Development and Prospect of the hottest packaging

2022-07-27
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Development and Prospect of packaging printing ink technology (I)

generally, there are three types of ink. According to the classification of printing plate types, there are flexible relief printing ink, gravure printing ink and 1. Temperature control range: + 30 ℃ ~ - 60 ℃ (room temperature ≤ 25 ℃) hole printing ink and roll coating printing ink. According to the main components of the ink, there are web and paperboard printing ink, alcohol soluble printing ink and water-based printing ink. According to the classification of ink uses, there are paper printing ink, plastic printing ink, etc. With the development of ink technology today, it shows the trend of environmental protection and high-tech. the technical content is getting higher and higher, and the damage to environmental protection is also decreasing

I. environmental friendly ink: realize green printing

1. The harmfulness of ink to the environment

in the printing industry, ink has a great impact on the environment. Moreover, when used in food packaging and printing, the harmful ingredients in ink will directly endanger the health of consumers. Environmental problems related to printing ink mainly include:

(1) harmful ingredients in printing ink

printing ink is composed of pigments, binders, solvents and auxiliary agents. Organic solvents and heavy metals are harmful to human body. There are two kinds of pigments in ink, namely inorganic pigments and organic pigments. It is insoluble in water and other media, and has bright color and stability. Some inorganic pigments contain heavy metal elements such as lead, chromium, cadmium and mercury, which have certain toxicity and can not be used for printing food packaging and children's toys. Some organic pigments contain benzidine, which contains carcinogenic ingredients, and should not be used. Organic solvents can dissolve many natural resins and synthetic resin, and are an important part of various inks. Organic solvents can damage human body and subcutaneous fat. Long term contact with some solvents will make the skin dry and rough; If it penetrates into the skin or blood vessels, it will endanger people's blood cells and hematopoietic function with the blood circulation; Solvent gas is sucked into the trachea, bronchus, lungs or transmitted to other organs through blood vessels and lymphatic vessels, and may even cause chronic poisoning of the body

in the production process of composite packaging materials, a large number of inks, organic solvents and adhesives are used. Although these auxiliary materials are not in direct contact with food, some toxic substances will migrate into food during the process of food packaging and storage, endangering people's health, which must be paid attention to. The toxicity of heavy metal ions in inks and the carcinogenicity of some components in pigments and dyes need to be carefully studied

ethanol, isopropanol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, xylene and other organic solvents are often used in printing inks. Although most of these organic solvents can be removed by drying, the migration of residual solvents to food will cause harm to human body. The solvents in gravure printing ink generally include butanone, xylene, toluene, butanol and other solvents with high boiling point, odor and toxicity. Especially butanone, the residual smell is very strong. Because the pigment particles in the ink are very small and have strong adsorption capacity, although they have been heated and dried during printing, they are often not completely dried due to short time and fast speed. In particular, there are too many residual solvents in the printed matter with large inking area and thick ink layer. These residual solvents are brought to the compounding process, which are difficult to run away after compounding, and will slowly migrate, permeate and recover. Therefore, the residual solvent must be controlled to a minimum

(2) air pollution and odor caused by solvent volatilization in inks

air pollution caused by solvent volatilization in inks is the most serious, because gravure inks use relatively high volatile organic compounds (UOC) as solvents. Long term exposure to high concentrations of UOC will cause great damage to the human body, especially the nervous system; UOC will also have photochemical reaction with the nitrogen oxidation Lake in the air, producing ozone and smoke, thus causing air pollution. In order to reduce UOC, there are two solutions: recycling and burning solvent emissions, but there are many gravure printing machines without such devices

in addition, the discharge of water for cleaning water-based ink will cause water pollution, and the discharge of offset printing fountain solution will also cause water pollution. The disposal of printing materials, ink containers and other industrial wastes is also a very difficult problem

2. Development of environmental friendly inks

in order to fundamentally improve the impact of inks on the environment, we should change the composition of inks, that is, try to use environmentally friendly materials to prepare new environmentally friendly inks. Researchers in various countries are stepping up their research and development in this regard. At present, this kind of ink mainly has three categories, namely, water-based ink, UV ink and water-based UV ink

