At present, white board paper and white paper board have been widely applied to various types of packaging. The customer's requirements for product quality are getting higher and higher. In addition to the requirements for beautiful printing, carton forming is also required to be more accurate and perfect. This undoubtedly gives The packaging and printing industry has raised new challenges and brought new issues to us. This article intends to focus on a brief discussion of the effects of board moisture changes on the quality of colored packaging cartons and how to deal with them. 
First, the paper's moisture content and balance moisture
Paper moisture content has a great influence on printing. Water is too low, paper is brittle, and static electricity is easily generated during printing. If the content is too high, the ink will be difficult to dry. Moisture changes have a great influence on various properties of paper. With the change of moisture, the quantitative, tensile strength, flexibility, and folding resistance will change, and the paper size will also expand and contract, even curling and warping. Edge, wrinkle, lotus leaf phenomenon. All kinds of paper have an optimum moisture content value. At this value, the various properties of the paper are in good condition. From Table 1, it can be seen that the optimum moisture content of cast coated paper and cast coated white paperboard is 7%±25%, white cardboard is 4% to 7%, and single-sided coated white cardboard is 8%±2%. This is the moisture content of the paper when shipped. 
During storage in a printing plant, paper is used as a hygroscopic material. It absorbs moisture from the air. The rate of absorption depends on the relative humidity and temperature of the air. It also transfers water to the air and loses moisture. The rate depends on the moisture content of the paper. And the environment temperature and humidity. When the moisture absorption rate and the water loss rate are the same, the paper and the air are in balance and the moisture content in the paper is constant. In this case, the moisture contained in the paper is called balanced moisture. 
The relative humidity refers to the ratio of the moisture content in air at a certain temperature to the moisture content that the air can hold to saturation at that temperature. The same paper equilibrates moisture at different relative humidity.
In addition, the balance of moisture changes also has the following characteristics:
1 affected by the nature of the paper. At the same relative humidity, the more hydrophilic the paper, the higher the equilibrium moisture, and vice versa. Papers without excipients have a higher moisture balance, and fillers, sizing, coated paper, and low moisture balance. In the same variety, thick products have higher moisture balance than thin products because of the high ratio of raw paper rich in water absorbency in thick products.
2 affected by temperature. At the same relative humidity, the temperature change is about 15°C, and the equilibrium moisture change of the paper is about 0.5% at maximum. However, the overprinting requirement on paper moisture content in printing is controlled at ±01%. Otherwise, the accuracy of overprinting will be affected. Therefore, the relative humidity of the color printing shop should be controlled at the same time, and the temperature change should be controlled at ±3°C.
3 is reached by the balance of the trip - the impact of moisture or moisture. Under certain relative humidity, the moisture content of the paper when it is in equilibrium with low moisture absorption is lower than the moisture content when it is dehydrated with high moisture in the same relative humidity. This is the hysteresis hysteresis effect of the paper. To make the water content of the paper consistent with the original, it is necessary to adopt the “correction†approach. That is, paper that reaches equilibrium at a certain relative humidity must be placed in an environment where the relative humidity is lower than the original relative humidity if it is to be dehumidified after moisture absorption in a high-humidity environment, and vice versa. In addition, the speed of moisture absorption and desorption is different, and the speed of moisture removal is much slower. However, regardless of moisture absorption and desorption, the starting speed is relatively fast, and the closer it is to equilibrium, the slower it is. This process is also related to paper and air mobility. Under standard wet and temperature conditions, a single sheet of cigarette paper can be treated for 35 minutes to achieve 5.8% balanced moisture; various types of printing paper require 2 to 4 hours to reach 5% to 8% of equilibrium moisture. It takes longer for packaging cardboard. This hysteresis between the change in relative humidity and the change in the moisture content of the paper causes a hysteresis between the deformation of the paper and the change in relative humidity.
