CA2003911A1

CA2003911A1 - Process for the preparation of open-cell hydrophilic polyurethane foams

Info

Publication number: CA2003911A1
Application number: CA002003911A
Authority: CA
Inventors: Rainer Welte; Hans-Joachim Scholl
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1988-12-15
Filing date: 1989-11-27
Publication date: 1990-06-15
Also published as: EP0373456A3; EP0373456A2; DE3842220A1; DK634489A; DK634489D0; JPH02212511A

Abstract

PROCESS FOR THE PREPARTION OF OPEN-CELL
HYDROPHILIC POLYURETHANE FOAMS

ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for preparing open-cell hydrophilic polyurethane foams having a density of 10 to 60 kg/m3 comprising reacting polyisocyanates with compounds having at least two hydrogen atoms that are reactive towards isocyanates and generally having a molecular weight of from about 400 to about 10,000, in the presence of water as a blowing agent, optional compounds having at least two hydrogen atoms that are reactive towards isocyanates and having a molecular weight of from 32 to 399, optional auxiliaries and additives, and about 1 to about 100 mmole of an acid per 100 g of the total amount of the polyol-side components.
The invention also relates to the use of such polyurethane foams as a fixing substrate for cut flowers.

Description

20039~.
Mo3262 LeA 26,554 PROCESS FOR THE PREPARATION OF OPEN-CELL
HYDROPHILIC POLYURETHANE FOAMS
BACKGROUND OF THE INYENTION
The inventlon relates to a novel process for the preparation of open-cell hydrophilic polyurethane foams and the 5 use of these foams as a fixing substrate for cut flowers.
Processes for the production of open-cell hydrophilic foams as a fixing substrate are known. See, for example, U.S.
Patents 2,988,441 and 3,373,009, German Auslegeschrift 1,229,662, and E. Weinbrenner and J. Niggemann, "Stecklingsvermehrung und Kultur in Blocksubstraten aus Polyurethane-Schaumstoff (Cutting propagation and culture in block substrates of polyurethane foam)", Gartenwelt, _ , 71-73 (1970). The disadvantage of this process is the low water retention capacity of the foams prepared.
German Offenlegungsschrift 2,304,892 represents a further development inasmuch as the disadvantages related to insufficient water retent~on capacity are essentially overcome by additionally using modified polyisocyanates, such as urethane- or urea-modifed polyisocyAnates or the like. The use of the 20 expensive 1socyanate modification for the preparation of such f1xing substrates is, however, A disadvantage. This also applies to German Offenlegungsschrift 2,441,843, which d1scloses similar isocyanate mod1ficat~ons with organic sulfonic acids, which allows the preparation of fixing substrates with an adequate water retention capacity.
German Offenlegungsschrlft 3,627,236 discloses a process for the preparation of fixing substrates uslng chlorofluorocarbon ("CFC") blowing agents without using Le A 26 554-US

20039~1 previously modified polyisocyanates. Apart from serious ecological disadvantages, the water retention capacity of such fixing substrates is deficient, as shown by the comparison examples below.
The object of the present invention is to provide a new process for the preparation of fixing substrates having an adequate water retent~on capacity and which (a~ dispenses with expensive prior isocyanate modifications and (b) avoids the use of CFC blowing agents. It has surprisingly been possible to 10 achieve this object with the process of the invention described in more detail below.
SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of open-cell hydrophilic polyurethane foams having a 15 density of 10 to 60 kg/m comprising reacting (a) polyisocyanates with (b) compounds having at least two hydrogen atoms that are reactive towards isocyanates and generally having a molecular weight of from about 400 to about 10,000, in the presence of (c) water as a blowing agent, (d) optionally, compounds having at least two hydrogen atoms that are reactive towards isocyanates and hav1ng a molecular weight of from 32 to 399, (e) optionally, auxiliaries and additives, and (f) about 1 to about 100 mmole (preferably 5 to 20 mmole) of an acid (preferably phosphoric acid or a substituted phosphoric acid) per 100 9 of the total amount of components (b), (c), (d), and (e).

