Process method for plastic parts to achieve similar metal drawing effect

The application of metal wire drawing in products is very common, such as construction, daily products, electronic products and other fields are widely used. However, due to the relatively high cost of metal wire drawing products, most of them are used in mid-to-high-end products. Therefore, low-cost plastic parts with visually similar metal wire drawing effects are gradually produced. It is not only beautiful, but also has a metal-like texture, and the cost is relatively low. At present, there are many applications in portable notebooks, tablets, home appliances and electronic products. How to make plastic products have the effect of brushed metal texture? The three most common methods are as follows:

1. Injection molding method

Simply put, it is to directly make a wire drawing effect on the plastic mold (usually in the master mold core). Through injection molding, the surface of the molded plastic product will have a similar wire drawing effect. The general process is as follows:

1) Use bronze as the core mold material to process the mold base, and use a diamond cutter on the core mold base to turn the wire drawing effect. The shape of the mold core is opposite;

2) Put the core copper mold base into the electroforming solution for precipitation, and the electroplating solution is generally a nickel solution. Selecting nickel as the electroforming fluid mainly considers the metal properties of nickel (nickel, a metal element that is approximately silver-white, hard, ductile and has ferromagnetic properties, it can be highly polished and anti-corrosion), which is conducive to the production of mold cores in the injection molding process. Anti-corrosion and mold maintenance;

3) Generally, the deposition time is longer, it takes ten to twenty days, and the thickness of the electroplating layer needs to meet the mold design requirements, which can generally reach 10-12mm.

4) Take out the copper core mold, and take out the replica of the copper core mold (ie the electroplating layer). This replica is the mold core used for production in the future. Of course, it needs to be processed and polished according to the mold design;

5) Place the processed nickel mold core into the processed mold steel mold base;

6) Carry out injection molding production. At this time, the surface of the injection molded product will have a wire drawing effect similar to metal.

The surface of the injection molded product has the following surface treatments:

1) It is directly the color of the plastic material. The dark-colored plastic parts are more likely to have the effect of brushed metal texture, and the visual effect is more like the effect of brushed metal than the light-colored ones;

2) The product is sprayed with metallic paint, so that the color and wire drawing of the plastic are visually closer to the texture of wire drawing, but there are certain differences from the real wire drawing, such as light hand feel, insufficient heat transfer speed, etc.;

3) Vacuum evaporation (nickel or chrome plating) on the product. Since the electroplating layer itself is metal, it is very close to the metal wire drawing and has a stronger texture, which is almost comparable to the texture of the real metal wire drawing effect, at least the texture is brighter.

Disadvantages or disadvantages of injection molding:

1) If the plastic surface needs to be sprayed, the wire drawing should be relatively thick, otherwise it will be easily covered by paint; in addition, the thickness of the spraying should be controlled, otherwise the wire drawing will be covered.

2) If vacuum plating is used, the cost of the product will be high;

3) The cost of the mold making process is relatively high and the cycle is relatively long;

4) The hardness of nickel is low, and it is easy to be bruised when the mold is produced, so prepare 3-5 more nickel mold cores in advance to avoid affecting the production.

5) If the plastic parts need vacuum plating, avoid large areas and sharp corners in the design. Generally, the partial decorative parts of the product are brushed.

2. Water plating drawing method

The electroplating process is described in detail in the previous article: the process introduction of electroplating and electroless plating. Simply put, the plastic products are subjected to wet electroplating (also known as water electroplating), and then the surface is drawn.

After the plastic is electroplated, its mechanical properties have been greatly improved, such as tensile stress, torsional stress and impact stress are greatly increased, and the corrosion resistance is also greatly enhanced, while the heat dissipation capacity of the plastic can be increased. In addition, due to the low cost and high production efficiency of plastic electroplating, plastic electroplating is widely used in electronics, automobiles, and household products. However, with the improvement of aesthetic requirements, it is hoped that the plastic electroplating can be made into a similar metal drawing effect (such as stainless steel drawing effect), so the plastic can be drawn after electroplating.

