Intermediate Transfer Belt for Duplex Digital Printing
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Solution Overview
Problem
Digital printing systems face challenges in achieving high-quality duplex printing due to issues like ink wetting, cockling, and image quality degradation on fibrous substrates, particularly with inkjet printing, which limits the ability to print on both sides of substrates effectively and results in poor image quality.
Innovation Solution
A digital printing system with a movable intermediate transfer member in the form of a flexible belt that allows for sequential printing on both sides of a substrate, using a dual printing tower setup with independently operable towers and a perfecting mechanism to enable printing on either side, along with a compressible blanket for conformability and image transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If inkjet printing is used directly onto fibrous substrates, then printing speed can be increased, but image quality deteriorates due to wicking and variation in distance between print head and substrate surface
Solution Approach 1:
An intermediate transfer member (belt) is introduced between the inkjet print head and the substrate. The belt receives ink droplets from the print head, allows the carrier liquid to evaporate, and then transfers the dried ink image to the substrate. This intermediary solves the wicking problem by providing a non-porous surface and maintains constant distance for high-quality printing.
Solution Approach 2:
The printing process is segmented into distinct stages: ink deposition on the belt, carrier liquid evaporation, and subsequent transfer to the substrate. This separation allows optimization of each stage independently, enabling high-speed printing while maintaining image quality through controlled drying before transfer.
2Device complexity
If liquid ink is printed directly onto the substrate, then the printing process can be simplified, but substrate wetting causes cockling and makes duplex printing difficult
Solution Approach 1:
The carrier liquid is evaporated from the ink image on the intermediate transfer member before the image is transferred to the substrate. This preliminary drying action prevents substrate wetting and cockling, enabling high-quality duplex printing without the harmful effects of liquid ink contact.
3Object-affected harmful factors
If aqueous based inks are used, then toxicity is reduced and image vividness is improved, but the hydrophobic silicone coated transfer member causes ink droplets to bead, making liquid removal difficult
Solution Approach 1:
The surface properties of the intermediate transfer member are modified by applying a corona discharge treatment or plasma treatment. This changes the surface energy characteristics, making the surface more hydrophilic and reducing ink beading. The treatment enables effective liquid removal while maintaining the advantages of aqueous-based inks.
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
Enables high-speed duplex printing with improved image quality by maintaining a constant distance between the print head and substrate, reducing substrate wetting, and allowing for efficient transfer of images onto both sides without the limitations of substrate properties, enhancing printing speed and image fidelity.
Implementation Method 1
a drying station for drying the ink image on the belt to leave an ink residue film on the outer surface of the belt
Implementation Method 2
a pressure cylinder carrying a compressible blanket for urging the belt against the substrate supported on the impression cylinder
Data Source
AI summary
A printing system for printing on a substrate. In embodiments, the system comprises: a movable intermediate transfer member in the form of a flexible, substantially inextensible, thin belt whose compressible layer has a thickness of at most 400 micrometers, the belt being guided to follow a closed path, an image forming station for depositing ink droplets onto an outer surface of the belt to form an ink image, a drying station for drying the ink image to leave an ink residue film, first and second impression stations spaced from one another in the direction of movement of the belt, each impression station comprising an impression cylinder for supporting and transporting the substrate and a pressure cylinder carrying a thick compressible blanket for urging the belt against the substrate supported on the impression cylinder, a thickness of the compressible blanket being at least 1 mm.