ANHYDROUSLY CURING POLYISOCYANATE-BASED ADHESIVES

Abstract

The present invention relates to adhesives which are characterized in that they cure in the absence of water and at room temperature with the formation of isocyanurate groups.

Claims

1-11. (canceled)

12. A process for producing an adhesive joint comprising: a) applying a coating composition to a surface to form a coated surface, the coating composition comprising: a polyisocyanate composition A having an average isocyanate functionality of at least 1.5, and at least one catalyst B, which at 23° C. catalyzes the reaction of NCO groups to form isocyanurate groups and/or uretdione groups, wherein an isocyanate content of the coating composition is 5% by weight to 60% by weight and a molar ratio of isocyanate groups to isocyanate-reactive groups optionally present in the coating composition is at least 5:1; b) contacting the coated surface with a further surface; and c) curing the coating composition at a temperature of at least 10° C. and at most 60° C.

13. The process as claimed in claim 12, additionally comprising providing the coating composition by mixing the polyisocyanate composition A and the at least one catalyst B prior to applying the coating composition, wherein a period of time of at least 30 minutes elapses between providing the coating composition and the end of process step b).

14. The process as claimed in claim 12, wherein in process step c) initially a temperature between 10° C. and 40° C. is maintained until the adhesive joint reaches a tensile shear strength according to DIN EN 1465 for adhesives of at least 0.5 N/mm.sup.2 and then a temperature of at least 50° C. is maintained until the adhesive joint reaches a strength of at least 2 N/mm.sup.2.

15. The process as claimed in claim 12, wherein in process step b) at least 20% of the isocyanate groups present in the coating composition at the start of process step b) are converted to isocyanurate groups and at most 30% of the isocyanate groups present in the coating composition at the start of process step b) are converted to urea groups.

16. The process as claimed in claim 12, wherein the coating composition additionally comprises at least one compound C comprising on average at least 1.0 group reactive with isocyanate groups per molecule.

17. The process as claimed in claim 16, wherein the compound C is selected from the group consisting of ethanol, 1-propanol, 1-butanol, ethanediol, glycol, 1,2,10-decanetriol, 1,2,8-octanetriol, 1,2,3-trihydroxybenzene, glycerol, 1, 1,1-trimethylolpropane, 1,1,1-trimethylolethane, pentaerythritol, sugar alcohols, polyethylene glycol (PEG) 200, PEG 300, PEG 400, PEG 600, diethanolamine, triethanolamine, and combinations thereof.

18. The process as claimed in claim 12, wherein the polyisocyanate composition A comprises isocyanate-terminated prepolymers.

19. The process as claimed in claim 12, wherein the coating composition comprises at least 5% by weight isocyanate groups, based on an organic phase of the coating composition.

20. The process as claimed in claim 12, wherein the coating composition comprises less than 0.1% by weight transition metals, based on a total weight of the coating composition.

21. The process as claimed in claim 12, wherein the coating composition additionally comprises at least one filler D.

22. The process as claimed in claim 12, wherein the polyisocyanate component A comprises at least 80% by weight polyisocyanates having aliphatically bonded isocyanate groups.

23. The process as claimed in claim 12, wherein the surface is selected from the group consisting of glass, ceramic, glass ceramic, concrete, mortar, brick, tiles, gypsum, natural stone, metal, metal coated with cathode electrodeposition material, plastic, leather, paper, wood, resin-bonded wood-based materials, textiles, resin-textile composites, polymer composites, and combinations thereof.

24. The process as claimed in claim 12, wherein the adhesive joint has a thickness of at least 1 mm.

25. The process as claimed in claim 12, wherein curing is completed after a maximum of 24 hours.

Description

EXAMPLES

[0173] All reported percentages are based on weight unless otherwise stated.

[0174] The methods detailed hereinafter for determination of the appropriate parameters are employed for conduction and evaluation of the examples and are also the methods for determination of the parameters of relevance in accordance with the invention in general.

[0175] The NCO contents are determined by titrimetric means to DIN EN ISO 11909.

[0176] Unless otherwise stated, the water content was determined in accordance with DIN EN ISO 15512: 2017-03, method B2.

[0177] The residual monomer contents of isocyanates are measured by gas chromatography according to DIN EN ISO 10283 using an internal standard.

