Mold etching (commonly known as mold drying, mold biting, etc.) is a common surface treatment process for injection molds. This process is mainly used to improve aesthetics and surface strength of product. Generally, process is divided into fine lines, rough lines and dermatoglyphs due to different thickness of lines. This process is widely used because of its low cost, rich effect and high efficiency. Mold etching usually has following effects:
Improve product decoration effect and make product more beautiful;
Reduce appearance of surface problems or defects such as scratches, dust, blemishes and ripples on product surface, and make appearance more smooth;
Good touch, with anti-slip and anti-rotation effects;
It can be made into pitted or matte surface, which can eliminate eye fatigue to a certain extent;
Pattern is made to facilitate demoulding action.

 

Figure 1: Mold etching process is often used to improve product aesthetics and surface strength

Basic process of traditional chemical etching process is explained as follows:
Mold washing: first use mold cleaner to clean oil or impurities that may exist on the surface of mold;
Mucosa: Use special tape to stick to surface of other molds that do not require etching process (generally recommend that tape is more than 3 layers). After completion, use wax to seal boundary of etched surface to protect it, or apply anti-corrosion paint on the surface of mold without etching process, then repeat cleaning of etched surface;
Chemical inspection: soak mold in a chemical agent (usually 5-10s). At this time, surface of mold without adhesive tape will be corroded by chemical agent, and it will appear black;
Surface treatment: Use a spray gun to evenly spray sand particles on the surface of mold to remove black oxide layer on the surface of mold. After sand washing, surface of mold becomes silvery white;
Printing treatment: wax evenly on the pattern plate that has passed film etching standard, and then transfer pattern onto a special film by a rolling machine to make wax paper. Stick wax paper on the surface of processed mold as required, and transfer pattern to mold;
Printing treatment: make film, paste film with pattern drawing on mold, dispense ink according to pattern, and spray it evenly on etched surface;
Chemical etching: Immerse transferred mold or film-attached mold in a chemical agent for local corrosion. Degree of corrosion is mainly controlled by immersion time;
Surface treatment: Refer to step 4 to remove black oxide layer on the surface of mold;
QC&Packaging

Precautions for traditional chemical etching are explained as follows:
When cleaning mold, ensure that impurities such as oil stains are cleaned to avoid uneven subsequent etching;
When etched surface and non-etched surface are transitioned at an R angle, R angle is generally not greater than R 0.5MM;
Pay attention to tempering in welding place. When material and hardness difference is not big after welding, etching lines can be separated and length of etching lines can be adjusted; when hardness difference is large, welding position can be locally heated and then lines can be etched;
When performing sandblasting, ensure uniform spraying;
If surface of mold to be engraved has been plated with nickel, hard chromium, Teflon or other surface coatings that can improve wear resistance/corrosion resistance of mold, this coating must be completely removed to ensure effect of mold etching processing.

 

Figure 2: Chemical etching process flow

Traditional chemical etching agent is corrosive to surface of steel, agent has higher requirements on material. If fire pattern on mold and processing of each part cause hardness of surface layer to be different, it will have a greater impact on etching effect; therefore, a new etching process ─ ─ laser etching is introduced in the follow-up. Surface of skin texture made by laser etching is even, three-dimensional effect is stronger, it has characteristics of high precision and high stability. It has begun to gradually replace chemical etching process. Table 1 shows comparison of the two process methods.

 
Table 1: Comparison of traditional chemical etching and laser etching
At present, most products use etching process to process mold in order to meet needs of appearance layering, three-dimensional feeling and tactile feeling. At the same time, in order to overcome shortcomings of traditional chemical etching processes, a variety of process methods have been gradually developed and optimized. It is believed that future etching processes will also meet requirements of environmental protection, energy saving and high efficiency.