Plastic Surface Finishes Guide: Mold Pre-Treatment & Injection Molding Post-Treatment

Generally, the coloring and surface texture decoration of plastic can be completed during plastic injection molding. However, in order to increase the life of the product and improve its aesthetics, we can carry out secondary processing of plastic surface finishes and various decorative treatments.

Why are various different plastic surface finishes required?

Plastic surface finishes are to form a surface layer with one or more special properties on the plastic surface by physical or chemical methods. The injection molded parts can have various surface treatments to optimize the appearance, texture and function to achieve better finished products.

The effect of plastic surface finishes is mainly reflected in:

• For appearance: color, pattern, logo, glossy line (3D, 2D).
• For texture: feel, roughness, life (quality), streamline, etc.
• For function: hardening, anti-fingerprint, anti-scratch, etc.

Color treatment of plastic parts

Product primary color

Injection molding products can retain the original color of the plastic (for example, the natural color of ABS is a beige particle state, and the PC material is transparent crystal)

Toner toning

Toner is added to the plastic raw material during injection molding to adjust the color of the product desired by the customer. Check color with the PANTONE colour chart.

Mold pretreatment to achieve plastic surface finishes

By machining the surface of the mold, the plastic parts after injection molding can have specific surface effects, such as smoothness and specific lines. Usually, the surface treatments on the mold are mirror surface, smooth surface, texture, etching, etc.

Mirror surface

The high-gloss effect generally requires UV treatment to prevent scratches on the surface (mold electroplating).

Glossy

The glossy surface is also called the glossy surface (if the mold is polished, the injection molded plastic will be very bright).

Texture

Sunburst is a common way of mold surface treatment. Specific textures are formed inside the mold through chemical potions, laser engraving, spraying and other processes. After injection molding, the plastic part also has a specific texture.

Etching

Etching is the use of chemicals such as concentrated sulfuric acid to corrode the interior of the plastic molding mold to form patterns in the form of snake patterns, etch patterns, and ploughing. Then, after the plastic is formed through the mold, the surface of the plastic has corresponding lines.

Advantages of etching technology:

• Improve product appearance and feel.
• Anti-skid .
• Increase the surface area, which is beneficial to heat dissipation .
• It is beneficial to demoulding and easy to form.

Product surface finishes after injection molding

After the injection molding of the product is completed, in order to improve the appearance quality of the product and make the product more beautiful and high-end, surface lamination treatment and surface decoration treatment can be added.

Common plastic surface treatments of products after injection molding include EMD, spraying, printing, water transfer printing and electroplating.

Plastic surface finishes- In-mold decoration technology (IMD)

IMD includes IML (no stretch, small curved surface), IMF (high stretch product, 3D), IMR (surface film is removed, leaving only ink on the surface).
IMD is a moulding method in which a printed patterned film is put into a metal mold, and molten plastic is injected into the metal mould to join the film, so that the printed film and the plastic are integrated and solidified into a finished product.

Plastic surface finishes-Printing

Printing includes pad printing, screen printing, transfer printing, etc. A process in which the desired pattern is printed on the surface of a plastic part by pad printing, screen printing, transfer printing, etc. It can print text, graphics and images on the surface of irregular-shaped objects, and is now becoming an important special printing.

Pad printing

It is an indirect gravure head printing technology. First, the designed pattern is etched on the printing plate, and the etched plate is coated with ink. Then, most of the ink is transferred to the plate through the silicone head. on printed objects.

Screen printing

It is a main printing method in stencil printing.
The printing plate is mesh. During printing, the ink on the printing plate leaks from the through-hole part of the layout to the substrate under the extrusion of the doctor blade. Usually, wire mesh is made of nylon, polyester, silk or metal mesh.

Water transfer

Use water as a medium to transfer the image and text to the transfer paper or transfer film with color groups. It is mainly used for graphic transfer on the surface of various products with complex shapes. Metal, ceramic, plastic, and wood can all be water-transferred.

Thermal transfer printing

It is a technique of printing patterns or patterns on heat-resistant adhesive tape, and printing the patterns of the ink layer on the finished material by heating and pressing.