4 Affected by the directionality of the paper. The so-called directionality means that the balance of paper moisture is inconsistent in the longitudinal and transverse directions, and the transverse stretch rate is far greater than the longitudinal stretch rate. Therefore, the transverse stretch deformation of the paper is larger than that of the longitudinal direction. Tests have shown that the stretch of a single fiber in the transverse direction corresponds to about 20 times the longitudinal dimension. However, the arrangement direction of the fibers in the paper is various, and the number of fibers arranged in the longitudinal direction is usually a little more. Therefore, the gap between the vertical and horizontal telescopic ratios of the paper is not as large as that of the single fiber. Taking the relative humidity from 50% to 60% as an example, the vertical and horizontal telescopic ratio is about 3:7, that is, about 2.3 times. This ratio differs depending on the degree of orientation of the fibers, and the stronger the directionality, the greater the ratio. The papermaking of paper with scattered and disorderly arrangement of fibers is one of the key issues for reducing the horizontal stretching rate and avoiding misregistration. In the actual printing operation, it is only necessary to control the lateral direction with a large expansion ratio in an allowable range.
5 Affected by both sides of the paper. A very flat paper, when its environment changes, the paper will absorb or dehumidify in the air. If it is hygroscopic, the opposite side of the stretch is larger than the front, the paper will curl to the front; if it is dehumidified, the reduction of the opposite side is greater than the front, the paper will curl to the opposite side. Regardless of the direction of curling, it is always oriented along the longitudinal direction of the paper. This is caused by the fact that the positive and negative sides of the paper are oriented differently. In particular, cardboard shows even more performance in this area.
Third, the impact of moisture on the printing quality
The printability is reflected in the moisture content of the paper and is generally required to be consistent with the relative humidity of the production environment. 200 grams per square meter or more of all kinds of cardboard, in the papermaking process is a multi-layer composite paper, and according to its production process requirements, many manufacturers are in the paper from the paper machine after rewinding, it will be timely cutting, sealing plastic Packaged and accurate delivery at any time. Due to the multi-layer compounding process requirements, the water content of the board is generally about 5% higher than the water content of the plain paper. Although the high water content of the paper is advantageous for printing, it will bring a lot of trouble to the printing production if it is not well preserved and used. If the package is damaged, the local humidity of the paper inside the package changes, causing the paper to become wavy, tightly edged, and appearing high on one side and low on one side; the paper feeding is difficult during printing, the ink and ink balance is difficult to grasp, and changes in humidity can cause the paper to expand and contract. Multi-color overprinting is not allowed, such as the quality of defects in the back corners; in particular, there are still die-cutting processes in the next process. Paper retracting can also cause irregularities in die making and inaccurate die-cutting dimensions.
Therefore, in the case of packaging cartons of 200 grams per square meter or more, the following two points should be made in the specific production practice:
1 Keep and store paper scientifically and reasonably. In view of the uniqueness of cardboard, in order to prevent the paperboard from dewetting or absorbing moisture and causing the paper to adapt to changes, in the transportation and storage of paper, the integrity of the product packaging should be paid attention to so as to prevent the packaging from being damaged due to improper transportation and operation. Storage should not only pay attention to ventilation, but also to avoid light and wind, temperature control at 15 ~ 25 °C, relative humidity 40% ~ 65%. The stacking of paper should be stacked according to the paper production date, product category, and production address. Paper use should be based on the order of production date in order to provide paper as much as possible to provide the next process with a more stable paper humidity fitness.
2 Effectively control the humidity of the paper. If it is necessary to properly store and rationally use the product before cutting, how should measures be taken to prevent changes in paper size caused by changes in temperature and humidity after cutting? First of all, it is necessary to be scientific and reasonable in the production and command. The paper strives to be printed along with printing, and it is best to be able to prepare the paper in one hour before printing. The large quantities cannot be opened and cut all at once, and must be batched according to the printing speed and progress. Cutting, and cutting paper is best to use a plastic cover with good sealing performance to cover the product, so as to minimize the time of direct contact with the air, especially when multi-color products are printed on single and double color machines. The method becomes even more important. Not only white paper but also every color must be processed in the same way to prevent the multicolor overprinting caused by the humidity change, and to ensure the quality of the printed product. 
