Adhesive formulations

Abstract

The present invention relates to adhesive formulations based on uretdione-group-comprising polyaddition compounds that are free of isocyanate groups and monomeric polyisocyanates, and to the use thereof for the production of adhesive bonds between substrates, in particular for the production of flexible film composites.

Claims

1. An adhesive formulation consisting of one or more uretdione-group-comprising polyaddition compound that comprising less than 2 wt. % free isocyanate groups and no monomeric polyisocyanates, and which can be used as an adhesive at temperatures of less than 100 C., wherein the uretdione-group-comprising polyaddition compound has a content of isocyanate groups present as uretdione of from 1 to 20 wt. %, a solvent, one or more polyols or a polyol formulation, and one or more additives, including an adhesion promoter, and wherein the solid content of the adhesive formulation is from 20 to 60 wt. %.

2. The adhesive formulation according to claim 1, wherein the uretdione-group-comprising polyaddition compound is combined with the one or more polyols or the polyol formulation while maintaining an equivalent ratio of uretdione groups to hydroxyl groups of from 0.5:1 to 2.0:1.

3. The adhesive formulation according to claim 1, wherein the solid content is from 25 to 50 wt. %.

4. The adhesive formulation according to claim 1, wherein the solid content is from 30 to 40 wt. %.

5. A method for bonding substrates comprising providing the adhesive formulation according to claim 1, applying the adhesive formulation to at least one substrate, exposing the adhesive formulation on the at least one substrate to a temperature of less than 100 C., and forming a bond between the substrates.

6. The method of claim 5, wherein the at least one substrate is paper, wood, plastic, metal or stoneware.

7. A process for the production of a film composite comprising applying the adhesive formula according to claim 1 at least partially over a surface of at least two identical or different plastic films and/or metal films, and bonding the films together.

8. A film composite obtained by the process according to claim 7.

Description

EXAMPLES

(1) Unless indicated otherwise, all percentages in the following examples are based on weight.

(2) Determination of the content of free isocyanate groups was carried out titrimetrically in accordance with DIN EN ISO 11909. Determination of the total isocyanate content (i.e. the sum of the content of free isocyanate groups and isocyanate groups present as uretdione) was carried out by so-called high-temperature titration, as described in detail, for example, in EP 0 601 793, Synthesis-Comparison Example 1. The content of isocyanate groups present in the form of uretdione structures was calculated from the difference between the total isocyanate content and the content of free isocyanate groups.

(3) The hydroxy content was determined titrimetrically in accordance with DIN 53240 T.2.

(4) The residual monomer contents were measured in accordance with DIN EN ISO 10283 by gas chromatography with an internal standard.

(5) All the viscosity measurements were carried out using a Rheolab QC rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219/A.

(6) The determination of the gelling time of an adhesive formulation was carried out manually on a 100 g batch. The batch is stirred in a beaker at room temperature (23 C.) with a wooden rod. The gelling time was taken as the time at which, when the wooden rod is lifted briefly, threads can no longer be pulled from the batch, but the batch tears like rubber.

(7) The determination of the application weight was carried out as described below: a circle having a size of 1 dm.sup.2 was cut out of the previously laminated film composite using a circular cutter and weighed. The films were then separated from one another, cleaned with acetone, dried and weighed again. The difference between the two weights multiplied by 100 gives the application weight in g/m.sup.2.

(8) The adhesion or peel strength of a previously laminated film composite was determined in accordance with DIN 53357-A by the 180 peel test on a tearing machine (Zwick I, manufacturer Zwick Roell). To that end, the test strips were clamped in the holders of the tearing machine in such a manner that they were pulled apart at an angle of 180 relative to one another during the determination (the individual strips formed a 90 angle with the adhesive layer). The speed with which the film composites were pulled apart was 100 mm/minute. The mean value of the applied force necessary to separate the test strips was given as the value of the adhesion.

(9) For determining the sealed-seam strength of a previously laminated film composite in accordance with DIN 55529, a strip approximately 15 cm wide was cut out transversely to the direction of travel of the composite. The strip was folded in the middle, in the direction of travel of the film composite, so that the sealing medium (LDPE) is located above one another on the inside. The sealed seam was sealed for 2 seconds at 120 C. by means of a thermal contact heat sealing device (manufacturer Otto Brugger). When the sealed piece of film had cooled to room temperature, 3 strips each 15 mm wide were cut out transversely to the sealed seam. The seal strength of the test strips was determined on the above-described tearing machine. To that end, the test strips were clamped in the holders of the tearing machine and then pulled apart at a speed of 100 mm/minute. The maximum applied force was given as the value of the seal strength. In addition, the tear profile was also assessed.

(10) Materials Used

(11) Crelane EF 403: a uretdione-group-comprising, cycloaliphatic polyurethane which is solid at room temperature and has a content of monomeric IPDI of <0.1%, a content of free isocyanate groups of 0.4% and a total isocyanate content of 13.5%; obtainable from Bayer MaterialScience AG.

