POLYURETHANE FOAM AND PROCESS FOR PRODUCING SAME

Abstract

The present invention relates to a process for producing an open-cell rigid polyurethane foam. Said foams can contain, besides urethane groups (PUR), also isocyanurate groups (PIR).

Claims

1. A polyol formulation P) suitable for producing open-celled rigid PUR/PIR foams 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) excluding a cell-opening compound, and a blowing agent component C), wherein the proportion of all primary OH functions present in the isocyanate-reactive component A) based on the total number of terminal OH functions in the component A) is at least 30% and wherein the blowing agent component C) comprises formic acid.

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

3. The polyol formulation P) as claimed in claim 1, wherein the isocyanate-reactive component A) comprises at least 65% by weight of the polyol component A1) which 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).

4. The polyol formulation P) as claimed in claim 1, wherein the isocyanate-reactive component A) comprises polyether polyol in an amount of at least 60% by weight.

5. The polyol formulation P) as claimed in claim 1, wherein the polyol formulation comprises the catalytically active compound D1) in an amount of 0.01% to <2% by weight based on the total weight of the component A).

6. A foam-forming reaction mixture R), comprising an isocyanate-reactive component A) comprising at least one polyol component A1) comprising at least one of polyether polyols, polyester polyols, polycarbonate polyols, polyether polycarbonate polyols and polyether ester polyols which has an OH functionality of >2.5, at least one polyisocyanate component B), a blowing agent component C), a catalyst component D) comprising a catalytically active compound D1) having Zerewitinoff-active hydrogens, an assistant or additive substance E) excluding a cell-opening compound, wherein the proportion of all primary OH functions present in the isocyanate-reactive component A) based on the total number of terminal OH functions in the component A) is at least 30% and wherein the blowing agent component C) comprises formic acid.

7. The foam-forming reaction mixture R) as claimed in claim 8, wherein the content of formic acid is 0.5-6% by weight based on the total amount of compounds having isocyanate-reactive hydrogen atoms in the foam-forming reaction mixture R).

8. A process for producing rigid PUR/PIR foams having an apparent density of 25-300 kg/m.sup.3, an open-cell content of >70%, and having an average cell diameter of 180 m, comprising the steps of i) producing a foam-forming reaction mixture R) as claimed in claim 6, ii) introducing the foam-forming reaction mixture R) into a mold, iii) foaming the foam-forming reaction mixture R) and iv) demolding a rigid PUR/PIR foam formed from the foam-forming reaction mixture R).

9. The process as claimed in claim 8, wherein step i) is performed in a mixing head or high-pressure mixing head.

10. The process as claimed in claim 8, wherein in step ii) the foam-forming reaction mixture R) is introduced into a closed mold, wherein a counterpressure in the mold during injection is 2-90 bar.

11. The process as claimed in claim 10, wherein in step iii) the counterpressure in the mold is held for a period 1 of 1-40 s after termination of step ii) and subsequently the counterpressure from the mold is released over a period 2 at a pressure release rate of 1-90 bar/s.

12. An open-celled rigid PUR/PIR foam obtainable by the process as claimed in claim 8.

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

Description

EXAMPLES

[0132] The comparative examples and examples which follow are intended to more particularly elucidate the invention without limiting it.

Employed Standards/Analytical Instruments

[0133] Determination of apparent density: Foams composed of rubber and plasticsdetermination of apparent density (ISO 845:2006); German version EN ISO 845:2009

[0134] Determination of open-cell content: Determination of the volume fraction of open and closed cells (ISO 4590:2002); German version EN ISO 4590:2003

[0135] Determination of compressive strength: Rigid foamsdetermination of pressure properties (ISO 844:2014); German version EN ISO 844:2014

[0136] Determination of OH number: Determination of hydroxyl numberpart 2: Method with catalyst according to DIN 53240-2, as at November 2007

[0137] 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.

[0138] The specified proportion of primary OH functions in [%] 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.

