Polymer foam insulation structure having a facing of a multi-layer sheet that contains a heat resistant polymer layer and a polylactide resin layer

Abstract

Thermal insulation structures include a polymer foam layer adhered to a multi-layer sheet having a non-cellular layer of a heat-resistant thermoplastic and a second non-cellular layer of a polylactide resin. The polylactide resin is a surprisingly good barrier to the diffusion of atmospheric gases into the foam layer and of blowing agents out of the foam layer. Accordingly, the diffusion of atmospheric gases and blowing agents is retarded substantially. This greatly reduces the loss of thermal insulation capacity of the structure due to the replacement of the blowing agent with atmospheric gases. The multi-layer sheet exhibits excellent thermal stability, even when the polylactide in the polylactide layer is highly amorphous.

Claims

1. A method that comprises applying a foam precursor mixture containing at least one polyisocyanate, water, and a physical hydrocarbon blowing agent having 3 to 8 carbon atoms to a surface of a first non-cellular layer of a multi-layer sheet, which multi-layer sheet includes i) the first non-cellular layer, which contains at least 50 weight % of one or more thermoplastic resins, wherein the one or more thermoplastic resins is not a polylactide resin and has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 70 C., said first non-cellular layer being sealingly affixed to ii) a second non-cellular layer containing at least 50 weight % of a polylactide resin and (2) curing the foam precursor mixture while in contact with the first non-cellular layer of the multi-layer sheet to form a polymer foam layer adhered to the first non-cellular layer of the multi-layer sheet.

2. The method of claim 1, wherein the one or more thermoplastic resins has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 100 C.

3. The method of claim 2, wherein the one or more thermoplastic resins are a homopolymer of methyl methacrylate or a copolymer containing at least 70 weight % polymerized methyl methacrylate.

4. The method of claim 2, wherein said first non-cellular layer constitutes at least 10% of the total thickness of the multi-layer sheet.

5. The method of claim 2, wherein the second non-cellular layer contains less than 25 J of polylactide crystallites per gram of polylactide resin in said second non-cellular layer.

6. The method of claim 2, wherein the foam precursor mixture is dispensed into a cavity formed by the multi-layer sheet and a second layer and cured within the cavity to form a polymer foam layer adhered to the multilayer sheet and the second layer.

Description

EXAMPLES 1 AND 2

(1) 0.4-mm bilayer sheets are prepared by coextruding a polylactide resin with a poly(methyl methacrylate) (PMMA) resin. The polylactide resin contains 95.5% of L-lactic units and 4.5% of D-lactic units, and has a relative viscosity of 3.5-4.5. For Examples 1A and 1B, the PMMA is Plexiglas V825 resin, which has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of about 111 C. For Examples 2A and 2B, the PMMA is Plexiglas Rnew B514, which has a Vicat softening temperature of about 78 C.

(2) The coextrusions are performed at different layer ratios using a Randcastle unit equipped with an AB feedblock and single manifold die. Extrusion conditions are as indicated in Table 1. All resins are dried as recommended by the respective manufacturers. For Example 1, the die temperatures are 240 C. for the A feedblock (PMMA) and 220 C. for the B feedblock (polylactide resin). For Example 2, the die temperature is 220 C. for each block.

(3) Layer thicknesses are determined for each of Examples 1A, 1B, 2A, and 2B by examination under a microscope. The layer thicknesses are as set forth in Table 1.

(4) The storage moduli at 80 C. of each of Examples 1A and 2B are tested by DMA using a TA Instruments RSAIII instrument at a frequency of 1 Hz and a heating rate of 5 C./min.

(5) Examples 1A, 2A, and 2B are thermoformed using a Frugal thermoformer at a sheet surface temperature between 120 C. and 180 C. The stretch ratio is 1.5. Thermoformed parts were placed in an oven and heated at 1 C./min from 25 C. to 125 C. and images of the samples were taken by a camera every 2 minutes. The images were analyzed to determine the first deformation temperature (FDT), which is the temperature at which deformation or movement of the part is first observed.

