During printing and storage, the hue, brightness, and saturation of the printed matter often change. Whether it is a single ink or two or more colors of ink, the inner and outer inks may become darker or darker. . High-quality print standards are: a batch of printed products before and after the darkness of the ink should be consistent, colorful to meet the proofs, ink hue and darkness in line with the proofs. There are many factors that affect the color change of printed materials. There are roughly the following aspects:
First, the ink is not resistant to light caused by discoloration and fading In the sunlight, the color and light will change to varying degrees, the absolute light does not change the hue of the ink is not, in the strong sunlight, all ink Colors will produce varying degrees of change. This change can be divided into two types:
1 Fading: Under the action of sunlight and ultraviolet light, the ink has poor light resistance, lost its original bright color, and its color becomes light gray. Especially light color inks, four-color dot printing, yellow and red colors fade faster, and vice versa, while cyan and black fade slowly.
2 Discoloration: Contrary to the fading of ink, the color change is dark in the effect of sunlight, and the color also changes people to call this change color. With the development of offset printing, four-color color overprinting is increasingly urgently needed for printing inks with good lightfastness: (1) The ink is required to be brilliant in color, and its graphics network is full and strong. 2 Maintain a constant color for a certain period of time.
Second, the impact of emulsification on the color of the imprint printed version of the printing plate can not be separated from the blank part of the printing plate with the wetting liquid, offset printing is the first ink after the water, the water will inevitably emulsified phenomenon. After the ink is emulsified, the color will be lightened, but the water can be restored after the evaporation of water, so the greater the moisture, the greater the emulsification, it will cause discoloration. In particular, the inks with completely different degrees of emulsification are mixed together, and the discoloration phenomenon is particularly prominent.
Therefore, offset printing should use the least amount of water on the premise of not contaminating the plate to reduce and control the emulsification so as to balance the ink and ink and keep the color as stable as possible.
Third, the nature of the paper and the relationship between the print copy 1 paper surface smoothness Paper surface smoothness is closely related to the copy of the print, uneven paper often requires a lot of pressure in order to make ink and it has a good contact . For example, the ink viscosity, fluidity, and thickness of the ink layer are kept constant. Increasing the pressure often increases the footprint of the imprinting. At the same time, the low-lying areas of the paper are still in poor contact. For example, if the effect of the imprinting on the coated paper and the newsprint printed on the same printing plate is quite different, the different reproduction effects can be clearly compared.
From this, it is inferred that the prints printed on rough-surfaced papers are difficult to maintain the ideal reproduction effect, so that fine print products must be printed with high-grade coated paper to ensure good copying results. However, paper with high smoothness causes a decrease in capillary suction force.
2 Absorption of paper Absorbability of paper is also related to the effect of copying. Usually when printing loose paper, if the ink has high fluidity and low viscosity, the paper will absorb more ink layer of the binder. If the diameter of the pores is larger than the diameter of the pigment particles, even the pigment will be absorbed. This reduces the saturation of the print. Need to properly increase the thickness of the ink layer. However, increasing the thickness of the ink layer can cause "spreading" to affect the copying effect at the moment of imprinting.
The absorptive paper can make most of the ink film appear on the surface of the paper, so that the ink film layer has better saturation. Different quality papers have obvious quality effects. The printed imprints on paper with loose structure and high absorbability are not ideal. The paper quality is difficult to print with high quality products, so the printability of paper is improved. For the printing company, it is necessary to select suitable paper according to the requirements of product quality.
3 Influence of Paper Penetration The permeability of the paper will make the thickness of the ink layer thinner, and the pores of the paper surface will be large, and some of the pigments will also be penetrated into the paper at the same time, so the color will have a lightening effect. For this reason, use paper with rough surface texture and paper with large ink flow, pay attention to discoloration.
Fourth, the effect of pigment heat resistance
In the drying process, the fast-drying, bright-type adhesive printing ink is an oxidized conjunctiva type drying. There is a fixing stage before drying. The oxidative polymerization of the ink is an exothermic reaction. When the drying is too fast, many heat will be released. Slow heat emission will discolor the thermostable pigment. For example: gold color ink darkens, lost gold.
