Introduction: With the continuous improvement of consumers’ consumption concepts, tailor-made personalized products are increasingly favored by consumers. Water transfer technology breaks through the uneven surface limitation that cannot be printed by flat printing. After water transfer printing, the product has a high degree of simulation, and its product addition is doubled. The personalized transfer printing also fully meets the consumer needs of modern people. This article shares the relevant knowledge of water transfer printing, the content is for the reference of friends:


Water transfer

Water transfer printing technology is a kind of printing that uses water pressure to hydrolyze the transfer paper/plastic film with color patterns. Its biggest technical advantage is that it does not require special equipment, is not restricted by media, does not require special consumables, and does not require high temperature heating, as long as there is an image input tool (scanner or digital camera), drawing tool (computer), image output tool (Inkjet printer), plus water transfer ink, water transfer paper, you can print any image on any solid object and any curved surface.


According to the characteristics of transfer, it is divided into water mark transfer and water coating transfer

Watermark transfer

Water mark transfer is a process of completely transferring the graphics and text on the transfer paper to the surface of the substrate. It is very similar to the heat transfer process, except that the transfer pressure depends on water pressure. It is a popular water transfer technology recently. A small area of ​​graphic information can be transferred on the surface of the substrate, which is similar to the printing effect of the pad printing process, but the investment cost is lower, the production process is relatively simple, and it is very popular with users. The water mark transfer process does not require activation by an activator, avoids the pollution of organic solvents, and has obvious advantages in the production of handicrafts and decorations.

Water coating transfer

The so-called water coating transfer is to decorate the entire surface of the object, cover the original face of the workpiece, and be able to print patterns on the entire surface of the object (three-dimensional). This is its advantage; but the disadvantage is also obvious, that is, flexibility. When the graphic carrier is completely in contact with the substrate, it is inevitable that it will be stretched and deformed. Therefore, in fact, it is difficult for the graphic to be transferred to the surface of the object to be realistic.

Most of the printed graphics and texts of water transfer paper used for transfer are composed of decorative ink color blocks and simple repeating patterns. There is no need to use fine photosensitive film for printing; water transfer films are mostly made of stretchable It is made of a good water-soluble film. The transfer film used for three-dimensional transfer is difficult to transfer and copy fine text and hierarchical images.

Transfer material
Water transfer substrate
The water transfer substrate can be a plastic film or water transfer paper. Many products are difficult to print directly. You can first print the graphics and text on the water transfer substrate through mature printing technology, and then transfer the graphics to the substrate. Material.

1) Three-dimensional curved surface water drape film
The water drape film is printed on the surface of the water-soluble polyvinyl alcohol film using a traditional gravure printing process. It has a very high stretch rate and is easy to cover the surface of the object to achieve three-dimensional transfer. The disadvantage is that in the coating process, the graphics and text are easily deformed due to the large flexibility of the substrate. For this reason, pictures and texts are generally designed as continuous patterns, even if the transfer is deformed, it will not affect the viewing effect. At the same time, the gravure water coating film uses water transfer ink. Compared with traditional inks, water transfer printing inks have good water resistance, and the drying method is volatile drying.

2) Water mark transfer paper
The base material of water-mark transfer paper is special paper. The base material must have stable quality, accurate size, strong adaptability to the printing environment, very small expansion rate, not easy to curl and deform, easy to print color, uniform surface adhesive layer coating, Features such as fast dehydration speed. Structurally, there is not much difference between water transfer paper and water coating transfer film, but the production process is very different. Generally speaking, watermark transfer paper is used to produce transfer graphics and text on the surface of the substrate by screen printing or offset printing. The most popular production method is to use inkjet printers to make watermark transfer paper. It is easy to make personalized graphics and texts according to your own preferences.

The activator is an organic mixed solvent that can quickly dissolve and destroy the polyvinyl alcohol film, but will not damage the graphic printing layer. After the activator acts on the graphic printing layer, it can activate and separate it from the polyvinyl alcohol film. Adsorbed on the surface of the substrate to achieve water transfer coating.

