Summary of the hottest green plastic flexible pack

Overview of green plastic flexible packaging technology (Part 1)

entering the new century, the deepening of the world economic adjustment and the transformation of sustainable development strategy are the general background of the world industrial reform, as well as the background of environmental changes in the plastic flexible packaging industry. With the impact of the wave of environmental protection, consumers put forward higher and higher requirements for commodity packaging. Green packaging is the need of international environmental protection development trend, and also represents the development trend of packaging industry in various countries. It is one of the important contents to improve product market competitiveness and avoid new trade barriers. Accordingly, the greening of plastic flexible packaging has also become an important development trend

I. what is green packaging

generally speaking, appropriate packaging that can be recycled, recycled or degraded, and does not cause public hazards to human body and the environment in the whole life cycle of the product is called green packaging. The most important meaning of green packaging is to protect the environment, but also has the significance of resource regeneration. Specifically, it should have the following meanings:

① implement packaging reduction. Green packaging should be the appropriate packaging with the least consumption under the conditions of meeting the functions of protection, convenience and sales, such as cutting off the old man dictionary. To save resources and energy, while minimizing the amount of packaging waste

② it should be easy to reuse or recycle. Through repeated use, or through recycling waste, producing recycled products, burning and utilizing heat energy, composting and improving soil, the purpose of recycling can be achieved

③ waste can be degraded and corrupted. In order not to form permanent waste, non recyclable packaging waste should be able to decompose and decay at a lower conversion rate, so as to improve the soil

④ the material should be non-toxic and harmless to human body and organisms. Packaging materials should not contain toxic elements, halogens, heavy metals, or the content should be controlled below the relevant standards

⑤ in the whole life cycle of packaging products, environmental pollution should not be caused. That is, the whole life process of packaging products from raw material collection, material processing, product manufacturing, product use, waste recycling to final treatment should not cause public hazards to human body and environment

according to the above requirements of green packaging, the plastic flexible packaging industry is undergoing a profound green transformation in terms of processing equipment, technology and material selection

II. Greening of plastic flexible packaging processing process

1 The greening of gravure printing process

gravure printing ink contains a large number of volatile organic solvents, accounting for almost 50% of gravure printing ink. Among them, solvents with low boiling point and high volatility, such as xylene, toluene, ethyl acetate and butanone, contain aromatic hydrocarbons that are toxic and combustible, which are the main factors of environmental pollution. In addition, the gravure printing speed is very high, so it must use highly volatile fast drying ink, and it also needs to rely on electric power or infrared heating for external drying (gravure printing has a drying process) to meet the printing requirements, which leads to a large amount of gravure waste gas emissions, making gravure printing particularly prominent in the environmental protection problems of all printing processes. Many authorities in the printing industry believe that unless practical measures are taken to solve the serious pollution problem of gravure printing and improve the environmental performance of gravure printing, gravure printing will lose its market competitiveness and eventually be replaced by other printing technologies

(1) reduce the impact of organic solvents on the environment

due to the large use of solvents in gravure processing, it is an important reason for solvent pollution in Gravure plastic flexible packaging industry. With the enhancement of people's environmental awareness, the environmental protection of solvents in gravure printing process has received extensive attention. In recent years, we have seen the strengthening of environmental awareness in the flexible packaging industry and relevant departments, which is reflected in the improvement of production processes and related product emissions. The exhaust gas containing solvent discharged by the exhaust emission system in gravure printing machine and compound machine has caused environmental pollution, and the volatilization of solvent in the process of use has also caused indoor pollution and safety problems. Therefore, the whole printing unit can be produced in a fully enclosed manner to reduce the diffusion of solvent in the workshop

adopt ultrasonic gravure roller cleaning system to reduce the use of solvent. By setting the pre cleaning device of the plate roller, the plate roller is automatically cleaned on the machine at the end of printing, which can effectively prevent the ink from drying on the plate roller. This cleaning device can complete most of the cleaning work of the plate cylinder, significantly reduce the workload of manual cleaning, and is also good for improving the operating environment

in the gravure printing discharge system, the solvent is treated by means of solvent recovery and treatment to reduce the discharge of solvent into the air; In order to make the solvent more convenient for recycling, some printing plants began to choose single solvent inks. At the same time, the lower explosion limit control system of volatile solvent concentration is adopted, and the drying energy consumption is saved to the greatest extent through the circulation of some hot gas

in order to reduce the total amount of solvent, developing high concentration and low viscosity inks suitable for light edition is an important research direction. Even solvent-free solid inks may be introduced to the market. Relevant people of Siegwerk ink company believe that the hottech ink technology they are developing has great application potential. This patented hottech ink technology is a solvent-free solid gravure ink, which dissolves immediately before being transferred to the printing plate roller, and is expected to be introduced to the market within a few years

