Stamping principle and process conditions analysis

In recent years, improving the packaging and decoration of goods has become an important means to promote the sale of goods. From cigarettes, alcohol, medicines, foods to clothing, fruits, liquid beverages, cosmetics, etc., all aspects of daily life have all reflected the development of packaging and decoration printing. Rapid momentum. As an important finishing technology for packaging and printing, hot stamping plays a crucial role in the packaging of goods, satisfies people's psychological needs for consumption, and has a promising development prospect.

The main material for hot stamping is anodized aluminum, also called hot stamp foil. It consists of two thin layers, the polyester film substrate and the transfer layer. During hot stamping, the transfer layer is pressed against all or part of the surface of the substrate by the action of heat and pressure. After the hot stamping is completed, the polyester film is pulled together with the untransferred portion.

The hot stamping process is divided into 4 steps:

(1) Hot stamping foil and substrate contact;
(2) With the heat and pressure, the transfer layer is transferred to the surface of the substrate;
(3) Remove the pressure and peel off the polyester film;
(4) Feed the hot stamping foil and replace it with the printing part that will be stamped.

The perfect hot stamping effect mainly depends on the level of cooperation among stamping temperature, stamping pressure and stamping time. In addition, consider whether the substrate, stamping machine, hot stamping plate, jigs, and offset plates are suitable. Finally, we should also study the environmental conditions, including indoor temperature, substrate temperature, indoor air cleanliness (dust content), humidity, etc., which are described below.

Hot stamping foil

Hot stamping foils are available in roll foil and leaflet foils. The reel foil can be divided into different models according to the ironing materials, such as 1#, 8#, 12#, 15#, 18#, general-purpose, etc., and can also be divided into gold, silver, brown-red and light blue according to its color. , black, red, green, etc.

Different types of aluminum have different properties, and the suitable materials are different, such as: 1# is suitable for hot stamping on paper, leather, linoleum, silk and plexiglass with light color ink and loose texture. On hard plastic; 8# anodized aluminum is suitable for hot stamping on paper, varnished cloth and leather; 12# anodized aluminum is suitable for hot stamping on plexiglass, hard plastic and some glossy paper; 15# anodized aluminum is suitable for hot stamping on plastic film, On soft plastic products; 18# anodized aluminum is suitable for hot stamping on paper and leather with dark ink and thick lines. Some of the electro-aluminums are of the same model, but the origin of the materials is different.

Single sheet gold foil is used for hot stamping of linoleum, satin, leather and other materials; gold foil (three kinds of red, green, and middle red), silver powder foil is suitable for cloth (including linoleum), paper pulp, etc., while silver foil is Suitable for hot stamping of cloth, vinyl, leather and other materials.

2. Stamping temperature

If the hot stamping temperature is too high, the hot stamping will lose the metallic luster, blistering, the edge is not clear or even the stencil; if the hot stamping temperature is too low, it will cause the hot stamping to be not firm or the hot stamping of the imprinted hair.
Various types of galvanized aluminum are suitable for different stamping temperatures, 1# is 80～95°C, 8# is 75～90°C, 12# is 75～90°C, 15# is 60～70°C, and pure gold foil is 80 ~ 130 °C, color foil, gold foil, silver foil is 70 ~ 120 °C.

3. Hot stamping pressure

Excessive hot stamping pressure will result in thicker paste or imprinting. When the hot stamping pressure is too low, the hot stamping foil cannot adhere to the substrate, and the hot stamping area cannot be cut.

The installation of hot stamping foil should not be too tight or too loose. When it is too tight, the handwriting will be cut off. If it is too loose, the writing will be unclear and the paste will be dirty.

4. Hot stamping speed

The hot stamping speed actually reflects the contact time between the substrate and the hot stamping foil during hot stamping and directly affects the fastness of the hot stamping. If the hot stamping speed is too fast, the hot stamping may not be caused or the imprinting may occur; the hot stamping speed is too slow, which affects both the stamping quality and the production efficiency. Various types of aluminum foil suitable for different hot stamping speed, such as: 8 #, 12 # suitable aluminum hot stamping speed of 18 to 30 sheets / minute, 15 # of aluminum hot stamping speed of 18 to 22 / Minutes, 1 # aluminum for fast hot stamping, such as 40 sheets / minute or so.

