Cracking the problem of paper curling on the outer packaging of gift boxes requires controlling these major factors effectively!

The outer packaging paper is one of the main components in gift box production, which plays an important role in printing, surface finishing, die-cutting, and pasting. However, during the production process, paper curling often occurs due to many factors, seriously affecting the orderly progress of production. The main reasons for curling are as follows: firstly, the moisture balance between the front and back of the paper is lost; The second is that the surface technology changes the tension on one side; Thirdly, environmental changes have disrupted the stability of paper, and fourthly, water molecules in adhesives have weakened the surface resistance of paper. In addition, the adaptability of material quality, the rationality of surface process design, and the standardization of process operation are all factors that cause the outer packaging paper to curl. This article provides a comprehensive analysis of the problem and formulates effective preventive measures, ultimately achieving the goal of controlling the curling of the outer packaging paper.
Material selection
Firstly, an analysis of the raw materials required for the gift box is conducted. In addition to using gray cardboard with different thicknesses, the gift box also uses 128g/m2, 157g/m2, and 200g/m2 copperplate paper as the main packaging materials for outer packaging, edging, inner pasting, sanding, edge insertion, and pulling. When these components curl during production, it has a huge impact on quality and production efficiency. Therefore, before being stored or put into use, important technical indicators of each batch of copperplate paper should be tested, such as moisture, smoothness, glossiness, coating strength, absorption, dryness, and a series of other items related to printing and post-processing suitability. Paper that exceeds technical indicators should be used with caution, and only reasonable selection can be beneficial for normal production.
01/The Influence of Moisture Content on Paper Flatness
Copperplate paper has a stable moisture content after production, and the surface of the paper is flat and smooth. When the external environment changes, the humidity will inevitably affect the flatness of the paper. When the environmental humidity is higher than the relative humidity of the paper, such as in rainy, snowy, or humid weather, the paper will absorb varying amounts of moisture. The side that absorbs more moisture will curl towards the opposite side of the paper; When the environmental humidity is lower than the relative humidity of the paper, the paper will release moisture outward. The side that loses more moisture loses its ability to maintain balance and curls towards the water surface. Therefore, the deviation between the relative humidity of the environment and the relative humidity of the paper should be controlled within 5% to avoid obvious curling phenomenon.
02/The Relationship between Paper Quantity and Flatness
The flatness of paper is closely related to its basis weight. In terms of resisting changes in environmental factors, high basis weight paper is superior to low basis weight paper due to its substrate thickness. The stress on the front and back of low basis weight paper is weaker, and when the surface is disturbed by environmental humidity, curling is inevitable. During the pasting process, the moisture in the adhesive penetrates low basis weight paper faster than high basis weight paper. Under the action of water molecules, the curling rate of low basis weight paper is much higher than that of high basis weight paper. Considering the characteristics of paper, when choosing outer packaging paper, while meeting the process requirements, small-sized products should use 128g/m2 copperplate paper, and large-sized products should use copperplate paper or art paper with a weight of 128g/m2 or more. This choice can ensure product quality and improve production efficiency.

03/Relationship between Single and Double sided Coating and Paper Flatness
Copperplate paper has double-sided coating and single-sided coating. Due to different processing techniques, double-sided coated copperplate paper has basically equal stress on both sides and maintains good flatness. Single sided coated copperplate paper has one side protected by coating, but the other side cannot effectively isolate the infiltration of moisture. When the moisture content increases, the balance between the front and back sides is disrupted, and the side that absorbs moisture will curl towards the coating surface. This is why single-sided coated paper is more prone to curling. Therefore, when designing gift box technology, it is advisable to avoid using single-sided copperplate paper as much as possible.
