(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected) The dot is the pixel of the printed image, which is the smallest unit of ink absorption in offset printing. It is responsible for transmitting the tone and tone of the original. According to color theory, color has three properties: hue, brightness, and saturation. The three primary color dots of yellow, magenta, and cyan are superimposed together, and by changing the size or coverage of the dots, tens of thousands of different colors can be formed. Therefore, no matter how rich the layers are and how the colors change, as long as the appropriate matching of the three primary color dots, the color and tone of the original can be simulated. The changes in the network copy process that we can encounter in production are mainly the following: Selection of printing materials: this includes paper, ink, blankets, printing plates, wetting fluids, etc. The choice of these raw materials will often directly affect the reproduction quality of the dots in printing. A successful printing is not only to get a better quality of our printed products, but also to achieve the minimum cost within the allowable quality range. Exposure: 1. Exposure. During the exposure of the PS plate, due to light penetration and other reasons, the dots on the printing plate will actually shrink compared to the dots on the film. Generally, the amount of shrinkage should be controlled within 3% to 5%. However, this number is not unchanged. Due to the vacuum of the printing equipment, the transparency of the printing glass, the control of the printing time, and the quality of the plate material, there are many different situations, so you should often use the printing control strip to Test the changes of the dots in the printing plate, and then feed back the data to the pre-press image processing unit; 2. Development: regularly test the concentration of the developer, and determine the development time through the test results. If the developing time is still the same after the developing agent is fatigued, the edge of the dot will not appear clear, causing the dot to increase. During the printing process, regularly check the working conditions of the printing machine and the development conditions are necessary. In this process, a special test strip for printing is sufficient, and the obtained results are fed back to the pre-press in time, so that Respond early. Effect of fountain solution: a PH value of fountain solution: PH value of fountain solution during printing should not be too low, preferably about 5 to 6, because too low pH value of fountain solution will affect the transfer of offset printing ink Very large, at the same time it will cause corrosion of the printing plate, reduce the printing durability of the printing plate, cause the loss of high-profile dots, or other printing problems; b Water amount on the printing plate: the water film thickness of the blank part of the printing plate is generally 0.5 to 1 The thickness of the ink film is 2 to 3 microns. If the moisture on the printing plate is too large, it will erode the ink film of the graphic part, resulting in empty dots; if the thickness of the ink film is large, then the ink will spread to the blank part under the effect of pressure, causing the dots to increase . Influence of ink: 1. Moderate fluidity. If the fluidity is too small, the cohesion of the ink is too strong, it is difficult to be evenly ground, thereby reducing the transferability of the ink; if the fluidity is too large, it will cause poor adhesion of the ink, and the printed dots will be flat, dull, or even spread around. Affect the quality of the product. Also note that the fluidity of the ink when printing dot products is smaller than the text, so that the printed dots are clear and full. 2. Choose the right ink. The ink is required to have fine texture, smooth, good flow performance, proper viscosity, no shortcomings of delayed version, bright and durable colors, and the ink color is preferably translucent. Reasonable emulsification of ink: This is an interesting phenomenon. Compared with other printing methods, offset printing is often due to the emulsification of ink and the color saturation is not enough. Therefore, in actual production, everyone is trying to reduce the emulsification of ink as much as possible. To achieve a more vivid ink color effect. But the actual situation is that there is no reasonable ink emulsification (we know through experiments that when the ink emulsification reaches 26% is an ideal emulsification state), the ink cannot be between the ink roller, the ink roller and the printing plate, the printing plate and the rubber There is a good transfer between cloths (the reason is that water will form a water film on the surface of the ink and hinder the transfer of the ink). The direct consequence will cause the deformation of the dots or emptiness. In addition, when the emulsification value of the ink exceeds 30%, a clear boundary will be lost between the water film and the ink film, and the edges of the dots will appear burrs, blurring, etc. The more serious consequence is that the pigment particles in the ink are separated from the resin , Stacked on the printing plate blanket, will also affect the transfer of ink. Pressure: 1. As long as the pressure of the water roller can make the water roller smoothly and uniformly transfer moisture to the printing plate, too large or too small pressure is not good for printing. When the pressure is too high, it will cause the water roller to jump at the mouth and cause friction. Under the pressure of the water, the dots will be squeezed to become smaller or deformed; of course, the effect of too little pressure is obvious, the amount of water cannot be transferred normally, The ink on the layout will spread to the blank space. 