(6) Results of the foregoing testing are as indicated in Table 1.

(7) TABLE-US-00001 TABLE 1 Layer A Layer B Storage PMMA (PMMA) thickness (polylactide) thickness Modulus, 80 C. FDT Designation type (% total sheet thickness) (% total sheet thickness) (MPa) ( C.) Example 1A Plexiglas 0.092 mm (23%) 0.308 mm (77%) >100 MPa >90 C. V825 Example 1B Plexiglas 0.116 mm (29%) 0.284 mm (71%) Not Not V825 determined determined Example 2A Plexiglas 0.084 mm (21%) 0.316 mm (79%) Not 60 C. Rnew determined Example 2B Plexiglas 0.104 mm (26%) 0.296 mm (74%) 20 MPa 60 C. Rnew

(8) These data show the advantage of using a resin with a higher Vicat softening point to prepare the first non-cellular layer. The storage modulus of Example 1A is much greater than that of Example 2B, even though in each case the PMMA layer constitutes only a small proportion of the total thickness of the sheet.

EXAMPLE 3

(9) 1-mm bilayer sheet Examples 3A, 3B, and 3C are prepared by coextruding a polylactide resin described in Example 1 with Plexiglas MI-7T acrylate resin, which has a Vicat softening temperature of about 108 C. Coextrusion conditions are similar to Examples 1 and 2. Layer thicknesses are determined microscopically as in Example 1. The first deformation temperature of each of Examples 3A, 3B, and 3C are measured. Examples 3A, 3B, and 3C each are thermoformed in the same manner as Examples 1A, 2A, and 2B.

(10) Results are as indicated in Table 2.

(11) TABLE-US-00002 TABLE 2 Layer A Layer B (PMMA) (polylactide) Storage thickness thickness Modulus, Desig- (% total sheet (% total sheet 80 C. FDT nation thickness) thickness) (MPa) ( C.) Exam- 0.37 mm (37%) 0.63 mm (63%) 220 MPa 93 C. ple 3A Exam- 0.05 mm (5%) 0.95 mm (95%) 34 MPa 56 C. ple 3B Exam- 0.07 mm (7%) 0.93 mm (93%) 11 MPa 68 C. ple 3C

(12) Examples 3A, 3B, and 3C show the effect of the thickness of the first non-cellular layer. Very thin layers provide the structure with thermal properties (storage modulus at 80 C. and FDT) that are similar to those of the polylactide resin layer by itself (<10 MPa and about 54 C., respectively).

EXAMPLES 4 AND 5

(13) 1.2-mm bilayer sheet Examples 4A, 4B, and 4C are made in the same general manner as Examples 1 and 2. The PMMA layer in each case is an impact-modified PMMA made by blending 98 parts by weight of Plexiglas V920 acrylate resin (Vicat softening temperature about 100 C.) with 2 parts by weight of a core-shell rubber. The polylactide layer in each case is made by blending 95 parts of the polylactide resin described in Example 1 with 2.6 parts titanium dioxide powder and 2.4 parts core-shell rubber.

(14) Bilayer sheet Examples 5A, 5B, and 5C are made in the same manner as Examples 4A, 4B, and 4C, respectively, except the Plexiglas V825 resin replaces the Plexiglas V920 resin.

(15) In each case, the layer thickness is measured as in the previous examples. Examples 4A, 4C, and 5B are thermoformed as in previous examples, and the storage modulus at 80 C. is measured.

(16) Results are as indicated in Table 3.

