(INK TRANSFER MODELS AND UTILIZATION IN PRACTICAL CONDITIONS)
Summary:
Over the years, we have been printing images onto substrates through ink transfer, and gravure printing is no exception.
The mechanism model of this printing method was first proposed by Walker and Van Scheuer in 1955. They established three basic steps for the transfer of printing inks through experiments:
1. The ink begins to come into contact with the paper;
2. The ink is cured on the substrate surface;
3. Ink separation.
Others are the transfer models proposed by Yuri Perry (1978) and Zang (1992), but the mechanism is the same. In the past, due to people's lack of understanding of the model in practice and the lack of relevant information, its importance was often overlooked. This article introduces the ink transfer model and its application in practice. It aims to promote the image printing quality and optimize the printing process.
Foreword
For a long time, printing is the process of transferring the ink onto the substrate to achieve image reproduction. Due to its high reliability, gravure printing has become a high-quality printing representative and has dominated the high-end printing market.
In 1955, Walker and Vansko set up the ink transfer model based on the letter printing machine, and put forward the relevant calculation formula. Afterwards, many experts have refined and improved it on the basis of practice in order to better conform to the actual situation and better describe the ink transfer mechanism in the printing process. Some models, such as Hartlin (1973) and Barrett (1978) models, derive the corresponding results through theory, and make people conceptually improve the understanding of ink transfer.
Unfortunately, their theories are based on a false premise - the transfer of ink is stable. Although this has some truth, it also has a certain degree of fitting with practice. After all, more than half of inks are delivered in this way. But to do accurate simulations, these are not enough. The correct description can help to theoretically improve the understanding of ink transmission methods.
This article starts with the description of the ink transfer mechanism. Through the introduction of various models, the ink transfer process is simulated theoretically and practically. Finally, the application of these models in practice is elaborated.
Ink delivery
The ink transfer in gravure printing is a physical inking process from the printing cylinder mesh to the print product. Here's a brief description of this process:
a. The surface of the cylinder is immersed in the ink tank, and the mesh on the surface is filled with ink.
b. The squeegee scrapes excess ink and fills the mesh with ink only. Due to the liquid tension, the ink forms a capillary concavity in the mesh.
c. The ink roller continues to rotate, and the ink roller, the printing material and the embossing roller contact each other. Under the effect of pressure, the ink in the mesh contacts with the printing material, and the first step of ink transfer is completed.
d. Because the substrate is absorbent, the surface ink that is in direct contact with the material is cured, while the remaining ink forms a "free" ink on the surface of the material.
e. As the cylinder continues to rotate, the ink droplets are drawn into a thin line between the ink roller and the printed material as they leave the dots, and the ink separation process begins. At this time, part of the ink flows to the prints, and part of the ink flows back to the ink roller openings. For ease of calculation, let us assume that their ratio is 1:1, that is, half of them remain on the prints and half return to the ink rollers.
Therefore, the ink transfer mechanism can be divided into three stages, namely:
1. Paper and ink begin to contact;
2. The ink is cured on the substrate surface;
3. Ink separation.
If we make a curve by comparing the amount of ink received by the process with the paper and the amount of ink on the plate, it will be an "S" curve. That is, when the ink amount of the ink hole is small, the transfer speed of the printing ink is very fast, but when the ink amount is large enough, the ink transfer speed hardly changes. It is also possible to use the relationship between the ratio of ink transfer and the amount of ink in the printing plate as a curve.
Some factors that affect ink transfer:
According to Kunz's research, the main factors affecting the transfer of printing inks are:
1. Printing speed
The printing speed mainly acts on the separation stage of the ink. When the printing speed is very low, the separation of the ink film can be kept uniform, but when the printing speed is faster, the stability of the liquid changes due to the effect of fluid mechanics. At this time, the separation process changes, and air holes and drawing occur. When the printing speed is particularly high and the pressure at the ink-jet point is much lower than the atmospheric pressure, a large number of air holes will be generated in the ink, which will cause the printing product to be blurred.
