The most significant feature of pad printing is indirect printing. The biggest advantage of indirect printing is that it maintains the independence of the position of the printing plate and the substrate. The change in the shape of the pad of the printing pad that transfers the ink on the printing plate to the surface of the substrate causes the shift. India's adaptability to the shape of the substrate has greatly increased.
Now we will give a brief introduction of the printing process technology involved in the printing of glasses, so that we can understand the application of pad printing technology in the optical industry.
1, ink selection
Ink selection plays a very important role in pad printing technology, which is widely related to the printing materials involved in pad printing technology. Because the frames are made of metal, the adhesion of the ink to the metal surface is required to be better. Nowadays, two-component inks are generally used, and the drying mode is dry. Lens printing requires glass inks, glass inks are usually two-component inks, and the drying method is dry. The two-component ink cured ink layer has high hardness and good adhesion, but the operation is slightly more troublesome.
The usage of two-component inks is briefly described as follows:
First, according to the ink instructions, the hardener is added to the ink and mixed uniformly, and is poured into an oil pan for printing. Since the two-component ink slowly cures, control the dosage.
The printing should be placed in a drying oven for drying to speed up drying. Two-component inks generally have a drying time of up to 10 hours at room temperature, which can affect the production efficiency. The drying method is ideal. Usually, the drying temperature is between 150Â° C. and 180Â° C. and the time is 5 to 10 minutes. .
2. Printing plastic head
The choice of pad printing head in the pad printing process is crucial. First of all, the shape of the print head should be able to print to the specified position, and secondly, the deformation should be smaller. Because the printing area of â€‹â€‹the frame is very small, the printing head should be slightly sharper. Through testing, the A7 plastic head with a cross-sectional area of â€‹â€‹38 mm is suitable. The printing effect of the A3 rubber head is also very good, but due to the slightly smaller cross section, the printing distortion is slightly larger.
The hardness of the printing head is another indicator that should be taken into consideration when selecting the printing head. The flexibility of the rubber head is wider, but the printing text is greatly deformed. Especially for products that are as small as eyeglass frames, the graphic font is very small. The graphic distortion is very easy to make the graphic lines stick together and become blurred. Therefore, it is better to choose a stiffer plastic head. Our test The result is a plastic head with a Shore hardness of 32 degrees to achieve the best print quality.
The selection of the plastic head for the printing of the nose pads shall take into account the limitations of the position. A plastic head with a smaller cross-sectional area shall be selected. Our test result is that the plastic head with a cross-sectional area under 15 mm is more suitable and the hardness should be above 32 degrees.
3. Steel plate
The printing plate of the pad printing machine is a steel plate. The method of producing the steel plate is an etching method. The printing frames of the frame and the lens are very small, so the size of the steel plate does not need to be too large. In accordance with the printing industry standards, the use of 75mm Ã— l00mm and 100mm Ã— 100mm two kinds of steel plates can be, but the longest side of the image frames printed frame length is only 20mm, so the text can use 75mm Ã— 100mm steel plate.
The steel plate is manufactured using a conventional etching method. Due to the small size of the font and the short exposure time, a uniform steel plate can be obtained.
In the production of steel plates, depth control is a major indicator. Too deep depths can easily cause stencils, and the transfer of ink is affected, and the strokes of the fonts are likely to be uneven in thickness, the pitch between the strokes becomes smaller, and the sharpness decreases. The disadvantage of being too shallow is also obvious. This is because the color saturation of the font is not high and the color is difficult to achieve eye-catching effects. Our test results are ideal for depth control at 19 Î¼m.
4. Printing machine
The frame of the spectacle frame has a small printing area and is only a trademark of a printing company. Therefore, it does not involve complicated graphics or color registration, and a small-area pad printer with a single color should be selected as the machine.
In the special printing industry, making jigs is a basic job. In general, the production jig is mainly to ensure that the printing area of â€‹â€‹the substrate and the plastic head have relatively fixed positions, so as to ensure the unity of the printing of the product. At the same time, it is easy to realize overprinting when multi-color overprinting is involved, so the position of the fixture in the pad printing process is indispensable. The inner edge of the spectacle frame is the area for printing images, and this position must be clamped by the clamp to ensure parallel with the print head. During the printing process, the spectacle frame cannot be loosened, and the fastening effect is required. The use of crystal glue cast fixtures should be preferred.
The method of casting the crystal glue is based on the principle that the unsaturated polyester resin solidifies under the action of the hardener, and it is very easy to cure according to the shape of the product. No matter how complicated the structure of the spectacle frame is, the jig produced by this method can fix the spectacle frame well and meet the printing requirements. The production method is: First, the resin A component and the B component are mixed and mixed uniformly into a previously prepared paper type until the resin is in a gelled state, and the spectacle frame can be removed.
Although the printing of frames and lenses is a very simple process, it can be seen from this that the characteristics of the printing process are:
Pad printing is very suitable for products with small printing area and irregular printing position; it is the specific parts of the optical products that need to be printed that make the printing process wonderfully applicable.
From the point of view of the printing process, in order to achieve an exquisite printing effect, the selection of a high-quality printing ink and a relatively high hardness printing head are two factors that must be considered.
The printing effect is inextricably linked with the fixture quality.