The process of catalytic reduction of metal ions in plating solution to form a metal coating on the surface of activated substrate. This is a process engineering, which mainly involves our process. Only through this process can post-electroplating be carried out, which is mostly used as the pretreatment process of plastic parts.

electroplating

The process of forming uniform, dense and well-bonded metal or alloy coating on the surface of parts by electrolysis is very complicated, but compared with similar processes, it has many advantages, such as a variety of deposited metals, diverse colors and low price.

electric forming

The process of manufacturing or duplicating a metal product by depositing metal on a mold by electrolysis (the mold can be separated from the metal deposit). This treatment method is used when the final product is required to have special surface effects, such as clear and obvious polishing and etching separation lines or special acute angles. Generally, after copper is used as the shape of the part, alloy is electroplated and deposited on its surface, with a thickness of tens of millimeters, and then the cavities are cut, inserted into the cavities of the mold respectively, and plastic parts are injected. The parts treated in this way will have special effects on the edges and corners and the boundaries of several surfaces to meet the needs of design. Usually, we see many plastic parts with clear highlights and etching effect after electroplating, which are usually designed by this means. If the angular keyboard is manufactured by electroforming process, it will achieve a good appearance effect.

vacuum plating

Vacuum coating mainly includes vacuum evaporation coating, sputtering coating and ion plating. They all deposit various metal and nonmetal films on the surface of plastic parts by distillation or sputtering under vacuum. In this way, a very thin surface coating can be obtained, and at the same time, it has the outstanding advantages of fast speed and good adhesion, but the price is also high and there are few kinds of operable metals. It is usually used as a functional coating for high-end products, for example, as an internal shielding layer.

Electroplating of plastics. Characteristics of plastic electroplating.

Electroplated plastic products have the characteristics of both plastic and metal. Small specific gravity, good corrosion resistance, simple molding, metallic luster and metallic texture, as well as electrical conductivity, magnetic permeability and welding characteristics. It can save complicated processing procedures and metal materials, and it is beautiful and decorative. At the same time, it also improves the mechanical strength of plastics. Because the metal coating has high stability to external factors such as light and atmosphere, it can prevent plastic from aging and prolong the service life of plastic parts after electroplating metal.

With the rapid development of industry and the increasingly wide application of plastic electroplating, it has become one of the important means of surface decoration of plastic products. At present, electroplating has been widely used in ABS, polypropylene, polysulfone, polycarbonate, nylon, phenolic FRP, polystyrene and other plastics at home and abroad, among which ABS plastic electroplating is the most widely used and the electroplating effect is the best.

Plastic process flow-the main process flow of electroplating plastic parts.

Plastic parts. Mechanical roughening. Chemical degreasing. Chemical roughening.

Sensitization-activation-reduction-electroless nickel plating-electroplating-finished product.

Main technological process of plastic electroplating

1, chemical degreasing

In order to prevent plastic deformation and dissolution, the adaptability of degreasing solution to plastic should be considered. When using alkaline degreasing solution, pay attention to the use temperature to prevent deformation; When using organic solvents to remove oil, pay attention to whether there is dissolved plastic.

2, coarsening

In order to improve the bonding strength, it is necessary to increase the contact area between coating and substrate as much as possible. There are two methods of coarsening: mechanical coarsening and chemical coarsening. Mechanical roughening, such as sandblasting, tumbling, grinding, etc. Chemical roughening can quickly make the surface of the workpiece slightly rough, and the roughened layer is uniform and detailed, without affecting the appearance of the workpiece.

3. Sensitization Treatment The sensitizer commonly used in industry is the aqueous solution of stannous chloride or titanium trichloride.

4. Activation treatment The so-called activation treatment is to soak the parts adsorbed with reducing agent in a solvent containing oxidant. Generally, it is immersed in a precious metal salt solution, so precious metal ions are reduced to precious metals by reducing agents, thus forming a precious metal film on the surface of the workpiece. This precious metal layer can play the role of active catalysis, also called catalytic membrane, which can accelerate the reduction reaction of electroless plating. Practice has proved that precious metals such as silver and palladium have this catalytic ability.

5. The plastic parts activated by reduction reaction can be chemically plated after washing. Before electroless plating, the plastic parts are immersed in a certain concentration of reducing agent solution to reduce the activator that has not been washed off by water, which is the reduction treatment. When electroless copper plating, sodium hypophosphite solution can be used for reduction treatment first.

