In the production of polyurethane foam, catalysts play an important role. With a good selection of the catalyst, the desired profile in reaction, foaming, flowability, and foam properties can be obtained. In this article a deeper insight into the molecular catalyst structure-polymer properties relationship will be given. The selection of catalyst is based on its activity as well as performance on physical foam properties. Depending on the molecular structure of the catalyst, the activity will be different. This activity relates to the catalysis of the gel and blow reaction but also the allophonate, biuret, and trimerisation reactions. Via a model system, each of these reactions is studied to understand the reaction mechanism in a better way.

In polyisocyanurate foam production, alkali metal catalysts of organic carboxylic acids and hydroxyalkyltrimethyl quaternary ammonium salts are traditional standards as polyisocyanurate foam catalysts. The activity of these catalysts, however, is not efficient at low temperature. Therefore, the initiation reactions are extremely delayed, and the flowability of the foam system is far too inferior. In addition, the foam exhibits shrinkage when the thickness of the sprayed layer was thin and the temperature was low while applying the sprayed foams. The combination of other tertiary amine catalysts could improve the flowability; however, the flammability of the foam would be a hazard because the isocyanurate reaction has not fully progressed.For the improvement of the above-mentioned problems, Tosoh Corp. has developed several new quaternary ammonium salt compounds, such as Toyocat-TR20. TR20, however, should be used in conjunction with an alkali 72 Downloaded from metal co-catalyst. Presently, Tosoh has succeeded in developing another new catalyst having even higher catalytic activity at low temperature, which can replace the use of the alkali metal catalyst. The new catalyst provides the low temperature dependency in the isocyanurate reaction activity compared to the traditional isocyanurate catalysts. The new catalyst provides the following advantages:1. The catalytic activity is high. 2. The isocyanurate reaction activity at low temperature is high. 3. The initial foaming reaction is improved, thereby the rise profile is now smooth.In this report, new quaternary ammonium salts will be introduced with comparison data using the FT-IR analytical methods, as well as the evaluation in panel and sprayed foams.

The establishment of CFC-free polyurethane foam systems, aimed at total CFC elimination by the year 1995, is of paramount importance in the present day polyurethane foam technology. Especially in rigid foam systems, the attempts to apply a variety of alternative blowing agents such as HCFC-22, -141b, and -142b, HFC-134a and -356, and hydrocarbons such as n-pentane, isopentane and cyclopentane, as well as all-water blown systems, are being examined. In all cases of alternative blown systems, however, there exist differences in foaming behavior as well as inferior foam properties compared to traditional CFC-11 blown systems. Especially in HCFC-141b and cyclopentane blown systems, which have gained the greatest interest among the above-mentioned options, the following three subjects are of major concern. The requirements involved in achieving the resolution of these problems are dependent not only on the development of major raw materials but also on the selection of suitable auxiliary intermediates such as catalysts and foam stabilizers. (1) Thermal Conductivity; HCFC-141b, cyclopentane and carbon dioxide, which is generated from the reaction of water and isocyanate, have high thermal conductivity compared to CFC-11, thereby causing inferior insulation performance of the foam. Fine cell technology is now being examined in order to improve the thermal conductivity. For the achievement of the fine cell structure, the selection of suitable amine catalyst systems is important, although the effect of foaming stabilizers has an especially large contribution. (2) Dimensional Stability; not only in all-water blown systems, but also in HCFC-141b and cyclopentane blown systems which use water in high concentration, dimensional stability becomes a large problem due to the diffusion of carbon dioxide gas from the foam cell. For the improvement of dimensional stability, there exists the option to increase the foam strength; moreover, it is important to improve the isotropy of cell structure by adjusting amine catalyst systems. (3) Foam density; since 141b and cyclopentane have relatively higher boiling points and less blowing efficiency, lowering the foam density becomes rather difficult. Moreover, lower foam density normally provides poor dimensional stability. It can be said that the catalytic activity ratio in blowing/gelling of amine catalysts play an important role for the lowering of foam density with improved dimensional stability. It is very difficult to improve these three factors simultaneously. In this report, however, the improvements of these subjects are discussed from a standpoint of amine catalysts; also special newly developed nucleation catalyst systems are introduced for cyclopentane and HCFC-141b blown systems.

No abstract

This paper will focus on the generalization of catalytic activities of a variety of typical amine and tin catalysts in the isocyanate reaction of gelation, blowing and crosslinking. Secondly the relationship between catalytic activities and foaming behavior, as well as foam properties, will be discussed from the standpoint of developing novel catalyst systems for all-water blown integral skin foams (ISF).Catalysts play an important role in the control and balance between the gelation and blowing reactions. Especially in ISF systems, this control becomes increasingly important for the improvement of surface skin formation in allwater blown systems, which are now required for eliminating CFC. That is to say, skin formation and cure become inferior when using water as a blowing agent, primarily because the role of CFC is to aid in skin formation. Moreover, other than the two primary reactions, it will be considered that the catalytic activity of the crosslinking reactions such as allophanate, biuret and isocyanurate formation will have some effect on foaming behavior as well as foam properties. Therefore it will be important to know the crosslinking activities for the design of novel catalyst systems.Concerning the catalytic activities for the primary gelation and blowing reactions, many reports have been presented in the past, where the relationships between catalytic activities and foaming behaviors, as well as foam properties have been reported. On the other hand, several reports have been recently presented on the crosslinking activities, based on the method using HPLC analysis techniques in a model reaction. Few reports, however, describe the reaction kinetic analysis of the catalytic crosslinking activities and the systematic examination of its relation to foaming behavior and foam properties.In this paper, the catalytic activity of a variety of typical amine and tin catalysts will be generalized with a review on gelation and blowing activities, secondly a reaction kinetic analysis of the crosslinking activities using HPLC analysis in a model reaction.In addition, the relationship between these catalytic activities and foaming behaviors, as well as foam properties, will be discussed in an all-water blown ISF system. As to the foaming reaction, the relationship between viscosity rise profiles, which may have a large relation to cure, will also be discussed. Concerning foam properties, the relation to cure and skin formation will be discussed. As a result, it will be shown that strong gelling catalysts with high crosslinking activities provide improvement in skin formation. This report will introduce novel catalyst systems in all-water blown ISF systems by suggesting the effectiveness of catalytic activities in the selection of a suitable catalyst system.