Digital Printing Using a Hydrophobic Transfer Surface to Prevent Ink Beading
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Solution Overview
Problem
Existing digital printing techniques face challenges in achieving high-quality photographic images due to ink beading on hydrophobic transfer members, leading to unstable ink images and difficulties in transferring to substrates, especially with aqueous-based inks, which result in poor image quality and require costly substrate coatings and additional drying steps.
Innovation Solution
A printing process utilizing an intermediate transfer member with a hydrophobic surface and ink droplets containing organic polymeric resin and a coloring agent, where attractive intermolecular forces between the ink and transfer member molecules counteract surface tension to maintain a flattened droplet shape, allowing for efficient drying and transfer of a residue film to the substrate without beading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If inkjet printing is used to spray droplets of ink directly onto a substrate, then the printing process is simple and fast, but the resolution is limited due to wicking by the inks into paper substrates and poor image quality
Solution Approach 1:
An intermediate transfer member is introduced between the inkjet print head and the substrate. The print head deposits ink droplets onto the transfer member, which then transfers the dried ink image to the substrate. This intermediary allows the ink to be deposited on a non-porous surface where it can dry without wicking, preserving image sharpness and resolution.
Solution Approach 2:
The printing process is divided into two separate stages: (1) depositing and drying ink droplets on the intermediate transfer member, and (2) transferring the dried ink image to the substrate. This segmentation allows each stage to be optimized independently - the first for high resolution and the second for substrate compatibility.
2Ease of manufacture
If inkjet printing is used with aqueous-based inks, then the ink is easy to handle and environmentally friendly, but the ink beads on hydrophobic transfer members leading to unstable ink images
Solution Approach 1:
The surface energy parameters of the intermediate transfer member are specifically controlled to create a hydrophilic surface that is compatible with aqueous-based inks. This parameter change prevents beading and ensures stable ink image formation while maintaining the environmental benefits of aqueous inks.
3Manufacturing precision
If substrate coatings are used to control ink absorption, then image quality can be improved, but the cost increases and additional drying steps are required
Solution Approach 1:
The intermediate transfer member serves as a mediator that eliminates the need for substrate coatings. By drying the ink on the transfer member before transfer, the substrate's absorption characteristics become irrelevant, simplifying the overall process and reducing costs.
4Ease of operation
If the substrate surface remains wet after printing, then the ink can be transferred easily, but additional costly and time-consuming drying steps are needed and the substrate may be smeared during handling
Solution Approach 1:
The ink is dried on the intermediate transfer member before being transferred to the substrate. This preliminary drying action prevents smearing during handling and eliminates the need for additional drying steps after substrate printing, saving time and improving operational efficiency.
5Strength
If excessive wetting of the substrate is used, then the ink adheres well to the substrate, but cockling occurs and printing on both sides of the substrate becomes difficult or impossible
Solution Approach 1:
The intermediate transfer member acts as a buffer that prevents excessive wetting of the substrate. The ink is transferred as a dried film, ensuring adequate adhesion without over-saturation, thereby maintaining substrate flatness and enabling double-sided printing.
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 process achieves high-quality, thin, uniform ink films on substrates with improved image resolution and reduced substrate wetting, enabling stable image transfer and eliminating the need for costly substrate coatings and additional drying steps, resulting in environmentally friendly and cost-effective printing.
Implementation Method 1
attractive intermolecular forces between the ink and transfer member molecules counteract surface tension to maintain a flattened droplet shape
Implementation Method 2
intermediate transfer member with a hydrophobic surface
Implementation Method 3
drying the ink while the ink image is being transported by the intermediate transfer member by evaporating the aqueous carrier from the ink image
Data Source
AI summary
A printing process is disclosed which comprises directing droplets of an ink onto an intermediate transfer member to form an ink image, the ink including an organic polymeric resin and a coloring agent in an aqueous carrier, and the transfer member having a hydrophobic outer surface so that each ink droplet in the ink image spreads on impinging upon the intermediate transfer member to form an ink film. The ink is dried while the ink image is being transported by the intermediate transfer member by evaporating the aqueous carrier from the ink image to leave a residue film of resin and coloring agent. The residue film is then transferred to a substrate. The chemical compositions of the ink and of the surface of the intermediate transfer member are selected such that attractive intermolecular forces between molecules in the outer skin of each droplet and on the surface of the intermediate transfer member counteract the tendency of the ink film produced by each droplet to bead under the action of the surface tension of the aqueous carrier, without causing each droplet to spread by wetting the surface of the intermediate transfer member.