Solvent free composite process has the advantages of environmental protection, low carbon and energy saving, safety, low cost and high speed compounding. Because of its obvious advantages, solvent-free composite has been "famous abroad" and has been widely promoted and applied in European and American markets. According to the relevant data, after so many years of development, only 80 solvent-free composite production lines have begun to enter the flexible packaging enterprises for production and test, and the number is less than 2% of the total number of composite equipment, which is far inferior to the market application status of dry lamination. The speed of solvent-free composite is slow in China. The author thinks that the most important reason is the lack of solvent-free composite process control. There is a big difference between solvent-free composite process and traditional mature process such as dry composite process. In the past five or six years, I have accumulated some experience on the control of solvent-free composite process. I will summarize it and share it with colleagues in the industry, hoping to bring some help to the production enterprises using solvent-free composite process.
The main difficulty of solvent-free composite process is that it is difficult to match the equipment, substrate, adhesive and process parameters. The main reasons are: first, it is difficult to control the tension, because the initial adhesion force is very low, and the setting and control of each section of tension are very strict. Second, it is difficult to control the coating amount, mainly because of the many control parameters (6-7), and the sensitive relationship between the coating amount and some parameters. Third, because of the need for curing time, the composite results show lag. Fourth, due to the high production speed, the overall control of the production process is more difficult. Therefore, the difficulty of process control and the risk of waste products increase obviously. In order to overcome these problems, the following key points should be strictly controlled, and each key link should be strictly controlled, so the solvent-free composite process will be easy to handle.
Detection of composite substrate
1. The main performance index of surface tension for composite substrate is surface tension. The commonly used film materials must be corona treated (the surface tension of PE and BOPP film is greater than 40 dyne, the worst must be greater than 38 dyne; the surface tension of VMPET film is greater than 42 dyne; the surface tension of PA film is not less than 50 Mn / M; the surface tension of PET film is not less than 45 mN/m）。 Its main purpose is to improve the leveling, coating and composite fastness of adhesive. On the contrary, when the surface tension of the substrate is lower than the required value, the composite fastness will be affected, and if it is serious, it will produce delamination.
2. The thickness of the substrate must be uniform, the thickness uniformity deviation should be controlled within 10%, and the quality should meet the relevant national or industrial standards.
3. The width of the substrate used for the width shall not exceed the maximum range allowed by the machine, and shall not be less than 60% of the maximum allowable range of the machine; the width of the second substrate shall be greater than the width of the coated substrate by 0-5mm; the minimum range of each test substrate must be at least 10 mm greater than the width of the transfer cot used for the test, However, it should be no more than 20 mm at most. For printing base materials, the pictures and texts must be clear, with regular mesh points, no scratches, no dirty spots, no paste, no knife thread and other defects. For non printing base materials, it is required to have good appearance, no impurities, no dust, no pollution and no moisture. Supplier is required to provide quality report, date of manufacture, date of manufacture, batch number, etc.
2、 Selection of glue and ink
The use of glue and ink is the most prone to problems in the process of compounding, so the supplier must be selected strictly. Maybe glue, ink manufacturers, large and small, uneven. It is better to go to the manufacturer for on-the-spot investigation to investigate its scale, production capacity, quality control and other aspects. In particular, solvent-free laminating glue, we should choose the supplier with high maturity. In the past, solvent-free polyurethane laminating adhesive mainly relied on imported foreign products, which was not only expensive, but also not timely and effective after-sales service. Once problems occurred in production, the consequences would be very serious, which could not solve the worries of solvent-free composite flexible packaging enterprises. Shanghai Kangda new chemical materials Co., Ltd. has been committed to the development and research of solvent-free polyurethane laminating adhesive since 2005. Now it has basically formed a series of products. It is also the first domestic manufacturer that can supply solvent-free laminating adhesive in batches. It is a national brand worthy of soft packaging enterprises to use with ease.