6. Up to now, many heavy metals can be deposited from aqueous solution by electroless copper plating. From the economic point of view, electroless copper plating has the lowest cost, so it is widely used. The appearance of electroless copper plating is copper red, which can not be used as decoration and protective layer. It is usually used as a conductive layer for electroplating thickening coatings such as nonmetal and hole metallization of printed circuit boards. Electroless copper plating can only coat plastic parts with a layer of conductive power supply, and the coating is very thin. If you want to continue to thicken other coatings, first use electroplated copper to thicken the electroless copper coating. When electroplating copper, you can use acidic copper plating or alkaline copper plating. After the plastic parts are electroplated with copper, other metal coatings can be electroplated as required.

Principle of metal spraying

In the process of metal spraying, the coating material is melted and atomized in a special nozzle or spray gun, and then sprayed on the substrate. This surface decoration method is sometimes called metal spraying. Oxygen-acetylene flame is usually used, but other gases are sometimes used. When the coated metal wire is automatically fed through the flame center, the metal wire melts and is atomized by the compressed air flow and sprayed onto the substrate. Almost any metal that can be made into silk can be sprayed in this way. Another spray gun uses powder materials to spray flames. The advantage of this method is that it can spray not only metals, but also cermet composites, oxides and cemented carbides.

surface treatment

Because the bonding between the plating material and the base material obtained by metal spraying is purely mechanical bonding, the base material must be properly prepared. So as to obtain a good mechanical bond. No matter what surface treatment method is adopted, the surface of the substrate must be clean and free of oil.

The most common surface treatment method is sand blasting. For this reason, sand is sharp enough to form a very rough surface. For a cylindrical surface that can be rotated on a lathe, an effective method is to turn a very thick thread, and then gently roll the crest with a rolling knife. An improved method that can be used on the plane is to cut a series of parallel grooves with a circular grooving knife, and then grasp the edge surface between the grooves with a knurling knife. If the electroplating surface is to be machined, the substrate surface should be prepared by rough machining or grooving to obtain the best preparation.

Application of metal spraying

Metal spraying has many important uses in product design. If zinc and aluminum are sprayed on the steel surface, a protective coating can be obtained to obtain corrosion resistance. Because metal spraying can spray metal on almost any kind of metal or nonmetal surface, it provides a simple method to coat conductive surfaces on poor conductors or non-conductors For this reason, copper or silver is often sprayed on glass or plastic. Since the sprayed metal can be treated in various ways, such as polishing, brushing or maintaining the sprayed state, the sprayed metal can be used as a decorative means in the product and construction industries.

Hot stamping of plastic parts

Hot stamping of plastic parts is one of the important surface decoration methods for industrial products (especially light industrial products). At present, in product design, it has developed from font hot stamping to pattern and large area plate hot stamping.

Hot stamping is the process of transferring the colored aluminum and wood grain on the hot stamping material (hot stamping foil) to the surface of plastic parts under certain pressure through the heat source and rubber roller (or rubber plate) shown in the hot stamping machine diagram, so as to obtain exquisite patterns and good decorative effects. Hot stamping originated in Europe in the17th century. At that time, it was only used by nobles for the surface decoration of books and bibles, and its tin foil was made of real gold and silver. With the appearance of polyester film and chemical synthetic foil, people turn to new decorative materials with low price and good quality, and use them in the surface decoration design of industrial products.

Characteristics of hot stamping-

1, the decorative effect of hot stamping is good. There are many varieties of hot stamping foil, which can be divided into gold, silver and various colors according to color; According to patterns and materials, it can be divided into metal foil, wood grain foil and paint foil. There are also various bright, matte and silky monochrome and multicolor patterns. Using these hot stamping foils can increase the decorative effect of products. The application of metal foil can be comparable to that of electroplated parts.

2. Hot stamping is economical.

Hot stamping is a dry decoration method, which does not need wet ink or adhesive coating. Plastic parts usually do not need pretreatment; The preparation time of the used equipment is short, and there is no long-term adjustment problem; Hot stamping parts can be taken out and transported at any time without drying time; Change the color or pattern, just change the hot stamping die and hot stamping foil roll; There is no need to clean the machine at the end of the operation. Low equipment investment and energy consumption, small floor space, high efficiency and low production cost, which is about 1/6 of electroplating.

