Drum screen printing process problems and solutions three

(2) Stretching of the device The stretched net of the device is also called self-expanding net. This kind of stretch net method uses more simple equipment to assist manual stretch nets, and its net frame is called self-tension net frame. This kind of frame is mostly made of metal. Its outstanding feature is that it can be pulled at any time. After the stencil is loose, it does not have to be replaced and it can be used again. In recent years, roll-type self-expanding nets have been successfully used for precision printing, and the market has expanded rapidly. Among them, the rolling frame has the best performance. It is composed of four aluminum tubes. The tube has a simple fastening device that clamps the screen. The two ends of each frame tube can be twisted with a wrench to complete the stretching.

(3) Motorized stretch net The motorized stretch net uses a mechanical stretcher. The mechanical stretcher has a buckle type, a screw type and a gear type. Large-scale stretch nets are generally motorized, while medium- and small-size stretch nets are mainly manual.

The biggest feature of the manual mechanical stretching machine is that it does not require electricity and gas. The quality of the stretching net is significantly higher than that of manual stretching, and it is close to the quality of the pneumatic stretching net.

(4) Pneumatic stretching net Pneumatic stretching machine uses compressed air as the air source to drive multiple cylinder pistons to synchronously push the net clamps to perform relative contraction movements in both vertical and horizontal directions, which produces uniform and consistent tension on the screen. Generally, the net pressure of the nylon mesh can be controlled at 0.8-1.0 MPa; the stretch net pressure of the polyester mesh can be controlled at 0.8-1.0 MPa; and the stretch net pressure of the stainless steel mesh can be controlled at 1.0-1.3 MPa.

When using the pneumatic stretching method, the net frame is first placed on the stretch net, and then the net is fixed horizontally on the net frame and the net is fixed on the chuck. Tension is applied according to the required tension, and the adhesive is applied on the contact surface of the frame and the screen. This method gives uniform tension.

3, the fixed screen

There are two methods for fixing the screen to the frame, namely the clamping method and the bonding method.

(1) Clamping method Clamping method is to clamp the screen between two objects and fix it with friction. The fixing method of the screen is not easy to loosen, but the tension of the stretching net is not easy to control, and the manual stretching net is commonly used.

(2) Bonding method The bonding method uses an adhesive to fix the screen. The screen tension of this fixing method is easy to control, but after a period of use, the screen will loosen. Commonly used adhesives are the following.

1 photosensitive adhesive

The photosensitive adhesive formulation is as follows: epoxy phenolic methacrylic resin 300 mL; benzoin butyl ether 10 ~ 12 mL; anhydrous ethanol 150 mL.

How to use: Apply the adhesive on the adhesive surface of the mesh frame so that the taut mesh adheres tightly to the adhesive surface. Apply a layer of adhesive to the joint between the mesh and the mesh frame. After being coated, it is cured with ultraviolet rays, that is, irradiated with a 1000W ultraviolet high-pressure mercury lamp at a distance of 500 mm for 5 to 8 minutes while cooling with a fan.

2 Polyvinyl acetal glue Diluted 4 parts of JSF-4 glue with 1 part absolute ethanol, brush on the adhesive surface of the mesh frame, tightly touch the tight mesh and then brush once, dry naturally or use infrared rays. dry. This adhesive is often used for the bonding of wooden net frames and metal net frame stretch nets.

3 Shellac The solution of shellac was prepared by dissolving 1 part of insect film in 3 parts of anhydrous ethanol. In order to facilitate the bonding, the surface of the frame can be pre-coated with shellac, dried and used. When sticking the net, a sufficient amount of absolute ethanol is directly applied on the screen of the adhesive layer to dissolve the shellac. After being dried, it can be used.

In addition, there are phenolic-neoprene, nitrile rubber, nitrile rubber, nitrocellulose gum, vinyl chloride rubber and so on.

It is usually purchased from the market. The commonly used imported adhesive nets are Japanese-made W-18 and Italian-made UG-3 adhesive, which makes the operation very easy. The tension of the stretch net is easy to control, and the net and frame are sticky. Firmly.