In the choice of glue and ink, but also to consider the compatibility of the two issues. At present, the solvent-free peritoneal glue in China is polyurethane chemical system, but the ink has benzene, ester soluble, alcohol soluble, water-based, polyamide and other classification. Therefore, to investigate the compatibility of the two, we can first determine the glue, and then use different systems, different brands of ink to match with it, so as to select the appropriate ink and glue.

In the application of glue, we should pay attention to the control of glue amount, which is a relative concept, and the glue amount on different substrates is usually different. Overall, it is controlled at 1-2g per square meter. Transparent material is usually 1 to 1.4g, aluminum plating is 1.5g to 1.8g. The specific dosage needs to be determined by field test. If the amount of glue is too large, it will not only cause uneven collection, but also cause the ink to peel off and transfer from the printing substrate. If the amount of glue is too small, it will not only reduce the peeling strength, but also leave bubbles due to the insufficient amount of glue and ink infiltration. This is more obvious on the composite of aluminum plating and white printing film.

3、 Equipment use
(a) The power supply voltage of the machine is stable, and the voltage fluctuation deviation is not more than 10%.
(b) The air source of the machine is stable and filtered by air dryer. The compressed air should be clean and dry, and the pressure should not be lower than 0.6MPa.
(c) the water source shall be clean and free of scale, and the water pressure shall not be less than 4kg, because there is a compressor for heating, so as to avoid damage to the compressor caused by unclean water source.
d) The cleaning and maintenance of the main engine is very important, especially the gluing coating and composite parts. Before going to work every day, the glue coating, the composite part and each roll must be cleaned.
e) The cleaning and maintenance of mixing machine is the premise and guarantee of solvent-free compound machine. The metering pump is a very important part, which must be checked regularly to see if it works well. The compressed air entering the metering pump should be kept dry, and dehumidification device should be added when necessary. Secondly, it is necessary to prevent the glue pump from clogging. Because there is no regular cleaning and maintenance, it is easy to cause the curing blockage in the glue pump. If the glue machine is used again, it will result in the wrong proportion of the adhesive. Once there is a problem, the loss will be huge.
f) The solvent-free laminating machine is well adjusted, and necessary action detection is carried out to check whether each guide roll is flexible and whether each guide roller is clean and undamaged. Clutch coating roll, back pressure roll, composite roll whether smooth and both ends synchronous.
g) Because of the low initial adhesion of solvent-free composite, it is very important to match the tension of each section and control the winding tension. Winding tension mainly includes main unwinding tension, traction tension after gluing, secondary unwinding tension and winding taper. The tension of each part is also different in different structures. The proper way to check the tension is to stop the machine during the lamination process, and mark an "X" shape on the composite film with a blade during winding up. If it is flat, it is appropriate to operate. If it is curled in one direction, it indicates that the tension of the film is too large, and it should be adjusted reasonably
4、 Compared with dry laminating machine, solventless lamination in compound workshop has strict environmental requirements. Domestic solvent-free do a lot of well done enterprises, are separate solvent-free composite equipment to build independent space. Fundamentally solve the problem of cleanliness. The environmental requirements are mainly considered from the following points.
1. The solvent-free composite adhesive is polyurethane type, and its main agent is isocyanate. The functional group of isocyanate is a very active group, which is easy to react with water in the air. After the adhesive is solidified, there will be bubbles. Therefore, the environmental humidity has a significant impact on the composite effect during the gluing process. Generally, the control humidity is less than 75%.
2. The workshop must be kept clean, because the solvent-free speed is very high. If there is dust, debris, mosquitoes, it will seriously affect the accuracy of the equipment and the transparency of the cost.
5、 First of all, the size of curing chamber should be appropriate, equipped with heating and ventilation facilities, good insulation effect, and can keep the indoor temperature constant and uniformity. 2. The temperature of curing chamber can be controlled automatically, and the temperature can be adjusted in the range of 35-50 ℃. If the indoor temperature deviation is less than 2%, if the indoor uniformity can not meet the requirements, the composite coil should be manually turned over during the curing process.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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