Process for preparing rigid and flexible polyurethane foams

Details Process for preparing rigid and flexible polyurethane foams Process for preparing rigid and flexible polyurethane foams

2000-02-25

2001-04-03

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...

C264S045100, C264S051000, C521S123000, C521S155000, C521S159000, C521S160000, C521S174000

Reexamination Certificate

active

06211258

ABSTRACT:

The present invention is concerned with a process for preparing water-blown polyurethane foams using a certain catalyst and the foams so obtained.
The preparation of water-blown polyurethane foams by reacting a polyisocyanate and a polyol and using water as blowing agent is widely known. The isocyanate groups react with the hydroxyl groups of the polyol to form urethane groups and with the water to form urea groups while liberating CO
2
which is responsible for the foaming. Such processes are used to prepare e.g. flexible foams, open-celled rigid foams and microcellular elastomers.
It is further widely known to use a catalyst or a catalyst package to enhance these reactions. Widely used catalysts are tertiary amines like diaminobicyclooctane and N,N,-dimethylaminoethanol, lead compounds like lead octoate and tin compounds like dibutyltin dilaurate and stannous carboxylates like stannous octoate; see e.g. The ICI Polyurethanes Book of George Woods—J. Wiley and sons—1987; page 27-45.
U.S. Pat. No. 5,426,124 discloses the preparation of polyurethane foam moldings having a density of at least 120 kg/m
3
wherein certain acids, as citric acid, are used as blowing agents.
U.S. Pat. No. 4,430,490 and U.S. Pat. No. 4,468,478 disclose the use of certain hydroxy carboxylic acids in order to eliminate the effects of alkaline catalysts in polyether polyols. The polyols are used to prepare foams using an amine as catalyst and FREON™ 11B as blowing agent (U.S. Pat. No. 4,430,490); in U.S. Pat. No. 4,468,478 the polyols have been used to prepare flexible foams using an amine catalyst, and to prepare a rigid polyurethane using stannous octoate wherein the acid was potassium salicylate and no blowing agent was used, and a rigid polyurethane foam using an amine catalyst and FREON 11 as blowing agent.
U.S. Pat. No. 5,132,333 discloses the use of alkali metal salt or alkaline earth metal salt of a hydroxy carboxylic acid in order to decrease the hardness of flexible polyurethane foams. A compound like disodium and trisodium citrate is used to prepare water-blown flexible foams using amines and tin compounds as catalysts, the amount of the acid being considerably greater than the amount of tin compounds.
U.S. Pat. No. 4,764,541 discloses the use of polyether acids in preparing flexible polyurethane foams using amine catalysts in order to slow down the polyurethane reaction; the system becomes reactive at higher temperature.
U.S. Pat. No. 4,686,240 discloses the use of a foam modifier which is an alkali metal or alkaline earth metal salt, the anion being the anion of a Brönsted acid having a pKa of greater than 1 in order to improve the stability and green strength of water-blown flexible polyurethane foams. As foam modifiers metal hydroxides, alkoxides, inorganic acids and monocarboxylic and polycarboxylic acids have been mentioned. In the preparation of the foams amine catalysts are used optionally together with tin catalysts; in case a tin catalyst was used the amount of tin catalyst was considerably lower than the amount of foam modifier, which was a potassium salt of succinic anhydride half acid of a polyol.
U.S. Pat. No. 5,124,369 discloses the use of polyelectrolytes as polyacrylic salts to lower the hardness of water-blown flexible foams. The foams made are based on toluene diisocyanate and as catalysts amine compounds and tin compounds are used. Applicant has conducted similar experiments using MDI as polyisocyanate; these experiments did not confirm the hardness reduction for MDI-based flexible foams.
Although satisfactory products have been made in the past room for improvement exists. In particular it was found that when tin catalysts are used the final foam shows thermal degradation, resulting in less favourable physical properties of the foam. There is a need to reduce such degradation or to avoid it.
