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A comprehensive introduction for acrylic resin

By Thomas Huang December 8th, 2023 82 views
Contents

I, What is acrylic resin?

Acrylic resin is a general term for acrylic acid, methacrylic acid, and its derivative polymers.

II, General description

 Chemical formula   (C3H4O2)n chemical structure of acrylic resin
 Melting point   106 ℃   Boiling point  116 ℃
 Density  1.09 g/cm³  Flashpoint  61.6 ℃
 Safety Description  S24/25  Hazard symbols  R45; R46; R34; R36/37/38
 CAS No.  9003-01-4   Hazardous Description  Corrosive; Irritant; Poisonous
 EINECS No.   618-347-7  Appearance  Colorless or light yellow viscous liquid
 Solubility  Acrylic resins are soluble in polar organic solvents such as ethanol, acetone and chloroform.
 Solubility in water, on the other hand, depends on the side chain groups in the molecular structure and the pH of the aqueous solution. Different models dissolve at different pH.

III, The advantages of acrylic resins:

- Strong color protection (washable)
- Water resistance
- Better adhesion
- Better barrier
- Resistance to cracking, better foaming
- Resistant to alkaline detergents
- Chemical stability and transparency
- Flexibility
- Processability
- Good adhesion
- Abrasion resistance

IV, Uses of Acrylic Resins

Acrylic resin is one of the most commonly used synthetic resins. The common applications are as follows:

4.1 Coatings

Acrylic resin is an excellent base material for coatings, which are widely used in construction, automobile, furniture, metal, aviation, and other fields. 
Among them, spray coatings and water-based coatings are the major types of coatings available in the market. 
Spray coatings:
The advantage of spray coatings is that they can create a variety of colors and textures on the surface of different materials, while acrylic resin spray coatings also offer significant waterproofing, pollution resistance, and durability.
photo of Acrylic Resins spray coating application
Water-based coatings:
Water-based coatings have the advantage of being environmentally friendly, low VOC emissions, and the finished coating has better properties such as gloss, adhesion, weatherability, and elasticity.
photo of Acrylic Resins water-based coating application

4.2 Adhesives

Acrylic resins are widely used in the preparation of adhesives for a variety of materials. 
Acrylic resin adhesives have good initial adhesion, high strength, and excellent resistance to various chemicals.
  It also offers the advantages of low cost, non-toxicity, and tunability, and is adaptable to different application environments and material properties.
photo of Acrylic Resins adhesives application

4.3 Printing inks

Acrylic resin is also one of the important components of printing inks. 
Printing ink is one of the excellent applications of acrylic resin, which has the advantages of cold luminescence and fast drying. 
 Printing ink usually consists of acrylic resin, pigment, diluent, additives, etc. It is suitable for a variety of printing materials, including paper and plastic.
photo of Acrylic Resins printing inks application

4.4 Plastic

Plastics include PP, HDPE, PC, ABS, PVC, HIPS, PET, and so on.
 Acrylic resin plastics are polymer materials that use acrylic monomer as the main component and are also a widely used plastic. Its main characteristics are weather resistance, insulation, chemical resistance, and strong water repellency, as well as a high conversion rate and high hardness for good processing.
 The products coated include airplanes, trains, automotive engineering machinery, household appliances, hardware products, toys, furniture, etc. 
photo of photo of Acrylic Resins plastic application
Its formula design is very complex.
The basic principle is that first of all different substrates and products determine the resin dosage from a solvent or water dosage form, and then according to the performance requirements determine the monomer composition.
Then according to the performance requirements, the monomer composition, glass transition temperature (Tg), solvent composition, initiator type and dosage, and polymerization process.
Finally, through the experiment for testing, and correction, to determine the best process and formulation.
The selection of monomers is the core of the formula design.

