Basic paper knowledge (below)

Waterproof performance

The waterproof performance of cardboard and corrugating medium is an indispensable property of corrugated boxes. Waterproof performance of boxboard paper is called the water absorbency, which is the water absorption weight per unit area in unit time. It is generally expressed in g/m2/2mins. The test method is called COBBSIZ-INGTEST, and the box board The water absorption of the positive and negative sides of the paper is equally important. The waterproof property of the corrugated medium is called the degree of sizing or water resistance. The test method is to place a sample of corrugated medium paper in a glass containing a thiocyanide solution. In the dish, a few drops of ferric chloride solution were dropped on the surface of the sample. When the two solutions came into contact, they turned red, and the degree of sizing was expressed as the penetration time of the two solutions (seconds, SEC).

Wetstrength (WETSTRENGTH) refers to the strength that the base paper retains after it is immersed in water for 24 hours or placed in high temperature (above 400C) high humidity (95% R.H.) air for a considerable period of time. The general test base paper has a wet burst strength, a wet tensile strength, a wet ring pressure strength, and the like. This performance is caused by the paper mill adding a wet strength agent to the paste during the papermaking operation, and the fiber is produced after the heat treatment. Waterproof layer to prevent the penetration of moisture, that is to produce a strong wet effect. If a corrugated carton needs to be stored in a humid environment for a long time or it is to be refrigerated, it is necessary to use wet processed paper.

Effect of Relative Humidity on the Physical Strength of Base Paper

The physical strength of the base paper is tested in accordance with the national standard; éš¹ GBl0739 Specification for pulp, paper and paperboard samples.

1 Before the sample is prepared, its moisture content should be dried to approximately half the water content in the standard condition (drying temperature should not exceed 600C).

2 Suspend the specimen in 20±20C and 65±2%RH air to make the surface fully in contact with the conditioned air.

3 Cardboard or paper with good waterproofness needs to be prepared for 24 hours or more, until there is no significant change in the total weight. Physical tests should also be conducted at the same temperature and humidity.

The United States belongs to the continental climate. Therefore, the tests are carried out under the standard conditions of 23±2°C and 50±2% RH. Therefore, the test conditions are different, and the test values ​​obtained cannot compare the advantages and disadvantages.

The base paper used in corrugated cartons is composed of vegetable fibers. The moisture content of plant fibers varies with the ambient air conditions. When the ambient air humidity is high, the base paper will become wet. When the humidity is low, the base paper will dry out. In the air of temperature and humidity, the moisture of the base paper will reach an equilibrium state; when two sheets of paper with large water content are modulated in the same temperature and humidity state, the lower the moisture content, the higher the moisture content; The equilibrium state is reached, but there is still a slight difference in the moisture content between the two. Therefore, before the sample is prepared, the moisture content of the raw paper sample should be dried to about half the moisture content in the standard condition, and the same moisture can be obtained by reabsorbing the moisture. Content, changes in moisture absorption and release of raw paper.

The balance of various types of paper moisture varies depending on the type of pulp, and the humidity is 60% R. H. Under the condition, when the moisture reaches the equilibrium point, the coated paper is about 6%, the newsprint is about 10%, and the corrugated paperboard base paper is about 9.5%.

The physical strength of the base paper is greatly influenced by the moisture content, and its variation is shown in Figure 2. Humidity 65%R. H. The intensity of time is 100.

Tensile strength in the humidity of 30 ~ 40% R. Between H, the humidity increases, the humidity continues to increase, and the tensile strength decreases rapidly.

The elongation increases with the increase of the humidity, and the longitudinal change of the base paper is large horizontally.

The fracture strength and tensile strength are the same, the humidity increases, the rupture strength decreases, and the reduction ratio is smaller than the tensile strength.

The tear strength increased with increasing humidity in both the longitudinal and transverse directions, but decreased again in the extreme high humidity range.

Corrugated board production requirements for base paper

The corrugating medium is pressed into a corrugated shape on a corrugating machine (CORRU-GATOR) and coated with corrugated corrugation and corrugated cardboard to form a corrugated cardboard. The appearance and strength of the corrugating medium is good or not, and is closely related to the base paper. The requirements for base paper are as follows:

The RUNINGABILITY of the base paper

Corrugating medium paper presses hundreds of corrugated irons in a minute at the time of pressing the corrugated medium, so the corrugating medium is very important. Therefore, the plasticity of the corrugated medium paper is very important, and it can be made into a straight and strong corrugated fiber when it reaches a certain standard. Recently, high-speed corrugated paper machines have been continuously increased and the speed has been continuously improved. For example, poor quality of the base paper is enough to affect the operation of the machinery, resulting in a decrease in production efficiency.

Raw paper uniformity

Kraft paperboard and corrugated medium paper, whether vertical or horizontal, have a large difference in water content, which can cause serious problems such as poor adhesion, paperboard curling, and falling down. The uneven thickness leads to poor operation adaptability, and the physical strength of the finished product is greatly affected. Therefore, the uniformity of moisture and thickness of the base paper is considered as one of the most important items in the acceptance and use of the base paper.

The appearance of the base paper The appearance of the base paper requires the formation of a smooth surface with no holes, cracks, contamination, and other obvious disadvantages. In addition, the color of the surface of the cardboard paper is also a project worthy of attention.

The original function of corrugated cartons in the course of their use was to achieve the integrity of the contents of their contents. Now it has evolved not only to protect the contents, but also to take up the responsibility of promoting sales and inspiring consumers' desire to purchase, as it is required in corrugated cartons. The surface is finely printed, and the hue of the cardboard surface is sufficient to affect the printing effect. However, in the papermaking process, due to the difference in the size of the slurry, such as excessive requirements for the surface hue, there are practical difficulties. On the acceptance of the surface color of container board paper, the upper limit of control and the lower limit of control shall be established, and the design of the printing pattern shall be supplemented with the cooperation of the ink, so as to achieve the beautification. (Finish)