With the development of social economy and the improvement of people's living standards, the status of gravure printing in various printing methods has become more prominent. The study of gravure printing technology has very important practical significance. Here is a brief discussion on the printability of gravure ink. Please correct your mistakes with your colleagues.
As with other printing inks, the main components of gravure inks are colored substances (pigments) and binders. Among them, the color material plays a role of coloration, and contrasts with the color of the substrate. Images appear on the substrate. Only the proportion of the components of the ink is well-distributed to achieve the proper printability and performance of the ink, so that the printing ink can be properly matched with the printing plate, the printing press, and the printing material, so that the printing process can proceed smoothly.
First, the raw material gravure ink is mostly volatile solvent type ink, composed of pigment, solid resin, volatile solvent, filler and additive.
1. pigment. Pigments are divided into two kinds of inorganic pigments and organic pigments. Inorganic pigments are mostly hard and dense crystal materials. These crystals are difficult to grind into fine particles without special treatment and can not be well dispersed into the binder, so the inorganic pigments are made of The printability of the ink is often not ideal, and it is easy to abrade the plate. The organic pigments can be mostly artificially modified and easily dispersed in the binder. The resulting inks have greater advantages in printability, but the prices are often higher. The pigment composition of the gravure ink is mostly organic pigments, which is determined by the gravure printing characteristics and the quality requirements of the prints.
The influence of the pigment on the printability in the oil is mainly determined by the nature of the pigment, such as the degree of dispersion, hiding power, specific volume, resistance, and the like.
1 Dispersion refers to the size of pigment particles. The pigment particles in the ink must be completely immersed in the binder in the ink film. The size of the pigment particles should not exceed the thickness of the ink film, generally about 5 μm, otherwise the gloss of the printed matter will be affected, and the smaller the particles, the higher the dispersion. The more saturated the hue of the ink is. Gravure printing is a web transfer printing and requires a high degree of pigment dispersion.
2 Coloring power refers to the ability of a pigment to affect the color of a mixed pigment after it is mixed with other pigments. Any pigment that is easily blended with a white substance and tends to lighten will have poor coloring power. The ink used for ink formulation should be pigmented with strong coloring power. It can be used to print inks with less ink and faster drying. This is critical for high-speed gravure printing that requires high ink dryness.
3 hiding power refers to the ability of pigments to cover the background. Whether the ink has hiding power depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When this ratio is 1, the pigment is transparent; when the ratio is greater than 1, the pigment is opaque, ie has hiding power. Different printing products have different requirements for the hiding power of pigments. For example, printing inks require strong hiding power of pigments to prevent the exposure of the background color, and four-color overprinting inks require high transparency of the pigments to make them overlap. The ink achieves a good color reduction effect.
4 The visual volume refers to the volume per gram of pigment, expressed in cubic centimeters. The same pigment with different particles, the apparent volume is different. The larger the visible passengers of the pigment, the smaller the specific gravity of the pigment and the less likely to precipitate in the binder, and the stability of the ink is good.
2. Link material. The binder is a dispersion medium in the ink and is a carrier of pigment particles. The printability of the ink is very close to that of the binder. The composition of the linking material is relatively complex, mainly including the oil type linking material, the resin type linking material, and the organic solvent.
1 Oil type linking material is prepared by heating vegetable oil to a certain temperature and keeping it warm at this temperature. Dry vegetable oil is a mixture of unsaturated fatty acid glycerides, and polymerization occurs upon heating to generate dimer and Trimer, the longer the heating and holding time, the greater the viscosity. The oil-based vehicle contains trace amounts of free fatty acids that act as surfactants, facilitating the mixing of pigments and binders. Oily binders have good adhesion and a certain degree of water resistance, and can form a relatively glossy ink film. However, the fixing speed is slow and the drying time is long.
