Basic paper knowledge

Corrugated cartons are made from corrugated cardboard, and corrugated cardboard is made from adhesives made from paper and corrugated paper.

Therefore, the base paper can be said to be the most important consumable in the purchase of corrugated boxes. Here are some basic knowledge about base paper.

The nature of the base paper

Quantitative (BASlSWElGHT)

The weight per unit area of ​​paper is called quantitative. The allowable difference between the surface paper and the corrugating medium is 5%. The various properties of the base paper are closely related to the basis weight. Exceeding this standard can affect the quality of the product.

Quantitative test according to the national standard GB451.2 paper and quantitative test prescribed on-site test sample should be hung in the air at the specified temperature (20 ± 20 °C) and relative humidity (65 ± 2%), so that the surface can be fully exposed The conditioned air was prepared for 24 hours and weighed using a balance with a sensitivity of 0.25%. The basis weight of the paper was calculated according to the following equation and expressed as 3 digits.

If it cannot be measured at the specified temperature and relative humidity, it can be calculated according to the following steps:

Step 1: Weigh the sample using a standard balance

The second step: Determination of moisture content of paper samples according to GB462 paper and paperboard moisture determination method

The third step: Calculate the weight of the sample by calculating the weight at a water content of 9% according to the following formula.

Quantitative sample (g/m2) = moisture content 0.09 thickness (THICKNESS or CALlPER)

The thickness of the paper is represented by the metric system in millimeters (mm), the inch system is expressed in inches, and the English and the United States generally use the “rail” for the corrugated medium paper. Each point is equal to 0.001 inch. For example, commonly used 26b/MSF2 corrugated paper thickness is 0009 inches, commonly known as "9 points" paper.

The thickness of the corrugated board can be obtained from the thickness of the base paper plus the height of the corrugated board, so that the degree of corrugating roller wear and the degree of damage to the corrugated board during processing can be clearly understood.

Burst strength is also called BurstlNGSTRENGTH.

Bursting strength is a very important item in the manufacture of corrugated boxes. Samples are in diameter l. In the area of ​​2 inches circle, the pressure is applied at a certain pressure to break it, and the pressure applied on the paper when it breaks is called the burst strength. According to the national standard, the GBl539 paperboard is used to determine the degree of rupture of the paperboard. Means of representation The metric system is expressed in kilograms per square centimeter (k9/cm2) and the English system is measured in pounds per square inch (Eb/in2).

The cardboard paper grade distinction is divided by the basis weight, such as 2009/m2, 2309/m2, 2509/m2..., and the other, according to the breaking index as the criterion for distinguishing, such as the national standard GB13024-91 board board paper Paper is divided into five levels as follows:

The burst resistance index is only another representation of the bursting resistance, which is easy for the industry to memorize. It must not be included in the inspection and acceptance of the original paper, and it must not be tied with the bursting resistance, that is, the bursting resistance and bursting resistance index should not be The same as the acceptance criteria. The relationship between burst resistance and burst resistance index is as follows:

In the early days, the strength of the base paper and corrugated boxes was mainly based on the degree of burst resistance. In the advanced countries of the corrugated box industry, such as the United States and Japan, the status has gradually changed, and the importance of the burst strength gradually becomes the strength of the ring pressure and the strength of the box pressure. PUNCTURESTRENGTH replaced.

Ring Pressure Strength (RINGCRUSH)

The original paper was cut into "6X1/2" specimens and rolled in the long direction toward the cylinder. The specimens were connected at both ends to test the pressure they could withstand. This strength was called the ring pressure strength. This strength is a unique test for the manufacture of corrugated boxes. The test method is based on the method for the determination of the ring pressure of GB 2679.8 cardboard. Because the corrugated paper is compressed in the vertical direction of the corrugated medium, it is horizontal to the base paper, and the compressive strength of the corrugated box can be estimated from the lateral crush strength of the combination base paper (including linerboard and corrugating medium). Only measure the lateral crushing strength of the base paper.

Tensile strength (TENSILESTRENGTH)

For a width of 1.5cm and a length of 18cm, a certain amount of tension is applied to the paper pattern, and the pattern is thus broken. The maximum tensile force that the pattern can withstand is called tensile strength, commonly known as tension.

In the manufacture of corrugated paperboard, in order to obtain a smooth corrugated paperboard, both kraft paperboard and corrugated fiberboard paper use braking methods, and a large pulling force is applied to the base paper so that the base paper can smoothly enter the corrugated paperboard machine, otherwise poor adhesion will occur. High and low levels of operation and poor operation affect the mechanical efficiency. In particular, corrugating medium is the most important. The corrugated paper on the corrugating machine has a line speed 1.3 to 1.6 times faster than the boxboard. At the same time, the corrugating medium must be corrugated at high temperature and high pressure. If the corrugated core paper does not have enough strength, it will break at the corrugation peak. If the tensile strength of the linerboard is not enough, during the production process of the corrugated paperboard, the linerboard breakage will occur at the position of the pressure line when the corrugation is performed. Breaks occur outside the four corners of the carton during operation. To improve the quality of corrugated boxes, the strength of the original paper is no less important than the burst strength. Normally only the longitudinal tensile strength of the base paper is tested.

The other expression of tensile strength is the breaking length BREAK-INGLENGTH), and its conversion formula is as follows:

Breaking length (km) = Tensile strength {;' £1} × 1000 Sample basis weight (g/m2) × Pattern width (mm)

Tearing tension (TEARINGSTRENGTH) commonly known as tearing force

The base paper must be torn with a certain amount of energy before being torn. The instrument for measuring this energy is a tear strength tester. The measured result is expressed in grams (g). When the carton carrier lifts the carton by inserting his hand into the carrying case L of the carton, if the tearing force of the original paper is insufficient, tearing may occur from the upper side of both ends of the portable hole and destroy the integrity of the carton. In addition, when the corrugated paperboard is made of base paper, the forces on both sides of the base paper are equal, and the easy side of the base paper is relatively tight, and one side of the base paper will have a beating phenomenon. If the tearing force is insufficient, then the base paper will break from the loose side.

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; 隹 GBl0739 Specification for pulp, paper and paperboard samples. 1 Before the preparation of the sample, the moisture content of the sample should be dried to approximately half the water content in the standard condition (drying temperature should not exceed 600C). 2 Hang the sample in air of 20±20C and 65±2%RH so that the surface is fully in contact with the conditioned air. 3 Cardboard or paper with good water resistance needs to be prepared for 24 hours or more, until the full weight has not changed significantly. Physical tests should also be held 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.