The invention also relates to the use of the polyurethane foams prepared according to the invention as a fixing substrate for cut flowers in order to maintain a wet 35 env1ronment for the cut flowers.

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DETAILED DESCRIPTION OF THE INVENTION
The use of acids, including inorganic or organic acids or mixtures thereof, is essential to the practice of the invention. Suitable inorganic acids include hydrochloric acid, 5 sulfuric acid, phosphoric acid, and mixtures thereof. Phosphoric acid is a preferred inorganic acid. Suitable organic acids include carboxylic acids; sulfonic acids; and acidic derivatives of phosphoric acid substituted with organic substituents, such as phosphoric acid monoesters and diesters. Organic acids having a 10 PKa less than 2, such as sulfon~c acids or phosphoric ac~d diesters, are preferred. Alkylbenzenesulfonic acid mixtures or dialkyl phosphates are particularly preferred organic acids.
The acids are employed in the process of the invention in amounts of about I to about 100 mmole (preferably 5 to 20 15 mmole) per 100 9 of "polyol mixture." As used herein, the term "polyol mixture" is understood as the sum of the polyols and other isocyanate-reactive compounds of components (b) and (d), water, and the optional additives and auxiliaries. The acid is usually introduced as part of the "polyol side" during foam 20 preparation, although the acld can, of course, also be introduced separately.
The following components are employed for carrylng out the process of the lnvention for the preparation of the open-cell hydrophllic f1xlng substrates:
1. Allphat1c, cycloaliphatic, araliphatic, aromatic, and heterocycltc polylsocyanates such as descrlbed by W. Slefken in Justus Lleblgs Annalen der Chemie, 362, pages 75 to I36, lncluding lsocyanate compounds of the formula Q(NCO)n ln which n is a number of from 2 to about 4 (preferably 2 to 3), and Q ls an allphatlc hydrocarbon group w1th 2 to about 18 35 ~preferably 6 to lO) carbon atoms, a cycloallphatic hydrocarbon Mo3262 200~9 group with about 4 to about 15 (preferably 5 to 10) carbon atoms, or an aromatic hydrocarbon group with 6 to about 15 (preferably 6 to 13) carbon atoms, for example, polyisocyanates such as those descr~bed in German Offenlegungsschrift 2,832,253, pages 10 to 5 11.
In general, the polyisocyanates that are commercially readily available, for example, tolylene 2,4- and 2,6-diisocyanate and mixtures of these isomers ("TDI"), and polyphenyl-polymethylene polyisocyanates such as are prepared by 10 aniline-formaldehyde condensation and subsequent phosgenation ("crude MDI"), are particularly preferred.
2. Compounds having at least two hydrogen atoms that are reactive towards isocyanates and generally having a molecular weight of from about 400 to about 10,000. Such compounds 15 include, in addition to compounds containing amino groups, thiol groups, or carboxyl groups, the preferred compounds containing hydroxyl groups. Particularly preferred compounds contain two to eight hydroxyl groups and have a molecular weight of from 1,000 to 6,000 ~most preferably 2,000 to 6,000), for example, 20 polycarbonates and polyester-am~des containing at least two (generally two to eight, but preferably 2 to 6) hydroxyl groups, such as those known for the preparation of homogeneous and cellular polyurethanes and descr~bed, for example, ~n German Offenlegungsschrift 2,832,253, pages 11 to 18. Products that are 25 rendered hydroph~lic by ~ncorporat~on of ethylene oxide and/or ethylene glycol or by another manner are preferred, ~n part~cular those containlng pr~mary hydroxyl groups to the extent of at least 50 wt.% (based on the total number of hydroxyl groups).

