Low-Viscosity, Rapid Curing Laminating Adhesive Composition

Abstract

The invention relates to a 2-component polyurethane adhesive, in particular for laminating films, wherein the PU adhesive, based on the total weight of the laminating adhesive composition, (a) contains as resin component at least one NCO-terminated polyurethane pre-polymer having a content of at least 40% by weight of diphenylmethandiisocyanate (MDI), wherein the MDI is 4,4-diphenylmethandiisocyanate or a mixture thereof with 2,4-diphenylmethandiisocyanate, and (b) contains as hardener component a polyol mixture comprising at least three different polyols. The invention further relates to the use of the adhesive for adhesively bonding films, to methods for producing composite films, and to composite films bonded by means of the described adhesive.

Claims

1. A polyurethane 2-component laminating adhesive composition comprising, based on the total weight of the laminating adhesive composition, (a) a resin component including at least one NCO-terminated polyurethane prepolymer prepared by reacting at least 40 wt % diphenylmethane diisocyanate (MDI) with one or more polyols, wherein the MDI is 4,4-diphenylmethane diisocyanate or a mixture thereof with 2,4-diphenylmethane diisocyanate, and (b) a curing component including a mixture comprising at least three different polyols, wherein the 2-component laminating adhesive composition has a polyester content of less than 10 wt. %, based on the total weight of the adhesive composition.

2. The laminating adhesive composition according to claim 1, wherein one of the at least three different polyols of the curing component is a triol, to which alkylene oxide (AO) is added and which has a molecular weight M.sub.w of less than 700 g/mol, and which is contained in the curing component at 5 to 90 wt. %

3. The laminating adhesive composition according to claim 2, wherein the one of the at least three different polyols of the curing component is a propylene oxide-based triol having a molecular weight M.sub.w of 400 to <700 g/mol.

4. The laminating adhesive composition according to claim 1, wherein one of the at least three different polyols of the curing component is an aliphatic, di- or polyvalent alcohol, having a molecular weight of <150 g/mol and/or a hydroxyl number of 700 to 2000 mgKOH/g, which is contained in the curing component at 0.5 to 10 wt. %

5. The laminating adhesive composition according to claim 1, wherein one of the at least three different polyols of the curing component is selected from the group consisting of ethylene glycol, propylene glycol, butanediol-1,4, pentanediol-1,5, hexanediol-1,6, heptanediol-1,7, octanediol-1,8, glycerol, trimethylolpropane and pentaerythritol.

6. The laminating adhesive composition according to claim 1, wherein one of the at least three different polyols of the curing component is (a) a triol, to which alkylene oxide (AO) is added, and which has a molecular weight M.sub.w of 700 to 1200 g/mol, or (b) castor oil which is contained in the curing component at 5 to 80 wt. %.

7. The laminating adhesive composition according to claim 1, wherein, the NCO:OH ratio of resin component to curing component is less than 1.4.

8. The laminating adhesive composition according to claim 1, wherein the curing component (b) of the laminating adhesive composition contains: (1) at least one triol based on glycerol or trimethylol propane (TMP) to which propylene oxide (PO) is added, and which has a molecular weight M.sub.W of less than 700 g/mol, (2) at least one aliphatic 2- to 4-valent monomeric alcohol; and (3) at least one triol based on glycerol or trimethylolpropane (TMP) to which propylene oxide (PO) is added and which has a molecular weight M.sub.W of more than 700 g/mol or castor oil.

9. The laminating adhesive composition according to claim 1, wherein: (a) the composition further contains at least one catalyst; (b) the composition has a viscosity of 500 to 5000 mPas at a temperature of 40 C.; (c) the composition is substantially free of organic solvents, or (d) any combination of (a), (b) and (c).

10. Cured reaction products of the laminating adhesive composition according to claim 1.

11. A method for producing composite films, comprising: providing a first film and a second film; wherein the films can be identical or different plastics; providing the resin component of claim 1; providing the curing component of claim 1; mixing the resin component and the curing component at a predetermined NCO:OH ratio to form a laminating adhesive; applying the laminating adhesive over some portion of a surface of the first film; and disposing the second film over the adhesive on the surface of the first film.

12. The method according to claim 11, wherein the laminating adhesive composition is applied in an amount of 1 to 5 g/m.sup.2 to the surface portion of the first film.

13. The method according to claim 11 wherein the mixed laminating adhesive has a viscosity of 500 to 900 mPas at 40 C. and the composite film produced using the mixed adhesive has less than 10 parts per billion of primary aromatic amines (PAA) after 5 days of curing.