2 Resin type binder is made by dissolving synthetic resin or modified resin in mineral oil, vegetable oil or volatile solvent, and can be divided into four types of resin: dissolved, dispersed, colloid and volatile. material. Commonly used synthetic resins include pentaerythritol rosin ester, alkyd resin, rosin modified phenol awake resin, polyacrylic resin, maleic acid resin, petroleum, and asphalt.
3 Organic solvents are also the main components in the ink binder. It makes the ink have a certain degree of fluidity. When the ink is transferred to the paper, the volatile solvent quickly evaporates. The solvent with low volatility penetrates into the paper by capillary action, which fixes the resin binder left on the surface of the paper. Paper surface and dry. Commonly used solvents include ethyl acetate, butyl acetate, isopropyl alcohol and the like.
3. Additives. Additives, also known as additives, are auxiliary components of the ink. Its function is to adjust the printing adaptability of the ink. For different purposes, different types and quantities of additives are added in the preparation of the ink to adjust the flowability and drying of the ink. Sex, hue, etc. Mainly plasticizers, slow drying agents, desiccants and so on.
1 Plasticizer is a high-boiling, low-volatile solvent or low-melting solid that increases the plasticity of high-molecular substances. Adding plasticizer to the ink can make the original brittle ink layer have better toughness and better adhesion between the ink layer and the printing material. In order for the plasticizer to perform these functions better, the molecules of the plasticizer must infiltrate between the long molecules of the linking material and act like a certain lubrication, so that the thermal motion of the long chain of the linking material is relatively free. The polymer becomes soft and elastic.
2 desiccant. For dry oils, the presence of a small amount of metal salts can greatly accelerate the oxidation reaction. Commonly used metal salts are salts of cobalt, manganese, and lead, which are called desiccants. The desiccant accelerates the drying of the ink during drying of the ink without any change in itself.
In addition, in order to improve the ink printability and other indicators, there are other additives in the ink, such as waxes, antioxidants, anti-smearing agents, surfactants, preservatives, removers, defoamers.
Second, performance gravure ink performance must first meet the gravure printing process needs, and second, the ink transferred to the paper or other materials on the film during the use of the print product to be able to withstand the follow-up processes and various conditions of use. These properties include flow properties, optical properties, and resistance properties.
1. The flow properties of the ink. The fluidity of ink is a major characteristic of printing inks, including viscosity, viscosity, viscoelasticity and so on.
1 ink viscosity. When a liquid is agitated, its flow rate is proportional to the applied force, ie Ï„ = MD (Ï„ shear stress, M constant, D shear rate), where M is a constant, ie the viscosity of the liquid, Different liquids have different properties and different concentrations determine the viscosity is not the same. If the viscosity of the ink binder material is large, the viscosity of the ink is also large. The type and amount of the solvent in the ink, the ratio of the pigment, the particle size, and the dispersion state thereof all affect the viscosity of the ink. The gravure ink can be approximated as a Newtonian fluid, and its yield value and thixotropy factor can not be considered, so the rheological curve is a straight line passing through the origin.
In the printing process, the viscosity of the ink is closely related to the ink transfer. Generally, the higher the speed, the faster the ink separation speed, the lower the viscosity of the ink, otherwise the transfer effect is not ideal. In addition, the surface strength of the paper is lower. Also, the lower the viscosity of the ink is, the easier it is to pull the paper. Therefore, in the gravure printing process, the viscosity of the ink must be strictly controlled to ensure the printing effect.
2 ink viscosity. The so-called viscosity of the ink is the hindrance ability of the ink layer in the peeling transfer, and the viscosity of the ink with a large viscosity is also large, but there is no necessary connection between the two inks. The highly viscous ink not only does not easily transfer to the surface of the paper, but also easily pulls the paper surface out of the paper, causing a quality accident.
3 ink viscoelasticity. The viscoelasticity of an ink is also the cohesion of the ink. The drawing of the ink is short, the retraction after breaking is fast, the viscoelasticity is strong, it is convenient for high-speed printing, the pattern is clear, and the ink is less. The viscoelasticity of the ink is closely related to the viscoelasticity of the binder.
