Mirror ink in the application of IMD technology

With the continuous development of IMD technology, the application of mirror ink on IMD has made IMD technology a step forward, increasing the aesthetics of IMD parts and improving the quality of the products. The so-called "mirror ink" is a metal-colored screen printing ink and is a solvent-evaporation type. It is made of a plastic resin mixed with a special metal toner for printing on transparent plastic sheets (polyester sheet, PC sheet, PVC sheet, PMMA, etc.) On the back, get a metallic mirror print effect, just like a mirror or bronzing surface.

There are three types of Seiko mirror inks that can be selected according to the material and application of the prints:
Mirror silver ink B - only suitable for printing polyester film (PET), with excellent mirror effect and strong adhesion to PET.
Mirror silver ink No.2 - Printable polyester sheet (PET), PC, PVC, PMMA.
Mirror silver ink No.3 - for other colors mirror effect printing. Can be used for PET, PC, PVC, PMMA, with gold, red gold, green gold and other colors.
The following is a brief description of the application process and flow of mirror ink in IMD technology:

1 Printing

The printing step is completed in two stages. First, a mirror ink is printed on the back surface of the sheet, and after drying thoroughly, an IMD-specific ink is printed on the mirror ink. After thoroughly drying, a layer of 10 μm-thick water-based adhesive is applied. Dry thoroughly and complete the printing process. The specific printing processes in these two stages are:

1.1 Mirror ink printing

1.1.1 Printing Process Parameters

Wire mesh: Use a polyester mesh of 270-300 mesh/inch.

Screen: solvent resistant screen.

Squeegee hardness: 80 ~ 85 °C.

Dilution: Dilute with T-1000 solvent. (The viscosity can be increased if the viscosity increases during the printing process).

Drying: Heat drying at 80°C, 10 to 15 minutes, or 60°C, 15 to 20 minutes, drying at room temperature for about 20 to 30 minutes, but the natural dry mirror effect is not as good as heating and drying.

Wash the mesh: T-15 or T-31 solvent.

1.1.2 Printing Technology Tips

1Because of the different proportions of metallic toner, plastic resin and additives and additives, the components in the ink will be layered when stored, so be sure to mix thoroughly before use.

2 Because the viscosity of the ink is lower, the screen with higher screen mesh should be selected when printing, and the doctor blade with higher hardness should be used. Generally 80° is used, and the printing pressure of the doctor blade is appropriately reduced during printing.

3 To prevent blocking of the net, be careful not to print in places where air flows.

4 The net distance should be smaller, and the tension of the screen should be slightly lower.

5 This ink is harder to print than ordinary ink. Please choose an experienced mechanic to print it as well.

6 In order to prevent the ink from absorbing moisture, the gloss of the mirror surface is low, the moisture is avoided during printing and storage, and the film is dried at a low temperature immediately after printing.

1.2 Printing of IMD ink

After the mirror ink is completely dried, apply a layer of IMD special ink (solvent type or photocurable type) evenly on the mirror ink. Usually use glossy or white ink to protect the mirror ink and prevent the high-temperature injection to the mirror ink. The flushing, because the mirror ink is not resistant to high temperatures, this layer should have a certain thickness, if the printing is too thin, can not evenly cover the mirror ink, you can print twice. (The location of the injection gate should be printed twice or printed with a temperature-resistant ink. In addition, the correct design of the position and direction of the injection port of the injection mold is also a very important factor) because of injection molding at the gate location. The liquid temperature is highest and the pressure is large and the impact is large, and the ink is easily washed away. This layer of IMD special ink can be used either as a solvent type such as Baolong Noriphan HTR, or as a UV ink such as Nuoji IMD UV ink. The process parameters are listed below.

1.2.1 Noriphan HTR printing process parameters

Wire Mesh: A polyester mesh of 90 to 120 mesh/cm.

Screen: solvent resistant screen.

Thinner: Noriphan® HTR 090 Thinner, Noriphan® HTR 097 Slow Dryer, Noriphan® HTR 097/003 Slow Dryer. Diluent is selected according to the temperature and humidity of the line printing environment. All solvents can be mixed at different ratios to achieve the desired drying speed.

Noriphan® HTR 097 is the most widely used and can use slow drying agent Noriphan® HTR 097/003 to extend screen drying time when printing fine lines.

Drying: After drying in a well-ventilated tunnel dryer at 60 to 80°C, dry it thoroughly in an IR oven at a temperature of 90°C for a period of 1 to 5 hours. The drying time depends on the total amount of residual solvent evaporated. Sometimes the drying time is too long. Long, it will also cause the brittleness of the ink film to increase, causing cracking or flying oil and other defects. It is hoped that it can be determined according to their own conditions.

Aquapress (aqueous binder) HF-093 was photocopied and dried at 80°C for 5 minutes.

1.2.2 Noguchi IMD special UV ink process parameters

Wire mesh: 120 to 180 mesh/cm PW polyester mesh.

Screen: solvent-resistant screens with a tension of about 20 N/cm. Auxiliaries: 073 stimulator, 100 thickener, 060 mesh spot varnish.

Drying: Two 120-watt/cm UV-curable medium-pressure mercury lamps with a curing speed of about 20 meters/minute.
Copy: Autotype SC (aqueous binder), dried at 80°C for 5 minutes.

2 Forming and forming methods

Since the bonding force between the PC sheet + mirror ink + injection molding 3 is less than the binding force of the PC sheet + injection molding plastic, the mirror printing ink cannot be full printed, that is, it has been printed to the edge and must be left with a PC The margin of the sheet material is such that the PC sheet and the injection molding material can be firmly bonded together, and the PC sheet and the injection molding plastic at the edge of the IMD work piece are firmly bonded, and the external mirror will not be torn when the external force is applied. The bond fastness of the ink to the PC sheet and injection molding plastic is not affected by the edge tear. In order to ensure that the mirror ink is not cracked during molding, the PC is not layered (separated) during injection molding. In addition to the graphic design of the graphic design, that is, when the mirror ink is printed, the effective mirror ink area is left with a PC sheet margin, and can also pass through. The change of mold structure is realized, so the design of the mold is also very important.

3 Cut

The shearing process is performed in a normal IMD process.

4 injection molding

There are two measures for the injection molding process for two different molding methods.
First: If the molding is performed according to the first molding method described above, the injection molding structure should be modified with the molding mold structure so that the injection molding mold and the molding are the normal injection molding process in the IMD process.
Second: If the molding die and the injection mold are not changed, they are produced according to the normal IMD process. After the injection molding, the edge of the mirror ink is subjected to ultrasonic welding or thermal welding, so that the bonding strength of the edge of the workpiece is ensured.
The application of mirror ink in IMD technology has further enhanced the application status of IMD products. This article hopes to give IMD manufacturers a reference role in the process of manufacturing IMD.

Source: China Chemical Industry Market Ren Fengxia Chen Deshan

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