FROST-RESISTANT ADHESIVES BASED ON POLYISOCYANATES

Abstract

The present invention relates to the use of hydrophilized polyisocyanates for the production of water-diluted coating compositions which have a polymeric polyol content of not more than 10%.

Claims

1. An adhesive composition comprising a water-thinned isocyanate component A having an isocyanate concentration between 2% by weight and 40% by weight, defined as a proportion by weight of the isocyanate group in the overall molecule that contains at least one hydrophilized polyisocyanate, the isocyanate groups of which are in direct contact with water, wherein the adhesive composition has a content of polymeric polyols of not more than 10% by weight.

2. The adhesive composition as claimed in claim 1, wherein the hydrophilized polyisocyanate has been hydrophilized by an external emulsifier not covalently bonded to the polyisocyanate.

3. The adhesive composition as claimed in claim 1, wherein the hydrophilized polyisocyanate has been hydrophilized by an internal emulsifier covalently bonded to the polyisocyanate.

4. The adhesive composition as claimed in claim 1, wherein the polymeric polyols have a number-average molecular weight of at least 20 000 g/mol.

5. The adhesive composition as claimed in claim 1, wherein the water content used to thin the isocyanate component A is such that the viscosity, determined to M014-ISO 3219/A.3, of the thinned isocyanate component A is lowered by at least 40% compared to an otherwise identical but anhydrous isocyanate component A.

6. The adhesive composition as claimed in claim 1, wherein the isocyanate component A is in the form of a dispersion having an average particle size of not more than 1000 nm or of an aqueous solution.

7. The adhesive composition as claimed in claim 1, additionally comprising a trimerization catalyst C.

8. The adhesive composition as claimed in claim 1, additionally comprising an isocyanate-reactive component B having a molecular weight of not more than 4500 g/mol and a water solubility of at least 50 g/I.

9. The adhesive composition as claimed in claim 8, wherein the isocyanate-reactive component B comprises at least one of glycerol, monoethylene glycol, butane-1,3-diol, butane-1,4-diol, trimethylolpropane, neopentyl glycol.sub.., and diethylene glycol.

10. The adhesive composition as claimed in claim 8, additionally comprising a urethanization catalyst D.

11. The adhesive composition as claimed in claim 1, having an isocyanurate content of at least 50% by weight based on solids content after curing.

12. The adhesive composition as claimed in claim 1, having a glass transition point after curing of at least 80 C.

13. A method of producing a bonded join, comprising a) thinning an isocyanate component A containing at least one hydrophilized polyisocyanate with water, such that the isocyanate groups of the hydrophilized isocyanate are in direct contact with water; b) applying the adhesive composition obtained in method step a) to at least one substrate and contacting the coated substrate with at least one second substrate, wherein at least 90% of the free isocyanate groups of the isocyanate component A that were present at the start of method step a) are still present at the start of method step b); and c) curing the adhesive composition, with the proviso that the curing adhesive composition has a content of polymeric polyols of not more than 10% by weight.

14. The method as claimed in claim 13, wherein, in method step a), the isocyanate component A is mixed with a water-dissolved isocyanate-reactive component B prior to performance of method step b).

15. A product of the adhesive bond obtained from the method as claimed in claim 13.

16. The use of the adhesive composition as claimed in claim 1 for bonding porous substrates.

Description

EXAMPLES

[0280] Description of the Test Methods

[0281] Pendulum hardness analogously to DIN EN ISO 1522: the pendulum damping test is a method of determining the viscoelastic properties of adhesives to DIN EN ISO 1522 in a pendulum damping instrument and is thus a measure of the hardness thereof. It consists of a sample table on which a pendulum can swing freely on a sample surface and a counter. The number of swings in a defined angle range is a measure of the hardness of an adhesive and is reported in seconds or number of swings.

[0282] Tensile test (DIN EN 1465). What is ascertained is the bond strength t bond as force/area in MPa (or N/mm.sup.2) for shear stresses (tensile shear strength). Standardized sample geometry: adherend: 100251.6 mm; adhesive bond: 12.525 mm.

[0283] Water resistance to DIN EN 204 D4: Classification of thermoplastic wood adhesives for non-structural applications after storage in water.

[0284] Formulation:

[0285] The adhesives of the invention are mixed in 2 stages. First the component (A) containing the hydrophilized isocyanate and, in parallel, the aqueous component (B) were mixed, each in a dissolver at 1500 rpm for at least 2 min. Thereafter, the two components were again mixed by means of a dissolver at 1500 rpm in the desired composition for at least 1 min.

[0286] The sequence of addition of the constituents to the dissolver for components A and B and for the mixture of A and B was:

[0287] A: isocyanate phase: 1. hydrophilized isocyanates, 2. further organic constituents, 3. additives, 4. fillers, 5. catalysts.

[0288] B: water phase: 1. water, 2. organic constituents, 3. additives, 4. fillers, 5. catalysts. A+B: 1. component A, 2. component B

[0289] Application:

[0290] 15 min after mixing, the adhesives were drawn down by means of a drawdown bar in thickness 0.12 mm onto both desired substrates to be bonded. The adhesive mixture on the substrate was vented at 23 C. for 10 min until the majority of the aqueous phase had evaporated, and the two substrates to be bonded were subsequently pressed with a pressure of 50 N/cm.sup.2 at RT for 24 h. After 7 days, drawdown shear strength was measured in accordance with DIN EN 1465:2009-07 and water resistance in accordance with DIN EN 204 D4. In both cases, the variance consisted in the size of the test specimen.

