Solutions to problems in the use of water-based co

2022-07-01
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At present, there are more and more water-based composite adhesives (referred to as water-based adhesives) in the market, and more and more manufacturers use water-based adhesives. However, when using water-based adhesives to composite products for the first time, there are some problems that need to be paid attention to. Otherwise, there may be a lot of trouble and unnecessary losses. The author has made some application experiments on the yh620s water-based adhesive produced by Beijing GAOMENG Chemical Co., Ltd. in the factory, and compared it with several existing products in the market. It is found that the weight has decreased from 15kg to 6kg. Some experiments have been made to find better solutions to these problems, which are summarized as the following aspects

I. how to select the top roller (line roller)? How much glue is suitable

the amount of water-based glue is small, so it is important to select the appropriate glue roller. For the water-based adhesive, the pit on the rubber roll should be shallow and the opening should be large, so that the adhesive can contact the substrate with the largest surface area. In this way, the coating is uniform, the drying speed is fast, the composite appearance is good, and the peel strength is high. Proper line roller is the premise to ensure the glue amount and peel strength. Users should adjust it according to equipment conditions and compounding speed. It is recommended to use 180 line/inch ~ 200 line/inch electric engraving roller, the pit is connected, and the pit depth is 32 μ~ thirty-five μ。 During the use process, the upper rubber roller shall be cleaned frequently to prevent blockage, and after a period of use, it shall be re chrome plated or engraved with a new line roller

the appropriate glue amount is 1.6g/m2 ~ 2.4g/m2, which should not be less than 1.6g/m2, otherwise the peel strength cannot be guaranteed. Too much glue will affect the drying of glue and the leveling of glue on the surface of plastic film, thus affecting the composite appearance and peel strength

II. How to solve the problem of too many bubbles during high-speed recombination? Can defoaming agent be added

in order to catch up with the production schedule and reduce the cost, some manufacturers have very fast compound machines, some of which reach more than 160m/min. For this compounding speed, the water-based adhesive is easy to produce more foam in the glue tank. If the production continues for several days, the foam will accumulate more and more, and even overflow out of the glue tank. At this time, if certain measures are not taken, problems such as small glue amount, low strength and white spots on the appearance may occur. The best solution is to put a uniform ink stick in the glue tank to play the role of defoaming. At the same time, the method of cyclic gluing is adopted to ensure that there is not too little glue in the glue tank. A spare rubber drum shall be used for recycling. In this way, if the foam in the rubber drum cannot be removed during long-term operation, the spare rubber drum can be used to apply glue, and it can be replaced after the foam in the original rubber drum is removed

yh620s product already contains defoamer, so it is generally unnecessary to add additional defoamer. Too much defoamer will affect the surface properties of the glue solution, thus affecting the composite appearance. The added defoamer can not be evenly mixed with the glue, which will also affect the composite appearance

III. can the water-based adhesive be diluted with water

at present, most water-based adhesives in the market are of lotion type. The principle is that high molecular polymers depend on emulsifiers to stabilize in water. In fact, it is a metastable state. Many external forces will lead to demulsification and delamination of the adhesive liquid and lose its function. The author does not recommend diluting the glue with water, because diluting with water will increase the surface tension of the glue, destroy the stability of the glue, and cause delamination. In addition, dilution will change the surface properties of the product, resulting in poor wettability and affecting the composite appearance

IV. when water-based adhesive is used for compounding, there are some white spots on the appearance, which disappear after ripening. What is the reason? How can this be avoided

generally, the water-based adhesive contains more than 50% of water, and it needs sufficient temperature and wind speed to completely volatilize in a short time. There are two reasons for white spots on the appearance of composite products: insufficient glue application and incomplete drying. The white spots that can disappear after a short period of ripening indicate that the drying is not complete, because ripening can further help the water volatilization; Otherwise, it means that the glue amount is insufficient

to avoid incomplete drying until the working surface of the board is cleaned through visual inspection, it is necessary to adjust the drying channel temperature and wind speed

the oven temperature can be set as 70 ℃ ~ 80 ℃ 90 ℃, but the author found that the actual temperature of many composite equipment is much lower than the set temperature, so it must be corrected if possible to avoid too large error. The wind speed is particularly important for the drying of water-based adhesive. It must be ensured that the wind speed reaches more than 6m/s, and the air outlet and air inlet of the equipment shall be cleaned frequently to prevent blockage. In addition, the temperature of the composite roll will also affect the composite appearance and the initial adhesion. It is necessary to ensure that the actual temperature of the composite roll reaches more than 50 ℃

v. whether the water-based adhesive composite membrane needs to be matured? Will the peel strength be improved after a period of ripening after getting off the machine? Will high temperature aging for a long time have any effect

generally speaking, the membrane compounded with yh620s does not need to be matured, and can be cut off when off the machine. Proper aging for a period of time can improve the peel strength. Because the molecular weight of the water-based adhesive is very high, it needs a certain period of time to level to achieve better strength. Therefore, it is better to put the composite membrane in 50 ℃ curing room for 1H ~ 4H when conditions permit. Aging at higher temperature (above 80 ℃) for a long time has a certain impact on the strength of the composite membrane, because the water-based adhesive polymer can not withstand high temperature for a long time

VI. will the water-based adhesive affect the adhesion of the ink on the film? Why is there a great difference in the appearance of films printed with different inks

the water-based adhesive has good adaptability to water-based ink and solvent based ink. The ink transfer is generally related to the quality of the ink. If the affinity between the ink and the film is poor, the adhesive may pull the ink from the film. This problem does not exist when using high-quality ink

the ink contains different waxes, smoothing agents, defoamers, plasticizers, etc. these components will have an adverse impact on the glue, and then affect the composite appearance. Therefore, after replacing the ink, the glue should be tested to avoid loss

reprinted from: printing industry

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