Two-Component Polyurethane Hot-Melt Adhesive With High Initial And Final Strength

Abstract

A two-pack polyurethane adhesive for semi-structural and structural adhesive bonds which are applied in melt form and have a high handling strength wherein the two-pack polyurethane adhesive includes a first pack A containing at least one polyester A1 which is solid at room temperature and at least one polyol A2 having a hydroxyl group functionality greater than 2.0, and a second pack B containing polyurethane prepolymers having isocyanate groups.

Claims

1. A two-pack polyurethane adhesive comprising a first pack A containing at least one polyester A1 which is solid at room temperature and at least one polyol A2 having a hydroxyl group functionality greater than 2.0, and a second pack B containing polyurethane prepolymers having isocyanate groups.

2. The two-pack polyurethane adhesive according to claim 1, wherein the polyesters A1 have a functionality of at least one hydroxyl end group.

3. The two-pack polyurethane adhesive according to claim 1, wherein the glass transition temperature and/or the melting point of A1 is above 23° C.

4. The two-pack polyurethane adhesive according to claim 1, wherein the polyol A2 is selected from the group including polyethers, polyacrylates, polycarbonates or hydroxyl-terminated polyolefins or polyesters.

5. The two-pack polyurethane adhesive according to claim 1, wherein the polyol A2 comprises polyesters.

6. The two-pack polyurethane adhesive according to claim 1, wherein the polyurethane prepolymers having isocyanate groups consist of the reaction product of at least one polyol with an excess of polyisocyanates.

7. The two-pack polyurethane adhesive according to claim 6, wherein polyisocyanates used are di- or multifunctional, aromatic, aliphatic or cycloaliphatic isocyanates, and carbodiimide-modified isocyanates or isocyanate-terminated prepolymers.

8-10. (canceled)

11. A method for producing adhesive bonds based on the two-pack polyurethane adhesive of claim 1, comprising the separate melting of the A and B packs, depending on the melt viscosity, at temperatures above the melting points and/or glass transition points of all the constituents in the two packs, mixing of the two liquid packs A and B and subsequent application to the substrates to be bonded.

12. The method according to claim 11, wherein the two liquid packs A and B are mixed with one another in a mixing ratio between 1:9 and 9:1 per cent by volume.

13. A two-pack polyurethane adhesive comprising a first pack A containing at least one polyester A1 which is solid at room temperature and at least one polyol A2 having a hydroxyl group functionality greater than 2.0 and additives, and a second pack B containing polyurethane prepolymers having isocyanate groups and additives.

14. The two-pack polyurethane adhesive according to claim 13, wherein the polyesters A1 have a functionality of at least one hydroxyl end group.

15. The two-pack polyurethane adhesive according to claim 13, wherein the glass transition temperature and/or the melting point of A1 is above 23° C.

16. The two-pack polyurethane adhesive according to claim 13, wherein the polyol A2 is selected from the group including polyethers, polyacrylates, polycarbonates, hydroxyl-terminated polyolefins, or polyesters.

17. The two-pack polyurethane adhesive according to claim 13, wherein the polyol A2 comprises polyesters.

18. The two-pack polyurethane adhesive according to claim 13, wherein the polyurethane prepolymers having isocyanate groups consist of the reaction product of at least one polyol with an excess of polyisocyanates.

19. The two-pack polyurethane adhesive according to claim 18, wherein polyisocyanates used are di- or multifunctional, aromatic, aliphatic or cycloaliphatic isocyanates, and carbodiimide-modified isocyanates or isocyanate-terminated prepolymers.

20. The two-pack polyurethane adhesive according to claim 13, wherein the additives for pack A and/or B are selected from the group comprising fillers, rheology modifiers, pigments or dyes, nonfunctionalized polymers, flame retardants, tackifiers, waxes, plasticizers, desiccants, adhesion promoters, fibers, latent hardeners, hydrolysis stabilizers, and ageing stabilizers and auxiliaries.

21. A method for producing adhesive bonds based on the two-pack polyurethane adhesive of claim 13, comprising the separate melting of the A and B packs, depending on the melt viscosity, at temperatures above the melting points and/or glass transition points of all the constituents in the two packs, mixing of the two liquid packs A and B and subsequent application to the substrates to be bonded.