Because the printed layer of the water-coated film has low hardness and is easy to scratch, the workpiece after the water-coated transfer must be sprayed with transparent paint to protect it, thereby further improving the decorative effect. Use PV transparent varnish or UV light curing transparent varnish coating to form a matte or mirror effect.

Substrate material

Picture from Baidu picture
Water transfer printing is suitable for most materials in daily life, such as plastic, metal, glass, ceramics, and wood. According to whether coating is required, substrate materials can be divided into the following two categories.
1) Materials that are easy to transfer (materials that do not require coating)
Some materials in plastics have good printing performance, such as: ABS, plexiglass, polycarbonate (PC), PET and other materials, which can be transferred without coating. This is similar to the principle of printing. In the plastic family, PS is a material that is more difficult to complete water coating transfer because it is easily corroded by solvents, and the active ingredients of the activator can easily cause serious damage to PS, so the transfer effect is relatively poor. However, water transfer printing on modified PS materials should be paid more attention.

2) Materials to be coated
Non-absorbent materials such as glass, metal, ceramics, non-polar materials such as polyethylene, polypropylene, and certain polyvinyl chloride materials require special coatings for coating transfer. Coatings are all kinds of paints that have good adhesion to special materials, and can be screen printed, sprayed, or rolled. From a printing point of view, coating technology has realized the possibility of surface decoration for many printed materials. Many popular transfer processes, such as sublimation transfer, hot melt transfer, ceramic decal transfer, pressure-sensitive transfer, etc., do not require coating technology for transfer on these materials.

Transfer technology
①Water coating transfer
Water drape transfer printing refers to decorating the entire surface of an object, covering the original face of the workpiece, and capable of pattern printing on the entire surface (three-dimensional) of the object.

Film activation
Spread the water-coated transfer film flat on the water surface of the transfer tank, with the graphic layer facing up, to keep the water in the tank clean and basically in a neutral state, spray evenly on the graphic surface with an activator to make the graphic The layer is activated and is easily separated from the carrier film. The activator is an organic mixed solvent mainly composed of aromatic hydrocarbons, which can quickly dissolve and destroy the polyvinyl alcohol, but will not damage the graphic layer, leaving the graphic in a free state.

Transfer process
The article that needs water transfer is gradually approached to the water transfer film along its contour. The image and text layer will slowly transfer to the product surface under the action of water pressure, due to the inherent adhesion of the ink layer and the printing material or special coating And produce adhesion. During the transfer process, the lamination speed of the substrate and the water-coated film should be kept uniform to avoid film wrinkles and unsightly graphics. In principle, you should ensure that the graphics and text are properly stretched, and try to avoid overlapping, especially in the joints. Too much overlap will give people a cluttered feeling. The more complex the product, the higher the operational requirements.

Influencing factors
If the water temperature is too low, the solubility of the substrate film may decrease; if the water temperature is too high, it is easy to damage the graphics and text, causing the graphics and text to be deformed. The transfer water tank can adopt an automatic temperature control device to control the water temperature in a stable range. For large-scale workpieces with relatively simple and uniform shapes, special water transfer equipment can also be used instead of manual operations, such as cylindrical workpieces, which can be fixed on a rotating shaft and rotated on the surface of the film to transfer the image and text layer.

②Watermark printing
Watermark printing is a process of completely transferring the graphics and text on the transfer paper to the surface of the substrate. It is very similar to the thermal transfer process, except that the transfer pressure depends on water pressure, which is a popular water transfer technology recently.

Transfer process
First cut the graphic water transfer paper to be transferred to the required specifications, put it in a clean water tank, and soak for about 20 seconds to separate the mask from the substrate and prepare for the transfer.

