The hottest new situation and corresponding techno

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The new situation and corresponding technology faced by the laminating industry today

first, the new situation faced

the in-depth development of the socialist market economy and the inevitable trend of economic globalization have prompted the printing industry to closely follow the development of high-tech in the world, adopt advanced digital technology and constantly develop new and excellent materials. The main body of printing processing has shifted from the traditional way of printing a number of books, newspapers and periodicals with the same content at one time to commercial printing such as multi variety, small quantity, high quality, constantly changing content and format, surface finishing and complex shaped packaging after printing. Digital transmission, high-resolution full force scanning and prepress production of direct plate making technology, coupled with a multi-color high-efficiency printing machine with a speed of more than 15000 pages per hour, have greatly shortened the printing cycle

the paper selection positioning of book covers, commodity packaging and personalized printing materials is increasingly moving towards high-grade coated and super polished fine paper or paperboard

commercial printing materials have higher requirements for printing substrate and surface finishing and beautification. These make the current process and technology of solid-phase glazing and film coating of post press finishing suffer a new impact. Only by studying these new situations, putting forward corresponding new technologies and solutions, and promoting the continuous innovation of post press film covering technology, can we improve the overall level of the printing industry and open up a broad market for the printing industry

II. The impact caused by the new situation

1. In order to unify with the international publication standards, the national publication administration has notified that since May 1, 2000, the 200 steel strand experimental machine has a high stiffness, the size, size and size of books and magazines must comply with the GB/t788-1999 standard. With the expansion of the size of books and periodicals, many provincial and district textbook publishing departments have changed the text paper to offset paper, and the illustrations and cover paper to coated paper

commercial printing tends to be high-volume coated paper and super polished paperboard

the basic difference between coated paper and uncoated paper, high weight coated paper and low weight coated paper is the smoothness of the paper. In order to improve the printing quality, coated paper or fine coated paper with high smoothness is used, and the printing effect is reflected in rich color expressiveness and realistic image restoration

the coating layer and full ink printing layer applied and calendered on the base paper substrate will reduce the surface tension of the paper, thus affecting the wettability and adhesion of the adhesive during lamination processing. The fine and dense coating layer and the external force on the coating calendering increase the density of the paper as well as the quantitative increase. The film covering technology under the same process conditions will not achieve the previous diffusion, penetration and dislocation anchoring of adhesive molecules to paper substrates. Not only the bonding strength of the composite under this surface state is reduced, but also the metallic printing ink such as gold and silver with coarse ink pigment particles is easy to fall off

2. The color design of a large number of publications and packaging materials adopts a large area of color blocks and two primary colors and black (four colors) as the main tone. The solid color of high-density dots or the intermediate color of dot overlap increases the thickness of the ink printing layer. Due to the paper receiving method of rapid printing and overlapping pressing and stacking, the ink printing layer can only be oxidized and dried on the surface of the printing layer at the moment of leaving the printing machine due to the lack of basic conditions such as time and area in contact with the air

the ink printing layer with dry surface and unable to dry inside will only be gradually dried with the extensive and effective contact of the air in the later stage of film covering, bookbinding, forming into a box or circulation use stage. In this process, the ink diluent (solvent) volatilized and escaped for drying will not only cause the blistering and film removal of the coating processed by the gluing wet composite process, but also cause the odor migration of solvent volatilization, which will make the packaged goods smell or deteriorate

3. The effect of greatly shortening the printing cycle is that the water content of the paper is still high during post press finishing. Under the working conditions of hot pressing, 3D printing of water contained in paper has been widely used in school education, product design, medical treatment, aviation and other fields. The water vapor produced by volatilization is not only an isolating agent to reduce the composite adhesion, but also a factor that destroys the surface crusting, leveling and permeability of hot melt adhesive

4. Eliminate the binding process reform of iron wire flat binding, making the wireless binding process an important technology for more than four printed books. The binding hot melt adhesive with softening point ≥ 170 ℃ puts forward new requirements for the heat resistance of film covered products. When the compound temperature is about 70 ℃, the solvent transfer type quasi pre coating film is very easy to lose adhesion and void at the back and side of the book

5. The diversification of post press molding, die cutting and indentation makes the coated products subject to the impact of different physical shapes and strengths in some parts. These local impact forces are far greater than the composite pressure. If the pressure is small and the tension of the film is large during compounding, the film at the local stress will rebound, void or fracture

III. corresponding new measures

since 1999, for more than two years, we have been studying the corresponding new measures of film covering technology for the technological progress of printing, binding, box making (box) and the change and upgrading of printing carrier substrate:

1 The application of the new process

the improvement of the smoothness of the surface state of the printing substrate, the shortening of the printing processing cycle, the increase of the water content of the paper and the residual solvent of the ink that is not completely dry, recombines with the organic solvent that is still preserved in a certain amount after the production of the products that are coated by the wet composite process, which aggravates the damage of the composite strength of the coated products. Ensuring zero pollution and high-strength lamination has become the necessity of film coating process reform

the pre coated film of hot melt adhesive coated by solvent-free melting (odorless, non stick by hand) is selected as the composite material, and the dry composite process of hot pressing is the basic measure