(17) TABLE-US-00003 TABLE 3 Layer A Layer B (PMMA) (polylactide) Storage thickness thickness Modulus, (% total sheet (% total sheet 80 C. Designation thickness) thickness) (MPa) Example 4A 0.174 mm (14.5%) 1.026 mm (85.5%) >100 MPa Example 4B 0.194 mm (16.2%) 1.006 mm (83.8%) Not determined Example 4C 0.282 mm (23.5%) 0.918 mm (76.5%) >100 MPa Example 5A 0.206 mm (17.2%) 0.994 mm (82.8%) Not determined Example 5B 0.180 mm (15.0%) 1.020 mm (85.0%) >100 MPa Example 5C 0.222 mm (18.5%) 0.978 mm (81.5%) Not determined

EXAMPLE 6

(18) 1.2-mm bilayer sheet Example 6 is made in the same general manner as Examples 1 and 2. The PMMA layer in each case is an impact-modified PMMA made by blending 98 parts by weight of Plexiglas V825 acrylate resin with 2 parts by weight of a core-shell rubber. Its thickness is 0.25 mm. The polylactide layer in each case has a thickness of 0.85 mm and is made by blending 80 parts of the polylactide resin described in Example 1 with 15 parts Plexiglas V825 acrylate resin, 2.6 parts titanium dioxide powder and 2.4 parts core-shell rubber. This example simulates a manufacturing setting in which some scrap material is recycled into the polylactide layer.

(19) The bilayer sheet is coextruded and thermoformed using the same process conditions as in Example 4. The storage modulus of the sheet at 80 C. is higher than 100 MPa.

EXAMPLE 7

(20) Foam insulation panels are made from each of bilayer sheet Examples 1-6. A 50-mm-thick layer of a closed-cell, rigid polyurethane foam is formed between the bilayer sheets in a pour-in-place process, to form a three-layer sandwich structure with the foam layer in the center and the PMMA layer facing the foam. The polyurethane foam is a product obtained by reacting a polyisocyanate, a polyol mixture and water in the presence of cyclopentane, and therefore contains a mixture of carbon dioxide and cyclopentane in its cells. All exposed edges of the foam layer are covered with a gas-impermeable metallic tape.

(21) The thermal conductivity of the resulting assembly (Ex. 1) is measured according to DIN 52616 at a mean temperature of 10 C. The assembly is then aged for 629 days under atmospheric pressure air at a temperature of 25 C. and 50% relative humidity. The thermal conductivity is measured periodically during and at the end of the aging period.

(22) For comparison, a similar assembly (Comp. Sample A) is prepared and evaluated in the same way, replacing the multilayer sheets with a layer of non-cellular high impact polystyrene (HIPS) of equivalent thickness.

(23) The foam insulation panels of the invention retain thermal conductivity better than Comparative Sample A over the course of the aging test.

Specific Embodiments

(24) 1. A foam insulation structure comprising a) a polymer foam layer having opposing major surfaces and gas-filled cells that contain a physical blowing agent and b) a multi-layer sheet affixed to at least one of said opposing major surfaces of the polymer foam layer, wherein the multi-layer sheet includes i) a first non-cellular layer containing at least 50 weight-% of one or more thermoplastic resins, wherein the one or more thermoplastic resins is not a polylactide resin and has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 70 C. and ii) a second non-cellular layer containing at least 50 weight-% of a polylactide resin, wherein the first non-cellular layer of the multi-layer sheet is sealingly affixed to the polymer foam layer and the second non-cellular layer of the multi-layer sheet is sealingly affixed to the first non-cellular layer of the multi-layer sheet.

(25) 2. The foam insulation structure of embodiment 1 wherein the one or more thermoplastic resins has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 100 C.

(26) 3. The foam insulation structure of embodiment 1 or 2 wherein the one or more thermoplastic resins are miscible with the polylactide resin.

(27) 4. The foam insulation structure of any preceding embodiment wherein the one or more thermoplastic resins are a homopolymer of methyl methacrylate or a copolymer containing at least 70 weight-% polymerized methyl methacrylate.

(28) 5. The foam insulation structure of any preceding embodiment wherein the one or more thermoplastic resins are impact-modified.

