C) Performance and Preparation of Common Developers
1. performance
The developer is mainly composed of a developer, a protective agent, an accelerating agent, and an inhibitor. The proportion of various components in the developer is different, which has different effects on the performance of the developer.
In the process of plate making, due to the contrast of various manuscripts, it is not only necessary to select an appropriate photosensitive material, but also a developer with various developing properties is used in conjunction with it. At present, the most commonly used is the M-Q developer combined with metol and hydroquinone, and the P-Q developer combined with pyridone and hydroquinone has also been gradually applied.
In the process of plate making, due to the contrast of various manuscripts, it is not only necessary to select an appropriate photosensitive material, but also a developer with various developing properties is used in conjunction with it. At present, the most commonly used is the M-Q developer combined with metol and hydroquinone, and the P-Q developer combined with pyridone and hydroquinone has also been gradually applied.
According to the different uses in the platemaking, the developer can be divided into hard, neutral, and soft three developer according to the contrast of the obtained image.
(1) Hard developer
The hard developer is used together with the appropriate photosensitive material to obtain a high-contrast, bright tone. It is suitable for direct-screen camera color separation, copying of dot prints, copying and shooting of text and line originals, separation of low-contrast originals, and screening and laser scanning of electronic color separation machines.
Hard developer formulations have the following features:
1 In order to obtain a high contrast and density, in M-Q developer formulated with metol and hydroquinone, and in P-Q developer formulated with pyripone and benzenediol, The proportion of hydroquinone is large. Some high contrast developers use hydroquinone alone.
2 PH value of the developer is relatively high, both are above 9.0. In general, alkaline sodium carbonate or sodium hydroxide is used as a developer accelerator and is used in larger amounts. This speeds up the development, but the image is coarser after development.
3 Potassium bromide, which is used more as an inhibitor, can prevent the development of film haze, and thus can obtain high-contrast images.
(2) soft developer
The soft developer can make the photosensitive material with rich contrast and fine granular low-contrast tone. Applicable to the production of natural color film manuscript before color separation, high contrast original color separation.
The soft developer formulation has the following features:
Both Mituol and Finnicone are rich in layers and soft in tone. They are indispensable in soft developer. In M-Q developer, the amount of metol is more than that in hard developability.
2 The content of sodium sulfite in the formula is more, which is favorable for the development of microparticles, and has rich layers and fine grains.
3 Use weaker promoters such as borax and sodium metaborate. The developer has a low pH, typically between 7.5-9.0. 0 The development speed is relatively slow and easy to obtain fine silver particles.
4 Inhibitor - Potassium bromide is used in small amounts to avoid loss of detail in the image.
Soft developer is characterized by slow development speed, low contrast, delicate image particles, rich layers. The developer is not easily oxidized, thereby increasing the life of the developer.
(3) Neutral developer
Neutral developer properties range between hard and soft liquids. The development is stable, the image density and contrast are moderate, the layers are rich, and the latitude is great. It is suitable for the color separation of the manuscript with moderate contrast, and it is also used with the sexy light material.
2. Preparation of developer
When preparing the developer, generally less than the total amount of water to be formulated, the temperature of the water is raised to about 40° C. to 50° C., the water temperature is too high, the developer and the protective agent are easily oxidized, and the water temperature is too low. The dissolution rate is too slow. Then according to the requirements of the developer formula, they are weighed and dissolved in turn. Under normal circumstances, a part of the protective agent is added to the water first, and after the developer is added, the rest is added. If all the protective agents are added at the beginning, the solubility of the developer will be affected. For example, Mitol is difficult to dissolve in a solution containing a large amount of sodium sulfite.
Accelerators need to be added after the developer and protective agent. If the accelerator is added before the protective agent, the developer is more easily oxidized in the alkaline medium. The order of addition of the inhibitors is not limited, and it is usually added last.
The use of domestic or imported supporting developer must be formulated in strict accordance with the conditions specified in the instructions for use.
The freshly prepared developer needs to be left for a period of time so that the performance of the developer can be stabilized before it can be used. The prepared developer is best kept away from light and sealed so as not to be degraded by air oxidation.
(4) Effect of developing conditions on photographic performance
When the components of the developer are fixed, changes in the developing conditions cause changes in the photographic performance. Therefore, strict control of the development conditions can ensure stable image quality.
1. Development time
During the development process, the gamma and the density of the photosensitive material change with the development time. In general, γ increases with time. When the gamma value reaches a certain value, it will begin to decline over time. As the development time continues to increase, the fog level rises sharply. Therefore, it is necessary to select an appropriate development time during the development process.
FIG. 1 shows the y-t developing power curve, and the developing power curve shows the influence of the developing time on the γ value of the photosensitive material.
