What is the dot gain? Mile Southworth defines it as the change in the dot size of the sensitized film and printing product used to make the printing plate. The dot gain is ubiquitous throughout the entire production process from scanning to printing. The printing test is a tool for dot gain evaluation and dot gain compensation. It is achieved by adjusting the characteristic curve of the final output film. In order to improve the product quality and shorten the product period, the network gain must be found out, measured, adjusted, monitored and controlled in time. There are two types of dot gain: the mechanical gain caused by the physical growth of the dots, and the optical enlargement due to the scattered light reflected by the dots, which in turn changes the apparent density, and we will discuss the gains in mechanical dot gain.
Adjust the mechanical dot gain.
The mechanical gain is the result of many preprinted variables. The variables affecting the gain of the flexographic screen are: plate material, liner (variation of model and thickness), ink viscosity, timing ink supply system, and dot radial runout of the plate. , Pressure, age and embossing conditions, number of anilox roller lines and wear, film condition and humidity. For the whole process of flexographic printing, the precise measurement of the dot gain is more stringent. The first step in the measurement of the flexographic dot gain is to conduct a print test on your press.
There are many commercial and non-commercial test methods. Their specifications, design and appearance have their own characteristics. These tests are to give a separation information to the color separation machine. It generally includes a specific printing required. Set of specific color separation information, including printing color sequence, field density, dot gain, optimal screen number, gray balance, film opacity. Before the printing test, the variables such as plate material, lining, density, and anilox roll must be determined. There are many manufacturers of photosensitive resin, and there are many models for each type of plate. Each model has unique printing characteristics. Should choose a better version of the ink remaining and latitude printing plate. The next variable is lining, in the printing press, printing plate, and paper. Under ideal conditions, the hard plate rigid body has a small dot expansion, no need for lining. However, in actual work, color printing must be lining up. Solid density is not only an important feature in color separation settings but also in print contrast. Print contrast affects the overall color characteristics of printed products. We generally set the final density between 120 and 135. This range requires high color saturation. Ink.
Last but not least, the selection of anilox rollers is an option. You can choose any kind of test on the product catalog. Generally, you choose a 360-line chrome roller or a 440-line chrome roller. According to the test results, you can adjust the anilox roller again. When printing tests on the variables on the machine, we must calibrate more variables and measure them. In particular, the printing speed and pressure, the printing speed will cause an interesting dynamic balance; in the duration you need high speed, but high speed It will affect the quality of printing. In the test, we used three speeds to observe the effect of speed on the quality of prints and the gain of dot gain. The pressure affects the gain of the dot, and two different pressures can be set when testing the pressure setting. Choosing us can see the latitude of the plate material and the impact of the liner on the pressure, as well as the change in dot gain.
When setting the pressure, you can ignore the gray scale of the screen and set the pressure. Then you set the pressure at the place where the dot gain level is clear. Thus we can analyze the best and more compromised pressure settings. You take a few samples, and then combine the parameters of the front, we can get the effect of anilox roller, printing speed and pressure. After the above three results are collected, we can analyze the data. Before that, we had to use the transmission densitometer to measure the film of the printing plate. The transmission density can measure the amount of light passing through the half-tone negative film and display it as a percentage of the dot. The name of the item to be tested must be measured and recorded. Next, the paper must be measured by reflection density. The operator tests the field, blank, and halftone areas respectively, and the densitometer calculates the percentage of the network after analyzing the three information. Dot Gain The next step is to draw a copy of the curve. After plotting the characteristic curve based on the test results, the curve will show an increase in the dot gain percentage from film to print. To independently evaluate each separate variable, we plot a curve for each variable.
When analyzing the test results, we cannot ignore the optical gain. Although the optical gain cannot be controlled, you should discern it as a visual phenomenon and incorporate it into the total dot gain. The optical gain is due to the fact that the human eye cannot see the result. The illusion caused by all the reflected light is mainly caused by the reflection light scattering of halftone dots. Optical dot gain is not physical, but simply because of the area of ​​the dot that is missing from the human eye's instrument.
The print test results provide a number of copying curves to the color separation worker. When the best curve is selected, the scanning worker will evaluate the curve, and then compensate for the phenomena caused by the enlargement of the dots such as gray balance and intermediate tone enlargement. We must Determine the highlights, extreme highlights, minimum dots, ghost masks, and GCRs. GCR is the technology that replaces neutral grays that are overprinted by three-color inks with black. The digital information obtained by the scanner can be output to the film or saved for later operation. The test results are input into the system and the network generation table, and then the screening is based on the test results. For example, if there are 35% dots printed and 20% dots are enlarged at 25%, the dot generation table will read 25% of the dots for output. The color electronic prepress system with curve compensation function can be revised. Text layout and overprint image adjustments.
Since the electronic file has no design size and dot structure, we can adjust it freely in terms of dot size, screen number, and curve characteristics. Regardless of whether or not to operate electronically, the final result we obtained was to check the accuracy of the film. At each step of the production process, we must perform pre-proofing. If the film is electronically calibrated, the curve-compensated proofs will be compared with the original scanned film proofs to evaluate the curve compensation and obtain the ideal dot gain. There are many types of pre-proofing. Each has its own advantages and disadvantages. Each color separation worker must find a suitable type. The use of a wide range of pre-proofing is the toner method, which means that the toner is adhered to the adhesive layer to form various color plates, and different ink hue and density can be mixed and matched. This is a great advantage for those prints where the color gamut is small and the ink density does not reach 130. Since the hand-coating toner is prone to unevenness, automatic adjustment devices are generally used. Over-exposure methods can be used to simulate dot gain. Another type of pre-proofing is pre-powdered toner layer. This method distributes SWOP ink and is constant in terms of size and density. Although limited due to lack of flexibility, this method has good uniformity. There are also color overlay legal proofing, electrostatic methods and inkjet methods. The last is the flexographic proofing method, which utilizes a flexographic ink, doctor blade, and a mesh spinning roll, with a central embossing roll and a rubber plate or photosensitive resin proofing on the paper, only one color at a time, only one complete maximum at a time Resolution. But by making different flexo plates and changing the ink hue, viscosity, and embossing pressure, you can better simulate actual printing.
Copper engraving In dot gain analysis, we only focus on photosensitive resins. In fact, copper-engraved copper plates are also related to the printing quality of color printing. When engraving a copper plate, the copper plate must be tested. After the test, we will perform printing quality analysis and dot gain analysis. The photosensitive resin plate is compensated during color separation, and the copper plate is not. It is compensated during engraving. Due to the inherent dot loss during deep engraving, the color of the pre-proof sample is darker. After engraving, we generally use overprinting ink proofing to check the color balance, then the copper plate can be etched again to change the dot size to better match the color, and then proofing for customer proofing; finally the dot gain compensation during printing, before etching Black-and-white proofing for each color group is required to observe dot gain during printing.
In order to ensure the quality of printed products (color, registration, etc.), dot gains must be defined to control compensation. Remember that dot gain compensation must be based on print test results.
Correction of Dot Gain in Separation of Flexible Plates
December 12 06:07:27, 2023
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