The essence of hot stamping / hot stamping is transfer, which is the process of transferring the pattern on anodized aluminum to the substrate by heat and pressure. When the printing plate is heated to a certain degree with the attached electrothermal master plate, it is embossed through the anodized aluminum film and paper, and the effect of temperature and pressure is used to convert the adhesive layer, metal aluminum layer and color layer attached to the polyester film. Printed on paper.
Hot stamping technology refers to the transfer of hot stamping materials (usually anodized aluminum film or other special coatings) on the hot stamped objects such as paper, cardboard, fabrics, coatings, etc. through a special hot stamping pattern. Processing technology on hot objects.
According to the degree of automation of the process, hot stamping can be divided into two types: automatic stamping and manual stamping.
1) Good quality, high precision, clear and sharp edges of hot stamped images.
2) The surface gloss is high, and the hot stamping pattern is bright and smooth.
3) Wide selection of hot stamping foils, such as different colors or different gloss effects, and hot stamping foils suitable for different substrates.
4) Three-dimensional hot stamping is possible. Can make the packaging have a unique touch. In addition, a three-dimensional hot stamping plate is made by using a computer numerical control engraving (CNC) method, which makes the three-dimensional layers of the graphics processed by the hot stamping obvious.
1) Hot stamping process requires special equipment
2) Hot stamping process requires heating device
3) The hot stamping process requires a heating device and a hot stamping plate. Therefore, hot stamping can obtain high-quality hot stamping effects, but the cost is also higher. The price of the rotary hot stamping cylinder is relatively high, which accounts for a larger part of the cost of the hot stamping process.
The pattern is clear, beautiful, colorful, eye-catching, wear-resistant and weather-resistant. On printed cigarette labels, the application of bronzing technology accounts for more than 85%, while bronzing in graphic design can play a finishing touch and highlight the design theme, especially for trademarks, registered names, the effect is more significant.
05 influencing factors
The electric heating temperature should be controlled between 70 ~ 180 ℃. The larger the hot stamping area, the higher the electric heating temperature. For small characters and lines, the hot stamping area should be lower. At the same time, various models of anodized aluminum are suitable for different stamping temperatures. 1 # is 80 ～ 95 ℃; 8 # is 75 ～ 95 ℃; 12 # is 75 ～ 90 ℃; 15 # is 60 ～ 70 ℃; while pure gold foil is 80 ～ 130 ℃; gold powder foil and silver powder foil are 70 ～ 120 ℃. Of course, the ideal hot stamping temperature should be based on the lowest and clear embossed lines, which can only be determined by test hot stamping.
The hot stamping transfer of the aluminum layer must be completed by pressure. The size of the hot stamping pressure affects the adhesion fastness of anodized aluminum. Even if the temperature is suitable, if the pressure is not enough, the anodized aluminum cannot be transferred to the substrate well, which will cause problems such as imprints and prints. On the contrary, if the pressure is too large, the compression deformation of the gasket and the substrate will be too large. The print will be thick, and even sticky and opaque. Usually, the stamping pressure should be adjusted to be small so as not to fade and good adhesion.
Adjusting the hot stamping pressure should integrate multiple factors such as substrate, hot stamping temperature, vehicle speed, and anodized aluminum itself. Generally speaking, when the paper is strong and smooth, the printing ink layer is thick, and the hot stamping temperature is high, and the speed of the car is slow, the hot stamping pressure should be lower, otherwise, it should be larger. The hot stamping pressure must be uniform. If local hot stamping and numbness are not found, it is likely that the pressure here is too low. A thin sheet of paper should be placed on the flat plate to make the pressure tend to balance.
The effect of hot stamped pads on pressure is also greater. Rigid pads can make prints beautiful, suitable for strong and smooth paper, such as coated paper, glass cardboard; soft pads, on the other hand, have thicker prints and are suitable for large-area hot stamping, especially the uneven surface , Paper with poor flatness, smoothness, and rough paper. At the same time, the installation of the hot stamping foil should not be too tight or too loose.
