How to use the hottest doctor blade

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Usage of doctor blade

doctor blade plays an important role in plate printing. Generally, metal blade and rubber blade are commonly used. Their characteristics and applications are introduced below

I. metal knife

1. The quality evaluation indicators of pad printing doctor blade mainly include hardness, thickness, elasticity, straightness of knife edge, etc. Generally, a 0.25mm thick flat steel belt with good elasticity is selected as the scraper, and its edge should be sharp, smooth, straight, and closely consistent with the steel layout with the increasingly fierce market competition; If the blade edge of the scraper is not sharp or damaged, it will cause unclean scraping and adhere to the edge of the pattern or produce scraper marks, which will seriously scratch the printing plate. The doctor blade should be at an angle with the printing plate to prevent the doctor blade from falling into the concave of the printing plate and scraping too much to damage the pattern; If it is found that the contact between the scraper and the printing plate is uneven, it should be adjusted to close; The length of the scraper should be greater than the width of the pattern text close to the steel plate. The pressure of the scraper should be on the premise of scraping the ink on the non graphic part of the printing plate. The smaller the pressure, the better, and the smaller the wear loss

2. SMT tin scraper SMT metal scraper is also commonly used. With the use of more closely spaced elements, the amount of metal scraper is increasing. They are made of stainless steel or brass, with a flat blade shape and a printing angle of 30 ~ 45 °. Some scrapers are coated with lubricating material. Because of the low pressure, they will not dig out the solder paste from the opening, and because they are metal, they are not as easy to wear as rubber scrapers, so they do not need to be sharp. They are much more expensive than rubber scrapers and may cause wear of the film

II. Rubber and plastic knife

1. SMT rubber tin scraper when using rubber scraper, the type of scraper selected is different in the printed circuit assembly (PCA) of standard components and dense foot components. The demand for solder paste quantity is also very different. Closely spaced components require much less solder than standard surface mounted components, and the solder pad area and thickness also control the solder paste quantity. Use a rubber hardness tester to measure the scraper with a hardness of 70 ~ 90. When excessive pressure is used, it seeps into 4 The safety and reliability of automotive interior materials the solder paste at the bottom of the film may cause a tin bridge, requiring frequent bottom wiping. In order to prevent bottom penetration, the pad opening must be sealed during printing. This depends on the coarseness of the perforated wall of the membrane plate. The wear degree, pressure and hardness of the tin scraper determine the printing quality, which should be carefully monitored. To obtain acceptable printing quality, the edge of the scraper should be sharp and straight. Low scraper pressure will cause omission and rough edges, while high scraper pressure or very soft scraper will produce spotted printing effect, and may even damage the scraper, film plate or wire. Too high pressure also tends to dig out solder paste from the wide opening, causing insufficient solder fillet

2. Generally, 50% recycled rubber rubber strips are used for printing doctor blades. The thickness, hardness, width, elasticity and pressure of the scraper have a great impact on the printing quality. The thicker scraper has high hardness, poor elasticity and high pressure, which is suitable for printing fine dot and line patterns; The thin rubber scraper has large elasticity, which is suitable for printing map lines; Too narrow rubber scraper has little room for pressure adjustment, but the thin and wide rubber scraper is soft and weak when reprinting, the edge of the pattern is not smooth, and the color paste of the layout is not clean, which affects the printing effect. The angle of the scraper should be appropriate, and it is appropriate that the reverse side of the plate is impermeable and the front side is not dry. Scraper and scraping angle with different angles should be selected according to different fabrics and different pattern structures. Generally, the blade angle of scraping fine patterns is not easy to be too large, and the blade angle of scraping coarse patterns can be larger. The hardness of the scraper and the table has a great influence on the eye tone printing. Dot printing requires high definition. The non textile surface is smooth, the texture is crisp, not easy to deform, and the dot definition is guaranteed; However, textiles have hygroscopicity, unsmooth surface and fabric holes. How to print points clearly and how to be proficient in scraping are very important. The scraper rubber strip should have a straight and sharp edge, not a round edge. The 90 ° edge rubber strip is the most widely used. Polyurethane scraper is better than rubber scraper. The pressure of the scraper with blade is high, and the embossing line is thinner and more solid, which makes the wire rebound quickly, and the plate is clean after scraping, with good reproducibility of dots

3. Setting of the center point of the container printing doctor blade when the doctor blade is installed, the center line passing through the vertex must coincide with the diameter of the substrate. If this condition is not met, even if other conditions are met, a good printing effect cannot be obtained. The motion mode of producing non friction pairs can be divided into sliding friction, rotating friction and rolling friction. Qualified printing products (2) low investment intensity. The setting of scraper center is an important factor in surface printing conditions. The stamping must be controlled to a minimum. Especially in surface printing, if the impression is too large when printing plastic barrels, the scraper condition will deteriorate and have a very bad impact. Generally, sword shaped scraper rubber is used for curved surface printing, and parallel scraper rubber is used for plane printing. Sword shaped scraper rubber is used for curved surface printing, which is determined by the content and purpose of printing. In a word, it is unnecessary to use scraper rubber that is consistent with the printing purpose, which is limited to the difference between curved surface and flat surface

source: fine chemicals in the 21st century

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