The problem of color difference of package printed matter has plagued the printing workers. The problem of color difference can be effectively controlled. It is a measure of the company's product quality, reputation and skill level of operation master. Therefore, The problems companies must pay attention to.
Printed color is roughly divided into two phenomena, one means: the same batch of product color, but with the color of the sample color. Two refers to: the same batch of color there is color, and some consistent with the sample, but some inconsistent with the sample.
Now from the following aspects we would like to discuss and analyze with you.
First, the first phenomenon (the same batch of products of the same color, but with the color of the sample color)
1, human factors:
And the captain's skill level has nothing to do, but with the captain's sense of responsibility, since the same batch of product color can be consistent, indicating the captain's skill level is not low, but why inconsistent with the sample dare to print down? First signature it? This is entirely the responsibility of the captain. (Nor does it exclude the signature error, if it is, this is again related to the signatory's sense of responsibility).
2, paper color:
Paper of different whiteness has different effects on the color appearance of the printing ink layer. Because the whiteness is equal to different black, red, blue or yellow in the ink, so in the printing despite the amount of ink, hue has not changed, but the actual ink has a certain transparency, the effect of color with the paper whiteness Differences appear, resulting in different color. In the opening, you must use the same lot of paper. Because of weight, size, size, although the same, but the production of different batch dates, whiteness of the paper there will be some differences, resulting in the color of the printed product color. So you must use the same white paper as the same product printed paper.
3, paper gloss and smoothness:
The gloss of the print depends on the gloss and smoothness of the paper. Offset color printing is the light incident upon the paper surface, the light reflected to the human eye retina, through the light-sensitive cells to accept photosynthesis and see the color. If the gloss and smoothness of the paper is high, the color we observe is basically the color that is reflected through the ink layer, and the main color light saturation is high. If the paper surface roughness, low gloss, it will have a diffuse reflection, it will reduce the saturation of the main color light, so that our human eyes feel the color of the print feel lighter. The same ink density is measured with a densitometer. Smoothness Glossy paper, high density. Smoothness Low gloss paper with low density.
4, printed sheet surface treatment:
Printed through the film, polishing, calendering, over the oil, printing and other surface treatment, there will be varying degrees of hue changes. Some of these changes are physical changes, some chemical changes. Physical changes are mainly reflected in the product surface increased specular reflection, which has a certain impact on color density. For example, the complex film, UV varnish, calendaring, etc., the color density will increase. Sub-sub-film, the matte color printing on the reduction of color density. Chemical changes are mainly from the glue, varnish, UV oil and so on. These materials contain a wide range of solvents, all of which cause a color change in the color of the ink. Therefore, as packaging offset printing, printing process if there is a post-press, the physical and chemical changes after printing process must be taken into account to determine the printing ink density and Lab values.
5, dry density value:
The offset printing product just after printing, the ink is still in a wet state, then the measured density value and the measured value after drying the printed density is different. Wet high density, dry density value is low, this is the phenomenon of dry-back density value. This is because the ink just printed has a certain level of leveling. The performance of the surface of the mirror-based, looks colorful, shiny good. When the ink layer is dry, the surface has diffuse reflection, the natural luster is fainter than when printed. In the usual printing in order to ensure that batch products as much as possible to reduce color, we use the same wet density test method to control. That is, the first time the product is wet, it is signed by the customer and immediately agreed with the measured value of the wet density and the value of L * a * b *. After printing the product (wet state), according to the first measured density value and L * a * b * value for color control. Of course, if using a densitometer with a polarizer device, it can eliminate the surface of the ink layer due to specular reflection of light. It measured the wet density and dry density is relatively close, but also can help reduce the control of color.
6, printing pressure:
Printing pressure is one of the conditions of ink transfer, because the printing plate surface, blanket, etc. can not be absolutely flat, the surface of the paper is inevitably there are subtle convex or uneven thickness. If the printing pressure is less than or uneven, the ink layer is prone to the phenomenon of uneven brightness, so the process required to achieve "three flat", which requires the printing plate surface, blanket and substrate and lining the surface to achieve a relatively flat Conditions, in order to thinner layer of ink through a balanced printing pressure to print on the print to get a more uniform ink color.
When the printing pressure is insufficient or uneven, the lining body and the printing plate surface there is poor contact, you need to increase the amount of ink to meet the layout inking visual effects. However, this will not only increase the ink consumption, but also easy to produce the printing color and printing dirty phenomenon, so do "Sanping" (roller ink, water roller, roller flat) using uniform and constant printing Pressure, in order to prevent due to inappropriate pressure caused by color.
