LOW FREE MDI PREPOLYMERS FOR ROTATIONAL CASTING

Abstract

Rotational cast polyurethane composition prepared from a prepolymer composition comprising: a) an isocyanate-terminated polyurethane prepolymer; and b) a curative agent comprising i) a polyol; ii) an aromatic diamine; iii) a thixotropic aliphatic amine; and iv) a thixotropic colloidal additive, wherein the prepolymer comprises a product produce by the reaction of a polyol with an organic diisocyanate monomer comprising 4,4-diisocyanato diphenylmethane (MDI), and which prepolymer comprises less than 1.0% by weight of free MDI monomer, based on the total weight of the prepolymer, exhibits a range of enhanced physical properties compared to those obtained from prepolymers comprising a higher level of free MDI monomer.

Claims

1. A rotational casting method for producing a polyurethane polymer coating on a cylindrical substrate, the method comprising: rotating the cylindrical substrate about an axis at a selected rotational speed, applying a polyurethane prepolymer composition to a surface of the rotating substrate by ejecting the polyurethane prepolymer composition through a die at a selected flow rate, effecting relative linear movement between the rotating substrate and the die in a direction parallel to the axis of rotation at a selected relative linear speed, and synchronizing the reaction mixture flow rate, the relative linear speed and the rotational speed in such a way that successive convolutions of the outlet streams of the polymeric reaction mixture overlap and meld together seamlessly; wherein the polyurethane prepolymer composition comprises: a) an isocyanate-terminated polyurethane prepolymer; prepared by reacting 4,4-diisocyanato diphenylmethane and a polytetramethylene ether glycol, and which prepolymer comprises less than 1.0% by weight of free 4,4-diisocyanato diphenylmethane monomer, based on the total weight of the prepolymer, and b) a curative comprising i) polytetramethylene ether glycol, ii) diamine diethyl toluene diamine and/or dimethylthio-toluene diamine, and iii) about 0.1 wt % to about 1.5 wt %, based on the total weight of the curative, of a thixotropic aliphatic amine selected from the group consisting of ethylene diamine, 1,6-hexanediamine, 1,12-dodecane diamine, 1,4-cyclohexane diamine, and diethylene triamine, and wherein the total active hydrogen content of the curative agent is equal to about 80-115% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer to provide the polyurethane polymer coating as a rotationally cast polyurethane layer.

2. The method according to claim 1 wherein the polyurethane prepolymer composition is ejected through a die dividing an inlet stream of the polymeric reaction mixture into plural outlet streams.

3. The method according to claim 1 wherein the prepolymer comprises less than 0.7% by weight of free 4,4-diisocyanato diphenylmethane monomer.

4. The method according to claim 1 wherein the prepolymer comprises less than 0.5% by weight of free 4,4-diisocyanato diphenylmethane monomer.

5. The method according to claim 1 wherein the prepolymer comprises less than 0.3% by weight of free 4,4-diisocyanato diphenylmethane monomer.

6. The method according to claim 1 wherein the curative further comprises iv) from about 1.0 wt % to about 10 wt %, based on the total weight of the curative, of a thixotropic colloidal additive selected from the group consisting of fumed silica, clay, bentonite, and talc.

7. The method according to claim 2 wherein the curative further comprises iv) from about 1.0 wt % to about 10 wt %, based on the total weight of the curative, of a thixotropic colloidal additive selected from the group consisting of fumed silica, clay, bentonite, and talc.

8. The method according to claim 1 wherein rotationally cast polyurethane layer has a hardness in the range of 40 to 70 Shore A.

9. The method according to claim 1 wherein rotationally cast polyurethane layer has a hardness in the range of 70 to 80 Shore A.

10. The method according to claim 1 wherein the substrate is a paper mill roll.

11. The method according to claim 2 wherein rotationally cast polyurethane layer has a hardness in the range of 40 to 70 Shore A.

12. The method according to claim 2 wherein rotationally cast polyurethane layer has a hardness in the range of 70 to 80 Shore A.

13. The method according to claim 2 wherein the substrate is a paper mill roll.

14. The method according to claim 6 wherein rotationally cast polyurethane layer has a hardness in the range of 40 to 70 Shore A.

