Duplex Printing via Intermediate Belt Transfer
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Solution Overview
Problem
Digital printing systems face challenges in achieving uniformity and quality due to issues like ink beading on hydrophobic transfer members, leading to unstable ink images and difficulties in printing on both sides of substrates, especially with aqueous inks.
Innovation Solution
A printing system with a flexible, substantially inextensible belt as an intermediate transfer member, guided along a closed path, and equipped with impression stations and a pressure cylinder for transferring ink images onto substrates, allowing for duplex printing and using a multi-nozzle print bar with image correction functions to enhance tone reproduction uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an indirect printing system with a hydrophobic belt is used to transfer ink images, then the distance between the print head and substrate can be maintained constant and substrate wetting is reduced, but ink beading occurs on the belt surface leading to unstable ink images
Solution Approach 1:
The patent changes the surface energy parameter of the belt from hydrophobic to hydrophilic, allowing aqueous inks to spread uniformly rather than bead up. This parameter change resolves the contradiction by maintaining both image uniformity and ink image stability on the belt surface.
2Productivity
If inkjet printing is performed directly onto porous paper substrates, then the process is simple, but the resolution is limited due to ink wicking into the substrate
Solution Approach 1:
The patent introduces a belt as an intermediary transfer member between the inkjet print head and the substrate. The belt receives the ink image, allows it to dry, and then transfers it to the substrate, preventing ink wicking while maintaining printing speed.
3Manufacturing precision
If coated substrates 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 belt acts as an intermediary that provides the drying function without requiring coated substrates. The ink dries on the belt surface during transfer, eliminating the need for additional drying steps and reducing process complexity while maintaining image quality.
4Ease of manufacture
If aqueous inks are used for printing, then the inks are non-toxic and easier to handle, but they bead up on hydrophobic transfer members reducing transfer stability
Solution Approach 1:
The patent changes the surface energy parameter of the belt from hydrophobic to hydrophilic, which allows aqueous inks to spread and adhere uniformly rather than bead up. This resolves the contradiction by maintaining both ease of ink handling and transfer stability.
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 system enables high-quality duplex printing with improved image uniformity and reduced substrate wetting, allowing for efficient transfer of ink images onto both sides of substrates while maintaining the stability of the ink film.
Implementation Method 1
an image forming station for depositing droplets of a liquid ink onto an outer surface of the belt to form an ink image
Implementation Method 2
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 3
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, comprises a movable intermediate transfer member in the form of a flexible, substantially inextensible, belt guided to follow a closed path, an image forming station for depositing droplets of a liquid ink onto an outer surface of the belt to form an ink image, a drying station for drying the ink image on the belt to leave an ink residue film on the outer surface of the belt, 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 compressible blanket for urging the belt against the substrate supported on the impression cylinder, and a transport system for transporting the substrate from the first impression station to the second impression station. The pressure cylinder of at least the first impression station is movable between a first position in which the belt is urged towards the impression cylinder to cause the residue film on the outer surface of the belt to be transferred onto the front side of the substrate supported on the impression cylinder, and a second position in which the belt is spaced from the impression cylinder to allow the ink image on the belt to pass through the first impression station and arrive intact at the second impression station for transfer onto the reverse side of the substrate supported on the second impression cylinder.