(29) 6. The foam insulation structure of any preceding embodiment wherein the physical blowing agent is selected from one or more of a hydrocarbon having 3 to 8 carbon atoms; a fluorocarbon, hydrofluorocarbon, fluorochlorocarbon, or hydrofluorochlorocarbon having up to 8 carbon atoms; a hydrohaloolefin having up to 8 carbon atoms; and a dialkyl ether having up to 8 carbon atoms.

(30) 7. The foam insulation structure of any preceding embodiment wherein the physical blowing agent includes a hydrocarbon having 3 to 8 carbon atoms.

(31) 8. The foam insulation structure of embodiment 7 wherein the physical blowing agent includes cyclopentane.

(32) 9. The foam insulation structure of any preceding embodiment wherein the polymer foam is a reaction product of a foam precursor mixture containing at least one polyisocyanate, water and the physical blowing agent.

(33) 10. The foam insulation structure of any preceding embodiment wherein the multi-layer sheet has a thickness of 0.4 to 10 mm.

(34) 11. The foam insulation structure of any preceding embodiment wherein said first non-cellular layer has a thickness of 0.05 to 9.875 mm.

(35) 12. The foam insulation structure of any preceding embodiment wherein said second non-cellular layer has a thickness of 0.05 to 9 mm.

(36) 13. The foam insulation structure of any preceding embodiment wherein the thickness of said first non-cellular layer constitutes at least 10% of the total thickness of the multi-layer sheet.

(37) 14. The foam insulation structure of any preceding embodiment, wherein the multi-layer sheet further contains a layer of a blend of the polylactide resin and the second thermoplastic resin.

(38) 15. The foam insulation structure of embodiment 14, wherein the layer of a blend of the polylactide resin and the second thermoplastic resin includes recycled scrap material.

(39) 16. The foam insulation structure of any preceding embodiment, wherein the second non-cellular layer includes up to 45% by weight of the second thermoplastic resin, based on the total weight of the second non-cellular layer.

(40) 17. The foam insulation structure of any preceding embodiment, wherein the second non-cellular layer contains less than 25 J of polylactide crystallites per gram of polylactide resin in said second non-cellular layer.

(41) 18. The foam insulation structure of any preceding embodiment, wherein the polylactide resin is impact-modified.

(42) 19. The foam insulation structure of embodiment 18, wherein the polylactide resin contains a core-shell rubber.

(43) 20. The foam insulation structure of any preceding embodiment, wherein the multi-layer sheet has a non-planar geometry produced by thermoforming.

(44) 21. The foam insulation structure of any preceding embodiment, wherein a multi-layer sheet b) is sealingly affixed to both opposing major surfaces of the polymer foam layer.

(45) 22. The foam insulation structure of any of embodiments 1-20, wherein a metal layer is sealingly affixed to the opposing major surface of the polymer foam layer.

(46) 23. The foam insulation structure of any preceding embodiment, wherein the polymer foam layer has a thickness of 0.25 to 12 cm.

(47) 24. The foam insulation structure of embodiment any preceding embodiment, wherein the multi-layer sheet has a storage modulus of at least 50 MPa at 80 C.

(48) 25. The foam insulation structure of any preceding embodiment, wherein the multi-layer sheet has a first deformation temperature of at least 80 C.

(49) 26. The foam insulation structure of any preceding embodiment, which constitutes all or a portion of an appliance cabinet or door.

(50) 27. A method that comprises (1) applying a foam precursor mixture containing at least one polyisocyanate, water, and a physical blowing agent to the surface of a first non-cellular layer of a multi-layer sheet, which multi-layer sheet includes i) the first non-cellular layer, which contains at least 50 weight-% of one or more thermoplastic resins, wherein the one or more thermoplastic resins is not a polylactide resin and has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 70 C., said first non-cellular layer being sealingly affixed to ii) a second non-cellular layer containing at least 50 weight-% of a polylactide resin and (2) curing the foam precursor mixture while in contact with the first non-cellular layer of the multi-layer sheet to form a polymer foam layer adhered to the first non-cellular layer of the multi-layer sheet.