2. The pressure of the ink roller should be flat and light, the pressure is too heavy, and the dots are easy to be pressed, which affects the quality of the product. 3. Keep the roller pressure moderate and even. Excessive pressure will cause the ink on the printing plate dots to spread and deform under the effect of large pressure; low pressure will directly reduce the transfer rate of the ink, and the ink transferred to the substrate is less and thin. However, if you encounter substrates with relatively low surface smoothness (such as textured paper, embossed paper, newsprint), you need to increase the printing pressure appropriately to compensate for the uneven surface of the substrate and improve the efficiency of ink transfer to ensure the transfer of dots. 4. Make sure that the linear speed of the drums is consistent (as much as possible). If the linear speed difference between two adjacent drums is large, the transmission of the dots between the drums will be deformed. Avoid "ghosting": refers to the double outlines of dots, lines or text of the same color appearing on the print. It is a directional increase in dots. Excessive pressure between the printing plate and the blanket or between the blanket and the impression cylinder can cause ghosting. Excessive pressure causes plastic deformation of the rubber surface of the blanket and changes the shape of the printed dots. Plate protection: 1. The plate coating glue should be thin and even. If the glue is too thick, it is not easy to clean after drying and it is easy to damage the dots. 2. When the printing plate is not in use, try not to place it facing the sun. If you stop for a long time, pay attention to the protection of the coating glue; clean the printing plate and do not scratch the printing plate. 3. Long downtime should be careful not to put the water roller directly on the printing plate to avoid the printing plate from contacting the fountain solution for a long time and causing the dots to be damaged. Failure to do these jobs will have a great impact on the dots on the printing plate. The normal working state of the printing machine: to ensure the normal working state of the printing machine is the key to the printing and copying network. In normal printing, the dots will increase by about 15% due to normal imprinting and other reasons. This is normal and can be compensated during the pre-press process. However, when the printing machine has abnormal vibration, for example, due to the abnormal meshing of the printing machine cylinder gear, the gap between the cylinder bearing and the bearing pad is too large, the printing pressure is too large, the water roller ink roller jumps, etc., will cause dots in the printing process There is a dot deformation during transmission (this deformation may be an increase in the dot or simply a change in the shape of the dot), so that the overlap of the dots changes and the density jumps abnormally. Changes in these dots will directly lead to failures such as bars, ghosting, grading, and dot loss on the printed matter. Sanqin: In the operation of the machine, we must ensure that Sanqin is used, that is, to stir the ink fountain (to ensure a certain fluidity of the ink), and to compare the printed proofs (according to the amount of ink on the proofs, to check the ink color on the printed matter), Observe the water volume of the board frequently (this is the frequent monitoring of the water volume control we mentioned earlier). The above-mentioned Sanqin must be done frequently in the operation of the printing press, these operations can better ensure the transfer and copy of the dots in the printing process. The above are just some issues that need to be paid attention to in the copy and delivery process of the outlets, and some brief introductions to some of the more important problems, and there is no more in-depth discussion. The problems that can be encountered in actual work should be more various. It can be said that it is endless, I hope this article can play a role in throwing bricks and attracting jade, triggering peers to have a more in-depth discussion on how to better control the dots in printing.
Outdoor furniture covers
are polyester outer sell with PVC coating inside, keeps the elements out covers
wipe clean with a damp cloth and mild soap, with a high seam strength and
durability, don`t fade or crack in the sun.
