Section 6 Printing of Plastic Products - 8

Fourth, special plastic printing (a) hot stamping technology Hot stamping technology is often used in plastic packaging parts surface decoration, protection. For example, it is widely used in the printing of plastic cases, frames, decorative parts, and various nameplates of electronic products such as radios, tape recorders, televisions, and computers, and can replace plastic plating, painting, and other processes. Hot stamping technology is described in detail in the fourth paragraph of this section.
(B) Penetration printing At room temperature, polyethylene and polypropylene are almost insoluble in all solvents and difficult to color, but at 70°C, they can be slightly soluble in terpineol, turpentine, mineral oil, etc. When the temperature is further increased At that time, the molecular motion is obviously aggravated and the volume swells. This provides the conditions for the dye to penetrate into the interior, which is the basis for polyolefin penetration printing. It goes without saying that the dispersion and permeability of the dye are very important in this printing.
In the first step of infiltration printing, the pattern is reverse printed on the carrier by gravure printing to form an inverted pattern, and then the patterns on these carriers are transferred to the surface of plastic film or other plastic products.
This method can be used to print materials such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, ABS and polyurethane.
The osmotic printing method can perform printing of multiple colors in a single operation without compromising the clarity and smoothness of the pattern. Even if the size of the print is changed, there is no obstruction and good reproducibility. Even without solvent. However, this method has a low production efficiency and cannot obtain a pattern with high transparency.
The key to the osmotic printing process is how to choose the right carrier and ink.
(1) Carrier According to the requirements of the product, the carrier may be a calendered paper or a polyvinyl butyral film.
(2) The effect of ink coloring is related to the type, chemical structure, relative molecular weight, sublimation performance, etc. of dyes. For polyolefin prints, it is necessary to use pure disperse dyes that are permeable (that is, original dyes without diffusion agent). ). Disperse dyes and blending agents (ie, thinners) are blended in an equal proportion and rolled by a three-roll mill to form a penetrating printing ink. The formulation of the blending agent was: turpentine oil 30%, terpineol 68%, and ethyl cellulose 2%.
(3) Operation The gravure printing method is used to print the pattern on the carrier, or it can be drawn by hand.
For polyolefin printed parts, a layer of turpentine oil or terpineol should be coated on the surface of the plastic product. Then, the printed carrier should be reversed on the surface of the product (printed on the surface of the product) and placed in a constant temperature oven. Processing. The conditions of heat-treated beads are shown in Table 3-52. Cold after the paper, washed with water to remove the color.
Table 3-52 Heat Treatment Reference Conditions
Low-density polyethylene High-density polyethylene Polyethylene
(3) The complex printing printing complex printing system uses the principle of metal complexation to achieve solid color printing.
In the printing of plastics, polyethylene and polypropylene are crystalline non-polar polymers, which have poor adhesiveness and are difficult to print. If a suitable amount of metal salt is incorporated into the polyolefin resin, after processing and molding, printing is performed with a disperse dye and heating is performed. Treatment, to promote adequate penetration of dyes, and metal complexes in plastic products, you can get good results.
(1) Product Processing In order to achieve the purpose of osmotic complexation, 0.1%-0.5% of metal salt (zinc stearate or nickel stearate, the latter is preferred) should be added to the polyolefin resin, mixed granulation, and processing forming.
(2) Printing and printing inks should be disperse dyes (complexation type), rolled into ink by a three-roller machine, the ink formulation list is 3-53, and the dyes can also be added to terpineol, and they are continuously ground into a saturated state. Ink.
Shi Cai method can be screen printing, or it can be drawn by hand.
Table 3-53 Reference formulae for penetrating printing inks
dye Dibutyl phthalate Epoxy resin glycerin
(3) Heat treatment The printed plastic products shall be treated according to the conditions of Table 3-54.
Table 3-54 Heat Treatment Conditions
Polyethylene Polypropylene
(4) Cleaning After treating the treated product to room temperature, use terpineol, ethanol or water to wash away the surface residual solvent and float the color.
(D) In-mold decorative mold interior decoration (also called in-mold decoration) is to put a printed transparent color printing film sheet in a cavity of an injection or hollow blow mold, with an ink facing the core, The other side is attached to the inner wall of the cavity, and then injected or blow-molded. The melted plastic is adhered to the printed carrier film and the pattern is sandwiched between the article and the carrier film and is effectively protected.
In-mold decoration can be used in a variety of thermoplastic plastic products, including polyolefins, polystyrene, ABS and polycarbonate.
The factors that affect the quality of the product include: selection of carrier film and ink, pattern and mold design, material temperature, etc.
The selected carrier film is different depending on the raw materials of the product. The specifications are shown in Table 3-55. Before printing, corona treatment is also required, especially for polyethylene and polypropylene films.
Table 3-55 Carrier Film Selection

The ink must be carefully selected to facilitate the ink fastness, such as the decorative parts of the long-term light, must also select the lightfastness of the ink.
When designing a mold, it must be noted that: a. The gate is at least 6.5 mm away from the decorative part. In order not to melt the carrier hot material and integrated with the product hot melt synthesis, will not be separated; b. The stream of the joint can not fall on the decorative parts, in order to avoid wrinkling of the carrier film.
Plastic films usually have static electricity, which can be attached to a specific part of the mold as needed, but are not very reliable. In order to prevent the printing film from being displaced during feeding, an electrostatic charging device can be used. The operator holds a flexible rod and puts it. The static electricity is transferred to the film so that it is firmly attached to the mold cavity. Although the voltage of the electrostatic charging device exceeds 10,000 V, it is absolutely safe because the current is limited to 10 μA.
(v) Roll-printing, also known as trench printing, involves gravure printing at the same time as ginning. It is an operation method that combines ginning and gravure printing. It can be used for embossing and printing of artificial leather and wallpaper. There are also printed gravure patterns printed on gravure PVC film, polyethylene artificial leather, and polyurethane artificial leather. A beautiful three-dimensional pattern appears on the surface. The process is shown in Figure 3-67.

Fifth, plastic film composite process Flexible packaging materials generally do not use a single material, but mainly composite film.
(I) Composite Method 1. The wet compound method is to apply a layer of water-soluble binder on the surface of the substrate (plastic film, aluminum foil), compound it with other materials (paper, cellophane) through the press roll, and then dry it through a hot drying tunnel. Become a composite film, as shown in Figure 3-68.
The binder used is mainly casein resin, nitrile latex, polyvinyl alcohol, sodium silicate, starch, polyvinyl acetate, polypropylene resin, natural resin, and the like.
The advantages of wet compounding are that the process is simple, the amount of the viscous agent is small, the cost is low, and the compounding speed is fast.
2. Dry-type compounding method A layer of solvent-based adhesive is applied to a plastic film, dried by removing the solvent through a drying tunnel, and bonded to a composite substrate (plastic film or aluminum foil) in a hot-pressed state to form a composite film. See Figure 3-69.
3. Extrusion Compounding Method The curtain-shaped molten polyethylene extruded from the slits of the T mold was pressed by a pinch roll, cast onto a paper or film, and subjected to polyethylene coating. Alternatively, other films may be supplied from the second paper-feeding section and polyethylene may be bonded as an adhesive layer, as shown in Fig. 3-70.