Fourth, the effect of moisture on the die-cutting accuracy
In order to increase the beauty of the product and increase the smoothness of the color box surface, 70% to 80% of the carton packs are now coated and calendered. Polishing is that the prints are evenly coated with a coating of varnish on the surface of the prints by a glazing roller, and then dried by heat to form a bright layer by evaporation of the solvent, and the light is reprocessed on the basis of the glazing of the prints. The high temperature of ~130°C and the pressure of about 138 kg/cm 2 make the bright layer formed on the surface of the printed matter more dense and higher in brightness. Due to this special process, the water content of the paper itself is severely dehydrated in a short time, and the paper inevitably shrinks. The amount of shrinkage is related to the structure of the paper and the initial humidity, although its shrinkage has nothing to do with the printing overlay. But directly affect the accuracy of die-cutting, such as a product original input size is x, width y, if you traverse 5 on a K paper, vertical 3, after printing will get a pattern size For 3y×5x products, the paper size shrinks after calendering, shrinks Δx in the transverse direction, shrinks Δy in the longitudinal direction, and die-cut after die-cutting with a die of the same size as the original will certainly result in die-cutting. Accuracy is inaccurate, and even the phenomenon of embossing, bleeding, and patterning is not centered. If customers are unsatisfied, it will cause some or all of the products to be scrapped and cause undue losses to the company. How to avoid or reduce such errors in specific production? Of course, the simpler method is to make the mold (dieboard) according to different paper and different shrinkage after finishing the calendering, but this often seriously delays the production cycle, and the size of the die cut will be smaller than the original size. For this purpose, we should gradually explore the humidity characteristics of various types of paper used in this unit and the horizontal and vertical shrinkage after calendering. Add this amount of shrinkage to the input size of the manuscript when printing, so that the final distance after contraction, The entire graphics size meets the standard requirements, which also allows the die-cut version to be produced in advance to ensure product quality and cycle time. 
Fifth, the effect of water on the folding resistance of the product after varnishing
Fold resistance refers to the paper crease property that occurs when the paper is folded, without cracks on the surface of the folding belt, peeling off of the slit coating, etc. It is usually used to indicate the toughness and surface strength of cardboard and board in the folded condition. . From the paper itself, the resistance to folding depends on the length, strength, flexibility of the fibers and the binding force between the fibers. A large part of China's papermaking raw materials are non-wood raw materials, of which more are grasses such as reeds, wheat straw, straw, and bagasse. Due to the influence of the properties of these raw materials, different toughness and brittleness will appear after paper is formed. The paper produced from raw materials such as hemp, hemp, and wood is better in toughness, but most grass materials have poor fiber length and a high content of heterocells. The paper we are using now, paper mills generally use grass fibers and wood fibers to properly match the toughness of the paper. However, due to the different proportions of wood pulp, the different filler production process makes the difference in the toughness of different papers. However, calendering is a high-temperature and high-pressure dehumidification process for paper, and through the calendering, the single fiber of the paper itself. Dewetting and becoming brittle, the ability of fibers to slip and disperse stress is greatly reduced, and the folding endurance is weakened, resulting in defects such as fluffing, peeling, cracking, and squashing during folding of the cardboard box in the die-cutting folder. It even caused the entire batch to be scrapped.