14. A composite film produced according to the method of claim 11.

15. A package, comprising a composite film produced by the method of claim 11 sealingly disposed around a food product or medicament.

Description

EXAMPLES

Example 1

According to the Invention

Resin Base:

[0077] NCO-terminated MDI prepolymer having an NCO content of 12-14 wt. % and an NCO:OH ratio of 3.9:1, consisting of

[0078] 50 wt. % of 4,4-diphenylmethane diisocyanate (MDI); 5 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 25 wt. % polypropylene glycol (PPG) having Mw=1000 g/mol; 10 wt. % polypropylene glycol (PPG) having Mw=2000 g/mol; 10 wt. % hexane-1,6-diisocyanate (HDI) trimer.

Curing Agent:

[0079] Polyol mixture having an OH value of 330-370 mgKOH/g and a functionality f=3, consisting of

[0080] 5 wt. % trimethylolpropane; 70 wt. % trifunctional polypropylene glycol (PPG) having Mw=450 g/mol; 25 wt. % castor oil.

[0081] Mixing ratio of resin:curing agent=100:40 parts by weight

Example 2

According to the Invention

Resin Base:

[0082] NCO-terminated MDI prepolymer having an NCO content of 12-14 wt. % and an NCO:OH ratio of 3.9:1, consisting of

[0083] 50 wt. % of 4,4-diphenylmethane diisocyanate (MDI); 5 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 25 wt. % polypropylene glycol (PPG) having Mw=1000 g/mol; 10 wt % polypropylene glycol (PPG) having Mw=2000 g/mol; 10 wt % hexane-1,6-diisocyanate (HDI) trimer.

Curing Agent:

[0084] Polyol mixture having an OH value of 270-310 mgKOH/g and a functionality f=3, consisting of

[0085] 5 wt. % trimethylolpropane; 30 wt. % trifunctional polypropylene glycol (PPG) having Mw=450 g/mol; 65 wt. % castor oil.

[0086] Mixing ratio of resin:curing agent=100:50 parts by weight

Example 3

According to the Invention

Resin Base:

[0087] NCO-terminated MDI prepolymer having an NCO content of 11.5-13.5 wt. % and an NCO:OH ratio of 3.9:1, consisting of

[0088] 50 wt. % 4,4-diphenylmethane diisocyanate (MDI); 5 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 25 wt. % polypropylene glycol (PPG) having Mw=1000 g/mol; 10 wt. % polypropylene glycol (PPG) having Mw=2000 g/mol; 10 wt. % toluene diisocyanate (TDI) prepolymer*.

Curing Agent:

[0089] Polyol mixture having an OH value of 330-370 mgKOH/g and a functionality f=3, consisting of

[0090] 5 wt % trimethylolpropane; 70 wt. % trifunctional polypropylene glycol (PPG) having Mw=450 g/mol; 25 wt. % castor oil.

[0091] *TDI prepolymer: Reaction product of 2,4-TDI with a polyether diol having Mw=400 . . . 1000, demonomerized

[0092] Mixing ratio of resin:curing agent=100:40 parts by weight

Example 4

Comparative Example

Resin Base:

[0093] NCO-terminated MDI prepolymer having an NCO content of 12.0-13.5 wt. % and an NCO:OH ratio of 3.1:1, consisting of

[0094] 55 wt. % 4,4-diphenylmethane diisocyanate (MDI); 15 wt. % polypropylene glycol (PPG) having Mw=1000 g/mol; 15 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 15 wt. % bifunctional polyester*.

Curing Agent:

[0095] Polyol mixture having an OH value of 155-175 mgKOH/g and a functionality f=3, consisting of

[0096] 100 wt. % castor oil.

[0097] *Polyester based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol.

[0098] Mixing ratio of resin:curing agent=100:75 parts by weight

Example 5

Comparative Example

Resin Base:

[0099] NCO-terminated MDI prepolymer having an NCO content of 13.0-15.0 wt % and an NCO:OH ratio of 3.7:1, consisting of 51 wt. % 4,4-diphenylmethane diisocyanate (MDI); 10 wt % 1,6-hexane diisocyanate (HDI) trimer; 13 wt % polypropylene glycol (PPG) having Mw=1000 g/mol; 13 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 13 wt. % bifunctional polyester*.

Curing Agent:

[0100] Polyol mixture having an OH value of 200-230 mgKOH/g and a functionality f2.3, consisting of

[0101] 75 wt % bifunctional polyester; 22 wt. % polypropylene glycol (PPG) trial having Mw=450 g/mol; 3 wt. % trimethylolpropane.