3. Hot stamping has a wide range of applications.

In addition to thermoplastics, thermosetting plastics can also be used for hot stamping. In addition, wood, written cloth, leather, textiles, paper, cardboard and painted metal can be hot stamped smoothly. At present, hot stamping technology has been widely used in household appliances, such as various dial covers, sound windows, window grilles, televisions, tape recorders, window air conditioning housings and other color surface decoration. , so that the whole machine can obtain various decorative effects such as metallic luster, line pattern and wood grain. , often used in trademarks, patterns and decorative parts of products, with good results.

4, hot stamping adhesion is good

Hot stamping transfer foil has high adhesion strength to decorative plastic parts, and the protective topcoat covering color and metal layer makes the hot stamping surface meet the physical and chemical properties required by technical specifications, and it is not easy to delaminate.

5, no pollution

Hot stamping adopts dry printing method, which is pollution-free, clean and hygienic compared with painting, electroplating, metal oxidation and coloring treatment, and greatly improves the environment and working conditions of operators.

IMD injection molding surface decoration technology

Chinese name of IMD: injection molding surface decoration technology, namely IMD (in-mold decoration). IMD is a popular surface decoration technology in the world at present, which is mainly applied to the surface decoration and functional panels of household appliances, and is often used in exterior components such as the lens and shell of mobile phone window, the control panel of washing machine, the control panel of refrigerator, the control panel of air conditioner, the dashboard of automobile and the control panel of rice cooker.

IMD is divided into IML and IMR. The biggest difference between the two processes is whether there is a transparent protective film on the surface of the product.

IML Chinese name: The inner insert of injection mold is characterized by a hardened transparent film on the surface, a printed pattern layer in the middle and a plastic layer on the back. Because there is ink in the middle, the product can be prevented from being scratched and worn, and the color can be kept bright for a long time, which is not easy to fade.

Chinese name of IMR: in-mold transfer

This process is to print the pattern on the film, and the film is stuck on the mold cavity by the film feeder for injection molding. After injection molding, the patterned ink layer is separated from the film, and the ink layer remains on the plastic part to obtain the plastic part with decorative patterns on the surface. There is no transparent protective film on the surface of the final product, and the film is just a carrier in the production process. The advantages of IMR are high degree of production automation and low cost of mass production. The disadvantage of IMR is that the printed pattern layer on the product surface is only a few microns thick. After the product is used for a period of time, it is easy to wear off the printed pattern layer and fade easily, resulting in an unsightly surface. In addition, the development cycle of new products is long, the development cost is high, and the pattern color cannot be changed flexibly in small batches, which is also the weakness that IMR technology cannot overcome.

First of all, it is necessary to explain conceptually:

IMD includes IML, international monetary fund and IMR.

Iml: Molded label (combination of printing compound and plastic)

International Monetary Fund: Molded film (same as IML)

Imr: In the forming roll (the key point is the release layer on the rubber compound. After PET film → printing release agent → printing ink → printing adhesive → internal plastic injection → ink and plastic bonding → mold opening, the glue will be automatically released from the ink. Japan calls it thermal transfer printing. This machine adopts roll-to-roll mode, and the alignment is operated by CCD computer ﹞

The fundamental difference between Lml and LMR lies in:

The difference between IML and IMR in lens surface is that there are PET or PC sheets on the surface of IML, while there is only ink on the surface of IMR. IMD is a complicated process,

IML can be made of PET or PC. PMMA and ABS are generally used as plastic particles. IML and IMR have their own advantages. IMR is not very wearable. Some phones of Nokia and Moto use IMR technology, which will also cause scratches for a little longer. The biggest disadvantage of IML is that it can't realize IML technology as a whole, and it is limited to a certain area.

The role of plastic coating

Plastic is easy to be colored, but the coloring of plastic has many limitations, such as no color, large amount of pigment and high cost.

