UV Curable Ink Adhesion via Inert Polyester Resins
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Solution Overview
Problem
Commercially available UV flexographic inks have poor adhesion on flexible plastic substrates without adhesion primers, and increasing UV reactivity often compromises adhesion due to shrinkage, while existing solutions for improved adhesion are not suitable for flexographic applications or food packaging.
Innovation Solution
A radiation curable composition comprising ethylenically unsaturated compounds and inert OH-terminated polyesters prepared from ethylene glycol and phthalic acid or phthalic anhydride, with a hydroxyl-to-carboxyl equivalent ratio exceeding 1.0 and minimal radiation curable reactive groups, enhancing adhesion and UV reactivity without the need for a primer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If inert resins are used to increase adhesion on plastic substrates, then adhesion is improved, but UV reactivity significantly decreases
Solution Approach 1:
The invention changes the chemical parameters of the resin system by using inert polyesters with specific hydroxyl values (30-150 mg KOH/g) and combining them with radiation-curable monomers and oligomers in optimized ratios (0.1-50 wt% inert polyester, 5-95 wt% curable compounds). This parameter optimization allows the system to maintain both adhesion (from the inert polyester) and UV reactivity (from the curable compounds at 85-95 wt% concentration).
Solution Approach 2:
The invention creates a composite binder system combining inert polyester resins (for adhesion) with radiation-curable monomers and oligomers (for UV reactivity). The composite formulation synergistically integrates the adhesive properties of inert polyesters with the cureability of acrylate/methacrylate compounds, resolving the contradiction between adhesion and UV reactivity.
2Reliability
If multifunctional acrylates are added to increase UV reactivity, then UV reactivity is improved, but adhesion decreases due to shrinkage increase after curing
Solution Approach 1:
The invention optimizes the functional group equivalence ratio by controlling the hydroxyl value of inert polyesters (30-150 mg KOH/g) and the ratio of hydroxyl groups to carboxyl groups (exceeding 1.0). This ensures minimal shrinkage while maintaining high UV reactivity through the ethylenically unsaturated compounds.
Solution Approach 2:
The invention assigns different functional roles to different components: inert polyesters provide adhesion and minimal shrinkage, while ethylenically unsaturated compounds (5-95 wt%) provide UV reactivity. This local functional differentiation allows the system to achieve both adhesion and UV reactivity without the negative effects of excessive shrinkage.
3Strength
If adhesion primer is applied to increase adhesion on plastic substrate, then adhesion is improved, but application process becomes more complex and costly
Solution Approach 1:
The invention makes the UV curable binder itself multi-functional by incorporating inert polyester resins that provide both adhesion to plastic substrates and compatibility with UV curing. This eliminates the need for separate adhesion primers, simplifying the application process from multiple steps (primer + ink) to a single-step direct printing system.
Solution Approach 2:
The invention merges the functions of adhesion promoter and UV curable binder into a single integrated formulation. The inert polyester-resin-ethylenically unsaturated compound system simultaneously provides substrate adhesion, pigment binding, and radiation curability, eliminating the need for separate adhesion primer applications.
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 composition achieves excellent adhesion on various substrates, including plastics, with high cure speed and low viscosity, eliminating the need for a primer and improving pigment wetting, making it suitable for flexographic and lithographic applications.
Implementation Method 1
radiation curable composition... when the radiation curable composition of the present invention is exposed to energy radiation, such as UV radiation
Data Source
AI summary
The present invention relates to a radiation curable composition comprising at least one ethylenically unsaturated compound (A) and at least one inert OH-terminated polyester (B) prepared from a polyol component that comprises ethylene glycol and from a polycarboxy component that comprises phthalic acid and/or phthalic anhydride. These polyesters can be further modified to bear moieties comprising photo-initiating activity. The present invention further relates to their preparation and their use in for instance lithographic and flexographic applications.