In recent years, with the gradual improvement of people's living standards, metal printing and packaging products have become more and more popular. At the same time, the requirements for the quality of its products are also rising. The quality of the printed iron products will directly affect the market competitiveness of the company. In the production of metal printing, the quality of printed products is ensured, and the quality problems caused by technical errors are eliminated. This is a task that companies must pay attention to. This course will be analyzed from the printing process and discuss with fellow students how to control the quality of printed iron products.
I. Product Standards The first production operator must clearly understand the product standard of the product to be produced.
Second, the development of product production process to provide customers with samples or product design pictures for analysis, and according to the product's logo requirements to develop the production process;
Third, version room operation process control
1. Effect of film film on printing quality
The process of developing and fixing the film after exposure is directly related to the sharpness and contrast of the image on the film. Therefore, the key to making a plated film is to look at the contrast between the graphic part and the non-graphic part of the densitometer. The higher the density, the greater the contrast and the better the quality of the plate-making film, and the quality of the printing plate produced with it can be guaranteed. In addition, the thickness of plate-making film base also has an impact on plate-making quality. Generally, thin-film film is better than thick-film film. (usually 0.1mm thick film)
2. Effect of Printing Plate on Printing Quality
During the printing process, the intensity of the light source, the distance of the light source from the plate material, and the length of the exposure time all affect the quality of the printing plate. Strong light source, short distance, relatively short exposure time; weak light source, long distance, relatively long exposure time. Under a certain light source and distance, with the increase of exposure time, the decomposition of the film in the visible part of the plate is intensified until the surface of the photopharmaceutical film is completely decomposed. If the exposure time continues to increase, no light is seen on the edge of the pellicle film surface due to exposure to strong light, and the photographic film gradually begins to decompose, so that the resulting printed image line will become thin, even missing and blurred. If the exposure time is insufficient, the non-graphic part of the photopharmaceutical film surface is not completely decomposed, and the non-graphic part of the printing plate is still covered with a film. When the printing is performed on the machine, it will become scratchy. (The general standard exposure time is about 3.8KW iodine lamp about 12-15 seconds, refers to the exposure time of the single lens exposure equipment) In addition, when the printing plate is vacuumed, the degree of adhesion of the film and the printing plate only affects the quality of the printing plate. If it is not true, there may be problems such as ghosting and blurring of the printed plate. (The general standard vacuuming time is 30 seconds, which refers to the single lens vacuum time of the drying equipment)
3, the impact of development on print quality
The concentration of developer is too large and the development is too fast, which can easily cause excessive development of the printing plate. The lines of the graphics become thin, the fine dots are missing or the graphic is unclear, which affects the printing quality. When the concentration of the developer is too small, the photo-degradation film surface is too small. Difficult to clean, easy to dirty when printing on the machine. (Concentration ratio of general developer solution: developer solution: volume of water = 1:4:1:8, if the device is used for automatic development, the solution is heated to approximately 27°C, the developer concentration ratio is 1:8, and the development time is 30 seconds; If manual development is used, the ratio of developer concentration is generally 1:4 and the development time is 60 seconds because it is a low normal temperature.
Fourth, the impact of ink transfer on print quality
The printing process is actually the process of ink transfer. In general, the overall ink transfer rate of offset printing is low, about 38%. After the printing plate is in contact with the blanket, the ink transfer rate is about 50%. When the blanket is contacted with the iron sheet, the ink transfer rate is about 76%. It is very important to control the transfer rate of the ink. Ink suitability, ink balance, plate, blanket performance, iron sheet, printer, etc. will all affect ink transfer.
1. Effect of ink performance on ink transfer
The inks with low viscosity and high fluidity are easier to transfer, and the transfer rate is higher; the transfer rate of inks with high viscosity and low fluidity is small. To increase the ink transfer rate, the annual and fluidity of the ink must be controlled. The performance of the ink will also vary slightly with the environment. When the temperature is high, the viscosity of the ink is relatively low; when the temperature is low, the viscosity of the ink is relatively high. In actual production, inks of different types, types, and different drying methods should be selected according to the time. In addition, adding a suitable amount of ink in the ink, you can adjust the ink performance, is conducive to control the dot increase to increase the degree of ink transfer.
