Everyone knows "Bronzing", but few people know about "Sweeping Gold"

In order to improve the aesthetic performance and grade of printed matter, the application of post-press finishing is becoming more and more extensive.

hot stamping and gold sweeping technology have good effects in improving the metallic, three-dimensional, gloss, and anti-counterfeiting properties of printed products.

As two similar post-press surface finishing techniques, the two are actually quite different. This article shares the comparison between bronzing and sweeping for your reference.

bronzing

hot stamping is a process of hot stamping anodized aluminum foil onto the surface of a substrate under a certain temperature and pressure. Hot stamping technology is familiar to everyone both at home and abroad. Hot stamping can be divided into traditional hot stamping, cold hot stamping, holographic positioning hot stamping, etc.


sweep gold

The process of attaching special metal powder to designated parts on commodity packaging or label printing to achieve metallic luster effect. This technology can get realistic metal texture and better luster, at the same time fine pattern, accurate overprinting.


difference in principle

The principle of bronzing

Take anodized aluminum bronzing as an example. Anodized aluminum consists of four layers, as shown in Figure 4:


Among them, the base film layer is often made of polyester film. During the hot stamping process, it is required that this layer will not be deformed due to temperature rise: the release layer has better release performance.

It is generally coated with silicone resin, etc.; the color layer has two functions: displaying the color and protecting the aluminized layer graphic and text stamped on the surface of the item from being oxidized; the function of the aluminized layer is to change the physical color of the color layer. nature, enhances lustre by reflecting light.

The hot stamping process mainly uses the principle of hot pressing transfer, and its process flow includes:

1) Press together to make the hot stamping plate, anodized aluminum and the substrate contact. As shown in Figure 5:


2) When the power is turned on, the hot stamping plate heats up, and the anodized aluminum in contact with it is also heated, the adhesion of the base film layer (polyester film) on the anodized aluminum decreases, and the release layer (thermal resin glue) melts and increases its viscosity.

3) Transfer, the color development and the aluminum layer are separated from the base film layer with the melting of the release layer and transferred to the substrate.

4) Cool down. When the pressure is released, the adhesive quickly cools and solidifies, and the color developing layer and the aluminized layer are firmly attached to the substrate.

The principle of sweeping gold

The steps of the gold sweeping process are as follows:

1) Prepare the original for scanning gold, the original is the printed matter for scanning gold after multi-color or single-color printing production.

2) Print glue on the gold-sweeping part, transfer the originals that need to be gold-sweeped to a single-color or multi-color offset printing machine, use a special PS version, adjust the rules of the offset printing machine to complete the registration work, and print and coat thin on the parts that need to be scanned. And even primer.

3) Transfer the printed sheet coated with the gum base ink to the gold sweeping machine. The gold sweeping machine mainly has 5 parts: paper feeding device, coating device, polishing device, cleaning device, and paper delivery device.

4) Paper feeding, send the printed matter printed with primer to the rubber conveyor belt with suction channel through the paper feeding device of the gold sweeping machine.

5) Coating, the coating roller is rotating slowly. When the side of the coating roller that absorbs the gold powder turns to the top of the paper, it changes from suction to blowing, and the gold powder is evenly sprayed on the surface of the paper.

6) Polishing, there are 4 special polishers to start polishing with the gold powder on the paper. The gold powder printed on the bottom glue part on the paper will be firmly adhered to the paper by the friction of polishing.

7) Cleaning, the cleaning work is mainly completed by 4 finger gold belts of the cleaning device, front rubber cleaner with suction channel, rear rubber cleaning roller with suction channel, suction channel, suction roller, finger gold belt Reciprocate in the opposite direction to the coating to remove the excess gold powder, and wipe the high vacuum adsorption composed of the gold belt. The multi-channel circulating cleaning system can remove all the excess gold powder on the paper, and the removed gold powder is transferred to the gold powder filling device for recycling.

8) Paper delivery, completed by delivery device.



Feature comparison

1) From the effect of the printed product

Both bronzing and sweeping have good gloss. In comparison, bronzing has stronger metallic luster and texture. Gold sweeping is a mid-range imitation gold effect processing technology, while bronzing can achieve higher-grade requirements; in terms of registration, sweeping gold technology has more advantages. It is difficult to register the bronzing. When it is a small pattern or a large area of bronzing, the quality is not easy to control, and the sweeping gold is easy to register regardless of the size of the area and the thickness of the line. In terms of not falling off powder and not sticking to dirt, the bronzing technology has done a better job.

Sweeping gold is prone to sticking and dusting, but bronzing does not. This is determined by the technical principles of the two. The gold powder of bronzing is imprinted, and the gold powder is also attached with pigments, so the coloring effect of the gold powder is stable; The gold sweeping technology is easy to stick to dirt and powder. The main reasons are: the humidity in the workshop is too high or the water content of the paper is too high, which will cause the cleaning device to be damp and unable to wipe off the excess gold powder; The gold powder is attached to the gold part or the bottom glue of the part that needs to be cleaned is not enough or the quality is not good enough, resulting in the phenomenon of gold powder falling off.

2) From the point of view of the working environment

The gold sweeping process has higher requirements on the environment than the bronzing machine. The suitable temperature range for the gold sweeping machine is 22~25℃, and the humidity range is 50%~55%. Otherwise, quality problems are prone to occur.

3) From the perspective of production efficiency

Both bronzing and gold sweeping are dry processing methods, which are ideal for packaging, transportation and efficiency immediately after printing. In comparison, the efficiency of bronzing is higher than that of sweeping.

4) From the simplicity of operation

Hot stamping is more complicated than sweeping.

5) From the perspective of cost

The production cost of bronzing is higher than that of sweeping.

6) From the perspective of color

The most commonly used colors for bronzing and gold sweeping are gold, and other colors can also be presented, such as silver, copper, lemon yellow, peacock blue, green, graphite and so on.

7) From the anti-counterfeiting function

Hot stamping and sweeping gold can play an anti-counterfeiting effect. For example, bronzing foil has UV dark anti-counterfeiting properties, and gold sweeping can achieve the effect of imitating gold by attaching special metal powder to the designated part of the product package.

8) From an environmental perspective

Both bronzing and gold sweeping can be fully enclosed, which will not pollute the environment.

From the comparison of the characteristics of bronzing and gold sweeping, it can be seen that both have their own advantages. For example, a single gold sweeping process is difficult to achieve the best metallic luster and texture at present, and a single bronzing technology is not as good as sweeping gold in imitation of gold in specific parts. Well, in practice, the combination of bronzing and gold sweeping can often achieve better decorative effects.