Polyurethane Resin Production via Prepolymerization and Viscosity Control
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Solution Overview
Problem
The production of polyurethane resins using aromatic isocyanates faces challenges such as rapid reaction heat generation, increased viscosity, and the occurrence of injection flow marks and striae, which hinder the manufacturing process and result in suboptimal optical materials.
Innovation Solution
A process involving prepolymerization of aromatic isocyanates with specific alcohols in the presence of acidic phosphoric acid ester and hindered amines, optimizing reaction conditions to maintain low viscosity and prevent rapid polymerization, using a mixing apparatus with a screw-shaped stirring blade to mix and inject the polymerizable composition at room temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If aromatic isocyanate and alcohol are reacted at high temperature to improve reaction rate, then productivity increases, but reaction heat generation accelerates and viscosity increases rapidly causing injection flow marks and striae
Solution Approach 1:
The patent applies preliminary action by conducting prepolymerization first to form a prepolymer with controlled molecular weight and structure before the main polymerization step. This preliminary step allows the system to establish a foundation that prevents runaway reactions and viscosity spikes during subsequent processing, thereby avoiding injection flow marks and striae while maintaining productivity
Solution Approach 2:
The patent utilizes parameter changes by carefully controlling the ratio of hydroxyl groups to isocyanato groups (10-20 mol%), maintaining reaction temperature at or below 30°C, and controlling prepolymer viscosity at or below 1,000 mPa·s. These parameter optimizations balance reaction rate with optical quality, preventing the harmful effects of rapid polymerization while maintaining efficient production
2Device complexity
If isocyanate and alcohol are reacted without prepolymerization to simplify the process, then device complexity decreases, but rapid heat generation and viscosity increase occur causing manufacturing defects
Solution Approach 1:
The patent applies preliminary action by conducting prepolymerization first to form a prepolymer with controlled molecular weight and structure before the main polymerization step. This preliminary step allows the system to establish a foundation that prevents runaway reactions and viscosity spikes during subsequent processing, thereby avoiding injection flow marks and striae while maintaining productivity
3Ease of operation
If prepolymerization is performed at high temperature to improve workability, then ease of operation increases, but heat generation accelerates the reaction causing viscosity to increase rapidly
Solution Approach 1:
The patent utilizes parameter changes by carefully controlling the ratio of hydroxyl groups to isocyanato groups (10-20 mol%), maintaining reaction temperature at or below 30°C, and controlling prepolymer viscosity at or below 1,000 mPa·s. These parameter optimizations balance reaction rate with optical quality, preventing the harmful effects of rapid polymerization while maintaining efficient production
Solution Approach 2:
The patent applies preliminary action by conducting prepolymerization first to form a prepolymer with controlled molecular weight and structure before the main polymerization step. This preliminary step allows the system to establish a foundation that prevents runaway reactions and viscosity spikes during subsequent processing, thereby avoiding injection flow marks and striae while maintaining productivity
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 enables the production of polyurethane resins with excellent yield and stability, preventing injection flow marks and striae, and is suitable for mass production of high-transparency optical materials.
Implementation Method 1
reacting the isocyanate (A) with the alcohol (B) in the presence of an acidic phosphoric acid ester (C) and a hindered amine-based compound (D)
Implementation Method 2
the quantity of heat produced by a reaction at the time of blending became great, the reaction was further accelerated due to the heat quantity
Data Source
Figure 1
AI summary
A process for producing a polyurethane resin of the present invention includes a step (i) of obtaining a prepolymer by adding an alcohol (B) to isocyanate (A) such that a ratio of hydroxyl groups to isocyanato groups of the isocyanate (A) falls into a range of 10 mol% to 20 mol% and reacting the isocyanate (A) with the alcohol (B) in the presence of an acidic phosphoric acid ester (C) and a hindered amine-based compound (D), a step (ii) of obtaining a polymerizable composition in a manner in which the alcohol (B) is further added to and mixed with the prepolymer at a temperature of equal to or less than 30°C, and a step (iii) of polymerizing the prepolymer and the alcohol (B) contained in the polymerizable composition. The isocyanate (A) is one or more kinds of isocyanate having two or more isocyanato groups, which contains aromatic isocyanate. The alcohol (B) includes one or more kinds of alcohol having two or more hydroxyl groups. In the alcohol (B), a ratio of secondary hydroxyl groups to a total molar number of primary and secondary hydroxyl groups is equal to or greater than 50 mol%.