# US 2021/0340419 A1 · Process for the Production of Hot Melt Adhesives Having a Low Emission of Monomeric Isocyanates

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- Number: US 2021/0340419 A1
- Document ID: US20210340419A1
- Status: Published application
- Kind: A1
- Application number: 17/377,847
- Filed: 2021-07-16
- Published: 2021-11-04
- Earliest claimed: 2019-01-17
- Assignees: Henkel AG & Co. KGaA
- Applicants: Henkel AG & Co. KGaA
- Inventors: Uwe FRANKEN; Hans-Georg KINZELMANN
- Web page: https://patentgrep.com/patent/US20210340419A1

## CPC

- C09J 175/08: from polyethers
- C08G 18/12: using two or more compounds having active hydrogen in the first polymerisation step
- C08G 18/3206: {aliphatic}
- C08G 18/4018: {Mixtures of compounds of group C08G18/42 with compounds of group C08G18/48}
- C08G 18/4216: {from mixtures or combinations of aromatic dicarboxylic acids and aliphatic dicarboxylic acids and dialcohols}
- C08G 18/4252: {derived from polyols containing polyether groups and polycarboxylic acids}
- C08G 18/4825: {Polyethers containing two hydroxy groups (C08G18/4833 - C08G18/5096 take precedence)}
- C08G 18/4829: {Polyethers containing at least three hydroxy groups (C08G18/4833 - C08G18/5096 take precedence)}
- C08G 18/721: {Two or more polyisocyanates not provided for in one single group C08G18/73 - C08G18/80}
- C08G 18/7614: {containing only one aromatic ring}
- C08G 18/7621: {being toluene diisocyanate including isomer mixtures}
- C08G 18/7671: {containing only one alkylene bisphenyl group}
- C09J 5/06: involving heating of the applied adhesive
- C09J 175/04: Polyurethanes
- C09J 2475/00: Presence of polyurethane
- C09J: ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES (preparation of glue or gelatine C09H)
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS

## Abstract

The present invention refers to a process for the production of hot melt adhesives having a low emission of monomeric isocyanates upon heating wherein in a first step a polyurethane prepolymer is generated which is subsequently reacted with a chain extender. Further, the present invention refers to hot melt adhesives obtained by the inventive process.

## Claims

### Claim 1

A process for the production of a hot melt adhesive including a polyurethane prepolymer, comprising:
reacting the polyurethane prepolymer with a chain extender wherein the polyurethane prepolymer is obtained by;
(i) reacting 2,4′-toluene diisocyanate (2,4′-TDI) with a polyol and in a subsequent step
(ii) reacting methylene diphenyldiisocyanate (MDI) to the reaction mixture of step (i);
wherein the hot melt adhesive has an application temperature of 80 to 160° C. and the chain extender is selected from the group consisting of 1,3-butane diol, 1,2-propane diol, 2-ethyl-1-hexanol, diethylene glycol, tripropylene glycol, isosorbide, resorcinol, 1,4-dimethylol cyclohexane, and mixtures thereof.

### Claim 2 (depends on 1)

The process according to claim 1 wherein step (i) and (ii) of the process are conducted in the presence of a catalyst selected from the group consisting of metal organic compounds and amine-containing organic compounds.

### Claim 3 (depends on 1)

The process according to claim 1 wherein the polyol employed in step (i) has an average number molecular weight Mn of 100 to 10000 g/mol, determined by GPC.

### Claim 4 (depends on 1)

The process according to claim 1 wherein polyetherpolyols and/or polyesterpolyols are employed as the polyol in step (i).

### Claim 5 (depends on 1)

The process according to claim 1 wherein the polyol has a hydroxyl value (OH value) of 50 to 1500 mg KOH/g.

### Claim 6 (depends on 1)

The process according to claim 1 wherein the ratio of isocyanate groups to hydroxyl groups (NCO:OH) in step (i) and/or step (ii) is 1.1:1 to 4:1.

