What is Flexographic Lamination Knowledge Sharing（3）

(2) Some Practical Realities

In practice, higher composite line speeds (faster machine start-up speeds) and higher film drawing line speeds lead to faster rotation speeds of the transfer rubber roller, consequently increasing the adhesive demand of the film. Only by correspondingly increasing the adhesive supply from Combination 1 and maintaining good transfer conditions can a stable adhesive application amount be maintained. Otherwise, excessive machine speed can cause insufficient supply or adhesive stringing during transfer, leading to poor adhesive application and transfer, resulting in white spots or uneven coating in the composite.

Conversely, lower composite speeds reduce the demand for adhesive; the supply from Combination 1 to Combination 2 must be correspondingly reduced. Otherwise, excessive adhesive supply can cause buildup on transfer roller 3 or over-transfer onto the film, forming adhesive streaks or overflow, which similarly adversely affects the composite result.

To adjust the relationship between machine speed and adhesive amount, Bobst adopted a range of line speed ratios to stabilize adhesive supply. This brings up an issue. For example, in the 201~250 m/min range, if the set speed differential ratio is the same value of 50%, it can be understood that the adhesive supply amount is consistent within this speed range.

Taking a composite film coating width of 1 meter as an example, under the same speed ratio condition, the film area produced per minute is 201~250 m². Assuming the adhesive supply per minute is 600g under this speed ratio condition, then at a machine speed of 201 m/min, the adhesive application amount is 600/201 = 3 g/m²; at a machine speed of 250 m/min, the adhesive amount is 600/250 = 2.4 g/m².

Can this be understood as follows: under equivalent transfer rates and fixed production conditions (constant metering roller pressure and gap after start-up), changes in machine speed cause variations in the actual adhesive application amount on the film. Under the same speed differential ratio, the range of variation in adhesive amount is 0%~20% ((3g - 2.4g)/3g = 20%).

Through communication with multiple factories, the author found that the adhesive application amount using flexographic equipment generally does not show a significant reduction compared to traditional gravure roller application. This contradicts the original intention of flexographic coating to substantially save adhesive. It is unclear whether this is due to insufficient mastery of the operational process or the reasons mentioned above.

It is believed that in the future, with equipment maturation, adhesive advancements, improved operational skills, and process enhancements, the adhesive application amount using flexographic coating will inevitably decrease significantly.

(3) Calculation of Cost Savings with Flexography

High working concentration coating primarily saves costs through reduced solvent usage (high working concentration), reduced adhesive amount (more uniform coating or increased coating area), increased production efficiency from higher machine speeds, and decreased unit energy consumption due to higher speeds.

Solvent Usage Savings

Flexography, employing roller transfer coating, allows for application at higher working viscosities compared to gravure roller coating. Increased working viscosity means higher working concentration, which in turn means less diluent usage.

According to surveys, the industry typically controls flexographic coating working viscosity between 22~70 seconds, with many using the 30~50 seconds range. Only a few manufacturers can produce at working viscosities above 70 seconds.

The increase in working viscosity brings higher working concentrations. Most flexographic processes operate around 50% concentration, with some manufacturers reaching about 60%, allowing for significant diluent (ethyl acetate) savings.

Taking Shanxi Helichang's 758 adhesive as an example, its high-solid, low-viscosity characteristics allow for good composite results on Bobst machinery at a working concentration of 56%, viscosity of 35 seconds, and a machine speed of 300 m/min.

Ultra-high concentration coating saves substantial solvent and reduces organic solvent emissions. Ultra-high machine speeds bring high production efficiency, yielding greater benefits for cost, energy, and labor efficiency control. See the analysis in the table below:

Note: Cost comparison table for coating at different working concentrations, based on a dry adhesive amount of 2.2g/m², adhesive unit price of 17 yuan/kg, and ethyl acetate unit price of 6.5 yuan/kg.

The table above shows that under the same 2.2g/m² application amount, when the working concentration increases from 35% to 45%, the cost difference per ton is 3095 yuan; when the working concentration increases to 55%, the cost difference per ton is 5046.94 yuan. This means that a 20% increase in working concentration can reduce adhesive usage cost by 5046.94 yuan per ton of adhesive. The cost difference per gram of dry adhesive is significant, leading to substantial savings per unit area, around 0.06 yuan/m². Due to changes in working concentration, the cost variation can exceed 20%.

Case Study on Dry Adhesive Amount Savings

Again, using the 758 adhesive (75% solid content) as an example, a cost comparison for different dry adhesive amounts under different working concentrations shows that reducing the adhesive amount has an even greater impact on composite production costs. That is, under the same working concentration, the usage cost varies significantly with different dry adhesive amounts. For instance, at a 60% working concentration and an application amount of 1.5g/m², the adhesive production cost is only 0.0373 yuan/m²; at the same working concentration, if the application amount increases to 2.5g/m², the cost rises to 0.0621 yuan/m².

