DIMENSIONALLY STABLE, WIPE-ON, MODIFIED-POLYETHER-POLYURETHANE-BASED ADHESIVE COMPOUND

Abstract

The present invention relates to a dimensionally stable adhesive compound which is formulated so as to be largely water- and solvent-free and can be brought into contact with the substrate to be bonded by being wiped on in the form of a thin adhesive film that is suitable in particular for bonding materials obtained from plant fibers. The organic constituent of the adhesive compound according to the invention consists predominantly of a mixture of polyether polyurethanes which are end-capped with at least two monohydric aliphatic alcohols of different chain lengths. The invention also relates to a method for applying a tacky film to a planar substrate, preferably to paper, by wiping the adhesive compound onto the point of contact with the substrate.

Claims

1. A dimensionally stable adhesive compound comprising: (a) an organic constituent, which is a mixture of polyether polyurethanes that are end-capped with a first monohydric aliphatic alcohol having 4 to 8 carbon atoms and a second monohydric aliphatic alcohol having 16 to 22 carbon atoms; (b) an inorganic constituent; and (c) water.

2. The adhesive compound according to claim 1, characterized in that the mixture of polyether polyurethanes is end-capped with the first monohydric aliphatic alcohol which is a linear, primary monohydric aliphatic alcohol and the second monohydric aliphatic alcohol which is a linear, primary monohydric aliphatic alcohol.

3. The adhesive compound according to claim 1, characterized in that the mixture of the polyether polyurethanes are based on polyether polyols, wherein the ether functions are bridged to one another via aliphatic divalent groups having 4 to 8 carbon atoms in the main chain.

4. The adhesive compound according to claim 3, characterized in that the polyether polyols have a hydroxyl number of 30 to 200 mg KOH/g, based on the entirety of the polyether polyols, which are a constituent of the polyether polyurethanes.

5. The adhesive compound according to claim 1, characterized in that the molar ratio of the first monohydric aliphatic alcohol to the second monohydric aliphatic alcohol is in the range of from 1:2 to 3:1.

6. The adhesive compound according to claim 5, characterized in that the mixture of the polyether polyurethanes is prepared by (i) adding at least trifunctional isocyanates selected from trimers of hexamethylene diisocyanate and/or pentamethylene diisocyanate to the polyether polyols and (ii) end-capping with the first monohydric aliphatic alcohols and the first monohydric aliphatic alcohols.

7. The adhesive compound according to claim 1, characterized in that the mixture of polyether polyurethanes has a dynamic Brookfield viscosity (spindle 27) at 80° C. of 2,000 to 140,000 mPas.

8. The adhesive compound according to claim 1, characterized in that the proportion of the mixture of the polyether polyurethanes which are end-capped with the first monohydric aliphatic alcohol and the second monohydric aliphatic alcohol, based on the entirety of polyether polyurethanes, is at least 80 wt.

9. The adhesive compound according to claim 1, characterized in that the proportion of the mixture of polyether polyurethanes which are end-capped with the first monohydric aliphatic alcohol and the second monohydric aliphatic alcohol, based on the organic constituent of the adhesive compound, is greater than 50 wt. %.

10. The adhesive compound according to claim 1, characterized in that the mixture of the polyether polyols of the polyester polyurethanes are semi-crystalline polyester polyols, which are prepared by polycondensation reaction of (i) dicarboxylic acids that are both saturated linear and aliphatic and have an even number of at least 8 methylene groups, and (ii) one or more diols selected from terminal diols that are both saturated linear and aliphatic and contain at least one ether function.

11. The adhesive compound according to claim 10, characterized in that the mixture of the polyester polyurethanes are prepared by adding at least trifunctional isocyanates to the semi-crystalline polyester polyols, and then end-capping with the first monohydric aliphatic alcohol and the second monohydric aliphatic alcohol.

12. The adhesive compound according to claim 1, characterized in that the proportion of organic constituents is at least 70 wt. % based on the adhesive compound.

13. The adhesive compound according to claim 1, characterized in that the proportion of water is less than 5 wt. %, based on the adhesive compound.

