Solvent-free composite production, we must pay attention to the uniformity of coating!
The economic significance of uniform coating
Regarding the economic significance of the uniformity of coating in solventless composite production, the author compares the cost through the following data analysis.
It is assumed that the amount of glue applied at 1.50 g/m2 is the minimum requirement for the composite appearance and peel strength of the flexible package .
The solvent-free composite device A has a uniformity of ±10%, and the average amount of glue required is 1.67 g/m2, that is, the local minimum point is 1.50 g/m2, and the local highest point is applied. The amount was 1.84 g/m 2 (10% to 15% on the basis of the average coating amount).
The uniformity of the coating of the solventless composite device B is ±5%, and the average coating amount required is 1.58 g/m2, that is, the local minimum point of the coating amount is 1.50 g/m2, and the local highest point is applied. The amount is 1.66 g/m2. That is to say, in the same flexible packaging composite product, the equipment A is required to have a coating amount of 1.67.58±=0.09 g/m2 per square meter of the equipment B, that is, it consumes 5.7% of the solvent-free adhesive.
Calculate the average amount of glue used in a solvent-free composite equipment of 4.0 tons/month. Equipment A should use 4.0×12×5.7%=2.736 tons of adhesive in one year, and the unit price of solvent-free adhesive is 23 yuan/ In kilograms, the direct cost loss is 2.736×1000×23=62928 yuan, and the direct economic loss in 5 years is nearly 320,000 yuan.
There are also some solvent-free composite equipment on the market that can only achieve a coating uniformity of ±15%. Although such equipment has relatively low procurement costs, it often means more solvent-free adhesives, so it is cheap. Not equal to the economy.
Quality loss
Most of our flexible packaging design is often used more large blocks of color, with white ink-based color ink overprint, while there are some parts of the hollow design, graphic design so it will increase the difficulty of solvent-free compound.
In the solventless composite production, it is assumed that the minimum amount of glue required for the red ink and white ink overprinting portion of the sample is 1.5 g/m2, and the coating amount of 1.0 g/m2 in the transparent portion can satisfy the appearance and strength requirements. When the amount of the glue is too much, the transparent portion will be gelatinized (lower transparency) and even bubbles will appear. Therefore, if the above-mentioned solvent-free composite equipment A (partial highest point of coating amount is 1.84g/m2) and solvent-free composite equipment B (partial highest point of coating amount of 1.66g/m2) are used, respectively. The sample, compared to transparency, produced a composite film that was significantly lower than the composite film produced by Equipment B. The lower the viscosity of the adhesive used, the more obvious the phenomenon of the rubber film produced by the composite film. It can be seen that the equipment with poor uniformity of coating has a more obvious influence on the composite quality of flexible packaging. The key is that it can not effectively meet the quality requirements of the composite film overlay and transparent. Faced with this situation, some industry people will adopt a method to increase the average amount of glue, which will not only improve the composite quality, but will increase the cost of glue. In addition, increasing the amount of solvent-free composite coating, there are technical risks such as increased friction coefficient and anti-sealing failure for PE composite film.
Technical safeguards for uniformity of rubber coating
1. Five-roll coating system
Figure 1 Five-roll coating system
The five-roll coating system is the general structure of solvent-free composite equipment in China, as shown in Figure 1. There are mainly metering steel rolls R1 (fixed metering steel rolls), transfer steel rolls R2 (rotary metering steel rolls), transfer rubber rolls R3, coated steel rolls R4, and coating rolls R5. Among them, R1 is always fixed in the solventless composite production process, and it is combined with R2 and the adjustable glue blocking mechanism on the sides of the two rolls to form a glue storage device for storing solvent-free adhesive. The rubber roller can be manually turned while the drum is being scrubbed or the foreign matter is removed. Among them, R5 and R3 are rubber rollers, which are used to reduce the friction between R3 and R2 and R4 during production, and reduce the friction heat, thereby effectively avoiding the phenomenon of "transpiration and fogging" of the adhesive.
By continuously adjusting the speed difference between the rolls, the accuracy of the low amount of glue can be ensured. In order for the adhesive to form a uniform film on the coating roll, it is necessary to set different line speeds for the metering roll and the transfer roll, and the line speed of the coating roll is also different, which is lower than the line of the coating roll. Speed ​​(ie host line speed), such as a reasonable line speed ratio between R3 and R4 should be 0.25. The change in the amount of the solvent-free adhesive applied depends on the linear velocity ratio between the transfer roller and the coating roller.
For the solventless composite equipment using the gear belt connection of the geared motor, the linear velocity ratio of R2 and R3 is constant, that is, the surface rate of R3 varies with the amount of glue applied, and when the amount of glue is different, The line speed ratios of R3 and R4 are also different, but this problem does not exist if independent servo-controlled, solvent-free composite equipment is used. It can be seen that the reasonable linear speed ratio of R3 and R4 is an important factor to ensure the uniformity of the coating of the five-roll coating system.
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