UV-curing hot melt adhesive containing low content of oligomers

Abstract

A reactive hot melt adhesive comprising a blend of a (meth)acrylate polymer, a polyurethane polymer containing (meth)acrylate groups and a polyurethane prepolymer containing NCO-groups wherein the content of low molecular weight (meth)acrylate urethanes is less than 1 wt % of the adhesive. The adhesive provides a fast and improved green strength during application.

Claims

1. A reactive hot melt adhesive comprising a blend of a (meth)acrylate polymer, a polyurethane polymer containing (meth)acrylate groups and a polyurethane prepolymer containing NCO-groups wherein the content of low molecular weight (meth)acrylate urethanes is less than 1 wt % of the adhesive.

2. A hot melt adhesive according to claim 1, wherein the (meth)acrylate polymer has a molecular weight (M.sub.N) of more than 5000 g/mol.

3. A hot melt adhesive according to claim 1, wherein the adhesive comprises 5 to 45 wt % of the (meth)acrylate polymer, the (meth)acrylate polymer has a molecular weight (M.sub.N) of more than 5000 g/mol and the (meth)acrylate polymer is non reactive.

4. A hot melt adhesive according to claim 1, wherein the polyurethane polymer containing (meth)acrylate groups comprises about 70 to 100 mol % of (meth)acrylate groups and 0 to 30 mol-% of remaining NCO-groups.

5. A hot melt adhesive according to claim 4, wherein the polyurethane polymer containing (meth)acrylate groups is prepared by reaction of a NCO-containing PU-prepolymer comprising less than 1 wt-% of monomeric diisocyanates with OH-alkyl-substituted (meth)acrylate esters in a ratio OH:NCO from 0.7:1 to 1.01:1.

6. A hot melt adhesive according to claim 4, wherein the adhesive comprises 5 to 50 wt % of the polyurethane polymer containing (meth)acrylate groups.

7. A hot melt adhesive according to claim 1, wherein the amount of the polyurethane prepolymer is from 10 to 50 wt-% of the adhesive composition.

8. A hot melt adhesive according to claim 1, optionally further comprising additives, fillers, stabilizers, tackifiers, plasticizers, adhesion promotors or additional non-reactive polymers.

9. A hot melt adhesive according to claim 1, having a viscosity of from 2000 to 20000 mPas at 100 C., measured according to Brookfield, Digital Viscometer RVT, EN ISO 2555, spindle 27, 10 rpm.

10. A hot melt adhesive according to claim 1, having an NCO-value of 2 to 12 wt %.

11. A process to manufacture a hot melt adhesive according to claim 1, comprising: preparing a low monomer content PU prepolymer; reacting the prepared low monomer content PU prepolymer with at least one OH-containing alkyl(meth)acrylate monomer in an OH:NCO ratio from 0.7:1 to 1.01:1 to form a PU polymer; and blending the PU polymer with an NCO-containing PU-prepolymer and a (meth)acrylate polymer.

12. A process to manufacture according to claim 11, wherein the process is carried out at a temperature of 70 to 120 C.

13. A process to manufacture according to claim 12, wherein the (meth)acrylate polymer is free of OH and/or NH groups.

14. A process to bond substrates, comprising; heating the hot melt adhesive according to claim 1 to a molten state; applying the molten hot melt adhesive onto a first substrate; exposing the disposed hot melt adhesive to ultraviolet radiation to initiate curing of that hot melt adhesive; and disposing a second substrate into contact with the disposed hot melt adhesive in a non-solidified state.

15. A process according to claim 14, wherein the adhesive is applied to the first substrate in an amount of 10 to 500 g/m.sup.2.

16. Cured reaction products of the hot melt adhesive according to claim 1.

Description

EXAMPLES

(1) PU-Polymer Containing Bound (Meth)Acrylate Groups (Polymer A):

(2) 10.0% by weight of 2-hydroxyethyl methacrylate and 90.0 wt.-% of demonomerized NCO terminated prepolymer (Desmodur VP LS 2397: a linear prepolymer based on polypropylene ether glycol and diphenylmethane diisocyanate (MDI), NCO content: 5.8 wt % measured according to ISO 11909, monomer content: less than 0.15 wt % measured according to DIN 55672-1) were charged into a steel reactor equipped with a stirrer and thermometer and dried at 80 C. for 7 hours. The resulting prepolymer was placed into a container under a dry nitrogen headspace to prevent the exposure to moisture. Due to the low monomer content of less than 0.15 wt % in the NCO terminated prepolymer, the content of low molecular weight (meth)acrylate urethanes as reactions products of residual monomeric diisocyanate (MDI) and 2-hydroxyethyl methacrylate is less than 1 wt % in the PU polymer.

(3) Polymethacrylate (Polymer B):

(4) The poly(meth)acrylate is a polymerization product of butyl methacrylate, methyl methacrylate and methacrylic acid as copolymer.

(5) MFI is 60 g/10 min at 150 C.

(6) Tg is about 59 C.

(7) Molecular weight (M.sub.N) is about 8000 g/mol.

(8) Polyol 1:

(9) Dynacoll 7360, a commercial polyester polyol, molecular weight (M.sub.N) about 3500 g/mol, hydroxyl value (OHV) about 30 mg KOH/g solid (measured according to DIN 53240).

(10) Polyol 2:

(11) PPG 2000, OHV about 56 mg KOH/g solid (measured according to DIN 53240).

