This process uses anti-corrosion transfer ink, screen-prints decorative patterns on decal paper, and transfers decorative pattern ink to mold by film method. After drying and trimming, cchemical corrosion is performed to obtain a concave-convex decorative pattern on mold.
Process flow:
Base map making→photographic platemaking→screen making→ink preparation→decal printing decorative pattern→ink drying→mold pretreatment→decal transfer printing→drying→finishing→corrosion→inspection→cleaning and rust prevention.

 

Process of decorative pattern mould

In addition to computer or manual drawing, most of decorative patterns are made of plastic samples and decorative patterns on artificial leather.
Plastic sample should choose a surface with a clear, uniform and flat pattern. First spray a layer of black self-drying paint. After drying, smear with white powder (calcium carbonate) of 200 mesh or more to fill in texture, then gently wipe off white powder on protruding surface to expose black until layout pattern is clear and black and white is distinct, and base map is completed.
If decorative pattern of artificial leather is used, artificial leather can be flattened and nailed on wooden board, and processed according to above requirements.

Use CR or SO film, 1:1 to shoot base image. Size of photographic negative is about 100mm* 200mm, which is convenient for making silk screen and decal transfer.

Using 200-300 mesh yellow polyester silk, 0.02mm thick blue photosensitive film, aluminum frame and photographic film, it is manufactured according to method of manufacturing printed circuit silk screen.

Select 500g of high-quality solid asphalt, put it into a clean and rust-free iron tank, add 300ml of kerosene, put it on a temperature-adjustable electric furnace to cook for 1-2 hours, control micro-boiling state, stir properly, and refine it to a consistency suitable for screen printing. At room temperature, it is soft and frozen, and surface is not crusted or wrinkled. This is asphalt ink.
Asphalt ink and 2711-4 ink (product of Tianjin Ink Factory) are mixed in a weight ratio of 1:1, and then add Peony brand No78 drying oil, dosage is 2% to 5% of weight of mixed ink, and mix thoroughly with an ink knife to obtain Resist transfer ink.

Use WPS400 type screen printing machine, install screen plate, put appropriate amount of anti-corrosion transfer ink on rubber scraper, first use waste blueprint to reverse printing, force should be uniform, light and important are moderate, do not return ink, until uniform and clear decorative pattern is printed, then use decal paper to print.
Decal paper should be cut to an appropriate size before printing, and smoothed with a clean rubber scraper. In printing process, if ink blocks mesh holes and pattern is not clear, it means that ink is too dry, and it can be diluted by adding an appropriate amount of kerosene;
If printed decorative pattern is easy to be blurred, it means that there is too much kerosene in ink. You can put ink on glass plate, mix it repeatedly with an ink knife, and then print volatilized part of kerosene.

Put printed decals on oven grid, with ink side up, spread out evenly without overlapping, control temperature at 40-45℃, bake until ink is half-dry and take out, that is, lightly touch ink on decals and not stick to your hands , a little pressure will stick to your hands, generally about 10 to 15 minutes. If ink is too dry, it will not stick to mold or has poor adhesion during transfer; if ink is too damp, transfer will be blurred.

This process should be done before decorative pattern is printed on decal paper.
Surface roughness of decorative pattern of mold should reach above, and there should be no sand holes or scratches to ensure that decorative pattern is complete, clear and consistent. If requirements are not met, grinding should be supplemented.
Scrub mold cavity and surrounding area with back silk dipped in gasoline to make surface clean. Surface without decorative pattern should be protected with nitro paint and vinyl chloride paint, and brushed two to three times. Holes and grooves can be protected by rubber stopper, plasticine and sealing tape.
After paint film is dry, use magnesium oxide water slurry to remove oil and clean surface of decorative pattern until surface can be completely wetted by water. Then, blot water dry with a sponge and blow dry with a hair dryer.

According to characteristics of mold cavity, cut decal paper into a shape that is easy to paste, gently peel off a layer of thin paper printed with decorative patterns, ink faces mold, and paste it carefully. It is required to be flat and not wrinkled, scrape flat surface with a rubber squeegee, knead curved surface into a ball with absorbent cotton, and press paper base vertically to transfer ink on decal paper to mold.
After transfer, wet decal paper with a sponge and a small amount of water, then gently peel off paper base, and use a sponge or absorbent paper to absorb water on mold.

Ink transferred to mold can be dried naturally in summer, and needs to be dried with infrared light in winter, surface and inside are required to be dry.

Junction of decal transfer and defective decorative pattern are repaired with No. 0 or No. 1 tracing pen dipped in transfer ink, dried with an infrared light after repairing, then use a pen-type repair knife to trim excess ink until decorative pattern is uniform and clear, connection is natural.

Ferric chloride 450～560g/L
Hydrochloric acid 5～10ml/L
Kerosene 10～15 drops/tank
Degree of corrosion of corrosive liquid is controlled at 36-40°Be.

Before mold is corroded, apply magnesium oxide water slurry to degreasing and clean decorative pattern, then spray tap water with a water gun for 1 minute to check whether ink and mold are firmly combined.
Then brush it with a wool pen dipped in corrosive liquid. Area without ink should be uniform gray and completely wet with water to ensure uniform corrosion. During above operation, if ink falls off, corrosion should be stopped immediately, and decal should be re-transferred.
Under normal operating conditions, combination of ink and mold is very strong, and reason for falling off is improper operation. No scraping is performed, and care should be taken during operation.

After confirming that mold can be corroded, three layers of double-sided self-adhesive paper and polyvinyl chloride plastic cloth are used around cavity to form a corrosion protection apron, which is 400-600mm longer than mold. Corrosion machine adopts a nozzle-type spherical nozzle, and 19 nozzles are evenly distributed in a half sphere, which can spray uniformly in three dimensions.
Hang mold with an electric hoist, with cavity facing down, nozzle facing up and in the center of protective apron. Two people hold mold to rotate slowly, start corrosion machine, and use a stopwatch to time corrosion for 7-10 minutes. Take lower limit in summer and upper limit in winter.
For molds with specific requirements for depth of decorative pattern corrosion, use same kind of steel as decorative pattern corrosion samples, and measure required time.

Lift mold out, rinse it quickly with tap water, emboss decorative pattern with a magnifying glass of 5 to 10 times or plasticine, and check depth of corrosion. If corrosion depth is not enough, it can be hoisted back to supplement corrosion. Meet requirements, immediately out of tank for cleaning.

Rinse mold with tap water, wash off residual ferric chloride, remove plastic apron, dry surface with a reel, peel off sealing tape and perchloroethylene paint, wipe off nitro paint with banana water, and wipe off ink with gasoline. After cleaning, blow dry mold with a hair dryer, and then apply surface of mold with rust-proof oil.
Process characteristics
(1) Use of self-prepared ink has advantages of good corrosion resistance, strong adhesion, natural drying, and good transfer performance;
(2) Using self-made spherical corrosion nozzle, corrosion liquid can be sprayed into a uniform hemispherical surface, which is suitable for complex cavity corrosion. In addition, with cavity facing down, corrosive liquid will not be accumulated, and decorative pattern with uniform corrosion depth, no corners, clear pattern and high quality can be obtained;
(3) Process method is simple, operation is easy, it is suitable for large, medium and small molds, and it is not limited by geometric shapes;
(4) Equipment is simple and material consumption is very small, mainly consuming decals, transfer inks and protective paints, with low cost and high economic benefits.