The influence of 04/composite process on paper flatness
Composite copperplate paper is a type of paper that has a thin film attached to one side of the paper. This type of paper is mainly used for gold and silver surface effects and UV printing is preferred. In addition to the flatness of the paper, the most critical technical indicators of this kind of paper also include the adhesion between the surface facial mask and the paper. The flatness is determined by the tension of the surface facial mask. As long as the paper with high tension surface facial mask is in contact with the natural environment, especially in the season with large humidity changes, due to the different water absorption of the front and back of the paper, the front of the paper is completely moisture-proof, while the back of the paper is very sensitive to the environment, and the process control is not strict, water molecules will take advantage of the situation and curl will occur.
In order to reduce the curling of paper, suppliers are required to increase the back coating process to prevent further moisture absorption on the back of the paper. When both sides of the paper are isolated from the environment, the curling phenomenon will be minimized. Therefore, in the design of gift box technology, the back coating process should be taken into consideration, especially when using low weight paper. In addition, considering the requirements for stiffness and adhesion of the outer packaging paper, it is advisable to control the back coating amount to around 3g/m2. This composite process design basically solves the curling of the printing surface and improves the stiffness, laying a stable foundation for the operation of subsequent processes.
The Influence of Storage Cycle of 05/Roll Paper on Paper Flatness
Flat paper is cut from roll paper, and the core part belongs to the small diameter range. If the roll paper is stored for a long time before cutting, there will be a certain memory of the paper grain direction. After cutting, if the storage time is short, the paper may curl at both ends when encountering environmental changes. Therefore, when purchasing paper, it is important to check the production date. For urgently needed paper, careful consideration should be given to its potential impact on production to prevent curling from causing uncertainty in normal production.
Printing Operation Standards and Control
Printing on the outer packaging of gift boxes is different from printing on cardboard boxes. Cardboard boxes are made of high basis weight materials, and their paper flatness can meet printing requirements well. However, the surface material of gift boxes is mainly low basis weight materials. Unstable control of each link, such as environmental control, machine operation, ink selection, and employee skills, can lead to poor printing quality. Therefore, regardless of the type of printing equipment used, it is necessary to strictly follow the process specifications. Only by establishing a high sense of responsibility can good products be printed, and vice versa. In order to provide a smooth printing surface for the next process, the following aspects should be taken into account first.

01/Workshop temperature and humidity control
The optimal working environment temperature for the printing workshop is 18-23 ℃, with a relative humidity of 55% -65%. To ensure the quality of printed products, it is necessary to create a production environment with relatively stable temperature and humidity. As is well known, paper is a material that is sensitive to changes in temperature and humidity. When the environmental humidity changes, the moisture content of paper also changes accordingly. The moisture content of paper is closely related to its printability. Under the interference of the above factors, paper deformation is inevitable, and it can also cause changes in other properties of the paper, such as an increase or decrease in moisture content, a decrease in the tensile strength and surface strength of the paper, and the phenomenon of double sheets caused by static electricity during printing. Therefore, temperature and humidity control in the printing workshop is the primary task in preventing paper curling.
02/Paper moisture content control
In the production process of gift boxes, the main factor affecting product quality is moisture. From environmental humidity to paper moisture content, from the water content on the printing machine to the water content control of the pasting glue, all of these factors can interfere with stable production. Therefore, before printing production, it is necessary to first check the moisture content of the paper. Paper changes within the range of less than 8% are basically stable, but regardless of whether the paper loses or absorbs water, the flatness of the paper will be affected. Therefore, the control of paper moisture content mainly considers the control of the base paper. Secondly, the non printing surface of the paper is sealed to reduce its sensitivity to environmental factors. In general, when the moisture content of the base paper is within the control range, the curvature of the printed surface will be minimized. In addition, in various stages of production and transportation, full wrap wrapping protection is adopted to maintain the stability of paper moisture content and reduce product curl.