In order to improve the decorative performance of plastics, it is necessary to achieve color matching decoration by painting, increase the variety and luster of the surface, make engineering plastics have a metallic appearance, and cover up the surface defects of plastic products (silver lines, water pits, inconspicuous joints, spots and stains, etc.). ) and coloring of dark plastic. In addition, plastic refrigeration can also play a protective role and some special functions. Although plastics don't rust, they don't dissolve in acid quickly. However, plastics are easily corroded by ultraviolet rays, oxygen, moisture, methane, solvents and other chemicals to varying degrees, and their wear resistance and mechanical properties are not as good as those of metals, so plastic products also need protection, such as: ① anti-aging and anti-oxidation. Mixing anti-ultraviolet agents and antioxidants into plastics can improve the weather resistance of products, but the cost is extremely high. Anti-oxidant and anti-ultraviolet agent are mixed into paint, which can shield ultraviolet rays and isolate oxygen when applied to the surface of plastic products. (2) Resistant to solvent corrosion, chemical corrosion and chemical corrosion. Except for polyethylene, polypropylene and polytetrafluoroethylene, many thermoplastics have poor deep resistance, so the parts of these products in contact with organic solvents should be protected with appropriate coatings. ③ Prevent plasticizer from volatilization and leakage. (4) moistureproof. ⑤ Prevent scratches, abrasions and abrasions.

In recent years, special functional coatings have developed rapidly, and coating these coatings on plastic products can expand the application scope of plastics. For example, fire retardant coatings and fire retardant coatings can prevent celluloid products, polypropylene and unsaturated polyester glass fiber reinforced plastic tiles from catching fire; Optical plastics used as lens needs to be coated with anti-reflective coating, antistatic coating, wear-resistant coating and scratch-resistant coating.

Chemical oxidation process of aluminum and its alloys

Chemical oxidation is to put the parts into an appropriate solution without external current to form an artificial oxide film on their surfaces. Generally, aluminum parts are immersed in chromate solution containing alkali and alkali metal, and aluminum interacts with the solution to form AL2O3 and AL(OH)3 films rapidly. This oxide film has strong adsorption capacity and is generally used as the bottom layer of surface coating in industry. After chemical oxidation, the corrosion resistance of aluminum and its alloy exterior decoration parts can be greatly improved, and the coating retention can be enhanced. The advantages of chemical oxidation of aluminum and its alloys are mainly high production efficiency, low cost, no power consumption and no special equipment, which is suitable for mass production.

Electrochemical oxidation of aluminum and its alloys

Electrochemical oxidation of aluminum and its alloys, also known as anodic oxidation treatment, is a method to obtain corrosion-resistant and decorative surfaces of aluminum products, which is widely used in industry. The reverse process of this process is the same as electroplating, that is, the workpiece is the anode of the electrolytic circuit. Instead of adding a layer of material (metal) on the surface of the workpiece, internal reaction is carried out to increase the thickness of the strong protective alumina layer usually existing on the aluminum surface.

1, anodic oxidation method generates oxide film through electrolytic reaction.

2. Sulfuric acid oxidation is widely used in protective and decorative anodic oxidation treatment.

3. Alumina chromate and aluminum alloy are anodized with chromic acid solution.

4. Oxalic acid anodizing process is also widely used in aviation industry, electrical appliance industry, aluminum products and so on. So as to obtain a better protective film.

5. Other anodizing methods of aluminum and its alloys

(1) porcelain anodic oxidation method

Also called imitation glaze oxidation, it is a new method for surface treatment of aluminum and its alloys. In fact, it comes from chromic acid anodizing. Adding oxalic acid and boric acid into chromic acid electrolyte, under certain technological conditions, an opalescent oxide film similar to enamel or pool porcelain can be obtained by anodic oxidation. It has good corrosion resistance, can be painted in various colors, has special luster (especially like plastic), and can obtain good decorative effect. Porcelain oxidation has the following characteristics: ① high hardness and wear resistance; (2) Excellent decoration, plastic-like film, glazed luster and elegant appearance; ③ High corrosion resistance, which is 1 ~ 2 times higher than that of ordinary oxide film; ④ Good heat preservation and electroplating allowance; (5) strong adsorption capacity, and can be dyed into various colors; ⑥ Good covering ability, so the requirements for surface processing of parts are low. It is suitable for the surface protection and decoration layer of various instruments, meters, electronic instruments, parts, appearance parts, daily necessities and food utensils.

