Polyurethane-based binder system

Abstract

The present invention relates to a binder system which contains an isocyanate-terminated polyurethane prepolymer as the resin component and a polyol mixture as the curing agent, said polyol mixture containing at least one alkoxylated diamine. The invention also relates to the use of the binder system as an adhesive/sealing material, in particular as a laminating adhesive for food packaging.

Claims

1. A two component, low migrate laminating adhesive for food packaging composite film, comprising: (i) a resin component comprising at least one isocyanate-terminated polyurethane prepolymer that is the reaction product of a mixture comprising a monomeric polyisocyanate and a resin component polyol, wherein the resin component has an aromatic polyisocyanate monomer content of 10 wt. % to 40 wt. % based on the total weight of the resin component and the resin component polyol is not a polyester polyol containing isophthalic acid moieties and is not a tertiary amino group containing polyether polyol; and (ii) a curing component comprising 0.5 wt. % to 20 wt. % at least one alkoxylated diamine based on the weight of the curing component and at least one curing component polyol, wherein the curing component polyol is not a polycondensation product of an aromatic phthalic acid, is not a polyester polyol containing isophthalic acid moieties, and is not polyester polyol of oleochemical origin; wherein the binder system is free of filler and free of solvent.

2. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the at least one alkoxylated diamine is a polyether polyol that, using diamine as a starter, is a polymerization product of ethylene oxide and/or propylene oxide.

3. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the at least one alkoxylated diamine is an ethoxylated alkylene diamine and/or a propoxylated alkylene diamine.

4. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the at least one alkoxylated diamine is a polyether polyol that, using diamine as a starter, is a polymerization product of ethylene oxide and/or propylene oxide, the diamine being selected from ethylene diamine, N,N-dimethylethylene diamine, N, N′-dimethylethylene diamine, propylene diamine, tetramethylene diamine, hexamethylene diamine, 2,4-toluene diamine, 2,6-toluene diamine, diphenylmethane-2,2′-diamine, diphenylmethane-2,4′-diamine, diphenylmethane-4,4′-diamine, isophorone diamine, dicyclohexylmethane-4,4′-diamine and xylylene diamine.

5. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the at least one alkoxylated diamine is a compound of Formula 1:
H—[O—CHR—CH.sub.2].sub.m—NR′—(CH.sub.2).sub.n—NR′—[CH.sub.2—CHR—O].sub.m—H  (1) wherein each R is independently selected from H, CH.sub.3 and CH.sub.2-CH.sub.3; each R′ is independently selected from H and —[CH.sub.2—CHR—O].sub.m—H; each m, independently, is a whole number from 1 to 10; n is a whole number from 1 to 10.

6. The low migrate laminating adhesive for food packaging composite film according to claim 5, wherein the at least one alkoxylated diamine is a propoxylated or ethoxylated/propoxylated ethylene diamine having 2 to 8 units of propylene oxide/ethylene oxide for every unit of ethylene diamine.

7. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the curing component contains 1 wt. % to 10 wt. % of the at least one alkoxylated diamine based on the curing component.

8. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the curing component polyol comprises a di- and/or tri-functional polyether polyol.

9. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the resin component polyol comprises a polyester polyol and polypropylene glycol, and the monomeric polyisocyanate comprises diphenylmethane diisocyanate (MDI).

10. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the isocyanate-terminated polyurethane prepolymer does not include a polyether segment in the prepolymer backbone.

11. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the mixture comprises up to 30 wt. % of monomeric polyisocyanate based on the total weight of the resin component.

12. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein the curing component comprises 0.5 wt. % to 20 wt. % of the at least one alkoxylated diamine and 80 wt. % to 99.5 wt. % of the polyol.

13. A composite film, comprising: a plastic first film having a first film surface; a second film having a second film surface; and cured reaction products of the mixed low migrate laminating adhesive for food packaging composite film of claim 1, bonding the first film surface to part or all of the second film surface.

14. The composite film according to claim 13, wherein the second film is a plastic film.

15. The low migrate laminating adhesive for food packaging composite film according to claim 1, wherein cured reaction products of the binder system have a primary aromatic amine content of <0.2 μg when measured in accordance with section 64 of the LFGB.

16. The two component, low migrate laminating adhesive for food packaging composite film of claim 1 being free of catalyst.

17. The cured reaction products of the two component, low migrate laminating adhesive for food packaging composite film of claim 1.

Description

EXAMPLES

(1) Test Series 1:

(2) Example 1a (not according to the invention):

(3) Resin component: Loctite Liofol LA 7731 (MDI-terminated polyether/polyester PU prepolymer, available from Henkel)

(4) Curing component: Loctite Liofol LA 6038 (polyol mixture made from dipropylene glycol (DPG) and trifunctional polyether polyols having predominantly secondary hydroxyl end groups; available from Henkel).