Figure 1 γ-t development power curve
2. Development temperature
The development speed is greatly affected by the temperature. As the development temperature increases, the development speed increases accordingly.
The development temperature not only affects the development speed but also causes a change in the photographic performance of the developer. For example, in the M-Q developer, the development activity of metol and hydroquinone, metol, changes little with temperature, and the development activity of hydroquinone varies with temperature. Therefore, when the temperature rises, the activity of hydroquinone increases a lot, and development tends to show photographic properties of hydroquinone. When the development temperature is lowered, the hydroquinone activity is greatly reduced. Also, when the temperature dropped below 13°C, hydroquinone hardly developed, so the developer was biased towards exhibiting the photographic properties of Mytoll.
Although the increase in the development temperature accelerates the development speed, the temperature increase transition causes a change in the development performance and it tends to cause the film emulsion film to excessively swell, resulting in melting. Therefore, in the general case, a room temperature of 18°C ​​to 20°C is selected as the development temperature. This temperature is easy to control, and the development speed is also moderate. This flushing process is called a conventional flushing process.
In the 1970s, foreign photosensitive materials used a new type of hardener, which greatly improved the quality of the film and the melting point of the drug and film. The processing temperature was raised to about 40°C, which greatly shortened the processing time. This process was called Rapid flushing process for high temperature.
3. Developer stirring
The developing solution penetrates into the emulsion layer of the film and undergoes a redox reaction with the exposed silver halide grains. To make the by-products of the reaction diffuse outwards in time, the fresh developer diffuses inwards in time to ensure normal reaction. Therefore, stirring the developer becomes an important measure to control the development.
When the agitating condition of the developer is not good, the development of the picture is not uniform, and a critical effect is also generated. This critical effect is caused by the different degrees of diffusion of the developer and oxidation products, as shown in Figure 2. Film a is a strong exposure, b is a weak exposure, when the film is in a static developer, a rapid development, the new developer constantly split to the a segment, while the developer infiltrated into the b segment also spread to the a segment Therefore, the development of the a-segment portion immediately adjacent to the ab junction is particularly sufficient, where the density is particularly high. The development oxidation product and bromide ion in the a-stage also continuously diffuse at a high b-stage, and thus the development of the b-stage portion immediately adjacent to the ab junction is inhibited, and the density is particularly low. This leads to a density change at the critical point, which is the critical effect produced during the development process, as shown in Figure 3.
Figure 2 Critical Effect Generation
Figure 2 Density diagram of critical effect
Second, fixing
(a) The principle of fixing
After development of the photosensitive material, the exposed silver halide grains form a visible image, and the unexposed emulsified silver is still present in the emulsion layer. These residual silver halides will continue to change after light is seen. Therefore, after development, a fixing process must be performed to remove residual silver halide on the film so that a stable visible image can be obtained.
The fixing method used in the development process is to use a compound as a fixer to dissolve the silver halide from the emulsion layer.
The compound as a fixer must have the following conditions:
1. It can generate stable compounds with one of the ions in silver halide. This compound is easily soluble in water and dissolves rapidly in water from the emulsion layer.
2. Stabilizing compounds formed from one of the ions in the fixer and the silver halide must have only a very low degree of ionization in water, and this degree of ionization is less than the degree of dissociation of the silver halide.
3. This fixer can only dissolve the silver halide, but has no or very little solubilizing effect on the metallic silver.
In order to find the ideal fixer, many compounds have been studied. Finally, silver ions in silver halide have been selected to have a stable complex.
(B) The composition of the fixing solution
The usual fixing solution consists of main components such as fixer, hardener, protective agent and acid.
1. Fixer
A certain compound reacts with the silver halide remaining in the emulsion layer during the development process to form a water-soluble stable complex. Such a human compound is called a fixer.
The commonly used fixative agent is represented by sodium thiosulfate, and sodium thiosulfate (Na2S2O3·5SH2O), commonly known as soda or sea wave, is a colorless and transparent monoclinic crystal and is easily soluble in water. The aqueous solution is weakly alkaline, and sulphur and sulphur dioxide are precipitated in case of strong acid. Sodium thiosulfate should be sealed and dried for storage. After being formulated as an aqueous solution, it should not be placed for too long to avoid the decomposition of sulfur and failure.
In the fixing process, sodium thiosulfate and silver halide form a water-soluble complex, and the reaction can be performed in two steps:
AgBr+Na2S2O3→Na[Ag(S2O3)] (1)
Na[Ag(S2O3)]+Na2S2O3→
Na3[Ag(S2O3)2] (2)
When the first reaction is completed, Na[Ag(S2O3)] is formed, and Na[Ag(S2O3)] is a water-soluble transparent crystal. It stays in the emulsion layer and gradually decomposes into a yellow-brown silver sulfide, so the image of the unfixed fixed image is distorted for a long time.
