REMOVABLE POLYURETHANE HOT MELT ADHESIVE AND THE USE THEREOF

Abstract

The invention relates to a polyurethane (PU) reactive hot melt adhesive removable at elevated temperature as well as having a high bonding strength at room temperature.

Claims

1. A reactive hot melt adhesive comprising a (meth)acrylate polymer and an isocyanate-functional polyurethane prepolymer, wherein the (meth)acrylate polymer has a melting point of from 90 to 140 C., and a number average molecular weight of from 20000 to 80000 g/mol.

2. The reactive hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer is a (meth)acrylate copolymer, and the monomers forming the (meth)acrylate polymer are selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate and combinations thereof.

3. The reactive hot melt adhesive according to claim 1, wherein the monomers forming the (meth)acrylate polymer are methyl methacrylate and butyl methacrylate.

4. The reactive hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer has a number average molecular weight of from 25000 to 60000 g/mol.

5. The reactive hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer has a number average molecular weight of from 30000 to 50000 g/mol.

6. The reactive hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer has a melting point of from 95 to 130 C.

7. The reactive hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer is selected from a copolymerization product of butyl acrylate and methyl methacrylate as monomers having a melting point about 100 C. and a number average molecular weight about 30000 g/mol; a copolymerization product of butyl acrylate and methyl methacrylate as monomers having a melting point about 120 C. and a number average molecular weight about 50000 g/mol; a copolymerization product of butyl methacrylate and methyl methacrylate as monomers having a melting point about 110 C. and a number average molecular weight about 60000 g/mol, and combinations thereof.

8. The reactive hot melt adhesive according to claim 1, wherein the amount of the (meth)acrylate polymer is from 5 to 40% by weight, based on the total weight of reactive hot melt adhesive.

9. The reactive hot melt adhesive according to claim 1, wherein the amount of the (meth)acrylate polymer is from 10 to 30% by weight, based on the total weight of reactive hot melt adhesive.

10. The reactive hot melt adhesive according to claim 1, wherein the isocyanate-functional polyurethane prepolymer is a reaction product of the reactants comprising one or more polyisocyanates and one or more polyols, wherein the molar ratio of NCO groups in the polyisocyanates to OH groups in the polyols is more than 1:1.

11. The reactive hot melt adhesive according to claim 1, wherein the isocyanate-functional polyurethane prepolymer is a reaction product of the reactants comprising one or more polyisocyanates and one or more polyols, wherein the molar ratio of NCO groups in the polyisocyanates to OH groups in the polyols is from 1.9:1 to 2.1:1.

12. The reactive hot melt adhesive according to claim 1, wherein the polyols are selected from polyester polyols, polyether polyols, and combination thereof.

13. The reactive hot melt adhesive according to claim 1, wherein the amount of the isocyanate-functional polyurethane prepolymer is from 60 to 90% by weight, based on the total weight of reactive hot melt adhesive.

14. The reactive hot melt adhesive according to claim 1, wherein the amount of the isocyanate-functional polyurethane prepolymer is from 65 to 85% by weight, based on the total weight of reactive hot melt adhesive.

15. The reactive hot melt adhesive according to claim 1, wherein the adhesive further comprises at least one additive selected from the group consisting of diluents, plasticizers, fillers, pigments, curing catalysts, dissociation catalysts, anti-oxidants, flow modifiers, dyestuffs, flame retardants, inhibitors, UV absorbers, adhesion promoters, stabilizers, thermoplastic polymers, tackifiers and waxes.

16. The reactive hot melt adhesive according to claim 1, wherein the adhesive further comprises tackifier including any compatible resins or mixtures selected from the group consisting of natural or modified rosins; glycerol and pentaerythritol esters of natural or modified rosins; copolymers and homopolymers of natural or modified terpenes and aromatic monomers, phenol and hydrogenated derivatives thereof; aliphatic petroleum hydrocarbon and hydrogenated derivatives thereof; alicyclic petroleum hydrocarbon resins and the hydrogenated derivatives thereof; aliphatic/aromatic or cycloaliphatic/aromatic copolymers and their hydrogenated derivatives; and aromatic resins.

17. The reactive hot melt adhesive according to claim 1, wherein the adhesive further comprises a thermoplastic polymer selected from the group consisting of homopolymers or random copolymers of any olefinic monomers, preferably acrylic acid, methacrylic acid, vinyl esters (vinyl acetate and vinyl propionate), vinyl ethers, styrene, acrylamides, methacrylamides, fumarates, maleates, acrylonitrile, ethylene, propylene and derivatives thereof, preferably selected from maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene.

