Second, the maintenance and preservation of squeegee
Correct maintenance is the key to ensure the quality of the squeegee and the print quality, so the following points should be noted.
(1) When using aggressive inks, such as UV inks, the use time of each side of the scraper should not exceed 4 hours. Rotating the doctor blade will have an unexpected effect on extending the life of the squeegee. Squeegee is as tiring as car tires. If you replace it every 5,000 or 4 hours, the squeegee will not bend or swell. Moreover, if the squeegee is used all the time until it is discarded, it will not be frequently exchanged, which will cause a lot of trouble for the squeegee to be reground.
Once the ink has blocked the mesh, the squeegee must be replaced. The general used squeegee is to restore the original physical properties after 24 to 48 hours before it can be ground or used on the machine.
(2) The blade must be laid flat when not in use. Blades using polyurethane should be stored in a dry and cold environment (23 to 27 °C). The purpose of flat placement is not to bend and deform the squeegee. Manufacturers and suppliers roll it into rolls for transportation convenience, but the finished products are best kept flat in the factory, and to maintain their stability, they should be stored in warehouses below 23°C. This will not affect the performance of the squeegee, but the storage time is too long will affect the ability of the squeegee ink, it is best to use the hardness tester to measure the hardness value of the squeegee from time to time in the production process. Some squeegee materials will become soft due to prolonged exposure to the air. If the squeegee becomes softer than 5% to 7% of the normal hardness, it is recommended that the squeegee be replaced.
(3) Select a suitable squeegee grinding method and control the amount of grinding. After the scraper is worn out, it can be restored to its accuracy by grinding. The tools for the squeegee grinding include belt sander, grinding wheel, diamond target, hot knife, cold knife and rotary knife. Each squeegee should be tested before grinding to find a suitable method. For example, polyurethane materials have good elasticity, some materials have good abrasion resistance, and some have low abrasion resistance and are easy to cut. The best evaluation method is to let the equipment manufacturers take out the grinding samples for identification. At present, there are many methods for squeegee grinding on the market, which can be considered from several aspects, such as reusability, cost, and robustness. Of course, the most reliable inspection method is printing on the machine.
In order to not affect the printing quality, many companies will design some programs to specify the amount of grinding. When the 3/8 inch by 2 inch (thickness x width) scraper is specified in the process standard, the height after grinding should be maintained at 1.6 to 1.75 inches. However, unlike the printed products, the requirements for the height of the squeegee are not the same. For example, different heights of squeegees are used for printing T-shirts, and the same height squeegee must be used for printed circuit boards and CD printing. The length of the scraper determines the degree of bending of the scraper during printing, and also affects the amount of ink. Therefore, the appropriate scraper height should be determined by the amount of ink under the actual application.
Third, squeegee new products
The biggest innovation in the past 15 years has been the advancement of synthetic squeegee technology, that is, the emergence of a variety of hardness scraper. Many scraper products on the market contain synthetic glass fibers and are composed of multiple layers of materials. The presence of these products has led to improved print quality.
1. Multiple hardness
During printing, the operator increases the amount of ink by increasing the blade pressure, but this can cause the blade to buckle. However, as shown in FIG. 2, by using a dual durometer stacked, dual durometer vertical, dual durometer vertical, and triple durometer. A fiberglass composite squeegee, as shown in Fig. 3, allows the printer to achieve a more desirable printing effect without deforming the blade.
The emergence of dual hardness blades is a leap forward in the squeegee technology. It is through the increase of the hardness of the soft material, making the contact between the squeegee and the screen when the printing is soft and the supporting material is rigid, greatly improving the printing effect. However, the double-hardness scraper has a great weakness, that is, the scraper can only be used for flat printing. The triple hardness blade has now replaced the double hardness blade, in which the interlayer hardness is higher than both sides and both sides can be used for printing.
2. Height control
The determination of the blade height is more important than the hardness. The height determination mainly refers to the distance from the printing edge of the doctor blade to the doctor blade holder. If the customer's chromatic aberration of the image is very demanding, controlling the blade height is the most important, as shown in Figure 4.
3. Price factors
All innovations will result in price changes due to rising costs. Synthetic glass fiber scraping materials are expensive, and sometimes they cannot be reground. In fact, there is no equipment for splicing synthetic glass fiber scrapers on the market. The three-hardness squeegee is particularly suitable for dot printing and four-color printing. The softness of the squeegee conforms to the requirements of the net cloth, and the rigidity of the substrate ensures that the ink is well transferred. The price of a double-layer, 3-layer squeegee is about twice that of a single-layer squeegee. The cost of the synthetic glass fiber squeegee is 4 to 5 times that of the single-layer squeegee. If you do not want to invest in a high-end squeegee, you can use the flex control holders shown in Figure 5 when using a cheaper single-layer squeegee. The biggest advantage is that you can control the degree of squeegee bending.
Selecting the scraper is not an easy task. The quality of the scraper is closely related to the entire printing process. As a printer, various factors must be taken into consideration, such as the characteristics and size of the printed graphics, the properties of the printing ink, and the characteristics of the substrate. Based on this, you can choose the right squeegee.
Source: "Printing Technology - Equipment and Special Printing"
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