(12) Desmodur XP 2730: a uretdione-group-comprising HDI polyisocyanate having a content of monomeric HDI of 0.18%, a content of free isocyanate groups of 22.7% and a viscosity at 23 C. of 90 mPa.Math.s, obtainable from Bayer MaterialScience AG. Hot titration of the product and subsequent calculation in accordance with the method described above gave a content of isocyanate groups present as uretdione of 18.4%.

(13) Desmodur E XP 2747: a monomer- and solvent-free prepolymer based on HDI, having a content of free isocyanate groups of 16.9% and a viscosity at 23 C. of 2600 mPa.Math.s, obtainable from Bayer MaterialScience AG.

(14) Desmodur E 23: a monomer-comprising, solvent-free prepolymer based on diphenylmethane diisocyanate (MDI), having a content of free isocyanate groups of 15.4% and a viscosity at 23 C. of 1800 mPa.Math.s, obtainable from Bayer MaterialScience AG.

(15) Desmophen 670: a weakly branched, solvent-free, hydroxyl-group-comprising polyester having a hydroxyl content of 4.3%, obtainable from Bayer MaterialScience AG.

(16) Desmophen 1380 BT: a polyol based on polyether, having a hydroxyl content of 11.5% and a viscosity at 25 C. of 600 mPa.Math.s, obtainable from Bayer MaterialScience AG.

(17) Baycolle AD 2047: a linear, solvent-free, hydroxyl-group-comprising polyester having a hydroxyl content of 1.7% and a viscosity at 75 C. of 7000 mPa.Math.s, obtainable from Bayer MaterialScience AG.

(18) Baycoll CD 2084: a linear, solvent-free, hydroxyl- and polyether-group-comprising polyester having a viscosity at 75 C. of 120 mPa.Math.s and a hydroxyl content of 2.5%, obtainable from Bayer MaterialScience AG.

(19) Catalyst C1): Addocat 1872, Rhein Chemie (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine)

(20) Catalyst C2): Lupragen N 700, BASF (1,8-diazabicyclo-5.4.0-undec-7-ene)

(21) Uretdione-Group-Comprising Polyaddition Compound A1):

(22) A 60% solution of Crelan EF 403 in ethyl acetate was used as the uretdione-group-comprising polyaddition compound A1). The solution had a viscosity at 23 C. of 3500 mPa.Math.s. The content of isocyanate groups present in the form of uretdione structures was 8.1%.

(23) Uretdione-Group-Comprising Polyaddition Compound A2):

(24) A uretdione-group-comprising IPDI polyisocyanate was prepared as described in Example 3 of EP-A 0 896 973. After removal of the excess monomer, a pale, viscous liquid having a content of free NCO groups of approximately 17.7% was obtained. The calculated content of isocyanate groups present in the form of uretdione groups was 20.1%.

(25) 120.0 g of this uretdione-group-comprising IPDI polyisocyanate were then placed in a reaction vessel together with 92.3 g of Desmodur XP 2730 and heated to 70 C., with stirring. When the mixture was homogenised, 0.09 g of dibutyltin dilaurate was added thereto, and then a mixture of 2,2,4-trimethyl-1,3-pentanediol (58.4 g) and 2-ethylhexan-1-ol (27.4 g) was added dropwise. The mixture was stirred at 70 C. until the titrated content of free isocyanate groups was 0.2%. Ethyl acetate (199.0 g) was then stirred in, and the product was drawn off. The following characteristic data were determined for the product: the content of free isocyanate groups=0.12%; viscosity at 23 C. 430 mPa.Math.s. The content of isocyanate groups present in the form of uretdione structures, determined by high-temperature titration, was 8.2%.

Examples 1 to 12

(26) Examples 1 to 12 were carried out according to the same pattern. The following description is accordingly an example for the whole series. 100 g of the adhesive formulation were prepared at room temperature (approximately 23 C.). To that end, the uretdione-group-comprising polyaddition compound, or the polyisocyanate component, was placed in a reaction vessel and stirred homogeneously with the polyol component. The solvent and the catalyst were then added, where appropriate, and homogenisation was again carried out. A portion of this mixture was immediately applied to the first film (the aluminium side of the precomposite of Wipak Walsrode GmbH WIPAK, PET/Alu (1212) thickness 25 m) by means of a spiral knife (Erichsen, 50 m wet layer thickness) and tempered in a circulating-air oven for 3 minutes at 60 C. in order to allow the solvent to evaporate. Immediately thereafter, the second film (LDPE film WL A 161/60 from Wipak Walsrode GmbH, thickness 60 m, corona pretreated) was applied and pressed down uniformly and without blisters by means of a 2 kg manual roller. The film composite was dried for 10 minutes at 60 C. in a circulating-air oven and then stored for 24 hours at 23 C. and 50% relative humidity.

(27) After storage, the peel strength and the sealed-seam strength of the film composite were determined. In parallel with the production of the film composite, the gelling time of the remaining mixture was also determined. The detailed examples are presented in Table 1 and Table 2.

