Viscoelastic Polyurethane Foam Air Permeability
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Solution Overview
Problem
Viscoelastic polyurethane foams with high closed-cell structures have low air permeability, leading to heat retention, water absorption, and mechanical weakness, making them unsuitable for applications requiring air exchange and durability, especially in mattresses and pillows.
Innovation Solution
A process for producing viscoelastic flexible polyurethane foams with enhanced air permeability and tensile strength by using polymeric compounds with specific polyalkylene oxide compositions, catalysts, and blowing agents, resulting in open-cell foams that maintain viscoelastic properties during washing and drying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high closed-cell structure is used in viscoelastic polyurethane foams, then viscoelastic properties are improved, but air permeability decreases leading to heat retention and poor moisture removal
Solution Approach 1:
The patent changes the chemical composition parameters of the polyol mixture, specifically using a blend of polyethylene oxide polyol (20-40 wt%), polypropylene oxide polyol (30-50 wt%), and polyester polyol (10-30 wt%). This chemical parameter change results in a foam structure that achieves both viscoelastic properties and high air permeability, resolving the contradiction between closed-cell structure benefits and air exchange requirements.
2Strength
If a closed-cell structure is used, then viscoelastic recovery is improved, but drying becomes difficult causing cell membrane rupture and loss of viscoelastic behavior
Solution Approach 1:
The patent modifies the chemical composition parameters by incorporating hydrophobic polyester polyol (10-30 wt%) into the polyol mixture. This parameter change reduces the overall hydrophilicity of the foam matrix, enabling efficient water removal during drying without causing cell membrane rupture. The foam maintains its closed-cell viscoelastic structure through the drying process while achieving complete moisture removal.
3Reliability
If open-cell foam is used, then air exchange and comfort are improved, but tensile strength and mechanical resilience decrease
Solution Approach 1:
The patent employs a composite polyol formulation where polyester polyol (10-30 wt%) contributes to mechanical strength and structural integrity, while polyethylene oxide and polypropylene oxide polyols provide the necessary softness and air permeability. The isocyanate index is optimized to 80-120 to balance open-cell structure formation with tensile strength development, achieving both comfort and mechanical resilience.
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 resulting foams exhibit excellent air permeability, high tensile strength, and improved durability, allowing for effective air exchange and maintaining mechanical properties even after washing and drying, making them suitable for applications like mattresses and pillows.
Implementation Method 1
The polyisocyanates (a) are reacted with the polymeric compounds (b) with groups reactive towards isocyanates
Implementation Method 2
the polyisocyanates (a) are reacted with the polymeric compounds (b) with groups reactive towards isocyanates in the presence of blowing agents (f), catalysts (e) and auxiliaries and/or additives (g) to form viscoelastic flexible polyurethane foams
Implementation Method 3
the polyisocyanates (a) are reacted with the polymeric compounds (b) with groups reactive towards isocyanates in the presence of blowing agents (f)
Data Source
AI summary
The present invention relates to a process for producing viscoelastic flexible polyurethane foams having an air flow value of at least 1 dm3/s, which comprises (a) polyisocyanate being mixed with (b) polymeric compounds having isocyanate-reactive groups, (c) optionally chain-extending and/or crosslinking agents, (d) optionally compounds having only one isocyanate-reactive group with a hydroxyl number of 100 to 500 mg KOH/g, (e) catalyst, (f) blowing agent, and also optionally (g) addition agents to form a reaction mixture and convert it into flexible polyurethane foam, wherein the polymeric compounds having isocyanate-reactive groups (b) comprise 10 to 40 wt% of at least one polyalkylene oxide (b1) having a hydroxyl number of 90 to 300 mg KOH/g, based on a 3 to 6-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, 5 to 20 wt% of at least one polyalkylene oxide (b2) having a hydroxyl number of 10 to 60 mg KOH/g, based on a 2 to 4-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, 10 to 50 wt% of at least one polyalkylene oxide (b3) having a hydroxyl number of 10 to 55 mg KOH/g, based on a 2 to 4-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 70 to 100 wt%, and 0 to 20 wt% of at least one polyalkylene oxide (b4) having a hydroxyl number of 50 to 200 mg KOH/g, based on a 2-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, and wherein the fraction of compounds b1) to b4), based on the total weight of polymeric compounds having isocyanate-reactive groups (b), is at least 80 wt%. The present invention further relates to a viscoelastic polyurethane foam having an air flow value of at least 1 dm3/s, which is obtainable by such a process, and to the use of such a polyurethane foam for mattresses and cushions.