(12) Polyol 3:

(13) Is a polyester polyol based on diethylene glycol and phthalic acid anhydride

(14) OH-value about 70 mg KOH/g solid (measured according to DIN 53240), equivalent weight about 800 g/mol.

(15) Adhesive, General Procedure:

(16) Polymer A is produced as above. Polymer B is a commercial product.

(17) The adhesive is prepared by blending polymer A, polymer B, polyol 1, polyol 2 and 3 as melt and mixed under vacuum.

(18) Then MDI was added and polymerization allowed to proceed with mixing under vacuum at 120 C. for 1 hour until the reaction is complete. Finally additives were added and the mixing was continued for another 10 minutes.

(19) The content of low molecular weight (meth)acrylate urethanes is less than 1 wt % (measured according to DIN 55672-1).

(20) TABLE-US-00001 TABLE 1 Adhesives of sample A, B, C and D Sample Sample Sample Sample D A B C comparative Polyol 2 44.0 39.0 34.0 64.0 Polymer A 20.0 25.0 30.0 Polymer B 64.2 64.2 64.2 64.2 Polyol 1 77.3 77.3 77.3 77.3 Polyol 3 51.3 51.3 51.3 51.3 MDI 42.3 40.9 40.5 42.3 Catalyst DMDEE 0.3 0.3 0.3 0.3 Silane coupling agent A189 1.5 1.5 1.5 1.5 Photoinitiator TPO-L 3.0 3.0 3.0 Viscosity (mPas @100 C.) 3700 3900 4000 4200

(21) TABLE-US-00002 TABLE 2 Bond strength and open time of sample A, B, C and D Sample Sample Sample Sample A B C D Stainless Steel-Glass (MPa) 1.23 1.5 1.38 0.58 PC/ABS-Glass 10 min (MPa) 1.22 1.28 1.6 0.55 PC/ABS-Stainless Steel (MPa) 0.89 1.37 1.38 0.38 PC/ABS-PC/ABS (MPa) 1.26 1.22 1.25 0.42 Open time (minutes, after UV 4.0 4.0 3.5 5.0 radiation)

(22) The bond strength after 10 min (also referred to as green strength) and the open time were tested and listed in Table 2. The bond strength is determined by the cross-tensile pull method (according to STM-831). For the determination of the open time the test specimen will be assembled at different waiting times after the application of the adhesive. The bond strength will be measured 24 h after cure as a function of the waiting time. The waiting time after which the bond strength is significantly decreasing is defined as the open time.

(23) All these data show that high initial strength and convenient application conditions can be achieved using this UV dual cure PUR hot melt.

(24) The comparative example D shows less green strength.

(25) Other examples are prepared according to the same general procedure.

(26) TABLE-US-00003 TABLE 3 Adhesives of sample D, E, F and G Sample Sample Sample Sample D E F G comparative Polyol 2 44.0 44.0 44.0 64.0 Polymer A 20.0 20.0 20.0 Polyol 1 77.3 77.3 77.3 77.3 Polyol 3 51.3 51.3 51.3 51.3 MDI 42.3 40.9 40.5 42.3 Thermoplastic non reactive 1.0 1.8 2.5 polymer Polymer B 63.2 62.4 61.7 64.2 Catalyst DMDEE 0.3 0.3 0.3 0.3 Silane coupling agent 1.5 1.5 1.5 1.5 Photoinitiator 3.0 3.0 3.0 Viscosity (cps @100 C.) 4200 4800 5800 4200

(27) TABLE-US-00004 TABLE 4 Bond strength and open time of sample D, E, F and G Sample Sample Sample Sample E F G D Stainless Steel-Glass (MPa) 1.25 1.27 1.38 0.58 PC/ABS-Glass (MPa) 1.31 1.31 1.54 0.55 PC/ABS-Stainless Steel (MPa) 1.12 1.24 1.28 0.38 PC/ABS-PC/ABS (MPa) 1.19 1.21 1.27 0.42 Open time (min, after UV 3.0 3.0 2.5 5.0 radiation)

(28) Additionally examples are prepared to show the effect of the invention.

(29) TABLE-US-00005 TABLE 5 Formulation, bond strength and open time of sample D, H and I Sample D Sample H Sample I comparative Polyol 2 44.0 44.0 64.0 Polymer A 20.0 20.0 Polyol 1 77.3 77.3 77.3 Polyol 3 51.3 51.3 51.3 MDI 42.3 42.3 42.3 Thermoplastic non reactive 1.0 1.0 polymer. Polymer B 63.2 63.2 64.2 Catalyst DMDEE 0.3 0.3 0.3 Silane coupling agent A189 1.5 1.5 1.5 Speedcure 84 0.75 1.5 Speedcure TPO-L 2.25 1.5 Viscosity (cps @100 C.) 4200 4400 4200 Stainless Steel-Glass (MPa) 1.30 1.10 0.58 PC/ABS-Glass (MPa) 1.26 0.91 0.55 PC/ABS-Stainless Steel (MPa) 1.22 0.86 0.38 PC/ABS-PC/ABS (MPa) 1.32 1.02 0.42 Open time (min, after UV 2.5 2.0 5.0 radiation)

(30) The adhesives according to the invention have a low viscosity. The application temperature is low.

(31) It is shown, that the adhesives have an improved open time and better adhesion according to the tests.