[0178] The pot life of the systems was determined as follows: The required amounts of the individual components are weighed into a PE beaker on a balance. In this case, the total weight of the mixture should be at least 50 g. Immediately after the last component has been weighed, a stopwatch is started and the mixture is stirred intensively with a stirrer bar for ca. 1 minute. Every 30 minutes the stirrer bar is pulled out of the mixture and the flow behavior of the mixture is observed. The pot life has been reached and is read off from the stopwatch when the thread breaks and the mixture no longer flows off the stirrer bar.

[0179] All viscosity measurements are taken using a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) according to DIN EN ISO 3219/A3. Unless otherwise stated, the viscosity specified is determined at 23° C.

[0180] In order to be able to observe the curing behavior of catalyzed adhesives and sealants over time, the development of the breaking strength with time is observed. For this purpose, test specimens are prepared which consist of two overlapping glued substrate parts. After specified times, these are then stretched in a destructive tension machine until they break and the required forces are measured (testing of the tensile shear strengths).

[0181] The substrates for the preparation of the test specimens were obtained from Rochholl and stored prior to use for at least 1 week during daytime at 23° C./50% rel. humidity.

TABLE-US-00001 Length Width Thickness Substrate [mm] [mm] [mm] Further details PVC 96 25 4 Komadur ES Eloxal 96 25 1.5 Aluminum specimen alloy 5005A (AlMgl), anodized E6 EV1 Beechwood 40 20 5 Dampened, planed, edges rounded, annual rings 30-90° KTL 96 25 0.8 Steel specimen DC 05, KTL coated, quality Daimler Kathoguard 500 PP 96 25 4 PP natural, Simona DWST PS 96 25 4 White polystyrene, manufacturer Metzeler

[0182] Five test specimens consisting of 2 overlapping bonded substrate parts are required for each measurement. A substrate part is coated with the adhesive to be tested on a length of 20 mm in the longitudinal direction. The second substrate part is placed in such a way that they completely overlap in terms of the width. The length of the overlap is 10 mm in each case. After pressing together by hand, any material emerging from the sides is removed with a spatula. In each case, 10 test specimens are stacked in a press so that the overlapping surfaces are on top of one other. The test specimens are stored at a pressing force of 0.7 N/mm2 for a specified time at 23° C./50% rel. humidity and are taken immediately prior to the test. The specified times (pressing times) in each case can be found in the following tables (figures in h).

[0183] The tensile shear strength was measured in each case on a tensile testing machine Zwick 1475 universal testing machine in analogy to DIN EN 1465 at a feed rate of 50 mm/min. In this case, the test specimens were stretched up to the breaking point and the maximum force value was determined. The results given correspond to the arithmetic mean of 5 tests.

[0184] Process According to the Invention for Producing the Adhesive Compositions

[0185] The amounts of the starting polyisocyanates given in the tables below were weighed into a polypropylene beaker together with the amounts of the catalyst component given in the tables below and optionally the amounts of the further additives given in the tables below (plasticizers, fillers, “compounds C”) and homogenized with the aid of a speed mixer DAC 150 FVZ (Hauschild, D E) at 2750 rpm for 1 min.

[0186] The process according to the invention is employed both for the production of inventive and non-inventive adhesive compositions.

[0187] The calculated NCO content of the mixture given in the tables below is calculated from the mass fraction of the various starting polyisocyanates and the NCO contents thereof, and also the mass fractions of the other components.

[0188] Process According to the Invention for Selecting the Catalyst

[0189] To select the catalysts according to the invention, ca. 20 g of the model substance for the starting polyisocyanate A together with 0.6 g (based on the active component) of the catalyst component are weighed into a polypropylene beaker and homogenized with the aid of a DAC 150 FVZ speed mixer (Hauschild, D E) at 2750 rpm for 1 min. 20 g of the mixture are filled into a glass bottle (volume 25 ml, opening diameter 1.7 cm) under dry nitrogen and this is stored tightly sealed at 23° C. for 168 hours. The condition of the mixture is then assessed. For this purpose, the bottle is opened and held with the opening face down for 10 minutes over a glass beaker of known weight so that all material that has flowed through the opening is collected. Optionally, the material that has flowed out is transferred into the glass beaker using a sheet of card. It is determined whether more or less than 10% of the amount of material has flowed out of the bottle.