(2) Ruby film oxidation method

Recently, Japan has studied a new process of synthesizing ruby thin films by anodic oxidation. The film obtained by this process has excellent appearance and optical properties, and is used in optics, decoration and other aspects. This is a new technology and has a broad application prospect. Firstly, a conventional anode wholesale porous membrane (amorphous AL2O3) is adopted, and the porous membrane absorbs chromium ions; Then the oxide film adsorbed with chromium ions is subjected to secondary anodic oxidation in acid sulfate molten salt; Through secondary electrolysis, the oxide film structure was transformed from amorphous to hairpin-shaped Al2O3, and thus the ruby film was obtained. The main colors of alumina film are: light purplish red, light grayish yellow, light gray, gray, khaki and so on. The fluorescent colors of the oxide film are: deep red, deep purple, red, bright red, bright purple and so on.

(3) Simulation spray oxidation method of milk protein.

Its appearance is similar to a milky white imitation spray paint layer. Beautiful and generous, hard and corrosion-resistant, especially after a long time, the color of the film is not easy to fade.

(4) Marble anodic oxidation

Aluminum and its alloy parts are pre-annealed at 600℃ 1h, etched with mixed solution of hydrofluoric acid, hydrochloric acid, nitric acid and water (1:1) until coarse-grained marbles appear, and then anodized in sulfuric acid solution, and etched with1. Because the oxide film in anodic oxidation is formed on the surface of coarse crystal after annealing and etching, it looks like natural marble and is very decorative.

< color anodic oxide film

The anodic oxide film of aluminum is colored by absorbing dyes.

Autochromic anodic oxide film

This anodic oxide film is a colored anodic oxide film spontaneously generated by the alloy itself under the action of electrolysis of a specific aluminum material in a suitable electrolyte (usually mainly organic acid).

Electrolytic coloring

The coloring of anodic oxide film is achieved by electrodeposition of metal or metal oxide between the oxide films. & gt

Decorative electroplating on common metal surface

chrome-plate

Chromium plating is the most widely used coating in product modeling design at present. Chromium is a silvery white metal with a slight blue color. cannot

As a protective coating, a copper-tin alloy, copper or nickel layer is usually used as a bottom layer to prevent corrosion of the base metal. There are five main types of chromium plating.

1, protection-decorative chromium plating

Plating a layer of chromium on the surface of copper, nickel or alloy coating can obtain silver with fine crystal, beautiful and bright appearance and mirror-like appearance.

Blue luster (some are called cover blue), such as the decorative layer of external parts of automobiles, trains, machine tools and household appliances. Because the decorative chrome-plated layer is bright and dazzling, it should be avoided to be used as a large-area decorative surface in product modeling, so as to avoid strong reflection stimulating the eyes of operators and users and causing fatigue.

2, black chromium plating

Black gives people a sense of solemnity, seriousness and perseverance. In the painting parts of machines, instruments, building decoration materials and hardware and electrical appliances, the combination of black is essential. There are many ways to obtain black color by surface decoration technology, such as painting black paint, galvanizing black, black oxidation of iron and iron wall parts, chemical and electrochemical oxidation of aluminum and magnesium, black dyeing, nickel plating and black chromium. From the aspects of color uniformity, wear resistance, decoration and protection, black chrome coating is the best, which is mainly used in optical systems such as aviation, instruments and cameras, as well as decoration and identification of other products.

3, milky white chromium

Milky white chromium is characterized by dullness, low hardness and no broken net. With the increase of coating thickness, porosity decreases and corrosion resistance is good. The opalescent chromium coating is easy to mark, and the user will not feel eye fatigue. Milky white chromium is widely used in measuring tools, graduated discs, dials, medical instruments and so on.

4, hard chromium plating

This kind of coating is characterized by highlighting the special properties of chromium layer itself through thick coating. Include heat resistance, wear resistance, corrosion resistance and low friction coefficient. Hard chromium is generally plated directly on the surface of steel parts, which is widely used. For example, hard chromium is used for parts of large equipment, such as the large plunger of high-tonnage hydraulic press. It is widely used. Many parts and equipment that will be scrapped due to corrosion and wear, such as machine tool spindle and crankshaft journal, can greatly extend their service life after being repaired by hard chromium plating.

