(1) Principle of color inspection
The most obvious impression of prints is its color, vividness, and authenticity of reflection. Except for the structure of the pattern and the level of printing, it is almost always expressed by color. Because there are a lot of printing plants, printing a certain type of product every month requires that the color of the ink be the same, otherwise it will lead to inconsistencies in the color of printed materials. Therefore, the inspection of the color and hue of the ink is very important.
There are two main methods for detecting the color of ink: one is the instrument inspection method; the other is the measurement using a reflection densitometer and a colorimeter (also known as a colorimeter, colorimeter). Another common test method is to apply ink to a base material for comparison and judgment. The method of coating on the base material is:
a. Scraper scraping method;
b. Ink roller roller coating and wire rod method;
c. A method of printing with a printability tester.
The conventional test method is a method of parallel observation and comparison by the person's eyes on the standard (quasi-) and test (inspection) samples. This method is relatively simple, but it cannot be represented by numbers. The instrumental method can be used to determine the tristimulus value and use it to calculate the dominant wavelength, purity and brightness in the CIE system or the hue chroma and brightness in the Munsell system. It can also be expressed by calculating the color difference data; Chromatic aberration is a method in which the difference in sensations between two colors is represented in a digital form, and the relationship between them is generally expressed in NBS (English American Standards Agency abbreviation) color difference units.
Here is the general inspection method, that is, scraping comparison method. Because this method is relatively simple and accurate in the production of ink; at the international level, this method is also commonly used.
(2) Tools and Materials
a, small tune ink knife;
b, squeegee;
c, scraping paper (or printed with a black cross, length 11 cm, width 6.5 cm).
(3) Test methods
a, using a small tune ink to take a large sample and a small amount of each sample, respectively, placed on a glass plate, and then mix thoroughly, and then use a small amount of ink to take a small sample of the standard sample on the upper left scraping paper, and then take a small amount of sample coated At the top right, the two should be adjacent and not connected.
b. Use a squeegee knife to force the ink to form a thin layer from the top to the bottom of the sample paper. After scraping it to 3 to 5 centimeters, the squeegee is gradually leveled (that is, the angle formed with the paper becomes smaller). The small pressure causes the ink to coat a thicker layer of ink on the paper. Figure 1
c. Examine the background color of the sample and the standard, the difference between the face color and the ink color.
(4) Precautions
a. Scratching is one of the important basic functions of ink makers and inspectors. Thin and fluid inks are easier to scratch. Thick (thick) inks with high viscosity are less likely to be scratched. Thick, short and rough inks have an untidy shape (which is often the case for engraved gravure inks), making them look ugly.
b. When the blade of the scraper is sharp, the ink layer scraped on the paper is relatively thin. On the contrary, the scraped ink layer is relatively thick.
c. When the thin ink is scraped, the angle of the knife can be smaller to ensure that the scraped ink layer is thicker. When scraping thick sticky inks, the angle of the knife should be made larger so that the ink remaining on the paper is thinner. ,
d. The quality of the paper has a great influence on the scratching. It is generally appropriate to use a paper with a uniform fiber and a smooth surface, or a high-grade forest paper. The color of the paper should be neutral white, no fluorescence, no watermark.
According to the situation in our country, the size of the scraped paper is about 6.5×10.5 cm. It is best to print a black line about 0.4 cm wide upward at the bottom of the paper at 4 cm to better observe the transparency or hiding power of the comparative ink.
Internationally, it is customary for the United States to place the standard on the right and the sample on the left, which is different from ours. Taking into account the convenience and convenience, we can think that our method is more reasonable.
The size of the international scratch paper is mostly about 2.5 x 19 centimeters, which is about 3.5 times larger than ours.
e, testing. Comparing colors includes three aspects: background color, face color, and ink color.
When judging the background color, the scraping paper should be backed to the light source and compared by perspective.
In China, the background color generally refers to the color of the scratched paper that faces away from the light source through observation. Face color refers to the color of the thin layer ink under normal conditions. To check the face color, black and color light can be performed at a light incident angle of 35-45°. Ink refers to the color of a thick layer of ink. All inspections should be performed within 30 minutes of scraping.
Internationally, the background color generally refers to the color of a thin layer of ink printed on paper. The face color refers to the color of the thick layer ink; the face color and the ink color are the word meanings.
f. View. When comparing colors, it should generally be performed under the light of the north to avoid illusions due to the use of different light sources, because the work of comparing colors is more stringent for light requirements.
g. Solvent-based inks can also be compared using this method for scraping. However, they can also be scraped by wire scraping.
h, lithographic ink and letterpress ink focus on the face color and background color; mesh version of the ink, gravure ink focus on the face color and ink.
i. For more accurate inspection of colors, printability tests (for example, IGT printability tester and RI-1 type printability tester) can be used for printing and comparison.
j. Offset printing is mostly multicolor printing, so the ink requires sufficient transparency to achieve color reduction when two or three colors are laminated together. For example, printing a blue plate on a yellow plate requires the display of green, otherwise it will lose the printing effect. To be able to show green, the blue ink must be sufficiently transparent so that the yellow can pass through the blue.
k, the transparency of the ink depends on the difference between the refractive index of the pigment and the binder, the smaller the difference, the more transparent the ink.
l. The ink made with highly disperse pigments has greater transparency and has a more vivid color. The use of high-transparency inks for multi-color overprinting may not be limited by the color sequence. The ink made of chrome yellow, because of its poor transparency, can only be printed as the first color. Therefore, it is important to note that the transparency of the ink is checked for printing overprints.
m, the transparency of the ink can be expressed by the transmittance of a certain thin layer of ink. Now the ink factory uses the scraping method to compare the darkness of the black bars in the paper.