[0190] In the case of obviously liquid material (viscosity at 23° C. at most 5 Pas), the pouring test can be dispensed with, as it is assumed that more than 10% of the material will pour out.

[0191] In this connection, polyisocyanates having aromatically bonded isocyanate groups are represented as model compound by Desmodur® E 23 (isocyanate-polyether prepolymer, MDI structural component, NCO content ca. 15.4 percent by weight, NCO functionality ca. 2.1, viscosity ca. 1800 mPas), available from Covestro Deutschland AG. Polyisocyanates having aliphatically bonded isocyanate groups are represented as model compound by Desmodur N® 3300 (polyisocyanurate, HDI structural component, NCO content ca. 21.8 percent by weight, NCO functionality ca. 3.4, viscosity ca. 3000) available from Covestro Deutschland AG. If these products are not accessible, those skilled in the art can use analogous substitute products having a comparable composition. When using in each case the same diisocyanate as structural component, it is important to ensure that the NCO functionality and NCO content are as similar as possible. The preparation methods are known to those skilled in the art or are described in the literature.

[0192] As a model compound for compounds having cycloaliphatically bonded isocyanate groups, an isocyanate prepolymer having an NCO content of 27% based on a polypropylene polyether of nominal OH functionality of 2, hydroxyl number 112 mg KOH/g and isophorone diisocyanate is suitable. This model substance can be prepared by reacting 226 g of Desmophen 1110 BD (Covestro, linear polypropylene polyether polyol, hydroxyl number 112 mg KOH/g, acidity at most 0.1 mg KOH/g, viscosity at 25° C. ca. 140 mPas, water content 0.05%) and 744 g of Desmodur I (Covestro, isophorone diisocyanate (IPDI), purity (GC) at least >95%, hydrolyzable chlorine at most 160 mg/kg, NCO content ca. 37.5%) at 100° C.

[0193] The remaining part of the mixture is poured onto a polyethylene film and this is covered with another polyethylene film. After 168 h, the upper polyethylene film is removed and the state of the mixture is visually assessed. In the case of completely or partially cured samples (i.e. if a mechanically resilient film has formed), this is analyzed by IR spectrometry. For this purpose, an IR spectrometer from Perkin-Elmer (Perkin Elmer Spectrum Two) with an ATR unit (UATR two) is used. Cured samples were measured with the optimum contact pressure (adjustable via the device). Liquids are measured directly on the ATR unit.

[0194] Comparative measurements of the liquid mixtures before storage are used to investigate whether the NCO groups have reduced and whether additional uretdione, isocyanurate and iminooxadiazinedione groups have formed. Those skilled in the art can find the position of characteristic bands in the literature or, if this is not possible, determine them by measuring comparative spectra of model substances which are accessible by methods known in the literature.

[0195] Starting Compounds

[0196] Filler Omyacarb 5 GU, calcium carbonate, Omya, Deutschland

[0197] Plasticizer Jayflex DINP, diisononyl phtalate, Exxon Mobile

[0198] 1,2-Ethanediol, Aldrich

[0199] All polyisocyanates used are either commercially available from Covestro Deutschland AG or can be prepared by methods described in the patent literature based on readily available monomers and catalysts.

[0200] Polyether A According to the Invention, Used as a Structural Component for Preparing Isocyanate Prepolymers According to the Invention

[0201] Polyether P1 was used, a bifunctional polypropylene glycol polyether started with propylene glycol, having a hydroxyl number of 500 mg KOH/g, viscosity 55 mPas, water content 0.01%, prepared using potassium hydroxide as catalyst, then worked up with sulfuric acid, distilled and filtered.

[0202] Polyether B According to the Invention, Used as Component C.

[0203] Desmophen® 2061 BD, linear polypropylene ether polyol having a hydroxyl number of 56 mg KOH/g, available from Covestro Deutschland AG.

[0204] Starting Isocyanate A, Desmodur® N3300

[0205] HDI polyisocyanate comprising isocyanurate groups, available from Covestro Deutschland AG.