V, Types of acrylic resin

5.1 As per production method.

Emulsion polymerization, Suspension polymerization, Intrinsic polymerization, Solution polymerization
The general formula of a synthesis reaction.
R (or R₁ or R₂ or R₃) + R₁ (or R₂ or R₃ or R4) → Acrylic resin
R=acrylic acid  R₁ =methacrylic acid R₂=acrylates R₃=methacrylates R4=other esters  

5.1.1 Emulsion polymerization:


It is made by polymerization with monomer, initiator, and distilled water together.
Generally, the resulting resin is an emulsion with 50% solids, which is a latex solution containing about 50% water. 
The emulsion synthesized is generally milky blue (Tyndall phenomenon), and the glass transition temperature is designed according to the FOX formula. Therefore, the molecular weight of this type of emulsion is high, but the solid content is generally 40%-50%. 
The production industry requires precise control, due to the use of water as a solvent, and environmentally friendly emulsions.
Emulsion Polymerization
Emulsion polymerization is a polymerization reaction in which the monomer is dispersed into an emulsion in water under the action of an emulsifier and with the help of mechanical stirring, initiated by a water-soluble initiator.
 Mechanism of emulsion polymerization:
 A very small amount of monomer and a small amount of emulsifier are dissolved in water in a molecularly dispersed state, and most of them are dissolved in water.
 Most of the emulsifier forms micelles, most of the monomer is dispersed into droplets, and a small amount of emulsifier is adsorbed on the surface of the monomer droplets.

5.1.2 Suspension polymerization:

Suspension polymerization is a method of polymerization in which the monomer dissolved in the initiator is suspended in water in the form of liquid droplets under the action of strong stirring and dispersant.
It is a more complex production process and is a method used for the production of solid resins. The solid acrylic resins, acrylates with methyl groups are used for polymerization. 
Acrylates with a methyl group are generally with a certain functional group. Its polymerization reaction in the reactor is not easy to control, easy to sticky to burst. 
Operation processes:
(1)Put the monomer, initiator, and additives into the reaction kettle and then put them into the distilled water to react.  
(2)Water washing after a certain time and temperature reaction. 
(3)Drying, filtration, and so on. 
The production control shall be strict. Any intermediate link may affect the quality if it is not properly completed. The main differences are the color and molecular weight.
System composition: 
Monomer + (oil-soluble) initiator + amphiphilic dispersant + deionized water

5.1.3 Bulk polymerization of acrylic resin.

5.1.3.1 Process. 
The process is to put the raw material into a special plastic film, and then react into lumps, take out the crushing, filter, and finish. 
5.1.3.2 Properties
(1)The solid acrylic resin made by this method with highest purity, and best stability among all the methods.
(2)Acrylic resin made by bulk polymerization has weak solvent solubility. Sometimes, it is several times harder than suspension polymerization with the same monomer and ratio, and the dispersion of pigments is not as good as by using suspension polymerization.
(3)Disadvantage of the bulk polymerization:  Hard to radiate.
Solution: Segmental polymerization
Pre-polymerization in the reactor, with a conversion rate of 10 ~ 40%, releases part of the heat of polymerization, having a certain viscosity.
Polymerize in the template, and gradually increase the temperature, so that the polymerization is complete.
5.1.3.3 Example
A large-scale application is to make polymethyl methacrylate, abbreviated PPMA (acrylic sheet), which belongs to the thermoplastic, with good transparency, chemical stability, weather resistance, easy to dye, easy to process, and beautiful appearance.
Acrylic plastic applications
arylic plastic photos
Lamps, lighting equipment, optical glass, instrument dials, covers, optical fibers, billboards, medical and military construction glass