Since the plastic electroplating layer is relatively thick, generally it can reach 0.08-0.2mm, and sometimes it can reach 0.3mm, so the surface can be thinned. The general process flow is as follows:

1) Stress relief: Due to the internal stress after plastic injection molding, in order to reduce the deformation of the product after electroplating, it is necessary to remove the internal stress, generally soaking in acetone solution;

2) Degreasing: In order to ensure uniform contact with the solution during roughening, the grease on the plastic parts must be removed first, and it is generally cleaned with a medium and low temperature alkaline liquid;

3) Roughening: The purpose is to ensure the contact area between the plastic parts and the liquid, generally using a high chromic acid solution;

4) Neutralization and reduction: remove impurities such as strong acids and oxides remaining on the surface of plastic parts, and improve the affinity of plastic parts;

5) Pre-dip: In order to attach divalent chromium ions to the surface of the plastic parts and prepare for activation;

6) Activation: For the needs of electroplating metal, a catalytically active metal layer needs to be adsorbed on the surface of the plastic part;

7) Reduction: Reduction treatment should be carried out after activation and cleaning to improve surface activity, accelerate deposition, and at the same time remove the activation solution on the surface to prevent it from being brought into the chemical plating solution to cause decomposition;

8) Electroless plating: The purpose is to form a coating with good conductivity on the surface of the plastic part, the coating is uniform, and the continuity is good, so that the circuit can form a loop to ensure the smooth progress of the next step;

9) Electroplating: Generally, copper, nickel, and chromium metal composite electroplating is used on the plastic surface to form a surface decoration layer;

10) Wire drawing: wire drawing on the surface, generally filament;

11) Spray varnish: clean and dry after drawing, and then spray varnish on the surface.

There are many special design requirements in the design of electroplated wire drawing parts, which are roughly as follows:

1) It is best to use electroplating grade ABS material as the base material, and its butadiene content of 15% to 16% has the best adhesion strength, and the price is also relatively low;

2) The surface quality of plastic parts is very high, and electroplating cannot hide some defects of injection, and usually makes these defects more obvious. If you can use decorative effects such as skin texture and knurling, you should try to use them as much as possible, because reducing the reflectivity of electroplated parts helps to cover up possible appearance defects, improve the yield, and also help reduce costs;

3) There are several points to pay attention to when designing the structure and mold. The shape should be suitable for electroplating treatment. When designing the structure, try to avoid large areas of electroplating and sharp corners. When designing the mold, the plastic inlet should not be too thin to prevent the water from breaking and falling off, preventing tip discharge, paying attention to the demoulding slope, reserving air vents, paying attention to the thickness of the thimble affecting the appearance, and the bonding line generated by the position of the plastic inlet. At the same time, the mold should be designed Fixtures or hanging points when plating.

4) It is best not to have metal inserts in the plastic parts. Due to the different expansion coefficients of the two, when the temperature rises, the electroplating liquid will seep into the gap, which will have a certain impact on the structure of the plastic parts.

5) For small or hollow parts, try to design as many as one mold on the mold to save processing time and electroplating time, and at the same time, it is also easy to hang during electroplating and improve production efficiency.

6) The surface to be drawn should be as flat as possible, otherwise it cannot be drawn. Generally, the local decorative parts in a product are electroplated and drawn to avoid large areas.

3.Bronzing transfer method

The process of hot stamping has also been introduced in detail in the previous article: the introduction of hot stamping (hot stamping) process, simply put a layer of metal film with a brushed texture on the plastic. That is, under the action of high temperature and high pressure of the hot stamping machine, the hot stamping film with wire drawing texture is transferred to the surface of the plastic product. The hot stamping film is a hot stamping material made of a film base by coating and vacuum evaporation and adding a layer of metal foil. Domestic bronzing film is generally 5 layers, base film layer, release layer, dyeing layer, aluminized layer and adhesive layer, the specific decomposition is as follows:

1) The base film layer is generally made of 16pim thick biaxially stretched polyester film (PET), which has high strength, tensile strength, high temperature resistance and other properties, and is not easy to deform due to temperature rise.

2) The release layer is mainly made of silicone resin. Its main function is to quickly release the color layer, aluminized layer and adhesive layer during hot stamping, that is, when heated or pressurized. The film is transferred and bonded to the surface of the hot stamped object.

3) The main components of the dyeing layer are synthetic resins and dyes, which have film-forming properties, heat resistance and transparency. The color layer has two main functions: to display the color and to protect the aluminized layer graphics (such as brushed texture or pattern, etc.) hot stamped on the surface of the item from being oxidized. The color of the color layer can include orange, yellow, gray, red, green, etc. as required. The color of the color layer is given luster after the aluminized layer, and the color changes to a certain extent. The color of the coating may not reflect the color after bronzing. For example, yellow is gold after aluminized, and gray is silver after aluminized.

4) The aluminized layer is to place the colored layer and other films in the vacuum chamber of the continuous aluminum plating machine. Under a certain degree of vacuum, through resistance heating, the aluminum wire is melted and continuously evaporated onto the color layer of the film, so that the Aluminized layer is formed, and its main function is to reflect light, change the color properties of the color layer, and make it glossy.

5) The adhesive layer is generally made of fusible thermoplastic resin on the aluminum layer through a coating machine, and then dried to form an adhesive layer. The main function of the adhesive layer is to bond the hot stamping material to the object to be hot.