Surprisingly we have found that such degradation may be reduced by using a novel catalyst composition.
Therefore the present invention is concerned with the use of a tin salt of a carboxylic acid having 2-18 carbon atoms (hereinafter called “catalyst 1”), together with a lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium and/or barium salt of a protic acid, the acid having at least 2 acidic hydrogen atoms and having a pK
a
in water 2-10 (hereinafter called “catalyst 2”), in a ratio of catalyst 1: catalyst 2 of 30:70 to 95:5 and in an amount of catalyst 1 and catalyst 2 of each 0.1-5% by weight (calculated on the weight of all ingredients used to prepare the foam) in the preparation of water-blown polyurethane foams with the proviso that the use of salts of polyelectrolytes in preparing flexible foams using toluene diisocyanate as the polyisocyanate and an amine catalyst are excluded.
For simplicity reasons the above salts of the protic acids are called “catalyst 2”; it is to be noted however that these compounds in fact have a deactivating effect upon catalyst 1.
Further the present invention is concerned with the preparation of polyurethane foams by reacting a polyisocyanate and a polyol in the presence of water and the above catalysts 1 and 2.
Without wishing to be bound by any theory it is believed that catalyst 2 supresses the formation of certain intermediate tin compounds during the preparation of the foam, which intermediate tin compounds would enhance certain undesirable hydrolytic processes which lead to said degradation.
The weight ratio of catalysts 1 and 2 as used in this process may range preferably from 50:50 to 90:10.
The carboxylic acid in catalyst 1 may be selected from saturated or unsatured aliphatic, cycloaliphatic and araliphatic hydrocarbons and from aromatic hydrocarbons having one carboxylic acid groups. Preferably they have 2-18 carbon atoms. Most preferred monocarboxylic acids are the saturated aliphatic carboxylic acids having 2-12 carbon atoms, like acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid and dodecanoic acid. Examples of tin catalysts of this type are dibutyltin dilaurate and stannous octoate.
The protic acid of catalyst 2 may be selected from a wide range of compounds. Preferably such compounds are selected from those containing at least 2 groups selected from —COOH and aromatic thiol.
Preferably the number of acidic hydrogen atoms is at least 3. Different metal salts may be used in combination. Further metal salts may be used wherein -all or only a part of the acidic hydrogens has been replaced by themetal ion. Preferably 10-90% of the acidic hydrogen atoms has been replaced with the metal ion; when the acid is used instead of its salt more tin catalyst is required in order to obtain the same gel time and when all acidic hydrogen atoms have been replaced with the metal ion scorching of the foam was observed when making bigger buns, e.g. from 1800 g material. Most preferred salts are the K- and Na-salts.
Preferably catalyst 2 has a solubility in water of at least 5 gram of catalyst 2 per liter water at 25° C.
Examples of useful catalysts are the Li, Na, K, Rb, Cs, Mg, Ca, Sr and/or Ba salts of:citric acid, 1,2,4,5 benzenetetracarboxylic acid (BCTA), ethylene-diaminetetraacetic acid (EDTA), ethylenebis-(oxyethylene-nitrilo)tetraacetic acid (EGTA). N-(2-hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), 1,3-diamino-2-hydroxypropane-N,N,N′,N′-tetraacetic acid (DHPTA), 2-merca-ptobenzoic acid (MBA), 2,2′-thiodiglycolic acid (TDGA), poly(acrylic acid) (PAcA), poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAcAmMPSA), copolymers of acrylamide and acrylic acid (PAcAm-co-PAcA), of acrylic acid and maleic acid (PAcA-co-PMA), of vinylpyrrolidone and acrylic acid (PVP-co-PAcA), said polymers and copolymers having average molecular weights between 500 and 1000000, preferably between 1000 and 500000.
The amount of catalyst 1 and catalyst 2 preferably varies from 0.2 to 3% by weight calculated on the weight of all ingredients used to prepare the polyurethane foam.
For preparing the water-blown

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