The Control of the Technology of Curling the Aluminized Paper Trademark
The surface of vacuum aluminized paper with its bright metallic color is beyond the spectrum color. Due to the strong metal texture on the surface of the aluminum-coated paper trademark, it can give people a rich and elegant feeling, which greatly improves the quality of the product. The good advantages of vacuum aluminized paper materials make it more and more widely used in various packaging printing, especially the printing of middle and high-grade alcohol label products. Alcoholic labels require that they have good stiffness and flatness after printing in order to facilitate the normal labeling of the labeling machine, make the trademark flat and uniform on the bottle wall, and improve the quality of the labeling process. However, if the trademark has obvious curling problems, it will directly affect the quality of the winery's labeling, and it may be prone to wrinkle labels, warping labels (the edges are not sticking), dropped labels, and skewed labels. Therefore, It is of great significance to correctly understand and control the curling performance of the vacuum aluminum-plated paper trademark.
1. Understanding of the curling index of aluminum coated paper trademark
The curling property of the aluminum-coated paper trademark refers to the time when the back surface is in full contact with normal temperature water until the horizontal paper curling activity is completely still. Its standard is ≥12s, and the sample area can generally take the specifications corresponding to the printed trademark area. In daily testing, it can be found that when the curling test of the base paper or trademark is performed, there are generally two basic performances. One is that the paper surface is obviously curled and then slowly returns to the original state, and the other is the horizontal paper sides. There was only slight curling, even no curling, it seems that there is no curling in the latter. In fact, the latter is less sensitive to moisture, and the labeling test shows that this kind of aluminum coated paper labeling is also no problem. The test analysis shows that the curl of the trademark is directly related to the curl of the base paper. In other words, if the curlability of the base paper is unacceptable, the curlability of the trademark is generally unacceptable. Therefore, to control the curling of the trademark, we must first control the aluminum coated paper to obtain a better control effect. Now, the technical standards of aluminum-coated paper are generally set by the manufacturers themselves, and the standards of various manufacturers are not the same. As for the curling index, the standard values ​​also have certain differences, and even some manufacturers have not formulated This standard. When the printing factory purchases aluminized paper, the manufacturer should be required to control the curling index to ≥12s, which will play a certain role in ensuring the quality of printing and labeling.
Second, the relationship between the characteristics of aluminized paper and the curl of the trademark
The base paper of aluminized paper is waterproof coated paper, also known as wet-strength coated paper in the industry. Compared with ordinary coated paper, it has good alkali permeability and wet strength. If the fiber of the base paper is loose and lacks stiffness and hardness; the wet strength agent performance is not good or the amount is not enough to make the pulp fiber effectively and quickly tightly combined; the quality of the base paper is not good, the paper surface is easy to absorb moisture, and the base paper Uneven thickness, poor stiffness and other undesirable conditions will make the trademark prone to curling. Therefore, it should be based on the quantitative of aluminum coated paper, alkali impregnation resistance, lye permeability, water absorption (back), horizontal elongation, longitudinal elongation, dry longitudinal tensile strength, wet longitudinal tensile strength, drying In order to ensure that the trademark curlability index is qualified, effective indicators such as transverse tensile strength and wet transverse tensile strength can be effectively controlled. The main detection and control standards for aluminized paper can be controlled by referring to the following table (enterprise standards) and inspection requirements:
1. Technical index of aluminized paper:
2. Inspection methods and rules
(1) Quantitative inspection: Punch 10 samples with an area of ​​100mm × 100mm with a circular quantitative sampler, weigh them with a precision electronic balance, and multiply by 10 to get the test result;
(2) Alkali immersion resistance test: cut one sample with a size of about 100mm × 100mm, put it in an alkaline solution container with a temperature of 80 ° C ± 2 ° C and a concentration of 2.5% to 3.0%. Several times, the test sample rupture should be ≤ 2 pieces;
(3) Alkaline immersion liquid penetration test: After folding the back edge of the sample paper into a concave shape, fix the four corners with staples firmly, then evenly spread phenolphthalein on the back of the paper pattern, and wipe it evenly with your fingers, the front side is facing Place it in an alkaline solution container with a temperature of 80 ° C ± 2 ° C and a concentration of 2.5% to 3.0%, and then press the stopwatch immediately. When there is obvious point-like penetration discoloration on the back of the sample, it is the alkaline solution penetration time;
