ENHANCEMENT OF LONG-TERM PROPERTIES OF CLOSED-CELL RIGID POLYURETHANE FOAMS

Abstract

Polybutylene terephthalate can be used as a gas diffusion barrier for closed-cell rigid polyurethane foams. A thermal insulation element containing a closed-cell, rigid polyurethane foam, which is at least partially covered by a layer system containing at least one layer formed by a polybutylene terephthalate composition, is useful. Articles and devices may contain a corresponding thermal insulation structure, such as refrigerators, insulation panels, pipe insulations, water heaters, and thermally insulated transport boxes.

Claims

1: A thermal insulation element, comprising: a closed-cell rigid polyurethane foam, which is at least partially covered by a layer system comprising at least one layer formed by a polybutylene terephthalate composition.

2: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises at least 30 wt.-% polybutylene terephthalate, based on a total weight of the polybutylene terephthalate composition.

3: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises at least one additional polymer.

4: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises; 50 to 95 wt % of polybutylene terephthalate as component A, 5 to 50 wt % of at least one additional polymer as component B, 0 to 30 wt % of mineral filler as component C and 0 to 20 wt % of further additives as component D, based on a total weight of the polybutylene terephthalate composition.

5: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises at least one additional polymer selected from thermoplastic polymers having a melting point below 220° C.

6: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises at least one additional polymer selected from the group consisting of a polyester based on aliphatic and/or aromatic dicarboxylic acids; a polyester based on aliphatic dihydroxy compounds; a thermoplastic elastomer; a copolymer of acrylic ester, styrene, and acrylonitrile; polylactic acid: polypropylene; polyethylene; and a mixture thereof.

7: The thermal insulation element according to claim 1, wherein the polybutylene terephthalate composition comprises at least one additional polymer selected from the group consisting of a polyester based on aliphatic and aromatic dicarboxylic acids and a polyester based on aliphatic dihydroxy compounds.

8: The thermal insulation element according to claim 1, wherein the at least one layer formed by the polybutylene terephthalate composition has a thickness of from 0.005 to 500 mm.

9: The thermal insulation element according to claim 1, wherein the layer system comprises at least one second layer selected from the group consisting of a metal layer, a paper layer, a coated paper layer, and a polymer layer.

10: The thermal insulation element according to claim 1, wherein the layer system comprises at least one second polymer layer, and wherein the layer system w %, as prepared by coextrusion of the at least one layer formed by the polybutylene terephthalate composition and the at least one second polymer layer.

11: The thermal insulation element according to any of claim 1, wherein the layer system is directly attached to the closed-cell rigid polyurethane foam.

12: The thermal insulation element according to claim 1, wherein the closed-cell rigid polyurethane foam was prepared by with at least one blowing agent selected from the group consisting of a non-halogenated hydrocarbon, a partially halogenated hydrocarbon, and water.

13: The thermal insulation element according to claim 1, wherein the closed-cell rigid polyurethane foam has a free rise density of at maximum 200 g/L.

14. (canceled)

15: A cooling device, comprising the thermal insulation element according to claim 1.

16: A process for producing the thermal insulation element according to claim 1, the process comprising: providing the layer system and preparing the closed-cell rigid polyurethane foam in situ by applying a polyurethane reaction mixture in direct contact to the layer system.

17: The cooling device according to claim 15, wherein the cooling device is selected from the group consisting of a refrigerator, a freezer, a heat storage system, a water heater, a battery system, an insulation panel for buildings, an insulation board for buildings, a truck, a trailer, a window frame, a door, a garage door, an insulated pipe, a mobile transport system, and an insulated transport box.

Description

EXAMPLES

[0078] 1. Measurement methods:

[0079] Cream Time:

[0080] The time from the commencement of mixing of the reaction mixture to the start of foam expansion. In Table 1 the cream time is denoted as start time.

[0081] String time (also named gel time or setting time)

[0082] Time from the commencement of mixing of the reaction mixture up to the time until it is possible to draw threads in contact with the foam (for example with a wooden rod). This point thus represents the transition from a liquid to a solid state.

[0083] Minimum fill density for a component/free rise density:

[0084] The minimum fill density is determined by introducing, into a mold of dimensions 2000×200×50 mm at a mold temperature of 45±2° C., an amount of polyurethane reaction mixture sufficient for the foam to exactly fill the mold without coming into contact with the end of the mold. The length of the flow path is measured and the minimum fill density calculated according to MFD=(m*L/(V*s)), where m=mass, L=length of the mold, s=flow path and V=volume of the mold. The free rise density is determined by foaming the polyurethane reaction mixture into a plastic bag at room temperature. The density is determined on a cube removed from the center of the foamed plastic bag.

[0085] Thermal Conductivity:

[0086] Thermal conductivity is determined using a Taurus TCA300 DTX apparatus at an average temperature of 10° C. For production of the test specimen, the polyurethane reaction mixture is introduced into a mold of dimensions 2000×200×50 mm (15% degree of overpacking) and demolded after 5 min. After storage for 24 hours under standard climatic conditions, a plurality of foam cuboids (positions 10, 900 and 1700 mm with respect to the start of the lance) of dimensions 200×200×50 mm are cut out from the center. Subsequently, the top and bottom sides are removed so that test specimens of dimensions 200×200×30 mm are obtained.