03/Other moisture control and use of additives
The transfer of moisture on the surface of the printing plate is indispensable during the printing process, but the moisture on the surface of the printing plate should be strictly controlled. Under the principle of not dirtying the printing plate, the smaller the moisture, the better. If the surface moisture content of the printing plate is too high, it will not only cause the coating on the paper surface to peel off and affect the ink quality, but also cause the paper to stretch and shrink, which in turn affects the printing of graphics and text and the complete reproduction of dots. In addition, some moisture can also penetrate into the ink, causing ink emulsification. The emulsified ink enhances the penetration of the paper, weakens the ink oxidation effect, and causes adverse phenomena such as slow drying or dirty printed surfaces. In order to effectively prevent the curling of the printing surface, anti curling additives can be added to the ink. This additive can achieve twice the result with half the effort in anti curling, but the amount added should be determined according to the area of the ink on the printing surface and the type of paper. Standardized and reasonable use has a very positive significance for anti curling.
Temperature and humidity difference control in different workshops

The entire production process of gift boxes is longer than that of cardboard boxes. From front-end printing to back-end production, from processing each component separately to assembling them, they are all processed in different workshops in order. Due to the involvement of multiple processes, consistency in temperature and humidity is required in different workshops. Only when the temperature and humidity are similar can the stability of product quality be guaranteed. If the difference exceeds the control range, the adaptability function of the product will be reduced, which will affect the smooth progress of production. Therefore, we require that the temperature and humidity in the back-end workshop should be similar to that in the printing workshop. Under the same environment, the physical changes of materials can remain stable.
But the reality tells us that it is generally difficult for the post-processing workshop to meet this standard because it involves numerous equipment, and the heat dissipation between the equipment absorbs some of the moisture in the environment. This operating state also keeps the temperature and humidity constantly changing. In addition, the frequent entry and exit of forklifts and paper tractors limit and weaken the effectiveness of the workshop's isolation from the outside world. It is still difficult to fully achieve the control indicators.
In view of the above issues, only modifications can be made to the entrance and exit, similar to the printing workshop, by installing a humidification system while ensuring temperature, in order to ensure stable environmental temperature and humidity. In addition, it is necessary to install an automatic lifting system for the gate, which means that the car can lift and the car can close, so that the isolation of the gate can be effective. With a stable indoor environment, the semi-finished products transported in the previous process can be kept in a constant temperature and humidity state. Under these conditions, the processing quality of the semi-finished products will not be affected.
The pasting process that needs to be mentioned here, like the subsequent hot stamping and die-cutting processes, has many heat sources, most of which come from the glue passing machine and hot melt glue machine. The heat and water vapor emitted during operation can cause subtle changes in the local environment. As these devices are located at the starting end of the production line, multiple production lines are arranged side by side, limiting the heat and water vapor to only linger locally, resulting in temperature and humidity differences between the head and tail positions of the production line. This difference has a certain impact on the outer packaging after glue coating. To address this, it is necessary to increase the air circulation in the workshop by using an electric fan to blow in the opposite direction to fully circulate the air. At the same time, adjust the blowing direction of the air conditioner to avoid blowing towards the products. Only by doing so can the temperature in the workshop be stabilized within 18-23 ℃ and the relative humidity be between 55% and 65%. Only then can the balance be maintained and the products be produced smoothly.
Outsourced factory production management and controlThe production of gift boxes is a process of multi craft design and application, which uses surface finishing techniques to superimpose and make the products more beautiful, thereby attracting more people's favor. To achieve perfect process results, mutual cooperation between production processes is required. However, most factories do not have the configuration of multiple process productions and equipment, which requires the support and cooperation of multiple outsourcing manufacturers to complete product production. But most of the outsourcing manufacturers we face have uneven levels of control, including open type ones without temperature control systems, as well as single equipment processing manufacturers. Doors and windows lack integrity, and the temperature inside and outside is the same, let alone dry and wet. When semi-finished products enter this environment, the paper will be disturbed by the uncertainty of the environment, and its adaptability function will be changed. Without basic guarantees, no matter what product, it can only seek more blessings on its own.
In view of this, it is particularly important to choose qualified and standardized outsourcing factories. Firstly, it is necessary to conduct an audit and evaluation of whether the factory's management meets the requirements, whether the skill level meets the process standards, whether the process operation has the stability of multi batch production, whether the production plan is arranged in an orderly and standardized manner, etc. Only qualified manufacturers can be included in the qualified supplier list. At the same time, these outsourced factories should be classified and managed, and targeted outsourcing should be carried out for different products. This is the best way to eliminate unqualified products.