[0206] NCO content: 21.8%

[0207] NCO functionality: 3.4

[0208] Monomeric HDI: 0.1%

[0209] Viscosity (23° C.): 3000 mPas

[0210] Starting Isocyanate B

[0211] Desmodur® E XP 2599, available from Covestro Deutschland AG, polyether allophanate based on 1,6-hexamethylene diisocyanate

[0212] NCO content: 6.0%

[0213] NCO functionality: 4

[0214] Monomeric HDI: 0.1%

[0215] Viscosity (23° C.): 2500 mPas

[0216] Starting Isocyanate C

[0217] Polyether-Allophanate Prepolymer Based on 1,6-Hexamethylene Diisocyanate

[0218] This was produced analogously to Example 1a from EP 1775313, except that in this case 221.2 g of polyether P1 were used. Before adding zinc(II) bis(2-ethylhexanoate), an NCO content of 42.9% by weight was achieved and, prior to removal of excess 1,6-hexane diisocyanate, an NCO content of 39.9% was achieved.

[0219] NCO content: 17.0%

[0220] NCO functionality: 4

[0221] Monomeric HDI: 0.1%

[0222] Viscosity (23° C.): 2550 mPas

[0223] Starting Isocyanate D

[0224] Polyether Urethane Prepolymer Based on 1,6-Hexamethylene Diisocyanate

[0225] This was produced analogously to Example 1a from EP 1775313, except that in this case 221.2 g of polyether P1 and 900 g of 1,6-hexane diisocyanate were used and neither isophthaloyl dichloride nor zinc(II) bis(2-ethylhexanoate) were added. The excess 1,6-hexamethylene diisocyanate was removed immediately after an NCO content of 31.4% was reached.

[0226] NCO content: 12.5%

[0227] NCO functionality: 2

[0228] Monomeric HDI: 0.1%

[0229] Viscosity (23° C.): 4200 mPas

[0230] Starting isocyanate E

[0231] Desmodur® E23

[0232] Aromatic polyisocyanate prepolymer based on diphenylmethane diisocyanate (MDI) comprising polyether groups, available from Covestro Deutschland AG

[0233] NCO content: 15.4%

[0234] NCO functionality: 2.1

[0235] Viscosity (23° C.): 1800 mPas

[0236] Starting Isocyanate F

[0237] Desmodur® E 15

[0238] Aromatic polyisocyanate prepolymer based on tolylene diisocyanate comprising polyether groups available from Covestro Deutschland AG

[0239] NCO content: 4.4%

[0240] NCO functionality: 2

[0241] Monomeric TDI: 0.2%

[0242] Viscosity (23° C.): 7000 mPas

[0243] Starting Isocyanate G

[0244] Desmodur® L75 (75% in ethyl acetate), 13.3% NCO

[0245] Aromatic polyisocyanate based on tolylene diisocyanate, ca. 75% by weight in ethyl acetate available from Covestro Deutschland AG

[0246] NCO content: 13.3%

[0247] NCO functionality: 2.7

[0248] Monomeric TDI: 0.2%

[0249] Viscosity (23° C.): 1600 mPas

[0250] Starting Isocyanate H

[0251] 922 g of starting isocyanate A were initially charged in a flange vessel under dry nitrogen and heated to 60° C. 78 g of polyether 1 were then added over one hour with stirring. The reaction mixture was then heated to 60° C. and stirred until an NCO content of 17.0% was reached.

[0252] NCO content: 17.0%

[0253] Viscosity (23° C.): 1600 mPas

[0254] Catalyst K1—Tetrabutylphosphonium Fluoride*nHF,

[0255] (70% by weight dissolved in isopropanol, prepared according to Example 1a from EP 0 962 454 B1, fluoride content (ion-selective electrode) 2.5%)

[0256] Active component 70% by weight

[0257] Catalyst K2—Potassium Acetate (60% by Weight in Diethylene Glycol)

[0258] Potassium acetate and diethylene glycol are available from Aldrich.

[0259] Active component 60% by weight

[0260] Catalyst K3—Potassium Neodecanoate, 60% by Weight

[0261] 31.7 g of potassium neodecanoate, 60% by weight in dipropylene glycol methyl ether (available under the name Baerostab K 10 from Baerlocher Italia) are mixed with 44.4 g of methoxypropyl acetate, 23.9 g of 18-crown-6 crown ether.