(28) TABLE-US-00001 TABLE 1 Examples 1 to 8 according to the invention Example 1 2 3 4 5 6 7 8 Polyuretdione A1(g) 72.47 71.96 72.42 87.10 Polyuretdione A2 (g) 72.16 71.65 72.16 87.00 Desmophen 670 (g) 27.53 27.33 27.58 27.84 27.64 27.84 Desmophen 1380 BT (g) 12.30 12.40 Addocat PU 1872 (g) 0.71 0.71 Lupragen N 700 (g) 0.14 0.60 0.14 0.60 Application weight (g/m.sup.2) * ~80 * ~85 ~36 ~52 * ~85 Gelling time (minutes) >24 h ~20 ~180 ~240 >24 h ~19 >240 >240 Peel strength (N/15 mm) 3.04 4.54 6.88 2.76 2.56 5.44 5.89 2.39 Sealed-seam strength 26.57 30.47 29.21 32.45 32.62 39.08 29.79 23.46 (N/15 mm) Tear profile Tear Tear Tear Tear Tear Delaminated Tear Delaminated * not measurable because of strong adhesion of the composite

(29) TABLE-US-00002 TABLE 2 Examples 9 to 12 not according to the invention Example 9 10 11 12 Desmodur E XP 2747 (g) 38.76 46.98 Desmodur E 23 (g) 40.87 49.18 Desmophen 670 (g) 61.24 53.02 59.13 50.82 Ethyl acetate (g) 10 10 10 10 Application weight (g/m.sup.2) ~75 ~60 ~65 ~67 Gelling time (minutes) >300 >500 60 45 Peel strength (N/15 mm) 3.56 2.74 5.33 6.00 Sealed-seam strength (N/15 mm) 21.03 16.41 30.18 42.03 Tear profile Tear Tear Delami- Tear nated

(30) Examples 1 to 8 according to the invention show that the isocyanate-group-free, uretdione-group-comprising polyaddition compounds are suitable, in combination with polyols, as adhesive formulations for producing film composites and yield equivalent composites to the aromatic 2K polyurethane systems (Examples 11 and 12). The optional concomitant use of suitable catalysts brings about an additional improvement in the adhesive properties (Examples 2 to 4 and 6 to 8).

(31) In addition, the corresponding formulations are distinguished by the fact that acceptable peel and sealed-seam strength is achieved after only one day's storage, which indicates higher reactivity as compared with the conventional aliphatic 2K polyurethane systems from Examples 9 and 10 not according to the invention.

Examples 13 to 16

(32) Examples 13 to 16 were carried out according to the same pattern. The following description is accordingly an example for the whole series. Because the adhesive formulations naturally have limited storability, they were prepared immediately before production of the film composite. 100 g of the adhesive formulation were prepared at room temperature (approximately 23 C.). To that end, the uretdione-group-comprising polyaddition compound, or the polyisocyanate component, was placed in a reaction vessel and stirred homogeneously with the polyol component. The solvent and the catalyst were then added, where appropriate, and homogenisation was again carried out. Adhesive formulation so prepared was used immediately after homogenisation to produce a flexible film composite. The film composites were produced by means of a laboratory coating system from Coatema (model BC 26, width 30 cm, length 12 m, dryer length 7 m). The film composites are produced from a PET/Alu precomposite from Wipak Walsrode GmbH WIPAK 1212 (thickness 25 m) and an LDPE film from Wipak Walsrode GmbH WIPAK WL A 161/60 (thickness 60 m, corona pretreated). The aluminium side of the PET/Alu precomposite was coated with the adhesive formulation by means of a pointed knife, dried, bonded to the LDPE and then wound onto a roll core. The belt speed was 2 m/minute, the dryer temperature with incoming air of approximately 100 m.sup.3/h was 60 C. Lamination was carried out at a pressure of 4.0 bar. The length of the film composite produced with the adhesive formulation was at least 20 m. The dry layer thickness of the adhesive formulation was between 5 and 10. The wound films were stored for 3 or 17 days at 23 C. and 50% relative humidity. After storage, the peel strength and the sealed-seam strength of the film composite were determined.

(33) TABLE-US-00003 TABLE 3 Examples 13 to 15 according to the invention amd Example 16 not according to the invention Example 13 14 15 16 Polyuretdione A1(g) Polyuretdione A2 (g) 60.7 60.7 60.8 Desmodur E 23 (g) 31.3 Desmophen 670 (g) 23.6 23.6 23.6 Baycoll AD 2047 (g) 37.8 Baycoll CD 2084 (g) 30.9 Addocat 1872 (g) 0.06 Lupragen N 700 (g) 0.06 Ethyl acetate 15.6 15.6 15.6 Peel strength (N/15 mm) after 3 days' storage 6.67 6.58 5.36 2.6 after 17 days' storage 9.17 6.76 5.22 2.9 Sealed-seam strength (N/15 mm) after 3 days' storage 30.54* 30.75** 28.29** 26.72** after 17 days' storage 32.92** 35.92** 31.13 26.47** *tearing of the sealed seam **tearing of the film

(34) It has been shown by means of Examples 13 to 15 that the isocyanate-group-free, uretdione-group-comprising polyaddition compounds are suitable according to the invention, in combination with polyols and optionally selected catalysts, for laminating composite films in a roll-to-roll process and yield composites which are even superior to the conventional monomer-comprising aromatic 2K polyurethane systems (Example 16) in terms of their properties.