15. The method according to claim 6 wherein rotationally cast polyurethane layer has a hardness in the range of 70 to 80 Shore A.

16. The method according to claim 6 wherein the substrate is a paper mill roll.

17. The method according to claim 7 wherein rotationally cast polyurethane layer has a hardness in the range of 40 to 70 Shore A.

18. The method according to claim 7 wherein rotationally cast polyurethane layer has a hardness in the range of 70 to 80 Shore A.

19. The method according to claim 7 wherein the substrate is a paper mill roll.

Description

DESCRIPTION OF THE INVENTION

[0020] One embodiment of the invention provides a polyurethane prepolymer composition comprising:

a) an isocyanate-terminated polyurethane prepolymer; [0021] wherein the isocyanate-terminated polyurethane prepolymer comprises a reaction product of an organic diisocyanate monomer and a polyol selected from the group consisting of ethylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, polytetramethylene ether glycol (PTMEG), polypropylene glycol, and dihydroxypolyesters, the organic diisocyanate monomer comprises 4,4-diisocyanato diphenylmethane (MDI), and which prepolymer comprises less than 1.0%, e.g., less than 0.7%, e.g., less than 0.5%, e.g., less than 0.3%, by weight of free MDI monomer, based on the total weight of the prepolymer, and
b) a curative comprising i) a polyol; ii) an aromatic diamine; and a thixotropic agent, for example a thixotropic agent comprising a thixotropic aliphatic amine and/or a thixotropic colloidal additive, often the thixotropic agent comprises a thixotropic aliphatic amine and a thixotropic colloidal additive.

[0022] It is anticipated of course that even if one were to introduce free MDI to the polyurethane prepolymer composition in a manner that is unrelated to the preparation of prepolymer component a), the amount of free MDI in the overall composition would still be limited relative to the amount of prepolymer present, e.g., the amount of free MDI present in the overall composition does not exceed 1%, 0.7%, 0.5% or 3% by weight based on the total amount of prepolymer present in the composition.

[0023] One embodiment of the invention comprises a) the prepolymer above and b) a curative comprising i) a polyol; ii) an aromatic diamine; iii) a thixotropic aliphatic amine; and iv) a thixotropic colloidal additive.

[0024] In other embodiments the curative may comprise a polyaspartic ester, often as part of a mixture comprising e.g., a co-curative selected from the group consisting aromatic diamines and diols and optionally thixotropic agents.

[0025] For the purposes of this invention, a material is thixotropic if its addition to the polyurethane composition results in a composition whose viscosity lowers under shear and whose viscosity rises (thickens) in the absence of shear.

[0026] Polyols useful in the preparation of the isocyanate-terminated polyurethane prepolymer can include high MW polyols, for example, having a number average molecular weight of at least about 250 and can be as high as, e.g., about 10,000, often from about 650 to 3000, and low MW polyols, e.g., 250 or less. Combinations of high MW and low MW polyols may be used.

[0027] For example, high MW polyols include polyalkylene ether polyols having the general formula HO(RO).sub.nH, wherein R is an alkylene radical and n is an integer large enough that the polyether polyol has a number average molecular weight of at least 250. Such polyalkylene ether polyols are well-known and can be prepared by the polymerization of cyclic ethers such as alkylene oxides and glycols, dihydroxyethers, and the like, using methods known in the art.

[0028] High MW polyol also may include polyester polyols, which can be prepared by reacting dibasic acids, e.g., adipic acid, sebacic, phthalic acid and the like, with diols such as ethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol and diethylene glycol, tetramethylene ether glycol, and the like. Some polyester polyols also employ caprolactone and dimerized unsaturated fatty acids in their manufacture, e.g., a polyester polyol obtained by the addition polymerization of e-caprolactone in the presence of an initiator.

[0029] Low MW polyols, i.e., polyols with an average molecular weight of less than 250, include aliphatic glycols such as ethylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and the like. Low MW polyols are most typically used as the minor part of a High MW/Low MW polyol mixture.

[0030] For example, polyols useful in the preparation of the isocyanate-terminated polyurethane prepolymer of this invention include polytetramethylene ether glycols (PTMEG), polypropylene glycols, and dihydroxypolyesters.

