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Injection molding process for pad printing of injection molded parts

by:Vowin Rapid Prototyping     2023-02-13
Pad printing of Shanghai Mulan Injection Molding Factory uses the principle of gravure printing. The tools include silicone rubber head, printing plate (steel or fiber) and ink with patterns, which can print various thin lines, fonts and patterns. Even four-color stencil images. Regardless of whether the surface of the printed matter is concave, convex or irregular, the ideal injection molding process effect can still be obtained.

1. Flow chart of pad printing injection molding process

Pattern design→output film→decorate and engrave stencil→install pad printing machine and stencil→install cleaning oil scraping system (oil pan, scraper)→deploy ink→debug pattern pad printing effect→pad printing and injection molding process production→inspection→package .

2. Pad printing equipment

1. Pad printing machine

Pad printing machine is the core of pad printing production. It uses compressed air as the original power, and uses electrical signals to control the movement of the rubber head and the pad printing action program to print single-color or overprint two-color to multi-color patterns, which can be used for 1~3 times of flow printing. , 1~2 color turntable printing and 2~6 color pusher printing. Shanghai Mulan Injection Molding Factory selects the pad printing machine according to the area and volume of the printed object, selects functions such as single-color, double-color or rolling printing according to needs, and selects dials and buttons according to the machine operation manual to determine the corresponding functions and Set the injection molding process parameters.

2. Steel plate

Shanghai Mulan Injection Molding Factory generally uses chrome steel with a hardness above 60 degrees chromium. The etching depth of the printing plate is 0.015~0.035mm, and the film thickness of pad printing ink is 0.004~0.008mm. It depends on the etching depth of the printing plate type and the hardness and shape of the printing head. The film thickness varies. The size of the printing plate is measured by the area of ​​the printed pattern. Usually the area of ​​the printing plate does not need to be too large, otherwise it is difficult to fix the steel plate on the oil pan.

3. Squeegee

The Rockwell hardness is about 55 degrees (not exceeding the steel version).

4. Ink

(1) Different inks should be used for plastic parts of different injection molding process materials.

(2) Understand the gloss, hiding power, and solidification rate characteristics of the ink.

(3) The ink cannot corrode the pad printing head.

(4) The speed of ink solidification should not be too fast, otherwise it is easy to dry in the oil pan, and it can be diluted with solvent at this time. If you want to speed up the air-drying speed, you can use a quick-drying agent or a hair dryer to assist.

(5) The ink should be adjusted to an appropriate viscosity. If the ink is too viscous, the lack of activity will cause printing difficulties; if the ink is too thin, the printed pattern color will not be clear enough or the lines will not be good; therefore, ink reconciliation is an important Work.

5. Glue head

The rubber head is generally made of silicone rubber, with a Shore hardness of 25~65. If it is harder, the printing and injection molding process will have a better effect, but if it is too soft, the graphics and texts will not be clear enough. The size of the pad printing head, if the size of the pad is too large, it will be wasteful. Different shapes of plastic parts need different types of pad printing pads. The shape of the pad printing rubber head is adjusted according to the unevenness of the pad printing rubber parts. The pad printing pad should bring the ink on the flat steel plate to the uneven printed part, so the end of the pad printing pad must be very flexible, and the shape of the pad printing pad must be suitable for the width of the plastic part. The pressure on the end of the rubber head can be spread evenly, so as to avoid printing the rubber head obliquely on the plane of the plastic part.

3. The printing process

The process of pad printing is as follows.

(1) The ink scraper applies the ink to the etched recess. During the return stroke, the blade scrapes the ink on the steel plate back into the ink container, and the ink left on the etched pattern can increase its surface viscosity after evaporation.

(2) The printing rubber head moves down to contact with the printed etching pattern.

(3) When the printing rubber head rises, the ink in the etched pattern is sucked on the rubber head.

(4) When the printing rubber head moves on the steel plate to the printed part, the attached ink bath agent gradually volatilizes, which increases the viscosity of the ink again, and the rubber head stays at the horizontal position above the plastic part.

(5) The printing rubber head is pressed against the printed plastic part, so that the attached ink is transferred to the surface of the plastic part injection molding process.

(6) The printing head rises again and returns to the original position above the plastic part.

Loopprint’s requirements for the substrate are the same as silk printing’s requirements for the substrate. Pad printing does not need to be dried with a special heat source, and it can be dried naturally or air-dried. The quality inspection of the injection molding process of pad printing patterns is basically consistent with the requirements of silk screen printing.

Fourth, the effect of pad printing pattern

(1) Color: 1~7 colors can be pad printed at the same time.

(2) Gloss: generally only semi-bright or matte effect can be printed.

(3) Hiding power: Due to the poor hiding power, the fidelity of the color is not very good, and the interference by the background color is obvious.

(4) Color printing of multiple colors: the accuracy of color registration depends on the precision of the pad printing machine used and the manufacturing precision of the fixture.

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