3. Opt~onally, compounds having at least two hydrogen atoms 30 that are reactive towards ~socyanates and hav~ng a molecular weight of from 32 to 399. Such compounds also include compounds conta~n~ng hydroxyl groups, am~no groups, th10l groups, carboxyl groups, or a comb~nation thereof, preferably compounds conta~ning hydroxyl groups andlor am~no groups, used as cha~n-extending 35 agents or crosslinking agents. In general, such compounds Mo3262 2003~

contain from 2 to about 8 (preferably 2 to 4) isocyanate-reactive hydrogen atoms. Examples are described in German Offen-legungsschrift 2,832,253, pages 19 to 20.

4. Water as the blow~ng agent. Preferably, the water is S used ln amounts of about S to about 14 percent by weight (more preferably 6 to 12 percent by weight) based on the isocyanate-reactive component 2 discussed above (often referred to as the "polyol component").

5. Optionally, auxiliaries and additives, such as the 10 following:
(a) Known catalysts in amounts of up to 50 wt.%, based on the amounts of the acid to be used according to the invention;
(b) Surface-active addit~ves, such as emulsifiers and foam stabilizers, (c) Known reaction retarders; cell regulators such as paraffins or fatty alcohols or dimethylpoly-siloxanes;
pigments or dyestuffs; known flameproofing agents, such as tris(chloroethyl) phosphate and tricresyl phosphate; furthermore stabilizers against agelng and weathering; plasticizers; and fungistatic and bacteriostatic agents; and fillers, such as barium sulfate, kieselguhr, carbon black, or prepared chalk.
Such aux11iar1es and additlves are descr~bed, for 25 example, 1n German Offenlegungsschrift 2,732,292, pages 21 to 24.
Other examples of surface-active additives, foam stabil~zers, cell regulators, reactlon retarders, stabilizers, flameproof~ng agents, plasticizers, dyestuffs, fillers, and funigistatic and bacterlostatic agents to be used accord1ng to the invention, as 30 well as details on the method of use and mode of action of these addit1ves, are described in Kunststoff-Handbuch (Plast1cs Handbook), Volume VII, publ~shed by Vieweg and Hochtlen, Carl-Hanser-Verlag, Munich, 1966, for example, on pages 103 to 113.

Mo3262 2 0~13 ~3 The open-cell hydrophilic polyurethane foams are produced according to methods known in the art.
The following examples further illustrate details for the process of this invention. The invention, which is set forth 5 in the foregoing disclosure, is not to be limited either in spirit or scope by these examples. Those skilled in the art will readlly understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all parts and percentages 0 are respectively parts by weight and percentages by weight.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Example 1 (comparison) This comparison example is a modification of the method described in German Offenlegungsschrlft 3,627,236 in Example 1 15 (columns 10 A component 15 parts 5:8 mixture of two polyethylene glycol ethers of OH
number 380 and 72, respectively 30 parts 1:3 mixture of two propylene oxide ethers started with ethylenediamine and having OH numbers of 650 and 810, respectively 10 parts polyoxypropylene polyol having OH number 400 prepared by using a mixture of sucrose and glycerin as starters 5 10 parts glycerin-started polyoxypropylenetriol having OH
number 400 parts graft polyether polyol having OH number 35 (Bayfit 3699 from Bayer AG) parts diethylene glycol 0 15 parts trimethylolpropane 4 parts water (R
0.2 parts polyoxyalkylene polysiloxane (Tegostab B from Goldschmidt AG) 0.4 parts N,N-dimethylcyclohexylamine 3 parts fluorotrichloromethane Mo3262 Z003~ 7 e component 113 parts crude MDI
The following characteristic data were determined under laboratory conditions:

