Anti-corrosion packaging technology (2)

Anti-corrosion packaging technology (2)

Second, anti-rust treatment technology
(1) Anti-rust treatment technology for anti-rust oil
If the metal surface is isolated from various factors that cause atmospheric corrosion (ie, the metal surface is protected), the purpose of preventing corrosion of the metal atmosphere can be achieved. The anti-rust oil packaging technology is based on this principle to prevent corrosion.
Anti-rust oil is a temporary anti-rust coating composed of oil-soluble or resinous substances and an oil-soluble corrosion inhibitor and other additive components. The grease or resinous substance in the rust preventive oil is applied as a film-forming substance to the surface of the metal, and has a certain insulating effect on the rust factor. However, the general oils and fats can dissolve a small amount of oxygen in the air, and can also dissolve a small amount of water. The use of oil alone cannot obtain a satisfactory anti-rust effect. Therefore, it is necessary to add a corrosion inhibitor, which has a very good anti-rust effect on the anti-rust oil. Great impact.
1. The principle of action of anti-rust oil
(1) Adsorption on metal surfaces
Due to the surface active substance, it has a common feature in the molecular structure--having a hydrophilic polar group and a lipophilic non-polar base. When the anti-rust oil is applied to the metal surface, the corrosion inhibition in the oil is dispersed. The agent molecules are oriented at the interface between the metal and the oil (polar group and metal adsorption, non-polar groups and oil adsorption), and can form an interfacial film of a multi-molecular layer. Tests have shown that if only one or two molecular layers of the film are formed, the rust-preventing ability is very poor. When the adsorbed layer is more than 6 molecular layers, it has a good anti-corrosion ability. The adsorption form of the molecule is shown in Figure 6-10.

This adsorption has a shielding effect on the rust factor. Second, it can improve the adhesion of the oil film to the metal surface. Since the surface of the adsorption film is hydrophobic, it has better water repellency and can increase the electrical resistance of the metal surface.
Many studies have shown that chemical adsorption of corrosion inhibitors on metal surfaces (forming valence bonds) reduces metal activity, which is one of the main reasons for rust prevention.
(2) It can reduce the interfacial tension between the water droplets and the oil layer falling on the oil film.
If water droplets form on the surface of the oil film (such as condensation, etc.), the interfacial tension between the water droplets and the oil makes the water droplets spherical, and it is easy to penetrate into the oil film to reach the metal surface by gravity. A surfactant such as a corrosion inhibitor can lower the surface tension of water, so that water droplets cannot exist in a spherical state on the oil film, and tend to spread out. This reduces the pressure of the water droplets on the oil film, making it difficult to penetrate the oil film to the surface of the metal. The flatter the water droplets spread on the surface of the oil film, the better the rust prevention effect of the oil. Therefore, determining the contact angle of water droplets on the oil film is the most common method for identifying the anti-rust effect of anti-rust oil (see Figure 6-11).

