Process for preparing polyurethane foam

Details Process for preparing polyurethane foam Process for preparing polyurethane foam

2002-08-06

2004-11-16

Cooney, Jr., John M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S114000, C521S115000, C521S130000, C521S131000, C521S163000, C521S164000, C521S167000, C521S170000, C521S172000, C521S174000

Reexamination Certificate

active

06818675

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention generally relates to process for producing polyurethane foams. The invention is especially adapted for producing polyurethane foams employing the one-shot foaming process, the quasi-prepolymer process and the pre-polymer process. Specifically, the invention relates to polyurethane catalysis with a delayed action catalyst system and optionally an organotin catalyst. The delayed action catalyst is composed of at least the reaction product of (a) one or more carboxylic acids having hydroxy and/or halo functionality; (b) one or more tertiary amine ureas and, optionally, (c) one or more specific reactive tertiary amine(s) and/or one or more specific tertiary amine carbamate(s) for promoting reactions involved in the production of polyurethanes, preferably one-shot polyurethanes, and particularly flexible polyurethane foams.
2. Background
Polyurethane foams are produced by reacting a di- or polyisocyanate with compounds containing two or more active hydrogens, generally in the presence of blowing agent(s), catalysts, silicone-based surfactants and other auxiliary agents. The active hydrogen-containing compounds are typically polyols, primary and secondary polyamines, and water. Two major reactions are promoted by the catalysts among the reactants during the preparation of polyurethane foam, gelling and blowing. These reactions must proceed simultaneously and at a competitively balanced rate during the process in order to yield polyurethane foam with desired physical characteristics.
Reaction between the isocyanate and the polyol or polyamine, usually referred to as the gel reaction, leads to the formation of a polymer of high molecular weight. This reaction is predominant in foams blown exclusively with low boiling point organic compounds. The progress of this reaction increases the viscosity of the mixture and generally contributes to crosslink formation with polyfunctional polyols. The second major reaction occurs between isocyanate and water. This reaction adds to urethane polymer growth, and is important for producing carbon dioxide gas which promotes foaming. As a result, this reaction often is referred to as the blow reaction. The blow reaction is essential for avoiding or reducing the use of auxiliary blowing agents.
Both the gel and blow reactions occur in foams blown partially or totally with the in-situ formation of carbon dioxide gas. In fact, the in-situ generation of carbon dioxide by the blow reaction plays an essential part in the preparation of “one-shot” water-blown polyurethane foams. Water-blown polyurethane foams, particularly flexible foams, are produced by both molded and slab foam processes.
As noted above, in order to obtain good urethane foam structure, the gel and blow reactions must proceed simultaneously and at optimum balanced rates. For example, if the carbon dioxide evolution is too rapid in comparison with the gel reaction, the foam tends to collapse. Alternatively, if the gel extension reaction is too rapid in comparison with the blow reaction generating carbon dioxide, foam rise will be restricted, resulting in a high-density foam. Also, poorly balanced crosslinking reactions will adversely impact foam stability. In practice, the balancing of these two reactions is controlled by the nature of the promoters and catalysts, generally amine and/or organometallic compounds, used in the process.
Flexible and rigid foam formulations usually include e.g., a polyol, a polyisocyanate, water, optional blowing agent (low boiling organic compound or inert gas, e.g., CO
2
), a silicone type surfactant, and catalysts. Flexible foams are generally open-celled materials, while rigid foams usually have a high proportion of closed cells.
Historically, catalysts for producing polyurethanes have been of two general types: tertiary amines (mono and poly) and organo-tin compounds. Organometallic tin catalysts predominantly favor the gelling reaction, while amine catalysts exhibit a more varied range of blow/gel balance. Using tin catalysts in flexible foam formulations also increases the quantity of closed cells contributing to foam tightness. Tertiary amines also are effective as catalysts for the chain extension reaction and can be used in combination with the organic tin catalysts. For example, in the preparation of flexible slabstock foams, the “one-shot” process has been used wherein triethylenediamine is employed for promoting the water-isocyanate reaction and the cross-linking reaction, while an organic tin compound is used in synergistic combination to promote the chain extension reaction.
Flexible polyurethane foams are commercially prepared as slabstock foam or in molds. Some slabstock foam is produced by pouring the mixed reactants in large boxes (discontinuous process), while other foam is prepared in a continuous manner by deposition of the reacting mixture on a paper lined conveyor. The foam rises and cures as the conveyor advances and the foam is cut into large blocks as it exits the foam machine. Some of the uses of flexible slabstock polyurethane foams include: furniture cushions, bedding, and carpet underlay.
In the discontinuous processes, the initiation of the reaction must be delayed to allow uniform laydown of the reacting mixture and allow excess air entrapped during reactant mixing to escape. Otherwise, foam splitting caused by the tardy release of such entrapped air may occur. In such situations, delayed action catalysts can be used to achieve the required reactivity profile. The problem also can be acute with slabstock foam produced by the continuous process on a machine with a short conveyor. In this case, the formulation has to be highly catalyzed in order to be sufficiently cured when the foam reaches the cutting saw. Thus, not only is delayed action necessary for a uniform laydown, but once activated, rapid catalytic action is critical.
The process for making molded foams typically involves the mixing of the starting materials with polyurethane foam production machinery and pouring the reacting mixture, as it exits the mix-head, into a mold. The principal uses of flexible molded polyurethane foams are, e.g., automotive seats, automotive headrests and armrests and furniture cushions. Some of the uses of semi-flexible molded foams include, e.g., automotive instrument panels, energy managing foam, and sound absorbing foam.
Amine emissions from polyurethane foams have become a major topic of discussion, particularly in car interior applications, and some car manufacturers request that all Volatile Organic Compound's (“VOC's”) be reduced. One of the main components of VOC's evaporating from flexible molded foams is the amine catalyst. To reduce such emissions, catalysts having a very low vapor pressure should be used. Alternatively, if the catalysts have reactive hydroxyl or amine groups they can be linked to the polymer network. If so, insignificant amine vapor will be detected in the fogging tests. However, the use of the reactive amines is not without difficulties. Reactive amines are known to degrade some fatigue properties such as, for example, humid aging compression set (“HACS”).
Modern molded flexible and semi-flexible polyurethane foam production processes have enjoyed significant growth. Processes such as those used in Just-in-Time (JIT) supply plants have increased the demand for rapid demold systems, i.e., systems in which the molding time is as short as possible. Gains in productivity and/or reduced part cost result from reduced cycle times. Rapid cure High Resilience (HR) molded flexible foam formulations typically achieve demold times of three to five minutes. This is accomplished by using one or more of the following: a higher mold temperature, more reactive intermediates (polyols and/or isocyanate), or increased quantity and/or activity of the catalysts.
High reactivity molded polyurethane systems give rise to a number of problems however. The fast initiation times require that the reacting chemicals be poured into a mold quickly. In some circumstances a

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