Electrohydrodynamic Adhesive Application on Moving Web
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Solution Overview
Problem
Conventional adhesive application methods for absorbent articles, such as disposable diapers, face challenges in controlling adhesive placement and amount on moving webs, leading to inefficiencies and excess material usage, especially at high speeds, and are prone to clogging and downtime due to adhesive buildup.
Innovation Solution
A system and process that applies adhesive in a controlled pattern of treated discrete areas with varying adhesive composition distribution, using a web deflecting device to intermittently contact the web with a nozzle, allowing precise control over adhesive flow and application, even at high speeds, and incorporating a self-cleaning mechanism to maintain nozzle integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If adhesive is sprayed using pressure-dependent nozzles on a moving web, then adhesive can be applied to the web, but control over adhesive placement and amount becomes difficult and collateral spray occurs
Solution Approach 1:
The patent replaces the pressure-dependent mechanical spray system with an electrohydrodynamic (EHD) system that uses electric fields to control adhesive ejection. The EHD nozzle uses a high-voltage electrode to create an electric field that pulls adhesive through a capillary orifice, enabling precise control of adhesive placement and amount without the collateral spray problems associated with pressure-based systems.
Solution Approach 2:
The patent changes the control parameter from pressure to electric field strength. By adjusting the voltage applied to the high-voltage electrode, the system can precisely control the amount and placement of adhesive ejected from the nozzle. This parameter change enables independent control of each nozzle's adhesive output, improving placement precision and eliminating the interdependence problems of pressure-based systems.
2Productivity
If hot melt adhesive is extruded onto a moving web at high speeds, then production speed increases, but adhesive forms long streaks requiring more material and creating waste
Solution Approach 1:
The EHD system applies adhesive in periodic, controlled pulses rather than continuous extrusion. The high-voltage electrode can be activated and deactivated rapidly to eject discrete amounts of adhesive only when needed, matching the periodic contact of the web with the nozzle. This eliminates the long continuous streaks formed at high speeds by extrusion systems and reduces adhesive waste.
Solution Approach 2:
The patent replaces the mechanical extrusion system with an EHD system that uses electric fields to control adhesive ejection. This substitution enables precise control of adhesive amount and placement even at high web speeds, preventing the formation of long adhesive streaks and reducing material waste while maintaining high productivity.
3Productivity
If the web is in constant contact with the adhesive head for extrusion, then adhesive can be applied continuously, but the process becomes rate-limiting at high speeds and requires longer adhesive streaks
Solution Approach 1:
The system uses periodic contact between the web and nozzle combined with pulsed EHD adhesive ejection. The web is deflected to contact the nozzle only during brief intervals, and adhesive is ejected in synchronized pulses during these contact periods. This periodic action eliminates the rate-limiting continuous contact requirement while maintaining efficient adhesive application at high speeds.
Solution Approach 2:
The patent introduces dynamic, intermittent contact between the web and adhesive nozzle rather than constant contact. The web deflecting device periodically brings the web into contact with the nozzle, and the EHD system dynamically controls adhesive ejection during these brief contact intervals. This dynamic approach enables high-speed processing without the inefficiencies of continuous contact extrusion.
4Manufacturing precision
If adhesive is applied in long streaks to cover the adhesive head contact area, then complete coverage is achieved, but excess material is used and cost increases
Solution Approach 1:
The EHD system applies adhesive with local precision, delivering adhesive only to the specific areas where web contact with the nozzle occurs. Rather than applying adhesive in long continuous streaks to ensure complete coverage, the system uses the electric field to target adhesive ejection precisely at the contact points, achieving complete coverage with minimal material consumption.
Solution Approach 2:
The patent replaces the mechanical extrusion system that requires long adhesive streaks for complete coverage with an EHD system that uses electric fields for precise adhesive placement. This substitution enables complete coverage of the contact area with minimal adhesive material, eliminating the excess material usage inherent in extrusion-based systems.
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
This approach minimizes adhesive usage, reduces streak length, and enables higher production speeds while maintaining adhesive strength, resulting in more efficient and cost-effective adhesive application with reduced material waste and downtime for maintenance.
Implementation Method 1
a web deflecting device that periodically causes the moving web to contact a nozzle
Implementation Method 2
a pattern of treated discrete areas reside on the first surface of the base web. The treated discrete areas are formed from an adhesive composition
Data Source
AI summary
A unique and distinctive adhesive pattern is applied to a base web, such as a nonwoven web. The adhesive pattern can include a plurality of treated discrete areas that can extend parallel in the longitudinal direction of the web. Each treated discrete area can include a head portion connected to a tail portion. The head portion, in one embodiment, can have a greater amount of adhesive composition based on mass per area in relation to the amount of adhesive composition contained in the tail portion. The overall length of the treated discrete area can be relatively short in relation to adhesive patterns produced in the past using conventional slot coating processes. The adhesive pattern provides a secure attachment to an adjoining material and can provide various processing advantages.