(2) develop and apply benzene free solvent inks and water-based inks to realize solvent-free benzene free and water-based gravure printing

currently used gravure inks are generally made of chlorinated polymers. In the process of ink production, chlorinated polymers need to be dissolved in strong solvents (such as aromatic solvents such as toluene), and toluene is needed to adjust the viscosity of ink in the printing process. Now, chlorinated polymer ink system is considered not suitable for environmental protection requirements. This is because the chlorofluorocarbons it volatilizes in production will destroy the ozone layer. In the process of ink production and printing, the use of aromatic solvents (toluene) will harm the health and safety of workers. In addition, solvent residue in packaging inks is another important issue that needs attention. As toluene is a slow drying solvent, it is very easy to remain in the dry ink film, which will corrupt the food in the greener and environmentally friendly packaging and produce harmful odor

the production of plastic gravure printing ink is being restricted by laws and regulations such as fire protection law, labor safety law and health law. Therefore, it will become an inevitable trend to actively develop and apply green gravure printing ink and water-based ink that meet the requirements of environmental protection

(3) water based gravure printing of film packaging materials

although water-based gravure printing ink has attracted a lot of attention as a substitute system for toluene ink, the oil ink based printing in packaging film has not yet reached the real practical stage

on the whole, the important reason why water-based gravure inks have not been further popularized is that the printing performance and quality still fail to meet the standards of solvent based gravure inks. This is mainly due to the high surface tension of water, which makes the ink difficult to wet. If we want to obtain the printing speed and printing quality of gravure solvent ink, not only the water-based ink itself needs advanced technology, but also the gravure equipment and printing plate roller need to be improved. For example, changing a etched or engraved plate roller with a groove depth of about 38-42 microns to a laser plate making roller with a groove depth of about 24-28 microns also requires more effective and powerful drying equipment and components such as a printing plate roller, an ink pump, and a scraper that must be made of corrosion-resistant materials. These improvements require considerable investment

(4) development and application of intaglio alcohol soluble composite plastic inks

because water-based intaglio inks can not fully replace toluene inks, the ink industry has been trying to develop alcohol soluble inks that can be accepted by the environment. Alcohol soluble inks can effectively solve the health damage caused by toluene inks and the impact of solvent residues on the quality of packaged food. In Europe and the United States, this development has become a trend. In Asia, such as Singapore, South Korea and other countries, toluene inks are being eliminated and will be replaced by alcohol soluble intaglio inks. Alcohol soluble inks have been widely used in the domestic gravure printing industry. It can be predicted that in the near future, alcohol soluble inks will occupy the main share of the ink market for high-end food and drug flexible packaging in China

gravure alcohol soluble composite plastic ink has the characteristics of low odor and no benzene. The use of this kind of environmental friendly ink will improve the competitiveness of gravure printing in the field of packaging and printing$ Page break $

2 Greening of composite processing process

(1) develop and apply composite adhesives with high solid content and low viscosity

domestic adhesive production enterprises have become mature, and their technological development strength has been greatly enhanced. There have been representative enterprises such as Zhejiang New Oriental, Beijing Chemical Research Institute, Beijing GAOMENG, etc. These enterprises have strong R & D capabilities, and their products are developing towards high solid content, low viscosity and functionality

at present, the use of adhesives with high solid content and low viscosity has become an important development direction of dry composite adhesives. In the past, the solid content of the main agent of two-component polyurethane adhesive was 35% or 50%, but now it has been increased to 75% or 80%. The two-component polyurethane adhesive with 75% solid content accounts for 60% of the market share, and the market share of the two-component polyurethane adhesive with 50% solid content is shrinking to less than 30%. Due to the characteristics of high solid content and low viscosity, it is possible to use high working solid content for high-speed composite processing

using high solid content adhesive under the same coating amount can effectively reduce the use of solvent, and has the following advantages:

① reduce solvent consumption

② reduce drying load, improve production efficiency and reduce energy consumption

③ reduce residual solvents

but increasing the solid content (working concentration) also brings some problems:

① due to the sharp change of 1069 drop of 1.93% when the solvent evaporates, it is difficult to uniformly coat the adhesive

② due to the short activation period, it is easy to cause blocking, and it is difficult to ensure a uniform coating amount. It is also easy to cause poor appearance

③ due to the small molecular weight (low viscosity) and cohesion of the adhesive, it is easy to cause processing faults such as tunnel effect. At present, some domestic adhesive manufacturers have produced high solid content and low viscosity products with high initial viscosity through the adjustment of molecular weight and molecular structure

(2) the development and application of water-soluble adhesives

the advantages of water-soluble adhesives are that water replaces organic solvents, there is no potential danger of combustion and explosion, there is no pollution to the environment and toxicity to operators, and the cost is low. However, the coating performance of this adhesive is poor, and its wettability to the composite substrate is poor (because the surface tension of water is 72mn/m, while the surface tension of the substrate is mostly only about 38mn/M), resulting in low adhesion. In addition, the heat capacity of the external water is large, and the drying of the ink will consume more energy, which not only limits the production speed, but also increases the production cost. At the same time, the water vapor also causes certain corrosion to the equipment. These factors limit the wide use of water-based adhesives to a certain extent

(3) develop solvent-free composite process

solvent free adhesive is basically composed of two-component polyurethane adhesive, its main agent and curing agent