Storage-stable polyurethane potting compound for embedding of hollow fibres in the production of filter elements

Abstract

Polyurethane encapsulating compounds for the embedding of hollow fibers of filter elements are provided. These are obtainable by mixing a polyol component (A) and an isocyanate component (B) to give a reaction mixture and reacting the mixture to completion to give the polyurethane encapsulating compound, wherein the polyol component (A) comprises (a1) at least one fatty-acid-based polyol, (a2) at least one amine compound having at least one tertiary nitrogen atom and at least one isocyanate-reactive hydrogen atom and (a3) at least one metal compound that functions as a polyurethane catalyst, wherein the polyurethane catalyst (a3) does not comprise any tin, lead and/or mercury and the isocyanate component (B) comprises at least one aromatic isocyanate having at least two isocyanate groups. Further provided is a method for producing filter elements using the polyurethane encapsulating compounds and the use of the polyurethane encapsulating compounds for the embedding of hollow fibers.

Claims

1. A polyurethane encapsulating compound for embedding hollow fibers of filter elements, obtainable by mixing a polyol component (A) and an isocyanate component (B) to give a reaction mixture and reacting the mixture to completion to give the polyurethane encapsulating compound, wherein the polyol component (A) comprises (a1) at least one fatty-acid-based polyol having a hydroxyl number of greater than 50 to less than 500 mg KOH/g and a functionality of from 2 to 6, (a2) at least one amine compound having at least one tertiary nitrogen atom and at least one isocyanate-reactive hydrogen atom and (a3) at least one metal compound that functions as a polyurethane catalyst wherein the polyurethane catalyst (a3) does not comprise any tin, lead and/or mercury and the isocyanate component (B) comprises at least one aromatic isocyanate having at least two isocyanate groups.

2. The polyurethane encapsulating compound according to claim 1, wherein the polyurethane catalyst (a3) comprises at least one compound selected from the group consisting of zinc compounds, zirconium compounds, bismuth compounds and titanium compounds.

3. The polyurethane encapsulating compound according to claim 2, wherein the polyurethane catalyst (a3) is a bismuth carboxylate.

4. The polyurethane encapsulating compound according to claim 1, wherein the amine compound (a2) has at least three isocyanate-reactive hydrogen atoms.

5. The polyurethane encapsulating compound according to claim 4, wherein the amine compound (a2) is an alkoxylated amine having a hydroxyl number of from 500 to 1200 mg KOH/g and having 3 to 6 hydrogen atoms that are reactive toward isocyanate groups.

6. The polyurethane encapsulating compound according to claim 5, wherein the amine compound (a2) is a diamine-started propylene oxide having a nominal functionality of from 3 to 6 and a hydroxyl number of from 500 to 900 mg KOH/g.

7. The polyurethane encapsulating compound according to claim 1, wherein the fatty-acid-based polyol (a1) comprises castor oil or an alkoxylation product of castor oil.

8. The polyurethane encapsulating compound according to claim 1, wherein the polyol component (A) comprises at least one, at least difunctional, polyol (a4) which has a functionality of from 2 to 8 and a hydroxyl number of from 600 to 1350 mg KOH/g and does not fall under a definition of the amine compound (a2).

9. The polyurethane encapsulating compound according to claim 8, wherein a proportion of the fatty-acid-based polyol (a1) is 60 to 99% by weight, a proportion of the amine compound (a2) is 0.2 to 15% by weight, a proportion of the polyurethane catalyst (a3) is 0.001 to 0.2% by weight and a proportion of the polyol (a4) is 0 to 25% by weight, based in each case on a total weight of components (a1) to (a4).

10. The polyurethane encapsulating compound according to claim 1, wherein the isocyanate component (B) comprises prepolymers of isomers and/or homologs of diphenylmethane diisocyanate.

11. A method for producing filter elements in which a bundle of hollow fibers is embedded (and cured) at their end in a polyurethane encapsulating compound according to claim 1.

12. The method according to claim 11, wherein the filter elements are filter elements for use in medicine.

13. The method according to claim 12, wherein the filter elements are dialysis filter elements.

14. The method according to claim 11, wherein the filter elements are water filter elements.

15. A method of encapsulating filter elements, the method comprising at least partially embedding a bundle of hollow fibers in the polyurethane encapsulating compound according to claim 1.

Description

(1) The invention will be illustrated below with reference to examples.

(2) Raw Materials Used

(3) Poly 1: DAB castor oil from Alberdingk Boley

(4) Poly 2: polyetherol based on trimethylolpropane and propylene oxide having an OH number of 935 mg KOH/g

(5) Poly 3: N,N,N″,N″-tetrakis(2-hydroxpropyl)ethylenediamine

(6) Poly 4: triethanolamine

(7) Poly 5: polyetherol based on trimethylolpropane and propylene oxide having an OH number of 160 mg KOH/g

(8) ISO1: isocyanate prepolymer based on MDI, dipropylene glycol and polypropylene glycol and having an NCO content of 23% by weight

(9) ISO2: isocyanate prepolymer based on MDI and polypropylene glycol and having an NCO content of 29% by weight