[0087] Thermal Cycling Test

[0088] A PUR rigid foam sample covered with a facing material runs through a temperature cycling test in that way that the temperature increases in 3 cycles each from −30° C. up to 60° C. over a period of 11 h.

[0089] Gas Permeation:

[0090] Oxygen Transmission Rates [cm.sup.3•μm/d•bar•m.sup.2] have been obtained at 23° C. and 85% relative humidity. The tests have been performed according to ASTM F1927-07.

[0091] Chemical Resistance Against Blowing Agents:

[0092] A sample of the respective facing material was placed in polyol blend (polyol comoponent A from table 1) equipped with the respective blowing agent (Cyclopentan 95:10 pbw (parts by weight) per 100 pbw polyol blend; HCFO, 1233zd(E), trans-1-chloro-3,3,3-trifluoropropene: 20 pbw per 100 pbw polyol blend) and stored at room temperature over 4 weeks. From these samples tensile strength bars were prepared and tensile strength was analyzed after 14 and 28 days. The initial tensile strength values were obtained from the facing material samples without treatment with a polyol blend.

[0093] Tensile Strength

[0094] Tensile strength was measured according to DIN 53504.

[0095] II. Feedstocks

[0096] Polyol A): Polyether polyol based on sucrose, glycerol and PO having an OH number of 450 mg KOH/g; functionality: 5.1

[0097] Polyol B): Polyether polyol based on vic-TDA and PO having an OH number of 399 mg KOH/g; functionality: 3.9*

[0098] Polyol C): Polyether polyol based on vic-TDA, ethylene oxide (EO) and PO having an OH number of 160 mg KOH/g; functionality: 3.9*

[0099] * The functionality for polyols B and C is <4.0 due to the presence of small amounts of water that were added via addition of the catalyst (aqueous KOH solution) to the starter TDA.

[0100] Catalyst mixture D) consisting of:

[0101] Catalyst D1): Dimethylcyclohexylamine

[0102] Catalyst D2): Pentamethyldiethylenetriamine or bis(2-dimethylaminoethyl) ether

[0103] Catalyst D3): Tris(dimethylaminopropyl)hexahydro-1,3,5-triazine

[0104] Catalyst D4): Dimethylbenzylamine

[0105] Stabilizer E):

[0106] Silicone-containing foam stabilizer, Tegostab B 84204® from Evonik

[0107] Propylenecarbonate

[0108] Cyclopentane 95 (CP 95): Cyclopentane having 95% purity

[0109] HCFO: 1233zd(E); trans-1-chloro-3,3,3-trifluoropropene

[0110] Furthermore, 13.5 pbw of cyclopentane 95 was additionally added to each polyol component, based on the total weight of the polyol components A) to C) plus D, E and propylene carbonate (in order to generate the foams).

[0111] 10 pbw of cyclopentane 95 or 20 pbw of HCFO (1233zd(E); trans-1-chloro-3,3,3-trifluoropropene) was additionally added to each polyol component, based on the total weight of the polyol components A) to C) plus D, E and propylene carbonate and subsequently used for tests of chemical resistance for PU rigid foam blowing agents.

[0112] Isocyanate:

[0113] Polymeric MDI having an NCO content of 31.5% by weight (Lupranat® M20)

[0114] Facing Materials:

[0115] Sheet Metal (Steel)

[0116] High impact polystyrene (HIPS, Styron A-Tech 1175 from Trinseo)

[0117] Acrylonitrile butadiene styrene (ABS, Röchling® ABS glossy)

[0118] Polyethylene terephthalate (PET; PET RT52 from Invista)

[0119] Polybutylene terephthalate (PBT; e.g. Ultradur® B4520 un from BASF)

[0120] III. Rigid PU Foams

[0121] Polyol components P) were prepared from the aforementioned feedstocks, to which components a physical blowing agent was added prior to foaming. By means of a high-pressure Puromat® PU 30/80 IQ (Elastogran GmbH) having a discharge rate of 250 g/s, the polyol components P) admixed with the physical blowing agent were each mixed with the required amount of the specified isocyanate, so that the desired isocyanate index was achieved.

[0122] The reaction mixture was injected into molds adjusted to a temperature of 40° C. and having dimensions of 2000 mm×200 mm×50 mm and allowed to foam up therein. The degree of overpacking was 17.5%, that is 17.5% more reaction mixture was used than would have been necessary to completely foam-fill the mold. The resulting specimens with a thickness of 50 mm are stored at a temperature T.sub.a in a range between 21° C. and 24° C. or at a temperature T.sub.b of 70° C.

[0123] Thermal conductivity were measured over time. In case a facing was used to shield the foam the respective facing material (steel, HIPS, ABS, PET, PBT) was placed on the top and the bottom of the mold prior the foaming step, so that a sample derives which is covered by the respective layer material.