During the hot stamping process, the hot stamping speed, the hot stamping pressure and the hot stamping temperature are mutually restricted, and the process parameters are always determined in the order of the hot stamping speed, the hot stamping pressure and the hot stamping temperature. First determine the hot stamping speed, under normal circumstances, as a constant treatment, not easily changed, and then find out the corresponding stamping pressure and hot stamping temperature, which can simplify the operating procedures, but also easy to control the quality of hot stamping.

5. Hot Stamping Machine

According to the hot stamping method, the hot stamping machine can be divided into three levels: flat pressure leveling, round pressure leveling and round pressure rounding; according to the hot stamping type placement mode, the hot stamping type machine can be divided into two types, vertical and horizontal.

6. Stampings

Offset paper, coated paper, whiteboard (cardboard), textured paper, linoleum, plastic, etc. can be used as stampings.

(1) Hot stamping of coated paper products

1 For the field version containing wax materials, when the number of hot stamping is small, use five layers of gauze to wrap the rosin powder on the hot stamping area. When the quantity is large, use 3% binder and 3% white dry mimeograph to rinse the ink once. After this treatment, the hot stamping effect is good.

2 For counter-pulling, corresponding measures shall be taken according to different situations. One of the reasons for the back-drawing is that the ink on the bottom layer of the print is not dried. The solution is to place the printed product in a ventilated and dry place to make the ink layer dry. Second, the white ink is used excessively on the light ink layer as a rinsing agent. Since the white ink pigment particles are coarse and the bonding force between the linking materials is poor, the hot stamping surface is powdered. The solution is to use bright light dilute agent and dry oil. First cover printing once again, and then hot stamping, but also can choose to use lower power aluminum foil for hot stamping.

(2) Hot Stamping of Gold Card Paper

Gold card paper prints have been widely welcomed because of their vivid colors, good gloss, moisture resistance and wear resistance, which have greatly improved the quality of packaging products. However, gold card printing is difficult, it is easy to stick dirty, ink is immediately removed, hot stamping is difficult, and these factors have limited its development. Here, combined with practice, talk about gold card paper printing, hot stamping should pay attention to several issues.

1 In terms of cross section, gold paperboard is divided into surface coating, aluminum foil layer, adhesive layer and paper base layer. The surface coating is equivalent to a layer of metal color preprinted, the surface is smooth, poor permeability, ink is not easy to adhere, even if it is difficult to dry, so it is best to use special ink for printing synthetic paper, and the amount of ink should be small, try to thin, Do not spray too much. Wait until the print is completely dry before printing. Another way to solve the problem of hot stamping is to apply a thin layer of background color to the hot stamping area before hot stamping so that the hot stamping foil adheres firmly to the ink.

2 Select the right hot stamping temperature, hot stamping pressure and hot stamping speed; copper foil stamping version to use, because of its good heat transfer performance, pressure resistance, wear resistance, not easy to deformation, graphic and blank parts of the height difference should be as far as possible Pull up so that it is not connected or paste.

In addition, the resin plate can also be used for hot stamping. Some manufacturers can't make copper and zinc plates because they can't make copper plates at home. Some of them can't go to the field to make copper and zinc plates. They try to use resin plates instead of copper and zinc plates. As long as the hot stamping temperature and stamping pressure match perfectly, you can also stamp out a good product. With resin stamping, the following points need to be noted:

1 The stamping temperature is too high, the resin plate will be scorched, and the stamping foil will also have a blocking phenomenon due to the influence of temperature.

2 Since the resin plate has toughness, it does not have to use too much pressure, and the stamping will be very clear.

3 Fix the resin plate with double-sided tape as much as possible. This tape is not heat-insulated and it is easy to grasp the stamping temperature.

Source: Printing Technology