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1. performance
The developer is mainly composed of a developer, a protective agent, an accelerating agent, and an inhibitor. The proportion of various components in the developer is different, which has different effects on the performance of the developer.
In the process of plate making, due to the contrast of various manuscripts, it is not only necessary to select an appropriate photosensitive material, but also a developer with various developing properties is used in conjunction with it. At present, the most commonly used is the M-Q developer combined with metol and hydroquinone, and the P-Q developer combined with pyridone and hydroquinone has also been gradually applied.
In the process of plate making, due to the contrast of various manuscripts, it is not only necessary to select an appropriate photosensitive material, but also a developer with various developing properties is used in conjunction with it. At present, the most commonly used is the M-Q developer combined with metol and hydroquinone, and the P-Q developer combined with pyridone and hydroquinone has also been gradually applied.
According to the different uses in the platemaking, the developer can be divided into hard, neutral, and soft three developer according to the contrast of the obtained image.
(1) Hard developer
The hard developer is used together with the appropriate photosensitive material to obtain a high-contrast, bright tone. It is suitable for direct-screen camera color separation, copying of dot prints, copying and shooting of text and line originals, separation of low-contrast originals, and screening and laser scanning of electronic color separation machines.
Hard developer formulations have the following features:
1 In order to obtain a high contrast and density, in M-Q developer formulated with metol and hydroquinone, and in P-Q developer formulated with pyripone and benzenediol, The proportion of hydroquinone is large. Some high contrast developers use hydroquinone alone.
2 PH value of the developer is relatively high, both are above 9.0. In general, alkaline sodium carbonate or sodium hydroxide is used as a developer accelerator and is used in larger amounts. This speeds up the development, but the image is coarser after development.
3 Potassium bromide, which is used more as an inhibitor, can prevent the development of film haze, and thus can obtain high-contrast images.
(2) soft developer
The soft developer can make the photosensitive material with rich contrast and fine granular low-contrast tone. Applicable to the production of natural color film manuscript before color separation, high contrast original color separation.
The soft developer formulation has the following features:
Both Mituol and Finnicone are rich in layers and soft in tone. They are indispensable in soft developer. In M-Q developer, the amount of metol is more than that in hard developability.
2 The content of sodium sulfite in the formula is more, which is favorable for the development of microparticles, and has rich layers and fine grains.
3 Use weaker promoters such as borax and sodium metaborate. The developer has a low pH, typically between 7.5-9.0. 0 The development speed is relatively slow and easy to obtain fine silver particles.
4 Inhibitor - Potassium bromide is used in small amounts to avoid loss of detail in the image.
Soft developer is characterized by slow development speed, low contrast, delicate image particles, rich layers. The developer is not easily oxidized, thereby increasing the life of the developer.
(3) Neutral developer
Neutral developer properties range between hard and soft liquids. The development is stable, the image density and contrast are moderate, the layers are rich, and the latitude is great. It is suitable for the color separation of the manuscript with moderate contrast, and it is also used with the sexy light material.
2. Preparation of developer
When preparing the developer, generally less than the total amount of water to be formulated, the temperature of the water is raised to about 40° C. to 50° C., the water temperature is too high, the developer and the protective agent are easily oxidized, and the water temperature is too low. The dissolution rate is too slow. Then according to the requirements of the developer formula, they are weighed and dissolved in turn. Under normal circumstances, a part of the protective agent is added to the water first, and after the developer is added, the rest is added. If all the protective agents are added at the beginning, the solubility of the developer will be affected. For example, Mitol is difficult to dissolve in a solution containing a large amount of sodium sulfite.
Accelerators need to be added after the developer and protective agent. If the accelerator is added before the protective agent, the developer is more easily oxidized in the alkaline medium. The order of addition of the inhibitors is not limited, and it is usually added last.
The use of domestic or imported supporting developer must be formulated in strict accordance with the conditions specified in the instructions for use.
The freshly prepared developer needs to be left for a period of time so that the performance of the developer can be stabilized before it can be used. The prepared developer is best kept away from light and sealed so as not to be degraded by air oxidation.
(4) Effect of developing conditions on photographic performance
When the components of the developer are fixed, changes in the developing conditions cause changes in the photographic performance. Therefore, strict control of the development conditions can ensure stable image quality.
1. Development time
During the development process, the gamma and the density of the photosensitive material change with the development time. In general, γ increases with time. When the gamma value reaches a certain value, it will begin to decline over time. As the development time continues to increase, the fog level rises sharply. Therefore, it is necessary to select an appropriate development time during the development process.
FIG. 1 shows the y-t developing power curve, and the developing power curve shows the influence of the developing time on the γ value of the photosensitive material.
