Water transfer definition
A transfer method in which the graphic ink layer and the substrate on the transfer material are separated by means of water during transfer.
According to the characteristics of the transfer, it is divided into water mark transfer and water-covered transfer. The former mainly completes the transfer of text and photo patterns, while the latter tends to perform complete transfer on the entire product surface. The difference between the two lies in the different transfer materials. Watermark transfer relies on transfer paper to achieve the transfer of graphics and text, while water-covered transfer relies on a flexible transfer film. The flexibility of the transfer film must make it stretch and deform when it comes into contact with the substrate, so the fineness of the water-covered transfer graphic is lower than that of the water mark transfer. However, for those products with complex shapes and large graphic areas, water-covered transfer has great advantages.The base material of the water-covered film has a very high expansion and contraction rate, making it easy to entangle tightly on the surface Therefore, no matter how complicated the product surface, the water-covered transfer technology can complete the decoration in a second time. Water transfer film with a special chemical treatment is printed on the surface of the water after printing the required color lines, and the color lines and patterns are evenly transferred on the surface of the product by the effect of water pressure. Automatically dissolve in water. After washing and drying, apply a transparent protective coating. At this time, the product has shown a completely different visual effect.
3. Water coating 1. Overview Water coating transfer is a technology that uses a flexible plastic film that can dissolve in water to wind on the surface of the product and transfer the graphics on the surface to the surface of the product.
2. Principle The principle of water-cover transfer is to send the water-covered film with printed graphics to the surface of water and spray the activator evenly on it. Activator is an organic mixed solvent mainly composed of aromatic hydrocarbons, which can quickly dissolve and destroy polyvinyl alcohol, but it will not damage the graphic layer and make the graphic free. Then, the product to be printed is gradually brought closer to the water coating film, and the free graphics are evenly transferred to the surface of the product by using the effect of water pressure. The water coating film is automatically dissolved in water, washed and dried before spraying. The upper layer of transparent protective coating forms a graphic on the product surface.
3. Process flow
4. Printing method Water-covered film is usually printed on the surface of water-soluble plastic film by gravure printing or inkjet printing. The main use is PVA film. PVA is polyvinyl alcohol, because of the large number of hydroxyl groups on the molecular chain, it has good water solubility. In addition, PVA also has good film-forming properties, adhesion, emulsification, oil and solvent resistance, so it is very suitable for use as a water transfer film. The physical properties of polyvinyl alcohol depend on the molecular weight and degree of alcoholysis. The molecular weight determines the degree of polymerization. Generally speaking, the greater the degree of polymerization, the greater the viscosity of the aqueous solution, the strength and solvent resistance after film formation, but the solubility in water decreases, and the elongation after film formation decreases. The water-coated film should have good strength, and the degree of polymerization is as high as possible; but the degree of polymerization is too high, and the film-forming property is not good, so the degree of polymerization should not be too high. The alcoholysis degree of polyvinyl alcohol determines its water solubility. Generally, the lower the alcoholysis degree, the easier it is to dissolve in cold water. Therefore, the coating film should use polyvinyl alcohol with low alcoholysis degree as much as possible.
When pure polyvinyl alcohol is dissolved, because the polymer chains in the film are not fully stretched and internal stresses exist, the film will undergo large deformation during the dissolution process, which will have a greater impact on printed graphics. Therefore, it is necessary to add an appropriate plasticizer to make the polymer chain of the PVA solution stretch as much as possible during the film formation process, and the internal stress of the film after the film formation is relatively small, and no large deformation will occur during dissolution. During the transfer process, the surface tension of the transfer film is also very important. If the tension is too high, it will not be easy to adhere to the printing material. Therefore, it is necessary to add a surfactant to the polyvinyl alcohol solution to reduce the tension at the interface between the PVA film and water. To improve its surface properties. Therefore, pure polyvinyl alcohol is difficult to meet the requirements of the water-coated film, and it needs to be appropriately modified.
