To understand the principle and formula of paint stripper

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   paint removerIt is a solvent or paste that can dissolve or swell the coating film. It is mainly composed of solvents with strong dissolving ability and paraffin wax, cellulose, etc. In the shipbuilding industry, the old coating is mainly removed by mechanical methods such as manual shovel, shot blasting, sand blasting, high-pressure water and abrasive jet, etc. However, for aluminum hull, because the mechanical method is easy to scratch aluminum, sandpaper polishing, paint remover and other methods are mainly used to remove the old coating. Compared with sandpaper sanding, the use of paint remover to remove the old coating film has the advantages of safety, environmental protection and high efficiency. The advantages of using paint remover are high efficiency, use at room temperature, low corrosion to metals, simple construction, and no need to increase equipment. Its disadvantage is that some paint remover is toxic, volatile, flammable, and costly. In recent years, a variety of new paint remover products continue to emerge, water-based paint remover is also produced, paint removal efficiency continues to increase, environmental performance continues to improve, non-toxic, low-toxic, non-combustible products have gradually occupied the mainstream market of paint remover.
Principle and Classification of 1. Paint Remover
1. Principle of paint stripping
Paint remover paint mainly by means of organic solvents in the paint remover can dissolve and swell most of the coating film, in order to achieve the purpose of removing the old coating film on the surface of the substrate. When the paint remover permeates the polymer chain gap of the coating polymer, it causes the polymer to swell, causing the volume of the coating film to increase continuously, and the internal stress generated by the increase in the volume of the coating polymer weakens and finally destroys the adhesion of the coating film to the substrate. The coating film swells from point to piece swelling, wrinkles the coating film, completely destroys the adhesion of the coating film to the substrate, and finally bites and removes the coating film.
2. Classification of paint remover
The paint remover is divided into two categories according to the different film-forming substances removed: one is made of organic solvents such as ketones, benzene and esters and paraffin wax, commonly known as white liquid medicine, which is mainly used to remove old coating films such as oil-based, alkyd and nitro-based paint. This kind of paint remover is mainly composed of some volatile organic solvents, there are flammable, toxic and other problems, the price is cheaper.
Another kind is dichloromethane, paraffin and cellulose ether as the main components of the preparation of chlorinated hydrocarbon paint remover, commonly known as water flush type paint remover, mainly used to remove epoxy asphalt, polyurethane, epoxy polyphthalein amine or amino alkyd resin and other curing of the old film. The paint removal efficiency is high, the toxicity is small, and the application is wide. The paint remover with dichloromethane as the main solvent is divided into neutral paint remover (pH = 7±1), alkaline paint remover (pH>7) and acidic paint remover (pH<7) according to the difference of pH value. At present, water-based non-toxic paint remover products have emerged as a new type of paint remover products.
Composition of 2. paint remover
1. Main solvent
The coating can be bitten up, mainly rely on the main solvent molecules penetration, swelling and dissolution process to complete. In chlorinated hydrocarbon solvents, chlorinated alkane compounds have the ability to remove paint, of which dichloromethane has a small molecular weight and strong penetration ability, which can penetrate into the polymer segment gap of the coating film and swell the polymer. It is most widely used in the main solvent of paint stripper at home and abroad.
2. Volatilization inhibitor
Dichloromethane, as the main solvent, has a boiling point of only 300C, and its volatilization speed is quite fast. When coated on the surface of the coating film, the coating film has not been bitten up, and the main solvent has been volatilized, thus the paint stripping effect is greatly reduced. Therefore, in the preparation of paint remover, we must try to reduce its volatilization rate, or prevent the main solvent volatilization, so that it can have enough time to stay and penetrate the old film, the film expansion or dissolution bite. Commonly used volatile retarder for paraffin wax, paraffin wax boiling point were 58-60 ℃ and 72-80 ℃, evenly dispersed in the paint remover of paraffin wax, coated on the surface of the coating film, the outermost surface of the paint remover to form a thin sheet sealing layer, play the role of slow low boiling point solvent volatilization. Paraffin wax is easy to remain on the surface of the base metal during the paint stripping process, which will affect the adhesion of the new paint layer to the substrate. Therefore, when using a paint remover with paraffin wax, the surface of the substrate must be thoroughly cleaned to completely remove the residual paraffin wax before repainting the new paint.
3. Thickener
The workpiece to be stripped has various sides. If the liquid paint remover flows, it will not have the effect of stripping, and thickener should be added appropriately. Commonly used thickeners are polyvinyl alcohol, methyl cellulose, ethyl cellulose, fumed silica (white carbon black), etc. The use of one or several thickeners not only improves the viscosity of the paint remover, making it suitable for painting on vertical surfaces or special parts without sagging and dripping, but also improves the stratification phenomenon and improves the storage stability of the paint remover.
4. Activator
At present, the use of epoxy, polyurethane and other two-component coatings, chemical resistance to the performance of the medium is better, to bring difficulties to the paint. In order to improve the efficiency of paint stripping, some nucleophilic solvent-activator can be added to the paint stripper to accelerate the destruction of macromolecular chain segments, strengthen the penetration and swelling of the main solvent to the coating, and play a role in accelerating paint stripping. Activators are mainly phenols, amines or some organic acids, commonly used are phenol, formic acid or ethanolamine. These chemicals have irritating and corrosive effects on operators. When using paint strippers containing these chemicals, attention must be paid to labor protection.
5. cosolvent
The commonly used cosolvents in paint remover are methanol, ethanol and isopropanol, etc. The addition of these alcohols. It can form a binary azeotrope with a lower temperature with the main solvent such as dichloromethane, and at the same time it is conducive to the dissolution of cellulose and plays the role of a latent solvent. The main solvent can fully penetrate into the coating film and accelerate the speed of paint removal. In addition, the use of alcohols and other cosolvents can also obtain better viscosity stability, and ethanol is generally used as a cosolvent.
6. Emulsifier
During paint removal, the emulsifier can improve the water washing performance of the paint removal surface, and at the same time can improve the storage stability of the paint remover and improve the consistency of the paint remover. There are many varieties of emulsifiers, such as OP-10,OP-7 and sodium alkylbenzene sulfonate.
7. Other additives
In the paint remover, according to the user's requirements, such as corrosion inhibitors, penetrants, wetting agents, etc. are added. Add a small amount of people but can play a very good role, such as adding a small amount of corrosion inhibitor can reduce the corrosion of paint remover on aluminum alloy. The new paint remover products are generally added with different additives to improve the performance of the paint remover, but also to make the variety of paint remover more diversified.