Introduction to aluminum washing process for packaging bags; How are aluminum washing bags made?

Aluminum-washed bags are characterized by clear images and text, high precision, strong three-dimensionality, rich layers, bright colors, smooth surface, and high wear resistance. From a commercial security perspective, aluminum-washed bags are also a type of packaging with strong anti-counterfeiting properties, helping to improve product grade and added value, and having stronger product market competitiveness.

I. Introduction to Aluminum-Washed Bags

Aluminum-washed bags, also called partially perforated aluminum-plated bags, are composite packaging bags made of plastic film and partially perforated aluminum-plated film (or partially aluminum-plated film with aluminum removed) that are partially transparent. 'Aluminum washing' refers to the removal or washing away of the partially aluminum-plated layer on the film.

Currently, aluminum-washed bags are among the packaging with high printing requirements and beautiful design effects, both domestically and internationally. They are also a relatively popular and advanced type of anti-counterfeiting packaging internationally. They are very popular in Japan and the United States, commonly used for the outer packaging of clothing, hardware, electronics, toys, and food.

Aluminum-washed bags have obvious differences from ordinary aluminum-plated bags. In ordinary aluminum-plated bags, the entire bag or the entire front (or back) of the bag is laminated with aluminum-plated film. Aluminum-washed bags are different; you can design and produce any part of the bag with an aluminum luster effect and any part with a transparent visual effect, not limited to a specific location or a certain regular pattern.

In terms of printing, aluminum-washed bags have better printing effects than ordinary composite bags. In terms of decoration grade, they are more beautiful and attractive than ordinary aluminum-plated bags. The aluminum-washing process for aluminum-plated film, also called the aluminum-removing process, is sometimes called the partial perforated aluminum-removing process. There are many names, but essentially it means the same thing: washing away the local aluminum plating layer of the film to form exquisite and anti-counterfeiting packaging bags.

Currently, the material structure of aluminum-washed bags is generally: PET + aluminum-plated layer CPP, BOPP + VMPET + CPP (PE). The design can be customized according to different customer needs.

II Aluminum Bag Process Characteristics

1. Traditional Alkaline Aluminum Washing Method

The traditional alkaline aluminum washing method is a process that uses semi-automatic equipment and an alkaline liquid to remove the aluminum plating layer. The main component of the alkaline liquid is sodium hydroxide solution, commonly known as lye water. It chemically reacts with the aluminum plating layer and, through the aluminum washing tank device, removes the aluminum plating layer of the corresponding aluminum-plated film.

The traditional aluminum washing method easily removes the aluminum film, but the operation releases hydrogen gas. It must be operated in a ventilated area and kept away from flames, posing a certain degree of danger. Furthermore, because of this traditional partial aluminum plating process, a protective agent is usually applied to the areas where the aluminum plating needs to be retained after printing and aluminum plating, and then washed with lye water. Because the protective agent cannot be overprinted, the yield is not high. At the same time, the lye will corrode the edges of the aluminum layer, making it difficult to retain fine lines or small characters completely.

2. Post-Printing Aluminum Plating Method

This method involves plating aluminum on a PET color-printed film with a printed pattern where aluminum plating is needed, and then laminating this PET color-printed aluminum-plated film with another film through a heat-sealable adhesive to process it into a color-printed film aluminum-plated packaging bag composite layer. Compared with the traditional aluminum washing process, it has the following advantages:

The processing technology is simple, simplifying the aluminum washing process and eliminating two layers of film, reducing production costs and product costs.

Using a heat-sealable adhesive cold-rolling lamination process, the color-printed film aluminum-plated packaging bag is strong and durable and will not crack.

3. Clear Water Aluminum Washing Method

This process can wash away the aluminum plating layer in the transparent area, improving the stability of aluminum washing and preventing pollution. The aluminum washing device includes at least one tank, a cleaning roller in the tank, and a guide roller above the tank to form an aluminum washing cleaning line. During cleaning, the packaging film continuously moves in the tank, and the clear water in the tank and the cleaning roller wash away the aluminum plating layer in the hydrophilic ink area. This cleaning method overcomes the disadvantages of existing alkaline aluminum washing devices, such as instability, long processing time, high energy consumption, and environmental pollution caused by chemical reactions. Using clear water in the tank for cleaning can also achieve excellent aluminum washing results, uniform and stable product quality, and complete and clear images and text; it enables large-scale mechanized production, making it very suitable for the production of aluminum-washed packaging bags.

4. Coating Stripping and Aluminum Removal Method

This is a method for manufacturing colored vacuum-plated aluminum paper packaging materials with high surface smoothness and strong resistance to organic solvents. Specifically, an easily peelable coating is applied to a polyester film, aluminum is sputtered, a paper layer is then adhered, the polyester film is peeled off, and then a coating containing pigments is applied to the easily peelable coating to obtain the product. The easily peelable coating is composed of nitrocellulose and acrylic resin. This method improves the easily peelable coating, enhancing its resistance to organic solvents, and allowing large-area coloring on its surface. Because the surface is covered with a relatively rough easily peelable layer, a mirror effect can be displayed, and the aluminum-plated paper can be printed again. The color difference can be controlled during the coloring process.

III Auxiliary Material Requirements

Based on the de-aluminizing process requirements of the aluminized layer, the aluminum-washing products have certain requirements for the inks and protective agents used. For example, special aluminum-washing inks require the addition of 2%-5% curing agent to each color ink. The larger the ink area ratio, the greater the amount of curing agent added; that is, the larger the pattern area, the higher the content of curing agent added. After printing, it should be placed in a curing oven at 35-45℃ for 24-36h before being sent for aluminum washing to remove the aluminized layer where no ink is applied. As for the protective agent, it protects the part of the aluminized layer that does not need to be washed away, ensuring that the lines at the hollowed-out position and the joining position of the aluminized layer are clear, and ensuring that the aluminized layer after aluminum washing is not oxidized and blackened. The aluminum-washing solution needs to ensure that the de-aluminized areas can be thoroughly cleaned, otherwise it will affect the final aluminum-washing packaging effect.