Printing pigments or dyes on paper, rubber or other carrier, and then printing onto the goods to be printed is called transfer printing, but in the narrow sense, transfer printing refers to the printing technique using needle textile as a carrier. Transfer printing is mainly used on polyester fiber products. With the increase of transfer printing, it is also widely used in nylon, acrylonitrile, cotton, hemp and wool.
The transfer printing is divided into various forms such as wet method, dry method, steam method, vacuum method, and thermal method. The transfer printing method can accurately reproduce the pattern, facilitate mechanized production, and has a simple process. In particular, the post-printing treatment process is simpler than the traditional printing and the printing touch is the same as the printing and dyeing, and thus gradually replaces the old printing. However, most of the printing and dyeing factories in China still use traditional printing and dyeing methods, and only a few production units use transfer printing for production.
At present, a wide range of hot melt resins are used in addition to polyester, such as polyamide, vinyl acetate copolymer and polyurethane. The main component of the polyester hot melt adhesive is a polyester resin, and the polyester resin is a polybasic acid. It is obtained by lipidation with a polyol. Polyamide hot melt adhesive has strong adhesion, toughness, low temperature resistance and nylon fabric affinity, and is suitable for preparing nylon transfer printing paper. The ethylene-vinyl acetate copolymer has a low melting point and strong adhesion, and is suitable for producing transfer printing paper after adding printing ink. Polyurethane hot melt adhesive is mainly used for leather and polypropylene plastic bonding. Transfer printing Because of the difference in the fabric to be printed, it is best to use a suitable hot melt adhesive ink.
First, the characteristics of transfer printing
(1) The transfer printing pattern has the characteristics of vivid flower pattern, fine pattern, clear layer and strong three-dimensional effect. Transfer printing can print natural landscapes and artistic patterns.
(2) Transfer printing equipment has the characteristics of simple structure, small footprint, low investment and high economic efficiency. Because the equipment is tension-free, it is suitable for all kinds of thick and thin printing. In addition, the transfer printing can be packaged without post-processing.
(3) There is no environmental pollution problem in transfer printing. Since the dry processing does not require processes such as washing, steaming, and drying, no exhaust gas or waste water is discharged.
(4) Transfer printing has the advantages of high production efficiency, labor saving and easy operation.
Second, the transfer printing mechanism
Transfer printing is mostly used for polyester fabrics. It is a printing method in which the dye is sublimed by heat at a high temperature (about 200 ° C) to agglomerate on the surface of the polyester, and then penetrates into the amorphous region of the fiber macromolecule, and is fixed inside the fiber after cooling.
Third, transfer printing requirements for dyes
For disperse dyes used in transfer printing, the sublimation temperature should be lower than the melting point of fiber macromolecules and the strength of the fabric should not be damaged. The suitable processing temperature for polyester is 180--210 °C. In this temperature range, the molecular weight of the varieties sublimated by dyes is between 230 and 270. There are generally three types of disperse dyes having a molecular weight in this range.
Fast-dye disperse dye: The temperature can be sublimated at 180 °C, the temperature is increased, the color changes, and the edge will be permeated.
Good disperse dyes: sublimation and color development in the temperature range of 180--210 °C. The hair color curve is flat. The effect of temperature on dyeing is not large, and it is a suitable disperse dye for transfer printing.
Late dyeing disperse dyes: dyes are not very good for sublimation and color development at 180--210 °C. If the temperature is raised, good hair color can be obtained. These dyes are highly temperature dependent when dyed.
According to the above situation, the dyes suitable for transfer printing should have the following conditions:
(1) The transfer-printed dye must be sufficiently sublimed and fixed on the fiber below 210 ° C, and good washing fastness and ironing fastness can be obtained.
(2) The dye of the transfer printing can be fully sublimated and converted into a gas-phase dye macromolecule after being heated, which is condensed on the surface of the fabric and can diffuse into the interior of the fiber.
(3) The dye for transfer printing has a small affinity for the transfer paper and a large affinity for the fabric.
(4) The dyes transferred to the printing should have bright, bright colors.
Fourth, the color ink of the printed transfer paper
Printing of transfer paper for transfer printing, most of which use printing and screen printing processes and equipment. The composition of the color ink is composed of a dye, a vehicle, a binder, and the like. The color ink is prepared by mixing the above three components and pouring them into a colloid mill or a three-roll mill to uniformly distribute the dye in the color ink.
(a) The vehicle carrier is used to uniformly distribute the dye in the color ink and transfer the dye from the printing device to the material on the transfer paper. The vehicle should have low-cost, non-toxic, non-combustible properties. According to this requirement, water is most suitable. However, the transfer paper is composed of cellulose. When water is used as the vehicle, the fiber is expanded, causing deformation of the fine pattern, and it is difficult to produce at high speed due to slow evaporation of water. If an organic solvent-based vehicle is used, although the paper is less deformed, the color ink can be printed with a fine pattern and has a suitable volatility, which is advantageous for the production of higher speed. However, it has the disadvantages of high cost and easy combustion. Strict attention should be paid when using it. Oil-based vehicles such as high-boiling oils can also be used. However, high boiling oil can cause the dye to diffuse deep into the transfer paper, thereby affecting the amount of dye transfer onto the fabric on the transfer paper.
(2) Adhesive bonding agent refers to a substance that controls the viscosity of a color ink. The amount of the binder is too small to ensure the viscosity of the color ink, resulting in poor printing transfer paper, and the amount of the binder is too large, so that the transfer speed of the dye from the transfer paper to the fabric is slowed, which causes residue on the transfer paper. Too much dye. The binder should be selected separately depending on the vehicle used. When water is used as the vehicle, the commonly used synthetic gelatin or carboxymethyl cellulose is used as a binder: when an organic solvent or an oil is used as a vehicle, ethyl cellulose can be used as a binder.
V. Transfer printing requirements for transfer paper
When transferring printed transfer paper, the transfer paper used should have the following characteristics:
(1) have sufficient strength;
(2) The affinity for the color ink should be small, but the transfer paper should have good coverage to the ink;
(3) The transfer paper should not be deformed, brittle and yellowed during the printing process.
(4) The transfer paper should have appropriate hygroscopicity. Poor hygroscopicity can cause color ink to color; excessive moisture absorption can cause deformation of the transfer paper. Therefore, the filler should be strictly controlled when producing transfer paper. It is more suitable to use the semi-filler in the paper industry.
According to the above requirements, the transfer paper should meet the following criteria:
Hygroscopicity 40--100g/m2
Tear strength is about 100kg/5x20cm
Breathability 500---2000l/min
Weight 60--70g/m2
Ph value 4.5--5.5
No dirt exists
The transfer paper is preferably made of softwood pulp. Among them, the pulp produced by chemical pulp and mechanical pulp account for half of each. This will ensure that the paper will not become brittle and yellow when processed at high temperatures. Sixth, the printing method of flower paper
The printing of the paper is a process of printing the pattern onto the transfer paper by printing the color ink through printing and screen printing. At present, transfer printing papers are mostly printed by printing methods. There are four printing methods for the paper, such as a gravure printing method, a letterpress printing method, a lithography method, and a screen printing method. Printing paper is printed by printing, and the gravure printing is the most extensive. The screen printing method is suitable for the printing of small-volume, multi-variety transfer printing paper, and can make homemade paper in the printing and dyeing factory. It has the characteristics of low cost, fast speed, rich color and easy operation. However, due to the use of water-soluble inks in the screen printing method, the three-dimensional texture and contour of the pattern on the flower paper are not good, the pattern is thick, and the transfer printing pattern is not exhibited.
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