Research Progress of Acrylic Emulsion and Its Application in Industrial Coatings

1 Technical progress of acrylic emulsion

1.

The performance of acrylic emulsion has a great relationship with the structure.
Different structural designs provide different performances.
Figure 1 shows the common acrylic structural designs in current literature reports [3].
Among them, monodisperse is the most common and simplest type.
Most acrylic emulsions are of monodisperse type, with simple process, easy-to-control structure, and stable product quality; there are mostly researches on core-shell structure [4], and there are also structures with special functions, such as bimodal structure, blended structure, and multi-microdomain.
structure, a multi-gate structure, hollow spheres [5], the polymer - pigment complex structures [6] and the like
.
Under the premise of ensuring good film-forming performance, the structure of synthetic design can improve certain aspects of performance, meet customer requirements for different performance [7], and expand the performance range and application fields of acrylic emulsion
.

Ma et al.
[8] reviewed various cutting-edge "core-shell structure" design ideas and methods in current emulsion polymerization, including gradient structure, sandwich structure, strawberry structure, snowman structure, etc.
Different structures can bring different performances.
; It also introduces inorganic and organic composite core-shell structural materials, such as SiO2, TiO2, ZnO, CaCO3, etc.
as the inorganic core of the research coating online coatingol.
com
.
Wood et al.
[9] introduced the modification methods of acrylic acid and PVDF, including cold mixing, core-shell and interpenetrating network methods, the film formation mechanism after modification, and the performance improvement brought about
.

1.

Acrylic emulsion has many advantages, but it also has many disadvantages when used alone, such as low hardness, poor mechanical properties, poor paint film compactness, and high film forming temperature, which limit its application range
.
In order to expand its application field, it is an important way to modify the acrylic emulsion to make its performance meet the application requirements
.
Modification of acrylic emulsion

Sexual research includes physical blending and chemical modification [10]

Calovi et al.
[16] added functionalized graphene oxide (FGO) flakes to acrylic electrophoretic coatings, and studied the effect of graphene oxide addition on the performance of carbon steel-based coatings
.
Guanhao Ma et al.
[17] synthesized fluorosilicone modified styrene-acrylic emulsion through emulsion polymerization process, and then prepared silica modified fluorine-containing silicone styrene-acrylic composite emulsion by sol-gel method with ethyl orthosilicate and nano-SiO2.
AFM analysis shows that a mountain-like structure is formed, the hydrophobic performance is greatly improved, and it has a good application prospect in the field of self-cleaning
.
Wang Xingwang[18] used monomers such as trifluoroethyl methacrylate, butyl acrylate, methyl methacrylate, etc.
, to prepare fluorine-containing emulsion by emulsion polymerization according to a certain ratio, and then used AgNO3, CuSO4, and KI according to a certain ratio.
Configure reversible color material, use melamine-formaldehyde-urea as the wall material, use the reversible color material as the core material, prepare the microcapsule as the color-changing material, and use the fluorosilicone emulsion as the film-forming material to prepare a medium temperature Reversible color coatings can be widely used in temperature-indicating coatings, warning coatings and other fields
.
Wu Jintian et al.
[19] prepared water-based ultra-thin fireproof coatings with silicone-acrylic emulsion and epoxy-modified acrylate emulsion.
The coating formed a dense "honeycomb" structure after thermal expansion, which has good fire resistance
.
Du Wei et al.
[20] used a semi-continuous dropwise addition method to compound nano-ATO with styrene-acrylic emulsion.
The study showed that as the content of nano-ATO increases, the light transmittance of the coating gradually decreases.
When the mass fraction of nano-ATO is 7%, the coating The heat insulation effect on glass is better, and it has application prospects in the field of transparent heat insulation
.
Shu Shujun [21] hybridized epoxy to acrylic acid to obtain acrylic hybrid emulsion, which has the characteristics of quick-drying, weather resistance and long pot life of acrylic emulsion, as well as the high adhesion and high salt spray resistance of epoxy.
, A good balance between the performance characteristics of the two, successfully applied to anti-corrosion, floor, diesel engine, parts and other fields
.

2 Application of acrylic emulsion in industrial coatings

Acrylic emulsion is widely used in various industrial coatings due to its excellent performance, convenient construction, and environmental protection

2.

Solvent-based alkyd coatings are one of the earliest and most mature products developed in China
.
With its excellent construction performance, low price and other characteristics, it has occupied a wide range of industrial anti-corrosion coatings market
.
In recent years, under the call of the "Blue Sky Defense War", the strict implementation of environmental protection policies in various places has made the replacement of solvent-based alkyds imminent
.
The market requires to provide similar surface gloss and salt spray resistance to solvent-based alkyd, while providing a solution that dries faster than alkyd and has better weather resistance
.
Some one-component acrylic emulsions have gloss display power comparable to solvent-based alkyd [23], faster drying speed, excellent early water resistance and salt spray resistance, and excellent weather resistance [24].
Recognized by customers, it has become a star product for light anti-corrosion applications in the coating industry
.
Despite the rapid development of water-based steel structure coatings, there are still some problems in the water-based steel structure anti-corrosion industry, such as submerged arc welding flash rust problem, low single-component hardness, slow drying speed under low temperature and high humidity conditions, and low surface treatment latitude On the low side, and so on, the performance still needs to be further improved and improved
.