(4) Water absorption test: Cobb Value method is used to test the sample, and the weight of water absorbed per square meter per minute is the test result;
(5) Elongation test: cut 5 specimens of about 100mm × 100mm in size, use a 70mm long die-cutting blade as the mold, and use a needle or awl to poke two longitudinal and lateral positions of each specimen. The mark with a straight line spacing of 70mm, the sample is immersed in normal temperature water immediately, after 5min, the sample is taken out and flattened naturally on a flat table, and then the distance between each sample mark is measured with a vernier ruler. The calculation formula of the vertical and horizontal elongation is: the average value of the length of 5 samples after water immersion-70 ÷ 70 × 100%;
(6) Tensile strength test of base paper: use a strength meter to measure the dry and wet tensile strength;
(7) Thickness test: each sample is used to measure the thickness of 3 points with a thickness meter, and then the average value is the test result;
(8) Delivery moisture: Take one 100mm × 100mm sample arbitrarily, weigh it with a precision electronic balance, put it in a moisture analyzer and bake it for 80s ± 20s, and then weigh it with an electronic balance. The formula for calculating the water content is: the original weight of the sample-the weight of the sample after drying ÷ the original weight of the sample;
Inspection rules: Randomly select one piece of each batch of products as a test sample, and the qualified ones can be used in the warehouse. [next]
3. The relationship between the production process of aluminum plating and the curling of the trademark
Wet-strength coated paper in the process of vacuum aluminum plating production process, if the process is not handled properly, it will easily affect the curl of the trademark. In the printing production process, we found that after unwrapping and cutting of some aluminized paper, curling phenomenon occurred on both sides of the horizontal paper surface quickly, no matter which side curled, it will affect the normal printing production, and the trademark after printing It is also prone to curling. So why is there a curling phenomenon? Observation and analysis through testing experiments, the author found that when the back of the aluminized paper is in contact with water, the two sides of the horizontal paper are immediately curled to the front, and when the aluminized paper is taken to dry, the two sides of the horizontal paper appear to curl toward the back. It can be seen that if the wet-strength coated paper is not properly controlled during the spraying process, it will be prone to curling and deformation during use. The aluminum-coated paper with sizing on the back is not sensitive to the temperature and humidity of the external environment, so it is not easy to curl when printing. However, the back-coated aluminum coated paper has poor water absorption, which is not conducive to normal labeling. In addition, the influence of other production processes of aluminized paper on its curlability is also relatively large. When I visited the aluminized paper manufacturer, I had a preliminary understanding of the vacuum aluminized production and trademark curling performance through on-site observation and understanding: After the base paper after the primer was subjected to aluminizing, steam box drying and top coating, Moisture content has a phenomenon of partial dryness, generally the moisture content is less than 4%, and it is sensitive to air humidity when used, it is easy to produce hygroscopic deformation phenomenon. Therefore, the aluminum-coated paper also needs to be treated with steam resurgence. Some manufacturers call it water resurgence. The process is generally: the paper roll after the topcoat passes through the steam box on the resurgence machine, so that the paper surface absorbs a certain amount of moisture, making The moisture content is controlled between 4.5% and 6%, and then embossing and slitting. It can be seen that whether the moisture regaining process of the aluminum-plated paper is proper or not has a great influence on the curl of the trademark. This requires that the paper surface must receive steam evenly, and at the same time, the temperature and humidity of the production site such as aluminum plating, steam resurgence treatment, embossing and slitting must be adapted to the temperature and humidity of the production environment of the printing plant, so that the plating can be produced. Aluminum paper, when put into printing, will not produce obvious curling phenomenon. In addition, if the depth of the embossing of the aluminized paper is too deep and the lines of the horizontal paper are too tightly arranged, the stiffness of the aluminized paper will be damaged and curling will occur easily. Therefore, the embossed depth of the aluminized paper is required To be appropriate, the arrangement between the lines should not be too tight, so as to achieve a good control of its curl.