2. The optical properties of the ink. 1 ink color. The color of the ink refers to the color of the ink applied on the surface of the substrate. It is related to the nature of the light source and generally refers to the color under the ideal light source. If the ink is completely opaque, when the light hits the surface of the ink, one part is absorbed and the other part is reflected. The combination of the reflected light is the color of the ink. If the ink is transparent, the light is irradiated on the surface of the ink, a portion is absorbed, a portion is reflected, another portion is transmitted to the surface of the paper and then reflected, and the ink layer comes out. The color that is directly combined with the reflected portion of light is the ink. colour.
There are many factors that affect the color of the ink. For example, if the ink layer is thick, the brightness is low, the color is dark, the ink is dry or not, and the reflectance, transmission, and absorption ratio of the light are also different, and the color displayed is also different. The color of the paper itself is different. The absorption of light by the whiteness also causes the ink color to change.
2 ink gloss. The gloss of an ink refers to the ability of the ink impression to reflect light at an angle. The quality of the ink gloss has a great influence on the appearance of the printed product. The gloss is good, the color is bright, and the grade of the printed product is high. Therefore, a high quality varnish must be selected during printing.
3. Ink resistance performance. Whether the printed matter can maintain its original color during use is a sign of good or bad quality of the printed matter, and it is also a good performance of the printing ink. Therefore, in order to guarantee the quality of printed products, especially the quality of some special-purpose printed products, the corresponding resistance properties of the ink must be improved.
Most of the pigments under the influence of sunlight, temperature and humidity, pH, the molecular structure or crystal structure is easy to change, resulting in color changes, generally the resistance of organic pigments is less resistant than inorganic pigments, therefore, gravure ink must Appropriate adjustments are made to the resistant material to improve its resistance.
In order to successfully produce high quality products for gravure printing, gravure inks must be effectively adjusted and carefully selected so that the characteristics of gravure printing with high efficiency and high quality are truly reflected in the printing industry, adding more to our lives. color.
As with other printing inks, the main components of gravure inks are colored substances (pigments) and binders. Among them, the color material plays a role of coloration, and contrasts with the color of the substrate. Images appear on the substrate. Only the proportion of the components of the ink is well-distributed to achieve the proper printability and performance of the ink, so that the printing ink can be properly matched with the printing plate, the printing press, and the printing material, so that the printing process can proceed smoothly.
First, the raw material gravure ink is mostly volatile solvent type ink, composed of pigment, solid resin, volatile solvent, filler and additive.
1. pigment. Pigments are divided into two kinds of inorganic pigments and organic pigments. Inorganic pigments are mostly hard and dense crystal materials. These crystals are difficult to grind into fine particles without special treatment and can not be well dispersed into the binder, so the inorganic pigments are made of The printability of the ink is often not ideal, and it is easy to abrade the plate. The organic pigments can be mostly artificially modified and easily dispersed in the binder. The resulting inks have greater advantages in printability, but the prices are often higher. The pigment composition of the gravure ink is mostly organic pigments, which is determined by the gravure printing characteristics and the quality requirements of the prints.
The influence of the pigment on the printability in the oil is mainly determined by the nature of the pigment, such as the degree of dispersion, hiding power, specific volume, resistance, and the like.
1 Dispersion refers to the size of pigment particles. The pigment particles in the ink must be completely immersed in the binder in the ink film. The size of the pigment particles should not exceed the thickness of the ink film, generally about 5 μm, otherwise the gloss of the printed matter will be affected, and the smaller the particles, the higher the dispersion. The more saturated the hue of the ink is. Gravure printing is a web transfer printing and requires a high degree of pigment dispersion.