2.

With the promotion of the China Container Association and the implementation of the industry self-regulatory convention [25], water-based container coatings ushered in the spring.
At the end of 2017, the standard container fully switched to water-based container coatings, and the water-based coating of cold box coatings was implemented in July 2021
.
The outer coating of container standard boxes generally adopts three systems: epoxy zinc-rich primer + epoxy intermediate paint + acrylic emulsion topcoat.
Almost all standard container topcoats are acrylic emulsion systems, with primer and intermediate paint.
It can provide excellent water resistance, salt spray resistance, water whitening resistance, weather resistance and hardness
.
Although the development of water-based container coatings is rapid and the conversion ratio is high, there are still some problems with water-based container coatings, such as coating pinholes, paint film sagging, thick film cracking, and fierce competition in the price of topcoats
.

2.

China is the world's largest producer of auto parts
.
From 2010 to 2019, the sales revenue of China's auto parts manufacturing industry continued to grow.
Not only did the domestic market grow significantly, but auto parts exports also maintained steady growth
.
In the classification of auto parts, metal parts account for more than half of the share, followed by plastics and accessories[26]
.
Most of the auto parts need to be coated and protected by coatings to protect them from corrosion, or increase the beauty and comfort
.
At present, the single-component epoxy ester system has problems such as high odor and high VOC emission in the application of auto parts; the development of high-performance acrylic emulsion to replace epoxy ester will have a large market space
.
Compared with epoxy ester system, single-component acrylic emulsion needs to provide excellent salt spray resistance, faster drying speed and excellent adhesion in addition to lower odor and VOC release to meet market demand
.

2.

The high-temperature baking paint uses metal as the base material and quickly forms a film through high-temperature baking.
The formed paint film has excellent gloss, hardness, flexibility, adhesion, impact resistance and other properties.
Among them, amino baking paint is the most common high-temperature baking paint.
Used in the coating field of various metal products
.
Solvent-based amino baking varnishes contain a large amount of toxic and harmful substances such as butanol and xylene, and the VOC release seriously exceeds the standard, polluting the environment and endangering health
.
With the advancement of water-based technology, water-based amino baking paint has gradually replaced solvent-based amino baking paint, and has been partially replaced by solvent-based paint in security doors, elevators, packaging barrels, bicycles, tricycles, wine bottle paint, hardware and other fields and successfully applied [27- 28]
.
As of the end of 2020, water-soluble acrylic acid accounts for the dominant position in water-based amino baking paints.
However, due to its high VOC and tightening of environmental protection policies, environmentally friendly acrylic emulsions are increasingly used in amino baking paints
.
Acrylic emulsion is used in water-based amino baking paint.
In addition to the real low VOC environmental protection performance, it also needs to show high gloss, flexibility, impact resistance, excellent weather resistance, boiling resistance, cost-effectiveness, and suitable for electrostatic spraying.
Such characteristics can usher in qualitative development in water-based amino baking paint
.

2.

Peelable paint is a kind of temporary protective paint, which is applied on the surface of the substrate to isolate corrosive media and avoid scratches, scratches, aging, pollution, dust, oil stains, fingerprints, etc.
during production, transportation or storage.
The impact, also called temporary protective coating, can provide temporary protection for the surface of various substrates.
The general protection period is a few days to several months.
After the protection is over, it can be easily peeled off from the substrate surface.
Any negative effects on the surface of the material
.
Acrylic emulsion, as a peelable temporary protective coating [29], has been successfully applied in shipbuilding, construction, glass processing, automobile manufacturing, auto parts, rail transit and other fields
.
Although water-based peelable coatings have made great progress and development, there are still many challenges.
For example, acrylic systems are difficult to peel or become brittle after high-temperature baking, and the solvent resistance and corrosion resistance of acrylic peelable systems are difficult to meet customer needs.
Some substrates are difficult to peel off after being protected by fluorocarbon
.

2.

Water-based dipping paint is commonly used in the coating of vehicle axles, cast workpieces, sofa brackets, parts, etc.
, with high efficiency, less waste, and high degree of automation
.
The solvent-based or water-soluble dipping paint currently in use consumes a lot of solvents, and the stability of the bath is also poor, and the paint film is prone to sag, shrinking, bottoming, blooming and other paint film defects
.
The acrylic emulsion type dip coating tank solution is stable, non-flammable and non-explosive, low in odor, convenient in construction, and wide in application.
It is suitable for large-scale industrial continuous production and exhibits good adhesion, gloss and color retention, and water resistance
.
One-component acrylic emulsions are widely used in dip coating applications, such as the dip coating protection of construction machinery tracks, steel structures, parts, sofa supports and other workpieces.
Common coating colors are black, blue, and yellow
.