Fourth, control the packaging and storage technology of aluminized paper to prevent curling and deformation of the trademark
Wet-strength aluminum-coated paper has strong water resistance on the front side and good moisture resistance. However, when the temperature difference in the storage environment is large, the aluminum-coated paper with poor packaging can easily lose or absorb moisture on the back side, resulting in variation in moisture content. This causes curling on the paper. Therefore, after the aluminized paper is cut, in addition to packaging each order of paper, a whole piece of aluminized paper should also be sealed with a plastic film for waterproof sealing, and several layers of waste paper should be used above and below each piece of paper Lining, and then use a wood board with good flatness to prevent deformation of the aluminum sheet on the surface. In addition, the temperature and humidity of the warehouse where the aluminum-coated paper is stored must also be well controlled. Its temperature and humidity must be compatible with the temperature and humidity of the printing workshop, and there cannot be a large disparity. In this way, the packaging and storage of aluminum coated paper are well controlled, and the trademark is not prone to curling and deformation.
Fifth, control the production process of trademarks to prevent curling and deformation of trademarks
1. Control the printing pressure. If the technical control is not in place during the printing process, the trademark may also be curled. If the printing pressure is heavy, especially the trademarks printed by the flexographic printing process, and the trademarks printed with the horizontal paper grain parallel to the radial direction of the cylinder, if the printing pressure is too heavy, it will be more prone to lateral curl deformation.
2. Control the water-ink balance process. The lithographic printing process should be printed with as little water as possible under the condition of water and ink balance, and the abnormal printing process of "large water and large ink" should be avoided to prevent the trademark from absorbing too much water and being prone to curling defects.
3. Control the coating amount of ink. In daily printing process practice, we can find that when printing a large-area layout, the trademark is most prone to curling. Therefore, for the spot color layout with a large printing area, the “dark ink thin printing†process should be used as much as possible, that is, the ink color should be adjusted darker to make the printing ink layer relatively thinner, so that the printed color can meet the requirements of the sample. It can also better avoid the curling phenomenon of the trademark due to the large amount of ink absorption on the paper surface.
4. Control the temperature and humidity of the trademark production environment. In the printing and inspection process of trademarks, because the single-sheet paper is printed or inspected, it is the easiest to absorb or lose moisture. Therefore, the printing and inspection production site must control the temperature and humidity, the general temperature should be controlled at about 25 ℃; the air humidity should be Controlled at about 60%, the temperature and humidity of the printing and inspection production site should not be significantly different, and the semi-finished products and boxed products must be sealed and packaged with plastic film, so as to better prevent trademark moisture changes and The phenomenon of curl deformation.
Due to the fact that during the production and use of aluminum-plated paper, it is inevitable that it will be affected by some variability factors. It is understandable to have a slight curl, but the obvious curl is bound to affect the normal labeling production of the winery, and it should not be. . The author believes that the technical control of the curling of the aluminum-coated paper trademark involves all aspects of the base paper material, aluminum-plated production process, production environment and printing process technology. However, the most critical thing is the technical control of the production process of the base paper. As long as the moisture content of the aluminized paper is properly controlled, the aluminized paper does not have a sensitive reaction to the temperature and humidity of the external environment, so the chance of curling during the printing process is relatively Less. Therefore, the correct understanding of the curling of aluminum-plated paper and its related influencing factors, focus on effective technical control from the source of quality, and at the same time, control all links in the printing process to make the printed trademark products have a good The flatness meets the labeling quality requirements of the winery.
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