5.1.4 Solution polymerization

5.1.4.1 Description
Solution polymerization happens in a solution that has the monomer and initiator dissolved in a suitable solvent.
5.1.4.2 System composition
Monomer + initiator + solvent
5.1.4.3 Selection of Solvent
(1) Can dissolve the monomer and resin. 
(2) Can be miscible with water  in any ratio, 
(3) Non-toxic or low-toxicity, non-irritating flavor, non-flammable, non-explosive, the boiling range should be appropriate, cheap, and economical.
(4) Follow the principle of "similar polarity" and "similar solubility parameters". 
(5) The solvents frequently used are ethanol, isopropanol, n-butanol, ethyl alcohol, ethylene glycol, and other co-solvents or co-solvents or mixtures of these solvents.
Comparison of the last three polymerization methods
 Bulk polymerization  High monomer concentration, high product purity.
 Not easy to heat dissipation and temperature control. The product is not easy to discharge.
 Solution polymerization  Easy heat dissipation and temperature control, products can be used directly.
 Low monomer concentration, low molecular weight
 Suspension polymerization  High monomer concentration, purity, and molecular weight.
 Easy heat dissipation and temperature control, and easy to separate products.

5.2 Acrylic resins for coatings are categorized according to their film-forming properties:

5.2.1 Thermosetting Acrylic Resins

5.2.1.1 Chemical compositions
Thermosetting acrylic resins are also known as cross-linked or reactive acrylic resins.
Acrylic monomers (methyl acrylate, ethyl acrylate, n-butyl acrylate methyl methacrylate, n-butyl methacrylate, etc.) are the basic components and are crosslinked to form a network structure of insoluble and non-melting acrylic polymers.
The body casting material is made by copolymerizing methacrylate with polyfunctional acrylic monomers or other polyfunctional alkene monomers to make a slurry and then polymerized by casting.
Mainly used as aircraft hatch covers and windshields.
Solution type, half-emulsion type, water-based thermosetting acrylic resin, need to be heated and baked crosslinking curing film, forming a network structure.
5.2.1.2 The crosslinking method is divided into two categories:
(1) Reaction cross-linking type,
The polymer functional groups do not have cross-linking reaction ability and must be added at least 2 functional groups of cross-linking components (such as melamine resin, epoxy resin, urea resin metal oxides, etc.)  cross-linking curing via the reaction. 
The cross-linking components can not be stored for a long time after being added to the mixture, they should be used immediately.
(2) Self-crosslinking type.
The polymer chain itself contains more than two functional groups (hydroxyl, carboxyl, amide, hydroxymethyl, etc.), heated to a certain temperature (or add a catalyst at the same time ), the functional groups react with each other to complete the cross-linking. 
These thermosetting acrylic resins are mainly used as fabrics, leather, paper treatment agents, industrial paints, and architectural coatings.
The cross-linking reactions of cross-linked acrylic resins are shown in the following table.
Acrylic resin functional group type Functional monomer Crosslinking reaction substance

5.2.1.3 Product Characteristics
Thermosetting acrylic resin means that it has certain functional groups in its structure, and forms a net structure by reacting with the functional groups in the amino resin, epoxy resin, polyurethane, etc. added during the paint making. It can overcome the shortcomings of thermoplastic acrylic resin, so that the mechanical properties of the coating film, and chemical resistance are greatly improved. 
The reason is that the film-forming process is accompanied by a cross-linking reaction, and eventually forms a network structure, which is neither fusible nor soluble. 
The molecular weight of thermosetting acrylic resins is usually low, around 10,000, and high solids resins are around 3,000.
 Thermosetting acrylic paints have excellent fullness, gloss, hardness, solvent resistance, and weather resistance, and do not change color or yellow when baked at high temperatures. photo of thermasetting acrylic paints

5.2.1.4 Applications:
In addition to the general properties of acrylic resins, it has excellent heat resistance, water resistance, solvent resistance, and abrasion and scratch resistance. 
It is available in a variety of forms including body casting material, solution type, emulsion type, and water-based type.
Hydroxy acrylic resin is the most important category, which is used to formulate room-temperature drying two-component acrylic-urethane coatings and acrylic-amino baking paints with polyisocyanate curing agents, which are widely used and produced in large quantities. 
 Acrylic-polyurethane coatings  Coatings of airplanes, automobiles, motorcycles, trains, industrial machinery, home appliances, furniture, decoration, and other products with high decorative requirements, and are important varieties of industrial or civil coatings.
 Acrylic-amino baking paint  Paint of automobiles, motorcycles, metal coils, home appliances, light industrial products, and other metal products, and is an important industrial coating.
 Carboxy acrylic resin   It is used to formulate powder coatings with epoxy resin.
 Epoxy acrylic resin   It is used to formulate powder coatings with carboxy polyester resin.
Powder coatings:
photo of powder coatings

