Preliminary study on the hottest water-based film

Preliminary study on water-based film coating process

in the 1980s, paper film coating processing technology rose in China's printing industry, and the main production process is the traditional oil-based film coating. The production process is as follows: the plastic film is coated with adhesive, pressurized by the rubber drum and the heating drum through the drying channel, and then bonded with the paper to form a paper plastic product. The water-based film covering is a new film covering process that came out in 1996. Because this process uses water-based environmental friendly glue, does not need heating and drying devices, and has high speed, energy saving and high gloss, it is welcomed by many manufacturers. However, due to the short time of the advent of water-based film coating and the lack of relevant data, many manufacturers have encountered many problems in actual production that cannot be solved. The technological process of water-based film coating is: paper feeding in the paper feeding Department → paper feeding in the paper feeding table → film coating adhesive → printing film pressing → winding → drying → slitting. This article will start from the basic technology to describe the water-based coating, in order to play a role of attracting jade

plastic film

the plastic film used for water-based coating is basically the same as the traditional oil-based coating, mainly polypropylene film, but also PVC film, polyethylene film, polyester film, etc. The film thickness is generally 0.01 ~ 0.02mm, which requires high transparency, light transmittance of more than 90%, light resistance, chemical corrosion resistance, stable geometric dimensions, certain mechanical strength, etc

due to their different processes and adhesives, water-based and oil-based coatings have different emphasis on the quality requirements of plastic films:

1 The water-based coating has lower requirements for corona treatment of films, and the storage time after coating is longer, while the oil-based coating has higher requirements for corona treatment of films

2. The water-based coating has high requirements for the rewinding quality and surface flatness of the film. Because the initial viscosity of the water-based adhesive is poor, and the tension and pressure on the film are very small, the wrinkles and rewinding tightness on the film are different, which will affect the water-based coating; The oil-based film covering will make up for the defects of the above film quality due to the good initial viscosity of the adhesive and the tensile and hot pressing of a certain force

adhesive

water based film covering adhesive is also called water-based adhesive, and its main raw material ratio is about: vinyl acetate ethylene polymerization lotion (VAE) 80%, rosin 5%, emulsifier 4%, water 8%

the production process of water-based adhesive is relatively simple, but the processing process is strict. The production steps are as follows: first put rosin into a stainless steel reactor to melt, then add emulsifier and water, and control the melting temperature at 80 ℃. Through the observation of the mirror, when it is in the molten state, add VAE lotion and stir for 1 hour. Then through colloid grinding and 200 mesh filtration, it can be loaded into barrels and sent out of the warehouse

the quality standard of water-based adhesive is: the storage period of the adhesive liquid shall not exceed 1 year, and the adhesive liquid shall not be layered, and the viscosity of the adhesive liquid shall not be less than 200 seconds (apply 4 cups, 20 ℃)

water-based film covering equipment

water-based film covering machine includes: paper feeding part, paper conveying positioning part, gluing part, pressing part, winding part, slitting part, etc

the water-based film coating does not need to be heated and dried, and it is rolled directly, so the machine speed is faster. The maximum speed can reach 80 meters/minute (about 7000 pieces/hour), which is comparable to the speed of ordinary offset presses

the paper feeding part and the paper conveying and positioning part are the same as the general paper offset press, and the gluing part and pressing part are similar to the oily laminating machine. The difference is that the water-based laminating machine has no heating and drying channel, so the distance between the gluing part and the pressing part is relatively close, and the gluing part is relatively simple. The pressing part is at room temperature, and there is no pressure roller, so the pressure is also small. The winding part is the same as that of the general manual oil laminating machine

factors affecting the quality of water-based film coating

the quality of water-based film coating is not only related to the development pattern of domestic new materials of raw materials, but also affected by the following factors:

1 The influence of the ink layer condition of printed matter

the ink layer condition of printed matter mainly refers to the size of the image and text area on the paper, the thickness of the ink layer and the performance of the ink. Their influence on the lamination is mainly manifested in the influence on the adhesion strength between the printed matter and the film. When the printed matter is large, the ink layer is thick and the image and text area is large, the ink changes the surface characteristics of the paper with many gaps, hinders the penetration and diffusion of the adhesive, and makes the printed matter difficult to bond with the plastic, prone to delamination, difficult to dry and other quality problems

2. The influence of diluent

if white ink is used as diluent in ink, there are obvious powdery particles in white ink, which make it not tightly combined with the binder, which will hinder the adhesion and cause weak adhesion

3. The influence of water-based adhesive

water-based adhesive has a certain "powder eating" ability to spray powder on printed matter, which can improve the gloss of the film. However, if too much powder is sprayed, snowflake like white spots will appear. This situation can be improved by increasing the amount of glue

in addition, if gold and silver inks are used for printing, if the amount of glue is too large, water will soak the gold and silver inks, causing the gold and silver inks to be blackened

4. Influence of ink drying

incomplete drying of ink will also cause foaming and delamination of products after coating

5. The influence of ordinary water-based laminating machine

because the ordinary water-based laminating machine does not have a drying channel, and the glue liquid is mainly dried by osmosis, it is not suitable for laminating gold, silver paperboard and hot stamping products. The special water-based laminating machine is equipped with a drying channel, which is similar to the oil-based laminating machine. It can film gold and silver cardboard, but the speed is low

6. The influence of paper

the first is the influence of paper deformation. Due to the poor initial viscosity of water-based adhesive, the viscosity is very small when it is not dry at the beginning. If the paper is seriously deformed, the paper will be separated from the film at the concave and convex places due to the deformation of the paper after coating, resulting in bubbles after drying

the second is the influence of paper thickness and stiffness. When the paper is thick or has high stiffness, the water-based film trailer has a slightly longer film, which will affect the finishing of the subsequent process

Author: Cui Xiaoming et al.

reprinted from: printing is more accurate and reliable in measuring Brinell hardness brush technology

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