The so-called liquid packaging film is a packaging film whose content is liquid. It has been widely used as a new way of plastic flexible packaging. Common liquid packaging film contents include soy sauce, vinegar, milk, soy milk, pesticides, cosmetics, etc. I will talk about the selection of base materials and inks when printing liquid packaging films from my own practical experience. It is for reference only by peers, and I also ask relevant experts to give axe.
There are two common production processes of liquid packaging film: one is surface printing liquid packaging film, and the other is inside printing liquid packaging film.
1 Surface printing liquid packaging film
1) Selection of substrate
Surface printing liquid packaging film is generally selected from three-layer co-extruded or five-layer co-extruded PE film (black and white film, milky white film, matte film, transparent PE film), mainly used for liquid packaging of milk, soy milk, soy sauce, vinegar, etc. Frozen packaging of frozen meat products. The liquid packaging film needs to undergo uniform corona treatment before printing, and the surface tension of the treated surface reaches 40 to 41 because of the best effect.
In short, when printing liquid packaging films, you must first carefully detect the corona treatment surface of the PE film, so as not to affect the adhesion of the ink because the corona treatment surface fails to meet the requirements.
2) Selection and use of ink
There are two forms of action for the ink to adhere to the film, namely: physical bonding and chemical bonding. The physical combination is the combination of the ink and the film, which is mainly attached to the film through the viscosity of the resin in the ink, and no chemical reaction occurs; the chemical combination is the ink through many active groups (unreacted chemical bonds) and treatment of the ink itself A chemical reaction takes place between the polar groups of the film, forming strong and stable chemical bonds. Obviously, printing liquid packaging film should use ink based on chemical combination.
At present, there are many types of inks on the market. How to buy high-quality inks based on chemical combination is the key to the production of liquid packaging films. The special packaging ink for liquid packaging film produced by Shijiazhuang Hengri Chemical Co., Ltd. used by our factory is HR-2008 (environmental protection type) and HR-40A (non-environmental protection type). These two types of inks mainly use chemical combination methods. This gives the liquid packaging film a variety of excellent properties. After nearly three years of production practice, I think these two inks are very effective, and I recommend them to everyone.
Of course, the quality of the ink is good, and it does not mean that high-quality liquid packaging films can be printed. The key is to learn how to use this type of ink. When using these two types of ink, be sure to clean the ink cartridge first, it is best to wrap the ink cartridge with a film, because they can not be mixed with ordinary polyamide ink or chlorinated polypropylene ink. Therefore, before printing a liquid packaging film, you must carefully study the product manual provided by the ink manufacturer, and flexibly choose the type of ink used according to the characteristics of the content. For example, when printing food-type liquid packaging films, we should choose HR-2008 environmentally friendly ink, and when using such ink, the temperature of the drying tunnel should reach 45 ℃ ~ 65 ℃, in order to promote the curing of the ink. When reducing the viscosity of the ink, use environmentally friendly solvents such as ethyl acetate, isopropyl alcohol, absolute ethanol, n-butanol, etc. According to the printing speed, ambient temperature, humidity, etc., the ratio of solvents is properly adjusted. Generally, the following ratios can be used: ethyl ester accounts for 30% and isopropyl alcohol accounts for 70%.
2 Inside printing liquid packaging film
The production process of the liquid packaging film in India is more complicated than the liquid packaging film printed on the surface. In the production, it is necessary to choose the appropriate printing substrate and laminating substrate according to the characteristics of the content and the filling method. The selection and use of inks and adhesives work hard.
1) Selection of substrates for printing and laminating
Common contents of liquid packaging film in India and India include milk (Inflatable filling with pressure), cosmetics and pesticide packaging. For milk film packaging, BOPP can be used. Polyethylene terephthalate (PET) is used as the printing substrate, and high-strength metallocene polyethylene is used as the laminating substrate. For the three-layer composite liquid packaging film, PET can be used as the surface material, and the middle layer is selected from aluminum foil or PET lead plating film, because of their good barrier properties. Then a layer of metallocene polyethylene with good heat sealability and high strength is compounded as the inner layer of the liquid packaging film. As a surface material, PET has higher mechanical strength, stronger toughness and excellent dimensional stability, so it is often used as a surface material for liquid packaging films. Corona treatment of printed PET substrates requires a surface tension of more than 50 dynes. The PET aluminized film in the middle layer of the composite film should be corona treated on both sides.
In addition, when compounding PET aluminum film, the temperature should be controlled below 50 ℃, never exceed 60 ℃, because the expansion coefficient of aluminum powder is 20 times greater than that of PET. Delamination, so the compound temperature should be controlled below 50 ℃.
2) Selection and use of ink
Select the appropriate ink according to the surface material used in the liquid packaging film. Ordinary chlorinated polypropylene ink can be used for BOPP printing, and PET special ink is generally used for PET printing. Because the price of PET special ink is generally higher, in order to reduce production costs, ordinary chlorinated polypropylene ink can be used, but it must be printed with a small ink area. For printing with large ink area, PET special ink must be used, especially for white ink used for large area white ink printing, PET special ink must be selected. Of course, it is best to use PET special inks when printing PET, because the same type of ink has good affinity when register printing.
Before using PET special ink, you should read the ink manual carefully. Do not mix PET special inks with hydrogenated polypropylene inks. It is recommended to pack the ink cartridges with plastic film before using the inks. This way, you can avoid the mixing of different inks and reduce the amount of ink stored in the ink cartridges. When printing with this type of ink, a mixed solvent of methyl ethyl ketone, toluene, xylene, and isopropyl alcohol must be used, and the ratio should be selected reasonably according to the specific printing conditions. Generally, the content of methyl ethyl ketone is ≥30%. Commonly used solvent ratios are: methyl ethyl ketone 30%, toluene 50%, and isopropyl alcohol 20%. The remaining ink must be sealed and stored separately, and then mixed with the newly prepared ink for the next use.
3) Selection and use of adhesive
The adhesive must be a two-component polyurethane adhesive. Although two-component polyether adhesives have the advantages of fast curing and low price, such adhesives cannot be used in the production of liquid packaging films, and polyurethane adhesives must be used. There are many types of polyurethane adhesives, such as ordinary boiled type, high temperature cooking type and so on. It can be selected according to the content characteristics of the liquid packaging film. When used, the solid content of the adhesive is adjusted down to between 25% and 40%. In order to completely evaporate the solvent on the film coated with adhesive, care must be taken to have sufficient air volume, air speed and temperature. Increasing the temperature of the heat roller can improve the transparency and peel strength of the film. The temperature of the composite roller is usually required to be 40 ° C to 60 ° C. Without damaging the film, the compounding pressure should be increased as much as possible, and the curing reaction starts after compounding. The products are sent to the curing room for 48 hours to 72 hours (the curing temperature is generally 50 ° C to 70 ° C), and then naturally cured at room temperature not lower than 20 ° C for 3 to 5 days to be fully cured.
Note: The pre-composited composite film should be matured as much as possible for at least one day before slitting and bag making. The three-layer composite film should be cut after 2 to 3 days, and the bag making process should be completed after curing.
4) Slitting and bag making
The compound products can be made into T-seal, three-side-seal, H-seal and other bags after aging and shaping, or directly sent to food, medicine, cosmetics and other packaging lines for automatic high-speed continuous packaging.
In short, when producing liquid packaging films, not only must all the links in the production process be flexibly and flexibly controlled according to the characteristics of the content, but also to deal with the small problems that may occur in each link, such as encountered in the printing process Faults such as reverse printing, paste printing, or pinholes or spots encountered in the compounding process. Only when everything is ready can high-quality liquid packaging film be produced.
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