5.2.2 Thermoplastic Acrylic Resins


5.2.2.1 Composition
Thermoplastic acrylic resins are a class of thermoplastic resins made by the polymerization of acrylic acid, methacrylic acid, and their derivatives (e.g. esters, nitriles, amides).
It can be repeatedly softened by heat and solidified by cooling. 
Generally linear polymer compounds can be a homopolymer or copolymer.
Coating industry thermoplastic acrylic resin molecular weight is generally 75,000 ~ 120,000, 
5.2.2.2 Category
Thermoplastic acrylic resin is a solvent-based acrylic resin, that can be melted, and dissolved in the appropriate solvent, the coating is formulated by the solvent volatilization of macromolecules into a film, no cross-linking reaction occurs when the film is formed, it is a non-reactive-coatings.
To achieve good physical and chemical properties, the molecular weight of the resin should be large, but the solid fraction can not be too low, so the molecular weight should not be too large. Generally, when the molecular weight is tens of thousands, the physical and chemical properties and the construction performance can be balanced.
5.2.2.3 Product Characteristics
with good physical and mechanical properties, weather resistance, chemical resistance, water resistance, and high light and color retention.
Thermoplastic acrylic resin does not undergo further cross-linking in the film-forming process, so it has a large molecular weight, good light and color retention, water, and chemical resistance, fast drying, convenient construction, easy to construct recoating and reworking, whiteness and positioning of aluminum powder in the preparation of aluminum powder paint.
5.2.2.4  Disadvantages
(1) Low solid fraction (high solid fraction viscosity, spraying prone to pulling phenomenon).
(2) Poor film fullness.
(3) Low-temperature easy to brittle cracking,
(4) High-temperature easy to sticky.
(5) Poor solvent release.
(6) Slow drying.
(7) Solvent resistance is not good.
5.2.2.5 Property improving material
Improve thermoplastic acrylic resin properties, which can be solved by formula design or by sparing other resins. 
(1) To design different glass transition temperatures according to the coating requirements of different substrates, 
For examples:
The  glass transition temperature for metal paint resin is usually 30 ~ 60 ℃, 
Plastic paint resin can be designed for higher glass transition temperatures (80 ~ 100 ℃), 
Solvent-based architectural coatings resin glass transition temperature is generally greater than 50 ℃; 
(2) The introduction of methacrylic acid n-butyl ester or methacrylic acid isobutyl ester, tert-butyl methacrylate, Lauryl methacrylate, octadecyl methacrylate, acrylonitrile to improve ethanol resistance. 
(3) The introduction of acrylic acid or methacrylic acid and hydroxyacrylates and other polar monomers can improve the resin on the filler wettability, to prevent the coating film coloring. 
An appropriate amount of nitrate cellulose or acetate butyrate cellulose can significantly improve the solvent release into the paint, leveling, or metal flash paint aluminum powder orientation.
(1)Construction materials: 
Window frames, curtain walls, sun shades, protective materials, acoustic materials, road signs, and other structural components.
(2)Automobile industry: 
Automobile body parts, interior parts, and exterior parts.
(3)Electronic and electrical appliances: 
TV, computer, cell phone, video games, power supply, capacitors, and insulating materials.
(4)Daily necessities: 
Kitchenware, toys, household products, stationery, cosmetics, medical equipment, and others.

5.3 Compositionally.

Acrylic resins include pure propylene resins, benzene propylene resins, silicone propylene resins, vinyl propylene resins, fluorine propylene resins, tertiary propylene (tertiary carbonate-acrylate) resins, and so on.