[0124] The cream time, setting time/string time and free rise density were ascertained by means of high-pressure mixing by machine (by means of a high-pressure Puromat® PU 30/80 IQ) and introduction into a PE bag. In this case, 900 g*100 g of material are inserted into the PE bag (diameter * 30 cm). If no processing by machine is possible (e.g. on account of inhomogeneities in the polyol component), the cream time, setting time and free foam density were determined by means of a beaker test by means of manual foaming. The components in this case are adjusted to a temperature of 20±0.5° C. The polyol component was initially charged in the corresponding paper cup, the isocyanate component was weighed in and the reaction mixture was stirred. The stopwatch is started at the beginning of stirring. The cream time is defined here as the period of time between the beginning of stirring and the start of volume expansion of the reaction mixture by means of foam formation. The setting time (fiber time) corresponds to the time from the beginning of mixing up to the time in the reaction process at which threads can be pulled out from the foam composition using a glass bar. In order to ascertain the free rise density in a cup test, the foam head is cut off after the foam has cured. The cut is made perpendicularly to the rise direction on the edge of the testing cup, with the result that the foam cutting face and the upper edge of the testing cup lie in one plane. The content of the cup is weighed and the free rise density is calculated.

[0125] Table 1 shows the data for the production of the PUR used and table 2 shows the measurement results for the rigid PU foams produced therefrom (degree of overpacking OP of the molded foams: 17.5%). Examples E1, E2 and E3 are inventive examples, examples CE1 to CE8 are comparative examples. Table 3 illustrates the respective gas barrier properties of PET (compari-son) and PBT (inventive) by means of oxygen as indication for the diffusion of air. Table 4 show the results of a thermal cycling test.

TABLE-US-00001 TABLE 1 Polyol component and resulting PUR rigid foam. Component//Property Polyol component [ppw] Polyol A 52 Polyol B 30 Polyol C 9.1 Propylene carbonate 1 Stabilizer 3 Catalyst package 2.4 H.sub.2O 2.5 Sum polyol component (A) 100 Cyclopentan 95 13.5 NCO-lndex 120 Machine Data Start time [s] 4 String time [s] 44 Free room density [g/L] 23.3 Minimum filling density [g/L] 31.4 Overpacking [s] 17.5

TABLE-US-00002 Table 2a and 2b. Ageing study at T.sub.a and T.sub.b. Comparison of PBT vs. standard materials. 2a. Ageing at T.sub.a (21-24° C.) CE1 CE2 CE3 E1 Facing Material/Layer none steel.sup.b HIPS PBT Layer thickness [mm] — 0.5 1 0.6 Foam thickness [mm] 50 50 50 50 Time (days) 1 120 1 120 1 120 1 120 TC.sup.a [mW/mK] 19.5 23.6 19.6 19.8 19.5 20.5 19.6 19.7 2b. Ageing at T.sub.b (70° C.) CE4 CE5 CE6 E2 Facing Material/Layer none steel.sup.b HIPS PBT Layer thickness [mm] — 0.5 1 0.6 Foam thickness [mm] 50 50 50 50 Time (days) 1 120 1 120 1 120 1 120 TC.sup.a [mW/mK] 19.2 23.4 19.5 19.7 19.2 21.8 19.5 19.7 .sup.aTC: Thermal conductivity; Lambda-value in mW/mK; .sup.bsteel as a sheet metal

TABLE-US-00003 TABLE 3 Comparison of gas diffusion of PBT (invention) in contrast to PET (comparison). Oxygen Transmission Rates [cm.sup.3 .Math. μm/d .Math. bar .Math. m.sup.2] PET PBT Injection molded plaque 1 mm thickness 2660 1910 Extruded film 1 mm thickness 2910 1910

TABLE-US-00004 TABLE 4 Thermal cycling test. Thermal cycling test CE7 CE8 E3 Facing Material/Layer HIPS PET PBT Thermal cycling test no change of Surface texture no change of surface texture deteriorates surface texture

TABLE-US-00005 TABLE 5 Test of chemical resistance for Cyclopentane 95 (10 pbw per 100 pbw polyol) as PU rigid foam blowing agent. Tensile Strength [MPa] CE9 E4 Facing Material/Layer HIPS PBT initial 24.0 37.3 14 days 5.4 38.3 28 days 2.9 37.7 Difference [%] −68 ±0* *within the experimental error

TABLE-US-00006 TABLE 6 Test of chemical resistance for HCFO (1233zd(E); 20 pbw per 100 pbw polyol) as PU rigid foam blowing agent. Tensile Strenght [MPa] CE10 E5 Facing Material/Layer HIPS PBT initial 24.0 37.3 14 days 22.5 36.5 28 days 21.2 35.9 Difference [%] −12 −4

[0126] The results displayed in Tables 5 and 6 show that a layer made of PBT possesses a higher chemical resistance against usual blowing agents for rigid closed-celled PU foams like cyclopentane or trans-1-chloro-3,3,3-trifluoropropene than HIPS as evidenced by the clear decrease of the tensile strength of HIPS in contrast to the small or not existent deterioration of the tensile strength of PBT.