The characteristics of 3D printing are: the pattern printed on the fabric has a captivating 3D effect, and is resistant to washing and friction.
The printing method, process, and equipment used in 3D printing are similar to general pigment printing, with the main difference being the presence of microcapsule preparations or foaming agents in the printing ink. Therefore, during post press heat treatment, the pattern can quickly expand and bulge, forming a gorgeous 3D shape. There are various types of 3D printing, among which velvet printing and foam printing are very famous. The foaming technology and the three-dimensional pattern formed by the two are completely different. Under a microscope, the surface of the velvet print is piled with countless tiny soap bubble like spherical shapes, while the foam print appears honeycomb shaped. Therefore, velvet printed products have a unique velvet embroidery effect, while foam printed products have a vivid relief effect.
The printing ink used for velvet printing is composed of microcapsule preparations, adhesives, crosslinking agents, urea, coatings, thickeners, or water. Microcapsules are small hollow spheres with a particle size of about 50/um, and the capsule wall is composed of a copolymer of vinyl chloride and acrylonitrile (about 2:1), while the core contains low boiling organic solvents such as petroleum ether. Microcapsules are dispersed in emulsions such as poly (methyl methacrylate). The above-mentioned solvents rapidly vaporize at high temperatures, just like blowing soap bubbles, causing the volume of microcapsules to expand, and the enlarged microcapsules are squeezed together, forming an overlapping distribution like fluff. Therefore, this foaming method belongs to physical foaming.
Generally, lotion based on butyl polyacrylate, or acrylate butyl acrylate copolymer, or methyl methacrylate, methyl acrylate and acrylamide copolymer lotion are used as the binder for raising printing. To improve the rigidity of three-dimensional printing patterns, ethyl acrylate and styrene copolymer lotion can be used. If necessary, crosslinking agents can also be added. The amount of coating should not be too much, otherwise, the coating accumulated between the microcapsules after puffing will have a negative impact on the pilling sensation.
Flat screen printing with a mesh size between 27.6-35.4 mesh/cm (70-90 mesh) is most suitable for velvet printing. After printing, dry at around 70 ℃ and heat treat with heat sources such as hot air, hot plate, hot roller, or infrared lamp at 100-140 ℃ for 30-60 seconds. The best effect is achieved by blowing the fabric printing surface with hot air. To prevent hindering expansion, it is advisable to use the back of the fabric in contact with the heat source when foaming with a hot plate or hot roller. The drawback of velvet printed fabrics is that they cannot be ironed after washing, otherwise the microcapsules will disappear and the velvet texture will disappear. This type of fabric is also prone to contamination. The remedy is to add a coating agent.
Foam printing agent is a mixture of a foaming agent, appropriate film-forming agent, crosslinking agent, emulsion paste, and coloring agent, printed on fabric. After printing, during high-temperature treatment, the foaming agent undergoes thermal decomposition, producing a large amount of gas that causes the film-forming agent to slightly expand and form a film. The gas released by the foaming agent is contained in the film, forming innovative three-dimensional patterns. This type of foam printing belongs to chemical foaming.
The commonly used foaming agent is called azodicarbonamide. It is a light yellow crystalline powder that is insoluble in water. 64% of its decomposition products are solids and 36% are gases, which are composed of nitrogen, carbon monoxide, and carbon dioxide. Adding urea, depending on the amount of urea used, can lower the decomposition temperature of azodicarbonamide from around 200 ° C to around 180 ° C or even 150 ° C. Azobisisobutyronitrile is a white crystal that is insoluble in water and can also be used as a foaming agent. Its decomposition temperature is only 90-115 ℃. However, its application is limited due to the presence of toxic tetramethylbutanedinitrile in its decomposition products. Foaming printing paste is generally composed of polystyrene, methyl methacrylate, butyl acrylate and acrylamide copolymer lotion, azodicarbonamide, urea, surfactant, thickening agent or water and colorant. Among them, polystyrene (or polyvinyl chloride) is a film-forming material, but it has poor adhesion to fabrics, so it needs to rely on the synergistic effect of acrylic copolymers.
Printed on a cold plate. According to the size of the pattern, nylon mesh sizes 11-14 are used for the sieve. After printing, dry with hot air at around 80 ℃. The foaming conditions should be around 180-185 ℃ and loose. The disadvantage of foam printed fabrics is that they are prone to dirt and sticky, making them suitable for small area use.
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