18. The reactive hot melt adhesive according to claim 1, wherein the viscosity of the adhesive is from 2000 to 20000 mPas at 100 C., measured according to EN ISO 2555 by Brookfield Digital Viscometer RVT using spindle 27 at 10 rpm.

19. Cured reaction products of the adhesive of claim 1.

20. An article comprising substrates bonded together by cured reaction products of the adhesive of claim 1.

Description

EXAMPLES

[0045] In the examples that follow, the following tests were used to determine viscosity, bonding strength and removability.

[0046] Testing Methods

[0047] Viscosity:

[0048] Brookfield Digital Viscometer RVT with Thermosel heating unit, using spindle 27, at 100 C., at 10 rpm, according to EN ISO 2555.

[0049] The values of bonding strength of the assembled parts (stainless steel to glass; plastics made of PC and ABS (PC/ABS) to glass; and PC/ABS to PC/ABS at room temperature were measured 24 hours after final curing according to conventional methods.

[0050] The values of bonding strength of the assembled parts (stainless steel to glass; PC/ABS to glass; and PC/ABS to PC/ABS) after aging were measured according to conventional methods.

[0051] Removability:

[0052] The removability of the hot melt adhesive according to the present invention (Examples A-C and E-I) and a conventional hot melt adhesive (Example D) was tested and evaluated according to the method consisting of the following steps: [0053] 1. Keep the substrates (assembly parts) bonded by the hot melt adhesives for 24 hours under indoor atmosphere conditions; [0054] 2. Place the bonded substrates into an oven heated to 80 C. for 20 minutes; [0055] 3. Detach the substrates and try to peel off the adhesive left on the substrate(s) by hand immediately after removing the substrates from the oven; and [0056] 4. Evaluate the removability by the following scales:
GOOD means that the adhesive residue was completely peeled off from the substrates, and
POOR means that most of the adhesive residue could not be successfully peeled off from the substrates and remained on the surface of the substrates.

[0057] Materials

[0058] Isocyanate:

[0059] 4,4-MDI: a commercial product under the trade name of 44C from Bayer.

[0060] (Meth)acrylate polymer 1:

[0061] A copolymerization product of butyl acrylate and methyl methacrylate as comonomers

[0062] Melting point: about 100 C.

[0063] Number average molecular weight: about 30000 g/mol.

[0064] (Meth)acrylate polymer 2:

[0065] A copolymerization product of butyl acrylate and methyl methacrylate as comonomers

[0066] Melting point: about 120 C.

[0067] Number average molecular weight: about 50000 g/mol.

[0068] (Meth)acrylate polymer 3:

[0069] A copolymerization product of butyl methacrylate and methyl methacrylate as comonomers

[0070] Melting point: about 110 C.

[0071] Number average molecular weight: about 60000 g/mol.

[0072] Polyols:

[0073] Polyester Polyol 1:

[0074] Dynacoll 7130; a commercial product comprising diethylene glycol, 1,2-propylene glycol and adipic acid from Creanova.

[0075] Polyester Polyol 2:

[0076] Dynacoll 7240; a commercial product comprising neopentyl glycol and phthalic anhydride, 2-methyl-1,3-propanediol and isophthalic acid from Creanova.

[0077] Polyether Polyol:

[0078] N240, a commercial product comprising ethylene glycol and diethylene glycol from Shanghai Gao Qiao Petrochemical Co., Ltd.

[0079] Catalyst:

[0080] 2,2-dimorpholinodiethyl ether (DMDEE): a commercial product under the trade name of Lupragen N106 from BASF SE.

[0081] Adhesive promoter:

[0082] 3-aminopropyltriethoxysilane: a commercial product under the trade name of XIAMETER OFS-6011 from Dow Corning.

[0083] Thermoplastic polymer:

[0084] A maleic anhydride-modified polyethylene: a commercial product under the trade name of MODIC L100F from Mitsubishi Petrochemical Company, Ltd.

