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Introduction to the working principle of the water transfer printing process

The water transfer printing process is a kind of printing that uses water as the dissolving medium to transfer the image and text to the transfer paper and transfer film with color patterns.
the water transfer printing process

With the improvement of people’s requirements for product packaging and decoration, the use of water transfer printing is becoming more and more extensive. The principle of indirect printing and the perfect printing effect solve many problems of surface decoration of special-shaped products and are mainly used for the transfer of graphics and texts on the surface of products with complex shapes.

Appreciation of water transfer product cases:

Introduction to the working principle of the water transfer printing process

Process features:

The principle of water transfer indirect printing and the perfect printing effect solve many problems of product surface decoration, and it is mainly used for image and text transfer on the surface of products with complex shapes.

Main raw material selection:

When selecting the raw materials for water transfer printing for different effects and surface properties, there are different processing methods according to the different materials of the workpiece and the color of the workpiece corresponding to the color after the transfer is completed.

Common equipment for the water transfer printing process:

Film coating equipment, washing equipment, drying equipment, spraying equipment.

Process details of each step:

The following introduces the detailed operation and precautions of the water transfer process section.

1. Primer: decontamination, degreasing, rust removal, impurity removal or flame treatment according to the material of the workpiece to be transferred;

2. Drying: choose the appropriate temperature to dry the primer according to the nature of the primer;

3. Film selection: select the pre-transfer pattern or customize it according to the solution provided by the customer;

4. Set the film: cut the film paper of the same size as the workpiece to be transferred, and lay it flat on the water surface (the printing side is facing down);

5. Activation: When the film paper sits on the water surface for 60-90 seconds, spray the activator evenly on the film paper. Lay the water transfer film flat on the water surface of the transfer water tank, with the graphic layer facing up, keep the water in the water tank clean and basically in a neutral state. Spray evenly on the graphic surface with an activator to activate the graphic layer and make it easy to separate from the carrier film. The activator is an organic mixed solvent mainly composed of aromatic hydrocarbons, which can quickly dissolve and destroy polyvinyl alcohol but will not damage the graphic layer and keep the graphic and text in a free state.

6. Transfer printing: about 5-10 seconds after spraying the activator, keep the belt transfer workpiece at a 35-degree angle to align the film paper from top to bottom and press down at an even speed. The items that need water transfer are gradually approached to the water transfer film along their outline, and the graphic layer will be slowly transferred to the surface of the product under the action of water pressure. Due to the inherent adhesion between the ink layer and the printing material or special coating produce adhesion. During the transfer process, the lamination speed of the substrate and the water-coated film should be kept uniform to avoid the wrinkle of the film and the unsightly images and texts. In principle, it should be ensured that the graphics and texts are properly stretched, and overlapping should be avoided as much as possible, especially at the junction. Too much overlap will give people a cluttered feeling. The more complex the product, the higher the operational requirements.

Water temperature is an important parameter that affects transfer quality.

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 cause damage to the graphics and texts, causing graphics and texts to be deformed. The transfer water tank can use an automatic temperature control device to control the water temperature within 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 are fixed on the rotating shaft and rotated on the surface of the film to transfer the graphic layer.

7. Soak: soak the transfer workpiece for about 30 seconds, so that the ink can be more stably attached to the workpiece;

8. Rinse: Take the workpiece out of the water tank, remove the residual film, and then wash off the floating layer that is not fixed on the surface of the product with clean water. Note that the water pressure should not be too large, otherwise it will easily cause damage to the transferred graphics.

9. Drying: Remove the moisture on the surface of the product to facilitate the complete drying of the transfer ink and increase the adhesion fastness. It can be dried with a hairdryer, or the product can be dried in a drying box. The drying temperature of plastic products should not be too high, about 50 to 60 °C. If the temperature is too high, the substrate may be deformed; the drying temperature of metal, glass, ceramics, and other materials can be appropriately increased.

10. Topcoat treatment: In order to enhance the resistance of the graphic layer to the environment, the surface should be sprayed. For spray paint, solvent-based varnish can be used, which can be dried naturally or heated after spraying; UV varnish can also be used, which is cured and dried by ultraviolet rays. In contrast, UV curing is more suitable for environmental protection requirements. Solvent-based varnish needs to be mixed with supporting hardener. For example, the water transfer printing varnish produced by a certain manufacturer is a varnish with polyurethane resin as the binder, which should be used with polyurethane PU hardener; the thickness of the coating can be passed through Add an appropriate amount of diluent to improve the viscosity of the varnish to control; be careful not to dry in the oven. For different printing materials, spray varnish is also divided into three types, namely varnish suitable for plastic materials, varnish suitable for flexible materials, and varnish suitable for non-absorbent materials such as metal and glass.

Watermark transfer process

A clean substrate surface is a must for high-quality transfer, and this is the same for any printing process. Make sure the substrate is completely exposed before transfer. In addition, a clean and tidy working environment is conducive to the close adhesion of the transfer ink layer to the surface of the substrate, and the dust floating in the air is most likely to affect the transfer effect.

Watermark transfer paper activation

Watermark transfer paper is divided into peelable watermark transfer paper and dissolving watermark transfer paper.

The image and text of the peelable watermark transfer paper can be separated from the substrate after activation to achieve transfer; after the dissolving watermark transfer paper is activated, the substrate dissolves in water, and the image and text are in a free state to achieve transfer.

The activation of the watermark transfer paper is different from the activation of the water-coated transfer film. It just immerses the transfer paper in water to separate the image and text from the substrate without a special solvent. As shown in the figure below, the process is simpler.

The specific process of watermark transfer paper activation: first cut the graphic water transfer paper that needs to be transferred into the required specifications, put it in a clean water tank, and soak it for about 20 seconds to separate the mask from the substrate, and prepare for the transfer. ready.

Watermark transfer paper processing: The process is shown in the figure below, 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 and text at the specified position, and carry out natural dry.

For peelable watermark transfer paper, dry it naturally and then put it in an oven to dry to improve the adhesion fastness of the image and text. The drying temperature is about 100 °C. Because there is a layer of protective varnish on the surface of the peelable watermark transfer paper, there is no need for spray protection. However, there is no protective layer on the surface of the soluble watermark transfer paper. It needs to be sprayed with varnish after natural drying, and the UV varnish should be cured with a curing machine.

When spraying varnish, you must pay attention 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 and spraying the amount of the varnish. Too much spraying will easily cause the uniformity to drop. For substrates with a large transfer area, using screen printing for glazing can obtain a thicker coating, which is also a very effective protection measure.

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