Polyurethane foam and process for producing same

Abstract

The invention relates to a process used to produce open-cell and extremely fine-cell PUR/PIR rigid foams, said process using a polyol formulation comprising a specific isocyanate-reactive component, a catalyst component having zerewitinoff-active hydrogens and a cell-opener component.

Claims

1. A process for producing rigid PUR/PIR foams having an apparent density of 30-90 kg/m.sup.3 according to ISO 845:2006, an open-cell content of >90% according to ISO 4590:2002, and having an average cell diameter of <50 μm according to optical microscopy evaluation, comprising the steps of i) producing reaction mixture R) comprising a polyol formulation P) comprising an isocyanate-reactive component A) comprising at least one polyol component A1) having a functionality of >2.5 comprising at least one of polyether polyols, polyester polyols, polycarbonate polyols, polyether polycarbonate polyols and polyether ester polyols, a catalyst component D) comprising a catalytically active compound D1) having Zerewitinoff-active hydrogens, an assistant or additive substance E) comprising a cell-opening compound, wherein a proportion of all primary OH functions present in the isocyanate-reactive component A) based on a total number of terminal OH functions in the component A) is at least 30%, a polyisocyanate component B) and CO.sub.2 in the supercritical state as blowing agent component C), ii) introducing the reaction mixture R) into a mold, iii) foaming the reaction mixture R) and iv) demolding a rigid PUR/PIR foam formed from the reaction mixture R).

2. The process as claimed in claim 1, wherein step i) and ii) are carried out under supercritical conditions.

3. The process as claimed in claim 1, wherein step i) is carried out in a mixing head or high-pressure mixing head.

4. The process as claimed in claim 1, wherein in step ii) the reaction mixture R) is introduced into a sealed mold, wherein the counterpressure in the mold during injection is 2-90 bar.

5. The process as claimed in claim 4, wherein in step iii) the pressure in the mold is maintained for a time period 1 of 1-40 seconds after termination of step ii) and subsequently the pressure is released from the mold over a time period 2 at a pressure release rate of 1-90 bar/s.

6. The process as claimed in claim 1, wherein the polyol component A1) has a hydroxyl number of 280-600 mg KOH/g according to DIN 53240-2 (2007).

7. The process as claimed in claim 1, wherein the isocyanate-reactive component A) comprises at least 65% by weight of the polyol component A1) wherein the polyol component A1) has a hydroxyl number between 280 to 600 mg KOH/g and a functionality of ≥2.8 to ≤6.0 and the proportion of primary OH functions in the component A) is at least 35% based on all terminal OH functions in the component A).

8. The process as claimed in claim 1, wherein the isocyanate-reactive component A) comprises at least 60% by weight of polyether polyol.

9. The process as claimed in claim 1, wherein the content of cell-opening component E) is 0.1-1.0% by weight.

10. The process as claimed in claim 1, wherein the catalytically active compound D1) is included in an amount of ≥0.01% to <2% by weight based on the total weight of the component A).

11. The process as claimed in claim 1, wherein the content of blowing agent component C) is 0.5% by weight to 15% by weight based on the total weight of R).

12. An open-celled rigid PUR/PIR foam having an apparent density of 30-90 kg/.sup.3 according to ISO 845:2006, an open-cell content of >90% according to ISO 4590:2002, and having an average cell diameter of <50 um according to optical microscopy evaluation obtainable by the process as claimed in claim 1.

13. A refrigerator, freezer or a fridge-freezer containing a rigid PUR/PIR foam as claimed in claim 12.

14. The process as claimed in claim 1, wherein after termination of step ii), the mold is decompressed at a pressure release rate of 1-90 bar/s.

Description

EXAMPLES

(1) Employed Standards/Analytical Instruments:

(2) Determination of apparent density: Foams composed of rubber and plastics—determination of apparent density (ISO 845:2006); German version EN ISO 845:2009

(3) Determination of open-cell content: Determination of the volume fraction of open and closed cells (ISO 4590:2002); German version EN ISO 4590:2003

(4) Determination of compressive strength: Rigid foams—determination of pressure properties (ISO 844:2014); German version EN ISO 844:2014

(5) Determination of OH number: Determination of hydroxyl number—part 2: Method with catalyst according to DIN 53240-2, as at November 2007

(6) Determination of cell size: Optical microscopy evaluation via VHX 5000 optical microscope; the test specimen to be measured is analyzed at 3 different points in each case over a circular region having a diameter of 5 mm. The resolution is chosen such that the selected region captures around 100 cells. 100 cells are then measured and the smallest and largest cell diameter as well as the average cell diameter are calculated.

(7) The reported functionality f in table 1 relates to the number-average functionality of the mixture of the polyols present in the formulation

(8) The specified proportion of primary OH functions in 1%1 in table 1 relates to the proportion of primary OH functions based on the total number of OH functions in the mixture of the polyols present in the formulation.