22. The two-pack polyurethane adhesive according to claim 14, wherein the glass transition temperature and/or the melting point of A1 is above 23° C.

23. The two-pack polyurethane adhesive according to claim 14, wherein the polyol A2 is selected from the group including polyethers, polyacrylates, polycarbonates or hydroxyl-terminated polyolefins or polyesters.

Description

EXAMPLES

[0062] In the context of the examples, the following polyesters are used as polyols:

[0063] P1 is a noncrystalline polyester which is solid at room temperature and is formed from C2, C5 and C10 diols and adipic acid, terephthalic acid and isophthalic acid, having an OH number of 50 mg KOH/g.

[0064] P2 is a crystalline polyester which is solid at room temperature and is formed from adipic acid and hexanediol, having an OH number of 50 mg KOH/g.

[0065] P3 is a polyester which is liquid at room temperature and is formed from C2 and C5 diols and adipic acid, terephthalic acid and isophthalic acid, having an OH number of 100 mg KOH/g.

[0066] P4 is a noncrystalline polyester which is solid at room temperature and is formed from C2 and C5 diols, terephthalic acid and isophthalic acid, having an OH number of 70 mg KOH/g.

[0067] P5 is a crystalline polyester which is solid at room temperature and is formed from adipic acid and hexanediol, having an OH number of 30 mg KOH/g.

[0068] General preparation method for the A pack:

[0069] In a flange flask, the amounts of polyesters P1, P2 and P3 specified in Table 1 are melted, homogenized at 130° C. for 30 minutes and dispensed in bubble-free form.

[0070] The fillers are incorporated in a Speedmixer (Speedmixer™ DAC 150 from Flack Tek Inc.) with exclusion of air humidity. For this purpose, the polyol mixture is melted, the weights of lamp black, Aerosil and talc specified in Table 1 are added, and the mixture is homogenized at 3000 revolutions/minute at 90° C. for 5 minutes and dispensed into a cartridge. Alternatively, the fillers can be incorporated in a Dispermat. For avoidance of bubbles, the mixture is subsequently degassed briefly.

[0071] General preparation method for the B pack:

[0072] In a flange flask, the amounts of the dried polyesters P1, P2 and P3 specified in Table 1 are melted at 130° C. Thereafter, the amount of diphenylmethane 4,4′-diisocyanate (MDI) specified in Table 1 is added and the mixture is homogenized rapidly. For complete conversion of the reactants, the mixture is stirred under a protective gas atmosphere at 130° C. for 30 minutes. Subsequently, the isocyanate-containing prepolymer is dispensed into moisture-tight cartridges in bubble-free form.

[0073] The fillers are incorporated in a Speedmixer (Speedmixer™ DAAC 150 from Flack Tek Inc.) with exclusion of air humidity. For this purpose, the prepolymer is melted, the weights of talc and chalk specified in the table are added, and the mixture is homogenized at 3000 revolutions/minute at 90° C. for 5 minutes and dispensed into a moisture-tight cartridge. Alternatively, the fillers can be incorporated in a Dispermat. For avoidance of bubbles, the mixture is subsequently degassed briefly.

TABLE-US-00001 TABLE 1 Production of the individual packs in a Speedmixer (Example 1) and in a Dispermat (Example 2) OH function- T.sub.g T.sub.m OH number Weight ality [° C.] [° C.] [mg KOH/g] [g] A pack A1 P1 2 24 — 50 12.5 A1 P2 2 −65 54 50 7.5 A2 P3 3 −29 — 100 40 Flammruβ 101 .sup.1) 0.6 Aerosil ® R 202 .sup.2) 1.2 Finntalc M 15 .sup.3) 6.0 B pack B1 P1 2 25 — 50 12.5 B1 P2 2 −65 54 50 17.5 B2 P3 3 −30 — 100 10 4,4′-MDI .sup.4) 18.4 Finntalc M 15 .sup.3) 5.8 Omyabond 520-OM chalk .sup.6) 23.6 .sup.1) carbon black from Orion Engineered Carbons .sup.2) silica-based thixotropic agent from Evonik Industries AG .sup.3) magnesium silicate from Mondo Minerals .sup.4) diphenylmethane 4,4′-diisocyanate, e.g. Lupranat ME from BASF .sup.5) calcium carbonate from Omya AG