2, blanket performance on the ink
The blanket must have good ink absorption and ink transfer properties, and it must also have properties such as oil resistance, acid resistance, alkali resistance, and good elasticity. If the blanket is not thoroughly cleaned after printing, the ink retained in the back of the blanket gradually consolidates and hardens, causing the viscous structure on the surface of the rubber to be damaged, directly affecting the ink-receiving rate of the blanket, and decreasing the ink transfer rate of the blanket. For this reason, after the printing is completed, the blanket should be washed thoroughly. If the downtime is relatively long, a layer of lime can be rubbed on the surface to make sure that the blanket always maintains a proper villous structure and that the blanket has a good Ink and ink transfer.
3, the printing plate quality of the impact of print quality
The quality of the printing plate base sand, the hydrophilicity of the metal plate, and the lipophilicity of the coated polymer resin film surface are related to the suitability of the printing plate, affecting the ink transfer and the layout ink balance. In the plate-making process, exposure and development will also affect the performance of the plate.
4. Effect of ink balance on printing quality
Ink and ink is a relatively balanced, not absolute balance. In the process of high-speed operation of the equipment, both the graphic part and the non-graphic part of the printing plate are inked and watered, and they infiltrate each other. Therefore, ink emulsification will inevitably occur on the printing plate. If the amount of water and ink is not well controlled, ink emulsification is bound to deepen, resulting in stencil and dirty plates in the printing plate. Printing methods are usually used to reduce the amount of water, the appropriate increase in the amount of ink, but some will reduce the amount of ink. In addition, the ink emulsification will vary with changes in the environment and conditions. In actual production, the viscosity of the ink and the pH of the fountain solution should be properly controlled to control the amount of ink and the amount of water. Paste, not dirty version prevail.
5, the impact of printing pressure on print quality
Printing pressure refers to the interaction between the plate cylinder and the blanket cylinder, the blanket cylinder and the impression cylinder, and it is a necessary condition for ink transfer. The printing pressure is too small, the ink is not easy to transmit, the ink is light and weak; the printing pressure is too large; the ink volume expands to the non-graphical part, making the dot gain serious and the image distorted. It is also easy to make the printing plate and the blanket resistant to printing force. decline. Therefore, the mechanical pressure must be properly adjusted. Different thicknesses of tinplate require different printing pressures. Only suitable printing pressure can ensure uniform ink and clear dots.
Fifth, production operation process control
1, the preparation of the printing plate
The production captain must make all preparations according to the production and construction plan before printing. Including the preparation of printing plates and inks. First of all, we must understand the contents of the construction list and do not make mistakes about the product, specifications, and dimensions. After the printing plate is taken, first check whether the product is correct, whether the printing plate number and the color are the same as the construction list, whether the thickness of the printing plate is the same, whether the printing plate size is suitable for the requirements of the printing machine, and the layout is very smooth and smooth. Whether there are scratches or scratches in the graphic and whether the missing points and rules are complete; whether the position of the bite is correct and whether the position of the graphic and text is appropriate; find out that the problem is solved in time.
2. Preparation of inks, coatings, and other solvents
According to the type of production and construction requirements, take the appropriate ink and paint. Should pay attention to the following questions:
1) Do not take ink coating wrongly;
2) master the basic characteristics of each color ink and coating, including hue, drying performance;
3) Understand the approximate usage of each color ink and coating to avoid waste, as well as mastering the amount of ink during printing;
4) Pay attention to the influence of climatic conditions on the suitability of ink coatings and take timely remedial measures;
5) Master the basic properties of the wipe and syrup.
6) The concentration of gum arabic should be appropriate, too thick or too thin is not conducive to protect the printing plate;
7) Petrol and kerosene should be marked on the outside of their container to avoid mistakes;
3, proofs and school iron preparation
In order to ensure that the colors of each batch of products are consistent, it is very important to keep proofs. Samples should be left in four types: full color, monochromatic, stacked and background colors. Sample sheets are the only basis in the printing process. The full color sample refers to the sample sealing after the printing of the product is complete; the monochromatic sample refers to the sealing of each color; the overlapping color sample refers to the sealing after the color registration in sequence; the background color refers to the large area in the field. Swatch. According to the color of the seal, it is strictly controlled with respect to the colors in the printing. It is required that the proofs be kept clean and tidy and not lost. After use, they are returned to the person concerned for safekeeping, so that the next batch of the same product can be used for printing. Samples should be placed in a dark room or a closed wooden shelf and replaced regularly (usually every six months). Because the color will change over time, it will lose the role of standards.
