1. The principle of metal vapor phase rust prevention

1.1 Corrosion of metals

Metal materials are deteriorated and damaged due to chemical or electrochemical interaction with the environmental medium in which they are located. This phenomenon is called corrosion. According to the reaction mechanism of metal corrosion, corrosion can be divided into electrochemical corrosion and chemical corrosion. Electrochemical corrosion refers to the damage caused by the electrochemical interaction between the metal surface and the ion-conducting medium; chemical corrosion refers to the damage caused by the pure chemical interaction between the metal surface and the non-electrolyte. Among them, electrochemical corrosion is the most common and common corrosion, because as long as there is condensed water in the medium that composes the environment, metal corrosion will proceed in the form of electrochemical corrosion.

1.2 Anti-rust principle of VCI plastic film

The anti-rust and anti-rust effect of the VCI plastic film is actually the anti-rust effect of the VCI using the plastic film as the carrier. VCI or VPI (VCI or VPI for short) can directly vaporize (or sublime) under normal temperature and pressure. Under normal temperature and pressure and relatively closed conditions, VCI uses its own material characteristics and The difference in the molecular structure of the polymer resin plays a sublimation effect, that is, the vapor phase rust inhibitor migrates stably and uniformly inside the plastic film package, and then vaporizes, and the vaporized and diffused gas gradually reaches a saturated state. The vapor phase rust inhibitor will diffusely immerse and adhere to the surface of the metal products and the inside of the components in the plastic film packaging to form a dense and transparent gaseous protective layer to prevent the metal from being corroded. And because the rust inhibitor molecule exists in a gaseous state, it has the function of permeating. No matter how complicated the shape of the inside and outside of the metal product, the rust preventive gas can still be effectively attached to the inner and outer surface of the metal component to prevent the oxidation of the metal product. , So as to obtain the ideal anti-rust effect.

2. Development status of VCI plastic film

VCI plastic film is a kind of anti-rust packaging material formed by adding corrosion inhibitor to plastic film in a certain way. In the early days, the coating type anti-rust film was the main representative. With the innovation of processing technology, the current mature vapor-phase anti-rust plastic film products are processed by extrusion blow molding, that is, VCI is added in the form of micro powder to be compatible with it. Among the high-molecular resins with good properties, the VCI plastic masterbatch is made by extrusion granulation, by which the masterbatch is added to the polyolefin resin, and then the film is made by extrusion blow molding. What is commonly used in the market is to combine anti-rust masterbatch and polyethylene (PE) resin.

After a certain process, it is blown into plastic films of different specifications. For example, Suzhou Qiyang Anticorrosion Technology Co., Ltd. adopts its self-developed vapor phase anticorrosion masterbatch and LDPF resin to mix with the international advanced three-layer co-extrusion blown film production line blow molding.

At the end of the 1990s, my country had independent intellectual property rights for the manufacture of VCI plastic film, which broke the international technology monopoly, realized the localization of VCI plastic film, and made the material rapidly popularized and applied. With the continuous expansion of the application field, the performance requirements of the vapor phase anti-corrosion plastic film are also multi-functional.

According to function and structure, it can be divided into the following main types:

VCI plastic film for general multi-metal: a product formed by uniformly dispersing the micropowder of vapor phase corrosion inhibitor in the plastic film, with simple structure and maximum dosage;

Antistatic type: a plastic film with antistatic function formed by adding an antistatic agent to an ordinary antirust film, which is mainly used for antirust packaging of electronic, electrical products and equipment with antistatic requirements;

Stretching type: It has ultra-high elongation, puncture resistance, self-adhesive, and can be used for tightly wound packaging of metal parts;

Shrinkable type: anti-rust film that shrinks when exposed to heat, mainly used for the fastening and packaging of metal parts;

Reinforced type: composite materials with high strength (such as tensile strength, puncture strength, tear strength, etc.) made by compounding high-strength materials, which are widely used in anti-rust packaging of heavy metal products;

High barrier type: films with high barrier properties made by multi-layer co-extrusion or compounding, such as aluminum-plastic composite anti-rust film, etc. This type of material has the characteristics of low moisture permeability and low air permeability, especially suitable for high Long-term sealing and rust prevention of precision and high value-added products.

VCI plastic film has many characteristics that paper products do not have, such as transparency, beauty, water resistance, oil resistance, good airtightness, recyclability, environmental protection, etc., and are widely used in electromechanical, auto parts, weaponry and other fields.

3. The sustainable development of VCI plastic film

3.1 Product planning, adhere to sustainable development

Safety, environmental protection, and sustainable development products have been reflected in various fields such as production and life. The implementation of green packaging and green design of products are the direction and focus of the efforts of all countries in the world. As a representative of advanced anti-corrosion packaging technology, the green design of vapor-phase anti-corrosion plastic film should focus on choosing safe, efficient, and multi-functional vapor-phase corrosion inhibitors, choosing recyclable or degradable carrier materials, and adopting innovative manufacturing processes , Effectively recycle and reuse waste, and achieve the design goal of green vapor phase anti-corrosion plastic film packaging.