2 Coloring power refers to the ability of a pigment to affect the color of a mixed pigment after it is mixed with other pigments. Any pigment that is easily blended with a white substance and tends to lighten will have poor coloring power. The ink used for ink formulation should be pigmented with strong coloring power. It can be used to print inks with less ink and faster drying. This is critical for high-speed gravure printing that requires high ink dryness.
3 hiding power refers to the ability of pigments to cover the background. Whether the ink has hiding power depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When this ratio is 1, the pigment is transparent; when the ratio is greater than 1, the pigment is opaque, ie has hiding power. Different printing products have different requirements for the hiding power of pigments. For example, printing inks require strong hiding power of pigments to prevent the exposure of the background color, and four-color overprinting inks require high transparency of the pigments to make them overlap. The ink achieves a good color reduction effect.
4 The visual volume refers to the volume per gram of pigment, expressed in cubic centimeters. The same pigment with different particles, the apparent volume is different. The larger the visible passengers of the pigment, the smaller the specific gravity of the pigment and the less likely to precipitate in the binder, and the stability of the ink is good.
2. Link material. The binder is a dispersion medium in the ink and is a carrier of pigment particles. The printability of the ink is very close to that of the binder. The composition of the linking material is relatively complex, mainly including the oil type linking material, the resin type linking material, and the organic solvent.
1 Oil type linking material is prepared by heating vegetable oil to a certain temperature and keeping it warm at this temperature. Dry vegetable oil is a mixture of unsaturated fatty acid glycerides, and polymerization occurs upon heating to generate dimer and Trimer, the longer the heating and holding time, the greater the viscosity. The oil-based vehicle contains trace amounts of free fatty acids that act as surfactants, facilitating the mixing of pigments and binders. Oily binders have good adhesion and a certain degree of water resistance, and can form a relatively glossy ink film. However, the fixing speed is slow and the drying time is long.
2 Resin type binder is made by dissolving synthetic resin or modified resin in mineral oil, vegetable oil or volatile solvent, and can be divided into four types of resin: dissolved, dispersed, colloid and volatile. material. Commonly used synthetic resins include pentaerythritol rosin ester, alkyd resin, rosin modified phenol awake resin, polyacrylic resin, maleic acid resin, petroleum, and asphalt.
3 Organic solvents are also the main components in the ink binder. It makes the ink have a certain degree of fluidity. When the ink is transferred to the paper, the volatile solvent quickly evaporates. The solvent with low volatility penetrates into the paper by capillary action, which fixes the resin binder left on the surface of the paper. Paper surface and dry. Commonly used solvents include ethyl acetate, butyl acetate, isopropyl alcohol and the like.
3. Additives. Additives, also known as additives, are auxiliary components of the ink. Its function is to adjust the printing adaptability of the ink. For different purposes, different types and quantities of additives are added in the preparation of the ink to adjust the flowability and drying of the ink. Sex, hue, etc. Mainly plasticizers, slow drying agents, desiccants and so on.
1 Plasticizer is a high-boiling, low-volatile solvent or low-melting solid that increases the plasticity of high-molecular substances. Adding plasticizer to the ink can make the original brittle ink layer have better toughness and better adhesion between the ink layer and the printing material. In order for the plasticizer to perform these functions better, the molecules of the plasticizer must infiltrate between the long molecules of the linking material and act like a certain lubrication, so that the thermal motion of the long chain of the linking material is relatively free. The polymer becomes soft and elastic.
2 desiccant. For dry oils, the presence of a small amount of metal salts can greatly accelerate the oxidation reaction. Commonly used metal salts are salts of cobalt, manganese, and lead, which are called desiccants. The desiccant accelerates the drying of the ink during drying of the ink without any change in itself.
In addition, in order to improve the ink printability and other indicators, there are other additives in the ink, such as waxes, antioxidants, anti-smearing agents, surfactants, preservatives, removers, defoamers.
Second, performance gravure ink performance must first meet the gravure printing process needs, and second, the ink transferred to the paper or other materials on the film during the use of the print product to be able to withstand the follow-up processes and various conditions of use. These properties include flow properties, optical properties, and resistance properties.