(51) 28. The method of embodiment 27 wherein the one or more thermoplastic resins has a Vicat softening temperature (ASTM D1525, 50 C./hr, 1 kg) of at least 100 C.

(52) 29. The method of embodiment 27 or 28 wherein the one or more thermoplastic resins are miscible with the polylactide resin.

(53) 30. The method of any of embodiments 27-29 wherein the one or more thermoplastic resins are a homopolymer of methyl methacrylate or a copolymer containing at least 70 weight-% polymerized methyl methacrylate.

(54) 31. The method of any of embodiments 27-30 wherein the one or more thermoplastic resins are impact-modified.

(55) 32. The method of any of embodiments 27-31 wherein the physical blowing agent is selected from one or more of a hydrocarbon having 3 to 8 carbon atoms; a fluorocarbon, hydrofluorocarbon, fluorochlorocarbon, or hydrofluorochlorocarbon having up to 8 carbon atoms; a hydrohaloolefin having up to 8 carbon atoms; and a dialkyl ether having up to 8 carbon atoms.

(56) 33. The method of embodiment 32 wherein the physical blowing agent includes a hydrocarbon having 3 to 8 carbon atoms.

(57) 34. The method of embodiment 33 wherein the physical blowing agent includes cyclopentane.

(58) 35. The method of any of embodiments 27-34 wherein the polylactide resin is impact-modified.

(59) 36. The method of embodiment 35 wherein the polylactide resin includes a core-shell rubber.

(60) 37. The method of any of embodiments 27-36 wherein the multi-layer sheet has a thickness of 0.4 to 10 mm.

(61) 38. The method of any of embodiments 27-37 wherein said first non-cellular layer has a thickness of 0.05 to 9.875 mm.

(62) 39. The method of any of embodiments 27-38 wherein said second non-cellular layer has a thickness of 0.05 to 9.875 mm.

(63) 40. The method of any of embodiments 27-39 wherein said first non-cellular layer constitutes at least 10% of the total thickness of the multi-layer sheet.

(64) 41. The method of any of embodiments 27-40, wherein the multi-layer sheet further contains a layer of a blend of the polylactide resin and the second thermoplastic resin.

(65) 42. The method of any of embodiments 27-41, wherein the layer of a blend of the polylactide resin and the second thermoplastic resin includes recycled scrap material.

(66) 43. The method of any of embodiments 27-42, wherein the second non-cellular layer includes up to 45% by weight of the second thermoplastic resin, based on the total weight of the second non-cellular layer.

(67) 44. The method of any of embodiments 27-43, wherein the second non-cellular layer contains less than 25 J of polylactide crystallites per gram of polylactide resin in said second non-cellular layer.

(68) 45. The method of any of embodiments 27-44, wherein the polylactide resin is impact-modified.

(69) 46. The method of any of embodiments 27-45, wherein the multi-layer sheet has a non-planar geometry produced by thermoforming.

(70) 47. The method of any of embodiments 27-46, wherein the polymer foam layer has a thickness of 0.25 to 12 cm.

(71) 48. The method of any of embodiments 27-47, wherein the multi-layer sheet has a storage modulus of at least 50 MPa at 80 C.

(72) 49. The method of any of embodiments 27-48, wherein the multi-layer sheet has a first deformation temperature of at least 80 C.

(73) 50. The method of any of embodiments 27-49, wherein the foam precursor mixture is dispensed into a cavity formed by the sheet of the multi-layer sheet and a second layer and cured within the cavity to form a polymer foam layer adhered to the multilayer sheet and the second layer.

(74) 51. The method of any of embodiments 27-50, wherein the foam insulation structure is an appliance cabinet or door.