Single-Layer Flexographic Printing for Low Ignition Propensity Cigarette Wrappers
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Solution Overview
Problem
Current methods for manufacturing Low Ignition Propensity (LIP) paper wrappers for smoking articles face challenges in achieving the desired reduction in air permeability and diffusivity while maintaining ink viscosity and print quality, particularly with high air permeability papers, and require complex multi-layer printing configurations that are difficult to control.
Innovation Solution
A single-layer flexographic printing method using a central drum with a single printing group and anilox, employing an ink with gum arabic as a film-forming substance and calcium carbonate as a filler, along with a combustion agent like potassium citrate, to achieve the desired diffusivity and air permeability reductions on paper wrappers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-layer printing configuration is used to achieve desired air permeability and diffusivity reductions, then the reduction in gas exchange is improved, but the device complexity and difficulty of control increase
Solution Approach 1:
The patent combines multiple printing functions into a single printing group by using an anilox roller with multiple cells of different capacities. Each cell deposits a different amount of ink in a single pass, effectively merging what would require multiple separate printing layers into one integrated printing operation. This reduces device complexity while maintaining the ability to achieve desired gas exchange reductions.
Solution Approach 2:
The patent changes the parameter of ink application by varying the anilox cell capacities rather than using multiple printing layers. The anilox roller contains cells with different volumes that deposit different amounts of ink, allowing precise control of ink application weight (0.5-7 g/m²) and resulting diffusivity (0.010-0.300 cm/s) without increasing mechanical complexity.
2Adaptability or versatility
If high air permeability paper is used, then the smoke ventilation is improved, but the amount of ink solids needed increases and viscosity control becomes difficult
Solution Approach 1:
The patent changes the parameter of ink application weight to optimize the balance between smoke ventilation and ink solids usage. By precisely controlling the anilox cell capacities and ink formulation (25-40% solids), the patent achieves effective gas exchange reduction on high air permeability papers without excessively increasing ink solids consumption or creating viscosity problems.
3Manufacturing precision
If ink viscosity is increased to maintain print quality, then the definition of texts and small drawings is improved, but the transfer of ink to the printing form becomes difficult
Solution Approach 1:
The patent optimizes the ink viscosity parameter within a specific range (25-40% solids) that balances print definition and transferability. The controlled ink application method using the anilox roller ensures consistent ink distribution without requiring excessive viscosity, thereby maintaining both print quality and ease of ink transfer to the printing form and paper wrapper.
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 method allows for precise control and flexibility in printing, reduces ink usage, and achieves the necessary diffusivity and air permeability reductions to ensure self-extinguishing cigarettes with lower ink application weights compared to multi-layer methods, enhancing print quality and operational ease.
Implementation Method 1
the transference of a liquid ink from a printing form to the paper wrapper... the printed band has to reduce the gas exchange between the atmosphere and the lit tobacco... the reduction of this gas exchange entails the closure of these pores
Implementation Method 2
the diffusivity, D*, of a gas through a substrate measures the molecular exchange rate between both faces of the substrate... the printed band has to reduce the gas exchange... only small pores, of a diameter of up to approximately 10 μm influence diffusivity
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a method for single-layer printing of an ink on a wrapper for smoking articles, to obtain a wrapper for smoking articles with low propensity to ignition using the flexographic technique, characterized in that (1) printing is performed on a central drum flexographic printing machine using a single printing unit, (2) said unit having an anilox with capacity of between 10 and 40 cm3/m2 and a print roll equipped with a printing form selected from a stencil plate plus an adhesive, and a sleeve, and (3) in that an ink is used that comprises at least one film-forming substance and a mineral filler, the present invention also relating to the wrapper that can be obtained by this method and to the smoking article that include said wrapper.