Watermark transfer paper processing process: Take out the water transfer paper and gently close it to the surface of the substrate, scrape the graphic surface with a scraper to squeeze out the water, keep the graphic flat on the specified position, and dry it naturally. For peelable water mark transfer paper, dry it naturally and then dry it in an oven to improve the adhesion fastness of graphics and text. The drying temperature is 65-100 degrees. Because there is a layer of protective varnish on the surface of the peelable water mark transfer paper, there is no need to spray protection. However, there is no protective layer on the graphic surface of soluble water mark transfer paper. It needs to be sprayed with varnish after natural drying, and sprayed with UV varnish to be cured with a curing machine. When spraying varnish, be sure to prevent dust from falling on the surface, otherwise the appearance of the product will be greatly affected. The control of the coating thickness is achieved by adjusting the viscosity of the varnish and the amount of spraying. Too much spraying can easily cause the uniformity to decrease. For substrates with a large transfer area, screen printing is used for glazing to obtain a thicker coating, which is also a very effective protection measure.

Test items
Side A:
Area ≧0.5mm (white spots/black spots are not allowed;
Particles below 0.1mm² do not significantly affect the appearance OK;
0.1mm²≦area≦0.5mm² The entire A side does not exceed 3 particles, and the distance between the two particles is greater than 6cm.

Side B:
No particles with area ≧0.7mm²;
Below 0.2mm² is OK;
0.2mm²≦area≦0.7mm² is not allowed to exceed 3.

② oil point
Side A:
0.1≦area≦0.5mm² no more than 2, and between two points ≧5cm
The oil point below 0.1mm² does not significantly affect the appearance.

Side B:
0.2≦area≦0.7mm² can not exceed 2;
The oil point is below 0.2mm² and does not significantly affect the appearance.

③Common appearance problems
Pattern: complete and clear pattern
Color point: No color point that obviously affects the appearance
Foreign matter: foreign matter that obviously affects the appearance must not be present
Flowing oil: obvious flow oil is not allowed
Scratches: no obvious scratches
Chromatic aberration: no obvious chromatic aberration (compared with the model)
Fracture: paint cracks are not allowed
Hemp noodles: Obviously pitted noodles are not allowed
Deformation: No deformation

④Appearance standard:
1) Classification standard
Class A surface: The outer surface that is often seen after assembly. The top surface can be seen by ordinary people and the surface can be seen without bending over.

Class B surface: A surface that is not often seen, but can be seen under certain conditions. Such as side, bottom, etc.

2) Inspection conditions
A. Light source requirements: Arctic daylight or indoor high-efficiency fluorescent lamps (illumination is about 1000 lumens).

B visual distance: 300mm for class A surface, 500mm for class B surface.

The inspection standard distinguishes the grade surface of the product according to the requirements of the light source standard. All grade surface coating films should be free of defects such as base material exposure and peeling, and all surfaces should be free of scratches, blisters, wrinkles, pinholes, powder accumulation and other defects. Scan and check at 3cm/s speed at the standard of the eye distance grade plane.

⑤ Performance standards:
1) Non-destructive inspection item gloss: Use a gloss meter to judge, the incident angle is 60°, and the error of ±5% is qualified. Color: The color must be in accordance with the design drawing and there is no obvious difference between the color plate.

2) Destructive inspection.

3) Adhesion test: One-hundred grid test method: After spraying, take a color plate and mark 11 horizontally and horizontally at intervals of 1mm on the surface of the coating film, and draw on the sprayed surface with appropriate strength (the scratches are subject to the exposed substrate) Make 100 squares, then cover with 3M tape and press tightly at a 45° angle, and then pull it off at a speed of 100mm/min. At this time, check whether the contents of the squares have fallen off. The acceptance standard is 0~1, which means it falls off. An area of ​​no more than 5% is qualified.

4) Hardness inspection

Use a sharpened HB pencil to fix it in the middle of the horizontal trolley at an angle of 45° to the surface of the coating film. Push it forward along a straight line for 15~30mm, wipe off the scratches with a rubber, and check the surface of the coating film. The judgment standard is: qualified when no scratches are revealed.

5) Solvent resistance test
Moisten a cotton swab with analytical alcohol (99.8% anhydrous alcohol), and wipe the film surface 50 times with 1 kg of force. The eligibility standard is: the outer film must not have any peeling, discoloration, or swelling, and gloss can be allowed. A little change.

6) Impact resistance test
Using the test equipment, use a 500g heavy hammer to freely fall from a height of 500mm. After the punch with a judgment standard of 1/4 is impacted by the front, the surface coating film has no cracking or film falling.