|
|
Two-Component Systems
Two-component systems, which consist of a base resin and hardener, are one of the most popular classes of coatings, inks, and adhesives developed nowadays, finding utility in an increasing number of industries due to their superior durability, adhesion, and functionality. Polyurethane and polyurea systems are among the most common two-component systems; they account for over 60% of today’s market share for coatings in terms of chemistry. |
Polyurethane and Polyurea Systems
Chemically, polyurethane systems consist of a polyol and a polyisocyanate, where the polyol is the base resin and the polyisocyanate is the hardener. The hydroxyl groups on the polyol react with isocyanate groups on the polyisocyanate to form urethane linkages. These cross-link the polyurethane polymer as part of the curing process and provide strength and durability to the system. Polyurea systems are created using a similar scheme, except they utilize a polyamine instead of a polyol as the base resin.
Several types of polyol and polyamine base resins can be used to create polyurethane and polyurea systems, such as polyester and polyether polyols, which are commonly used to make systems with good durability, resistance to heat and chemicals, and customization of physical properties. However, in cases where improved performance and visual quality are necessary, acrylic polyols and polyamines are preferred.
Elvacite® Acrylic Polyols and Polyamines
Mitsubishi Chemical Group, located in Pasadena, Texas, manufactures a vast portfolio of Elvacite® acrylic resins renowned in the coating, ink, and adhesive space for the high degree of performance and functionality they provide formulators. The Elvacite® acrylic resin portfolio features polyols and polyamines specifically designed for two-component polyurethane and polyurea systems and imparts the following properties:
- Outstanding resistance to weathering and degradation by UV exposure
- Excellent abrasion resistance
- Improved adhesion to low–surface energy surfaces
- Superior chemical resistance against water, alcohol, dilute acids, alkali, chemical fumes, and corrosive and oxidizing environments
- High gloss and transparency
Elvacite® acrylic polyols have been modified with carboxylic acid functionality to provide additional functionality, including improved pigment dispersion properties and compatibility with other resin systems. Several options are available in a variety of molecular weights and hydroxyl numbers to provide flexibility and optimization in different coating and adhesive applications. The Elvacite® acrylic resins developed for two-component systems are as follows:
*# assumes the total incorporation of a functional monomer
Applications
Two-Component Coatings
Polyurethane coatings that require higher UV and weathering resistance, increased adhesion, and better gloss and chemical resistance will benefit from using high–hydroxyl number Elvacite® acrylic polyols, like Elvacite® 4254 and Elvacite® 4412. Higher–hydroxyl number resins are preferred in coating applications because they present more reactive sites to increase cross-link density, which in turn increases hardness and toughness. These grades may also be used to react with melamine resins to form ether linkages that provide high strength, durability, and chemical resistance in baking systems.
Elvacite® 4115, which incorporates dimethylaminoethyl methacrylate, has been functionalized with amine groups and is an ideal polyamine for polyurea coatings to improve adhesion and pigment dispersion and incorporate UV-reactive sites.
Reactive Hot-Melt Adhesives
Reactive hot-melt adhesives are also a type of system that benefits from including Elvacite® acrylic polyols. Based on polyurethane chemistry, these adhesives are increasingly being used in assembly applications in the medical, automotive, and construction industries because they provide long open times, high bond strength, and excellent resistance to chemical and temperature degradation. Elvacite® polyols, like Elvacite® 4402 and Elvacite® 4273, which have low hydroxyl numbers, are ideal for improving the cohesive and green strength of the adhesive. The low number of hydroxyl groups on these resins leads to low cross-link densities that facilitate easier remelt properties. Heat resistance of these adhesives are also improved due to the increased cross-linking point the hydroxyl groups provide. Other Elvacite® resins that are not hydroxyl functionalized may also be blended into reactive hot-melt adhesive systems to improve green strength for higher line speed operations. For a full list of Elvacite® resins, click here.
Preparing Solutions with Elvacite®
While Elvacite® acrylic resins offer excellent functionality and compatibility, proper technique must be used to make solutions maximally effective. A few tips pertaining to this are listed below.
- Preventing solvent-swollen granules of Elvacite® acrylic bead resins is critical; constant low-shear agitation for up to 12 hours may be required to prevent agglomerates from forming
- Elvacite® acrylic beads should be added directly into the vortex of the solvent being mixed to ensure good wet out and dispersion
- After the solution appears clear in the mixing tank, a sample should be spread on a Leneta card or glass to check for solid acrylic particles; if these are present, further mixing is required
- Different Elvacite® grades feature different solubility and viscosity characteristics, as shown below
| Grade |
Toluene |
n-Butyl acetate |
Dimethyl carbonate |
t-Butyl acetate |
PCBTF |
| Elvacite® 4402 |
S |
112 cPs |
S |
218 cPs |
1,130 cPs |
| Elvacite® 4273 |
S |
S |
S |
I |
Unknown |
| Elvacite® 4254 |
S |
S |
S |
S |
887 cPs |
| Elvacite® 4412 |
S |
S |
S |
I |
I |
S = Soluble, viscosity not measured
I = Insoluble
Summary
The Elvacite® portfolio contains hydroxyl- and amine-functionalized acrylic resins ideal for two-component coating and adhesive systems, such as polyurethane, polyurea, acrylic-melamine coatings, and reactive hot-melt adhesives. These acrylic polyol and polyamine resins provide superior resistance to UV exposure, abrasion, chemicals, and weathering and exhibit excellent adhesion, gloss, and compatibility with various resin systems and solvents. Click below to request a sample or more information on Elvacite® acrylic resins.
