Keywords coated paperboard base paper multi-layered structural coatings receptive appearance strength forming coated paperboard including coated white paperboard, coated boxboard, cast white paperboard and coated white paperboard. They are white paperboard or cardboard as base paper, cast or pigmented. It is mainly used for making cards, folding cartons and cartons. The quality of raw paper for coated paperboard not only directly affects the production, processing and final product quality, but also has a great influence on the quality of the packaging, storage and transportation of goods. The author believes that the basic paper that meets production, processing, and commodity circulation requirements should have the following basic requirements.
1 Multilayer Structure and Corresponding Slurry Proportioning The coated paperboard base paper is made from a cardboard machine equipped with 3 to 8 formers. The slurry layer is divided into a surface layer, a liner layer, a core layer, and a bottom layer. Each layer is made of 1 to 3 formers. The ratio of slurry, excipients and additives in each layer will vary depending on the quality requirements of the final product. Each layer has different effects on the properties of coated paper base paper.
The surface layer has the greatest impact on the folding paper, smoothness, gloss, whiteness or brightness, surface strength, and liquid retention properties of the coating. The high-grade coated paperboard base paper is made of natural or bleached softwood pulp or needle-leaved and broad-leaved mixed wood pulp. The mid-range product incorporates a certain amount of chemical straw (such as bleached mash) and imported OCC. Low-grade products use imported waste paper and domestic waste paper. Surface layer quantitative range of 30 ~ 40g/m2.
The lining plays a very important role in whiteness, elasticity, printing adaptability, hue saturation, and “link†surface and core layers. Generally use 100% DIP. The lining is made by one or two formers. The quantitative range is 40-50g/m2.
The core layer plays a leading role in the looseness of the base paper and the product cost, and is often made from cheap raw materials. The coated base paper paper base paper was made of two or more formers using TMP or CTMP. The quantitative range is 100 to 400 g/m2.
The bottom layer is the inner surface of the card and the carton. There should be a certain degree of smoothness, small dust, uniform color, and surface strength. It has a great effect on the strength and stiffness of the base paper. Except for the coated 100% bleached wood pulp used for the base paper of the coated white cardboard, the rest was mixed with waste pulp or used pulp. The bottom of the quantitative range of 40 ~ 50g/m2.
2 Good paint acceptance In order to make the surface of the base paper fiber and fiber floc cover a uniform, flat surface with certain characteristics, whether or not the surface of the base paper can accept the coating uniformly is a problem that must be solved. For this reason, in addition to using a suitable coating formulation and using a high quality coating head, it is worth noting the following aspects.
2.1 Appropriate surface water resistance During the coating and drying process, the adhesive migration of the coating will increase the macroscopic roughness of the coated cardboard, affecting its optical properties and coating strength. The essence of the migration is capillary penetration to reduce the water retention value of the coating fluid. Internal sizing and simultaneous surface sizing are good ways to control capillary penetration. Dispersed rosin gum, AKD is a commonly used internal sizing agent. CMC and hydroxyethyl starch are good paperboard surface sizing agents. Sizing press, calender surface sizing, film size press, all can be used as surface sizing device. The author once applied surface coating to the kraft boxboard. As a result, the smoothness was improved more than twice than that of the base paper, the printing glossiness was increased by 1.6 times, and the bursting strength was improved by more than 20%. The adaptability of printing is greatly improved, and the effect of sizing is that the surface water absorption is not more than 40g/m2 (2 min).
2.2 Smooth base paper surface Compared with coated paper base paper, the macro and micro roughness of coated paper base paper is relatively large. For a uniform distribution of the coating color on the base paper, a smooth surface with a moderate finish is necessary. However, the excessively smooth base paper will reduce the adaptability of the box and the resistance of carton stacking and transportation friction. Production practice shows that the smoothness of the base paper is generally controlled to be not less than 15 seconds, and the smoothness of the coated white paper base paper is more than 20 seconds, and the difference between the smoothness of the front and back surfaces is appropriate.
2.3 Uniformity of raw paper moisture The uniform moisture in both the longitudinal and transverse directions is an important condition for the smoothness of the base paper, and it is also the basis for the even distribution of the coating and its combination with the base paper. General control in the range of 7% to 9%.
3 Integrity, cleanliness, and consistent color appearance Because coating cannot change or completely obscure the flaws of the base paper, paper defects, such as holes, creases, carpet marks, and gaps, should be minimized. Break rate should be controlled to a minimum. All layers of slurries, especially surface and lining slurries, must have perfect deslagging, screening and purification equipment, and strict process management to minimize the amount of dust. Dust above 0.7mm2 should be as small as possible (white paperboard base paper should be coated. No allowed).