During printing, the sheet is stacked on the delivery table. Due to stacking too much, the middle part of the sheet, the ink oxidative polymerization exothermic reaction, the heat is not easily dissipated, the temperature is too high, the discoloration is more in the middle, so the printed sheet is overheated When it is necessary, try to dissipate heat in time to prevent discoloration. Do not put too much driers in the ink (red and white dry oil). Do not stack the printed sheets too high. Isolation and stacking with wooden plywood, ventilation, etc. The discoloration.
Fifth, the effect of dry oil on the imprint discoloration
Light color ink belongs to cold tone, green, blue and other color ink, do not use red dry oil, because the red dry oil itself has a deep purple, will affect the color of the faded color ink, so shallow Light-colored ink is best to use dry white oil to avoid the effect of dry oil on the color of the ink. White dry oil looks white, but after the oxidation conjunctiva is light brown, if the amount of dry white oil is more, then it is estimated that the blot will have a yellowish-brown color after drying and fixation; dark ink such as: blue and black The color of red dry ink used in colors such as purple and purple will not be greatly affected.
Sixth, the ink does not have the influence of the alkali The printing uses the paper PH value =7, the neutral paper is ideal. Under normal circumstances, inorganic pigments produced by the ink is relatively poor alkali resistance, organic pigments better alkali resistance, especially in the blue, dark blue ink will meet the alkali fade, the yellow ink in the case of alkali becomes reddish, hot stamping The electro-aluminum foil will turn pale yellow when it encounters alkaline substances, making it unlustre, and it tends to be weaker and more alkaline. In the later stage of printing, the binder will contain alkaline adhesives. If the packaging is decorated and printed, Is used to pack alkaline substances soap, soap, detergent and other substances, we must consider the ink alkali resistance, saponification resistance is stronger, peacock blue ink alkali resistance is better.
Seven, paper in the storage and use of the process of discoloration Most of the long-term storage of printed products, it will inevitably show a pan-yellow phenomenon, for the following reasons.
1 The fibers of the paper contain lignin that is yellow and brittle, such as newspapers printed on newspapers that are most prone to yellowing and brittleness.
2 For color printing products, most of them are exposed to direct light for a long time, wind and rain, temperature and humidity, etc. The reason is that ink pigments are discolored or discolored due to their resistance to light. (Wen / Wang Xincheng) ("China Packaging News")
First, the ink is not resistant to light caused by discoloration and fading In the sunlight, the color and light will change to varying degrees, the absolute light does not change the hue of the ink is not, in the strong sunlight, all ink Colors will produce varying degrees of change. This change can be divided into two types:
1 Fading: Under the action of sunlight and ultraviolet light, the ink has poor light resistance, lost its original bright color, and its color becomes light gray. Especially light color inks, four-color dot printing, yellow and red colors fade faster, and vice versa, while cyan and black fade slowly.
2 Discoloration: Contrary to the fading of ink, the color change is dark in the effect of sunlight, and the color also changes people to call this change color. With the development of offset printing, four-color color overprinting is increasingly urgently needed for printing inks with good lightfastness: (1) The ink is required to be brilliant in color, and its graphics network is full and strong. 2 Maintain a constant color for a certain period of time.
Second, the impact of emulsification on the color of the imprint printed version of the printing plate can not be separated from the blank part of the printing plate with the wetting liquid, offset printing is the first ink after the water, the water will inevitably emulsified phenomenon. After the ink is emulsified, the color will be lightened, but the water can be restored after the evaporation of water, so the greater the moisture, the greater the emulsification, it will cause discoloration. In particular, the inks with completely different degrees of emulsification are mixed together, and the discoloration phenomenon is particularly prominent.
Therefore, offset printing should use the least amount of water on the premise of not contaminating the plate to reduce and control the emulsification so as to balance the ink and ink and keep the color as stable as possible.
Third, the nature of the paper and the relationship between the print copy 1 paper surface smoothness Paper surface smoothness is closely related to the copy of the print, uneven paper often requires a lot of pressure in order to make ink and it has a good contact . For example, the ink viscosity, fluidity, and thickness of the ink layer are kept constant. Increasing the pressure often increases the footprint of the imprinting. At the same time, the low-lying areas of the paper are still in poor contact. For example, if the effect of the imprinting on the coated paper and the newsprint printed on the same printing plate is quite different, the different reproduction effects can be clearly compared.
