Water-Based Cellulosic Coatings Balancing Heat Seal and Roll Blocking
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Solution Overview
Problem
Existing cellulose-based packaging materials face challenges with coatings that provide conflicting properties of good heat seal strength and roll block resistance, are not recyclable, and do not disintegrate during recycling, leading to environmental issues.
Innovation Solution
A water-based coating composition comprising polymer binders with a glass transition temperature less than 10°C and heat seal onset temperature below 200°C, combined with particles larger than 4 μm, providing both heat seal strength and roll block resistance, and being recyclable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LDPE coating is used to provide good liquid barrier properties and heat sealability, then liquid resistance and heat seal strength are improved, but the coating creates problems in recovering fiber during recycling and does not disintegrate
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by using biodegradable polymers (PLA, PHA, PBAT, PCL) instead of conventional LDPE. This parameter change maintains liquid barrier properties while enabling the coating to disintegrate during repulping, thus resolving the recyclability issue.
Solution Approach 2:
The patent employs biodegradable and compostable polymers that are designed to break down under specific conditions (industrial composting, repulping). These materials serve as disposable protective layers that fulfill their function during use but can be easily discarded and decomposed, enabling fiber recovery without contamination.
2Strength
If coating provides good heat seal strength, then heat sealability is improved, but roll block resistance deteriorates
Solution Approach 1:
The patent adjusts the glass transition temperature (Tg) parameter of the polymer coating to below 10°C. This parameter change enables the coating to remain flexible at room temperature (reducing roll block) while still providing adequate heat seal strength when heated, as the low Tg allows the polymer to become sufficiently pliable under heat for sealing.
Solution Approach 2:
The patent uses composite polymer systems combining multiple biodegradable polymers (PLA, PHA, PBAT, PCL) with complementary properties. This composite approach balances heat seal strength and roll block resistance by leveraging the different thermal and mechanical characteristics of each polymer component.
3Object-generated harmful factors
If coating provides good block resistance, then roll block resistance is improved, but heat seal strength deteriorates
Solution Approach 1:
The patent specifically targets the glass transition temperature parameter, setting it below 10°C. This ensures the coating remains soft and flexible at operating temperatures (preventing roll block) while the low Tg also facilitates easy heat sealing by allowing the polymer to deform and bond at lower temperatures, thus maintaining heat seal strength.
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 coating composition achieves liquid resistance, heat sealability, and minimal roll blocking while being environmentally friendly and repulpable, addressing the limitations of current coatings.
Implementation Method 1
at least one polymer binder has a glass transition temperature (Tg) less than 10° C.
Implementation Method 2
at least one polymer binder has a heat seal onset temperature of less than 200° C.
Implementation Method 3
imparting liquid resistance to the cellulosic substrate
Data Source
AI summary
The present invention provides water-based coatings that provide liquid resistance when applied to various substrates. The coatings are particularly suitable for cellulosic substrates such as paper or paper board. In addition to liquid resistance, the coatings have good heat sealability, and are resistant to roll blocking. Preferably, the coatings are recyclable and/or repulpable with the substrates to which they are applied. The coating compositions comprise one or more polymer binders, and one or more particles. Preferably, at least one polymer binder has a glass transition temperature (Tg) less than 10° C. Preferably, at least one polymer binder has a heat seal onset temperature of less than 200° C. Preferably, at least one particle has a mean particle size greater than 4 μm. It is also preferable that the particles have a melting point greater than 60° C.