Thin film material is a non-absorbent material with low surface energy (surface tension), such as the surface without some kind of pretreatment, improving the surface tension, using ordinary ink printing regardless of the application method, the ink is difficult to achieve the ideal run In the wet state, it is difficult for the ink to achieve a good firmness, and the ink layer can not be avoided.
For this reason, in order to improve the fastness of the ink layer on the surface of a thin film material, the printing industry generally adopts a corona treatment or a method of preliminarily coating an ink-receptive coating on its surface to ensure the firmness of the ink. After the surface is pretreated, the fastness of the ink layer on the surface of the film is greatly improved. According to the usual detection methods in the printing industry, both the tape test and the friction test are used for the friction test, and the results meet the standards promulgated by the domestic standards department. For example, the firmness of our thin-film label sample ink has passed the National Packaging and Decoration Quality Inspection Center and is tested according to the national standard GB-7706-87 test standard. At the same time, some customers have their own detection methods (such as some Taiwanese printing plants), use their own equipment to detect their own printed film material labels, their ink layer resistance to friction and the relevant indicators fully qualified.
However, although the ink firmness of the film material label has passed the inspection, the scratch resistance of the ink layer has not been fundamentally solved in actual applications. For example, some domestic cosmetic customers, the plastic bottles after the labeling are directly placed into the packaging box, without any partitions or fillers between the bottles, and then shipped to the sales. During transportation, the bottles collide with each other and cause friction. Finally, the ink on the label surface of the bottle is seriously worn out and cannot be sold normally.
In order to solve this serious problem of ink layer wear, in addition to the final customer to take measures in the product packaging, the printing factory usually adopts three methods to solve.
Direct screen printing on packaging bottles
Screen printing, due to the use of special ink and thick ink layer can solve the ink scratch, wear problems, but screen printing only for ordinary text, color and line printing. For high-resolution color patterns, screen printing cannot be achieved. Can not achieve the product packaging and decoration effect.
In addition, after the screen printing, the pattern on the surface of the bottle body is difficult to remove, and it is difficult for the customer to perform the quantitative printing process of the bottle body, and the bottle body printing quantity is too large or not enough, which will bring customers Unnecessary waste. Therefore, the screen printing method for printing bottles is only suitable for simple, mass-produced products, and it is difficult to promote on high-grade secondary products.
Composite BOPP film and protective ink on the surface of the printed film sticker
Label surface coating, protection of ink, ink layer to solve the problem of wear, this process is commonly used in some domestic ink factory, received a certain effect, but also brought some negative effects. According to our visits to customers and investigations in recent years, the following points are summarized for the disadvantages of the membrane process:
First, the finished product label increases the cost and the customer increases the cost
The price of the film adhesive material itself is much higher than that of the ordinary paper label material, and the BOPP film used for film lamination on the film surface should be made of high-grade materials with good transparency and small deformation. The average price is 3 to 3 Between 5 yuan, this increases the overall cost of the sticker, and customers increase the cost.
Second, changed the physical properties of the film adhesive material
BOPP laminating material is a biaxially stretched film material that does not substantially deform itself, and there are many varieties of non-drying adhesive film materials, each of which has different characteristics. For example, uniaxial tensile deformation (Primax, FasClear), and some biaxial tensile deformation (PVC, PE). Such materials such as compounded BOPP film lose their own characteristics, change the physical properties, and cannot be applied to deformable bottles such as cosmetics or shampoo plastic bottles.
Third, the thickness of the label has been thickened, internal stress has been generated, and the possibility of warping and detachment of the label has been increased.
The BOPP used for laminating is generally about 15 μm. No matter what type of laminating mechanism is used, BOPP must be given a certain amount of tension so that it fits flatly on the label surface. Under the action of tension, the composite label produces internal stress that rises upwards, so that whether the label is attached to a flat or curved body, the possibility of outward curling is increased.
In addition, the thinner the overall label is, the smaller the internal stress is after deformation, and the firmer the adhesive is. After the film is overlaminated, the label is thickened. After the deformation, the underlying material is squeezed and the overlaminated material is stretched. All of them have internal stress that restores the deformation. Therefore, the probability of curling after labeling after lamination is very high. Large, especially when the temperature is too low, the glue flow is poor, or the label surface is not fully compressed when labeling.
Fourth, the lamination process generates a large amount of static electricity, making it difficult for printing and final application of automatic labeling by customers.
Plastic film material is a kind of material with very unstable polarity. During the printing process, static electricity will be generated, and the combination of the two film materials will generate a large amount of static electricity. This kind of static electricity brings troubles to printing and processing, especially die-cutting and waste-discharging stations. Static electricity can cause tags to fall off frequently and make the machine unable to produce at high speed. What is more serious is that the static electricity remaining in the finished roll will affect the normal use of the label. For example, labels on the labeling machine are not properly labelled, skewed, and sometimes even the labeling machine cannot operate normally and can only be manually labelled, which seriously affects production.