Figure 1 γ-t development power curve
2. Development temperature
The development speed is greatly affected by the temperature. As the development temperature increases, the development speed increases accordingly.
The development temperature not only affects the development speed but also causes a change in the photographic performance of the developer. For example, in the M-Q developer, the development activity of metol and hydroquinone, metol, changes little with temperature, and the development activity of hydroquinone varies with temperature. Therefore, when the temperature rises, the activity of hydroquinone increases a lot, and development tends to show photographic properties of hydroquinone. When the development temperature is lowered, the hydroquinone activity is greatly reduced. Also, when the temperature dropped below 13°C, hydroquinone hardly developed, so the developer was biased towards exhibiting the photographic properties of Mytoll.
Although the increase in the development temperature accelerates the development speed, the temperature increase transition causes a change in the development performance and it tends to cause the film emulsion film to excessively swell, resulting in melting. Therefore, in the general case, a room temperature of 18°C ​​to 20°C is selected as the development temperature. This temperature is easy to control, and the development speed is also moderate. This flushing process is called a conventional flushing process.
In the 1970s, foreign photosensitive materials used a new type of hardener, which greatly improved the quality of the film and the melting point of the drug and film. The processing temperature was raised to about 40°C, which greatly shortened the processing time. This process was called Rapid flushing process for high temperature.
3. Developer stirring
The developing solution penetrates into the emulsion layer of the film and undergoes a redox reaction with the exposed silver halide grains. To make the by-products of the reaction diffuse outwards in time, the fresh developer diffuses inwards in time to ensure normal reaction. Therefore, stirring the developer becomes an important measure to control the development.
When the agitating condition of the developer is not good, the development of the picture is not uniform, and a critical effect is also generated. This critical effect is caused by the different degrees of diffusion of the developer and oxidation products, as shown in Figure 2. Film a is a strong exposure, b is a weak exposure, when the film is in a static developer, a rapid development, the new developer constantly split to the a segment, while the developer infiltrated into the b segment also spread to the a segment Therefore, the development of the a-segment portion immediately adjacent to the ab junction is particularly sufficient, where the density is particularly high. The development oxidation product and bromide ion in the a-stage also continuously diffuse at a high b-stage, and thus the development of the b-stage portion immediately adjacent to the ab junction is inhibited, and the density is particularly low. This leads to a density change at the critical point, which is the critical effect produced during the development process, as shown in Figure 3.
Figure 2 Critical Effect Generation
Figure 2 Density diagram of critical effect
Second, fixing
(a) The principle of fixing
After development of the photosensitive material, the exposed silver halide grains form a visible image, and the unexposed emulsified silver is still present in the emulsion layer. These residual silver halides will continue to change after light is seen. Therefore, after development, a fixing process must be performed to remove residual silver halide on the film so that a stable visible image can be obtained.
The fixing method used in the development process is to use a compound as a fixer to dissolve the silver halide from the emulsion layer.
The compound as a fixer must have the following conditions:
1. It can generate stable compounds with one of the ions in silver halide. This compound is easily soluble in water and dissolves rapidly in water from the emulsion layer.
2. Stabilizing compounds formed from one of the ions in the fixer and the silver halide must have only a very low degree of ionization in water, and this degree of ionization is less than the degree of dissociation of the silver halide.
3. This fixer can only dissolve the silver halide, but has no or very little solubilizing effect on the metallic silver.
In order to find the ideal fixer, many compounds have been studied. Finally, silver ions in silver halide have been selected to have a stable complex.
(B) The composition of the fixing solution
The usual fixing solution consists of main components such as fixer, hardener, protective agent and acid.
1. Fixer
A certain compound reacts with the silver halide remaining in the emulsion layer during the development process to form a water-soluble stable complex. Such a human compound is called a fixer.
The commonly used fixative agent is represented by sodium thiosulfate, and sodium thiosulfate (Na2S2O3·5SH2O), commonly known as soda or sea wave, is a colorless and transparent monoclinic crystal and is easily soluble in water. The aqueous solution is weakly alkaline, and sulphur and sulphur dioxide are precipitated in case of strong acid. Sodium thiosulfate should be sealed and dried for storage. After being formulated as an aqueous solution, it should not be placed for too long to avoid the decomposition of sulfur and failure.
In the fixing process, sodium thiosulfate and silver halide form a water-soluble complex, and the reaction can be performed in two steps:
AgBr+Na2S2O3→Na[Ag(S2O3)] (1)
Na[Ag(S2O3)]+Na2S2O3→
Na3[Ag(S2O3)2] (2)
When the first reaction is completed, Na[Ag(S2O3)] is formed, and Na[Ag(S2O3)] is a water-soluble transparent crystal. It stays in the emulsion layer and gradually decomposes into a yellow-brown silver sulfide, so the image of the unfixed fixed image is distorted for a long time.
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