[0291] Raw Materials Used:

[0292] Dried beechwood in pieces, 2 cm * 5 cm * 0.4 cm. In a departure from DIN EN 1465 and DIN EN 204, the piece of beechwood was bonded with an overlap of 4 cm.sup.2.

[0293] Application thickness to the substrate prior to joining: in each case about 100 g/m.sup.2 wet, about 60 g/m.sup.2 dry.

[0294] Excess adhesive that was expressed from the bonded join was cautiously removed after curing with a razor blade at the edge of the bonded join prior to the tensile test.

[0295] Hydrophilized Isocyanates:

[0296] Hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate, having a viscosity of 35001000 mPa.Math.s to M014-ISO 3219/A.3 at 23 C., NCO content 20.3-21.3% by weight M105-ISO 11909, 11909, Hazen color number <60 M017-EN 1557, monomeric HDI0.24% M106-ISO 10283, flashpoint about 192 C. DIN EN ISO 2719, density about 1.16 g/cm.sup.3 DIN EN ISO 2811, sourced as Bayhydur XP 2655 from Covestro Deutschland AG

[0297] Polyols

[0298] Ethylene glycol, butane-1,4-diol, diethylene glycol, glycerol were sourced from Aldrich.

[0299] Linear aliphatic polycarbonate ester diol, acid number 3 mg KOH/g DIN EN ISO 2114, viscosity at 23 C. 30 5005500 mPa.Math.s DIN EN ISO 3219, hydroxyl content 6.50.45% DIN 53 240/2, water content 0.1% DIN 51 777/1, equivalent weight about 260, density at 20 C. about 1.17 g/ml DIN EN ISO 2811-2, flashpoint about 150 C. DIN EN ISO 2719, pour point approx. 3 C. DIN ISO 3016, *Theory, sourced as Desmophen C 1100 from Covestro Deutschland AG

[0300] Anionic, high molecular weight polyurethane dispersion, about 50% in water, nonvolatile content (1 g/1 h/125 C.) 49-51% DIN EN ISO 3251, viscosity at 23 C. spindle L 2/30 rpm. 40-600 mPa.Math.s DIN 53 019, pH 6.0-9.0 DIN ISO 976. Minimum film formation temperature about 5 C. DIN ISO 2115, sourced as Desmophen U54 from Covestro Deutschland AG.

[0301] Additives

[0302] DBTL (catalyst) was sourced from TIBChemicals as TIBKAT 218

[0303] Lithium molybolate was prepared by the method from DE 102006005165 A1 and used as catalyst in the isocyanate phase.

TABLE-US-00001 Inventive examples are identified by * Experiment 1* 2* 3* 4* 5* Composition of isocyanate phase (component A) Bayhydur XP (g) 21 21 21 21 21 Composition of water phase (component B) Glycerol (g) 2.65 Monoethylene glycol (g) 2.27 Butane-1.4-diol (g) 3.16 Diethylene glycol (g) 3.64 Lithium molybdate (g) 0.1 0.1 0.1 0.1 0.1 Water (g) 16 16 16 16 16 Example 1* 2* 3* 4* 5* Tensile shear strength N/mm.sup.2 15 14.5 14.7 13.6 14.5 D4 criteria met yes yes yes yes yes

[0304] In a further experiment, the freezing stability of various formulations was examined. For this purpose, an isocyanate-reactive component A was subjected to heat treatment at 10 C. for 1 h and at 50 C. for 1 h, in 5 repetitions in each case.

[0305] The isocyanate-reactive component A showed no change at all after the freeze-thaw cycles. The isocyanate-reactive component B of inventive examples 2-5 was formulated in each case for the freezing stability test so as to give a solids content of 20% by weight.

[0306] Comparative examples of the formulations of component B

TABLE-US-00002 6. Desmophen C1100 20 g thinned with 80 g of water separate phase 7. Bayhydrol U54 40 g thinned with 60 g of water coagulated

[0307] After a cold cycle of 1 h at 10 C. and 1 h at 50 C., in 5 repetitions, all noninventive formulations of component B showed distinct instability manifested by complete coagulation and/or irreversible separation between water phase and polyol phase.

[0308] On the basis of polyols of low water solubility and only poor dispersibility, no frost and shear-stable aqueous components B were obtained. If these phases were mixed with an inventive component A after the frost cycle, only inhomogeneous adhesive applications and bonds were obtained after drying.

[0309] Inadequate frost and shear stability was observed when conventional aqueous adhesive dispersions and emulsions were used as component B. These products, which are known to be of excellent suitability for use as 2K polyurethane adhesives, thus exhibit poor freezing stability, and therefore complex precautionary measures, for example temperature control, have to be taken in transport and storage.

[0310] By contrast, the inventive components B for use in combination with an isocyanate phase comprising a hydrophilized isocyanate in component A exhibit excellent freezing and shear stability. This is manifested in that, even after freezing or high shear stress, the blends in component B form stable phases which, if required, can be converted back to their original form after complete freezing and thawing by simple stirring. It is thus possible for the first time, on the basis of the formulations of the invention, to produce transport- and freezing-stable 2-component isocyanate-based aqueous adhesive formulations.