[0031] In a particular embodiment the isocyanate-terminated polyurethane prepolymer a) comprises a polytetramethylene ether glycol (PTMEG).

[0032] In certain embodiments the curative b) comprises a polyol selected from the group consisting of ethylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butanediol, PTMEG, polypropylene glycol, and a dihydroxypolyester.

[0033] In certain embodiments the curative b) comprises an aromatic amine selected from the group consisting of 4,4-methylene-bis-(3-chloro)aniline (MBCA), 4,4methylene-bis-(3-chloro-2,6-diethyl)aniline (MCDEA), diethyl toluene diamine (DETDA), tertiary butyl toluene diamine (TBTDA), dimethylthio-toluene diamine, trimethylene glycol di-p-aminobenzoate, 1,2-bis(2-aminophenylthio)ethane, 4,4-methylene bis(2-chloroaniline), 2,25-trichloro-4,4-methylene-diamine, naphthalene-1,5-diamine, ortho-phenylene diamine, meta-phenylene diamine, para-phenylene diamine, toluene-2,4-diamine, dichlorobenzidine, diphenylether-4,4-diamine, and mixtures thereof.

[0034] In certain embodiments the curative b) comprises a thixotropic aliphatic amine selected from the group consisting of ethylene diamine, 1,6-hexanediamine, 1,12-dodecane diamine, 1,4-cyclohexane diamine, isophorone diamine, diethylene triamine, triethylene tetramine, amine-terminated polyoxypropylenes, xylene diamine, and piperazine.

[0035] In certain specific embodiments the curative b) comprises a thixotropic colloidal additive selected from the group consisting of fumed silica, clay, bentonite, and talc.

[0036] One specific embodiment of the invention provides a polyurethane prepolymer composition comprising:

a) an isocyanate-terminated polyurethane prepolymer prepared by reacting an organic diisocyanate monomer with a polyol, which prepolymer comprises a reaction product of PTMEG and MDI, and which prepolymer comprises less than 1.0%, e.g., less than 0.7%, e.g., less than 0.5%, e.g., less than 0.3%, by weight of free MDI monomer, based on the total weight of the prepolymer;
and
b) a curative comprising, based on the total weight of the curative agent: [0037] i) about 10 wt % to about 90 wt % of a polyol selected from the group consisting of ethylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butanediol, PTMEG, polypropylene glycol, and a dihydroxypolyester; [0038] ii) about 10 wt % to about 90 wt % of an aromatic diamine selected from the group consisting of 4,4-methylene-bis-(3-chloro)aniline (MBCA), 4,4methylene-bis-(3-chloro-2,6-diethyl)aniline (MCDEA), diethyl toluene diamine (DETDA), tertiary butyl toluene diamine (TBTDA), dimethylthio-toluene diamine, trimethylene glycol di-p-aminobenzoate, 1,2-bis(2-aminophenylthio)ethane, 4,4-methylene bis(2-chloroaniline), 2,25-trichloro-4,4-methylene-diamine, naphthalene-1,5-diamine, ortho-phenylene diamine, meta-phenylene diamine, para-phenylene diamine, toluene-2,4-diamine, dichlorobenzidine, diphenylether-4,4-diamine, and mixtures thereof; [0039] iii) about 0.1 wt % to about 1.5 wt % of a thixotropic aliphatic amine selected from the group consisting of ethylene diamine, 1,6-hexanediamine, 1,12-dodecane diamine, 1,4-cyclohexane diamine, isophorone diamine, diethylene triamine, triethylene tetramine, amine-terminated polyoxypropylenes, xylene diamine, and piperazine; and [0040] iv) about 1.0 wt % to about 10 wt % of a thixotropic colloidal additive selected from the group consisting of fumed silica, clay, bentonite, and talc,
wherein the total active hydrogen content of the curative is equal to about 80-115% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer.

[0041] For example, the composition above wherein

a) the isocyanate-terminated polyurethane prepolymer comprises a prepolymer prepared by reacting an organic diisocyanate monomer with a polyol, in a mole ratio of organic diisocyanate monomer to polyol ranging from about 1.7:1 to about 4:1; and
b) the curative comprises [0042] i) about 30 to about 60 wt % of the polyol; [0043] ii) about 20 to about 80 wt % of the aromatic diamine; [0044] iii) about 0.2 to 0.7 wt % of the thixotropic aliphatic amine; and [0045] iv) about 2 to about 5 wt % of the thixotropic colloidal additive,
wherein the total active hydrogen content of the curative agent is equal to about 90-95% of the total isocyanate content of the isocyanate-terminated polyurethane prepolymer.