5.Water-soluble PVA film
The film-forming substance of water-soluble P V A is polyvinyl alcohol with a low degree of alcoholysis, and contains a small amount of auxiliary substances for improving its physical, mechanical, and water-soluble properties. Starch is commonly used. Adding some auxiliaries in the film-forming process, such as surfactants, plasticizers, anti-sticking agents, etc., under certain process conditions, a water-soluble P V A film is obtained.
1) Water-soluble P V A film has many excellent features:
Excellent water-soluble water transfer requires higher water temperature, the higher the water temperature, the faster the film activation speed, but too high water temperature is easy to form wrinkles on the film surface, causing damage to graphics; too low water temperature, water on the base The solubility of the material film is reduced again. Therefore, the water temperature of the water transfer is generally maintained at 30 ° C to 40 ° C. Water-soluble P V A film still maintains good water solubility at low water temperature, fast water-dissolving speed, less residue after dissolution, fully meet the requirements of water-coated film.
It has excellent printing properties. There is a group of hydroxyl groups in the molecular chain of polyvinyl alcohol. The film surface can be printed without special treatment, and it can reproduce clear graphics with ordinary printing methods.
Environmental protection, safety, and degradation. Because its film-forming components (including added auxiliaries) are all C, H, and O compounds, the final products of degradation are CO₂ and H₂O, which will not cause harm to the environment.
Excellent mechanical properties, good toughness, large tensile strength, tear resistance, flex resistance and weather resistance.
Compared with other plastic films, it has good antistatic properties.
Resistance has good oil resistance, fat resistance, organic solvent and carbohydrate resistance, but it is not resistant to strong acids, strong bases, ammonia free radicals and other substances that can react with PVA.
The permeability has strong permeability to moisture and ammonia gas, but has good barrier properties to oxygen, nitrogen, hydrogen and carbon dioxide. Water-soluble P V A’s excellent water solubility, printing properties and mechanical properties meet the requirements of water-coated films, while full degradability ensures that the water transfer conforms to the trend of green printing.
2) Application and development The excellent properties of water-soluble P V A film not only make it play a role in water coating transfer, but also have obtained certain applications in agriculture, medicine, daily life and other aspects. For example, it can be used for packaging products such as pigments, dyes, detergents, water treatment agents, etc. to be used in water; packaging powder, chemical fertilizers, chemical products that are not suitable for human contact; packaging seeds, agricultural seedlings and other agricultural products; , Oral ulcer film, hand washing film and other carrier film materials.
Market application Water transfer transfers the pattern to the surface of the substrate by using a special carrier and water as the medium. Therefore, its production process and material cost are higher than ordinary printing, and the production process is more complicated, but it is a more versatile one. Kinds of printing. This is not only because it can achieve printing effects that cannot be achieved by other printing processes, but more importantly, it has relatively low requirements on the shape of the substrate, whether it is flat, curved, prismatic, or concave, etc., it can meet. For example, daily necessities and decorative materials for home use can break the restrictions of other special printing on the shape (large, small, irregular, etc.) of the substrate. Therefore, its application range is very wide. From the perspective of raw materials, water transfer printing is suitable for materials with smooth surfaces such as glass, ceramics, hardware, wood, plastic, leather, and marble. Water transfer does not require pressure and heating during the transfer process, so it is the preferred process for some ultra-thin materials that are not resistant to high temperatures and pressure.
2. The market prospect is unlimited Although there are many problems in the water transfer market, its market potential is very huge.
With the continuous development of the economy, consumers have higher and higher requirements for product packaging, painting and grade. For the printing industry, the concept of printing is no longer the traditional paper printing in people’s impression. From daily necessities to office appliances, and even home improvement and the automotive industry, more, better and more practical surface packaging is required. Most of this packaging is achieved by transfer printing. Therefore, there is still a long way to go after water transfer, and the application range will become wider and wider, and the market prospect is unlimited. In terms of market chaos, small scale, low technology content, and poor quality, the industry still needs unremitting efforts to catch up with the international market.