The preparation of school iron can not be regarded as irrelevant. Its role is to use the school edition and ink, and there is enough school edition iron to control the scrap rate of the product and avoid the appearance of dozens of colors in front of each pack of iron. The phenomenon occurs. Therefore, the school iron must be placed on a fixed shelf. Store according to different specifications. Before use, check whether the surface is smooth and clean. Can not be stained with impurities, oil, and school iron should be replaced regularly.
Six, tinplate coating and printing common quality problems are as follows
Failure name
Cause of failure
Method of exclusion
Furnace ash
Flower iron frame, furnace chain, oven interior is not clean
Adjust the burner burner to make the flame blue instead of red; regularly clean the flower iron frame and clean the inside of the oven; regularly add heat-resistant oil to the oven chain
Toothed stripes
The gears of the coater are not well-toothed and do not rotate smoothly, resulting in unequal coating film thickness and stripe spots. In addition, the diameter of the coating roller used may be too large or too small compared to the specified size.
If the gears are worn, they need to be replaced. Check whether the diameter of the coating roller is too large.
Uneven coating
The paint between the ink fountain roller and the ink distribution roller should be evenly distributed between the two rollers. However, when the ink fountain roller has too much paint, it is sprayed onto the material to be coated. The higher the coating machine speed, The greater this trend is.
It is possible to reduce the viscosity or replace the solvent with a small surface tension. In addition, because the paint supply is not performed in one place, holes can be made, and the entire roller can be evenly coated with a material such as a duct to help solve the problem.
Flying ink
When the coater rotates at a high speed, and the coating layer is once on the surface of one roller, the wire is cut into droplets and scattered due to the centrifugal force. Generally, the coating with high "stickiness" tends to be large.
It is effective to reduce the viscosity of the coating cloth or add a surfactant to reduce the surface tension. If it is a white coating, the concentration or content of the pigment is increased, and the thickness of the coating film in the wet state can be reduced, which can also prevent the formation of droplets during separation.
Back dirty
The back of tinplate and other coated materials, in other words after the scraping of the scraper, there is a small amount of paint left on the embossing roller, mainly due to the scraping of the paint by the scraper, and if the surface of the imprinting roller is rough and there are scars, it cannot be damaged. When scratched, back dirt appears.
The re-grinding of the blade, in contrast to flying ink, can increase the surface tension and worsen the wettability of the roller. In addition, in order to make the blade wear less, the most recent coating machine is such that the impression cylinder is often used before the blade. All the paint is wet, and the paint can be used like a lubricant. At this time, the solvent of the wetting impression cylinder is better than the paint. The double scraper structure is based on the product of this consideration. The back surface is flawed and the white paint is prone to occur. , because it is easy to see, this is because the pigment particles become a kind of grinding machine, the front edge of the blade is worn out, and also affected by the size and shape of the titanium oxide particles (the particles have a corner and wear more)
Climbing pattern
When the temperature in winter is low, the rapidly heated portion of the furnace (near the hot blast) is prone to occur, and a thick coating film is formed around the furnace like a moon-shaped crater. This is because the movement of molecules in the low-temperature coating is in a slow state. Rapidly at a high temperature, the low-boiling solvent evaporates immediately and the polymer solvent in the resin remains intact and the polymer solvent in the resin is left intact and remains in a non-evaporable state. If it is further heated, it melts. Aggregation occurs due to surface tension, and in this state, it is dried to form a circular ridge.
In the high and low boiling point solvents, if the solvent with a small difference in surface tension is replaced, the problem can be basically solved.
Sticky
Insufficient baking temperature or insufficient cooling at the furnace outlet, when the plate is stacked at a high temperature, the plate and the plate stick together. If it is peeled open, there will be a “Balibary†sound, accompanied by the back of the coating film. There has been a rash.
Improve the baking conditions, adjust and improve the cold and part of the oven, can solve this failure.
phantom
During baking, the shape of the iron grille like the flower iron frame is formed, the color of the coating film becomes light, and the phenomenon that the enamel can be seen is because the heat is absorbed by the bracket iron grille to absorb the insufficient baking and the solvent of this part. Evaporation slows, and the surface tension pulls it, the coating becomes thinner and lighter, and the larger the amount of coating, the more easily the phenomenon is seen.
