Gravure printing faces condensation challenges? Find low-cost solutions here!

Gravure printing faces condensation challenges? Find low-cost solutions here!

Due to the structure of gravure presses and the metal layer on the surface of the aluminum coating, condensation is highly likely to occur during the rainy season each year, with condensation being even more severe in southern regions. If condensation occurs during printing, it greatly affects print quality control management and printing quality, directly impacting subsequent production processes and the finished product rate. In response to the above issues and situations, the author will summarize experiences and offer insights based on practical production conditions.

The occurrence of condensation phenomena

01/ Causes of condensation

Condensation is when a gas or liquid condenses upon cooling, such as water vapor turning into water when cold, and water turning into ice when cold. Therefore, the greater the temperature difference between the material surface and the ambient environment, the higher the relative humidity in the air, making condensation more likely. At a certain temperature, the less water vapor in a given volume of air, the drier the air becomes; The more moisture there is, the more humid the air.

02/ Condensation phenomenon in the aluminum coating

Aluminized film is a film made by vacuum aluminum plating in which high-purity aluminum wire is vaporized at high temperatures (1100~1200°C) into gas. Then, when the plastic film passes through the vacuum evaporation chamber, the gaseous aluminum molecules precipitate onto the surface of the plastic film, forming a bright, metallic film.

Aluminum is an excellent conductor of heat, with thermal conductivity three times greater than iron. Industrially, aluminum is commonly used to manufacture various heat exchangers and heat dissipation materials. Therefore, aluminum materials heat up and cool quickly at relative temperatures, easily forming temperature differences with the ambient temperature. When the surface temperature of the material is lower than the ambient temperature, surrounding moisture will condense and adsorb onto the material. With such temperature differences combined with the relatively high humidity during the plum rain season, the aluminum layer on the surface of the aluminum coating easily forms a "water mist" invisible to the naked eye, which is the condensation phenomenon of the aluminum coating. However, aluminum coating is one of the essential materials in the flexible packaging industry. Whether as a composite material or a printing material, condensation has a significant impact on subsequent processing.

03/ Condensation phenomenon in gravure plate rollers and ink plates

The gravure plate roller consists of a base steel roller, nickel layer, copper layer, and chrome layer. The manufacturing process involves electroplating the other layers onto the steel roller surface based on the steel roller. The plate rollers are made of metal from the inner to the outer layers, and various metal materials are also prone to temperature differences with the environment.

The ink tray is one of the indispensable devices in gravure printing, carrying prepared printing ink and diluted solvent. The plate roller is soaked in the ink in the ink plate. In the high-temperature summer environment, the evaporation of solvent in the ink plate accelerates, and the evaporation of the solvent carries away the heat from the surface of the plate roller and the ink in the ink disk, causing both the plate roller and ink to simultaneously generate a temperature difference with the relative ambient temperature. When the air is relatively humid and there is a lot of moisture nearby, the condensed water will adsorb onto the plate roller to form a "water mist," which remains in the ink and causes excessive moisture content. At the same time, the evaporation balance of the dilution solvent is disrupted, causing resin to swell and precipitate, resulting in printing sticking and plate paste phenomena, directly affecting drying speed and print quality.

Analysis of existing industry solutions

Currently, some medium and large enterprises enclose each printing machine unit and install a constant temperature dehumidification device (power consumption about 10~15kW) to ensure the overall production environment maintains a controlled state of constant temperature and humidity. However, other small and micro enterprises have had to abandon this idea for various reasons, and can only produce some low- and low-end printing and packaging products. For printing materials, medium and large enterprises have the solution to store aluminized film materials in a warehouse equipped with refrigeration and dehumidification equipment. However, for companies that print small batches and do not have the necessary storage conditions, printing materials directly affect printing quality.

01/ Advantages of existing solutions

The advantage of existing solutions is that from unwinding to winding, regardless of how many groups are printing, the production process from substrate and ink to plate rollers always operates in a relatively stable and controllable temperature environment, making it highly adaptable to the production environment and unaffected by seasonal temperature and humidity. Various printing materials such as films, aluminized films, paper, inks, and solvents are also unaffected by environmental changes.

02/ Disadvantages of existing solutions

The drawback of existing solutions is that enclosed production requires a large amount of space, and the cost of enclosed space is higher when operating as an entire printing equipment workshop. The purchase cost of dehumidification equipment is high, ranging from as little as a hundred thousand yuan to as much as two or three hundred thousand yuan. Additionally, it violates the law of conservation of energy. Printing equipment is all dried by thermal energy, and the main principle of dehumidification equipment is to use compressor cooling, which can only achieve dehumidification at relatively low temperatures. It is necessary to ensure both the operating temperature of the printing and drying mechanism and the constant temperature of the production workshop, which increases electricity consumption and thus affects production costs. These issues are the direct reason why small and micro enterprises hesitate to adopt large-scale cooling and dehumidification equipment.

Innovative solutions and ideas

01/ Aluminized film moisture solution

(1) Regardless of size, gravure printing enterprises have medium-sized or small composite curing rooms. Before printing during the high-temperature plum rain season, the aluminized film is baked in a curing room for 6~12 hours, and printing must be completed within one hour after baking. Other moisture-prone printing materials can also use the above methods, such as PA nylon materials.

(2) Before printing with aluminum coating, use the first color group oven to bake before entering the second color group for printing. If some manufacturers or products use all color groups, only a pre-baking device can be added between the unwinding mechanism and the first color group. The heating device should be 50~100cm long, with well-developed air inlet and outlet systems, and an effective baking temperature of 60~80°C being appropriate.

02/ Solutions for plate rollers and ink plate condensation phenomena

The plate roller and ink plate interact with each other. The idea provided in this solution is to use the cooling function of the condenser to achieve a constant temperature (temperature control around 26°C) dehumidification. Moisture from the air around the plate roller and ink plate will adsorb onto the condenser as the temperature drops, which can also reduce the evaporation of solvents in the ink. The heat discharged by the evaporator in the refrigeration device can be mixed into the oven mechanism, thereby reducing the energy consumption required for oven heating.

Each color group is equipped with a separate cooling and dehumidification device, with a power of 1.0~1.5 HP and energy consumption of about 750~1200W. The advantage is that some printed products can use several sets separately without full-color sets. Partial sealing between color groups is done for lower cost and easier control. The condensation device is installed in the stainless steel groove at the bottom of the ink pad as designed. For a typical printing machine with 7~10 color sets, the cost can be controlled at 20,000~30,000 yuan. Including partial closure and modifications, the total cost will not exceed 40,000~50,000 yuan. Moreover, through heat recovery, actual energy consumption and costs are lower than the book figures.

In summary, the proposed solution in this paper is one of the methods to address the formation of water mist in metal film materials, moisture-prone film materials, and plate roller ink plates under the influence of high temperature and humidity during the plum rain season. Compared to previous approaches, this solution is suitable for a wider range of enterprises, has lower costs, has lower energy consumption, and better aligns with national energy conservation and emission reduction policies.