Standardized printing , in addition to a comprehensive technical team and appropriate equipment, the use of standards-compliant and high-stability materials is necessary, otherwise it will disrupt the consistency of production, affecting productivity and quality. Therefore, the cognition and requirements of materials are especially important. It is worthwhile to pursue low prices only in terms of purchase price without deep understanding of product performance. There are a lot of materials needed for printing. What Ming Gong wants to share with the readers is that it seems to be simple, but it is actually a very important standard for four-color, spot color inks and a way to distinguish their quality. I hope that readers can make informed choices based on their basis.
Four-color ink
1. Color standard ISO 2846-2 : 2007 issue
In recent years, the requirements of the color management system used in the printing standards are in accordance with the ISO 12647-2:2013 " Printing Technology - Screening, Separation and Printing Production Process Part 2: Offset Printing " basis. Therefore, it is important to use a four-color ink that conforms to the ISO 2846-2:2007 "Printing Technology - Color and Transparency of Four-Color Printing Inks Part 2: Cold-Set Offset" standard. The author knows that there are many four-color inks in the market that meet the ISO 2846-2:2007 "Printing Technology - Color and Transparency of Four-Color Printing Inks Part 2: Cold-Set Offset Printing" standards, but most of them cannot be The printed matter fully meets the requirements of the ISO12647-2:2013 standard. One of the main reasons is that the US agency that evaluates ISO 2846-2:2007 four-color inks only requires four-color inks on the paper of the specified standard value, and the four-color full-color strips produced by the general color-developing machine, as long as they are L *a*b* value, transparency and ink layer thickness reach its very loose qualifying range, E5. There is no requirement for dot gain values ​​for 4-color inks. Therefore, the 4-color ink that does not meet the dot gain value can also be qualified. Generally, the four-color ink may have a dot increase. Usually, the printing department will make a reduction point adjustment method when the printing plate is not produced according to the standard dot value increment method. If the above-mentioned E5 four-color ink is used, it is impossible to adjust when it encounters a print that requires color-stack printing, and takes into account the standard of the dot gain value. Usually the printing master will replace the overprinted part with a spot color or print the overprint and dot portions twice. Very time consuming. Only by selecting a set of low-difference and standard-compliant 4-color inks can the effect of increasing productivity be achieved.
2. The relationship between pre-drying, full drying and ink concentration
In the first hour after printing, the prints were almost pre-dried by osmosis, and then the oxidized conjunctiva was used to complete the drying. However, the generally cheaper ink formulation has a lower concentration, and the relatively cheap binder, especially the mineral oil which will volatilize after drying, has a large amount of dry color value after printing, and the wet color value when printed. The difference is great. Ink is used in the formulation to reduce the cost of mineral oil, not only will increase the content of VOCs, but also make the ink excessively penetrate into the paper. When the print is dry, it will find much less than expected. If you want to avoid this excessive wet and dry color difference, the printer can only use the palliative method to increase the amount of ink. In addition to a large amount of waste of ink and environmental protection, it will also be difficult to dry and require more dusting. It is easy to back print and the negative consequences of excessive outlets. Therefore, the general printing master tests the newly printed printing with the feel of the hand. It is a wrong understanding that the ink which is considered to be drying faster is better. The faster the predrying time, the faster the ink penetrates into the paper instead of the real quick-drying ink. . As long as the ink used does not need to use more dusting during printing and the printing is not printed, it can be dried in a reasonable time. Especially for the bottom eight-color printing, it is even more difficult to use pre-drying ink.
3. The importance of ink balance during ink emulsification
This problem, which is generally not mentioned in depth, is actually the biggest key to determining whether the ink is stable or not in the printing process. Many printing masters believe that emulsification is a savage beast. In fact, the ink must be emulsified with the water bath before transfer, otherwise the ink will not transfer properly. In other words, emulsification is "water-mixing", and as long as the ratio of "water-mixed oil" can be stabilized during long printing periods, the transfer properties of these inks will be better. A set of high-quality four-color inks, without the influence of external factors (such as paper wool), can continuously print tens of thousands of sheets without stopping the cleaning of the blanket. Otherwise, the volatile cleaning fluid used to clean the blanket each time plus expensive downtime is neither environmentally friendly nor less productive.
Therefore, in addition to knowing the choice of high-quality four-color inks, it is equally important to use high-quality water bath and isopropyl alcohol (IPA) to maintain acid-base (ph) and stable conductivity. Of course, the temperature of the ink roller during printing must be stably maintained within the range of 29 to 33 degrees, otherwise the normal value of the dot gain will be affected. (Do not listen to any add-on additives that have adverse effects on prints, especially color values, and affect printing stability. It is appropriate for the ink to be processed by a real ink engineer!)
4. Method for testing four-color ink
Select a few sets of 4-color inks at the right price. First, make the color strips in the same amount of ink in the standard color machine. First test whether the color value is in the range of ISO 2846-2:2007, and then measure it every three hours or so. L*a*b* value and dry condition. Then select the L*a*b* wet-dry value drop of 4 colors of E2 for the printing test. The ink with a wet dry value exceeding L*a*b* E2 is made of the above-mentioned volatility and cheaper binder.
It is recommended that each printing factory should have a set of ISO12647-2:2013 standard files for testing four-color inks. As a general test file, there should be a full version, overprint, gray balance and dot gain as the basis for testing, and then make appropriate adjustments according to the scope of the different papers according to ISO12647-2 or the standard range required by the printing buyer. . If the printing factory has already assessed G7, GMI or other internationally recognized certifications, it can take its files for testing. The 4-color inks tested on the press must be tested under the same printing conditions. The paper to be tested requires two or three different papers such as coated paper, gray paper and book paper. It is recommended that at least 3,000 sheets of each paper be used as the minimum test for the test, because the more paper, the more stable the ink can be tested.
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