Technical Data of Hot Stamping
- Categories:Technical Support
- Time of issue:2020-09-25 00:00:00
With the improvement of national economy and development of printing and packaging industry, people demand high-end, exquisite, environmentally friendly and personalized packages. In the final process of packaging products, hot stamping technique is favored by people due to its unique surface finishing effect, and widely applied in money, cigarette trademarks and high-end packages for pharmaceuticals and cosmetics, etc. Hot stamping has two main functions. Firstly, decorate the surface to increase added value of products. Chinese people love happy events and splendid and magnificent appearance. The combination of hot stamping and embossing can show off the luxury. Secondly, hot stamping offers high anti-counterfeit performance. Use holographic positioning method to stamp trademarks can prevent counterfeit and protect brands. At the same time, gold foil can demonstrate the individuation of product package and is safe and environmentally friendly. Therefore, many high-end packages have adopted hot stamping process.
1，Hot stamping principle: At certain temperature and pressure, the pigment foil attaches patterns and characters of the masterplate onto the plastics surface instantly.
2，Necessary conditions for hot stamping: 1. temperature; 2. air pressure; 3. pigment foil; 4. hot stamping masterplate
3， Hot stamping masterplate
High-quality hot stamping masterplate is the primary factor that ensures the hot stamping quality. Currently, hot stamping masterplate is made of copper plate or zinc plate mainly by photoetching and electronic engraving technologies. Copper plate, fine and smooth, has superior degree of finish and heat transfer effect than zinc plate. Quality copper plate can help to improve the gloss and edge sharpness of stamped patterns and characters. It is simple and inexpensive to use traditional photoetching technology to make hot stamping masterplates. The photoetching technology is mainly used to produce hot stamping masterplates with characters, coarse lines and general images. For the production of hot stamping masterplates with delicate and uneven patterns and characters, it is necessary to adopt secondary processing or electronic engraving technology. By using electronic engraving technology, the hot stamping plate can display rich and delicate levels change, and greatly beautify the package. This technology is environmentally friendly but requires high investment. In addition, the present engraving depth is not ideal and it is easy to cause masterplate tinting. As the technical requirement is high, the holographic anti-counterfeit masterplate was mainly produced in Taiwan or foreign countries previously. It takes a long time to produce and is only adopted in the package of fixed products with large batch quantities.
The hot stamping masterplate is mainly made of the following materials:
(1) Silica gel plate: Applicable to general plastic shell, with a thickness of 1.5mm; suitable temperature: 180℃-380℃;
(1)、Thickness of pigment foil: The thickness of pigment foil is 6U-35U; the factory mainly uses 12U pigment foil for hot stamping decoration. The thicker the pigment foil, the blurrier the characters are.
(2)、Pigment foil is divided into five layers: PE film, release agent, coloring layer, adhesive layer and adhesive agent.
(3)、Category of pigment foil:
a.Universal type: generally used in ABS, PVC, PS and PC
Currently, our hot stamping workshop has flat hot stamping machines, round hot stamping machines, irregular hot stamping machines, burning hot stamping machines, and double-circular hot stamping machines.
Flat hot stamping machine: used to stamp flat products.
Double-circular hot stamping machine: used to stamp products with round surface.
The model selection of hot stamping equipment is the key factor deciding hot stamping quality. Sheet-fed hot stamping machines have three models – flat pressing flat, round pressing flat, and round pressing round. At present, flat pressing flat hot stamping machine is mostly widely applied. These three models have both advantages and disadvantages. Adopting linear pressure, round pressing round and round pressing flat hot stamping machines feature small total pressure; both models can complete hot stamping in a large area with relatively less pressure and stable movement. In addition, with higher production efficiency, the round pressing round model is especially suitable for large quantities of live pieces hot stamping; however, as it is difficult to process the circular arc of copper plate, this model has higher production costs, and it is more difficult to heat the roller than the flat pressing flat model. Flat pressing flat model is suitable for short masterplate as its operation is flexible and convenient. Domestic hot stamping equipment has obvious advantages in performance and price compared to imported hot stamping equipment. The price of domestic hot stamping equipment is only 1/5-1/4 of overseas similar products. However, imported hot stamping equipment is superior to domestic counterparts in overprinting accuracy, stability, function and durability, and is suitable for processing high-end packaging products with fixed quantities. Therefore, product type and quantity are key factors determining the selection of hot stamping equipment. Customers now prefer manufacturers with BOBST and other high-end hot stamping and die-cutting equipment.
6，Features of Hot Stamping：
Clear patterns, beautiful appearance, bright colors, wear resistance and climate resistance. On stamped cigarette trademarks, hot stamping technique applications account for over 85%. Hot stamping on planar design can make the finishing point and highlight the design theme. In particular, its effect is more significant on trademarks and registered names.
(2) Holographic positioning hot stamping. Holographic laser positioning anodized aluminum belongs to special application in design. With corresponding anti-counterfeit patterns, it can greatly improve the anti-counterfeit performance and grade of products. Such anodized aluminum is generally made in China. Compared to imported products, it features low price but inferior hot stamping performance. Holographic laser positioning anodized aluminum has high requirements for hot stamping temperature, hot stamping pressure, operating speed, and even hot stamping machine model.