[0139] Production of the foams according to examples 1 (inventive) and examples 2-4 (comparative) employed the following substances:

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] Polyol 7: Polyether polyol based on glycerol and saccharose and propylene oxide having a hydroxyl number of 470 mg KOH/g and a functionality of 4.9

[0147] Polyol 8: Polyether polyol based on propylene glycol and propylene oxide having a hydroxyl number of 260 mg KOH/g and a functionality of 2

[0148] B 8443: Foam stabilizer (Evonik)

[0149] B 8870: Foam stabilizer (Evonik)

[0150] Ortegol 500: Cell opener (Evonik)

[0151] Ortegol 501: Cell opener (Evonik)

[0152] Potassium acetate/DEG: Catalyst, 25% potassium acetate in diethylene glycol (Covestro)

[0153] Dabco NE1070: Catalyst, about 60% 3-(dimethylamino)propylurea in diethylene glycol (Air Products)

[0154] Polycat 58: Catalyst (Air Products)

[0155] Potassium acetate/EG: Catalyst, 25% potassium acetate in ethylene glycol c-/i-Pentane mixture: Mixture of cyclopentane and isopentane in a 70:30 weight ratio, physical blowing agent

[0156] Water: Blowing agent

[0157] Formic acid: Blowing agent, 95% formic acid

[0158] Isocyanate 1: Mixture of monomeric and polymeric MDI having a viscosity of about 290 m Pa*s at 20 C. (Desmodur 44V20L, Covestro)

[0159] Isocyanate 2: Mixture of monomeric and polymeric MDI having a viscosity of about 1070 m Pa*s at 20 C. (Desmodur 44V70L, Covestro)

Production of Free-Rise Polyurethane Foams

[0160] To produce free-rise polyurethane foams in the laboratory 200 g of the respective polyol formulation composed of the isocyanate-reactive compounds, stabilizers, catalysts, formic acid or physical blowing agents, listed in table 1 below, were weighed in and homogenized using a stirrer. The thus-obtained isocyanate-reactive composition was mixed with the appropriate amount of isocyanate using a Pendraulik stirrer for 10 seconds at 23 C. and poured into an open-top mold (20 cm20 cm18 cm). The precise formulations including the results of appropriate physical tests are summarized in table 1.

TABLE-US-00001 TABLE 1 Example 1 2* 3* 4* Formulation Polyol 1 13.00 13.00 13.00 Polyol 2 32.50 32.50 Polyol 3 32.50 Polyol 4 13.50 44.1 13.50 13.50 Polyol 5 9.50 9.50 9.50 Polyol 6 27.00 27.00 27.00 Polyol 7 44.1 Polyol 8 9.15 Water 0.55 B 8443 1.50 1.50 1.50 B 8870 0.9 Ortegol 500 0.50 0.50 Ortegol 501 1.8 0.50 Potassium 1.00 1.00 acetate/DEG Dabco NE1070 0.65 0.65 0.65 Potassium 0.7 acetate/EG Polycat 58 0.5 Formic acid 2.5 Polyol functionality 2.9 3.87 Proportion of [%] 46.0 0.0 46.0 0.0 primary OH Isocyanate 1 107.2 92.60 92.60 Isocyanate 2 197 n-Pentane 6.70 6.70 c-/i-Pentane mixture 244 Index NCO/OH 100 244 100 100 Free-rise foam reaction times Cream time [s] 15 120 34 50 Fiber time [s] 60 270 45 87 Rise time [s] 80 360 55 90 Tack-free time [s] 95 420 55 95 *Comparison

[0161] The obtained free-rise foams were subsequently characterized with the abovementioned methods of measurement. Their properties are summarized in table 2.

TABLE-US-00002 TABLE 2 Example 1 2* 3* 4* Apparent density kg/m.sup.3 70 63 63 63 Compressive strength at MPa 0.42 0.41 0.41 0.41 10% compression (parallel) Compressive strength at MPa 0.37 0.36 0.29 0.36 10% compression (transverse) Open-cell content % 96 93 95.6 25.6 Average cell size m 67 137 150 126 Cell size of smallest cell m 25 21 43 73 Cell size of largest cell m 129 299 217 174

[0162] Example 1 shows that the specified formulation makes it possible to produce very fine-celled rigid foams having a high proportion of open cells.

[0163] The average cell sizes of the inventive example are markedly smaller than in the comparative examples where no formic acid was used. A comparison of example 1 and comparative example 2, the latter corresponding to example 1 from EP 2 072 548, shows that the cell size of example 1 is about 51% smaller with an average cell size of 67 m. This is a distinct advantage in respect of the use of the foams as a core material for vacuum insulation applications since this makes it possible to achieve a lower lambda value at identical pressure.

[0164] Example 1 further shows that even with a polyol formulation without cell-opening substances (Ortegol) foams having a higher open-cell content and a finer cell structure are obtainable when formic acid is employed as a blowing agent.