[0085] Preparation:

[0086] Reactive hot melt adhesives having the formulations shown in Table 1 (by weight) according to the present invention were prepared as Examples A-C, and E-I. In the preparation, all the polyols and (meth)acrylate polymers were added to melt and mix under vacuum until homogeneous and free of moisture. Then MDI was added and polymerization allowed to proceed with mixing under vacuum at 100 C. until reaction is complete after one hour. Finally, additives were added, and the resulting mixture was stirred at 100 C. for 10 minutes. The resulting reactive hot melt adhesive was then placed into a container under a dry nitrogen headspace to prevent exposure to moisture. A comparative example representing conventional reactive hot melt technology without (meth)acrylate polymer was prepared by the same process and is referred as Example D.

[0087] Over a period of time after bonding, the bonding strength of assembled parts at room temperature, the bonding strength of assembled parts at an elevated temperature, removability, and anti-aging performance were tested and the results are listed in Tables 2 and 3.

TABLE-US-00001 TABLE 1 Formulations of Examples A-I Example Example Example Example Example Example Example Example Example A B C D E F G H I Polyether polyol 44.0 44.0 44.0 64.0 44.0 44.0 44.0 64.0 64.0 (meth)acrylate polymer 1 64.2 59.1 50.5 (meth)acrylate polymer 2 63.2 62.4 61.7 (meth)acrylate polymer 3 69.1 39.1 Polyester polyol 1 128.6 128.6 128.6 128.6 Polyester polyol 2 128.6 128.6 128.6 128.6 128.6 Isocyanate 42.3 42.3 42.3 42.3 42.3 40.9 40.5 42.3 42.3 Catalyst 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Adhesion promoter 1.5 1.5 1.5 1 1.5 1 1 1.5 1.5 Thermoplastic polymer 1.0 1.8 2.5 Viscosity (cps @ 100 C., 3700 3900 4000 4200 4200 4600 4900 4550 4200 averaged)

TABLE-US-00002 TABLE 2 Bonding strength of assembled parts at room temperature Example Example Example Example Example Example Example Example Example A B C D E F G H I Stainless Steel-Glass (MPa) 6.5 6.1 5.3 5.1 6.1 6.0 5.7 6.9 5.8 PC/ABS-Glass (MPa) 6.1 5.8 5.1 4.8 6.3 5.2 5.6 5.3 5.4 Stainless Steel-Glass after 7 5.9 5.8 5.1 4.9 5.7 5.5 5.1 5.7 5.2 days 85 C., 85% RH aging

TABLE-US-00003 TABLE 3 Bonding strength of assembled parts at an elevated temperature and removability Example Example Example Example Example Example Example Example Example A B C D E F G H I PC/ABS-Stainless Steel 0.80 0.73 0.71 1.58 0.78 0.75 0.73 0.76 0.82 at 70-90 C. (MPa) Removability GOOD GOOD GOOD POOR GOOD GOOD GOOD GOOD GOOD PC/ABS-PC/ABS at 0.78 0.71 0.66 1.69 0.79 0.76 0.69 0.71 0.79 70-90 C. (MPa) Removability GOOD GOOD GOOD POOR GOOD GOOD GOOD GOOD GOOD

[0088] The results of viscosity of the resulting PU hot melt adhesives in Table 1 show that all of the adhesive examples according to the present invention are easy to apply and thus suitable for the use in part assembly.

[0089] It can be seen from Table 2 that all of the adhesive examples according to the present invention exhibit good bonding strength for the combinations of same or different type of substrate. The assembly parts can be firmly attached by such bonding strength at room temperature. In addition, compared to Example D, the inventive examples each possess better bonding strength at room temperature in each case.

[0090] As shown in Table 3, it can be surprisingly found that each of the bonding strength values at an elevated temperature of adhesive examples according to the present invention are significantly lower than that of Example D, which does not contain the specific (meth)acrylate used in the present invention. Accordingly, each of the adhesive examples according to the present invention possess better removability than that of the comparative Example D.

[0091] In addition, it can be found in Tables 2 and 3 that even after aging, the values of bonding strength at room temperature and elevated temperature of the adhesives according to the present invention are only slightly decreased, which demonstrates a good stability after storing over a long term.

[0092] Therefore, all these results demonstrate that with respect to the hot melt adhesive having specifically selected (meth)acrylates according to the present invention, the following advantages of property can be achieved: a high bonding strength at room temperature, a significantly low bonding strength at an elevated temperature, an appropriate viscosity for application, a good stability for long term using, an convenient application method and a versatile process, especially in the field of handheld devices and displays.