It is best to warm up before entering the furnace.
Eye hole
The reason for this is very small, also known as pinholes. The holes in the coating sometimes have a thin coating film, and sometimes they do not, and the surface of the sheet is exposed. The reasons are as follows:
I. When the surface of the coating roller is rough
II. There is oil on the metal plate and the paint cannot be applied
IIIã€Paints and coating materials with impurities
IV. When it comes in contact with a conveyor belt or static electricity
V. Problems occurring during the manufacture of paints (eg insufficient dehydration during phenol production, etc.)
When the cause of the roller is changed, there is no other way. When the reason for facing the iron plate is to coat it with 200°C or so before coating or printing, or when the condition is not serious, reduce the viscosity, add the solvent, and increase the amount of wet coating to cover. When the cause of static electricity is increased, the viscosity of the paint may also be solved.
Flower iron frame markings
It can be considered that the coating on the iron plate is in contact with the front shelf when the coating is not dry, and a trace is generated. It can also be considered whether the plate is bent, or the hot air is too strong, the iron plate jumps, or the flower iron frame is not smoothly driven. Intermittent vibration causes contact.
Flowers and horses are spotted in the cold winter prone to failure:
I, iron waste heat, to eliminate the temperature difference between the iron plate, in addition, the monthly preheating equipment, before coating, from the need to consider the heating, you can make the grill on the roasting line idling.
II, because the coating material viscosity drop is too low prone to this failure, so pay attention to the adjustment of viscosity, if the use of fast evaporation diluent, although effective but poor fluidity, before use after inspection.
III. Because the amount of coating film is also high, it is necessary to check whether the amount of coating film is suitable.
Heavy skin
When the rubber roller has a notch, the accumulated coating material flows out of the notch, and the paint “drip†is formed above the notch. Like the curtain, the white paint is prone to occur. This is because the rubber roller is too hard and it adheres too much to the paint. It is the viscosity drop is too low.
I. If the rubber degradation of the roller is hardened, this phenomenon is likely to occur. Replace the new roller and observe the effect.
II. Because the viscosity drop is too low, it is easy to adjust the viscosity. In addition, it is better to use a thinner that evaporates quickly.
III. A little more than the amount of coating film, the coating in the notch groove is easy to accumulate, and it is the cause of this failure. Be careful.
IV. If the temperature of the coating liquid is low, it is effective if the liquid temperature is increased.
Zebra stripes
In the case of a streak-like occurrence of a coating material, the occurrence of the paint transfer from the roller to the board cannot be smoothly extended on the board surface, and the separation from the roller when it is stuck in the shape of a mountain occurs due to excessive viscosity or excessive evaporation of the solvent.
First, use the evaporated solvent test to reduce the temperature, and when the winter or vacation is over, the paint will be too cold, so it is easy to observe the liquid temperature, slightly warm, this is better, because the surface hardness of the roller is too high, this phenomenon also occurs. It is also necessary to change the new soft roller to take a look. Immiscible paints mixed into the occasion, can cause this failure, before the part of the paint used, very much remains in the pipeline, the problem will occur in unexpected places, this time must thoroughly clean the paint input tube and replace all the paint.
Wrinkling
The coating film is uniform and smooth to the coating position. After baking, the appearance of the coating film disappears, and part of the gloss disappears. This forms a wrinkle surface. This is called a gas crack (wrinkle). This term is used to describe incomplete combustion of gases. The appearance of cracks is not complete, but it also occurs when there is cold air in the furnace and the hot air does not fully flow. Patterns can be produced in various ways. There are large spider nests, dots, and frost-drops. .
The furnace is fully vented and ventilated to allow the iron plate to pass through, and checking for overcooling is also a special operation in which it intentionally lowers the baking temperature and only allows the surface to dry and then raises the temperature to produce a wrinkled surface.
Point
After baking, the coating film is not smooth and smooth. It becomes a pockmarked surface like an orange skin. It is coated on the inner surface of the coating first. If there is a wax component (lubricant in lubricant lubricant), stearic acid (for example, silver paint contains Aluminium) etc. During the accumulation, back spalling occurs. This causes the occurrence of pitting and also the rejection of paint.