(1) water based inks

water based inks are characterized by no pollution to the environment, no impact on human health, not easy to burn, good safety, stable inkability, bright colors, no corrosion to plates, simple operation, low price, good post press adhesion, strong water resistance, rapid drying, printing speed up to 150-200m/min, especially suitable for food, medicine Printing and use of cosmetics and other packaging and decoration printing products with strict requirements on sanitary conditions

the biggest difference between water-based ink and solvent based ink is that the solvent used in water-based ink is water rather than organic solvent. Because solvent based inks are mostly volatile and dry, the lower the boiling point of the solvent, the more volatile it is. When volatile, toxic gas is released, polluting the surrounding environment and harmful to workers. After printing, there are also residual harmful substances on the surface, which is not suitable for printing food packaging, drug packaging, children's toys and other packaging. According to relevant information, at present, 40% of plastic film printing in the United States uses water-based ink, and other economically developed countries, such as Japan, Germany and France, use more and more water-based ink in plastic film printing. In june2001, the UK legislated to prohibit solvent based inks from printing food films

according to the information, the United States has a regulation on organic solvents that can cause photochemical smog: the total amount of UOC (organic volatile matter) emissions is limited, and the water-based inks that meet UOC regulations must meet the following two standards: ① in the composition of inks in use, the proportion of volatile components is less than 25% and the water content is more than 75%; ② Less water in the use of ink, non selective ingredients in more than 60%. In recent years, China has also made some provisions on food packaging, and the status of "green" printing materials will be further improved. When using water-based inks, the same emphasis should be placed on waste water treatment. The waste water from roller washing, tank washing and bucket washing should be concentrated in a waste water treatment tank and added with acidic substances for sedimentation

a Sino foreign joint venture food production enterprise in Tianjin used the OPP/CPP composite film packaging food produced by a company in Shantou. After opening the line, it smelled a strong odor. After testing by the national packaging product quality supervision Yuling center, the xylene residue alone reached 18.03mg/m2, and the total solvent residue reached 21.4mg/m2, seriously exceeding the standard. Although the food production enterprise later received economic compensation, its credit losses could not be completely recovered. This is caused by the fact that the food production enterprise did not strictly control the quality of packaging materials before using packaging materials. Each food packaging factory should learn a lesson from it. The thorough solution is to use water-based ink for printing, and use hot-melt adhesive pre Cong film. There is no solvent, and no odor and migration will occur

water based inks are usually used for printing paper products, including paper plastic composite products. Its characteristic is that it can meet the ink absorption of paper printing, making the four brushes full of color. What is more difficult is that its solvent is water and ethanol, which has little pollution to the environment, so it is known as an environmental friendly green ink

(2) UV ink

UV ink has bright colors and high image definition. UV flexo printing is a promising process, whether from the perspective of environmental protection or technological development. UV ink is a kind of UV curable ink that can change from liquid to solid under certain wavelength of UV irradiation. UV ink has the advantages of no solvent, environmental protection, fast drying, low energy consumption, good gloss, bright color, water resistance, wear resistance, oil resistance, solvent resistance, etc

the main ingredients of UV curing ink include photopolymerizable prepolymer, photosensitive monomer, photopolymerization initiator, organic pigment and additives. The photoinitiator in the ink is a compound that is easily excited by light. After absorbing photons, it is excited into free radicals and the energy is transferred to the photosensitive photons or photo crosslinking agent, so that the UV ink undergoes a UV curing reaction

uv ink can only be dried by the worm gear reducer under UV light irradiation (many products now combine deceleration with electromechanical). Even if it is responsible for the amplifier range change, data collection, data transmission, experimental mode selection and long-term storage of the liquid crystal display in the ink bucket, the performance can remain stable, the drying speed is fast (up to 500m/min) and complete, and there is no solvent discharge, There is no need to take powder spraying measures to prevent contamination between prints. The printing machine and workshop environment are clean and free of dust pollution. The printed paper can be recycled. When using UV ink, ozone generated by ultraviolet light should be removed, and attention should be paid to protecting human eyes from ultraviolet light

(3) water based UV ink

water based UV ink is a new research direction in the field of UV ink. The viscosity of prepolymer in ordinary UV ink is usually very high, so it needs to be diluted with active diluent. At present, the active diluent acrylates have different degrees of skin irritation and toxicity. Therefore, while developing low viscosity prepolymers and low toxicity active diluents, on the other hand, we should develop water-based UV inks

using ethanol as solvent will have good compatibility and excellent adhesion to alcohol soluble inks. Ethyl acetate has an erosive effect on some printing inks, which will cause ink blooming. This problem often occurs in surface printing inks

in the process of developing environmental friendly ink, the improvement of solvent ink should be strengthened to improve the safety. The safety of solvents is mainly reflected by the toxicity and flammability of solvents. Special attention should be paid to: (1) ethers can generate explosive peroxides; (2) Non flammable solvent or carbon tetrachloride can react explosively with sodium, potassium, calcium, magnesium, barium and other metals in contact; (3) Trichloroethylene will contact with sodium hydroxide and potassium hydroxide to generate dichloroacetylene, which is easy to explode due to self oxidation

advanced countries have proposed not to use benzene solvents. China has stipulated in the international gb9685-94 hygienic standard for the use of additives for food containers and packaging materials that the solvents used in coatings, adhesives and inks include ethanol and butanol, but due to various factors, acetone and ethyl acetate. GB/t10004-1998 cooking resistant composite films and bags specifies that the total amount of solvent residue is 10mg/m2, and benzene solvent is 3.0mg/m2

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