From this, it is inferred that the prints printed on rough-surfaced papers are difficult to maintain the ideal reproduction effect, so that fine print products must be printed with high-grade coated paper to ensure good copying results. However, paper with high smoothness causes a decrease in capillary suction force.
2 Absorption of paper Absorbability of paper is also related to the effect of copying. Usually when printing loose paper, if the ink has high fluidity and low viscosity, the paper will absorb more ink layer of the binder. If the diameter of the pores is larger than the diameter of the pigment particles, even the pigment will be absorbed. This reduces the saturation of the print. Need to properly increase the thickness of the ink layer. However, increasing the thickness of the ink layer can cause "spreading" to affect the copying effect at the moment of imprinting.
The absorptive paper can make most of the ink film appear on the surface of the paper, so that the ink film layer has better saturation. Different quality papers have obvious quality effects. The printed imprints on paper with loose structure and high absorbability are not ideal. The paper quality is difficult to print with high quality products, so the printability of paper is improved. For the printing company, it is necessary to select suitable paper according to the requirements of product quality.
3 Influence of Paper Penetration The permeability of the paper will make the thickness of the ink layer thinner, and the pores of the paper surface will be large, and some of the pigments will also be penetrated into the paper at the same time, so the color will have a lightening effect. For this reason, use paper with rough surface texture and paper with large ink flow, pay attention to discoloration.
Fourth, the effect of pigment heat resistance
In the drying process, the fast-drying, bright-type adhesive printing ink is an oxidized conjunctiva type drying. There is a fixing stage before drying. The oxidative polymerization of the ink is an exothermic reaction. When the drying is too fast, many heat will be released. Slow heat emission will discolor the thermostable pigment. For example: gold color ink darkens, lost gold.
During printing, the sheet is stacked on the delivery table. Due to stacking too much, the middle part of the sheet, the ink oxidative polymerization exothermic reaction, the heat is not easily dissipated, the temperature is too high, the discoloration is more in the middle, so the printed sheet is overheated When it is necessary, try to dissipate heat in time to prevent discoloration. Do not put too much driers in the ink (red and white dry oil). Do not stack the printed sheets too high. Isolation and stacking with wooden plywood, ventilation, etc. The discoloration.
Fifth, the effect of dry oil on the imprint discoloration
Light color ink belongs to cold tone, green, blue and other color ink, do not use red dry oil, because the red dry oil itself has a deep purple, will affect the color of the faded color ink, so shallow Light-colored ink is best to use dry white oil to avoid the effect of dry oil on the color of the ink. White dry oil looks white, but after the oxidation conjunctiva is light brown, if the amount of dry white oil is more, then it is estimated that the blot will have a yellowish-brown color after drying and fixation; dark ink such as: blue and black The color of red dry ink used in colors such as purple and purple will not be greatly affected.
Sixth, the ink does not have the influence of the alkali The printing uses the paper PH value =7, the neutral paper is ideal. Under normal circumstances, inorganic pigments produced by the ink is relatively poor alkali resistance, organic pigments better alkali resistance, especially in the blue, dark blue ink will meet the alkali fade, the yellow ink in the case of alkali becomes reddish, hot stamping The electro-aluminum foil will turn pale yellow when it encounters alkaline substances, making it unlustre, and it tends to be weaker and more alkaline. In the later stage of printing, the binder will contain alkaline adhesives. If the packaging is decorated and printed, Is used to pack alkaline substances soap, soap, detergent and other substances, we must consider the ink alkali resistance, saponification resistance is stronger, peacock blue ink alkali resistance is better.
Seven, paper in the storage and use of the process of discoloration Most of the long-term storage of printed products, it will inevitably show a pan-yellow phenomenon, for the following reasons.
1 The fibers of the paper contain lignin that is yellow and brittle, such as newspapers printed on newspapers that are most prone to yellowing and brittleness.
2 For color printing products, most of them are exposed to direct light for a long time, wind and rain, temperature and humidity, etc. The reason is that ink pigments are discolored or discolored due to their resistance to light. (Wen / Wang Xincheng) ("China Packaging News")
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