[0262] Active component 19.0% by weight

[0263] Catalyst K4—Dibutyltin Dilaurate, 95%, Available from Aldrich

[0264] Active component 95%

[0265] Catalyst K5—2,2′-Dimorpholinodieethyl Ether (DMDEE), 97%, Available from Aldrich

[0266] Active component 97%

[0267] Comparative tests are marked with an * in the following.

[0268] Examples of the Selection of Suitable Catalysts

[0269] Catalyst selection for systems with predominantly aromatically, araliphatically bonded isocyanate groups

[0270] In accordance with the instructions given above, tests for selecting a catalyst were carried out with starting polyisocyanate E and various catalysts. The material obtained was investigated by infrared spectroscopy (ATR-IR spectroscopy) as described above. The IR spectra were printed out as measured on DIN A4 paper. A horizontal line (0 line) at the level of 100% transmission is drawn with a pencil, parallel to the x-axis (wave numbers). For characteristic bands, for the wave number at which the transmission is minimal, a perpendicular line (signal line) is drawn up to the x-axis (wave numbers). The distance of the intersection of this line with the curve of the transmission values and the 0-line is then determined by measuring with a ruler and given in mm.

[0271] Low transmission values result in larger distance values in mm and higher distance values in mm indicate a higher proportion of these groups in the sample investigated. Alternatively, those skilled in the art can also carry out an analogous evaluation directly by comparing the transmission values of characteristic bands.

[0272] Those skilled in the art can find the position of characteristic bands in the literature or—if this is not possible—determine them by measuring comparative spectra of model substances which are accessible by methods known in the literature.

TABLE-US-00002 IR data [mm] peak height after 168 h Condition NCO Dimer Trimer after 24 h and aromatic aromatic aromatic proportion that has (2263-2275 (1755-1780 (1690-1720 flowed out cm.sup.−1) cm.sup.−1) cm.sup.−1) — Liquid 88 — — K1 solid, <10% 6 6 23 K2 solid, <10% 1 — 40 K3 liquid <10% 20 — 66 K4* liquid >10% n.d. n.d. n.d.

[0273] The catalysts K1, K2 and K3 are sufficiently active in the model system for systems with predominantly aromatically bonded isocyanate groups, since curing can be observed (solid after 168 hours, no liquid runs out). It can also be shown that, compared to the product without addition of a catalyst, the content of NCO groups decreases and the content of dimers (uretdione groups) and trimers (isocyanurate groups) increases, which can be read from the decreased ratio of the signal intensity between NCO and trimer. Apparently, K1, K2, and K3 acted as trimerization catalysts.

[0274] Catalyst Selection for Systems with Aliphatically Bonded Isocyanate Groups

[0275] In accordance with the instructions given above, tests for selecting a catalyst were carried out with starting polyisocyanate A and various catalysts. The material obtained was investigated by infrared spectroscopy (ATR-IR spectroscopy).

TABLE-US-00003 IR data [mm] peak height after 168 h Condition NCO after 168 h aliphatic Trimer aliphatic Catalyst or start.sup.S (2256 cm.sup.−1) (1569 cm.sup.−1) Without liquid.sup.S 70.sup.S 86.sup.S K1 solid, <10% 0 23 K2 solid, <10% 49 75 K4* liquid >10% n.d. n.d. K5* liquid >10% n.d. n.d.

[0276] Percentages above refer to the fraction by weight of material leaked out.

[0277] The model compound without catalyst can be stored for weeks without any measurable change in the NCO content and the viscosity, and so only the starting value was given. The catalyst K1 is particularly active in the model system for systems with predominantly aliphatically bonded isocyanate groups, since curing can be observed (solid after 168 h, no liquid runs out). The catalyst K2 is also sufficiently active and results in curing. It can also be shown that, compared to the storage-stable model compound without addition of a catalyst, the content of NCO groups decreases and the content of trimers (isocyanurate groups) increases, which can be read from the decreased ratio of the signal intensity between NCO and trimer. Obviously, K1 and K2 acted as trimerization catalysts, the decrease in NCO groups proceeding significantly faster when using K1 than with K2.

