beating". The bursting strength, folding strength and ring compression strength of the carton board depend on the beating effect to varying degrees. During beating, the fiber length should be kept as much as possible, and at the same time, the fiber should be fully water absorbing and swelling, less cutting, more brooming, which greatly increases the specific surface area of the fiber and the number of free hydroxyl groups, and makes the fiber layout disordered during paper forming, which can significantly improve the bursting strength and other indicators

in addition, another major factor affecting the bursting strength is the adhesion between fibers. Usually, enhanced starch, especially cassava starch, can be added to the pulp to improve the bursting resistance of the base paper


tensile strength of base paper

the tensile strength of corrugated base paper depends on the fiber structure of the base paper and the bonding force between the fibers. The tensile strength not only affects the tensile strength of the base paper in the machine during the use process, but also affects the compressive quality of the carton after molding

if the annular compressive strength of the paper is very good, but the fracture length and tensile strength are not good, it will often cause the deformation of the carton during the compression test to be large, and the final deformation will be like an accordion. This is because of the texture, structure of the fibers or the poor connecting force between the fibers. When the carton is subjected to the compression test, the fibers at the edge of the pressing line are stressed first, This loose and weak fiber can not well transmit the force on the carton to the whole carton. With the local collapse of the edge, the stressed part will gradually move towards the middle of the box, forming an accordion shaped test phenomenon. If the tensile strength is good, this kind of situation will not occur, and the carton will bear a lot of pressure with a small amount of deformation


physical properties (4) a misunderstanding of the understanding that the products heat treated after forming are easy to remove residual stress

judging the quality of paper is not judged by a single physical index, but the physical properties of paper should be a comprehensive index. Sometimes, in order to prevent carton enterprises from cutting corners, carton users not only put forward requirements for the compression resistance index of cartons, but also put forward too high weight requirements for the matching of base paper. In order to meet the requirements of customers, carton enterprises can only increase the weight of paper and reduce the strength of paper to ensure the cost

this requirement of customers has turned away the corrugated base paper with low gram weight and high strength. In fact, considering the comprehensive performance, the corrugated base paper with low gram weight and high strength is much more stable than the corrugated base paper with low strength and high gram weight. Moreover, the stability of the base paper reduces the differences between individuals in the physical properties of the carton and increases the safety of the carton, which is difficult for the paper with low strength and high gram weight to achieve this effect


comprehensive control measures for physical properties of base paper

1 Fully adjust and review the raw material fiber structure, pulping and papermaking process, production capacity and technology, and quality control ability of base paper suppliers, and select stable suppliers as qualified suppliers

2. Formulate base paper inspection standards and acceptance specifications. Confirm with the supplier that this is the basis for contract acceptance. The base paper that does not meet the requirements of the allowable range can be degraded or returned. In particular, we should strictly control the detection of bursting index, ring pressure strength, banner quantification and moisture content. The range that does not meet the index requirements will not be accepted as qualified raw materials

3. Strengthen the stock management and protection measures of base paper. First, the warehouse should be well ventilated and free from moisture, and the moisture deviation of the base paper should be controlled. The second is to avoid the dropping, flattening or flattening of the base paper in the process of handling, so as to ensure the tension balance of the base paper in the process of use. Third, try to be first in first out, so that the physical strength of the base paper will not be greatly reduced due to storage for too long

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