[0046] Processes for combining the components of the prepolymer composition of the invention are well known in the art and need not be discussed here.

[0047] The inventive prepolymer composition provides polyurethane resins, in particular, rotationally cast polyurethanes, with physical properties not readily obtainable from other similar prepolymer compositions. For example, the majority of rotational cast polyurethane systems available on the commercial market can produce hardness ranges between 70 and 95 Shore A. In order to produce a rotational cast polyurethane system with a lower hardness, a softening additive such as plasticizers are added.

[0048] However, the low free MDI prepolymer composition of the invention can be used to prepare a rotationally cast polyurethane layer with a hardness in the range of 40 to 70 Shore A without the use of any softening additive. These layers are also shown to have improved tensile properties and exceptional toughness.

[0049] Various devices are known for preparing rotational cast polyurethanes, the references cited above describe a few examples of known methods and devices, e.g., U.S. Pat. No. 5,601,881 describes single polyurethane outlet systems including e.g., slit die systems, 2004/0091617 describes systems that provide dual polyurethane outlet streams, etc. The prepolymer compositions are well suited for use with any rotation casted method or device. One embodiment of the invention is to the process of preparing a rotationally cast polyurethane from the prepolymer composition of the invention. Another embodiment is to the polyurethane so produced and another embodiment is to an article comprising said polyurethane.

[0050] The compositions and methods of the invention can be used in the production of any article where rotational casting is employed, e.g., polyurethane covered rolls, wheels, etc.

Examples

[0051] Polyurethane resins prepared from conventional rotational casting prepolymer compositions and low free MDI prepolymer compositions of the invention were prepared and physical properties, tensile and abrasion loss, were tested. Polymers of different hardnesses were prepared by varying the ratio of the two curatives listed as known in the art. The curatives employed comprise PTMEG, DETDA, dimethylthio-toluene diamine, plus thixotropic additives.

TABLE-US-00001 Conventional System 70A-95A (Comparison Composition) Prepolymer: Adiprene RFA 1001 MDI PTMEG Curative: Adiprene Ribbon Flow LM B229E Prepolymer Curative: Adiprene Ribbon Flow LM B136E LF MDI System 70A-95A (Inventive Composition) Prepolymer: Adiprene Duracast LM A615E LF MDI PTMEG Curative: Adiprene Ribbon Flow LM B229E Prepolymer Curative: Adiprene Ribbon Flow LM B136E

[0052] The tensile properties are given in the following table. The LF MDI based ribbon flow materials have higher tensile properties in comparison to the conventional RF grades at the equivalent hardness range.

TABLE-US-00002 Stress Strain Hardness Modulus MPa at Break at Break Shore A 50% 100% 200% 300% N/mm.sub.2 % 70 Comp 1.62 2.42 3.47 4.98 6.61 350.75 70 INV 1.83 2.70 4.17 7.74 21.25 387.68 75 Comp 2.03 2.84 4.05 5.90 28.14 487.26 75 INV 2.02 3.01 4.56 7.42 41.86 440.08 80 Comp 2.69 3.53 4.94 7.16 40.63 513.33 80 INV 2.62 3.81 5.91 10.66 36.16 394.41 85 Comp 3.33 4.19 5.76 8.33 44.58 521.32 85 INV 3.38 4.75 7.40 14.69 46.01 397.77 90 Comp 4.10 5.30 8.00 14.10 46.30 416.70 90 INV 6.25 8.55 16.37 43.45 45.14 304.70 95 Comp 6.05 7.20 10.26 17.06 45.75 414.75 95 INV 6.80 8.92 16.14 39.76 56.33 345.39

[0053] Abrasion loss was found to be improved at the lower hardnesses for the LFMDI prepolymers with little difference at the high hardness ranges.

TABLE-US-00003 Hardness DIN Abrasion Loss Shore A Comp INV 70 75 21 75 45 26 80 34 31 85 37 40 90 57 69 95 52 68