The key to driving ink fineness detection
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Fineness is an important indicator directly related to the rheological properties and economic benefits of the ink. The fineness generally means the degree to which the solid powdery substance such as a pigment or a filler mixed in the binder is dispersed. If the ink is too thick, it will cause ruining and paste printing in printing, and it is not suitable for printing high-grade printed matter with fine mesh. The ink of the same pigment content has higher fineness than those with finer fineness.
At present, the method for detecting the fineness of ink in domestic enterprises mainly uses the scraper fineness method. The following is an example of an offset ink.
A certain amount of ink is placed on the glass plate, a certain proportion of the No. 6 oil is added according to the fluidity of the ink, and the ink is evenly adjusted by the ink adjusting knife, and the uniformly-adjusted ink is placed on the groove depth of the scraper fineness meter. Then, hold the scraper with the thumb and fingers of both hands, vertically across the ink deep in the groove of the scraper, and scrape the scraper from top to bottom vertically to the shallowest part of the scraper, and immediately scrape the scraper. The surface of the instrument was tilted at a 30 degree angle to observe the ink fineness.
During the inspection process, due to instrument error, human error, and environmental conditions, the ink fineness is often detected. There is a dispute between the production control and the company-level quality center, between the company-level quality inspection center and the printing factory. . So how do you measure the fineness? In other words, what are the main factors affecting the results of the fineness test?
First, the impact of the scraper fineness meter
The scraper fineness meter can be verified by the Institute of Metrology and Technology. The company-level quality testing center, production control and printing factory have several scraper fineness meters. Due to frequent use, they need to be replaced regularly. Generally, only a scraper fineness meter of the company's quality machine testing center is sent for inspection. Transfer to other scraper fineness meters.
The scraper fineness meter is composed of two parts, a scraper and a scraper.
1. Scraper
Sharpness accuracy:
(1) The plane flatness of the squeegee is 0.003 mm.
(2) The plane flatness of the bottom of the inclined groove is 0.003 mm.
The squeegee is calibrated using an optical comparator, but the user of the slab is not equipped with an optical comparator, which is generally only factory inspection. Check the plane flatness of the chaotic board to take a finite number of points. Flat on a micron scale
The surface is 0 μm, and the groove depth is measured; in another position, the micro-scale line plane is 0 μm, the other groove depth is measured, and so on. There are two points to note:
(1) Whether the micrometer number of the reference plane of any micron scale line is 0 μm, in short, is the plane on both sides of the scraper groove flat? Producers generally talk about how to grind out the plane, to ensure that the plane error is within, and bring the user to the wrong zone. There are simple ways to overcome it.
Using the method described above, use the calibrated scraper to scrape the adjusted ink from top to bottom. If both sides can be scraped without hanging ink, the surface can be generally considered flat; if the surface is adjacent to the groove after scraping It can be scraped, and the position farther away from the groove surface is determined to be medium-high; otherwise, it is concave. If there are patterns on both sides of the groove after the scraping, the surface of the scraper is not a flat surface.
(2) Assuming that the surface of the squeegee is flat, the flatness of the bottom plane of the slant groove is 0.003 mm. For the ink worker, the acceptable error of the plane flatness of the squeegee or the flatness of the bottom plane of the slant groove can only be ≤±
1 μm. In addition to the middle slot, the ideal squeegee has a flat surface, the zero point is aligned, and the error between each groove depth and the marked value does not exceed ±1 μm. even if
There is also an error in the fineness value within the allowable range.
2. Scraper
Scraper accuracy: the straightness of the blade is 0.002mm.
To achieve the flatness of the blade, some manufacturers grind the edge into a facet perpendicular to the blade. Although the flatness of the knife reaches the index, it can only scrape the ink when the knife edge is completely vertical. The other angles are not applicable. In severe cases, the ink on the planes on both sides of the groove is not scraped, which is the kind of "full house" scraper. Accurate test results cannot be obtained with this scraper.
The scraper should be scraped with a vertical grip, which is only visually vertical. There is always a certain error in the specific operation. The ideal blade edge is ground into a 15 degree arc to avoid this error. Generally speaking, the smaller the curvature, the lower the fineness of the knife and the lower the fineness (fine), and vice versa. .
The ink industry requires a high degree of accuracy for the scraper, and both the scraper and the scraper cause measurement errors. How can I get accurate results after the test? We can use the matching method to solve this problem.
The squeegee with a higher micron number matches the squeegee with a smaller curvature.
A low-micron squeegee matches a slightly curved squeegee.
The matched scraper fineness meter is compared with the scraping fineness meter verified by the company's quality inspection center in the national metrological verification, if it is not suitable to replace the scraper or scraper until it is suitable.
If the squeegee technology is available, the contrast squeegee fineness meter can be basically the same as the standard slab fineness meter by the squeegee.
Second, the impact of the tools and equipment used
1. Ink knives
The plane of the ink knives should be smooth, preferably calendered and polished. The surface of the rough knives will retain ink. In addition, the knives are preferably ground at an angle of 30 to 40 degrees with the plane of the knives, and the straightness is ≤ 1 μm. Scrape the ink on the glass plate and wipe it off each time it is rubbed.
2. Wipe supplies
The scraper should be wiped before use. It should be wiped during operation. Generally, soft cotton yarn is used to remove a little solvent. If the cotton yarn is not clean, leaving dust or lint will affect the test results. There is an industrial paper. Solvent wiping can avoid this problem.
3. Diluted with No. 6 oil
No. 6 oil is used as a dilution oil for offset printing ink. It is currently filtered with filter paper to a fineness of ≤7.5 μm.
Remove mechanical impurities. If the No. 6 oil is thickened only by a slight polymerization, the heating method can also be used to achieve the fineness requirement. Imagine if the No. 6 oil itself is thick, then is your ink fineness judged? You can prepare a small bottle for spare time in your spare time.
Third, the impact of the operation mode
1. Take the ink sample
The surface of the offset ink is bound by oxidation. When the ink is taken, the surface dry skin should be removed first, and the ink at four positions is taken to make it representative. The ink taken was transferred 15 times on a glass plate, and the round trip was once. Take a small portion of it, for example 0.3ml each.
2. Dilute with No. 6 oil
The amount of fuel is determined based on the fluidity of the ink. It should be noted that do not add the oil all at once, and add the ink to make it even. If you add all the ink at a time, it will look like a large particle. In addition, when the ink is basically adjusted, the knife should be wiped and adjusted. Especially for red ink and blue ink, there is an unsmooth ink on the knife. , shadow detection results.
3. The scraper should be as vertical as possible when scraping the ink. The value of the fineness obtained by tilting the knife backward is small (thin), and the fineness obtained by tilting forward is too large (thick). When wiping the ink, use both hands with a knife to make it even, not to focus on one side.
4. Immediately after scraping the ink, the surface of the scraper should be 30.
Observing the light source obliquely, the number of particles in a scale range on the concentration point and the concentration point is quickly determined within 30 seconds to determine the fineness value, and the observation must be fast and accurate.
5. For an ink, if the item to be measured is not one, first measure the fineness to avoid contamination of the ink when other items are measured. Measure the fineness, scratch the color film and measure the tinting strength, and then do other items.
Fourth, other influencing factors
1. The environment for detecting fineness should be kept free of flying dust, and the auxiliary materials such as cotton yarn should be prepared in advance and the solvent filtered. The ambient temperature should not be too low. It is customary to say that the detection of fineness is not related to temperature and humidity. It is best to test under standard temperature and humidity conditions.
2. The light source for observing the fineness is preferably a standard light source. If there is no condition, the brightness of the light source should be suitable and assisted by a magnifying glass.