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How much do you know about packaging offset printing (153

153. How to calculate the mixing amount of ink?

the mixing amount of ink should be slightly more than the actual amount, but it should be controlled within the minimum range to avoid waste. The mixing amount can be calculated according to the following formula:

mixing amount = printing amount × Printing area × Ink consumption per unit area + remaining ink

printing area refers to the spreading area of ink on a single print. If it is a eye-catching image, the image area should be multiplied by the point percentage. The ink consumption per unit area depends on the thickness of the ink layer printed and the absorbency of the paper. The inker should have an approximate estimate of the amount of ink required for a particular paper and image. In my personal experience, printing on coated paper consumes about 1kg of ink per 5million cm2. When printing eye tone images, the ink layer thickness is thinner and the ink consumption is less; Printing uncoated paper consumes more ink per unit area. There should be some residual ink after printing, otherwise the last part of the printing sheet cannot get a normal and uniform ink supply. If the printing area is large, the remaining ink should be more; If you print a small area of image, the remaining ink can be less. The ink volume is also related to the ink density. The ink consumed in printing is a volume related stretch. If the ink with high density is calculated by weight, the ink volume is larger

154. What should we pay attention to in inking and blending

the inking sequence should be from large to small, that is, the main color ink with a large proportion should be added first. For the deployment of light ink, first put diluent, and then gradually add dark ink to the diluent. There are two methods of mixing ink: mixing a small amount of ink by hand; A large amount of ink should be mixed mechanically

155. What should we pay attention to when coating ink samples

① because the color rendering effect of the same ink on different papers is very different, the paper to be used in the same batch of live parts should be used to coat the ink sample

② the thickness of the ink layer has a great influence on the color presented. It requires rich experience to strictly control the thickness of the ink layer of the coated ink sample to match the thickness of the ink layer to be printed

156. What should we pay attention to when comparing and evaluating the color of ink samples

① light source. To evaluate the ink color under the illumination of a light source with excellent color rendering performance, factories with conditions should be equipped with D65 standard light source

and semi crystalline plastic ② sample viewing method. The coated ink sample should be folded or torn off the blank edge of the ink sample, the color to be evaluated on the ink sample and the color sample (the color block on the chromatography or the color of the original) should be close together, placed in the same field of view, and carefully evaluated under the magnifying glass

③ if the original color sample is processed by coating, calendering and other surface processing, it is important to paste a transparent adhesive film on the coated ink sample, and then compare it with the color sample

157. What is the hiding power of ink

the hiding power of ink refers to the ability of ink to cover the background color. The stronger the hiding power, the lower the transparency of the ink. Four color color printing requires high transparency of ink, otherwise it will affect the color restoration effect of printed matter

158. What factors are related to the hiding power of ink

① the performance of the ink itself. It mainly depends on the ratio of the refractive index of the pigment and binder in the ink. The closer the ratio is to 1, the higher the transparency is

② ink emulsification during printing. The more serious the emulsification is, the worse the transparency is and the more turbid the color is

159. What does the adjustment of ink printability include

in production, it is often necessary to adjust the speed of ink drying and the fluidity of ink. Among them, the adjustment of fluidity is mainly to adjust the adhesion and viscosity of ink

160. What is the adhesion of ink

ink adhesion refers to the ability of the ink film to prevent itself from being stretched and broken during the transfer of ink. Its essence is a manifestation of ink cohesion under the action of adhesion

161. What effect does the size of ink adhesion have on offset prints

① possible disadvantages of excessive ink adhesion: when the surface strength of the paper is not high enough, the paper is prone to "roughening" and "peeling"; Poor ink transmission and transfer, uneven ink layer distribution, and printing materials are prone to uneven ink color

② the disadvantages that may be brought about by too small ink adhesion: the cohesion of the ink is not large enough, and the ink wire after fracture rebounds weakly, resulting in the printing point is not smooth and increases, and the level of the copied image is lost and the definition is poor; Ink is easy to emulsify

③ when the multi-color machine presses wet overprint, the adhesion of the former color ink must be greater than that of the latter color, otherwise the ink printed first will be "stripped away" by the ink printed later, resulting in the phenomenon of "reverse overprint"

162. What factors regulate the adhesion of ink in printing

① surface strength of paper. The surface strength of paper is large, and the ink adhesion can be adjusted more; On the contrary, the adhesion should be reduced, otherwise the paper will "lose powder" and "lose hair" seriously, which will seriously affect the product quality and production efficiency, which is often the main motivation to adjust the ink adhesion

② printing speed. When the speed is fast, the requirements for adhesive deployment are smaller, otherwise, it is larger. The faster the speed is, the more prone it is to "roughening" and uneven ink transfer. It is necessary to reduce the first adhesion to adapt to it

③ graphic structure of the layout. When printing eye-catching images, the most important thing is that the shape and area of the points should be copied correctly, and the adhesion should be adjusted more. When printing field images, you want to get a uniform and thick field, and since there is no point increase problem, the adhesion should be adjusted less

④ workshop temperature. As the temperature increases, the cohesion of the ink will decrease, which is more likely to cause problems such as increased emulsification and dot increase rate. When adjusting the ink, the adhesion of the ink should be increased in advance. On the contrary, reduce the adhesion of the ink

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