UV Curable Hot Melt Coating for Wood Substrates
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Solution Overview
Problem
Current solvent-free coating compositions, particularly UV curable hot melt coatings, face challenges such as high viscosity issues, limited thermal stability, and the need for multiple layers due to low molecular weight monomers, which lead to inefficiencies in application and curing processes, and require special packaging to prevent moisture-induced reactions.
Innovation Solution
A radiation curable hot melt coating composition comprising a polymer component with poly(meth)acrylate and/or polyurethane segments, an oligomer component, and a monomer component, all with functional groups activatable by UV radiation, allowing for curing at elevated temperatures without moisture barriers and providing improved thermal stability and application ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If low viscosity reactive monomers are used to reduce coating viscosity for good flow and levelling at room temperature, then the coating can be applied easily, but the monomers can penetrate into porous substrates and become too deep to be cured by UV radiation, causing safety, health and environmental problems
Solution Approach 1:
The patent changes the molecular weight parameter of the monomers from low viscosity (low molecular weight) to high viscosity (high molecular weight, Mn > 1000 g/mol). This parameter change reduces monomer penetration into porous substrates while maintaining adequate flow and levelling properties through the use of high molecular weight compounds that balance viscosity and penetration resistance.
Solution Approach 2:
The patent uses a composite coating system combining polyol components (Mn > 5000 g/mol) with high molecular weight monomers (Mn > 1000 g/mol) that contain UV-curable functional groups. This composite approach creates a coating that achieves both good flow properties and effective UV curing by combining the advantages of high molecular weight materials.
2Reliability
If three to four layers of varnish are applied to protect substrates in wood-working and furniture applications, then adequate protection can be achieved, but the process becomes time consuming, expensive and requires lots of space
Solution Approach 1:
The patent merges multiple coating layers into a single application by using a formulation that achieves adequate protection in one layer. The high molecular weight monomers and polyols provide sufficient film build and protection in a single coating application, eliminating the need for multiple thin layers and associated sanding operations.
Solution Approach 2:
The patent changes the molecular weight parameters of the coating components to achieve adequate film build and protection in a single layer. By using high molecular weight monomers (Mn > 1000 g/mol) and polyols (Mn > 5000 g/mol), the coating achieves sufficient protective properties without requiring multiple applications.
3Productivity
If a moisture curable polyurethane hot melt is used to achieve desired layer thicknesses in a single operation, then application efficiency improves, but curing takes at least several days because it depends on moisture and the coated part cannot be processed or packaged rapidly
Solution Approach 1:
The patent creates a coating system that performs multiple curing functions simultaneously - both UV curing and moisture curing are enabled through the inclusion of UV-curable functional groups in the polyol and monomer components. This multi-functionality allows the coating to cure rapidly via UV radiation while also being capable of moisture curing, eliminating the need for separate curing processes.
Solution Approach 2:
The patent changes the chemical composition parameters by incorporating UV-curable functional groups into the polyol (Mn > 5000 g/mol) and monomer (Mn > 1000 g/mol) components. This parameter change enables UV curing capability while maintaining the hot melt formulation, allowing rapid curing through UV exposure without requiring extended moisture curing periods.
4Ease of operation
If UV curable lacquer is applied on top of moisture curable hot melt to enable immediate surface drying, then handling improves, but the bulk of the hot melt coating still requires at least several days to cure via moisture
Solution Approach 1:
The patent merges the UV curing and moisture curing capabilities into a single integrated coating formulation. The polyol and monomer components both contain UV-curable functional groups, allowing the entire coating bulk to cure via UV radiation rather than requiring a separate UV top coat. This eliminates the time delay associated with moisture curing of the bulk coating.
Solution Approach 2:
The patent creates a universal coating system where both UV and moisture curing pathways are available simultaneously. The high molecular weight monomers and polyols with UV-curable groups enable rapid UV curing of the bulk coating while maintaining compatibility with moisture curing, providing both immediate surface handling capability and complete bulk curing through UV exposure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables single-layer application with enhanced thermal stability, efficient curing, and improved handling of coated substrates, reducing processing time and costs while maintaining scratch, abrasion, and solvent resistance.
Implementation Method 1
Under suitable UV wavelengths, the photoinitiators produce free-radicals which polymerise the acrylate functional groups to produce a crosslinked network
Data Source
AI summary
The invention provides an isocyanate free UV curable hot melt composition which may be hardened upon exposure to UV radiation to provide a protective coating. The coating is particularly useful in wood-working and furniture applications.