2. Scraper
The angle and type of squeegee will affect the squeegee effect and the amount of ink in the ink roller mesh.
3. Embossing roller
Experiments show that the impact of the imprinting roller on the ink transfer is huge. The greater the pressure, the better the ink transfer effect.
4. Ink roller mesh geometry
The mesh shape, width, and depth generated by different manufacturing processes have a greater impact on the effect of ink transfer. The process includes chemical etching, electromechanical engraving, laser etching and other methods. Kunz's research results show that although the optical density of the mesh is the same, the ink holes produced by different manufacturing processes have different effects on the ink transfer, and the ink-membrane-engraved ink holes have the best transmission effect. But Shi Pu also found that if only from the print quality point of view, electromechanical engraving and laser etching ink roller is not much difference.
5. Electrostatic process
Helps to improve the transmission of ink in the fine-grained part, which can avoid the phenomenon of dot-fading.
Other factors that affect the characteristics of printing inks and printing materials include:
1. Ink fluid characteristics:
Fluidity has a great influence on the transfer of ink. If the ink is more viscous, there will be a lot of resistance to the flow of the ink during the separation process. Conversely, if the ink is thin, the ink will have a strong fluidity.
2. Temperature
The temperature of the ink cannot be ignored because it affects the viscosity of the ink, which in turn affects the ink transfer performance.
3. Other characteristics of ink
The content of ink in the ink, pigments, additives, etc. will affect the ink transfer performance.
4. Finishing materials
The surface structure of the printing material also has a great influence on the transfer of the ink. In particular, the first step in printing, the contact between the ink and the printed product, and the adhesion and fixation of the ink on the surface of the printed product, have a great influence.
5. Material flexibility
Flexibility can affect the range of ink and substrate contact. The softer the material, the easier it is to contact the ink in the ink roller mesh under the impression roller.
6. Other features:
Tension and humidity on the surface of the material can increase or decrease the ink transfer rate.
The above factors have different effects on the specific value of the ink transfer effect. However, the established model should include all relevant factors in order to better describe the mechanism of ink transfer.
Summary:
Over the years, we have been printing images onto substrates through ink transfer, and gravure printing is no exception.
The mechanism model of this printing method was first proposed by Walker and Van Scheuer in 1955. They established three basic steps for the transfer of printing inks through experiments:
1. The ink begins to come into contact with the paper;
2. The ink is cured on the substrate surface;
3. Ink separation.
Others are the transfer models proposed by Yuri Perry (1978) and Zang (1992), but the mechanism is the same. In the past, due to people's lack of understanding of the model in practice and the lack of relevant information, its importance was often overlooked. This article introduces the ink transfer model and its application in practice. It aims to promote the image printing quality and optimize the printing process.
Foreword
For a long time, printing is the process of transferring the ink onto the substrate to achieve image reproduction. Due to its high reliability, gravure printing has become a high-quality printing representative and has dominated the high-end printing market.
In 1955, Walker and Vansko set up the ink transfer model based on the letter printing machine, and put forward the relevant calculation formula. Afterwards, many experts have refined and improved it on the basis of practice in order to better conform to the actual situation and better describe the ink transfer mechanism in the printing process. Some models, such as Hartlin (1973) and Barrett (1978) models, derive the corresponding results through theory, and make people conceptually improve the understanding of ink transfer.
Unfortunately, their theories are based on a false premise - the transfer of ink is stable. Although this has some truth, it also has a certain degree of fitting with practice. After all, more than half of inks are delivered in this way. But to do accurate simulations, these are not enough. The correct description can help to theoretically improve the understanding of ink transmission methods.
This article starts with the description of the ink transfer mechanism. Through the introduction of various models, the ink transfer process is simulated theoretically and practically. Finally, the application of these models in practice is elaborated.
