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cool guy |
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2007-02-28 오후 1:24:14 |
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hdgolove@hotmail.com |
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스크린 인쇄에 영향을 주는 frame, mesh, squeegee등에 대한 개략적인 설명입니다. 가벼운 맘으로 읽어봅시다.
coolguy~
Screen printing.
Screen printing is a technology, where the print material is pressed by a squeegee through a mesh that is fixed on a frame. The mesh carries a photoresist layer with openings defining the pattern to be printed.
Screen frame.
The screen frame is the most fundamental element of the screen-printing process. The function of the screen frame is to providing a means for mounting the mesh, withstanding the force of the tensioned mesh, standing up to additional forces applied during printing, remaining flat and square and being light enough to handle easily.
Once tension is applied to the mesh and the mesh is affixed to the frame, the flatness of the frame becomes critical. The frame's job is to resist the forces of that tension. A suitable frame will remain flat and square for the time of use. Among other things, distortion of the frame causes mesh threads to follow the same, curved direction as the beams, resulting in mesh distortion at the edges of the screen. This drastically reduces the screen's "sweet spot" or maximum print area. It also leads to tension inconsistencies that further complicate your ability to achieve good registration from color to color.
For applications in LCD manufacturing and in the electronic industry the screens are made from massive aluminum alloys in order to achieve the required high printing precision. For other applications aluminum pipe screen frames are available.
The size of the screen frame is important for the max. resolution of the print. The image-to-frame ratio is critical for avoiding image distortion. This term refers to the size of the image area relative to the total screen area, which is usually represented by the frame's inside dimensions. The less a screen is deflected during the print stroke, the lower is the force against the mesh and the lower the possibility of distorting the printed image. Squeegee length and stroke length also figures into the relationship between image size and total mesh area.
For printing seals on glass plates only 25-35% of the screen sizes are used for the image.
Mesh.
Mesh selection is a series of compromises. A coarse mesh will allow the printing material to pass through the screen easily. This will result in thick layers, fast prints and low resolution. A fine mesh will create difficulties in printing a bright design on dark-colored substrates and it is difficult to press viscose material through the screen. However you can achieve very good resolution using fine mesh screens. This is the most important point in LCD manufacturing, where silk screens are used for printing. High resolution silk screens have more than 330 meshes per inch, enabling them to print lines with a width down to 50µm. The layer thickness is in the range of 10µm normally, which is regarded as a "thick" layer in LCD manufacturing.
For creating the image, the mesh is coated by a photosensitive emulsion, which is exposed using a mask, made from a glass or polymer film. The unexposed portion of the coating is washed off afterward. This portion let the seal material go through and you have its pattern on the substrate.
Squeegee.
The squeegee plays a major role in screen printing. It has four functions that influence or are influenced by any number of processing variables:
1. Forcing the print material into the mesh - influenced by mesh opening size and viscosity.
2. Keeping the mesh in contact with the substrate - influenced by screen tension and off-contact distance
3. Adapting the mesh to the surface of the substrate - influenced by substrate hardness, roughness, and evenness.
4. Removing excess print material from the screen - influences thickness of the printed layer, as well as image definition
Squeegees for seal printing are made from a stiff material like hard polyurethane with a hardness of up to 80 duromete |
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