(10) Cat 1: Tinstab OTS 16 tin catalyst from Akcros

(11) Cat 2: Bicat 8118M bismuth catalyst from Shepherd

(12) Cat 3: Coscat 83 bismuth catalyst

(13) Cat 4: TIB Kat 716 bismuth catalyst

(14) Cat 5: Borchi Kat 315 bismuth catalyst

(15) Cat 6: titanium(IV) isopropoxide (CAS No. 546-68-9) procured from Sigma-Aldrich

(16) For the determination of the storage stability of the polyol mixture, polyols and catalysts were mixed as indicated in tables 1 to 3 to give a polyol component; all figures in the tables correspond to parts by weight unless otherwise indicated. The polyol components obtained were stored as indicated at room temperature and with the exclusion of air in a sealed container. Prior to sampling, the mixture was homogenized and then degassed. The first measurement for determining the starting reactivity was conducted 24 hours after the polyol mixture had been made up, so that the system could settle. After that, the gel time was determined at various intervals.

(17) The gel time was determined here as follows. The required amount of isocyanate at an isocyanate index of 105 was added to a corresponding amount of polyol mixture. The amounts of the isocyanate component and the polyol component were selected here such that 100 g of reaction mixture were obtained. The reaction mixture was mixed in a Speedmixer™ PP130 cup at 25° C. for 30 s at 1800 rpm by means of a Speedmixer™ from Haunschild and at the same time measurement was started on a SHYODU Gel Timer. After the mixing time of 30 seconds the PP130 cup was placed beneath the Gel Timer and the gel time was determined. The gel time is determined here as the time in which the viscosity of the reaction mixture at constant temperature increases to such an extent that the stirring force required exceeds the stirring force provided by the Shyodu Gel Timer.

(18) The following examples are intended to illustrate the effect of the composition according to the invention.

(19) TABLE-US-00001 TABLE 1 C1 C2 C3 C4 C5 C6 Poly 1 100 95.0 90.0 85.0 94.98 94.98 Poly 2 5.00 4.5 Poly 3 5.0 10.0 15.0 0.5 Cat 1 0.02 0.02 Iso 1 X X X X Iso 2 X X Hardness 18 56 70 76 [Shore D] Gel time [hh:mm:ss]  1 d 01:14:06 00:38:11 00:19:10 00:08:16 00:06:17 00:06:20 14 d 00:05:55 00:06:01

(20) As is apparent from comparative examples C1 to C4, the use of N,N,N″,N″-tetrakis(2-hydroxypropyl)ethylenediamine leads to a shortening of the open time and thus to an increase in the reactivity. However, rapid cycle times can only be achieved with high concentrations of N,N,N″,N″-tetrakis(2-hydroxpropyl)ethylenediamine. This has the disadvantage though that the systems show a distinct gain in hardness and hence the cuttability of the systems suffers. Example C5 further reveals that tin catalysis as described in the prior art leads to stable reactivity. Likewise, it is apparent from comparative example C6 that a combination of an alkanolamine such as N,N,N″,N″-tetrakis(2-hydroxpropyl)ethylenediamine and tin catalysis affords no advantages with respect to stability.

(21) TABLE-US-00002 TABLE 2 C7 C8 E1 E2 E3 E4 E5 Poly 1 94.9 94.9 94.9 94.9 94.9 94.9 Poly 2 5.0 5.04 4.5 2.5 4.5 3.0 Poly 3 0.5 2.5 5.0 Poly 4 0.5 2.0 Poly 5 94.91 Cat 3 0.1 0.05 0.1 0.1 0.1 0.1 0.1 Iso 1 X X X X X X X Gel time [mm:ss]  1 d 03:29 00:48 03:16 04:30 05:32 03:25 03:27 14 d 04:48 n.d. 03:29 05:00 05:56 03:40 03:32 56 d 08:45 00:58 03:41 05:09 05:45 03:49 03:30

(22) TABLE-US-00003 TABLE 3 E6 E7 E8 E9 C9 E10 E11 Poly 1 89.9 94.9 94.9 94.9 94.95 94.95 94.95 Poly 2 5.0 Poly 3 10.0 5.0 5.0 5.0 5.0 Poly 4 5.0 Cat 2 0.1 Cat 3 0.1 Cat 4 0.1 Cat 5 0.1 Cat 6 0.05 0.05 0.05 Iso 1 X X X X X X X Gel time [hh:mm:ss]  1 d 00:03:25 00:05:06 00:04:44 00:05:10 00:11:19 00:05:24 00:16:08  7 d 00:09:16 00:05:48 n.m. 14 d 00:03:31 00:05:23 00:04:54 00:05:35 00:07:22 00:05:20 00:16:04 21 d 00:06:31 00:05:24 n.m. 28 d 00:03:27 n.d. 00:05:03 00:05:35 n.m. n.m. n.m.

(23) Examples C7 and C9 reveal the disadvantage of other metal catalysts such as bismuth or titanium. The reactivity of the system falls considerably over time. C8 additionally shows that bismuth catalysts can be used as a suitable tin substitute in polyurethane encapsulating compounds based on synthetic polyols. It becomes apparent from examples E1 to E11 that the combination of bismuth or titanium catalysts and alkanolamines has an advantageous influence on the stability of the reaction rate in systems comprising fatty-acid-based polyols. The reactivity changes here only to a markedly small degree.