Therefore, in the specific production arrangements, customers choose paper, pay special attention to the performance of the paper and the effect of calendering on the folding resistance of the paper. Under normal circumstances, 250 ~ 380g of white board, white cardboard, better folding resistance, can be considered calendering process; and gray-white paper, not suitable for calendering, and due to the inherent characteristics of paper fibers, vertical folding resistance Sex is significantly better than the transverse folding resistance. This factor should be fully taken into account in the calculation of the vertical and horizontal arrangement of the carton and the calculation of the open size. Before the calendered product is cross-cut, it is first necessary to carry out the folding resistance test in the transverse and longitudinal directions of the calendered paper. If it is found that the folding endurance is poor, the calendered product can be passed on the machine from the reverse side of the paper again. Water, if the cycle is available, can also be placed in a place where the humidity is relatively high and the humidity is naturally adjusted so that, after proper moisture absorption, the paper has enhanced fiber strength and flexibility, improved folding resistance, and reduced waste and loss. (Wu Ruisheng Pan Zhenming)
First, the paper's moisture content and balance moisture
Paper moisture content has a great influence on printing. Water is too low, paper is brittle, and static electricity is easily generated during printing. If the content is too high, the ink will be difficult to dry. Moisture changes have a great influence on various properties of paper. With the change of moisture, the quantitative, tensile strength, flexibility, and folding resistance will change, and the paper size will also expand and contract, even curling and warping. Edge, wrinkle, lotus leaf phenomenon. All kinds of paper have an optimum moisture content value. At this value, the various properties of the paper are in good condition. From Table 1, it can be seen that the optimum moisture content of cast coated paper and cast coated white paperboard is 7%±25%, white cardboard is 4% to 7%, and single-sided coated white cardboard is 8%±2%. This is the moisture content of the paper when shipped. 
During storage in a printing plant, paper is used as a hygroscopic material. It absorbs moisture from the air. The rate of absorption depends on the relative humidity and temperature of the air. It also transfers water to the air and loses moisture. The rate depends on the moisture content of the paper. And the environment temperature and humidity. When the moisture absorption rate and the water loss rate are the same, the paper and the air are in balance and the moisture content in the paper is constant. In this case, the moisture contained in the paper is called balanced moisture. 
The relative humidity refers to the ratio of the moisture content in air at a certain temperature to the moisture content that the air can hold to saturation at that temperature. The same paper equilibrates moisture at different relative humidity.
In addition, the balance of moisture changes also has the following characteristics:
1 affected by the nature of the paper. At the same relative humidity, the more hydrophilic the paper, the higher the equilibrium moisture, and vice versa. Papers without excipients have a higher moisture balance, and fillers, sizing, coated paper, and low moisture balance. In the same variety, thick products have higher moisture balance than thin products because of the high ratio of raw paper rich in water absorbency in thick products.
2 affected by temperature. At the same relative humidity, the temperature change is about 15°C, and the equilibrium moisture change of the paper is about 0.5% at maximum. However, the overprinting requirement on paper moisture content in printing is controlled at ±01%. Otherwise, the accuracy of overprinting will be affected. Therefore, the relative humidity of the color printing shop should be controlled at the same time, and the temperature change should be controlled at ±3°C.
3 is reached by the balance of the trip - the impact of moisture or moisture. Under certain relative humidity, the moisture content of the paper when it is in equilibrium with low moisture absorption is lower than the moisture content when it is dehydrated with high moisture in the same relative humidity. This is the hysteresis hysteresis effect of the paper. To make the water content of the paper consistent with the original, it is necessary to adopt the “correction†approach. That is, paper that reaches equilibrium at a certain relative humidity must be placed in an environment where the relative humidity is lower than the original relative humidity if it is to be dehumidified after moisture absorption in a high-humidity environment, and vice versa. In addition, the speed of moisture absorption and desorption is different, and the speed of moisture removal is much slower. However, regardless of moisture absorption and desorption, the starting speed is relatively fast, and the closer it is to equilibrium, the slower it is. This process is also related to paper and air mobility. Under standard wet and temperature conditions, a single sheet of cigarette paper can be treated for 35 minutes to achieve 5.8% balanced moisture; various types of printing paper require 2 to 4 hours to reach 5% to 8% of equilibrium moisture. It takes longer for packaging cardboard. This hysteresis between the change in relative humidity and the change in the moisture content of the paper causes a hysteresis between the deformation of the paper and the change in relative humidity.
