Ink fineness is an important index directly related to the rheological properties and economic benefits of ink. Fineness generally refers to the degree of dispersion of pigments, fillers and other solid powder materials mixed in binder. If the ink is too thick, it will damage the plate and paste the plate, and it is not suitable for printing high-grade printing products with thin screen. The ink with the same pigment content has higher coloring power with thinner fineness than that with coarse ink. At present, domestic enterprises mainly use scraper fineness meter method to detect ink fineness. The following is an example of offset printing ink. Take a certain amount of ink on the glass plate, add a certain proportion of No. 6 oil according to the ink fluidity, mix it evenly with an ink mixing knife, place the evenly mixed ink in the groove depth of the scraper fineness meter, hold the scraper with the thumb and double fingers of both hands, vertically and horizontally place the scraper on the ink in the groove of the scraper, and scrape the scraper vertically from top to bottom to the top of the scraper Shallow, immediately scraper surface with a 30 degree angle to the light source, observe the ink fineness. In the process of testing, due to instrument error, human operation error, environmental conditions and other factors often lead to ink fineness detection, there are disputes between the production control center and the company level quality value center, between the company level quality inspection center and the printing factory. How to measure the fineness? In other words, what are the main factors affecting the fineness test results? 1、 The influence of the scraper fineness meter can be verified by the Institute of metrology technology. There are several scraper fineness meters in the company level quality inspection center, production control inspection and printing factory. Due to frequent use, they need to be replaced regularly. Generally, only one scraper fineness meter from the company's quality and mechanical testing center is sent for inspection, and then other scraper fineness meters are transmitted. The scraper fineness meter is composed of scraper and scraper. 1. Scraping accuracy of scraper: (1) flatness of upper plane of scraper is 0.003 mm. (2) The flatness of the bottom plane of the chute is 0.003 mm. The scraper is verified by optical comparator, but the users of the disordered board instrument do not have optical comparator, which is generally only factory inspection. The flatness of the plane on the disordered board is checked by a limited number of points. Take a certain micrometer scale line plane as 0 μ m, measure the groove depth at that point; then measure the groove depth of another point with the plane of micrometer scale line at another position as 0 μ m, and so on. Two points need to be noted: (1) whether the number of micrometers in the reference plane of any micrometer scale line is 0 μ m, in short, whether the two sides of the scraper groove are flat? Generally speaking, the producers talk about how to grind out the plane to ensure that the plane error is within how much, which will lead users to misunderstanding. There are simple ways to overcome it. Using the method described above, scrape the adjusted ink from top to bottom with a qualified scraper. If both sides can be scraped without ink hanging, the surface can be generally regarded as flat; if the surface adjacent to the groove edge can be scraped clean after scraping, it will be judged as medium high if the surface far away from the groove surface cannot be scraped; otherwise, it is concave. If there are patterns on both sides of the groove after scraping, it means that the upper surface of the scraper is not a plane. (2) Assuming that the upper surface of the scraper is plane and the flatness of the bottom plane of the chute is 0.003mm, the acceptable error of the flatness of the upper plane of the scraper and the flatness of the bottom plane of the chute can only be ≤± 1 μ m for the ink workers. Except for the middle groove, the whole surface of the scraper is a plane, the zero point is aligned, and the groove depth of each point is within ± 1 μ M. Even within the allowable range, the fineness value has error.2. Scraper accuracy: the straightness of two blade edges of scraper is 0.002mm. In order to achieve the straightness index of the scraper, some manufacturers grind the blade into a small plane perpendicular to the blade. Although the straightness of this kind of knife reaches the target, it can only scrape ink when the blade is completely vertical. Other angles are not applicable. In serious cases, the ink on the plane on both sides of the groove can not be scraped, which is the "full of red" scraper. It is impossible to get accurate test results with this kind of scraper. The scraper should be vertical, which is only visual inspection. There is always a certain error in the specific operation. The ideal blade edge is ground into a 15 degree arc to avoid this kind of error. Generally speaking, the smaller the radian is, the sharper the knife is, the lower the fineness of the scraping is, and vice versa. The accuracy of the scraper is very high in the ink industry, and both the scraper and the scraper will cause measurement error? How to get accurate test results? We can use matching method to solve this problem. The scraper with higher micron number matches the scraper with smaller radian. The scraper with lower micron number matches the scraper with larger radian. After matching, the scraper fineness meter is compared with the scraper fineness meter verified by the National Metrology Verification Institute of the company's quality inspection center. If it is not suitable, replace the scraper or scraper until it is suitable. If the technology of grinding scraper is available, the fineness value of the comparison scraper fineness meter and standard disordered plate fineness meter can be basically the same by grinding the scraper. 2、 The influence of the tools and equipment used 1. The ink adjusting knife plane should be smooth, preferably calendered and polished. The rough surface of the knife will retain ink. In addition, the blade should be ground to an angle of 30-40 degrees with a flatness of less than 1 μ M. only in this way can the ink be wiped off on the glass plate, and it can be wiped off each time. 2. Wipe the scraper before each use, and wipe it during operation. Generally, use a soft cotton yarn dipped in a little solvent. If the cotton yarn is not clean, dust or hair will affect the test results. There is a kind of industrial paper. This paper dipped in solvent can avoid this problem. 3. No.6 oil is used as the diluting oil of offset printing ink. At present, filter paper should be used to filter to the fineness ≤ 7.5 μ m to remove mechanical impurities. If No. 6 oil is thickened only because of a little polymerization, heating method can also be used to meet the fineness requirements. Imagine if No. 6 oil itself is thick, is your ink fineness OK? You can prepare a small bottle in your spare time. 3、 In order to make it representative, the dry skin should be removed first. Will take the ink on the glass plate 15 times, back and forth for a time. Take a small part of it, such as 0.3ml, and use it for each. 2. Dilute with No. 6 oil, and determine the amount of oil to be added according to the fluidity of the ink. It should be noted that do not add the oil all at once, adjust with the addition, and mix the ink evenly. If all the ink is added at one time, the ink block will be formed, which looks like large particles. In addition, when the ink is basically adjusted, the knife should be wiped clean and adjusted again, especially for red ink and blue ink. If there is uneven ink on the knife, it is a large particle, and the detection result will be affected. 3. When scraping ink, the scraper should be vertical as far as possible. The fineness value obtained by tilting the knife backward is smaller (thinner), while the fineness obtained by tilting forward is too large (coarse). When scraping the ink, both hands should be even with knife, without bias on one side. 4. After scraping the ink, the surface of the scraper should be observed at an angle of 30 degrees to the light source. The concentration point and the number of particles within a scale range on the concentration point should be determined within 30 seconds to determine the fineness value. The observation must be fast and accurate. 5. For an ink, if the item to be measured is not one, then measure the fineness first, so as to avoid ink pollution when measuring other items. Measure the fineness, scrape the color sheet and measure the coloring force, and then do other projects. 4、 Other influencing factors: 1. The environment for testing fineness should be kept free of flying dust. The auxiliary materials such as cotton yarn should be prepared in advance and the solvent should be filtered well. The ambient temperature should not be too low. It is improper to say that the detection fineness has nothing to do with temperature and humidity. It is better to test under standard temperature and humidity. 2. The best light source to observe the fineness is the standard light source. If the conditions are not met, the brightness of the light source should be appropriate and the observation should be assisted by a magnifying glass.
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