Cream tlme 17 sec Gel time 33 sec Rise time 40 sec The cell structure of the foam was uniform and fine.
After cooling (during which time the foam shrinks greatly) the gross density was 66 kg/m . The gross density of a foam prepared by this method is much too high. In addition, the fixing capacity is not adequate. Although the water uptake of about 11 15 volume percent is also considerably higher than that of normal polyurethane rigid foam~ the water uptake is much too low for use as a commerclal hydrophilic fixing foam.
Examples 2 to 6 The preparative ingredients and properties of foams 20 prepared according to the invention and of comparison foams are descrlbed in the following Table:

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TABLE
Example no.: 2 3 4 5 6 ~1) Polyol (parts) 88 88 88 88 88 Water (parts~ 8 8 10 1.8 8 Stabilizer(2 (parts) 2 2 2 2 2 s 85% Phosphoric acid (parts) - 1 -10~ Hydrochloric acid (parts) - - - 8 Dibutyl phosphate (parts) - - - - 2 Polyisocyanate(3) (parts) - - 135 MDI (crude) (parts) 135 135 135 Stirring tLme (sec) 15 15 15 15 15 Cream time (sec) 30 23 28 28 27 Rise tlme (sec) 72 63 85 62 68 Tack-free time (sec) 78 66 100 75 77 15 Cell size fine fine fine finefine Cell structure u n i f o r m Shrinkage at room none none none nonenone temperature Gross density (kg/m3) 24.6 26.2 24.5 29 22.3 .
20 Fixing capacity good good good moderate good Water uptake (volX) 3.4 85.9 25.4 20 80 (1) Polyether m~xture of the following composition: 18 parts by welght trifunctional polyether (glycerol + 55% propylene oxide + 45X ethylene oxide, OH number 56); 37 parts by weight amlno-polyether (ethylenediamine + propylene ox~de, OH number 630); 15 parts by we~ght glycerol; and 30 parts by we~ght trifunctional polyether (trimethylolpropane + 33%
polyethylene oxide 67X ethylene ox~de, OH number 615) (2) Polyether-siloxane from Br~t~sh Petroleum oO. 0 (3) Prepolymer prepared from 110 parts by weight crude MDI and 10 parts by weight Marlo AS-3 acid (clo-cl3-alkylbenzenesulfonic acid from Huls AG), NCO content 28 wt.X

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Example 2 (comparison) shows that although a usable foam can be produced without phosphoric acid and with a polyol formulation correspondlng to the standard formulatlon, the water uptake is completely unsatisfactory.
Example 3 shows the dramatic improvement in water uptake by addition of phosphoric acid.
Example 4 (comparison) shows the standard recipe using modifled ~socyanate (as descr~bed in German Offenlegungsschrift 2,441,843).
Example S shows the use of a different inorganic acid.
Example 6 shows the use of a substituted phosphoric acid.

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Claims

1. A process for the preparation of an open-cell hydrophilic polyurethane foam having a density of 10 to 60 kg/m3 comprising reacting (a) a polyisocyanate with (b) a compound having at least two hydrogen atoms that are reactive towards isocyanates and having a molecular weight of from about 400 to about 10,000, in the presence of (c) water as a blowing agent, (d) optionally, a compound having at least two hydrogen atoms that are reactive towards isocyanates and having a molecular weight of from 32 to 399, (e) optionally, auxiliaries and additives, and (f) about 1 to about 100 mmole of an acid per 100 g of the total amount of components (b), (c), (d), and (e).

2. A process according to Claim 1 wherein 5 to 20 mmole of the acid is used.

3. A process according to Claim 1 wherein the acid is phosphoric acid or a substituted phosphoric acid.

4. A process according to Claim 1 wherein the acid is phosphoric acid.

5. A process according to Claim 1 wherein the acid is a dialkyl phosphate.

6. A process according to Claim 5 wherein the dialkyl phosphate is dibutyl phosphate.

7. A method for maintaining a wet environment for cut flowers comprising using a polyurethane foam prepared according to Claim 1 as a fixing substrate for said cut flowers.

8. A fixing substrate for cut flowers comprising a polyurethane foam prepared according to Claim 1.