Management standards for semi-finished product transfer process
Every product is considered a semi-finished product during the process before production is completed. These semi-finished products undergo a transfer process during the implementation of surface technology, such as workshop to workshop, downstairs to upstairs, indoor to outdoor, each scene will have differences. Without standardized operation or arbitrary adjustment of process procedures, the physical properties of the semi-finished product itself will be affected. If each process is not strictly controlled, it is impossible to know which link has a problem, which brings certain difficulties to solving problems.
Therefore, it is necessary to establish standards for the operation of the process, and timely use wrapping film to protect the processed components. There are clear regulations on the number of layers of paper wrapping, and random wrapping or gaps between films cannot achieve isolation. The most lethal factor is the semi-finished products placed outdoors, which are affected by factors such as spring, summer, autumn, winter, cloudy, sunny, rainy, snowy, temperature and humidity, which can cause the semi-finished products to absorb or release some moisture. With the extension of storage time, in addition to stretching, there will also be lotus leaf edges, wavy surfaces, and curling phenomena that cannot be avoided. These problems lead to the inability of the next process to produce normally, seriously affecting the production progress of the product and delaying the delivery time.
Pasting process control

The pasting process is an indispensable part of gift box production. Scientific and standardized control of the pasting process is an important step in ensuring paper flatness. Key control points such as temperature, humidity, processing conditions, and operating standards are closely related to product quality. In addition, the amount of coating is also an important part of the operation. Excessive coating can cause the high molecular weight in the glue to crowd together, unable to produce good tensile force, and the strongest attraction between them is also affected, only playing a filling role rather than a bonding role. The accumulation of a large amount of glue also makes it difficult for the water between the polymer bodies to evaporate, and most of it stays on the surface of the paper, changing the balance between the two sides of the paper. Under the action of single-sided stress, it forms curling conditions.
Therefore, it is necessary to control the pasting process with data. Firstly, check whether the temperature reaches 18-23 ℃ and the relative humidity reaches 55% -65%. Then, test the viscosity of the glue. The viscosity of the white latex must be above 3000cPs, the solid content must be above 45%, and the coating amount must be 31 ± 2g/m2. The animal protein gel is completely dissolved, stirred evenly, and the concentration reaches 55 ± 2%. The coating amount is generally controlled at 33 ± 2g/m2.
Of course, the change of seasons causes changes in temperature and humidity, and the technical indicators and opening time of the glue should also be adjusted. For example, animal protein glue has formula standards for winter, spring, and summer. In summer, the temperature is higher, and the opening time of the glue must be extended. In winter, the temperature is lower and the volatility is less, so the opening time of the glue is correspondingly shortened. Regardless of the type of adhesive, the control of the amount is the most crucial. The coating amount depends on the distance between the rubber rollers. The most accurate method is to use a ruler to correct it. After keeping the technical parameters on both sides consistent, observe the balance of the printing surface coating with the naked eye. Then use the index finger to dip the adhesive layer that stays on the paper. Wherever the finger goes, the outer packaging paper can be lifted and instantly peeled off, indicating that the coating amount basically meets the requirements of pasting and pasting.
This testing method, although simple, serves the purpose of initial detection. After completing the initial inspection, use the weighing method for precise verification. The specific method is to calculate the packaging area, weigh the packaging paper, apply glue, and re weigh the total mass of the packaging. Production can only begin after the coating amount reaches the standard value. After determining the coating amount, it is also necessary to consider the corresponding relationship between the opening time of the adhesive and the operating range. If the transmission distance is too long, the adhesive will form an irregular adhesive force in advance, which seriously affects the bonding quality. Therefore, it is recommended that after the adhesive coating of the outer packaging paper is completed, it should be positioned and formed with the gray board box in the shortest possible time, and the pasting should be completed before the deformation of the outer packaging paper, so as to minimize the impact of the outer packaging paper roll on production.