Our
outdoor furniture covers provide an unparalleled level of protection for your
outdoor furnishings. Designed with meticulous detail, these durable covers with
polyester outer shell and a layer of water-resistant PVC to ensure superior
performance and long-lasting functionality in searing sun, blinding rain,
prodigious snow, and bitter cold.
• Lined with a layer of water-resistant
PVC
• Soft fleece underside protects
aluminum frames
• Won't fade in the hottest sun, or
crack in temperatures dropping to 0°F
• Elastic edging and/or reinforced ties
hold covers securely in place
If
you have any questions, please contact with us directly. Outdoor Furniture Covers
are produced by Golden Eagle Outdoor Furniture With High Quality and Good
Appearance. Welcome you visit our Factory. For any inquiry,Please send mail
directly to us.
Outdoor Furnniture Covers,Outdoor Furnniture Rain Covers,Outdoor Covers For Furniture,Outdoor Patio Furniture Covers Golden Eagle Outdoor Furniture Co., LTD. , https://www.gesunumbrella.com
When evaluating the quality of color prints, the reproduction quality of the dots is the most important indicator. Among them, many standards related to the reproduction quality of printed products, such as uniform ink color, no deformation of dots, no ghosting on printed products, and ink bars, are almost all related to the control of dots.
Changes in dots can cause problems such as changes in clarity and subtle levels, changes in color, and contrast, ink hue, ink density, and ink color overprint. Although electronic methods can be used to predict and prevent some dot changes, it is still necessary to control the dot changes to ensure print quality.
The size of the dots and the position between them determine the color tone of the print. For example, large dots printed very closely will form dark areas, and small dots with large spacing will form highlight areas. Therefore, the increase of the dots can greatly affect the reproduction of mesh tone and color photos in these areas, and has a great influence on the midtones.
It is for the reasons mentioned above that we put forward the concept of dot control, that is, to control the quality of dots in all aspects of the entire workflow of printing and copying. Due to the close connection between the various processes, we must also pay attention to the quality control of coordination and response.
Although the term digital printing has been proposed for many years, in the traditional printing method that is relatively widely used, the conversion of dot information between devices is still more using analog information transfer, precisely because this transfer is achieved using analog information Yes, it will inevitably cause changes in the information of the outlets that we do not want to see between the devices (such as the increase of the outlets, the shrinkage of the outlets, the deformation of the outlets, and the loss or merge of the outlets).
Now we are more common in dot printing (the printing methods mentioned in this article are all offset printing). The workflow of copying is as follows:
Manuscript → color separation (now mainly uses scanning or electronic color separation) → image processing (including tone adjustment and compression, image and text mixing, color separation, screening, etc., this process is mostly done by computer ) → Composition of large-scale plates → Publishing (exposure, development, fixing) → Exposure (exposure, development, and baking plates are also used for large printing volume) → on-machine printing → end of printing.
The above is a relatively common workflow. The dots are formed from the image processing stage to the completion of printing. The whole process is through light, film, plates, printing machines (mainly plates and blankets), inks, and substrates. To complete, but due to many inherent reasons such as equipment and technology, the nature of the transmission itself determines the change of the outlet. In addition, these materials and equipment itself have a lot of uncertainties, resulting in the outlet cannot be done at every step. Accurate copying and transmission means that no matter how we do it, it is impossible to completely avoid the changes of the dots during these transfers (the above-mentioned dot deformation, dot increase, shrink, etc.). In actual production, what we have to do is how to control the changes of the outlets within a reasonable and predictable range, and at the same time standardize the production process and reduce the fluctuation of the changing parameters in the production process.
1. Dot reduction, that is, the area of ​​the copied dots is reduced relative to the upper layer (upper process) carrier of the dots.
2. Increased dots: Compared with the upper carrier of the dots, the area of ​​the dots obtained after replication increases, and the density of the resulting replica becomes larger.
The dot increase can be divided into mechanical dot increase and optical dot increase.