The speed of hot stamping actually reflects the contact time between the substrate and the hot stamping foil during hot stamping, which directly affects the fastness of hot stamping. If the speed of hot stamping is too fast, it will cause the hot stamping to fail or the prints to appear bloated; if the speed of hot stamping is too slow, it will affect the quality of the hot stamping and the production efficiency.
Cold stamping technology
Cold stamping technology refers to the method of transferring hot stamping foil to the printing material by using UV adhesive. Cold stamping process can be divided into dry film cold stamping and wet film cold stamping.
Dry lamination cold stamping process
The coated UV adhesive is cured before hot stamping. When the cold stamping technology just came out, the dry film cold stamping process was used. The main process steps are as follows:
1) Print a cationic UV adhesive on a roll substrate.
2) Curing the UV adhesive.
3) The cold stamping foil and the printing material are compounded together by means of a pressure roller.
4) Peel off the extra hot stamping foil from the printing material, leaving only the required hot stamping text on the part coated with the adhesive.
It is worth noting that when using the dry lamination cold stamping process, the curing of UV adhesive should be performed quickly, but it cannot be completely cured. It must ensure that it still has a certain viscosity after curing, so as to be very hot Bonds together well.
Wet lamination cold stamping process
After the UV adhesive is applied, first stamping and then curing the UV adhesive, the main process steps are as follows:
1) Printing free-radical UV adhesive on roll substrate.
2) Compound cold stamping foil on the printing material.
3) The radical UV adhesive is cured. Since the adhesive is sandwiched between the cold stamping foil and the printing material at this time, the UV light must pass through the hot stamping foil to reach the adhesive layer.
4) The hot stamping foil is peeled from the printing material, and a hot stamping text is formed on the printing material.
It should be noted:
Wet-laminated cold stamping process replaces traditional cationic UV adhesives with free radical UV adhesives;
The UV adhesive must have a strong initial tack, and it can no longer be tacky after curing;
The aluminized layer of the hot stamping foil should have a certain degree of light transmission to ensure that UV light can pass through and trigger the curing reaction of the UV adhesive.
The wet laminating cold stamping process can connect hot stamping metal foil or holographic foil on the printing machine, and its application range is becoming wider and wider. At present, many narrow-width carton and label flexographic printing presses already have this kind of inline cold stamping capability.
1) No special expensive stamping equipment is required.
2) Ordinary flexible plate can be used, no need to make metal hot stamping plate. The plate making speed is fast, the cycle is short, and the production cost of the hot stamping plate is low.
3) Fast stamping speed, up to 450fpm.
4) No heating device is needed, saving energy.
5) Using a photosensitive resin plate can complete the hot stamping of the halftone image and the solid color block at the same time, that is, the halftone image and the solid color block to be hot stamped can be made on the same hot stamping plate. Of course, just as the screen and solid color blocks are printed on the same printing plate, the hot stamping effect and quality of both may be lost.
6) The application scope of the hot stamping substrate is wide, and it can be hot stamped on heat-sensitive materials, plastic films, and in-mold labels.
1) Hot stamping cost and process complexity: cold hot stamping graphics usually require film or glazing for secondary processing protection.
2) The aesthetic appearance of the product is relatively reduced: the coated high-viscosity adhesive has poor leveling and is not smooth, which causes diffuse reflection on the surface of the cold stamping foil, which affects the color and gloss of the stamped graphics.
1) Design flexibility can be achieved (various graphics, multiple colors, multiple materials, multiple processes);
2) Fine patterns, hollowed out text, dots, and large fields;
3) Gradient effect of metallic color;
4) High accuracy of overprint after printing;
5) Flexible post-printing-offline or online;
6) Does not damage the material of the substrate;
7) The surface of the substrate is not deformed (no temperature / pressure required);
8) There is no indentation on the back of the substrate, which is especially important for some printed products, such as magazines and book covers.