### Claim 7 (depends on 1)

The process according to claim 1 wherein the content of monomeric toluene diisocyanate in the hot melt adhesive is less than 0.02 wt.-%, based on the total weight of the hot-melt adhesive.

### Claim 8 (depends on 1)

The process according to claim 1 wherein the content of monomeric methylene diphenyl diisocyanate in the hot melt adhesive is less than 0.1 wt.-%, based on the total weight of the hot-melt adhesive.

### Claim 9 (depends on 1)

The process according to claim 1 wherein the hot melt adhesive has a softening point of more than 40° C., determined according to the method of ring & ball.

### Claim 10 (depends on 1)

A hot melt adhesive obtained by the process according to claim 1, wherein the content of monomeric toluene diisocyanate in the hot melt adhesive is less than 0.02 wt.-%, based on the total weight of the hot-melt adhesive.

### Claim 11 (depends on 10)

The hot melt adhesive according to claim 10 wherein the content of monomeric methylene diphenyl diisocyanate in the hot melt adhesive is less than 0.1wt.-%, based on the total weight of the hot-melt adhesive.

### Claim 12 (depends on 10)

The hot melt adhesive according to claim 10, wherein the hot melt adhesive shows an increase in viscosity while being kept at application temperature for a period of 2 hours of no more than 20%.

### Claim 13 (depends on 10)

The hot melt adhesive according to claim 10, wherein an emission rate of toluene diisocyanate is less than 2 ppb.

### Claim 14

A hot melt adhesive comprising a chain extended polyurethane prepolymer, wherein the chain extended polyurethane prepolymer is the reaction product of a polyurethane prepolymer and a chain extender, wherein:
the polyurethane prepolymer is the reaction product of 2,4′-toluene diisocyanate (2,4′-TDI), a polyol and methylene diphenyl diisocyanate (MDI);
the chain extender is selected from the group consisting of 1,3-butane diol, 1,2-propane diol, 2-ethyl-1-hexanol, diethylene glycol, tripropylene glycol, isosorbide, resorcinol, 1,4-dimethylol cyclohexane, and mixture thereof; and
the hot melt adhesive has an application temperature of 80 to 160° C., the content of monomeric toluene diisocyanate is less than 0.02 wt.-%, based on the total weight of the hot-melt adhesive and the content of monomeric methylene diphenyl diisocyanate in the hot melt adhesive is less than 0.1 wt.-%, based on the total weight of the hot-melt adhesive.

### Claim 15 (depends on 14)

The hot melt adhesive of claim 14 wherein the polyurethane prepolymer is the reaction product of a sequence of reaction steps comprising (i) a reaction of the 2,4′-toluene diisocyanate (2,4′-TDI) and the polyol in a first step to form an intermediate and (ii) a reaction of the intermediate with methylene diphenyl diisocyanate (MDI) to form the polyurethane prepolymer.

### Claim 16 (depends on 14)

The hot melt adhesive of claim 14 wherein the polyurethane prepolymer is the reaction product of a sequence of reaction steps comprising (i) a reaction of a molar excess of 2,4′-toluene diisocyanate (2,4′-TDI) and the polyol in a first step to form an intermediate and (ii) a reaction of the intermediate with a molar excess of methylene diphenyl diisocyanate (MDI) to form the polyurethane prepolymer.

### Claim 17 (depends on 14)

The hot melt adhesive of claim 14 wherein the polyurethane prepolymer is the reaction product of a sequence of reaction steps comprising (i) a reaction of 2,4′-toluene diisocyanate (2,4′-TDI) and a molar excess of the polyol in a first step to form an intermediate and (ii) a reaction of the intermediate with a molar excess of methylene diphenyl diisocyanate (MDI) to form the polyurethane prepolymer.

### Claim 18 (depends on 14)

The hot melt adhesive according to claim 14, wherein the chain extended polyurethane prepolymer comprises NCO moieties.

### Claim 19 (depends on 14)

The hot melt adhesive according to claim 14, having an emission rate of toluene diisocyanate is less than 2 ppb.