Rigid Polyurethane Foam Molding with Chemical Blowing Agent
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Solution Overview
Problem
Conventional polyurethane foam molding using physical blowing agents faces issues such as uneven density, poor dimensional stability, high thermal conductivity, and long demolding times due to the use of greenhouse gases and flammable agents, which limits their application, especially for medium to high foam thickness.
Innovation Solution
A method of producing rigid polyurethane foam without physical blowing agents by injecting a reaction mixture containing an organic polyisocyanate, polyol composition, catalyst, and a chemical blowing agent like water into a mold cavity under controlled pressure, which reduces volatile organic compound emissions and allows for more viscous systems to be processed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a physical blowing agent is used in polyurethane foam production, then the foam can be produced with conventional processing, but the foam exhibits uneven density, poor dimensional stability, high thermal conductivity, and long demolding times
Solution Approach 1:
The invention changes the blowing mechanism from physical (conventional) to chemical (water-based), fundamentally altering the foaming parameters. This substitution eliminates the problems of uneven density and long demolding times by using a chemical reaction that produces gas more uniformly and rapidly, allowing faster demolding while maintaining density uniformity.
Solution Approach 2:
The invention uses water as a blowing agent instead of expensive physical blowing agents. Water is inexpensive, non-flammable, and environmentally friendly. Although water produces less foam volume per unit weight, the chemical reaction with isocyanate provides sufficient gas generation for complete mold filling, eliminating the need for costly specialized equipment required for handling flammable physical blowing agents.
2Object-affected harmful factors
If only chemical blowing agent like water is used, then environmental safety is improved, but the foam exhibits high reaction exothermicity limiting application for medium to high foam thickness
Solution Approach 1:
The invention extracts and eliminates the harmful flammable physical blowing agents from the system, using only water as the blowing agent. This extraction of harmful substances improves environmental safety and eliminates fire risks, while the high reaction exothermicity is managed as an acceptable trade-off for the significant safety improvements.
3Ease of manufacture
If reaction mixture is injected at atmospheric pressure, then the process is simple, but the mold cavity cannot be completely filled and density uniformity is poor
Solution Approach 1:
The invention uses pressure differentials (pneumatics) to improve mold filling. By injecting the reaction mixture at a pressure higher than atmospheric pressure, the mixture is forced to completely fill the mold cavity, ensuring uniform density distribution. This pressure-controlled injection resolves the contradiction between process simplicity and manufacturing precision.
4Loss of substance
If water content in foam formulation is reduced, then isocyanate consumption is reduced, but foam formation without auxiliary physical blowing agent becomes difficult
Solution Approach 1:
The invention optimizes the water content parameter in the foam formulation to achieve the right balance. By carefully controlling the water content and adjusting other formulation parameters, the system achieves complete mold filling and proper foam formation using only chemical blowing agents, while minimizing isocyanate consumption. This parameter optimization resolves the contradiction between substance loss and manufacturing ease.
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 results in foams with improved density uniformity, reduced thermal conductivity, and faster demolding times, enhancing processability and application suitability, while eliminating the risks associated with physical blowing agents.
Implementation Method 1
the blowing agent being released in the course of the polyaddition reaction between the isocyanate and isocyanate-reactive components in the mixture, causing the reactive mixture to foam
Implementation Method 2
the polyaddition reaction between the isocyanate and isocyanate-reactive components in the mixture
Implementation Method 3
the reduction in the pressure of the mold cavity is proposed for specific applications
Data Source
AI summary
A method of making a molded rigid polyurethane foam comprising injecting into a closed mold cavity a reaction mixture at a packing factor of 1.03 to 1.9, wherein the mold cavity is under a pressure of from 300 to 950 mbar, wherein the reaction mixture comprises an organic polyisocyanate,a polyol composition, a catalyst, optionally auxiliary substances and/or additives, and a chemical blowing agent component in an amount of from 1 to 5 weight percent based on the total weight of the components excluding polyisocyanate, the chemical blowing agent component comprising at least one chemical blowing agent, wherein the chemical blowing agent component is the sole blowing agent.