1. The flow properties of the ink. The fluidity of ink is a major characteristic of printing inks, including viscosity, viscosity, viscoelasticity and so on.
1 ink viscosity. When a liquid is agitated, its flow rate is proportional to the applied force, ie Ï„ = MD (Ï„ shear stress, M constant, D shear rate), where M is a constant, ie the viscosity of the liquid, Different liquids have different properties and different concentrations determine the viscosity is not the same. If the viscosity of the ink binder material is large, the viscosity of the ink is also large. The type and amount of the solvent in the ink, the ratio of the pigment, the particle size, and the dispersion state thereof all affect the viscosity of the ink. The gravure ink can be approximated as a Newtonian fluid, and its yield value and thixotropy factor can not be considered, so the rheological curve is a straight line passing through the origin.
In the printing process, the viscosity of the ink is closely related to the ink transfer. Generally, the higher the speed, the faster the ink separation speed, the lower the viscosity of the ink, otherwise the transfer effect is not ideal. In addition, the surface strength of the paper is lower. Also, the lower the viscosity of the ink is, the easier it is to pull the paper. Therefore, in the gravure printing process, the viscosity of the ink must be strictly controlled to ensure the printing effect.
2 ink viscosity. The so-called viscosity of the ink is the hindrance ability of the ink layer in the peeling transfer, and the viscosity of the ink with a large viscosity is also large, but there is no necessary connection between the two inks. The highly viscous ink not only does not easily transfer to the surface of the paper, but also easily pulls the paper surface out of the paper, causing a quality accident.
3 ink viscoelasticity. The viscoelasticity of an ink is also the cohesion of the ink. The drawing of the ink is short, the retraction after breaking is fast, the viscoelasticity is strong, it is convenient for high-speed printing, the pattern is clear, and the ink is less. The viscoelasticity of the ink is closely related to the viscoelasticity of the binder.
2. The optical properties of the ink. 1 ink color. The color of the ink refers to the color of the ink applied on the surface of the substrate. It is related to the nature of the light source and generally refers to the color under the ideal light source. If the ink is completely opaque, when the light hits the surface of the ink, one part is absorbed and the other part is reflected. The combination of the reflected light is the color of the ink. If the ink is transparent, the light is irradiated on the surface of the ink, a portion is absorbed, a portion is reflected, another portion is transmitted to the surface of the paper and then reflected, and the ink layer comes out. The color that is directly combined with the reflected portion of light is the ink. colour.
There are many factors that affect the color of the ink. For example, if the ink layer is thick, the brightness is low, the color is dark, the ink is dry or not, and the reflectance, transmission, and absorption ratio of the light are also different, and the color displayed is also different. The color of the paper itself is different. The absorption of light by the whiteness also causes the ink color to change.
2 ink gloss. The gloss of an ink refers to the ability of the ink impression to reflect light at an angle. The quality of the ink gloss has a great influence on the appearance of the printed product. The gloss is good, the color is bright, and the grade of the printed product is high. Therefore, a high quality varnish must be selected during printing.
3. Ink resistance performance. Whether the printed matter can maintain its original color during use is a sign of good or bad quality of the printed matter, and it is also a good performance of the printing ink. Therefore, in order to guarantee the quality of printed products, especially the quality of some special-purpose printed products, the corresponding resistance properties of the ink must be improved.
Most of the pigments under the influence of sunlight, temperature and humidity, pH, the molecular structure or crystal structure is easy to change, resulting in color changes, generally the resistance of organic pigments is less resistant than inorganic pigments, therefore, gravure ink must Appropriate adjustments are made to the resistant material to improve its resistance.
In order to successfully produce high quality products for gravure printing, gravure inks must be effectively adjusted and carefully selected so that the characteristics of gravure printing with high efficiency and high quality are truly reflected in the printing industry, adding more to our lives. color.
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