The advantages of solvent-free composite technology, such as: no risk of residual compound solvent, friendly operation environment, no organic solvent emission, low cost of glue and high processing efficiency, have been recognized by the industry. It has been successfully applied in developed countries such as Europe and the United States. There are also many successful cases in domestic manufacturers. It is recognized as one of the three major environmental protection technologies.
It seems that the development of solvent-free composite in China is only a process of technology transplantation and localization. However, the matching and development degree of film, ink, adhesive, equipment, and technical ability of workers in China are still in the stage of further improvement, so there are some problems that are difficult to solve for a while. In this paper, some problems and technical exchanges with you.
1、 Two common problems
1. Appearance of composite membrane
The appearance of solvent-free composite membrane has been recognized by most of the composite structures, such as OPP / / PE (CPP), OPP / / VMCPP (vnpet), PET / / PE (CPP), OPP / / Al, etc., but there are still obvious small white spots in PET / / VMPET, pet / / Al structures with good barrier properties on both sides. Of course, the phenomenon of white spots is related to the amount of glue, the micro smoothness after the split transfer of glue, and the relative humidity of the environment. Due to the characteristics of barrier materials, before the glue loses its fluidity in the aging process, the gas inclusions in the film (including the air brought in during the compounding process, or the CO2 gas generated by the reaction of the adsorbed water on the surface of the material, the residual moisture in the ink layer in the ink layer) and the curing agent react It is difficult to seep through the membrane, resulting in white spots. In other words, the barrier of the material directly affects the secondary leveling effect of the glue.
With the improvement of process technology, the appearance quality of PET / / VMPET and PET / / Al composite films will be well solved. At the same time, the industry should not put forward too strict requirements on the appearance quality. We should pay more attention to the health and safety performance of the composite films.
2. The friction coefficient increases
The current high-speed automatic packaging requires that the film has a small friction coefficient (for automatic packaging, it is precisely the friction coefficient between the composite film and the mechanical guide roller and the formed steel plate, rather than the friction coefficient between the inner layer of the composite film and the inner layer of the composite film) to reduce the transmission resistance of the film. However, according to the general reaction of the industry, the friction coefficient of the solvent-free composite film increases obviously after aging, especially when the PE thickness is less than 45 μ. At the same time, the same PE inner membrane, using the traditional dry composite, but no similar problems.
Obviously, the increase of friction coefficient is related to the characteristics of solvent-free adhesives. It is believed that "MDI type isocyanate compounds will gradually migrate to the surface through the inner film, and react with water vapor to form polyurea heat-resistant sealing layer" and "smooth agent migrates into the adhesive layer". It can be seen that the matching test of specific adhesive model and inner membrane is the key to avoid similar quality problems.
2、 How to avoid batch quality loss

The speed of solventless laminating machine is fast. For example, the maximum mechanical speed of a ssl-s solventless laminating machine can reach 450m / min, and the normal speed of general solventless laminating machine can reach 250-300m / min. in the case of deviation of process conditions, high efficiency also means high quality risk. The most difficult problem is the lagging performance of composite quality, which can not be detected in time like the appearance quality of printing. Therefore, the composite process is also called "special process". How to minimize the risk of solvent-free compounding?

1. Necessary process small sample
The unconscious changes of raw material formula and process conditions often lead to batch quality problems. For example, the formula of film material, the type and type of inks and adhesives. At present, the quality level of raw materials from different suppliers is uneven, so it is not easy to think that the same material name can replace each other. Moreover, there are still problems in the matching of membrane materials, inks, adhesives, process conditions, etc., such as the phenomenon of "ink being stained" in solvent-free composite, as shown in the figure (the picture is from Tongze courseware). For example, the - Oh in the widely used polyurethane ink resin will consume a certain amount of glue curing agent. The consumption degree is related to the thickness of the ink layer and the proportion of resin in the ink. Will the adhesive layer at the ink layer not dry (the adhesive layer in the blank part is dry)? Is it necessary to adjust the proportion of curing agent?
After the sample is tested to be qualified, the standard technical documents shall be formulated, the production shall be carried out in strict accordance with the established process route, and the raw material supplier shall be required to provide products with stable formula. If there are significant changes in raw material formula or process conditions, sample confirmation shall be conducted again.