The grades, manufacturers and quantity of slurry, rubber, fillers, dyes and auxiliaries are kept stable, and the process management is strict. The color tone of the base paper is stable, and favorable conditions are created for the stability of the coating operation. It is reported that if the whiteness of the white cardboard surface differs by 1%, the surface whiteness of the coated paper will differ by about 4.5% to 5.0%. The lining whiteness difference of 9%, the whiteness of the original paper 3% difference, there is a difference of 0.8% after coating, there is a difference of 1.2% after painting or calendering. Therefore, we must pay attention to surface whiteness, and we must also strive for higher whiteness of the lining layer (DIP). It is generally believed that the whiteness range of the base paper is preferably from 75% to 80%.
4 sufficient base paper strength The base paper strength determines the strength of the coated paperboard. The transverse folding endurance, ring pressure strength, stiffness and surface strength of the base paper indicate the stress that the coating process, the printing process, and the card manufacturing and box making processes can withstand, as well as the carton and carton carrying performance, packaging and stacking. Adaptability during transportation. Too low intensity can cause loss of papermaking, processing, and even the quality of product packaging. Therefore, attention should be paid to the process management and operation of slurry processing, filling, and papermaking, so that the strength index of the base paper can be stabilized at the current national standard value for white cardboard or cardboard. When necessary, the company's internal control standards should also be specified. Surface ash should not exceed 5% to ensure adequate surface strength.
5 Excellent Forming Quality The uniform paper sheet forming is an important guarantee for uniform coating of the cardboard surface. The original paper is integrated into the current horizontal, vertical porosity, smoothness, finishing, especially the uniformity of the quantitative and thickness. Many factories have made strict control of banner quantification and thickness as one of the main parameters for production control. It is generally believed that the quantification difference of banners should not be better than 3%.
The paper forming quality is related to the ratio of slurry, purification and beating. Special attention should be paid to slurry screening and purification. To set up an efficient net sizing process, select the pre-screening, purifying equipment, and slushing pumps. To stabilize the technical conditions and operation of the paper splicing, we must select a suitable shaper for the finished product and lay it out rationally. Cardboard machines that use stacked web formation have become commonplace. Pressure rotary screen formers have been used to make sheetstock slurry. The active curved plate mesh slot with the square cone tube cloth is an appropriate choice for the board machine below 100m/min. (Liu Yi You Zhimin Tianjin Paperboard Factory, 300350) ("Paper and Paper")
1 Multilayer Structure and Corresponding Slurry Proportioning The coated paperboard base paper is made from a cardboard machine equipped with 3 to 8 formers. The slurry layer is divided into a surface layer, a liner layer, a core layer, and a bottom layer. Each layer is made of 1 to 3 formers. The ratio of slurry, excipients and additives in each layer will vary depending on the quality requirements of the final product. Each layer has different effects on the properties of coated paper base paper.
The surface layer has the greatest impact on the folding paper, smoothness, gloss, whiteness or brightness, surface strength, and liquid retention properties of the coating. The high-grade coated paperboard base paper is made of natural or bleached softwood pulp or needle-leaved and broad-leaved mixed wood pulp. The mid-range product incorporates a certain amount of chemical straw (such as bleached mash) and imported OCC. Low-grade products use imported waste paper and domestic waste paper. Surface layer quantitative range of 30 ~ 40g/m2.
The lining plays a very important role in whiteness, elasticity, printing adaptability, hue saturation, and “link†surface and core layers. Generally use 100% DIP. The lining is made by one or two formers. The quantitative range is 40-50g/m2.
The core layer plays a leading role in the looseness of the base paper and the product cost, and is often made from cheap raw materials. The coated base paper paper base paper was made of two or more formers using TMP or CTMP. The quantitative range is 100 to 400 g/m2.
The bottom layer is the inner surface of the card and the carton. There should be a certain degree of smoothness, small dust, uniform color, and surface strength. It has a great effect on the strength and stiffness of the base paper. Except for the coated 100% bleached wood pulp used for the base paper of the coated white cardboard, the rest was mixed with waste pulp or used pulp. The bottom of the quantitative range of 40 ~ 50g/m2.
2 Good paint acceptance In order to make the surface of the base paper fiber and fiber floc cover a uniform, flat surface with certain characteristics, whether or not the surface of the base paper can accept the coating uniformly is a problem that must be solved. For this reason, in addition to using a suitable coating formulation and using a high quality coating head, it is worth noting the following aspects.
