Influencing factors in the detection of ink fineness

Fineness of the ink is an important indicator directly related to the rheological properties and economic benefits of the ink. Fineness generally refers to the extent to which solid powdered substances such as pigments and fillers mixed in a binder are dispersed. The ink is too thick, which can cause prints to be destroyed or stenciled, and is not suitable for high-grade prints with finer printed wire. Finer inks with finer pigments have higher coloring power than those with finer fineness.

At present, the method for detecting fineness of ink in domestic companies is mainly based on scraper fineness metering. The following uses offset printing ink as an example.

Take a certain amount of ink on the glass plate, add a certain proportion of No. 6 oil according to the size of the ink fluidity, and use the ink-adjusting knife to adjust the uniformity and place the evenly-distributed ink in the depth of the groove on the scraper fineness meter. Place, then use the thumb and heavy finger of both hands to hold the blade, vertically across the ink in the depth of the groove of the scraper, scrape the blade from the top down to the shallowest position of the scraper, immediately scraper The instrument surface is inclined at a 30 degree angle to the light source, and the ink fineness is observed.

In the inspection process, due to instrumental error, human error, and environmental conditions, the same factors often cause ink fineness detection, there is a dispute between the production control company and the company quality center, the company quality inspection center and the printing plant. . How to measure the fineness? In other words, what are the main factors that affect the fineness test results?

First, the impact of scraper fineness meter

The scraper fineness meter can be certified by the Institute of Metrology and Technology (the Institute). The company-level quality inspection center, production control inspection, and printing factory all have several scraper fineness gauges, which are regularly replaced due to frequent use, and generally only a scraper fineness meter at the company's quality testing center is sent for inspection. Then pass on other scraper fineness gauges.

Scraper fineness meter is composed of scraper and scraper.

Scraper

Scratch accuracy:
(1) The plane flatness on the squeegee is 0.003 mm.
(2) The flatness of the bottom plane of the chute is 0.003 mm.

The squeegee was calibrated using an optical comparator. However, the users of the scrabble meter did not have an optical comparator. Usually, they were only tested at the factory. Check the plane flatness on the chaos for a limited number of points. The groove depth is measured at a scale of 0 μm for one micrometer, and the groove depth is measured at that point; the micrometer scale plane at the other position is 0 μm, the groove depth at another point is measured, and so on. There are two things to note:

(1) Whether the micrometer number of the reference plane of any micrometer scale line is 0μm, in short, whether the two sides of the squeegee groove are plane? Producers generally talk about how to grind the plane and ensure that the plane error is within the number of users and bring the user to the wrong zone. There are simple ways to overcome.

Using the method described above, use a calibrated scraper to scrape the adjusted ink from top to bottom. If the two sides can scrape off the ink, generally the surface is considered to be flat; if the scraped surface is adjacent to the edge of the groove Can scrape clean, away from the groove surface position is not judged as medium high; the other hand is concave. If there is a pattern on the surface of both sides of the scraper, the surface on the scraper is not a flat surface.

(2) Assume that the surface of the squeegee is flat, and the flatness of the bottom plane of the chute is 0.003mm. For ink workers, the acceptable error whether the plane flatness on the squeegee or the flatness of the bottom of the chute is acceptable ≤± 1μm. The ideal squeegee instrument except for the middle groove, the surface of the entire squeegee is a plane, the zero point is trimmed, and the error between the groove depth and the marked value of each point does not exceed ±1 μm. Even if the fineness value is within the allowable range, there is an error.

2. Scraper

Squeegee accuracy: scraper two knife mouth straightness 0.002mm.

In order to achieve the blade straightness index, some manufacturers grind the knife edge into facets perpendicular to the blade. Although the flatness of this knife reaches the target, but the detection can only scrape the ink when the knife edge is completely vertical, and other angles are not applicable. In severe cases, the ink on the two sides of the clear groove is not scraped, which is the kind of "full house" scraper. Using this squeegee can not get accurate test results.

Squeegee squeegee should be scraped off vertically. This is only visually vertical. There is always a certain amount of error in the specific operation. The ideal edge of the scraper is ground into a 15 degree arc to avoid this error. In general, the smaller the arc, the finer the sharper knife scraped, and vice versa. .

The ink industry has high requirements on the accuracy of the scraper, and the scraper and scraper can cause measurement errors. How can you come to an accurate test result? We can use the matching method to solve this problem.

o The scraper with a high micron number matches the scraper with a small curvature.

The micron-sized scraper matches the oversized scraper.

The matched scraper fineness meter is calibrated with the company's quality inspection center and verified by the national metrological verification laboratory. If not, replace the scraper or scraper until it is suitable.

If it is equipped with a squeegee technology, it can also use a squeegee to make the comparative screed fineness meter and the standard screed fineness meter have substantially the same fineness value.

Second, the impact of the use of tools and equipment

1. Ink knife

The ink-adjusting knife surface should be smooth, preferably with calendering and polishing, the rough knife surface will retain the ink, and the other knife edge is preferably ground into a 30-40 degree angle with the knife plane, flatness ≤ 1μm, such a knife edge can be The ink on the glass plate is scraped and wiped every time.

2. Wipe supplies

Scraper should be wiped before each use, during the operation to wipe, usually with a soft cotton yarn dipped in a little solvent, if the cotton yarn is not clean, leaving dust or lint will affect the test results, the existing kind of industrial paper, this kind of paper Solvent wipes can avoid this problem.

3. Dilution oil No. 6

No. 6 oil is used as dilution oil for offset printing inks. It is currently necessary to use filter paper to filter fineness ≤7.5μm to remove mechanical impurities. If the No. 6 oil is only thickened due to slight polymerization, it can be heated to achieve the fineness requirements. Imagine if the No. 6 oil itself is thick, then can you judge the ink fineness? You can prepare a vial for use during your spare time.

Third, the impact of operating methods

1. Take the ink on the surface of the offset ink for conjunctiva formation due to oxidation. Remove the dry skin on the surface when taking the ink and take the ink in four positions to make it representative. The ink was taken 15 times on a glass plate, and the round trip was once. Take a small part of it, such as 0.3ml each.
2. Dilute with No. 6 oil to determine the amount of oil based on the fluidity of the ink. It should be noted that the oil should not be added all at once. If you add ink blocks at a time, they will look like large particles. In addition, when the ink is basically adjusted, the knife should be wiped and adjusted again. This is especially important for red ink and blue ink. There are uncoordinated inks on the blade that are large particles. , screening test results.
3. The scraper should be as vertical as possible when scraping ink. When the knife is tilted backward, the fineness is small (thin), and when it is tilted forward, the fineness is larger (thick). When wiping the ink, use both hands to use the knife evenly and do not emphasize one side.
4. After wiping the ink, the surface of the squeegee should be observed obliquely at a 30-degree angle to the light source. Within 30 seconds, the number of particles in a scale range at the focal point and the concentration point should be quickly determined to determine the fineness value. The observation must be fast and accurate.
5. For an ink, if the item to be measured is not an item, first measure the fineness so as not to contaminate the ink when measuring other items. Measure the fineness, scrape the color film and measure the coloring force, and then do other projects.

Fourth, other influencing factors

1. The fineness of the environment to be tested should be kept free of dust, and accessories such as cotton yarn should be prepared in advance and the solvents should be filtered. The ambient temperature should not be too low. It is customary to say that the detection fineness is not related to temperature and humidity. It is best to test under standard conditions of temperature and humidity.

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 a magnifying glass should be used for observation.

Reprinted from: Emperorsoft Technology