Example 1 and Comparative Examples 2 and 3

(9) Polyurethane foams blown with CO.sub.2 and n-pentane were produced according to the formulations recited in table 1 which follows. Reported amounts are to be understood as meaning parts by weight unless otherwise stated. The following substances were employed: Polyol 1: Polyether polyol based on trimethylolpropane and propylene oxide having a hydroxyl number of 800 mg KOH/g, a functionality of 3 and a viscosity of 6100 mPas at 25° C. Polyol 2: Polyether polyol based on trimethylolpropane and ethylene oxide having a hydroxyl number of 550 mg KOH/g, a functionality of 3 and a viscosity of 505 mPas at 25° C. Polyol 3: Polyether polyol based on trimethylolpropane and propylene oxide having a hydroxyl number of 550 mg KOH/g, a functionality of 3 and a viscosity of 1800 mPas at 25° C. Polyol 4: Polyether polyol based on 1,2-propanediol and propylene oxide having a hydroxyl number of 56 mg KOH/g, a functionality of 2 and a viscosity of 310 mPas at 25° C. Polyol 5: Polyether polyol based on 1,2-propanediol and propylene oxide having a hydroxyl number of 112 mg KOH/g, a functionality of 2 and a viscosity of 140 mPas at 25° C. Polyol 6: Polyether polyol based on glycerol and propylene oxide having a hydroxyl number of 231 mg KOH/g, a functionality of 3 and a viscosity of 350 mPas at 20° C. B 8443: Foam stabilizer (Evonik) Ortegol 500: Cell opener (Evonik) Desmorapid PU 1972: Catalyst, 25% potassium acetate in diethylene glycol (Covestro) Dabco NE1070: Catalyst, 3-(dimethylamino)propylurea (Air Products) n-Pentane: Blowing agent Isocyanate: Mixture of monomeric and polymeric MDI having a viscosity of about 290 m Pa.Math.s at 20° C. (Desmodur 44V20L, Covestro)

Production of Free-Rise Polyurethane Foams, Comparative Example 3

(10) To produce free-rise polyurethane foams in the laboratory 200 g of a composition of the respective polyol formulation composed of the polyols, stabilizers and catalysts listed in table 1 below and also blowing agent was produced. To produce the reaction mixture this composition of polyol formulation and blowing agent was mixed with the corresponding amount of isocyanate for 10 seconds at 23° C. using a Pendraulik stirrer and poured out into an open-top mold (20 cm×20 cm×18 cm). The precise formulations are summarized in table 1 and the results of the properties of the reaction mixtures and of the physical tests on the foams are summarized in table 2.

Production of Molded Polyurethane Foams, Comparative Example 2

(11) To produce molded polyurethane foams in the laboratory 100 g of a composition of the respective polyol formulation composed of the polyols, stabilizers and catalysts listed in table 1 below and also blowing agent was produced. To produce the reaction mixture this composition of polyol formulation and blowing agent was mixed with the corresponding amount of isocyanate for 10 seconds at 23° C. using a Pendraulik stirrer and poured out into a mold (20 cm×20 cm×6 cm). The mold was tightly sealed immediately after pouring. The molded article thus produced was demolded from the mold after 5 min. The precise formulations are summarized in table 1 and the results of the physical tests on the foams are summarized in table 2.

Production of Molded Polyurethane Foams in a High-Pressure Plant, Example 1

(12) To produce free-rise polyurethane foams in a high-pressure plant a polyol formulation composed of the polyols, stabilizers and catalysts listed in table 1 was produced. This was employed as the polyol component in a standard high-pressure mixing plant and mixed with the blowing agent CO.sub.2 at a pressure of 150 bar and a temperature of 50° C. The blowing agent was thus under supercritical conditions here. In a high-pressure mixing head this mixture was mixed with the isocyanate which was conveyed at a pressure of 150 bar and a temperature of 35° C. The shot quantity was 40 g/s corresponding to a volume flow of 48 ml/s (density of the mixture 1.2 g/ml). The thus-obtained reaction mixture was injected into a sealed mold (having a volume of 1 1) prestressed with a counterpressure of 10 bar at a mold temperature of 50° C. After termination of the injection the prestressed counterpressure of 10 bar was maintained for a further 12 s and only then decompressed to ambient pressure over <2 s. The thus-produced molded article was demolded from the mold after 5 min. The precise formulations are summarized in table 1 and the results of the physical tests on the foams are summarized in table 2.

(13) TABLE-US-00001 TABLE 1 Comparative Comparative Example 2 Example 1 Example 3 Molded Molded Frec-rise foam foam foam Polyol 1 [% by wt] 13.00 13.00 13.00 Polyol 2 [% by wt] 32.50 32.50 — Polyol 3 [% by wt] — — 32.50 Polyol 4 [% by wt] 13.50 13.50 13.50 Polyol 5 [% by wt]  9.50 9.50 9.50 Polyol 6 [% by wt] 27.00 27.00 27.00 B 8443 [% by wt]  1.00 1.00 1.50 Ortegol 500 [% by wt]  0.13 0.13 0.50 Desmorapid [% by wt]  1.00 1.00 1.00 PU 1792 Dabco NE 1070 [% by wt]  0.65 0.65 0.65 Functionality f 2.9 2.9 2.9 Proportion of primary OH 46.0  46.0 0.0 functions [%] Isocyanate [% by wt] 92.60 92.60 92.60 n-Pentane [% by wt] 10.00 6.70 scCO2 [% by wt] 5.00 Index NCO/OH 100 00  100.00 100.00

(14) TABLE-US-00002 TABLE 2 Comparative Comparative example 2 Example 1 example 3 Cream time [s] — — 50 Fiber time [s] — — 87 Rise time [s] — — 90 Tack-free time [s] — — 95 Apparent density [kg/m3] 61 67 63 Compressive strength [MPa] parallel 0.34 not determined 0.41 at 10% compression transverse 0.34 0.29 Open cell content [%] 96.4 95.5 25.6 Cell site average μm 83 17 126 Cell size smallest cell μm 33 3 73 Cell size largest cell μm 141 38 174

(15) Example 1 shows that the specified formulation can be used to produce a very fine-celled rigid foam having a high proportion of open cells.

(16) Example 1 shows clearly that processing of the formulation in a high-pressure plant with supercritical CO.sub.2 as the blowing agent and 10 bar of counterpressure on the mold results in finer (than for example in comparison 2 with identical formulation), simultaneously open-celled rigid foams.

(17) While substitution of polyol 2 by polyol 3 in comparative example 5 does make it possible to achieve the average cell size of 126 μm, the proportion of open cells is only 25.6%.