PUR/PIR Foam Cold Cracking via Polyol Formulation
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Solution Overview
Problem
Polyurethane and polyisocyanurate rigid foams become brittle in cold temperatures, leading to cracking and damage in metal composite elements, especially in the first few weeks after production.
Innovation Solution
A polyol formulation comprising 50-80 wt.% of a polyester or polyetherester polyol with an aromatic moiety, 0-5 wt.% of a polyol with a higher hydroxyl number, 8.0 - 12.0 wt.% of a long-chain polyether polyol alkoxylated with a mixture of ethylene oxide and propylene oxide, and additional components to enhance isocyanate reactivity and foam properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If predominantly aromatic polyols are used in the polyol formulation, then the foam exhibits good mechanical properties and adhesion, but the susceptibility to cracking in cold temperatures increases significantly
Solution Approach 1:
The patent modifies the chemical composition parameters of the polyol formulation by introducing polyether polyols with specific molecular weight ranges (10,000-100,000 g/mol) and controlling the ratio of aromatic to aliphatic polyols. This parameter change transforms the foam's molecular structure to achieve both good adhesion and reduced cold-temperature cracking susceptibility.
Solution Approach 2:
The invention creates a composite polyol system combining aromatic polyester polyols (for adhesion and mechanical properties) with aliphatic polyether polyols (for flexibility and cold-temperature resistance). This composite approach allows the foam to exhibit both strong bonding to substrates and resistance to brittle cracking at low temperatures.
2Strength
If the foam is produced with high aromatic polyol content, then good initial mechanical properties are achieved, but damage in the form of longitudinal cracks occurs particularly in the first few weeks after production
Solution Approach 1:
The patent incorporates flexible polyether polyol segments into the formulation before foam production, which act as internal cushioning elements. These flexible segments prevent stress concentration and crack propagation during the critical early aging period, thereby extending the time before crack development occurs.
Solution Approach 2:
The invention adjusts the molecular weight distribution and chemical composition parameters of the polyol blend to create a more stable molecular network. This parameter optimization ensures that the foam maintains its mechanical integrity over extended periods, delaying the onset of cracking beyond the typical few-week timeframe.
3Strength
If long-chain polyether polyols are added to improve adhesion properties, then adhesion is enhanced, but the complexity of the polyol formulation increases
Solution Approach 1:
The patent applies the principle of local quality by selecting polyether polyols with specific molecular weight ranges (10,000-100,000 g/mol) that provide adhesion enhancement without excessive complexity. The formulation targets specific performance zones (adhesion and cold-temperature flexibility) while maintaining manageable formulation complexity through controlled component selection.
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 polyol formulation significantly reduces the susceptibility to cracking in cold temperatures of metal composite elements with a PUR/PIR foam core, while maintaining good mechanical properties and foam structure.
Implementation Method 1
component a3) consisting of one or more polyols selected from polyether polyols having an OH number of 10 to 80 KOH/g and an average functionality of ≥ 2.0 to ≤ 3.0, prepared by alkoxylation of a suitable starter component, with a mixture of ethylene oxide (EO) and propylene oxide (PO)
Implementation Method 2
component a4) consisting of one or more polyols selected from polyether polyols having an OH number in the range of 350 - 500 mg KOH/g, in particular 390 - 440 mg KOH/g, prepared by alkoxylation of an aromatic amine with at least one alkylene oxide
Data Source
AI summary
The present invention relates to polyol formulations on the basis of an aromatic polyester polyol component and a specific polyether polyol component, to a process for producing rigid polyurethane foams or rigid polyurethane / polyisocyanate foams using this polyol formulation, and to the rigid PUR / PIR foams produced therefrom. Composite metal elements containing these rigid foams have an especially low cold cracking susceptibility.