Hydrophobic polyurethane adhesive

Abstract

The present invention relates to a polyurethane adhesive comprising an isocyanate component A and a polyol component B where the isocyanate component A comprises at least one diisocyanate or polyisocyanate and the polyol component B comprises the alkoxylation product of a mixture of castor oil or ricinoleic acid (i), of an aromatic di- or polyol (ii), and of an OH-functional compound having aliphatically bonded OH groups and OH-functionality of from 1 to 8 (iii), and also optionally of a compound (iv), selected from the group consisting of cyclic anhydrides of dicarboxylic acids, and optionally of a compound (v) selected from the group consisting of cyclic mono- or diesters. The present invention further relates to a process for adhesive bonding with use of the polyurethane adhesive of the invention, to an item adhesive-bonded with the use of the polyurethane adhesive, and to the use of said item in the construction of wind turbines.

Claims

1. A polyurethane adhesive comprising an isocyanate component A and a polyol component B, wherein: the isocyanate component A comprises a diisocyanate or a polyisocyanate, and the polyol component B comprises an alkoxylation product of a mixture comprising 30-90 wt. % of castor oil or ricinoleic acid (i), an aromatic di- or polyol (ii), and an OH-functional compound having aliphatically bonded OH groups and OH-functionality of from 1 to 8 (iii), and also optionally a compound (iv) that is a cyclic anhydride of a dicarboxylic acid, and optionally a compound (v) that is a cyclic mono- or diester, wherein wt. % is based on a total weight of components (i) to (iii) and, if present (iv) and (v).

2. The polyurethane adhesive according to claim 1, wherein said alkoxylation product is achieved with the aid of a nucleophilic and/or basic catalyst and of at least one alkylene oxide.

3. The polyurethane adhesive according to claim 2, wherein the alkylene oxide comprises propylene oxide.

4. The polyurethane adhesive according to claim 1, wherein the mixture comprises an aromatic diol comprising two phenol groups.

5. The polyurethane adhesive according to claim 4, wherein the aromatic diol comprises a bisphenol.

6. The polyurethane adhesive according to claim 1, wherein the OH-functional compound (iii) has from 5 to 8 OH groups.

7. The polyurethane adhesive according to claim 1, wherein the isocyanate component A comprises a mixture of monomeric diphenylmethane diisocyanate and of diphenylmethane diisocyanate having a larger number of rings than monomeric diphenylmethane diisocyanate.

8. The polyurethane adhesive according to claim 1, wherein the OH number of the alkoxylation product is in the range from 80 to 800.

9. The polyurethane adhesive according to claim 1, wherein the proportion of castor oil or ricinoleic acid (i) is from 30 to 80% by weight, the proportion of an aromatic di- or polyol (ii) is from 4 to 25% by weight, and the proportion of an OH-functional compound having aliphatically bonded OH groups and OH-functionality of from 1 to 8 (iii) is from 10 to 40% by weight, and the proportion of an optional compound (iv) that is a cyclic anhydride of a dicarboxylic acid is from 0 to 30% by weight, and the proportion of an optional compound (v) that is a cyclic mono- or diester is from 0 to 30% by weight, based in each case on the total weight of components (i) to (v).

10. The polyurethane adhesive according to claim 1, wherein the mixture comprises the compound (iv).

11. The polyurethane adhesive according to claim 1, wherein the mixture comprises the compound (v).

12. The polyurethane adhesive according to claim 1, wherein the mixture comprises the compound (iv) and the compound (v).

13. The polyurethane adhesive according to claim 1, wherein said polyol component B excludes castor oil.

14. A process for adhesive bonding, comprising: mixing the isocyanate component A and the polyol component B of the polyurethane adhesive according to claim 1, applying the mixed polyurethane adhesive to at least one substrate surface requiring adhesive bonding, forming a joint within an open time, and hardening the polyurethane adhesive.

15. The process according to claim 14, wherein the at least one substrate surface requiring adhesive bonding is a plastic.

16. An adhesive-bonded item obtained by the process according to claim 14.

17. A wind turbine comprising the adhesive-bonded item according to claim 16.

Description

(1) Examples will be used below to illustrate the invention.

(2) Raw Materials Used:

(3) Polyol 1: Sovermol 805, a mixture of castor oil with a ketone resin in a mixing ratio of about 80/20 parts by weight with OH number 173 mg KOH/g, obtainable commercially from BASF SE

(4) Polyol 2: A sucrose/glycerol-containing propoxylate with OH number 490 mg KOH/g and with average functionality 4.3

(5) Polyol 3: Propoxylate based on bisphenol A as starter with OH number 280 mg KOH/g.