TABLE-US-00002 TABLE 2 Production of the individual packs in a Speedmixer (Example 3) and in a Dispermat (Example 4) OH function- T.sub.g T.sub.m OH number Mass ality [° C.] [° C.] [mg KOH/g] [g] A pack A1 P4 2 20 — 70 10 A1 P5 2 −60 55 30 9 A2 P3 3 −29 — 100 40 Flammruss 101 lamp black 0.6 Aerosil R 202 1.2 Finntalc M 15 5.9 B pack B1 P4 2 20 — 70 10 B1 P5 2 −60 55 30 21 B2 P3 3 −30 100 10 4,4′-MIDI 17.9 Finntalc M 15 5.9 Omyabond 520-OM chalk 23.4

[0074] Use of the Two-Pack Polyurethane Adhesives with Use of a Static Mixer

[0075] The two packs A and B are each stored separately from one another and melted at 90° C. prior to use. The two cartridges are of equal size in order to establish a mixing ratio of 1:1. The cartridges which have been heated to 90° C. are assembled, a static mixer (Sulzer MCH 13-24) which has likewise been heated to 90° C. is screwed on and they are inserted into a cartridge gun. The pressure applied in the cartridge gun causes the individual packs to be forced through the static mixer and mixed as a result of the operation of the gun trigger. In order to assure complete mixing of the two packs, the first strand of the length of the static mixer discharged is discarded. The adhesive thus mixed is applied to the substrates to be bonded within the open time and characterized. The adhesive join of the uncured adhesive is 2 mm. The resultant adhesive properties are summarized in Table 3.

TABLE-US-00003 TABLE 3 Adhesive properties Example Example Example Example 1 2 3 4 Open time [s] 510 590 200 210 Setting time [s] 480 450 180 180 Handling strength [min] 30 30 10 10 Tensile strength [N/mm.sup.2] 15 12 19 16 Elongation at break [%] 240 200 190 170 Tensile shear strength PC 10 10 10 9 [MPa] Tensile shear strength CFP 11 9 12 10 [MPa]

[0076] To determine the open time, paper strips are pressed onto the adhesive bead at time intervals of 30 seconds. As soon as the surface of the adhesive bead is tack-free, the paper strips are pulled off. The open time corresponds to the time interval within which the paper strip can be removed without fibers tearing out.

[0077] The setting time is understood to mean the time which is required for two wood substrates bonded in a T shape, having a length of 100 mm, a width of 20 mm and a thickness of 5 mm, to achieve such a strength that they cannot be separated again by a load of 2 kg. The bonded area is 400 mm.sup.2.

[0078] To produce the bond, the adhesive is applied with a layer thickness of 2 mm to the area of the first substrate to be bonded and bonded to the other substrate in the shape of a “T”. The long limb is then subjected to a load of 2 kg at time intervals of 30 seconds.

[0079] The setting time reported is the time of suspension of the weight where the bond withstands the load.

[0080] To determine tensile strength and elongation at break, a film of thickness 2 mm is produced from the adhesive composition. After a storage time of 7 days at 20° C. and 65% relative humidity, dumbbell-shaped samples having a length of 80 mm, a bar length of 30 mm and a bar width of 4 mm according to DIN EN 53504 are cut out with a die, and the ultimate tensile strength is determined with a tensile tester at 23+/−2° C. with a speed of 100 mm/minute. Tensile strength is calculated from the ratio of maximum force measured and initial cross section of the sample. Elongation at break is the quotient of the change in length relative to the starting length in per cent.

[0081] Tensile shear strengths are determined on single-lap bonds to DIN EN 1465 by means of a tensile tester with a speed of 12 mm/minute at a temperature of 23+/−2° C. until the bond breaks. The polycarbonate substrates (PC) to be bonded are cleaned with isopropanol. In the case of the carbon fiber-reinforced plastic substrates based on an epoxy resin matrix (CFP) that are to be bonded, the peel ply is removed. There are no further pretreatments. The adhesive thickness is 2 mm. The bonded area is 300 mm.sup.2.

[0082] The bonds are stored at 20° C. and 65% relative humidity for 7 days until testing. In each case, the bond was broken in a cohesive manner.

[0083] In the determination of the handling strength, the time after the joining of the CFP substrates where the tensile shear strength is 0.3 MPa is determined.