5. Porous chromium plating

Porous chromium plating is a special form of wear-resistant chromium plating. The difference is that there are reticular grooves or punctate pores on the surface of the coating, which is convenient for storing lubricating oil, thus reducing the friction between the chromium-plated workpiece and its sliding fit workpiece and improving the wear resistance of the workpiece. Mainly used in cylinder cavity, piston ring, sliding bearing, machine tool spindle and so on of internal combustion engine.

Silver plating on

Silver is a white, bright, ductile, plastic and highly reflective precious metal. Its hardness is slightly lower than that of copper and higher than that of gold. Silver is very stable in alkaline solution and some organic acids, but it is easily soluble in nitric acid and slightly soluble in sulfuric acid. In the general atmosphere, silver is relatively stable, but in the air containing oxides and sulfides, the surface of silver coating will quickly change color and lose its reflective ability. In addition, silver has excellent electrical properties. Of all metals, silver has the best conductivity. Because of its good conductivity and low contact resistance, silver can improve the electrical properties of products.

Silver has a beautiful silvery white luster and is often used for decoration. The silver plating layer is mainly used for the surfaces of instruments and meters, light industrial products, lamps, reflectors, searchlights and other items that need protective decorative coating and reflective surface coating. The object of silver plating is generally copper or copper synthetic gold sheet. For silver plating of steel and metal parts, plate a layer of other metals or alloys (such as cadmium, brass, bronze, etc.). ) To prevent metal from being corroded, it must be electroplated first. Parts that often come into contact with hard rubber (containing sulfur) are not suitable for silver plating. If high gloss is needed, the parts must be carefully polished before and after electroplating.

There are two main silver plating methods, namely cyanide silver plating and cyanide-free silver plating. Cyanide silver plating is an old process in recent hundred years. Cyanide silver plating solution is stable and reliable, with high current efficiency, good dispersibility and covering ability, and fine coating particles. However, because its solution contains highly toxic cyanide, which seriously endangers the health of electroplating workers, the discharged wastewater will become a "public hazard", which is the biggest disadvantage. Fluorine-free silver plating developed in recent years has been applied after a lot of experiments and research.

alloy plating

With the development of industrial production and science and technology, people put forward various new requirements for the surface properties and appearance of metals. For example, when products are electroplated in a large area, people increasingly hate the shiny electroplating luster and turn to smoky tones and satin-like elegant tones. Therefore, electroplating alloys have been developed. Several decorative electroplating alloys that have been applied to product surface decoration are briefly introduced.

1, electroplating tin-cobalt alloy

Tin-cobalt alloy electroplating is similar to cobalt electroplating in tone, but softer, and is loved by people. At present, it is mostly used to replace chromium abroad. Cobalt electroplating is not easy to barrel plate, and tin-cobalt alloy electroplating is suitable for barrel plating of small parts. In addition, tin-cobalt alloy electroplating has excellent uniform electroplating ability and barrel plating ability, so it can be applied to workpieces with complex shapes. If double-layer nickel is electroplated on the bottom layer, its corrosion resistance is no less than chromium plating. In order to prevent the surface from discoloring, it is treated with chromate, which can also improve its corrosion resistance.

Its appearance is a faint rose color, which makes people feel very comfortable and has excellent corrosion resistance. As for luster

A good glossy surface can be obtained by electroplating tin-nickel alloy on the substrate or bright nickel electroplating layer. If the dull surface (pear pattern) is electroplated, the original condition of the surface can be reproduced. Electroplating layer has excellent plating ability and almost no leveling effect, which is suitable for electroplating products requiring extremely fine lines and rotary machining.

3. Electroplating Cu-Sn alloy

The low tin bronze coating is pink or golden yellow with good crystallization. It has high corrosion resistance and good polishing performance, and is often used as a protective and decorative nickel primer, which is widely used in light industry, handicraft industry, mechanical instrument industry and other industries. The medium tin bronze coating is golden yellow and has good corrosion resistance. Mainly used as the bottom layer of decorative chromium plating. Its hardness and stability in air are higher than that of low tin bronze coating. However, due to the high tin content in the coating, the protective decorative coating is prone to frost after chrome plating, which is the weakness of the medium tin bronze coating. High tin bronze coating has beautiful silvery white luster, good polishing performance, high hardness and wear resistance. It is used to replace silver or chromium as a protective and decorative surface coating for reflective instruments, meters and daily commodities in industrial design.