Film coating process control
The outer packaging paper of gift boxes mostly adopts laminating technology, and the film plays a good role in beautifying and protecting the surface of the product. However, due to some non-standard operations, the flatness of the outer packaging paper is affected. Normally, the tension on the film surface determines the direction of curling. If the outer packaging paper curls upwards, it indicates that the tension on the film is too high; If the outer packaging paper curls downwards, it indicates that the tension of the film is too low.

During the film covering process, the tension of the film during operation varies slightly. The tension in the starting and ending sections is different. The tension of the entire film roll is relatively small at the beginning, and it increases as it reaches the center of the roll. Therefore, during the laminating process, attention should be paid to observing changes in tension and adjusting them in a timely manner to minimize the tension difference between the front and rear stages, ensuring controllable process and stable tension. We can use a simple method to verify whether the tension control meets the process technology requirements. First, take the laminated printing surface and wait for its heat to be completely released. Then, use an art knife to cut a 5cm × 20cm long paper strip on the printing surface. The cutting position is selected on both sides of the printing surface along the direction of the paper pattern. Then, cut one strip on each side of the printing surface perpendicular to the direction of the paper pattern. Place the film surface on the table and observe its changes carefully for about 20 minutes. If it is flat and there is no change, it indicates that the tension of the film is appropriate. If it curls upwards, it indicates that the tension of the film is too tight. If it curls downwards, it indicates that the tension of the film is insufficient. At this time, adjust the tension of the film according to the specific situation. Different devices should be determined according to the actual situation.
In addition, while controlling the tension, it is also necessary to regulate the operating speed. It is reasonable to control the film coating speed at 20-30m/min. In addition, the control of drum temperature should not be taken lightly. Excessive temperature not only causes the film to shrink and deform, but also easily wrinkles and bubbles the printed surface. At the same time, it also stores too much heat inside the paper, resulting in prolonged release time. If the temperature cannot be dissipated in a timely manner, it will change with the influence of environmental factors, which will bring trouble to the subsequent process operations. Finally, it should be mentioned that regardless of the type of paper used, as long as the surface finishing process chooses film coating, it is recommended that the paper's silk lines intersect perpendicularly with the film's silk lines. This can not only improve the flatness of the printing surface, but also provide convenience for subsequent processing.
Post process control

Many gift box packaging papers often use post printing processes such as reverse printing, snowflake printing, and frosted printing. During the implementation of these processes, UV curing is indispensable. Although UV ink is cured, it improves its adaptability and adhesion. However, the paper loses a large amount of water under high temperature and strong light irradiation, reducing its moisture content and maximizing its thermal energy storage. Due to the additional surface technology, it hinders the full dissipation of thermal energy. The only way to quickly release thermal energy is on the back of the paper. When it is affected by the environment or invaded by water molecules, the moisture absorption process will occur on this surface.
When there is enough moisture immersed, it becomes inevitable for the paper to curl upwards. In this regard, when implementing post press process operations, manual paper collection should be set up at the end of the equipment. The main purpose is to shake the paper fan on the completed printing surface, allowing an appropriate amount of wind to enter the paper gap and help it release internal heat, in order to improve its ability to adapt to the environment. After the temperature of the printed surface decreases, pour the foot plate again and then wrap it with wrapping film to seal it. Before use, it should be placed in the processing workshop for no less than 12 hours to allow it to have a sufficient adaptability process. Production can only be arranged after it has been tested and fully meets the technical requirements of the process. These simple and convenient operations weaken the impact of printing surface curling on production, and product quality can also be guaranteed to a certain extent.
By optimizing the paper processing technology, the tension value on the paper surface has been stabilized, and the moisture content has also been controlled within a reasonable range. With materials that meet the requirements of printing technology, production between each process can be orderly. Order means stability, and stability can improve efficiency and reduce costs. In addition, it also has a positive promoting effect on the level of on-site management and lean production management, thereby creating conditions for the healthy development of the enterprise.