Plastics metallization - procedure technology
Chemical metallization of plastics makes it possible to manufacture such industrial types of products and semi-finished products as printed circuit boards, light filters, catalysts, as well as blanks for electroplating and many others.
Metallization will make it possible to improve the resistance of plastic to mechanical influences, high temperatures and moisture.
Moreover, parts that use a combination of metal and plastic weigh much less than just metal.
Copper is most often used as a sublayer surface for electroplating. It is the copper layer that will act as a damper for the plastic, due to which the voltage will be stabilized, which are inevitable with a significant difference in the coefficient of thermal stress of such dissimilar materials.
the sub-layer will be additionally chrome-plated or nickel-plated as described below.
Composition of layers:
- Brushed copper layer.
- Shiny copper layer.
- A metal with a chemical type of deposition.
- Nickel high-gloss layer.
- Semi-shiny nickel layer.
- Nickel matt layer.
- Shiny chrome layer.
- Conversion layer.
- Shiny and matt metallic layer.
The structural components that are applied to the electrically conductive sub-layer of the coating can vary greatly. We can talk about films of shiny, velor, clarified, blackened, patinated and other types.
The fact is that nickel can compress plastics, strongly strengthening the material.
Features of the structural composition that will be applied to the electrically conductive coating layer can vary greatly. We are talking about films of clarified, shiny, blackened, velor, patinated and other types. The purpose of films is not only to improve the appearance of products. For example, nickel plated coatings extend the life of plastics.
The point is that nickel can settle down on plastic, significantly strengthening the material. To be able to create an electroplating coating, an electrolyte is required.
There are different types of electrolytes used, including:
Other metals such as zinc or tin should also be used. But before applying these types of metals, passivation is required, after which a film will appear on the surface (with or without color). These types of films will keep the material from rusting or depositing.Chemical metallization of plastics is characterized by the fact that the sublayers of the metal type do not have high electrical conductivity. In any case, the conductivity will be much lower than in the case of the electrolyte.
For this reason, during electrochemical deposition, the current density used should be low - from 0.5 to 1 Ampere per square decimeter. If the density is higher, a bipolar effect will appear, which will lead to dissolution of the coating near the place where there is contact with the conductive suspension. In certain cases, nickel or copper will be deposited on the chemically deposited metal layer to avoid dissolution of the coating. In this case, all this is done at a low electric current density, but further layers will be applied in the standard mode.
Features of obtaining electroplated coating
First of all, the galvanic layer will ensure the resistance of the metal to corrosion processes. During galvanization, the parts will be in dense electrolytes. Thus, for the operation to be successful, special weights will be hung on the parts.
Note that electroplated coatings will differ from metallic ones in that much more contacts are required to create them. The process of galvanizing plastics will also be characterized by the complexity of the preparation stage, because in this case it will be much more difficult to ensure an excellent degree of adhesion.
Adhesive properties of materials
A little more about the metallization of plastics. The adhesion will be characterized by the quality of adhesion by different types of elements (in this case, it will be about adhesion between plastic and metal). The bond strength between plastic and metal coatings should be between 0.8 and 1.5 kN per meter for peel, and equal to 14 MPa at break.
The maximum possible degree of adhesion attainable with modern technological means is approximately 14 kN per meter. The adhesion properties of materials will be a rather complex phenomenon. We can also say that there is no single theory that can fully answer all questions regarding the adhesion of various materials to each other.
From the point of view of chemical science, adhesion is a chemical relationship between bodies of different types. Chemical interactions can be seen on plastic surfaces.
In such places, there are functionally active groups that will contact with metals or cover metal surfaces with oxides. The molecular approach interprets adhesion as a consequence of the presence of intermolecular forces at the interface, as well as the interaction of two poles or the appearance of hydrogen bonds.
This will explain, for example, the adhesion of wet etched polyethylene films after drying.If we talk from the point of view of electrical theory, adhesive qualities appear due to the fact that a double electric layer appears during the interaction of a pair of bodies. As a result of this action, the layer will not allow the bodies to move away from each other, because electrostatic forces of the reciprocal type of attraction of various charges work.
According to the diffusion theory (the most popular), adhesion will occur due to interactions of the intermolecular type, which features are clearly manifested during the mutual penetration of molecules into the surface layers. At the same time, a certain intermediate layer appears, as a result of which one can observe the absence of a clear boundary between the materials. And finally, the mechanical version of the theory would explain adhesion by an anchorage type of adhesion, which protrudes parts of the metal into depressions on the plastic surface. Such depressions are rather insignificant in area (several micrometers), but when the metal deposited by the chemical method gets into them, so-called mechanical locks appear.
Other parameters will also affect adhesion, among which the following can be distinguished:
- Strength characteristics of plastic.
- The presence of favorable reactions of reactive groups on the surface of plastics.
- The presence of stimulators of adhesion processes, which may otherwise be called promoters (tin and chromium compounds, as well as plasticizers).
- Lack of anti-promoters that can prevent the strengthening or even destruction of the intermediate layer type.
- The structure of the material that is chemically deposited, as well as the parameters at which deposition occurs.
The technology of vacuum metallization of plastics will consist of spraying nichrome or aluminum plastic on the surface by means of a vacuum.
The application of metal to plastic using a vacuum is carried out in a special chamber. The technique is widely used to apply metal film to various surfaces, for example, automotive parts, plumbing fixtures, plastic fittings, lighting equipment, and more. To clean the metal, special paints and varnishes are used, which are distinguished by an increased degree of hardness and resistance to moisture.
There are only a few methods of self-deposition of metal on a plastic coating. The most accessible of these is chemical.
In this case, no specialized equipment is required. The metals used for the process are copper and silver. The resulting film will be only a few microns thick, but will give the base a beautiful metallic-type look.
Before starting processing should be sanded and degreased as best as possible. If the part has bulges (defects), which should be carefully reduced to nothing.
Sprinkle abrasives on the surface and wipe the surfaces with a swab. If you are dealing with polyacrylates, you will need a caustic soda solution for degreasing, in which the parts must be soaked throughout the day.
Gasoline is recommended for degreasing polyamides. When the product is defatted, it should be washed in distilled water, and then for 60 seconds we keep it in a 0.5% solution of tin chloride and hydrochloric acid (0.
04 kg per liter).
This process is called sensitization. Its purpose will be to obtain a tin hydroxide film on the plastic. After this process, the surface should be activated. To do this, soak the part in a solution of silver nitrate for 3-4 minutes (2 grams of silver per 1 liter and 2 grams of ethyl alcohol).
Next, place the item in a solution, which consists of the following ingredients:
The solution temperature should be from +18 to +25 degrees, and the processing time will be 1 hour.
Metallization with silver
Pre-treatment of the plastic should be carried out in the same way as in the case of copper - sand and apply a layer of abrasive. Wash the surface in soapy water and then in distilled water.
The product should be degreased using the following solution:
- Chromic anhydride - 0.1 kg per liter.
- Iron sulfate - 0.01 kg per liter.
After degreasing, it must be rinsed again with the part in distilled water. The sensitization process should be carried out in a solution of stannous chloride (only 2 grams per 1 liter).
Then place the product in a solution containing the following components:
The recommended solution temperature is from +19 to +25 degrees. The processing time is 1 hour, and as a result, a shiny and even layer of silver should appear. If, however, there is heterogeneity somewhere, then this can be explained by insufficient degreasing of the surface. In this case, remove the applied silver and repeat the work again.
To remove silver from the surface of the plastic, the following solution is required:
We recommend treating a uniform film with a varnish layer that will protect the plastic. Further surface treatment by galvanic method is also possible.
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