4 Affected by the directionality of the paper. The so-called directionality means that the balance of paper moisture is inconsistent in the longitudinal and transverse directions, and the transverse stretch rate is far greater than the longitudinal stretch rate. Therefore, the transverse stretch deformation of the paper is larger than that of the longitudinal direction. Tests have shown that the stretch of a single fiber in the transverse direction corresponds to about 20 times the longitudinal dimension. However, the arrangement direction of the fibers in the paper is various, and the number of fibers arranged in the longitudinal direction is usually a little more. Therefore, the gap between the vertical and horizontal telescopic ratios of the paper is not as large as that of the single fiber. Taking the relative humidity from 50% to 60% as an example, the vertical and horizontal telescopic ratio is about 3:7, that is, about 2.3 times. This ratio differs depending on the degree of orientation of the fibers, and the stronger the directionality, the greater the ratio. The papermaking of paper with scattered and disorderly arrangement of fibers is one of the key issues for reducing the horizontal stretching rate and avoiding misregistration. In the actual printing operation, it is only necessary to control the lateral direction with a large expansion ratio in an allowable range.
5 Affected by both sides of the paper. A very flat paper, when its environment changes, the paper will absorb or dehumidify in the air. If it is hygroscopic, the opposite side of the stretch is larger than the front, the paper will curl to the front; if it is dehumidified, the reduction of the opposite side is greater than the front, the paper will curl to the opposite side. Regardless of the direction of curling, it is always oriented along the longitudinal direction of the paper. This is caused by the fact that the positive and negative sides of the paper are oriented differently. In particular, cardboard shows even more performance in this area.
Third, the impact of moisture on the printing quality
The printability is reflected in the moisture content of the paper and is generally required to be consistent with the relative humidity of the production environment. 200 grams per square meter or more of all kinds of cardboard, in the papermaking process is a multi-layer composite paper, and according to its production process requirements, many manufacturers are in the paper from the paper machine after rewinding, it will be timely cutting, sealing plastic Packaged and accurate delivery at any time. Due to the multi-layer compounding process requirements, the water content of the board is generally about 5% higher than the water content of the plain paper. Although the high water content of the paper is advantageous for printing, it will bring a lot of trouble to the printing production if it is not well preserved and used. If the package is damaged, the local humidity of the paper inside the package changes, causing the paper to become wavy, tightly edged, and appearing high on one side and low on one side; the paper feeding is difficult during printing, the ink and ink balance is difficult to grasp, and changes in humidity can cause the paper to expand and contract. Multi-color overprinting is not allowed, such as the quality of defects in the back corners; in particular, there are still die-cutting processes in the next process. Paper retracting can also cause irregularities in die making and inaccurate die-cutting dimensions.
Therefore, in the case of packaging cartons of 200 grams per square meter or more, the following two points should be made in the specific production practice:
1 Keep and store paper scientifically and reasonably. In view of the uniqueness of cardboard, in order to prevent the paperboard from dewetting or absorbing moisture and causing the paper to adapt to changes, in the transportation and storage of paper, the integrity of the product packaging should be paid attention to so as to prevent the packaging from being damaged due to improper transportation and operation. Storage should not only pay attention to ventilation, but also to avoid light and wind, temperature control at 15 ~ 25 °C, relative humidity 40% ~ 65%. The stacking of paper should be stacked according to the paper production date, product category, and production address. Paper use should be based on the order of production date in order to provide paper as much as possible to provide the next process with a more stable paper humidity fitness.
2 Effectively control the humidity of the paper. If it is necessary to properly store and rationally use the product before cutting, how should measures be taken to prevent changes in paper size caused by changes in temperature and humidity after cutting? First of all, it is necessary to be scientific and reasonable in the production and command. The paper strives to be printed along with printing, and it is best to be able to prepare the paper in one hour before printing. The large quantities cannot be opened and cut all at once, and must be batched according to the printing speed and progress. Cutting, and cutting paper is best to use a plastic cover with good sealing performance to cover the product, so as to minimize the time of direct contact with the air, especially when multi-color products are printed on single and double color machines. The method becomes even more important. Not only white paper but also every color must be processed in the same way to prevent the multicolor overprinting caused by the humidity change, and to ensure the quality of the printed product. 