5.4 From the coating agent type.

There are mainly solvent-based coatings, water-based coatings, high-solid component coatings, and powder coatings.
Acrylic and methacrylic monomers are important monomers for the synthesis of acrylic resins.
This kind of monomer has many varieties, a wide range of uses, moderate activity, and can be homopolymerized or copolymerized with many other monomers.
In addition, the commonly used non-acrylic monomers are styrene, acrylic eyes, vinyl acetate, vinyl chloride, divinyl benzene, ethyl (butyl) glycol diacrylate, and so on.
Functional monomers include: 
Silicone monomers, tertiary carbonate monomers (Veova 10, Veova 9, Veova 11), fluorine monomers (including alkene fluorine monomers: chlorotrifluoroethylene, vinylidene fluoride, tetrafluoroethylene, fluoroacrylic acid monomer), surface-active monomers, and surface-active monomers. 

5.4.1 Solvent-based coatings 

5.4.1.1 Description
 Solvent-based acrylic resin is a class of acrylic resin that can be used as a film-forming substance for solvent coatings, the solution is a light yellow or water-white transparent viscous liquid.
 The synthesis of solvent-based acrylic resin mainly uses solution polymerization, if you choose the right solvent (often mixed solvents), such as good solubility, volatility to meet the construction requirements, safety, low-toxicity, etc., the polymer solution can be used directly as a coating base material for coating preparation. This application of it is very convenient.
photo of solvent-based acrylic resin
5.4.1.2 Monomer Solution Production Method
The solution copolymerization of acrylic monomers is mostly produced by kettle kettle-type reactor batch method.

 Polymerization kettle is generally used with a jacketed stainless steel or glass-lined kettle, through the jacket heat transfer, to heat, exclude the polymerization heat, or make the material cool down, at the same time, the reactor kettle is equipped with stirring and reflux condenser, there are monomers and initiator feed port, and inert gas inlet, and the installation of explosion-proof membrane. 
The basic process is as follows.
(1) Copolymerization monomer mixing. 
The key is metering, no matter large materials (such as hard and soft monomers) or small materials (such as functional monomers, initiators, molecular weight adjusters, etc.) It is best to be accurate to 0.2% or less, to ensure that the formulation of the accurate implementation. The product should be prepared when used.
(2) Add kettle bottom material. 
Add the formulated amount of (mixed) solvent to the reactor, gradually warm up to reflux temperature, hold about 0.5h, and expel the oxygen.
(3) Notice.
Add the mixed solution of monomer and initiator dropwise according to the process requirements at reflux temperature. Drop acceleration should be uniform, reduce the drop rate if the system temperature rise is too fast.
(4)  Polymerize with heat preservation. 
After the monomer drops, hold the temperature of the reaction for a certain time to ensure further polymerization of the monomer. 
(5) Post-elimination. 
After the end of the above process, the initiator can be replenished in two or more intervals to improve the conversion rate.
(6) Holding temperature once again.
(7) Sampling and analysis. 
Mainly measure the indicators such as appearance, solid content, viscosity, and so on. 
(8) Adjust the indicators.
(9) Filtering, packaging, quality control, storage.
5.4.1.3 Classification and applications of solvent-based coatings
Solvent-based acrylic resin is popular for its flat coating film, good gloss, strong adhesion, and other characteristics, mainly used in decorative coatings, electronic products coating, billboard production, and other fields.
(1)High solids acrylic coatings. 
Coatings using modified present acrylic resin as the main film-forming substance, the construction solids of which shall not be less than 60% by mass or 80% by volume. 
Compared with water-based coatings and powder coatings, high solid acrylic coatings are environmentally friendly and good coatings. 
Its shortcomings are high viscosity, poor pigment wettability, ease of hanging the film, etc., and available anti-sagging agents and other additives to solve this shortcoming. 
At present, it is mainly used in the preparation of thermosetting coatings, used for automobile painting or overglaze top coats.
(2)SAC series acrylic coatings. 
SAC series solid acrylic resin dissolved in organic solvents, and then titanium dioxide, light calcium carbonate, and other fillers and additives, dispersed, ground solvent-based acrylic coatings.
It is a high-quality interior and exterior wall with environmentally friendly coatings. 
SAC series of acrylic resin is a kind of solid acrylic resin that can be dissolved in petroleum solvents mainly composed of fatty hydrocarbons. 
Its most important characteristic is that it is non-toxic and soluble in aliphatic hydrocarbon solvents. 
It is an environmentally friendly non-toxic solvent-based coatings. 
It is a coating for building exterior decoration widely used in the United States and the United Kingdom.
(3)Multi-functional, high-quality solvent-based acrylic coatings. 
Multifunctional, high-quality solvent-based acrylic coatings include silicone-modified acrylic coatings, HDI-type polyurethane-modified acrylic coatings, and fluorine-modified acrylic coatings. 
The most important features of these coatings are weather resistance, durability, and good decorative properties, which can reduce the times of recoating and pollution.