The relationship between the contact angle of water droplets on the oil surface and the interfacial tension is as follows:
So-Suo=Sucosθ
Cosθ=(So-Suo)/Su
Where: So--oil surface tension
Su--surface tension of water
Suo--interfacial tension of oil and water
(3) Displacement of water
A surface-active corrosion inhibitor that can displace water adsorbed on the metal surface by its interfacial adsorption. In addition, the moisture contained in the oil can be stabilized in the oil by the colloidal or interfacial film of the corrosion inhibitor so that it cannot be in direct contact with the metal.
All of the above effects inhibit the formation of rusted cells on the metal surface, thereby achieving the purpose of preventing corrosion of metal products.
2, the type of anti-rust oil
There are many types of anti-rust oils, and anti-rust oils suitable for packaging metal products mainly include anti-rust grease, solvent-diluted anti-rust oil, and thin-layer oil and instrument anti-rust oil.
(1) Anti-rust grease
Antirust grease is a type of antirust oil based on petrolatum which is fat at normal temperature. It is composed of a film-forming substance (or base oil) and a corrosion inhibitor.
Film-forming substances (or base oils): mainly Vaseline and lubricating oil. Vaseline is generally made of industrial petroleum jelly. Its chemical composition is 15% paraffin, 45% petroleum grease, 25% cylinder oil and 15% mechanical oil. For anti-rust oil, petrolatum is required to be non-corrosive, free of moisture, and has a certain degree of water resistance. The dropping point temperature is 45 °C. Lubricating oils commonly used in anti-rust oils include mechanical oils, spindle oils, and cylinder oils. Its chemical composition is mainly alkane, cycloalkane and aromatic hydrocarbons, as well as a small amount of oxides and sulfides.
Corrosion inhibitor: The oil-soluble corrosion inhibitor commonly used in anti-rust grease mainly includes petroleum sulfonate, aluminum stearate, zinc naphthenate, oxidized petroleum grease, lanolin and its derivatives, etc. Add benzotriazole and the like. The type of corrosion inhibitor used in the anti-rust grease can affect the performance of the anti-rust grease. For example, the anti-rust grease added with aluminum stearate has good salt water resistance, but the adhesion to metal is weak; the anti-rust grease added with barium petroleum sulfonate has better salt resistance and can be used for rust prevention in the marine atmosphere; The anti-rust grease added with lanolin and its soap has strong adhesion to metal, has certain emulsifying ability to water, and has strong anti-rusting ability; zinc naphthenate anti-rust grease has strong adhesion to metal and has certain Resistance to salt water, but poor anti-rust ability to cast iron; rust-preventing grease added to oxidized petroleum grease and its soap is superior to fatty acid soap, but its resistance to salt water is poor; addition of anti-salt-80-type synthetic lipid Grease has poor thermal stability and is corrosive to copper. Benzotriazole has excellent anti-rust effect on copper and its alloys. In practice, in order to obtain satisfactory results, a combination of several corrosion inhibitors is often used.
The anti-rust grease is in the form of ointment at normal temperature, so the film layer is generally thick (up to 0.5 mm), is not easy to lose, and is not volatile. After sealing and packaging, the general anti-rust period is longer, up to two years.
The coating method of the anti-rust grease is mainly a hot dip method, that is, the anti-rust grease is heated and melted to a flowing state before coating, and the washed, rust-removed, dried metal product is immersed for a while, and then taken out and cooled to solidify the oil film. In hot dip coating, the same type of oil has different oil film thickness due to different dip coating temperatures. The lower the temperature, the greater the oil film thickness and the stronger the oil repellency. Large-scale parts can be painted by hot brushing. The hot-melted anti-rust grease is applied to the surface of metal products with a soft brush. After the metal products are oiled, they should be covered with paraffin paper or plastic bags in time to prevent the oil layer from drying out. And contaminated packaging.
(2) Solvent diluted antirust oil
The solvent-diluted rust preventive oil is composed of a solvent added to a rust preventive oil containing a mineral oil or a resin as a film-forming agent, and other additives such as an antioxidant, a stabilizer, and the like are also added. Such rust preventive oils can be classified into three types according to the type of solvent: petroleum series solvent, organic solvent and water dilution, wherein the organic solvent is toxic, so the application is less. According to the nature of the oil film, such rust preventive oil can be further divided into hard coat oil and soft film oil.