Fourth, the effect of moisture on the die-cutting accuracy
In order to increase the beauty of the product and increase the smoothness of the color box surface, 70% to 80% of the carton packs are now coated and calendered. Polishing is that the prints are evenly coated with a coating of varnish on the surface of the prints by a glazing roller, and then dried by heat to form a bright layer by evaporation of the solvent, and the light is reprocessed on the basis of the glazing of the prints. The high temperature of ~130°C and the pressure of about 138 kg/cm 2 make the bright layer formed on the surface of the printed matter more dense and higher in brightness. Due to this special process, the water content of the paper itself is severely dehydrated in a short time, and the paper inevitably shrinks. The amount of shrinkage is related to the structure of the paper and the initial humidity, although its shrinkage has nothing to do with the printing overlay. But directly affect the accuracy of die-cutting, such as a product original input size is x, width y, if you traverse 5 on a K paper, vertical 3, after printing will get a pattern size For 3y×5x products, the paper size shrinks after calendering, shrinks Δx in the transverse direction, shrinks Δy in the longitudinal direction, and die-cut after die-cutting with a die of the same size as the original will certainly result in die-cutting. Accuracy is inaccurate, and even the phenomenon of embossing, bleeding, and patterning is not centered. If customers are unsatisfied, it will cause some or all of the products to be scrapped and cause undue losses to the company. How to avoid or reduce such errors in specific production? Of course, the simpler method is to make the mold (dieboard) according to different paper and different shrinkage after finishing the calendering, but this often seriously delays the production cycle, and the size of the die cut will be smaller than the original size. For this purpose, we should gradually explore the humidity characteristics of various types of paper used in this unit and the horizontal and vertical shrinkage after calendering. Add this amount of shrinkage to the input size of the manuscript when printing, so that the final distance after contraction, The entire graphics size meets the standard requirements, which also allows the die-cut version to be produced in advance to ensure product quality and cycle time. 
Fifth, the effect of water on the folding resistance of the product after varnishing
Fold resistance refers to the paper crease property that occurs when the paper is folded, without cracks on the surface of the folding belt, peeling off of the slit coating, etc. It is usually used to indicate the toughness and surface strength of cardboard and board in the folded condition. . From the paper itself, the resistance to folding depends on the length, strength, flexibility of the fibers and the binding force between the fibers. A large part of China's papermaking raw materials are non-wood raw materials, of which more are grasses such as reeds, wheat straw, straw, and bagasse. Due to the influence of the properties of these raw materials, different toughness and brittleness will appear after paper is formed. The paper produced from raw materials such as hemp, hemp, and wood is better in toughness, but most grass materials have poor fiber length and a high content of heterocells. The paper we are using now, paper mills generally use grass fibers and wood fibers to properly match the toughness of the paper. However, due to the different proportions of wood pulp, the different filler production process makes the difference in the toughness of different papers. However, calendering is a high-temperature and high-pressure dehumidification process for paper, and through the calendering, the single fiber of the paper itself. Dewetting and becoming brittle, the ability of fibers to slip and disperse stress is greatly reduced, and the folding endurance is weakened, resulting in defects such as fluffing, peeling, cracking, and squashing during folding of the cardboard box in the die-cutting folder. It even caused the entire batch to be scrapped.
Therefore, in the specific production arrangements, customers choose paper, pay special attention to the performance of the paper and the effect of calendering on the folding resistance of the paper. Under normal circumstances, 250 ~ 380g of white board, white cardboard, better folding resistance, can be considered calendering process; and gray-white paper, not suitable for calendering, and due to the inherent characteristics of paper fibers, vertical folding resistance Sex is significantly better than the transverse folding resistance. This factor should be fully taken into account in the calculation of the vertical and horizontal arrangement of the carton and the calculation of the open size. Before the calendered product is cross-cut, it is first necessary to carry out the folding resistance test in the transverse and longitudinal directions of the calendered paper. If it is found that the folding endurance is poor, the calendered product can be passed on the machine from the reverse side of the paper again. Water, if the cycle is available, can also be placed in a place where the humidity is relatively high and the humidity is naturally adjusted so that, after proper moisture absorption, the paper has enhanced fiber strength and flexibility, improved folding resistance, and reduced waste and loss. (Wu Ruisheng Pan Zhenming)
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