"Mechanical dot increase" (also called physical dot increase) is the physical increase of the dot size. The most common form of mechanical dot increase is non-directional. If it is excessively increased, it may cause lay-up. This increase is caused by ink film thickness, substrate type, high screen count, or ink transfer under pressure between the blanket and the printing plate, and between the blanket and the substrate.
"Increase in optical dots" is a visual phenomenon formed by the light absorption characteristics of the ink and the light dispersion characteristics of the substrate. When light is irradiated on a non-image area, that is, a "blank area", the light diffuses, and a part of the light near the dot is suppressed. This light is considered "absorbed" because it cannot be reflected back into the observer's eyes. The dots appear to be larger than the actual density and size, and it seems that dot gain has occurred.
3. Deformation of dots: The shape of the dots obtained after copying has changed. For example, the original round dots may become ellipse after copying, or the dots with no fixed shape.
The three issues mentioned above have a great impact on the entire reproduction stage of the printed matter. But when we can more accurately predict the changes that the outlets transmit between the devices, we can more effectively compensate for the changes that will occur before the outlets change. For example, if the dots of a printed product appear as follows during the copying process: the copy-positive dots will shrink by 2%; the drying dots will shrink by 4%; the printing dots will increase by 15%; the dots will increase by 12%. Then after a simple mathematical addition and subtraction, we will find that as long as the dots are pre-compensated by 21% before the dots start to transfer, we will get the effect we want after the transfer. Although the actual dot compensation setting is not as simple as the above, the compensation and dot changes are not just a linear relationship, and the change trend of different percentages of dots during the replication process is different, but we only need It is enough to understand the above compensation relationship. Tell the software about the changes that will occur in the outlets (typically the rate of change at 50% of the outlets), and the rest can be left to the computer.
The reason mentioned above seems to be very simple, but as soon as it comes to actual operation, we will find that due to the many types of work involved in the transfer of outlets, it is actually not easy to truly achieve management standardization and operation standardization. However, this is an indispensable and important aspect for dot reproduction on printed matter. Only by strictly implementing management standardization and operation standardization can it be targeted in pre-press image processing and dot compensation, which is precisely a lot What printing companies can't do. The actual situation is often made separately for plate making and printing, which is very unfavorable for the correct reproduction of the outlets.
In the following, we will discuss some issues that need to be noticed in actual production and factors that can easily cause abnormal deformation of the network.
The choice of plate-making process: This is a very large and wide-ranging problem, but when it comes to the reproduction of the dots, the most important thing is nothing more than the shape of the dots and the number of screens. The correct choice of dot shape can have a great influence on the surface effect of the printed matter. The more important thing is to note that the nature of each dot shape is different. For example, square dots have a large tone jump at 50%, and the total dot increase rate of square dots is also larger than other dots, so in the color separation and screening process of high-end printed products with rich midtones Squares cannot be used, and diamond or elliptical dots are the primary consideration. The higher the line number of the dots, the richer the layers of dot prints will be, and the screen will appear more delicate, but at the same time, because the length and length of the dots on the entire layout will also be larger, according to the theoretical conditions of dot increase , We know that the changing trend of outlets is also greater. In many cases, blindly increasing the number of dot lines will cause the copy quality of the dots to decrease but decline. Therefore, in actual production, we must weigh the number of dots based on the comprehensive conditions of many factors such as printed paper, ink, and machinery. . The increase of dots with the same percentage of dots and different numbers of dots: In the case of the same percentage of dots, and the same value of dot increase, the higher the number of dots, the greater the dot increase rate; In the case of the same percentage And the dot increase value is the same, the higher the line number, the larger the percentage of the dot increase area.
Ghosting can also occur on plates and blanket cylinders with different diameters. If the blanket on the sheet-fed offset press is too tight on the cylinder and the plate is too loose on the cylinder, the surface speed of the blanket cylinder will exceed the surface speed of the plate cylinder, and the resulting friction will cause dots Increase. The dots can be ghosted from one side to the other in the lateral direction of the cylinder, or they can appear in the printing direction around the cylinder. 