(3) Special technological application of anodized aluminum. Printing after stamping is the new originality of the cigarette design and printing industry. This technological application has very high requirements for anodized aluminum. Except accurate hot stamping position, smooth and bright surface, balanced pressure, evenness, non-foaming and non-tinting, other requirements include there should be no obvious impression at the edge of hot stamping patterns, the anodized aluminum should have excellent adhesion at the hot stamping surface, and there should no obvious abrasion marks or scratches. We all know that hot stamping is actually a process of paper being heated and pressed. Special attention should be paid to semi-finished products of white cards and glass cards. Various unfavorable factors for paper deformation should be minimized during the production, in order to facilitate smooth operation of procedures after hot stamping and improve product percent of pass greatly.
The so-called hot stamping adaptability refers to the model selection of anodized aluminum and the matching of hot stamping speed, temperature, pressure and other factors. Under the circumstance that equipment and other hardware are fixed, mastering the hot stamping adaptability correctly is the most important means to improve hot stamping quality. We provide the following analyses on some quality problems found in actual operation so that you may master the hot stamping adaptability in a scientific way.
(1) Patterns or characters cannot be stamped on or slightly stamped
This is related to many factors, including surface characteristics of substrates, properties of anodized aluminum, stamping temperature and pressure. ① The substrate surface has been sprayed with too much dust, or contains additives like reducer and high gloss slurry, which will hinder the adsorption of anodized aluminum and paper. Solution: Dedust the surface; solve the problem in the printing process. ② Improperly selected anodized aluminum directly affects hot stamping fastness. It is recommended to consider what model of anodized aluminum should be selected according to the size of hot stamping area and the characteristics of the stamped materials. Our domestic anodized aluminum is mainly the Peacock series produced by Shanghai Shenyong Stamping Foil Co., Ltd. Our imported anodized aluminum is mainly the PM and LK series of Germany KURZ, A, K and H series of Japan, and SP series of South Korea KOLON. According to our practices and tests, the following categories can be referred while selecting anodized aluminum. Hot stamping (general ink color) anodized aluminum on common products: 88-l model, KURZ PM model; hot stamping anodized aluminum on (including gold and silver) printed work with dark ink color for cigarette packets and cosmetics packages: 88-2 model; hot stamping anodized aluminum on cigarette trademarks and cosmetics packages with thin characters: 88-3, 88-4 and PM288 models; hot stamping anodized aluminum on OPP or PET laminated paper, or cardboard and glazed paper with UV inks: 88-4 model, K Series, LK series and SP series. ⑧ If the match between hot stamping equipment, hot pressing time and hot stamping temperature is not well mastered, the hot stamping fastness and sharpness of graphic outline will be affected. Due to various equipment and stamped materials, the hot pressing time and hot stamping temperature are not the same. For example, the high-speed round pressing round machine enjoys high speed; therefore, its temperature of stamping line contact and stamping temperature is higher than that of round pressing flat or flat pressing flat machine. In general, the stamping temperature of round pressing round machine is 190℃-220℃, the stamping temperature of round pressing flat machine is about 130℃-150℃, and the stamping temperature of flat pressing flat machine is about 100℃-120℃. The hot pressing time, hot stamping temperature and production efficiency are certainly constrained by the performance of anodized aluminum transfer to a great extent.
(2) Reverse Drawing
Reverse drawing refers that anodized aluminum pulls the printing ink or gloss oil away after hot stamping. This is mainly because the ink on the surface of the printed work is not dry or surface UV of the printed work has improper post processing, which results in unfirm adhesion between surface oil, UV oil and paper surface. Solution: Bronze after the printed work is dry. You may also select anodized aluminum with low separating force and excellent heat transitivity.
(3) Tinting & color change of anodized aluminum after hot stamping Tinting is mainly due to poorly produced hot stamping masterplate, loose installation of anodized aluminum, or incorrect foil feeding of anodized aluminum. The color change of anodized aluminum after hot stamping is mainly because the hot stamping temperature is too high. In addition, anodized aluminum crumpling can easily result in uneven color overlapping and color change. This can be resolved by reducing temperature properly. For the round pressing flat machine, a fan can be installed at the foil feeding place to maintain smooth foil feeding and prevent anodized aluminum burning by touching the hot stamping masterplate before hot stamping.
(4) Improper process arrangement destroys the surface gloss of anodized aluminum and results in blurred outline of patterns and characters.
The stamping foil which requires film laminating, people are worried that the foil may easily be wiped off; therefore, they often stamp first and coat film later. This may easily lead to: ① The film (especially matte film) will destroy the surface gloss of anodized aluminum. It is not recommended to use water-soluble glue for film laminating, otherwise the surface of anodized aluminum will become black; and it is very likely that golden powder sticks to the graphic edge and make the printed work blurred. ② After hot stamping, the stamped part will sag because of pressure; furthermore, the glue will not penetrate the surface of anodized aluminum easily, which may cause the separation between OPP at the stamped part and the paper, and consequently the production quality is affected. The correct process is stamping after film coating. It is advised to select anodized aluminum that matches OPP.
In short, there are many factors that affect the hot stamping quality. Producing high-quality hot stamping masterplate and correctly mastering hot stamping adaptability is the key to improve hot stamping quality.
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