14. The adhesive compound according to claim 1, containing A. up to 80 wt. %, based on the adhesive compound, of the organic constituent comprising a) at least 40 wt. % of a mixture of the polyether polyurethanes that are end-capped with the first monohydric aliphatic alcohol having 4 to 8 carbon atoms and the second monohydric aliphatic alcohol is having 16 to 22 carbon atoms; b) up to 50 wt. % of polyester polyurethanes; c) up to 20 wt. % of polyolefin waxes; d) up to 5 wt. % of tackifiers; and e) up to 5 wt. % of polyalkoxylated C12-C22 fatty alcohols, B. up to 20 wt. %, based on the adhesive compound, of the inorganic constituents selected from pigments, fillers or salts; and C. up to 5 wt. % based on the adhesive compound, of water.

15. A method for applying a tacky film to a planar paper substrate comprising pressing the dimensionally stable adhesive compound according to claim 1 onto the substrate and subsequently changing the relative position while maintaining a contact pressure perpendicularly to the surface normal to the substrate.

Description

PRACTICAL EXAMPLES

[0050] In the following, first the preparation of mixtures of polyether polyurethanes is outlined, which as such were cast to form cylindrical, dimensionally stable adhesive compounds according to the invention and characterized with regard to wiping behavior and bonding of paper.

[0051] First, 150 g of polytetrahydrofuran (PolyTHF 1000, BASF SE) were weighed into a three-necked flask and stirred for approximately 90 minutes at 80° C. and 30 mbar vacuum. 173.4 g of isocyanate trimer Desmodur® N3300 (Covestro AG) were then added so that an NCO/OH ratio of 3.0 was ensured. The reaction mixture was heated to 80-100° C. and stirred for about 30-45 minutes. Then 53.4 g of n-octanol and 49.7 g of n-hexadecanol (mixture A) or 30.4 g of n-butanol (mixture B) and 49.7 g of n-hexadecanol were added for the end-capping and stirred for 2-3 hours at 80-120° C. before the batch was bottled.

[0052] For the purpose of chromatographic characterization by gel permeation chromatography (GPC), a sample of the reaction mixture was dissolved with tetrahydrofuran and applied to the column, and subsequently also eluted with tetrahydrofuran. Gel permeation chromatography (GPC) with an RI detector after calibration by means of polystyrene standards was performed at a column oven temperature of 40° C. and a temperature in the detector of likewise 40° C. The relative number-average and weight-average molar mass values were determined from the molar mass distribution curve and the polydispersity was determined therefrom. Mixture A of the polyether polyurethanes had a number-average molar mass of approx. 3,800 g/mol with a polydispersity of 5.2, whereas for mixture B a polydispersity of 7.0 and a number-average molar mass of approx. 4,250 g/mol were determined.

[0053] Mixtures A and B of the polyester polyurethanes were melted at 110° C. and cast in a cylindrical stick shape (diameter 2 cm, length 6-8 cm) and stored for 24 hours at 20° C. before the handling behavior of the stick-shaped adhesive compounds and the property of the wiped-on adhesive film were determined.

[0054] The wiping, determined after 10° incision of the cylindrical stick and wiping via the cut surface on paper with a grammage of 80 g/m2 and a contact pressure of 5 N/cm2, was given the value “4” for mixture A and the value “3” for mixture B (scale from 1: stiff, wiping comparable with an eraser, to 5: like Pritt® Original Stick from Henkel AG & Co. KGaA)

[0055] The paper tear, determined after bonding a sheet of paper with a grammage of 80 g/m2, which was provided with an adhesive film according to the wiping test and then folded for bonding and pulled apart again after 1 hour at 20° C., was given the value “5” (1: no paper tear, 2: less than 30%, 3: less than 60%, 4: less than 90%, 5: more than 90% of the bond area shows paper tears) for both mixtures.

[0056] The softening point of the adhesive compound or of the mixtures A and B of polyether polyurethanes, measured using the ring-and-ball method in accordance with DIN EN ISO 4625-1:2006-04, was 64° C. (mixture A) and 63° C. (mixture B). The adhesive compounds were thus sufficiently temperature-stable to be able to be offered free of packaging.