Examples 1-3

[0278]

TABLE-US-00004 1* 2 3 Weight of component [g] Starting polyisocyanate G 75 75 75 Starting polyisocyanate F 25 25 25 Catalyst K2 0 2 0 Catalyst K1 0 0 0.8 Calculated 11 11 11 NCO content of the mixture [%] KTL tensile shear strength 0 17 16 [N/mm.sup.2] 24 h

[0279] Experiment 1* shows that a mixture of the starting polyisocyanates G and F having highly reactive aromatically attached isocyanate groups (NCO content 11%), without addition of a catalyst and without ingress of sufficient amounts of moisture, does not lead to any tensile shear strength of the bonded substrates even after 24 hours, since there is obviously insufficient curing. In contrast, in tests 2 and 3, an addition of catalysts K2 and K1 according to the invention without ingress of moisture and in the absence of other compounds having isocyanate-reactive groups leads to high tensile shear strength in the event of substrate failure (detachment of the KTL coating from the sheet metal).

Examples 4-11

[0280]

TABLE-US-00005 4 5* 6 7 8 9 10 11 Weight of component [g] Starting 100 100 polyisocyanate C Starting 97 81 50 75 100 polyisocyanate A Starting 25 polyisocyanate B Starting 50 polyisocyanate D Starting 100 polyisocyanate H Catalyst K1 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Catalyst K4 0.2 1,2-ethanediol 1.1 3 Polyether B 19 Calculated 17 17 21 17 17 17 22 17 NCO content of the mixture [%] Pot life [min] 240 30 360 n.d. n.d. 200 60 30 Eloxal tensile 5 shear strength [N/mm.sup.2] 24 h Tensile shear 11 strength 24 h Beechwood [N/mm .sup.2 ] Tensile 9 shear strength 24 h PVC [N/mm.sup.2] Tensile 2 shear strength 24 h Polystyrene [N/mm.sup.2 ] KTL tensile shear 5 strength 3 h [N/mm.sup.2 ] KTL tensile shear 16 strength 14 h [N/mm.sup.2 ] KTL tensile shear 17 11 16 12.sup.1) 11 11 17 17 strength 24 h [N/mm.sup.2 ] .sup.1)substrate failure n.d. = not determined

[0281] It can be seen that the two-component polyurethane system with DBTL as the urethanization catalyst (comparative test 5*) has a less favorable ratio of attained strength and pot life compared to the systems according to the invention based on aliphatic and aromatic polyisocyanates. Comparative test 5* has a lower strength than test 4 according to the invention with a shorter pot life. High tensile strengths are achieved on many typical substrates. The bonds on KTL show that after just a few hours such high strengths are achieved that the substrates can be handled safely. This enables short pressing times to be achieved.

Example 12-16

[0282]

TABLE-US-00006 12* 13 14 15 16 Weight of component [g] Starting polyisocyanate A 72 45 17 0 Starting polyisocyanate B 0 28 55 83 100 Starting polyisocyanate F 100 Catalyst K3 3 3 3 3 3 Calculated 4 18 13 9 6 NCO content of the mixture [%] KTL Tensile shear strength 0 16 10 3 1 24 h [N/mm.sup.2]

[0283] In test 12*, a non-inventive starting polyisocyanate having an NCO content of ca. 4% is used in combination with the catalyst K3. This adhesive composition does not result in sufficient tensile shear strength, since after 24 hours there is clearly insufficient curing. Examples 13 to 16 according to the invention show that lower tensile shear strengths are determined as the NCO content decreases.

Examples 17-22

[0284]

TABLE-US-00007 17 18 19 20 21 22 Weight of component [g] Starting polyisocyanate A 80 60 40 80 60 40 Catalyst K1 0.8 0.8 0.8 0.8 0.8 0.8 filler 20 40 60 plasticizer 20 40 60 Calculated 17 13 9 17 13 9 NCO content of the mixture [%] KTL Tensile shear strength 11 5 2 10 4 2 24 h [N/mm.sup.2 ]

[0285] Analogously to this, further examples 17-22 with the catalyst K1 show that even with the addition of fillers and/or plasticizers, adhesive compositions can achieve high tensile shear strengths and can thus be used. However, as the NCO content of the mixture decreases, lower tensile shear strengths are also obtained here.