2. Standard operability

when laminating the substrate of calendered coated paper with small surface tension, it is necessary to ensure that the adhesive has good leveling. For the synthetic modified thermoplastic adhesive, it is only of guiding significance for material performance analysis and structural design. Under the thermal condition of no less than 80 ℃, there is a good solid-liquid phase transition, and the tackifying resin and main tackifying resin can play a role. At this time, the heat provided by the composite machinery will be continuously absorbed by the composite substrate paper. If the substrate has large quantity, small tightness, high humidity, thick ink printing layer and heavy color, it has greater absorption of heat. In addition, the heat is unstable, uneven, and the supply is not enough, which makes the thermal energy acting on the adhesive attenuate. Therefore, the compound production process is often in the process of heating up. The temperature set during production operation should be appropriately increased considering the actual influence of the above factors and various conditions such as the temperature, humidity and ventilation energy of the production environment, which lead to the decline of composite heat. Generally, the minimum value of composite set temperature shall not be lower than 85 ℃, and the maximum value shall not exceed 115 ℃. When the composite working pressure and workpiece running speed are determined, and the continuous production operation, the heating system should always be in the state of maintaining temperature, and the composite finished product with good brightness is normal. The heating process operation of "gathering the source of high-end material display quality" - Shanghai aluminum industry exhibition value should be avoided at the end of the set temperature

lamination is produced by hot pressing. The guarantee of its heat also needs pressure coordination. The working pressure should be 8 ~ 15MPa. Depending on the basic conditions of the machined parts, the pressure supply can be appropriately increased, but should not be reduced

the running speed of the workpiece determines the actual action value of the composite working conditions (heat and pressure). When the temperature and pressure are fixed values, take the speed of the main machine of the laminating machine as 300 R/min as the benchmark, and in the adjustment area of R/min, increase the speed of the main machine by 100 turns per minute as a gear change for adjustment. The composite effect was tested. For each grade of speed increase, the temperature and pressure decreased by 3.4% and 9.4% respectively compared with that before the increase; Still in the adjustment area of 600 ~ 800r/min with this rate of change, the decrease range of temperature is 5.2% and pressure is 11.1% for each grade of speed increase; When this equivalent continues to increase by a level, that is, to 900r/min, compared with 800r/min, the reduction rates of temperature and pressure increase to 8% or 13% respectively

based on the actual conditions of the current composite substrate (printed matter compounded with BOPP film), in order to ensure good initial viscosity and better later effect, the running speed of the workpiece should not exceed 12m/min (the rotating speed of the host is 600r/min), subject to the high brightness and good fastness of the composite

3. Surface pretreatment

the above two measures are to adapt to the process and technical operation changes after the smoothness of the substrate surface state is improved

for large-area printed matter with deep color and thick printing layer, the perfect effect cannot be achieved only by technical adjustment. It is important to pretreat the surface of the substrate, increase the surface tension without changing the appearance and color performance of the print, and provide reliable operability and later curing durability for the initial bonding strength of the composite. Practice has proved that electrostatic pretreatment of substrate surface is another technological innovation of film coating process in recent years

its principle is:

220v or 380V, 50Hz conventional electricity, through the silicon controlled circuit, generates 20 ~ 30KV, 15 ~ 20kV high-voltage high-frequency current, which is applied to a pair of electrodes with dielectric (commonly used as quartz) as the interval, forming a silent diffuse blue purple glow discharge

this blue purple spark with uniform dispersion and moderate strength between electrodes has an impact on the paper printing medium passing through it. Electrostatic field can not only adsorb and remove dust, oil and moisture on the surface of paper prints, but also stimulate the activity of resin molecules in surface coatings and ink combinations. While cleaning the sundries attached to the paper surface, it can improve the surface performance, increase the surface tension, and improve the affinity between the coating or ink layer and the adhesive

ozone will be generated by ionization of oxygen-containing gas in electrode gap during discharge. Ozone is an excellent oxidant. The chemical reaction process of oxygen ionization in the air can promote the drying and solidification of offset resin ink, and change the situation that the epidermal conjunctiva of the ink layer is dry and the interior is not dry after printing

4. Drying to reduce moisture

the shortening of the printing cycle makes it difficult for the moisture absorbed by the paper to volatilize during printing. The water that has not yet volatilized is generated into steam at the hot pressing working interface. Through the extremely short instant of the interface (when the workpiece runs at a speed of 12m/min, the instant is 0.11s) and the extremely small included angle (almost coincident with the covered film), the water that escapes from the paper matrix and turns into steam is clamped between the film and the paper in a gaseous state, which is covered as a whole with the nature of the isolation layer. It affects the transparency and bonding strength of the composite

it has become another basic new technology of post press processing after the progress of printing technology to heat the printed matter before laminating to reduce its moisture content. It can not only improve the transparency and composite strength, but also help to reduce the occurrence of composite wrinkles and waste

for small batch processing, the printed matter can be spread out in the laminating machine or in the environment with other heat sources. Hot air blowing or dehumidification can also be carried out by paper drying machine or clamping mode

large quantities of printed matter can be changed into a paper drying room. In the room with closed doors and windows, a paper drying device composed of several infrared electric heating tubes and fans is installed. The generated heat is blown to the paper stack from different angles by the fan. The ventilation fan and automatic temperature control device for external ventilation can keep the indoor humidity and temperature at 50% and 30 ℃ respectively. The printed matter just off the machine is here

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