7, to see the light source:
Offset printing products in the observation of color must have a light source, no light can not see the color, but if the light source is not the same, then the color difference will be great. In general, we require color observation under natural light conditions (ie standard light sources). If you use ordinary light bulbs as light source color, then the color will appear yellow, it is difficult to accurately identify the color, the final product will have a serious color cast. In addition, the strength of the light and illumination angle will also affect the color identification. In the same light source, the sample is illuminated on the reflection of light intensity, mainly by the sample and the light source to determine the distance. Near strong, far weaker. Therefore, we usually pay attention to two points during work day or night: one is to use a standard light source (wavelength 400-700 or so), and the other is to pay attention to the light source intensity and irradiation angle equal. For products with high color requirements, printing ink samples should be placed on top of the standard for comparison, so that due to the observation of small differences in the color of the relatively accurate identification. Therefore, the process of practice tells us that the characteristics of light sources and observation of the differences will directly affect the color of the accurate identification.
Second, the second phenomenon (the same color there is color, some with the same sample, but some inconsistent with the sample)
1, human factors:
That the first few hue prospective, in the ink has not yet balance the case, began to open all the way, the printing process of non-stop adjustment of water, ink, side tune aside, is bound to result in the same batch of color print color, This is the captain's skill level, experience, character has a great relationship, both belong to the same ability to produce the same batch of product color.
2, fountain solution:
Offset printing is the use of the principle of oil-water repulsion. This water refers to fountain solution. Its size directly affects the color of the ink layer. Large ink layer light color, water, small ink layer will color depth. The greater the water, the more serious emulsion of ink. Emulsified ink matte, color is light. Emulsified ink printed matter is not only bad color, but also produce dirty, quit, imprint is not strong, and so quality problems. So in the printing, the operation must strictly control the size of the dampening solution on the printing plate, and work well on the balance of ink and ink. The less water is required, the better.
3, printing speed:
The speed of printing will affect the color of printed matter. This is because the speed of the car will affect the ink balance. Express plate of water and slow version of the water on the plate varies. Express plate evaporation of water is small, slow plate large water vapor evaporation. Due to changes in the size of the water led to imbalance in the ink, it will inevitably lead to changes in the color of the ink. So usually in the printing must pay attention to a constant speed, absolutely can not drive fast. For a while slow, so printed prints will produce color. At the same time must also be based on the situation of the machine, adjust to a most stable speed. For example, some imported offset printing machines indicate the maximum speed of 16,000 sheets / hour and the maximum speed of domestic machines of 8,000 sheets / hour. These speeds are not stable speed. In general, both the imported machine and domestic machine, the stable speed is 70% of the maximum speed is the most ideal, that is: import machine at 11,000 / hour, domestic machine at 5600 / hour, this speed can be relatively easy to control Ink balance, reduce color.
4, bad roller:
Offset printing process, printed matter can get uniform ink color, roller quality has a very important role. General Cots have ink roller, ink roller and ink roller three, they have a great influence on ink color shades. The flexibility, stickiness, roundness, hardness and surface finish of the ink roller largely determines the quality of the printed ink. If there is ink roller poor elasticity, lack of viscosity, roll eccentric. Good colloidal and colloidal aging, etc., the printing process is likely to cause inking uneven or unstable, so that prepared printing inks inconsistent. Therefore, when printing to ensure the quality of cots, in order to ensure that each printing cycle coated on the plate of the ink is basically the same. Therefore, in usual work, the rubber roller should be cleaned so that the paper dust and impurities remaining on the rubber roller can be removed and the ink can be uniformly transmitted. At the same time, the contact pressure between the ink rollers and the ink roller and the printing plate should also be adjusted. Otherwise, uneven ink transfer may occur, resulting in serious color difference.
5, equipment maintenance:
Maintaining the good performance of the machine is a reliable guarantee to improve the quality of printing ink. If the machine is not stable, for example, the pressure is inconsistent, the feeding is not stable, printing often appear empty, multiple cases. Is bound to cause the color of the printing color. So usually we have to do a good job of equipment maintenance, attention to the key parts of the machine lubrication, to prevent wear and tear aggravate the equipment in a stable state. As a offset press to do a good job, "Miyoshi" (good management, good use, repair), "four will" (will be used, will be maintained, will check, will troubleshoot).
There are many reasons for the formation of printing color, control methods also more than that, which requires us to constantly explore in the printing operation, accumulation, develop a good habit of taking notes is conducive to improving their own ability to see more spare time The book on the theory of printing, there are theories to do the guidelines, you can take a lot less detours, the quality of printed products customers are getting higher and higher, for us, the pressure is more motivation, I believe as long as a positive attitude Face, you will be on the road to success more and more smooth.