Plastic surface finishes- Electroplating

Electroplating allows plastics to obtain metal-effect surfaces at a lower cost. Electroplating is chemical plating, and there are vacuum electroplating and water electroplating. This is a process that uses electrolysis to attach a metal film to the surface of metal and plastic, thereby preventing metal oxidation, improving wear resistance, electrical conductivity, light reflection, corrosion resistance and enhancing aesthetics. Many coins The outer layer is also electroplated.

• Advantages of electroplating: It can prevent corrosion, improve wear resistance, electrical conductivity, light reflection, etc. (covering force is stronger than vacuum plating).
• Electroplating effect: high-gloss electroplating, matt electroplating (10-20% expensive), etched electroplating, pearl chrome and other surface effects.
• Electroplating range: nickel plating (few colors), galvanized (commonly used antennas, screws, etc. can be made in a variety of colors) chrome plating (high hardness, bright appearance, not environmentally friendly) gold plating silver plating copper plating nickel plating wire drawing.

Plastic surface finishes- Spraying

Through spraying, the powder is electrostatically adsorbed on the surface of the workpiece, and when it is completely dry, a protective film will be formed on the surface of the plastic.

Chassis paint

Chassis paint is mainly to make the surface of plastic products reflect the feeling of metal material. Commonly used in hair dryer, audio and other electronic products.

Rubber paint

As the name suggests, the paint adheres to the surface of the product, making the product visually and perceptually elastic as rubber. Commonly used in mobile phone cases, water cups, cameras and other products.

Etching

Etching is to corrode the mold to produce serpentine, etched and other textures. After the plastic product is formed by the mold, the surface will have corresponding textures. For example, we often see rough graininess or some special patterns on the surface of plastic products.
Features: non-slip, beautiful.
Commonly used in electronic products such as mice, headphones, and air conditioners.

Spray paint

Spray paint makes products appear in different colors, but many products are adjusted by plastic materials.

Spray UV

UV paint is a transparent coating, also known as UV varnish. UV paint is hard and scratch-resistant, which can protect the paint or coating in the previous process and protect the product. At the same time, UV spraying can improve the product’s wear resistance, acid and alkali resistance, and salt spray resistance, and can also adjust the gloss of the paint to make the product more beautiful.

However, spraying UV has high requirements on the production environment (dust-proof workshops above 10,000 grades), and the production equipment is relatively expensive.
Commonly used in: air conditioners, TVs, headphones and other products, the application fields are relatively wide.

Luminous paint

Luminous paint allows the product to glow in the dark. It is commonly used in watches, decorations and other products.

Pearl powder

The pearlescent powder is often used in transparent or translucent plastics, making it attractive in color. It is widely used in cosmetic containers, various packaging, toys, decorative materials, various films and other plastic products.
In addition, pearlescent coatings are also widely used in automobiles, building materials and other fields, making them appear pearlescent and metallic.

High temperature baking paint

High-temperature baking paint is a curing process. After painting or brushing, the workpiece is cured by electric heating or far-infrared heating instead of natural curing.

Plastic surface finishes- Laser engraving

Laser engraving, also known as laser marking, is a surface treatment process using optical principles. Through laser engraving, typing or patterns can be placed on the surface of the product.
Using high energy density, the workpiece is partially irradiated to vaporize the surface material or undergo a chemical reaction that changes color. The high-end keyboard and mouse will use laser engraving.

Plastic surface finishes services-injection molding factory

The processing technology of a product is a complex process, and sometimes a product may use several different processes. As an industrial designer or product designer, we do not need to fully understand the processing engineering of the process, but we must know the effect, cost, and perception of each process. Ultimately bringing the perfect product to market.

Sungplastic is a Chinese manufacturer with 20 years of experience in manufacturing plastic products. We are familiar with the properties of various materials and can help designers improve their products. We are familiar with the plastic injection molding manufacturing process and can identify possible problems in advance to avoid defects caused by injection molding. For various products, according to different surface requirements and usage scenarios, we will recommend the correct and suitable surface treatment process to you.
If you have a new project that requires design, development, and production, we are always ready to assist you with our professional industry knowledge.