3.2 Choose safe and efficient raw materials to create a green source

3.2.1 Selection of vapor phase corrosion inhibitors, adhere to diversification, high performance, and environmental protection

There are many types of vapor phase corrosion inhibitors, each of the following types is listed below to illustrate:

category

Corrosion inhibitor

Action metal

Harmful

Use alone

Organic amines and their salts

Hexamethine tetramine (Urotropine)

Ferrous metal, aluminum alloy

No obvious toxicity

can

Organic acids and their salts

3,5-Dinitrobenzoic acid hexamethyleneimine

Universal vapor phase corrosion inhibitor

No obvious toxicity

can

Nitrite

Sodium Nitrite

black metal

poisonous

can

Carbonate

Cyclohexylamine carbonate

Steel, cast iron

Non-toxic

can

Heterocyclic compound

Benzotriazole

Copper, silver

Non-toxic

can

Chromates

Cyclohexylamine Chromate

Steel, copper, aluminum, zinc

poisonous

can

A kind of vapor phase corrosion inhibitor alone is not very effective, and the effect is single. It will be better to use different vapor phase corrosion inhibitors in combination. For example, the combination of urotropine, sodium benzoate and sodium nitrite can be integrated The advantages of these three have a wide range of applications to metals, a more ideal corrosion inhibition effect, and a longer action time. According to national environmental protection requirements, the following substances in packaging materials are restricted substances: Cd cadmium, Pb lead, Hg mercury, Cr hexavalent chromium, polybrominated biphenyls, polybrominated diphenyl ethers, phthalates, polycyclic aromatic hydrocarbons, halogens, perfluorooctanoates And lipids, polyvinyl chloride and other substances.

Based on the needs of environmental protection and sustainable development strategies, industrial corrosion inhibitors require not only good corrosion inhibition performance, but also safety and environmental protection, and no harm or adverse effects on the environment and humans. The research and development of environmentally friendly corrosion inhibitors are proposed . Cinnamaldehyde, benzoate, fatty acid, fatty amine, carboxylate, gluconic acid and its salts, amino acid derivatives, silicate, phosphate, etc. are all environmentally friendly vapor phase corrosion inhibitors.

3.2.2 Plastic raw material resin, insist on selecting functional and environmentally friendly materials

The commonly used plastic materials and functions are shown in the following table:

scientific name

Abbreviation

Chinese scientific name

Common name

use

Polyethylene

PE

Polyethylene

Food packaging bags, tableware

Polypropylene

PP

Polypropylene

100% plastic, plastic

Microwave lunch box

High Density Polyethylene

HDPE

High-density polyethylene

Hard soft glue

Cleaning supplies, bath products

Low Density Polyethylene

LDPE

Low-density polyethylene

Cling film, plastic film, etc.

Linear Low Density Polyethylene

LLDPE

Linear low density polyethylene

Polyvinyl Chloride

PVC

Polyvinyl chloride

Vinyl

Rarely used for food packaging

Polyethylene Terephthalate

PET

Polyethylene terephthalate

Polyester

Mineral water bottle, carbonated drink bottle

Polybutylene Terephthalate

PBT

Polybutylene terephthalate

Polyamide(Nylon 6.66)

PA

Polyamide

nylon

Polycarbonates

PC

Polycarbonate

Bulletproof glue

Kettle, water cup, milk bottle

Polyacetal

POM

Polyoxymethylene resin

Saigang, Duogang

Polyphenyleneoxide

PPO

Polyphenylene ether

Noryl

Polyphenylenesulfide

PPS

Polyphenylene sulfide

Polyphenylene sulfide

Polyurethanes

PU

Polyurethane

Polyurethane

Polystyrene

PS

Polystyrene

Bowl of instant noodle box, fast food box

3.3 Treatment of packaging waste, adhere to recycling and sustainable development

Develop degradable plastic carriers. Degradable resin material is used as the carrier of vapor phase corrosion inhibitor to produce degradable vapor phase rust preventive plastic film to prevent packaging waste pollution from the source.

The recycling of packaging waste is currently the most important aspect of the world's green packaging and circular economy. The recycling of anti-rust packaging has good economic and ecological benefits. In view of the many types of vapor phase anti-corrosion plastic films, the recycling process should be collected and processed separately to facilitate reuse. It is necessary to increase investment in technology and capital in the recycling and reuse of waste gas phase anti-corrosion plastic films.

4. Prospects for the sustainable development of VCI plastic film

As an emerging product and technology, VCI plastic film plays an increasingly important role in the field of metal anticorrosion. Under the requirements of environmental protection and sustainable development, VCI plastic film will have the following development trends: Corrosion inhibitors for rust films are developing towards universal, high-efficiency, non-toxic and environmental protection. Suitable for multi-metal anti-rust protection, general-purpose vapor-phase anti-corrosion film products that do not contain harmful substances such as nitrite; developing in the direction of product structure diversification, form diversification, and substrate resin diversification, such as vapor-phase anti-corrosion biodegradable film , Polyvinyl acetate anti-rust film, etc.

references:

[1] Zhang Daquan. Vapor phase corrosion inhibitor and its application [M]. Beijing: Chemical Industry Press. 2007.5.

[2] Jiang Wei, Gong Min, Zhao Jinping. Research progress of natural plant green corrosion inhibitors[J]. Corrosion Science and Protection Technology, 2007, 19(4): 278-281.

[3]Sun Kai. Development trend and improvement direction of vapor phase anticorrosive plastic film [Journal Paper]. Plastic Packaging. 2014(3).

[4]Liu Hong, Tang Yanqiu, Shen Ping, Bai Fang, Zhou Xianliang, Zhao Baidong. Green design of VCI packaging materials [Journal Paper]. 2010.07.002.

[5] Wu Yinshun, Zheng Jiashen. Electrochemical protection and corrosion inhibitor application technology [M]. Beijing: Chemical Industry Press. 2005.6.