Ink fineness (Fineness) is an important indicator directly related to the rheological properties and economic benefits of ink. Fineness generally refers to the degree to which solid powdery substances such as pigments and fillers mixed in the binder are dispersed. If the ink is too thick, it will cause ruin and paste in printing, and it is not suitable for printing high-end printed products with finer screen lines. Ink with the same pigment content, the finer the finer the finer than the thicker, the higher the coloring power.
At present, the methods for domestic companies to detect the fineness of ink mainly use the scraper fineness method. The following uses offset printing ink as an example.
Take a certain amount of ink and place it on a glass plate, add a certain proportion of No. 6 oil according to the fluidity of the ink, use an ink knife to reconcile evenly, and place the reconciled ink on the depth of the groove on the scraper fineness meter. Then, hold the scraper with the thumb and fingers of both hands, and place it horizontally on the ink deep in the groove of the scraper. Scraper the scraper vertically from the top to the shallowest part of the scraper. Observe the fineness of the ink on the surface of the instrument at an angle of 30 degrees.
In the testing process, due to instrumental errors, human operation errors, and environmental conditions that often cause ink fineness testing, there is a dispute between the production control and the company-level quality value center, between the company-level quality inspection center and the printing plant . So how to measure the fineness? In other words, what are the main factors that affect the results of fineness testing?
1. The influence of scraper fineness meter
The scraper fineness meter can be verified at the Institute of Metrology and Technology (Institute). There are several scraper fineness gauges in the company-level quality inspection center, production central control inspection and printing plant. Due to frequent use, they must be replaced regularly. Generally, only one scraper fineness gauge in the company's quality machine testing center is sent for inspection, and then Then transfer to other scraper fineness gauges.
The scraper fineness meter is composed of a scraper and a scraper.
1. Scraper
Scraper precision:
(1) The flatness of the plane on the scraper is 0.003 mm.
(2) The flatness of the bottom surface of the chute is 0.003 mm.
The squeegee is tested with an optical comparator, but the users of the scrambler do not have an optical comparator, which is generally just a factory inspection. Check the flatness of the chaotic board to take a limited number of points. Take a certain micrometer scale plane as 0 μm and measure the groove depth at this point; then use another micrometer scale plane as 0 μm and measure another groove depth, and so on. There are two points to note:
(1) Is the number of micrometers on the reference plane of any micrometer scale line 0 μm? In short, are both sides of the groove of the squeegee 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 area. There is a simple way to overcome it.
Using the method described above, use a certified scraper to scrape the adjusted ink from top to bottom. If the ink can be scraped off on both sides, the surface can generally be regarded as a flat surface; if the surface near the groove edge is scraped It can be scraped off, and the position that is not far away from the surface of the groove is judged to be medium-high; otherwise, it is concave. If there is a pattern on the surface of both sides of the groove after scraping, it means that the surface of the scraper is not a plane.
(2) Assuming that the surface of the squeegee is flat and the flatness of the bottom surface of the chute is 0.003mm, for ink workers, the acceptable error can only be ≤ ± 1μm. In the ideal scraper, except for the middle groove, the entire scraper surface is a flat surface, and the zero point is aligned, and the error between the groove depth and the marked value at each point does not exceed ± 1μm. Even within the allowable range, the fineness value has errors.
2. Scraper
Scraper accuracy: the straightness of the two edges of the scraper is 0.002mm.
In order to achieve the straightness index of the doctor blade, some manufacturers grind the blade edge into a small plane perpendicular to the blade body. Although the straightness of this kind of knife reaches the index, it can scrape ink only when the knife edge is completely vertical in the test. Other angles are not applicable. In severe cases, it can't scrape the ink on the plane on both sides of the clean slot, that is, the "full house red" scraper. No accurate test results can be obtained with this scraper.
Squeegee scraping should be done by holding the knife vertically, which is only 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 arc, the sharper the blade is, the lower the fineness (thin), and vice versa .
The ink industry has very high requirements for the accuracy of the squeegee, and both the squeegee and the squeegee will cause measurement errors? How to get accurate test results later? We can use the matching method to solve this problem.
Scrapers with a high micron count match those with a small curvature.
Scrapers with a low micron count match those with a large arc.
The matched scraper fineness meter is compared and corrected with the scraper fineness meter verified by the company's quality inspection center in the national metrology verification. If it is not suitable, replace the scraper or scraper until it is suitable.
If equipped with the scraper blade technology, the fineness value of the comparative scraper fineness gauge and the standard chamfered fineness gauge can be basically the same by grinding the scraper. [next]
Second, the impact of the tools and equipment used
1. Ink Adjusting Knife
The flattening blade surface should be smooth. It is best to use calendering and polishing. The rough blade surface will retain ink. In addition, the blade edge should be ground at an angle of 30-40 degrees with the blade plane, and the straightness ≤1μm. The ink is scraped off on the glass plate and can be wiped off every time it is wiped.
2. Wiping supplies
The scraper should be wiped before each use, and wiped during the operation. Generally, a soft cotton yarn is dipped in a little solvent. If the cotton yarn is not clean, leaving dust or lint will affect the test results. There is an industrial paper that is dipped Solvent wiping can avoid this problem.
3. No. 6 oil for dilution
Oil No. 6 is used as the dilution oil for offset printing inks. Currently, it needs to be filtered with filter paper to a fineness ≤7.5μm to remove mechanical impurities. If the No. 6 oil becomes thicker due to slight polymerization, you can also use the heating method to meet the fineness requirements. Imagine if the No. 6 oil itself is coarse, is your ink fineness good? You can prepare a small bottle for use during spare time.
Third, the impact of operating methods
1. Take ink samples
The surface layer of offset printing ink is condensed due to oxidation. When taking ink, the surface dry skin should be removed first, and the ink in four positions should be taken to make it representative. Transfer the taken ink 15 times on the glass plate, one round trip. Take a small part of it, for example 0.3ml each.
2. Dilute with No. 6 oil
Based on the fluidity of the ink, the amount of fueling is determined. It should be noted that the oil should not be added all at once, and the ink should be adjusted as it is added. If it is added all at once, it will form ink sticks, which look like large particles. In addition, when the ink is basically adjusted, the knife should be cleaned and adjusted, especially for red ink and blue ink. , The test result between the shadows.
3. When scraping ink, the scraper should be as vertical as possible. The fineness value obtained by tilting the knife backward is small (fine), and the fineness value obtained by tilting forward is large (thick). When scraping the ink, use both hands with the knife evenly, not on one side.
4. Immediately after scraping the ink, observe the surface of the squeegee at a 30-degree angle to the light source. Determine the concentration point and the number of particles within a scale on the concentration point to determine the fineness value within 30 seconds. Observation must be fast and accurate.
5. For an ink, if the item to be measured is not an item, then measure the fineness first, so as not to pollute the ink when measuring other items. Measure the fineness, scrape the color film and measure the color strength, and then do other projects.
4. Other influencing factors
1. The environment for detecting fineness should be kept free of flying dust, and auxiliary materials such as cotton yarn should be prepared in advance and the solvent filtered. The ambient temperature should not be too low, and it is customary that the detection fineness has nothing to do with 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 the conditions are not met, the brightness of the light source should be appropriate, and use a magnifying glass to assist observation.
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