Plastic gravure printing inks commonly used in China contain a large amount of organic solvents (about 50%). Solvents such as toluene, ethyl acetate, and methyl ethyl ketone have low boiling points, high volatility, and aromatic hydrocarbons. They are both toxic and flammable. Not only are organic solvent residues easily produced on the packaging, but they are also the main source of environmental pollution caused by gravure printing.
Commonly used in domestic plastic composite (inner printing) gravure inks are generally made of chlorinated polymers. In the ink production process, chlorinated polymers need to be dissolved with a strong solvent (such as aromatic solvents such as toluene), and toluene is used to adjust the viscosity of the ink during the printing process. The chlorofluorocarbon gas volatilized during the production of chlorinated polymer inks will destroy the ozone layer of the atmosphere. The use of aromatic solvents (toluene) during printing can be hazardous to workers' health and safety (fire risk). In addition, ink solvent residues in food flexible packaging products are a problem that needs attention. Benzene is very easy to remain in the dry ink film layer (low-speed printing requires xylene to adjust the drying speed of the printing ink, but the volatilization rate of xylene is slower than toluene, so it is more likely to cause an increase in benzene residue). Residues can contaminate food or supplies in the package. Although alcohol-soluble gravure inks are more “environmentally friendly”, they contain about 1% to 10% of toluene, which will still pollute the environment and leave solvents behind. Although benzene-free and ketone-free plastic gravure printing alcohol ester inks are the best among plastic gravure printing alcohol-soluble inks, but because of the poor leakage resistance and strong adsorption of PE (polyethylene) films , it is very easy to use The packaging PE (polyethylene) film was stained with bad smell of ethyl acetate.
The production of plastic gravure inks in China is being restricted by regulations such as the Fire Protection Law, the Labor Safety Law, the Food Safety Law ... The printing and packaging manufacturing industry is also facing increasing calls for green environmental protection and the increasingly severe multiple attacks from the state on environmental protection policies and food safety laws. Plastic water-based gravure printing ink will become an inevitable trend in the application of plastic flexible packaging gravure printing. Plastic water-based gravure printing inks, as an alternative system for solvent-based inks, have attracted the attention of the color printing and packaging industry , the printing ink production industry, and various sectors of society. The water-based ink of plastic flexible packaging film gravure printing is also a general trend. It is imperative. So how long will it take for the water-based printing of plastic gravure printing inks?
1. There are five main reasons why water-based gravure inks have not been popularized:
1. The binder (resin) for making water-based ink has not been selected in China.
It is completely soluble in water and suitable for use as a binder (resin) for plastic gravure printing inks. At present, domestic ink companies are experimenting with the selection.
2. The color of water-based ink printing has not been recognized in China.
Generally Chinese people like bright and bright colors. The color of water-based inks is not as bright as that of solvent-based inks, so it is difficult to be generally accepted. Its printing performance and quality can not reach the effect of solvent-based gravure printing ink printing.
3. The existing domestic plastic gravure printing machinery needs to be modified or updated to make the plastic gravure printing ink completely water-based.
The solvent in water-based ink, water, is not volatile but evaporates, so it is necessary to retrofit the original gravure printing machine to set up a more powerful and effective ink drying system, otherwise the printing speed will not go up, and the existing gravure printing If the machine uses water-based ink to print on plastic film, the printing speed can only reach 65% ~ 70% of the original printing speed. In addition, if the drying box of the printing machine is enlarged or increased in heating function, the printing film coming out of the drying box needs to be quickly cooled and shaped to prevent stretching due to heating. Installing a cooling device on a printing press is not only laborious and expensive, but there is no place to install it on many original printing presses. Moreover, the printing machine's ink scraper and other equipment components must be replaced with rust-resistant metal to make. These improvements or updates require considerable investment and a long time.
4. Apply water-based gravure printing ink to achieve the same printing speed and printing quality as solvent-based gravure printing ink, and the material and production of the printing plate roller also need to be changed.
For example, the printing plate roll with a screen depth of about 38um to 42um, and a printing plate roll made by etching or electro-engraving, is replaced with a printing plate roll with a screen depth of about 24um to 28um. Such printing plate rollers need to be made by laser engraving and plate making. Laser engraving and plate making has not yet been popularized in China, and there are few, and printing plate rollers also need to be made of rust-resistant materials.
5. Water-based inks are used for plastic film printing, and the printing adaptability of inks needs to be improved.
Due to the large surface tension of water, it is difficult for the ink to expand on the plastic film, which reduces the adhesion of the printing ink on the plastic film. This is also the main reason why water-based gravure printing inks can not completely replace solvent-based inks except for printing on paper.
2. How long will it take for water-based inks for plastic gravure printing in China?
In previous years, Japan, South Korea, and Southeast Asian countries have eliminated toluene-based printing inks, and benzene-based gravure inks have been replaced by alcohol-soluble gravure printing inks. Alcohol-soluble plastic gravure and letterpress printing inks have been promoted and popularized in Japan, Southeast Asian countries, and Eastern European countries. Europe strongly advocates that flexographic printing and gravure printing also require the use of alcohol-soluble inks. The use of benzene-soluble inks is prohibited and the alcohol content of the inks is also limited. The use of solvent-based inks is prohibited in domestic printing, and the development of water-based inks has taken the lead in the world.