2.1 Appropriate surface water resistance During the coating and drying process, the adhesive migration of the coating will increase the macroscopic roughness of the coated cardboard, affecting its optical properties and coating strength. The essence of the migration is capillary penetration to reduce the water retention value of the coating fluid. Internal sizing and simultaneous surface sizing are good ways to control capillary penetration. Dispersed rosin gum, AKD is a commonly used internal sizing agent. CMC and hydroxyethyl starch are good paperboard surface sizing agents. Sizing press, calender surface sizing, film size press, all can be used as surface sizing device. The author once applied surface coating to the kraft boxboard. As a result, the smoothness was improved more than twice than that of the base paper, the printing glossiness was increased by 1.6 times, and the bursting strength was improved by more than 20%. The adaptability of printing is greatly improved, and the effect of sizing is that the surface water absorption is not more than 40g/m2 (2 min).
2.2 Smooth base paper surface Compared with coated paper base paper, the macro and micro roughness of coated paper base paper is relatively large. For a uniform distribution of the coating color on the base paper, a smooth surface with a moderate finish is necessary. However, the excessively smooth base paper will reduce the adaptability of the box and the resistance of carton stacking and transportation friction. Production practice shows that the smoothness of the base paper is generally controlled to be not less than 15 seconds, and the smoothness of the coated white paper base paper is more than 20 seconds, and the difference between the smoothness of the front and back surfaces is appropriate.
2.3 Uniformity of raw paper moisture The uniform moisture in both the longitudinal and transverse directions is an important condition for the smoothness of the base paper, and it is also the basis for the even distribution of the coating and its combination with the base paper. General control in the range of 7% to 9%.
3 Integrity, cleanliness, and consistent color appearance Because coating cannot change or completely obscure the flaws of the base paper, paper defects, such as holes, creases, carpet marks, and gaps, should be minimized. Break rate should be controlled to a minimum. All layers of slurries, especially surface and lining slurries, must have perfect deslagging, screening and purification equipment, and strict process management to minimize the amount of dust. Dust above 0.7mm2 should be as small as possible (white paperboard base paper should be coated. No allowed).
The grades, manufacturers and quantity of slurry, rubber, fillers, dyes and auxiliaries are kept stable, and the process management is strict. The color tone of the base paper is stable, and favorable conditions are created for the stability of the coating operation. It is reported that if the whiteness of the white cardboard surface differs by 1%, the surface whiteness of the coated paper will differ by about 4.5% to 5.0%. The lining whiteness difference of 9%, the whiteness of the original paper 3% difference, there is a difference of 0.8% after coating, there is a difference of 1.2% after painting or calendering. Therefore, we must pay attention to surface whiteness, and we must also strive for higher whiteness of the lining layer (DIP). It is generally believed that the whiteness range of the base paper is preferably from 75% to 80%.
4 sufficient base paper strength The base paper strength determines the strength of the coated paperboard. The transverse folding endurance, ring pressure strength, stiffness and surface strength of the base paper indicate the stress that the coating process, the printing process, and the card manufacturing and box making processes can withstand, as well as the carton and carton carrying performance, packaging and stacking. Adaptability during transportation. Too low intensity can cause loss of papermaking, processing, and even the quality of product packaging. Therefore, attention should be paid to the process management and operation of slurry processing, filling, and papermaking, so that the strength index of the base paper can be stabilized at the current national standard value for white cardboard or cardboard. When necessary, the company's internal control standards should also be specified. Surface ash should not exceed 5% to ensure adequate surface strength.
5 Excellent Forming Quality The uniform paper sheet forming is an important guarantee for uniform coating of the cardboard surface. The original paper is integrated into the current horizontal, vertical porosity, smoothness, finishing, especially the uniformity of the quantitative and thickness. Many factories have made strict control of banner quantification and thickness as one of the main parameters for production control. It is generally believed that the quantification difference of banners should not be better than 3%.
The paper forming quality is related to the ratio of slurry, purification and beating. Special attention should be paid to slurry screening and purification. To set up an efficient net sizing process, select the pre-screening, purifying equipment, and slushing pumps. To stabilize the technical conditions and operation of the paper splicing, we must select a suitable shaper for the finished product and lay it out rationally. Cardboard machines that use stacked web formation have become commonplace. Pressure rotary screen formers have been used to make sheetstock slurry. The active curved plate mesh slot with the square cone tube cloth is an appropriate choice for the board machine below 100m/min. (Liu Yi You Zhimin Tianjin Paperboard Factory, 300350) ("Paper and Paper")
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