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Amine Emission-Free Catalyst System for Flexible Foam
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R. van Maris (Tosoh Europe B.V., The Netherlands)
H. Kometani, Y. Tamano, H. Nakamura, K. Tokumoto (Tosoh Corporation, Japan)
Table of Contents:
Abstract
Introduction
Suggested Special Amine Catalyst Systems
Experimental
Results and Discussion
Conclusion
Abstract
In this report, the automotive industry's requirement to reduce the emission of the amine PU catalyst will be discussed. It will be illustrated that, by replacing the currently used catalyst package (TEDA L33/TOYOCAT® ET) with a new catalyst system based on reactive amines (TOYOCAT® RX20, RX21), good foam properties can be obtained without the disadvantage of giving in on wet set and curing.
Introduction
There is growing pressure from the automotive industry to reduce the emission of volatile organic compounds; in particular the emission of amine polyurethane catalysts is receiving attention. Currently, TEDA L33/TOYOCAT® ET is a very popular catalyst system. However, these catalysts can emit during the use of the polyurethane parts inside the car. The new industry requirement is aiming for:
- Improvement of air quality in cars,
- Improvement of environmental work place conditions,
- Reduction of fogging.
Besides the above requirements the following issues should not be neglected:
- lncrease of productivity,
- lmprovement of quality,
- Decrease in foam density maintaining good foam properties.
Suggested Special Amine Catalyst Systems
 Low Volatile Catalysts
This amine catalyst has a high boiling point, i.e. less volatile, so therefore not expected to cause fogging. However, the catalyst is in the free state in the polyurethane foam, and thus there remains a possibility of release from the foam. A disadvantage is that amine emissions cannot be reduced to zero.
Reactive Amine Catalysts
Reactive amine catalysts contain hydroxyl or amino functional groups, which will react with isocyanate groups and become built into the polymer structure. Therefore, it is understood that these reactive amines will not cause emissions. At higher temperatures, however, the formed bond could break, causing the amine catalyst to emit. Each reactive amine exhibits a different behaviour, so any selection should be made with caution. In the case of reactive amine catalysts, the foam properties, especially wet set and curing, will deteriorate. The Results and Discussion section below will illustrate how to overcome this problem.
Experimental
The new catalyst systems TOYOCAT® RX20 and TOYOCAT® RX21 have been evaluated in High Resilience Moulded Foam formulations based on either TDI/MDI blend and all-MDI respectively. Here, we present only the use of TOYOCAT® RX20 in TDI/MDI based formulation. The formulation used for evaluation is given in Table 1.
Table 1. HR Moulded Foam Formulation
| Ingredient Amount |
(pbw) |
| Polyether polyol 1) |
60 |
| Polymer polyol 2) |
40 |
| Water |
3.2 |
| Silicone surfactant |
1.0 |
| Diethanolamine |
1.0 |
| Triethanolamine |
2.0 |
| Catalyst |
Varied |
| T-80/crude MDI (80/20) |
IsoIndex=105 | 1) KC246 ex Sanyo Chemical, glycerol based, OH value = 30 mgKOH/g
2) FA728R ex Sanyo Chemical, glycerol based, OH value = 27.5 mgKOH/g
The foaming conditions are given in Table 2.
Table 2. Foaming Conditions
| Liquid temperature |
20ºC |
| Mixing (5 seconds) |
6000 rpm |
| Mould temperature |
50ºC |
| Mould dimensions |
35 x 35 x 10 cm |
Results and Discussion
As mentioned in the introduction, the ultimate aim is to have zero amine emission. To make a good selection from an emission point of view, the foams were given a heat treatment and checked for emission.
Figure 1. Emission of several evaluated reactive amine catalysts systems in HR Moulded foams.
In Figure 1 the emission of several reactive catalysts systems is presented. As can be seen from the figure, all evaluated catalysts emit from the foam after the given heat treatment. However, the newly developed catalysts systems TOYOCAT® RX20 and RX21 showed the lowest emission of all. Furthermore, Figure 1 shows that some of the reactive amines, despite the functional group, show even higher emission compared to the standard TEDA L33 reference system. The supposition is that either the reactive amine catalyst did not react with an isocyanate group or the catalyst bond to the polymer network was broken again at higher temperature. This requires further investigation.
In the next stage, the foams were further evaluated for reaction profile, physical properties and fogging/emission. The results of this evaluation are given in Table 3. Evaluation on reaction profile, physical properties and fogging/emission of reactive amine catalysts in TDI/MDI based HR Moulded Foam.
As can be seen from the table, the biggest differences are obtained in: ILD, First cycle, at demoulding, wet set, curing function, fogging value of amine.
Regarding ILD at demoulding, a catalyst like HPI shows far too high a value, signifying unsatisfactory cell opening of the foam. As for wet set, it is clear that the evaluated amines all come close to the reference foam; however, the value of the reference foam is in itself rather high. The curing function is evaluated by looking at several issues such as mould flow, appearance of the skin of the foam, etc. TOYOCAT® RX20 showed good curing, whereas some other reactive amines, specifically HPI and TMP, showed poorer curing and had to be used in higher amounts in order to obtain the same reaction profile.
Figure 2. The emission of several reactive amine catalysts, analysed from the fogging deposit.
The evaluation of amine emission was carried out by the fogging test method, DIN 75201 Gravimetric method. The deposit on the Al-foil was collected and analysed on the specific amine. As can be seen in Figure 2, the reactive amine catalysts BDM and DMEA showed even higher emission values compared to the reference foam based on TEDA L33. In the case of the other evaluated amines, they still caused emission whereas in the case of TOYOCAT® RX20 and RX21 no emission was detected.
Conclusion
TOYOCAT®-RX20 & RX21:
- Provide no amine emission even at high temperatures.
- Although they are reactive amine catalysts, they provide good foam properties such as wet set and curing.
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