5.4.2 Water-based coatings 

5.4.2.1 Properties
 Compared with traditional solvent-based coatings, water-based coatings have the advantages of low price, safe use, saving resources and energy, reducing environmental pollution and public health, and thus have become the main direction of the current development of the coatings industry. 
 Water-based acrylic resin coatings are the fastest growing water-based coatings, the most varieties of non-polluting coatings.
photo of water-based coating
5.4.2.2 Types
Water-based acrylic resin includes acrylic resin emulsion, acrylic resin aqueous dispersion (also known as water-dilutable acrylic), and acrylic resin aqueous solution. 
Emulsions are mainly synthesized by emulsifying oily alkene monomers in water under the initiation of aqueous radical initiators.
According to the monomer composition is usually divided into pure propylene emulsion, benzene propylene emulsion, vinyl propylene emulsion, silicone propylene emulsion, tertiary vinegar (tertiary carbonate - vinyl acetate) emulsions, tertiary propylene (tertiary carbonate - acrylate) emulsions and so on.
Resin aqueous dispersions are synthesized by different processes such as free radical solution polymerization or stepwise solution polymerization. 
From the particle size point of view: 
Emulsion particle size > Resin aqueous dispersion particle size > Aqueous solution particle size. 
5.4.2.3 Applications
(1)Acrylic emulsion is mainly used for emulsion paint base material, in the architectural coatings market and occupies an important application, and its application is still expanding; 
(2)Acrylic resin aqueous dispersion is used as industrial coatings and civil coatings. 
5.4.2.4 Synthesis of acrylic emulsions

Synthesis of acrylic emulsions equiments
The oily monomer is dispersed into an emulsion in an aqueous medium by an emulsifier, and the polymerization initiated by a water-soluble initiator is called emulsion polymerization. 
Emulsion polymerization is an important free radical polymerization implementation method. 
Due to its unique polymerization mechanism, high molecular weight polymers can be synthesized at a high polymerization rate, and it is an important polymerization method for resins for rubber (styrene-butadiene rubber) and latex paint base materials. Acrylic emulsion is the most important emulsion paint base material, with features of fine particles, good elasticity, light resistance, weather resistance, and water resistance. 
Features of emulsion polymerization.
(1) Use water as a dispersing medium, low viscosity, stable, inexpensive, and safe.
(2) Unique mechanism, can simultaneously increase the rate of polymerization and polymer molecular weight.  The polymerization can be carried out at a lower temperature in the oxidation-reduction initiation system. 
(3) It is more convenient for the direct application of latex (emulsion), such as coatings, adhesives, aqueous inks, and so on.
(4) Obtaining solid polymers is subject to processes such as emulsion breaking, washing, dehydration, drying, etc., purification is difficult, and the production cost is higher than that of suspension polymerization.
(5) Emulsion polymerization is fast and high average molecular weight compared with other free radical polymerization methods.
5.4.2.5 Synthesis formulation of acrylic emulsions
Oily (can contain a small amount of water) monomer: 30% ~ 60%; 
Deionized water: 40% ~ 70%; 
Water-soluble initiator: 0.3 ~ 0.7%; 
Emulsifier (Emulsifier): 1% ~ 3%.
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