Aiming at the residue and pollution of benzene solvents on food plastic flexible packaging and complying with the requirements of environmental protection, in plastic gravure printing, alcohol-soluble gravure printing inks are substituted for benzene-soluble chlorinated polypropylene composite inks. Alcohol-soluble composite plastic gravure printing ink has the characteristics of low odor, little or no benzene, less environmental pollution, and reduced benzene residue. It can help us to solve toluene-based inks, the benzene damage to health and the impact of benzene residue. Quality issues of packaged food. Alcohol-soluble inks have also been gradually applied in the gravure printing industry in China. It is foreseeable that in the near future, the development trend of plastic gravure printing inks for flexible packaging in our country is: benzene-soluble plastic gravure printing inks will be used by alcohol-soluble plastic gravure printing inks. Instead, the alcohol-soluble plastic gravure printing ink is a transition from solvent-based to water-based plastic gravure printing ink.
The common alcohol-soluble plastic gravure printing inks introduced in China in recent years are made of alcohol-soluble polyamide resin. Contains a trace amount of toluene, benzene accounts for 1% to -10% of the total solvent content of the ink, and is suitable for boiled packaging. It is a substitute for benzene-soluble plastic gravure surface printing inks. In order to reduce the residual benzene solvent in printed matter, toluene and xylene are not used as much as possible in the diluent, and its price is slightly higher than that of benzene-soluble plastic gravure surface printing ink.
Alcohol ester inks in plastic gravure printing inks, also known as benzene-free and ketone-free inks, are alcohol-soluble polyurethane resin inks, the best in alcohol-soluble inks, with low odor, benzene and ketone-free characteristics. However, its vividness is slightly inferior and its cost is high. When printed on PP (polypropylene) film, the color film has a slightly weaker fastness. The benzene-free and ketone-free ink still has environmental pollution and solvent residues, and the cost of the solvent is also high. And it is easy to infect the bad smell of ethyl acetate on the PE (polyethylene) film with poor barrier and strong taste absorption.
Therefore, in recent years, alcohol-based plastic gravure printing inks for acrylic resins have been introduced on the market. At present, the color inks of alcohol-based plastic gravure printing have not been recognized by the public, so only white alcohol-based inks have been promoted.
Alcohol-based plastic gravure printing ink, made of modified paint-type acrylic resin, diluted with a single solvent containing 70% to 50% ethanol. Alcohol-based plastic gravure printing white ink can be mixed with common benzene-soluble chlorinated polypropylene composite gravure printing ink. The three primary colors of ordinary composite inks are used to maintain vivid colors. The bottom white ink is replaced with an alcohol-based ink. The two have a good combination, not only the solvent residue is reduced (white ink generally accounts for about 60% in printed matter), the ink thinner is cheap, and the amount of white ink is reduced by 20% ~ 30. %. Alcohol-based plastic gravure white ink with fine and uniform ink color and strong hiding power, which basically eliminates the gray or white dots on the graphics after the composite aluminized film, effectively preventing the adhesion of PET (polyester) plastic film after printing. Printing PET (polyester) plastic film in the above manner can greatly reduce printing costs. The application of alcohol-based plastic gravure inks for several years has shown excellent performance and high economic benefits. At present, it has become increasingly mature in plastic film printing and has entered the stage of promotion and popularization.
3. Concluding remarks The existing gravure printing presses of China's flexible packaging enterprises today are extremely diverse, with values ranging from tens of thousands to ten million yuan. Except for a few imported machines, many domestic gravure printing machines are irrational in design and non-standard in technology, especially drying boxes, squeegee holders, ink circulation systems, etc. Often the same ink is used on different printing presses, but the results of printed products are very different. This not only increases the difficulty of ink development, but also reflects the lack of printing knowledge and application technology of ink manufacturing enterprises, which also puts forward higher requirements for the after-sales service of ink sellers: in different enterprises, different gravure printing presses, Different printing products, even the same enterprise and the same gravure printing machine, but different teams (that is, different operators), need to develop and improve printing inks with different performances, and provide or perform different after-sales application technical services.
In view of the fact that the production and application of plastic flexible packaging in China is still at the stage of perceptual awareness, the gravure printing industry has not yet formed a theoretical system that can draw on inheritance. As a result, the production and application technology of plastic flexible packaging. Personal teaching cannot be uttered. In addition, the operators of printing presses have not been trained in the system, and they are all self-taught in the operation of the equipment. Not only is the operation lacking standardization, but also the lack of understanding of the performance of printing presses and printing inks. Therefore, how long will it take for plastic gravure printing inks to become completely water-based, which requires the active support of the flexible packaging industry and related companies, and the vigorous publicity of major media, and the urgent need for the introduction, supervision and support of relevant government departments' scientific management policies.
Only with the concerted efforts of the whole society will the period of complete water-based plastic gravure printing inks be shortened. It is expected that only a single water is used as the solvent, and surface printing, back printing, compounding, and cooking are combined. All kinds of plastic films are applicable, all climates are suitable, high speed, medium speed, and low speed are suitable. The price is low and the environment is truly environmentally friendly. Plastic gravure printing water-based ink, appeared early in the domestic ink market and has been widely used.