On the basis of checking whether there is back squeegee or not, re-select silver paint, varnish, wash or rub on the back and there is no way to get back, although there is no back smashing and pitting occurs because the viscosity of the paint is too high, similar to zebra-streak phenomenon.
Print overprint is not allowed
Improper overprinting caused by improper adjustment and improper operation of the printing press and poor precision of parts and components; misprints caused by improper printing plates and process operations are not allowed. These include improper deformation of the printing plate, improper lining of the roller, and misalignment due to deformation of the blanket. Metal plate size is irregular, uneven, deformation caused by overprinting is not allowed.
(1) Re-adjust the printing machine's iron plate conveying and positioning components to achieve overprinting requirements; (2) Four-color plates must be printed at the same time so as to avoid overprint due to the different expansion and contraction of the films; (3) Mastering the equipment Edition techniques to avoid abnormal stretching deformation, so that the tensile deformation is controlled to a minimum; (4) to properly measure and select the drum liner thickness; (5) the correct selection and installation of blankets, pay attention to prevent the rubber layout Department of elastic uneven The phenomenon; (6) Replace the metal plate that meets the requirements; (7) The tinplate indicates that the rust is wiped clean, and sealed or placed in a dry environment.
Heap ink
Ink volume is too large; pigment particles in ink are large; pigment content in ink is large
(1) reduce the amount of ink supply; (2) increase the dilute agent; (3) diligently wash plates and blankets.
Dirty version
The water roller is improperly adjusted; the water tank is not clean; the water roller pressure is too large or too small; the pH value of the dampening solution is improper; the ink roller pressure is too great; the water volume is too low; the ink is too dry; the blanket is too loose; the ambient temperature is too high; There is photosensitive adhesive left on the layout.
(1) Clean or replace the water roller; (2) Adjust the water roller pressure; (3) Adjust the pH of the fountain solution; (4) Increase the water supply, adjust the ink roller pressure, and reduce the ink volume; (5) Tighten the rubber cloth.
Water pollution
The water supply of the bucket is too high; the pressure of the water roller is too large or too small; the amount of ink is too small; the layout is smooth and the blisters are polished.
(1) reduce the swing amplitude of the water transfer roller; (2) adjust the water roller pressure; (3) increase the amount of ink input; (4) reduce the pressure of one roller and water roller and ink roller.
Oil pollution
Incorrect prints cause greasy; improper printing causes greasy.
(1) reprinting; (2) adjusting the pressure of the ink roller and plate; (3) cleaning and maintenance of the ink roller, and the ink on the surface of the ink roller must be washed after each color change; (4) Water roller pressure regulation is appropriate; (5) to ensure a stable alcohol concentration; the use of appropriate Arab gum content; (6) control the size of the layout of the water, the main ink balance.
Color is not bright
The amount of water is too large; the fountain solution is too acidic; the temperature in the drying room is too high; the ink is discolored by heat during drying.
(1) reduce the amount of fountain solution; (2) adjust the pH of the fountain solution; (3) adjust the temperature of the drying room; (4) the printing ink is of high temperature type.
Color difference with the board
Uneven pressure; gasket displacement; uneven metal plate; damage to ink balance; improper configuration of fountain solution;
(1)Conciliate the pressure of ink and water delivery systems to ensure that the pressure is uniform and suitable; (2) Inspect the blankets and, if necessary, replace the blanket linings; (3) Check the metal plates to ensure their flatness, if necessary. Change the metal plate; (4) Control the pH and concentration of the plate solution, the general PH value is 5-7; (5) control the amount of water, ink, to ensure the ink and water balance; (6) carefully inspect the printing press parts and find that the wear parts should be Replace it in time.
There are bumps on the board
Embossing roller sticky
Always clean the embossing roller. Do not scratch it with paper or iron. Once it is found that there is debris, the first time should stop cleaning.
Mopi
Ink has black skin or sundries
The remaining ink should be kept clean and reused when it is used. If the remaining amount is small, it should be dealt with promptly. For each color washing machine, wash the ink roller with hot water for about 2-3 minutes until the last stage, and then rinse it with gasoline.
Every pack of iron starts with dozens of distinct colors
The pressure iron is not enough (also called school iron)
Because the ink level and the water level will be uneven when the equipment is turned off and then turned on, the iron pressure and the water level must be set enough when each package of iron begins production (not less than 20 sheets at a time). Balance makes the color consistent.