Process to enhance polyurethane foam performance

Details Process to enhance polyurethane foam performance Process to enhance polyurethane foam performance

2001-02-15

2002-05-14

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...

C521S116000, C521S117000, C521S118000, C521S128000, C521S129000, C521S159000, C521S163000, C521S164000, C521S167000, C521S170000, C521S130000

Reexamination Certificate

active

06387972

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to tertiary amine carboxylic acid salt catalysts for producing polyurethane foam. The invention is especially adapted for making polyurethane foam using the one-shot foaming process, the quasi-prepolymer process or the pre-polymer process. The invention specifically relates to polyurethane catalysis with catalysts composed of (1) specific reactive tertiary amine(s) and (2) salts formed by the reaction between the specific reactive tertiary amine(s) and hydroxy- and/or halo-carboxylic acids. The expression “specific reactive tertiary amine(s)” and expressions of like import as utilized herein refers to the identified amine compounds useful in the practice of the invention herein, i.e., bis(dimethylaminopropyl)amino-2-propanol, bis(dimethylaminopropyl)amine, dimethylaminopropyldipropanolamine, bis(dimethylamino)-2-propanol, N,N,N′-trimethyl-N′-hydroxyethyl-bis(aminoethyl)ether and mixtures thereof.
Polyurethane foams are produced by reacting a di- or polyisocyanate with isocyanate-reactive compounds containing two or more reactive sites, generally in the presence of blowing agent(s), catalysts, silicone-based surfactants and other auxiliary agents. For example, the isocyanate-reactive compounds are typically polyols, primary and secondary polyamines, and water. Two major reactions among the reactants, gelling and blowing, are promoted by the catalysts during the preparation of polyurethane foam. 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: organo-tin compounds and tertiary amines (mono and poly). 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 organo-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 organo-tin compound is used in synergistic combination to promote the chain extension reaction.
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 foam have become a major topic of discussion particularly in car interior applications, and some car manufacturers request that all VOCs (Volatile Organic Compounds) are reduced. One of the main components of VOCs 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 reactive amine is not without difficulties. Reactive amines are known to degrade some fatigue properties such as humid aging compression set.
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 rapid build-up of the viscosity of the rising foam causes a deterioration of its flow properties and can result in defects in the molded parts. Additionally, rapidly rising foam can reach the parting line of the mold cavity before the cover has had time to close resulting in collapsed areas in the foam. In such situations, catalysts with a long initiation time, i.e., delayed action catalysts, can potentially be used to improve the initial system flow and allow sufficient time to close the mold. As utilized herein, the expression “delayed action catalysts” is intended to refer to catalysts that display the desirable property of having a slow start followed by increased activity. That is, a delayed action catalyst will exhibit a low activity at first followed by increased activity at a later time. Catalysts exhibiting high catalytic activity following activation are especially useful. However, increasing the level of reactive catalysts in order to achieve good curing generally results in worsening the fatigue properties of the produced parts.
Another difficulty experienced in the production of molded foams, which is usually worse in the case of rapid cure foam formulations, is foam tightness. A high proportion of closed cells causes f

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