2. Comprehensive quality inspection
We often focus on the appearance, peel strength, heat sealing strength, further heat sealing temperature, solvent residue and other items of the composite membrane, but rarely carry out comprehensive physical and chemical performance analysis according to GB 9683, such as p-toluidine (4% acetic acid), evaporation residue (4% acetic acid, n-hexane, 65% ethanol), potassium permanganate consumption, heavy metals and other indicators. At the same time, food packaging and drug packaging are different in sample processing, soaking method, soaking conditions (time / temperature), index unit, etc.
Today, the safety of food and drug packaging is widely concerned, and the safety testing of packaging materials is also one of the important contents to reduce business risk.
3. Fully understand the technical characteristics of solventless compounding
The biggest characteristics of solvent-free composite and dry composite are low initial adhesion and low coating amount. Most of the quality problems are related to these two factors. Therefore, many "experiences" of dry compounding can not be simply transplanted into solvent-free composite practice.
For example, when the flow of glue at both ends of the baffle plate is insufficient, it is easy to aging, resulting in the decrease of glue amount, resulting in insufficient peeling strength at both ends of the composite film. At this time, the glue on the baffle side should be stirred regularly.
At the same time, it is necessary to ensure the correctness of the proportion of the main agent and curing agent of the two-component adhesive. The blockage of metering pump will lead to the error in the proportion of the main agent and curing agent of the two-component glue, such as insufficient curing dose, resulting in dry glue of composite membrane, insufficient peeling strength and low heat sealing strength. It is necessary to correctly detect the refractive index of coating glue liquid and monitor the accuracy of mixing ratio, so as to avoid the situation that "the mixing pump does not alarm due to the failure of maintenance and the imbalance of adhesive proportion".
3、 How to cut into solvent free composite process correctly
The advantages of solvent-free composite technology are very obvious, but its advantages of low cost and high efficiency can be brought into full play if it is applied well. Find the right starting point, and reduce the risk and unnecessary loss through the step-by-step way of "sample - small batch production - normal process batch production". Don't let too much "failure experience" to form a "consensus". Finally, the introduction of solvent-free composite equipment has failed to be practical.
I agree with Tongze on this point
1. Try before using
The process test shall cover "parameter determination, peel strength, compatibility of glue / ink / material, heat sealing bag making, friction coefficient change", etc., and relevant test records shall be made to provide data preparation for mass production.
2. Simple first and complicated later
In the choice of composite structure, first choose simple structure, on the basis of accumulated experience, choose more complex structure in order, strive to apply one, stable one, mature one.
3. Slow first, then fast
In the grasp of the speed of equipment operation, we should not rush forward. We should gradually speed up the production and operation speed of the equipment with the operator's grasp of the equipment and technology.
4、 How to train technical personnel
The development of solventless compound talents is a long-term problem, and the operation captain is only one aspect of the industry talent dilemma. Solventless composite industry needs personnel with theoretical analysis ability and constantly updating practical knowledge, so as to upgrade from empirical knowledge to theoretical recognition The height of knowledge.
Solvent free composite technology is in the mature stage in our country. There is no invariable experience. Once the experience is out of date, it will produce negative value. I think that the industry should speed up the construction of solvent-free composite technology talent team from the following aspects.
1. Abandon the experience of traditional dry method combination, and do not form a theoretical misunderstanding.
2. The voice of glue suppliers and equipment manufacturers should not be the only voice of technical exchanges and cooperation. We flexible packaging enterprises should also actively share successful experiences and confusions with peers.
3. Industry magazines and journals should keep abreast of the technical trends of the industry, and do more technical topics on solvent-free compounding, so as to promote knowledge dissemination.
4. Media organizations, magazines, industry associations and so on carry out more national "forum", "conference" and other forms of training.
5. People with insight in the industry systematically summarize the theoretical system of solvent-free composite technology, compile and publish technical monographs, so that more professionals in the industry can learn the theoretical system of the system at low cost.
Through the joint efforts of our flexible packaging industry, the localization process of solvent-free composite technology in China will be accelerated, and the gap with developed countries in Europe and America will be shortened.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, a world famous manufacturing city, is a subsidiary company of Beite packaging (China) Co., Ltd
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