Ink delivery
The ink transfer in gravure printing is a physical inking process from the printing cylinder mesh to the print product. Here's a brief description of this process:
a. The surface of the cylinder is immersed in the ink tank, and the mesh on the surface is filled with ink.
b. The squeegee scrapes excess ink and fills the mesh with ink only. Due to the liquid tension, the ink forms a capillary concavity in the mesh.
c. The ink roller continues to rotate, and the ink roller, the printing material and the embossing roller contact each other. Under the effect of pressure, the ink in the mesh contacts with the printing material, and the first step of ink transfer is completed.
d. Because the substrate is absorbent, the surface ink that is in direct contact with the material is cured, while the remaining ink forms a "free" ink on the surface of the material.
e. As the cylinder continues to rotate, the ink droplets are drawn into a thin line between the ink roller and the printed material as they leave the dots, and the ink separation process begins. At this time, part of the ink flows to the prints, and part of the ink flows back to the ink roller openings. For ease of calculation, let us assume that their ratio is 1:1, that is, half of them remain on the prints and half return to the ink rollers.
Therefore, the ink transfer mechanism can be divided into three stages, namely:
1. Paper and ink begin to contact;
2. The ink is cured on the substrate surface;
3. Ink separation.
If we make a curve by comparing the amount of ink received by the process with the paper and the amount of ink on the plate, it will be an "S" curve. That is, when the ink amount of the ink hole is small, the transfer speed of the printing ink is very fast, but when the ink amount is large enough, the ink transfer speed hardly changes. It is also possible to use the relationship between the ratio of ink transfer and the amount of ink in the printing plate as a curve.
Some factors that affect ink transfer:
According to Kunz's research, the main factors affecting the transfer of printing inks are:
1. Printing speed
The printing speed mainly acts on the separation stage of the ink. When the printing speed is very low, the separation of the ink film can be kept uniform, but when the printing speed is faster, the stability of the liquid changes due to the effect of fluid mechanics. At this time, the separation process changes, and air holes and drawing occur. When the printing speed is particularly high and the pressure at the ink-jet point is much lower than the atmospheric pressure, a large number of air holes will be generated in the ink, which will cause the printing product to be blurred.
2. Scraper
The angle and type of squeegee will affect the squeegee effect and the amount of ink in the ink roller mesh.
3. Embossing roller
Experiments show that the impact of the imprinting roller on the ink transfer is huge. The greater the pressure, the better the ink transfer effect.
4. Ink roller mesh geometry
The mesh shape, width, and depth generated by different manufacturing processes have a greater impact on the effect of ink transfer. The process includes chemical etching, electromechanical engraving, laser etching and other methods. Kunz's research results show that although the optical density of the mesh is the same, the ink holes produced by different manufacturing processes have different effects on the ink transfer, and the ink-membrane-engraved ink holes have the best transmission effect. But Shi Pu also found that if only from the print quality point of view, electromechanical engraving and laser etching ink roller is not much difference.
5. Electrostatic process
Helps to improve the transmission of ink in the fine-grained part, which can avoid the phenomenon of dot-fading.
Other factors that affect the characteristics of printing inks and printing materials include:
1. Ink fluid characteristics:
Fluidity has a great influence on the transfer of ink. If the ink is more viscous, there will be a lot of resistance to the flow of the ink during the separation process. Conversely, if the ink is thin, the ink will have a strong fluidity.
2. Temperature
The temperature of the ink cannot be ignored because it affects the viscosity of the ink, which in turn affects the ink transfer performance.
3. Other characteristics of ink
The content of ink in the ink, pigments, additives, etc. will affect the ink transfer performance.
4. Finishing materials
The surface structure of the printing material also has a great influence on the transfer of the ink. In particular, the first step in printing, the contact between the ink and the printed product, and the adhesion and fixation of the ink on the surface of the printed product, have a great influence.
5. Material flexibility
Flexibility can affect the range of ink and substrate contact. The softer the material, the easier it is to contact the ink in the ink roller mesh under the impression roller.
6. Other features:
Tension and humidity on the surface of the material can increase or decrease the ink transfer rate.
The above factors have different effects on the specific value of the ink transfer effect. However, the established model should include all relevant factors in order to better describe the mechanism of ink transfer.
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