Discussion on Key Technologies of CI Flexo+Solventless Composite (Liyin Composite)
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At present, in the context of energy conservation and environmental protection, as people's awareness of environmental protection continues to increase, people's focus on goods is also changing, especially the requirements for commodity packaging materials no longer only focus on the protection of content, and It is more focused on the protection of the environment and people's health. To this end, the packaging and printing industry is stepping up the development and application of green printing materials and processes.
Composite flexible packaging as a common form of packaging, the main production method is gravure and dry composite combination process, but in order to meet the green development trend, wide-format satellite flexo and solvent-free composite combination process came into being, it has low carbon The characteristics of emission reduction, economy, and green are the future development directions of the composite flexible packaging production process. This paper mainly discusses the research and application of key technologies related to wide-format satellite flexo printing and solventless composite (lithographic composite).
High line number wide film satellite
Research on flexographic technology
1. Study on printing alcohol-soluble inks in high color density
Compared with gravure and ordinary flexo printing, high-line flexo printing uses an anilox roller with a high number of lines and a low amount of ink. The thickness of the ink layer is only 1/4 to 1/3 of the gravure, and the print is achieved. The color density consistent with the gravure printing, the flexo printing ink must not only achieve ultra-high color density (the pigment content is about 20%), but also ensure high-speed printing adaptability and better printing durability; The production process requires excellent composite strength.
In response to these technical problems, we verified the effects of different color concentrations, different systems, different white titanium dioxide particle sizes, different viscosities, and solvent grading volatilization rates on the quality of composite flexible packaging products.
2. Adjustment of ink resin formula
Since the flexo ink requires high color density and low viscosity performance relative to the gravure ink, the relative molecular mass of the flexographic ink resin is smaller than that of the gravure ink resin. In order to improve the composite strength of the resin and the composite adhesive, we have specially optimized the formulation of the flexographic ink resin, especially adding a polymer resin with a large number of crosslinkable functional groups, which can react with the reactive groups of the composite adhesive. The cross-linking chemical bond is formed, and the relative molecular mass and molecular weight uniformity of the resin are further improved on the basis of satisfying the printing performance, so that the resin is sufficiently crystallized, thereby improving the composite strength.
3. Control of small molecules
According to the theory of molecular diffusion, the mobility of small molecules is very strong, and it is easy to destroy the stability of the composite structure, resulting in a decrease in the composite peel strength. Therefore, we conducted a small molecule control study. The small ink molecules are mainly composed of a wetting agent and a dispersing agent. When the type of the wetting agent is changed and the amount of the dispersing agent is controlled, the composite strength can be improved.
4. Selection of anilox roller
In flexo printing, the anilox roller is a precise metering roller, especially the high-line flexo printing is more strict on the selection and control of the anilox roller. High-line film printing requires special anilox rolls, and the ceramic density, laser engraving angle, engraving energy, mesh wall width, cell shape, polishing finish and other parameters will affect the quality of the printed matter.
Research on solvent-free composite technology
Mainly focused on solvent-free composite strength control technology, adhesive quantitative control technology, tension control technology, winding control and post-processing technology. Compared with dry compounding, solvent-free compounding has the advantages of low energy consumption, non-toxic and non-VOCs emission, hygienic safety, etc., but in the matching of wide-format film flexo printing and solvent-free composite processes, through the selection of adhesives and The control of solvent-free composite related technology is studied in two aspects, and the solvent-free composite technology can achieve the purpose of mass production of composite flexible packaging materials in large quantities, and meet the requirements of key indexes such as composite strength, appearance and friction coefficient of the same gravure flexible packaging. Cost optimization and excellent quality.
1. Selection of different composite structural adhesives
Solvent-free adhesive and solvent-based adhesive main resin composition difference, due to the absence of organic solvents, low molecular weight (usually below 10,000), at room temperature due to intermolecular hydrogen bonding as a viscous liquid, viscosity is usually Tens of thousands of MPa•s or even hundreds of thousands of MPa•s. When heated to 60-100 ° C, the hydrogen bond is broken and the viscosity is greatly reduced. At this time, the coating performance is good.
2. Tension control technology
In a solventless compounding process, tension control is extremely important and must be very precise. The tension control includes the main unwinding tension, the film tension after the glue application, the secondary unwinding tension, the winding tension, and the winding taper. Generally, the tension after film coating is slightly larger than the main unwinding tension, and the winding tension is slightly larger than the unwinding tension, and the winding taper is controlled within 25%. For different materials, the tension of each part in the compounding process is also different. Even the film of the same material produced by different manufacturers has a slightly different tension. For a composite film of PA/PE structure, the tension of the PE film is approximately 1.5 to 2.5 N, and the tension of the PA film can be controlled at 7 to 15 N according to actual conditions.
3. Key technology for rubber coating control
The amount of glue applied is a key factor affecting the quality of the composite product, and the glue gap plays an important role in controlling the amount of glue applied.
Before starting the machine, after the metering roller is completely preheated, adjust the distance between the fixed roller and the metering roller (steel roller), and the distance between the left and right sides should be consistent to ensure uniform coating. The applicator roller must maintain a good finish and no foreign matter can be present.
The amount of glue applied can be adjusted according to product requirements and adjusted with 0.6mm, 0.8mm, 1.0mm thick steel rule. In general, when the film without the printed pattern is combined, the amount of the glue can be controlled to be 0.8 to 1.6 g/m 2 ; when the film with the printed pattern is combined, the amount of the glue can be controlled to 1.5 to 3.0 g according to the size of the printing area. M2. It should be noted that since the resins and pigments used for different types of inks are different, the amount of glue required is also different.
Research on low carbon clean production technology
In order to solve the environmental pollution caused by the solvent discharged during the printing production process and the harm to the human body, the state and the industry have continuously demonstrated in recent years that in order to find a feasible solution, many enterprises have invested huge amounts of money in how to recycle and treat the solvent. Due to the low solvent usage, the flexo discharge is significantly smaller than the gravure printing, and the exhaust gas treatment device such as RTO can be used to discharge the standard.
In the future, satellite flexo printing can completely print films using aqueous inks. Through multiple rounds of testing, we successfully produced composite flexible packaging for batch orders, all of which met the requirements, and the products were delivered to customers for use in odor testing, physical indicators, printing color saturation, high-speed printing 300m/min, high-light transfer, etc. The aspects have achieved good results, but due to the high price of imported water-based inks and the delivery cycle, they are not widely used in mass production. This article focuses on the realization of the flexographic composite flexible packaging process, and will not repeat the exhaust gas treatment technology and wastewater recycling technology. I believe that readers have seen too many introductions, but the recovery rate and post-recycling usage, operating costs, cost optimization, etc. will be discussed in depth in subsequent articles.
Flexo-free solvent-free composite flexible packaging has no solvent residue and low energy consumption. After being put into the market, it has been favored by users. It has been confirmed by many well-known food manufacturers. After using it, the indicators are completely in line with food packaging safety. Environmental protection requirements, can be widely used in all types of high-end food packaging. Moreover, the product is easy to use, safe and hygienic, and is safe and environmentally friendly to operators and users during production and use, and is suitable for the current development trend of energy saving, safety and environmental protection.