Fifth, laminating process affects machine speed and increases overall consumption
The tension of the lamination film is proportional to the machine speed, so the speed of the lamination machine is limited. Generally, the lamination speed on the rotary labeling machine in China is within 30 m/min, and the lamination is not lamination and only printing (glazing) is performed. Machine (flexo) color printing, the speed up to 80 ~ 100m/min. This means that the lamination process is inefficient.
At present, the maximum length of the bottomless paper BOPP composite film that can be purchased on the market is 200 meters, which means that the labeling machine must stop and replace the composite film every time it runs less than 200 meters, so the machine is on and off. According to the principle of printing, when the printer is stopped and turned on, it causes changes in the inking system, which changes the amount of ink applied to the printed material. Finally, the color of the label is changed, resulting in waste. This is also one of the reasons for the high cost of lamination.
Sixth, the use of UV coating on the surface of the film material to protect the ink
UV glazing technology is currently used in the domestic label printing industry in the mid-round transformation, half-round transformation of the label machine to paper or film materials commonly used methods to protect the ink. The UV glazing process improves the brightness of the print surface, and it is even more important to protect the ink layer and prevent the ink from being scratched off due to its strength and friction resistance.
Compared with the lamination process, although the strength of the varnish is not as good as that of the BOPP film and the finished product label, there is a clear advantage in the overall characteristics.
Seventh, reduced the overall cost of label printing
The cost of the UV coating process is much cheaper than the compounding of the BOPP compound film. At present, there are many types of UV varnish in the country, and the performance is not the same, so the price varies greatly. We recommend customers to use high transparency, scratch resistance, low shrinkage, fast drying and high strength. The price of this type of varnishes is generally around 150-200 yuan/kg, with 2g per square meter counted, the cost per square meter is 0.3-0.4 yuan, the price is almost one-tenth of the composite film price, so Say reduced the overall cost of the label print.
Eight, do not change the physical properties of film materials
The thickness of the UV varnish after drying is 2-5μm, which is integrated with the ink layer, which has little effect on the overall thickness of the label. The coating material used after coating will not affect the deformation and bending ability due to the varnish layer. Keep the flatness of the label itself. The same UV coating process avoids the phenomenon that the label is detached on the packaging bottle body due to the deformation of the material itself, which is also one of the reasons why some domestic customers select the coating process.
Nine, will not generate static electricity
UV coating process basically does not generate static electricity, on the contrary, you can add "static agent" in the coating oil, which can eliminate static electricity on the surface of the printed matter, so that other processing processes after the coating process smoothly, such as die cutting, row Waste, cut or overwrapped. There is no static labeling problem when the end customer uses the label.
Ten, can be quickly on-line glazing, improve productivity, reduce consumption
The speed of the press is not affected by the glazing process and can be printed quickly. Generally, the flexo printing machine prints complex graphic labels with an average speed of 60-80 m/min, and does not need to stop when there is no paper change in the middle; while the speed of the laminating process is 30-40 m/min, and frequent parking of the composite film affects Registration and ink uniformity. When used, the glazing process improves efficiency and reduces consumption.
In summary, in order to protect the ink layer on the surface of the film and improve its scratch resistance and wear resistance, among the three methods used in the label printing industry, the UV coating process is the best one. At present, the on-line coating process is widely used in developed countries, and the lamination process is rarely used unless the customer requests it. The same is true in China. In areas where label printing is well-developed, such as Shanghai, Guangzhou, Tianjin, and other large-scale professional label printing plants commonly use UV coating technology.
To this end, we advocate and promote the use of UV coating after printing on the surface of the film sticker to protect the ink layer. For the glazing process, after years of hard work, summarizing the practice of the printing factory, and especially the trial and error of our company's training center on the arsoma flexographic press and the IGT printability instrument in the last year or two, we have summarized many experiences. . These experiences include selection of UV coating, control of printing speed, adjustment of drying and curing power, and control of coating coatings. Now, these experiences have been successfully applied in some printing plants. The samples we tested were generally recognized by some large cosmetic customers.
To further illustrate our experience, we first introduce the basic methods of UV coating in the domestic label industry;
The use of UV letterpress machine, offset printing machine (post-curing) direct printing light coating thin, poor gloss, can be single or reel coating, can be partially or as a whole, coating oil viscosity.
The coating glaze is coated with a two or three roll device. Can be installed on the label machine to run synchronously, suitable for web. Can also be used as a polishing machine independent coating, suitable for sheetfed. The coating has low static electricity, and the glazing layer is affected by the speed change and the accuracy of the glazing device. The glazing oil has low viscosity and is suitable for glazing.
The advanced glazing principle of the stencil coating machine, which uses the reticle stick to precisely control the amount of coating, can partially or entirely polish the sizing, and the sizing oil has low viscosity.
In order to guarantee the quality of UV coating, we have summarized three experiences:
First, it is necessary to use UV varnishes and auxiliaries that are compatible with the ink. Otherwise, it will affect the firmness of the glazing layer or the chemical reaction between the ink and lacquer.
Second, to