The most obvious impression of prints is its color, vividness, and authenticity of reflection. Except for the structure of the pattern and the level of printing, it is almost always expressed by color. Because there are a lot of printing plants, printing a certain type of product every month requires that the color of the ink be the same, otherwise it will lead to inconsistencies in the color of printed materials. Therefore, the inspection of the color and hue of the ink is very important.
There are two main methods for detecting the color of ink: one is the instrument inspection method; the other is the measurement using a reflection densitometer and a colorimeter (also known as a colorimeter, colorimeter). Another common test method is to apply ink to a base material for comparison and judgment. The method of coating on the base material is:
a. Scraper scraping method;
b. Ink roller roller coating and wire rod method;
c. A method of printing with a printability tester.
The conventional test method is a method of parallel observation and comparison by the person's eyes on the standard (quasi-) and test (inspection) samples. This method is relatively simple, but it cannot be represented by numbers. The instrumental method can be used to determine the tristimulus value and use it to calculate the dominant wavelength, purity and brightness in the CIE system or the hue chroma and brightness in the Munsell system. It can also be expressed by calculating the color difference data; Chromatic aberration is a method in which the difference in sensations between two colors is represented in a digital form, and the relationship between them is generally expressed in NBS (English American Standards Agency abbreviation) color difference units.
Here is the general inspection method, that is, scraping comparison method. Because this method is relatively simple and accurate in the production of ink; at the international level, this method is also commonly used.
(2) Tools and Materials
a, small tune ink knife;
b, squeegee;
c, scraping paper (or printed with a black cross, length 11 cm, width 6.5 cm).
(3) Test methods
a, using a small tune ink to take a large sample and a small amount of each sample, respectively, placed on a glass plate, and then mix thoroughly, and then use a small amount of ink to take a small sample of the standard sample on the upper left scraping paper, and then take a small amount of sample coated At the top right, the two should be adjacent and not connected.
b. Use a squeegee knife to force the ink to form a thin layer from the top to the bottom of the sample paper. After scraping it to 3 to 5 centimeters, the squeegee is gradually leveled (that is, the angle formed with the paper becomes smaller). The small pressure causes the ink to coat a thicker layer of ink on the paper. Figure 1
c. Examine the background color of the sample and the standard, the difference between the face color and the ink color.
(4) Precautions
a. Scratching is one of the important basic functions of ink makers and inspectors. Thin and fluid inks are easier to scratch. Thick (thick) inks with high viscosity are less likely to be scratched. Thick, short and rough inks have an untidy shape (which is often the case for engraved gravure inks), making them look ugly.
b. When the blade of the scraper is sharp, the ink layer scraped on the paper is relatively thin. On the contrary, the scraped ink layer is relatively thick.
c. When the thin ink is scraped, the angle of the knife can be smaller to ensure that the scraped ink layer is thicker. When scraping thick sticky inks, the angle of the knife should be made larger so that the ink remaining on the paper is thinner. ,
d. The quality of the paper has a great influence on the scratching. It is generally appropriate to use a paper with a uniform fiber and a smooth surface, or a high-grade forest paper. The color of the paper should be neutral white, no fluorescence, no watermark.
According to the situation in our country, the size of the scraped paper is about 6.5×10.5 cm. It is best to print a black line about 0.4 cm wide upward at the bottom of the paper at 4 cm to better observe the transparency or hiding power of the comparative ink.
Internationally, it is customary for the United States to place the standard on the right and the sample on the left, which is different from ours. Taking into account the convenience and convenience, we can think that our method is more reasonable.
The size of the international scratch paper is mostly about 2.5 x 19 centimeters, which is about 3.5 times larger than ours.
e, testing. Comparing colors includes three aspects: background color, face color, and ink color.
When judging the background color, the scraping paper should be backed to the light source and compared by perspective.
In China, the background color generally refers to the color of the scratched paper that faces away from the light source through observation. Face color refers to the color of the thin layer ink under normal conditions. To check the face color, black and color light can be performed at a light incident angle of 35-45°. Ink refers to the color of a thick layer of ink. All inspections should be performed within 30 minutes of scraping.
Internationally, the background color generally refers to the color of a thin layer of ink printed on paper. The face color refers to the color of the thick layer ink; the face color and the ink color are the word meanings.
f. View. When comparing colors, it should generally be performed under the light of the north to avoid illusions due to the use of different light sources, because the work of comparing colors is more stringent for light requirements.
g. Solvent-based inks can also be compared using this method for scraping. However, they can also be scraped by wire scraping.
h, lithographic ink and letterpress ink focus on the face color and background color; mesh version of the ink, gravure ink focus on the face color and ink.
i. For more accurate inspection of colors, printability tests (for example, IGT printability tester and RI-1 type printability tester) can be used for printing and comparison.
j. Offset printing is mostly multicolor printing, so the ink requires sufficient transparency to achieve color reduction when two or three colors are laminated together. For example, printing a blue plate on a yellow plate requires the display of green, otherwise it will lose the printing effect. To be able to show green, the blue ink must be sufficiently transparent so that the yellow can pass through the blue.
k, the transparency of the ink depends on the difference between the refractive index of the pigment and the binder, the smaller the difference, the more transparent the ink.
l. The ink made with highly disperse pigments has greater transparency and has a more vivid color. The use of high-transparency inks for multi-color overprinting may not be limited by the color sequence. The ink made of chrome yellow, because of its poor transparency, can only be printed as the first color. Therefore, it is important to note that the transparency of the ink is checked for printing overprints.
m, the transparency of the ink can be expressed by the transmittance of a certain thin layer of ink. Now the ink factory uses the scraping method to compare the darkness of the black bars in the paper.
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