2.

Acrylic emulsion can also be applied to applications such as aqueous paint road marking, reflective coatings tunnel, tunnel fire coatings roads, bridges, tunnels and the like
.
GB/T 38597-2020 "Technical Requirements for Low Volatile Organic Compound Content Coating Products" stipulates that the limit of volatile organic compound content in road marking paint is 150 g/L
.
Acrylic emulsion has excellent quick-drying, low VOC release and good adhesion to glass beads.
It is used in many highways and urban roads to provide long-lasting wear resistance and excellent reflectivity
.

2.

In industrial production methods to prevent metal corrosion, surface treatment is a more commonly used method
.
At present, the passivation process containing hexavalent chromium is the most mature and widely used
.
However, hexavalent chromium is a heavy metal with high toxicity.
The search for high-performance, non-toxic chromium-free passivation technology has become the main research direction at present
.
At present, chromium-free passivation technology is mainly divided into three categories: ① inorganic salt passivation; ② organic compound passivation; ③ inorganic-organic composite passivation
.
Zhang Zhenxing [30] synthesized self-crosslinking silicone modified acrylic emulsion, matched with commercially available acrylic emulsion, added silane coupling agent KH560 and different corrosion inhibitors, and passed electrochemical and neutral salt spray tests to obtain composite passivation Optimal formula and technology of chemical liquid
.

2.

At this stage, the raw materials for the preparation of water-based wood coating emulsions are mainly water-based polyurethane dispersions (PUD), water-based acrylic emulsions and acrylic-modified water-based polyurethane emulsions (PUA)
.
At present, wood coatings on the market are still mainly solvent-based, and there are still many problems in water-based systems that need to be solved, such as improving transparency, sealing tannins, anti-swelling, anti-stacking, and solvent resistance
.
Among them, acrylic emulsion has the characteristics of gloss retention, color retention, good adhesion, high hardness, and good water resistance.
It has been widely used in water-based wood coatings.
However, acrylic emulsions have the disadvantages of poor solvent resistance, hot stickiness and cold brittleness, and improve the performance of acrylic emulsions.
Sealing tannins, swelling resistance, while providing good primer sanding and stacking resistance, will be the focus of future research and development
.

2.

Due to the low surface energy of the plastic surface, acrylic emulsion is used similar to ABS (acrylonitrile\-butadiene-styrene), PC (polycarbonate), PET (polyethylene terephthalate), PVC ( Substrates such as polyvinyl chloride) are more effective, but there are adhesion problems with substrates such as PE (polyethylene) and PP (polypropylene)
.
In addition to the requirements for adhesion, plastic coatings also require high hardness, fast drying speed, good scratch resistance, and solvent wipe resistance
.
The most commonly used plastic paint is silver powder paint.
Silver powder paint requires a relatively good silver powder orientation effect and a good metal texture.
The main application areas are mobile phones, computers, household appliances, children's toys, clothing molding, and motorcycles.
and other accessories
.
The current slow development of water-based coatings for plastics is mainly due to the large gap between the surface energy of water-based systems and plastic substrates, and it is difficult to have good wetting and adhesion, requiring technological breakthroughs
.

In addition to the above application fields, there are many industrial fields that use water-based acrylic emulsions, such as inks, inorganic coatings, paper coatings, leather coatings, one-component floor coatings, reflective thermal insulation coatings, damping coatings, waterproof coatings, and fireproof coatings.
, Anti-graffiti coatings, adhesives, seed coatings, interface agents, modified asphalt coatings, single-component floor coatings, etc.
, different industrial coating applications, their application formulations and application technologies are also very different
.

3 Development trend of acrylic emulsion

Acrylic emulsion has achieved great success in the field of architectural coatings.
Under the call of "Blue Sky Defense", acrylic emulsion has entered the fast lane in the development of industrial coatings due to its excellent performance, low odor and low VOC release
.
At present, it has achieved success in the application fields of water-based steel structure coatings, water-based container coatings, and water-based wood coatings.
In the future, it will develop in the direction of functionalization, high performance, and environmental protection
.

In addition, acrylic emulsion will also penetrate into more industrial subdivisions
.
However, acrylic emulsions still have many problems to be improved and resolved.
For example, the single-component acrylic emulsion coating system has insufficient coating hardness and insufficient flash rust resistance, especially in submerged arc welding where flash rust is serious, and salt spray resistance encounters a bottleneck; The water-based acrylic emulsion system cannot be constructed in winter in the north, and it dries slowly in the low-temperature and humid environment in the south
.
Using special functionalization, hybridization, blending, modification and other methods to maximize the strengths and avoid weaknesses to allow acrylic emulsions to play a larger application space is the focus of future research
.