(6) Iso 1: Polymer MDI with functionality about 2.7 and with NCO content 31.5% by weight, obtainable with trademark Lupranat M20 from BASF SE.

(7) Water scavenger: Zeolitic water scavenger, dispersed in castor oil (50% by weight).

(8) Polyol Synthesis Examples

(9) Polyol Synthesis Example 1 (Synthesis 1):

(10) 175.2 g of glycerol, 0.5 g of imidazole, 275.45 g of sorbitol, and 425.1 g of bisphenol A, and 2751.7 g of castor oil (FSG quality) were charged at 25 C. to a 5 L reactor. This was then inertized with nitrogen. The vessel was heated to 150 C., and 1372.1 g of propylene oxide were added. After 11 h of reaction time, the system was evacuated at 100 C. for 40 minutes under maximum vacuum and then cooled to 25 C. This gave 4933 g of product.

(11) The Properties of the Resultant Polyetherester were as Follows:

(12) OH number: 300.2 mg KOH/g

(13) Viscosity (25 C.): 2021 mPas

(14) Acid number: less than 0.01 mg KOH/g

(15) Water content: 0.02% by weight

(16) Residual content of bisphenol A: less than 10 mg/kg determined by HPLC

(17) Polyol Synthesis Example 2 (Synthesis 2):

(18) 5.7 g of glycerol, 0.02 g of imidazole, 14.5 g of sorbitol, and 30.2 g of bisphenol A, and 122.4 g of castor oil (FSG quality) were charged at 25 C. to a 300 mL reactor. This was then inertized with nitrogen. The vessel was heated to 150 C., and 67.2 g of propylene oxide were added. After 19 h of reaction time, the system was evacuated at 100 C. for 40 minutes under maximum vacuum and then cooled to 25 C. This gave 225.9 g of product.

(19) The Properties of the Resultant Polyetherester were as Follows:

(20) OH number: 314.7 mg KOH/g

(21) Average OH functionality 3.2

(22) Viscosity (25 C.): 3170 mPas

(23) Acid number: less than 0.01 mg KOH/g

(24) Water content: 0.04% by weight

(25) Residual content of bisphenol A: less than 10 mg/kg determined by HPLC

(26) Polyol Synthesis Example 3 (Synthesis 3):

(27) 3.4 g of glycerol, 0.02 g of imidazole, 22.3 g of sucrose, and 36.0 g of bisphenol A, and 112.4 g of castor oil (FSG quality) were charged at 25 C. to a 300 mL reactor. This was then inertized with nitrogen. The vessel was heated to 130 C., and 65.9 g of propylene oxide were added. After 10 h of reaction time, the system was evacuated at 100 C. for 40 minutes under maximum vacuum and then cooled to 25 C. This gave 229.0 g of product.

(28) The Properties of the Resultant Polyetherester were as Follows:

(29) OH number: 310.6 mg KOH/g

(30) Average OH functionality 3.4

(31) Viscosity (25 C.): 7786 mPas

(32) Acid number: less than 0.01 mg KOH/g

(33) Water content: 0.04% by weight

(34) Residual content of bisphenol A: less than 10 mg/kg determined by HPLC??

(35) Polyol Synthesis Example 4 (Synthesis 4; Comparative Example Without Bisphenol A):

(36) 210.0 g of glycerol, 0.5 g of imidazole, 335.0 g of sorbitol, and 2749.7 g of castor oil (FSG quality) were charged at 25 C. to a 5000 mL reactor. This was then inertized with nitrogen. The vessel was heated to 150 C., and 1704.8 g of propylene oxide were added. After 4 h of reaction time, the system was evacuated at 100 C. for 60 minutes under maximum vacuum and then cooled to 25 C. This gave 4982.5 g of product.

(37) The properties of the resultant polyetherester were as follows:

(38) OH number: 308.9 mg KOH/g

(39) Viscosity (25 C.): 1287 mPas

(40) Acid number: less than 0.01 mg KOH/g

(41) Water content: less than 0.01%

(42) Adhesive Bonding and Production of a Sheet from the Same Reaction Mixture:

(43) Adhesive Bonding:

(44) The samples for determination of shear strength (shear strength at 0.5 mm) were produced with reference to DIN EN 1465 Determination of tensile-lap-shear strength of bonded assemblies. For this, the starting materials as in Table 1 were mixed with isocyanate index 105 in a high-speed mixer for 90 sec at 1600 rpm and then for 30 sec at 2100 rpm. The adhesive was then applied to a glassfiber-reinforced epoxy sheet (Vetronit EGS 619, 100252 mm, Rocholl GmbH). The sheet, with applied adhesive, was then placed for 60 min in a cabinet under controlled climatic conditions at 25 C. and 70% humidity. A second sheet was placed onto this pretreated sheet. The thickness of the adhesive layer here is 0.5 mm. The adhesive bond is loaded with a weight of 1 kg until the adhesive has almost completely hardened. Residual adhesive is then removed, and the adhesive-bonded sheets are further hardened for 2 h at 80 C. The shear samples are cut to size in accordance with the standard DIN EN 1465, and tested.

(45) Mechanical Properties of 2 mm and 4 mm Sheets

(46) An open mold of the desired depth (2 mm or 4 mm) is preheated for about 45 min in a drying oven heated to 80 C. The evacuated components are weighed into the beaker of a high-speed mixer and mixed in the high-speed mixer 60 s at 1600 rpm and then for 120 s at 2100 rpm. After the stirring procedure has ended, the reaction mixture is charged to the mold and smoothed by a doctor. The sheet is hardened at 80 C. for 2 h. The test samples are then punched out from the resultant sheets. Mechanical properties are determined in accordance with DIN EN ISO 527 on test samples of thickness 2 mm, and glass transition temperature is determined by differential scanning calorimetry (DSC) at a heating rate of 20 K/min in accordance with DIN EN ISO 11357.

(47) Determination of Open Time:

(48) Open time is determined by measuring reaction viscosity in a rheometer with plate-on-plate geometry, with diameter 20 mm and gap width 1 mm. The reaction mixture for testing is produced by mixing the starting components as in Table 1 at an isocyanate index of 105 for 5 s at 1600 rpm in a high-speed mixer. Immediately thereafter, sufficient adhesive is applied to the test plate to fill the available space completely. Before the test, the sample is subjected to preshearing for 10 seconds with shear rate no more than 100 s.sup.1, and excess material is removed during the subsequent pause lasting 120 seconds. In the actual test, open time is determined as the time required to reach a viscosity of 400 Pas at a shear rate of s.sup.1.

(49) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Comparison 1 Comparison 2 Comparison 3 Comparison 4 Synthesis 1 57.05 Synthesis 2 57.05 Synthesis 3 57.05 Synthesis 4 57.05 47.05 Castor oil 16.0 Polyol 1 28.55 31.3 Polyol 2 12.5 8.0 Polyol 3 10.000 15.0 7.0 Glycerol 1.0 Chalk 33.0 33.0 32.6 33.0 33.0 33.0 22.0 Fumed silica 0.1 0.1 0.5 0.1 0.1 0.1 1.5 4,4-Methylene-bis(2,6- 1.8 1.8 1.8 1.8 1.8 1.8 2.2 diethylaniline) Antifoam 0.05 0.05 0.05 0.05 0.05 0.05 Water scavenger 8.0 8.0 8.0 8.0 8.0 8.0 12.0 Isocyanate Iso 1 Iso 1 Iso 1 Iso 1 Iso 1 Iso 1 Iso 1 Open time (min) 94 72 65 110 95 46 50 Hardness after 2 h 82 83 82 81 83 85 81 at 80 C. (Shore D) Tensile strength 35.4 39.6 45 29.5 36.7 40.9 34.4 (MPa) Tensile strain 10 6 6 11 10 6 45 at break (%) Modulus of elasticity 3006 2567 2997 1686 2118 2648 1996 (MPa) T.sub.g ( C.) 63 69 70 n.d. n.d. 72 39 Shear strength at 11 12 15 4 1 7 n.d. 0.5 mm thickness (N/mm.sup.2)

(50) Table 1 shows that use of polyols of the invention gives adhesives with excellent properties, in particular with glass transition temperature above 60 C., shear strength above 10 N/mm.sup.2, and high tensile strength above 35 MPa. The open time of adhesives of the invention here is more than 60 minutes, and therefore also permits adhesive bonding of large-surface-area structures, for example blades of wind turbines. In contrast to this, use of finished polyols based on bisphenol A, a pentafunctional starter, and castor oil, as described by way of example in EP 2468789, gives either glass transition temperatures that are too low (comparison 4) or shear strengths that are too low (comparison 3). Omission of bisphenol A in the synthesis polyol (comparison 1) or separate addition of bisphenol A polyol to a synthesis polyol without bisphenol A (comparison 2) also gives adhesives with inadequate shear strength values.