Durum oil - the resin used as a hard coat oil should first have a large solubility in gasoline and kerosene, followed by corrosion of various metals. Currently selected resins are tert-butylphenol formaldehyde resin (ie 2402), long oil alkyd resin, melamine formaldehyde resin, terpene resin, petroleum resin and alkyl acid resin. Among them, 2402 resin and alkyl acid resin are preferred. Commonly used hard coat oils are hard-1, hard-3, 1, 2, 74A-2. Both hard-1 and -3 use 2402 resin as the film-forming substance, but the amount of 2402 in the hard 1 is large, so the oil film has poor toughness, which is not suitable for sharp-edged metal products, and may be powdered in long-term sealed packaging. However, the content of 2402 in hard-3 is less, and the addition of 389-9 alkyd resin improves the toughness of the oil film. However, hard-3 is less adaptable to non-ferrous metals such as copper alloys than hard-1. For ease of identification, there is a small amount of 3902 oil soluble red pigment in the hard-3. 74A-2 is a hard alkyl oil which is a film-forming material of an alkyl acid amino resin and an oxidized petroleum film cerium soap. It is suitable for various metals (including magnesium alloys), has good stability and strong adhesion. The hard film anti-rust oil has good film-forming protection, the film surface is smooth and non-sticky, and it does not flow in winter without cracking, and the construction is convenient and the price is cheap, but the hard film is not easy to remove. The natural drying time of the film formation is about 1 h.
Soft film oil - commonly used soft film oil is 204-1, Hu Shi 0-1, F-35, 112-5, 704, No. 3 anti-rust oil, 33-612 and soft-1. 204-1 oil is a sulfonated lanolin calcium soap as a film forming agent and a corrosion inhibitor. Hu Shi 0-1, F-35 is based on Vaseline as a film former. 112-5, 704, and 3 anti-corrosion oils, 33-6 and soft-1 are all anti-corrosive oils with oxidized petroleum saponin soap (T743 saponin) as a film-forming agent and corrosion inhibitor. The main feature of the solvent-based soft film oil is that the metal surface can form a film, so that the loss is small but it is not easy to remove, and the rust prevention period is short.
Since rust preventive oil is used as a rust-proof sealing coating, there are many disadvantages, such as environmental pollution during construction, affecting the appearance of metal products, and removing the film during use. Therefore, the anti-rust coating for sealing has been gradually replaced by thin films and ultra-thin films.
The film anti-rust coating can form a complete film with a thickness of 1~2μm or less. The film has strong adhesion to the metal surface. The film has good rust resistance and does not affect the performance of the lubricant. When used, there is no need to remove rust. At present, the film and ultra-thin film anti-rust coatings mainly include polyvinyl fluoride and polyvinyl fluoride, and other types of synthetic resin, silicone silicone and silicone resin.
The soft film oil in the solvent-diluted anti-rust oil is mainly suitable for the sealing of metal products. It can be sprayed or dip coated (the solvent can be used less); then sealed in a plastic bag. The main coating method of dura mater oil is sprayed with compressed air, but this spray method will not be partially sprayed. The metal surface without local anti-rust coating will continue to rust in the air, and even rust will be faster.
(3) Thin layer oil
This is an anti-rust oil which is a film-forming material of a resin or the like, and is characterized in that the anti-rust period is long, the oil film is thin and transparent, and the use amount is good. Thin layer oils are solvent based and solvent free.
Thin layer oils are usually dip coated or spray coated.
(4) Instrument anti-rust oil
This is a low-viscosity anti-rust oil. It is mainly based on the combination of corrosion inhibitors such as lubricating oil and other liquid mineral oils. It is commonly used in the full-immersion sealing packaging of instruments and instrument parts, that is, in closed packaging containers. Add rust preventive oil, immerse the instrument or precision parts in oil for sealing, or use dip coating and sealed packaging.

(2) Gas phase anti-rust packaging technology
The gas phase anti-rust packaging technology is a technology for preventing rust of metal products in a sealed packaging container by using a vapor phase corrosion inhibitor (volatile corrosion inhibitor). A vapor phase inhibitor is a substance that slows or completely stops the destruction process of a metal in an aggressive medium. It is volatile at normal temperature and volatilizes or sublimates in a sealed package in a short time. The corrosion inhibitor gas can fill the corners and gaps of the entire packaging container and adsorb on the surface of the metal product, thereby suppressing the corrosion of the atmosphere to the metal. Since the gas phase rustproof packaging technology does not need to be coated on the surface of the metal product, the rustproof packaging method does not affect the appearance of the metal product, and the product is also slightly peeled off from the product, and does not pollute the package. The anti-rust period is long, and the effective anti-rust period can reach 3 to 5 years, and some can reach more than 10 years. However, its resistance to sweat rust is poor, and many vapor phase inhibitors cannot be used in a variety of metal combinations, and the irritating odor is large.