[0102] *Polyester based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol.

[0103] Mixing ratio of resin:curing agent=100:65 parts by weight

Example 6

Comparative Example

Resin Base:

[0104] NCO-terminated MDI prepolymer having an NCO content of 11.0-13.0 wt. % and an NCO:OH ratio of 2.6:1, consisting of

[0105] 30 wt % 4,4-diphenylmethane diisocyanate (MDI); 5 wt. % toluene diisocyanate (TDI); 10 wt. % 1,6-hexane diisocyanate (HDI) trimer; 15 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 20 wt. % polypropylene glycol (PPG) having Mw=1000 g/mol; 10 wt. % polypropylene glycol (PPG) having Mw=2000 g/mol; 10 wt. % bifunctional polyester*.

[0106] *Polyester based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol.

Curing Agent:

[0107] Polyol mixture having an OH value of 240-270 mgKOH/g and a functionality f2.3, consisting of

[0108] 15 wt. % bifunctional polyester A*; 50 wt. % bifunctional polyester B**; 10 wt. % polypropylene glycol (PPG) having Mw=400 g/mol; 20 wt. % polypropylene glycol (PPG) triol having Mw=450 g/mol; 5 wt. % trimethylolpropane.

[0109] Mixing ratio of resin:curing agent=100:45 parts by weight

[0110] *Polyester A based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol.

[0111] **Polyester B based on isophthalic acid, adipic acid, diethylene glycol.

Example 7

Comparative Example

Resin Base:

[0112] NCO-terminated TDI prepolymer having an NCO content of 9.0-10.5 wt. %, consisting of 100 wt. % toluene diisocyanate (TDI) prepolymer*.

Curing Agent:

[0113] Polyester mixture having an OH value of 155-175 mgKOH/g and a functionality f=2.5, consisting of

[0114] 100 wt. % polyester C***

[0115] *TDI prepolymer: Reaction product of 2,4-TDI with a polyether diol having Mw=400 . . . 1000, demonomerized.

[0116] ***Polyester C based on isophthalic acid, diethylene glycol, castor oil.

[0117] Mixing ratio of resin:curing agent=100:55 parts by weight

Composite Film:

[0118] The composite films are produced using a Super Combi 2000 laminator. The adhesive composition is applied in an amount of 2 g/m.sup.2 to one of the films to be bonded (OPA or metOPP) and this film is then laminated under pressure with the second film (PE or OPP). The effective roller pressure of the laminating unit corresponds to a force of up to 200 N (20 kg).

Bond Adhesion:

[0119] The bond adhesion is determined by means of a tensile testing machine from Instron (Instron 4301) on the basis of the DIN 53357 standard after 14 days of curing at room temperature. For this purpose, test strips of the composite film (sample width of 15 mm) are clamped between clamping jaws and then pulled apart at a pull-off speed of 100 m/min, a pull-off angle of 90 and a pull-off length of 5 to 10 cm. The mean value of a triple determination of the maximum applied force in relation to the sample width of 15 mm is given.

Primary Aromatic Amines (PAA) Content:

[0120] The time to wait after bonding the films until the adhesive is considered to be substantially migration-free is indicated. This is the case when the content of primary aromatic amines (PAA) is less than 0.2 pg/100 ml of filling material. 3% acetic acid is used as filling material or filling material simulant. The packaging used is an OPA/PE laminate which is produced by means of the adhesive and encloses the filling material by means of heat sealing, the PE side forming the inside of the packaging and the inside of the sealing seam. The content of primary aromatic amines is determined by photometry according to 64 of the Food, Commodities and Feed Code of the Federal Republic of Germany (LFGB) according to the method L 00.006.

Composite Materials:

[0121] OPA: oriented polyamide [0122] PE: polyethylene [0123] PET: polyethylene terephthalate [0124] OPP: oriented polypropylene [0125] metOPP: metallized OPP (OPP coated with aluminum)

TABLE-US-00001 TABLE 1 Experimental parameters Parameter Widest range Narrowest range 1 Mixing viscosity at <1000 mPas 600-900 mPas application temperature 2 Pot life/viscosity increase <5000 mPas after 30 min <4500 mPas after 30 min <25,000 mPas after 60 <20,000 mPas after 60 3 Run time: Super Combi machine Super Combi machine Experimental trial on >300 m/min without >300 m/min without lamination equipment misting misting 4 Increase in bond strength: >3 N/15 mm after 1 day PET tear after 1 day PET/PE 5 Crease test No delamination after 1 No delamination after 1 day day 6 PAA PAA-free after <5 days PAA-free after <5 days