As can be seen from the table above, at a 50% working concentration, reducing the adhesive amount by 0.5g/m² (from 3g to 2.5g) equates to an increase in coating area per ton of adhesive by 50,000 m². Multiplying by the cost of 2.5g/m² dry adhesive (0.0675 yuan), this translates to a saving of 3375 yuan per ton of adhesive.

From the above analysis, the following can be concluded for the composite process:

① With a constant dry adhesive amount, the usage cost of adhesive varies with different working concentrations. Increasing the working concentration by 10% reduces the cost by approximately 3000 yuan per ton; increasing it by 20% reduces the cost by approximately 5000 yuan per ton.

② When coating at the same 50% working concentration, the cost difference is significant for different dry adhesive amounts. Each 0.5g/m² reduction saves approximately 3375 yuan per ton of adhesive.

③ Under conditions of a 20% increase in working concentration and a 0.5g/m² reduction in application amount, the actual usage cost saving per ton of adhesive is ① + ② = 3375 + 5000 = 8375 yuan.

④ If the application amount is not reduced, merely increasing the adhesive working concentration has limited cost-saving benefits. For a single composite machine using 100 tons of adhesive annually, a 10% increase in working concentration could save about 300,000 yuan/year; a 20% increase could save about 500,000 yuan/year. For many small and medium-sized enterprises, improving management and operational skills is crucial. They need to calculate the return on investment carefully and budget according to their actual needs.

IV. Current Status of Flexography and Personal Insights

As a new process, understanding the characteristics of flexographic composite equipment and mastering the process are very important. Regardless, cost reduction, efficiency improvement, energy saving, emission reduction, and green low-carbon practices are eternal themes in flexible packaging development. Improving the coating state and maximizing the potential of flexography require collaboration between equipment, adhesive, and users, and is a subject requiring continuous in-depth research.

Adopting flexographic composite requires attention to the match between adhesive and operational skills. Control the working concentration and viscosity of the adhesive solution well. Under varying conditions of metering roller gap, pressure, and line speed ratio, identify the actual data on adhesive amount changes at different speeds to set the process accurately. Precise coating is essential for cost reduction, including considering the impact of line speed, roller pressure, roller gap, and rubber roller speed differential ratio on coating under different working conditions. Thoughtful consideration and improvement are needed.

The true benefits of flexographic coating lie in the tripartite cooperation of equipment, process, and adhesive. Different adhesives have varying initial viscosities and solid contents, leading to significant cost differences. The adhesive greatly influences the composite process, start-up efficiency, and overall cost. Selecting the right adhesive is key to successful flexography.

The best partner for flexography remains high-solid, low-viscosity adhesive. There are many types available on the market. Personally, I believe that only those with a solid content above 70% can be called high-solid, and those with a viscosity below 2000 cps can be called low-viscosity. Both conditions must be met to be considered a true high-solid, low-viscosity adhesive.

High-solid, low-viscosity adhesives often have low initial tack. Therefore, when selecting an adhesive, comprehensive evaluation of its initial tack, final peel strength, temperature resistance, compliance, and other functions is necessary. Choosing a cost-effective adhesive is paramount.

Generally, the price of ordinary dry composite adhesive does not exceed 15 yuan/kg, functional adhesive does not exceed 20 yuan/kg, and special function adhesives are slightly more expensive. For adhesives with similar performance, foreign brands are typically 20%~50% more expensive than domestic ones. How to choose and use them is a lesson operators need to learn well.

Since the rubber rollers and anilox rollers in flexographic composite are immersed in the adhesive pan, the pan is relatively large and difficult to seal. Full consideration must be given to viscosity changes caused by solvent evaporation in the pan, and the impact of high-concentration coating on adhesive thickening (pot life) will also increase. Those with the conditions can choose automatic adhesive mixing machines to stabilize the working viscosity of the adhesive and maintain its working stability.

Transfer rubber rollers of the sleeve type are composite structures of fiberglass and carbon fiber, then rubber-coated. Installation using an air expansion principle places very high demands on the rollers and carries the risk of operational deformation during installation. The risk of swelling and deformation due to long-term immersion in solvent and friction must also be considered. The quality and price of composite rubber rollers also require cost and quality assessment.

The investment in flexographic composite equipment is substantial, with market prices ranging from 2 million to 5 million yuan, representing a significant capital outlay compared to traditional gravure dry composite machines. Of course, efficiency can also be greatly improved, which is beneficial with the support of orders, technology, and personnel. Enterprises need to evaluate based on their own situation before deciding.

Traditional gravure coating remains an alternative. After all, with improvements in the production efficiency of ordinary dry composite machines, and advancements in high-solid, low-viscosity adhesives, squeeze rollers, laser-engraved rollers, and other gravure roller technologies, the traditional labels of low efficiency, high energy consumption, and large emissions associated with dry composite have changed. Comprehensive competitiveness has been significantly enhanced. The key lies in how to apply them.