(5) Example 1b (according to the invention): as in Example 1a, except that the 5 wt % DPG in the curing component is exchanged for Voranol R800 (OH number of 780-820 mg KOH/g; oxypropylene adduct of ethylene diamine, available from The Dow Chemical company)

(6) Example 1c (according to the invention): as in Example 1a, except that the 5 wt % DPG in the curing component is exchanged for Voranol R640 (OH number of 615-665 mg KOH/g; oxypropylene adduct of ethylene diamine, available from The Dow Chemical company)

(7) Example 1b (according to the invention): as in Example 1a, except that the 5 wt % DPG in the curing component is exchanged for Voranol RA500 (OH number of approx. 500 mg KOH/g; oxypropylene adduct of ethylene diamine, available from The Dow Chemical company)

(8) Example 1e (not according to the invention): as in Example 1a, except that the 0.05 wt % polyether polyol in the curing component is exchanged for dioctyltin dilaurate (DOTL)

(9) Example 1f (not according to the invention): as in Example 1a, except that the 0.1 wt % polyether polyol in the curing component is exchanged for 1,4-Diazabicyclo[2.2.2]octane (DABCO)

(10) Example 1g (not according to the invention): as in Example a, except that the 1 wt % polyether polyol in the curing component is exchanged for triethanolamine

(11) Test Series 2:

(12) Example 2a (not according to the invention): as in Example 1a

(13) Example 2b (according to the invention): as in Example 1d

(14) Example 2c (not according to the invention): as in Example 1b

(15) Example 2d (not according to the invention): as in Example 1a, except that the 5 wt % DPG in the curing component is exchanged for Desmophen V 155 (oxypropylene adduct of triethanolamine, available from Bayer MaterialScience)

(16) Example 2e (not according to the invention): as in Example 1a, except that the 5 wt % DPG in the curing component is exchanged for TIPA (triisopropanolamine)

(17) Example 2f (not according to the invention): as in Example 1a, except that, instead of the resin component, a prepolymer made from a tertiary amine-initiated polyetherpolyol (Voranol Voractiv VM 779, available from The Dow Chemical company), polypropylene glycol (PPG2000), and 2,4′-/4,4′-MDI (Desmodur 2460, available from Bayer MaterialScience) are used.

(18) An OPA/PE structure laminated with 1.8 g/m.sup.2 adhesive was used in order to measure PAA in the filler simulant (3% acetic acid) using the BfR method. The results are shown in Table 1 and indicated as the amount of PAA in pg/100 mL of filler simulant. The target value is <2 μg PAA/100 mL filler simulant. Variations in the testing procedure, for example in the quality of the films and/or the weights of adhesive applied, may have had an influence on the PAA values measured. For this reason, absolute PAA values should be compared only within a test series, hence in the present case only within test series 1 and within test series 2.

(19) Moreover, the interlayer adhesion (VH) is determined in accordance with the DIN ISO 53357 standard. Using a strip cutter, 15 mm-wide strips of the composite were cut in order to determine the interlayer adhesion. The composite was then separated by hand or on a hot sealing jaw edge. In the case the composites have cured, it may be helpful to insert one end of the composite strip into ethyl acetate. The measurement was performed using a universal tensile testing machine, force range 0-20 N (from Instron or Zwick, for example). The composite strips that were previously separated were clamped in, and the tensile testing machine was started up at a draw-off rate of 100 mm/min; the draw-off angle was 90° (to be maintained manually) and the draw-off length was 5-10 cm (depending on the range of fluctuation). The result is provided as an interlayer adhesion in N/15 mm, and the indicated value is the average of three measurements. In case of a tear in the film, the maximum value is indicated.

(20) Sealed seam strength (SNH) is determined in accordance with the DIN ISO 55529 standard. For this purpose, the OPA/PE structure was first sealed against itself (PE on PE) at 150° C. for 1 sec. while applying a force of 650 N against a surface 1 cm×15 cm. The sealed seam strength was then determined using a universal tensile testing machine, force range 0-20 N (from Instron or Zwick, for example). Using a strip cutter, 15 mm-wide strips of the composite were then cut, the composite strips were clamped in, and the tensile testing machine was started up at a draw-off rate of 100 mm/min; the draw-off angle was 90° (to be maintained manually) and the draw-off length was 5-10 cm (depending on the range of fluctuation). The result is provided as a sealed seam strength in N/15 mm, and the indicated value is the average of three measurements.

(21) The viscosity (in mPas) was determined 60 minutes after mixing and at 40° C.

(22) The NCO content of the resin (in wt %) and the OH number of the curing agent (in mg KOH/g) were also determined.

(23) The mixture ratio is indicated in parts by mass (g/g).

(24) Table 1 shows an overview of the measured values.

(25) TABLE-US-00001 TABLE 1 NCO OH Ratio of SNH content number resin to PAA (BfR) (N/15 VH of of curing curing [μg/100 mL] mm) (N/15 mm) Viscosity resin agent agent Example 2 d 4 d 7 d 7 d 7 d 14 d (mPas) (%) (mg KOH/g) (g/g) 1a 24.82 3.82 0.99 60* 5.8*7 6.2* 4425 13 246 100:48 1b 17.97 2.75 0.50 62* .0* 7.0* 3750 13 244 100:50 1c 8.31 0.66 0.18 55* 6.7* 7.0* 10900 13 236 100:55 1d 5.76 0.66 0.19 54* 6.9* 6.8* 9500 13 229 100:55 1e 17.90 0.92 0.48 50* 5.9* 6.8* *** 13 246 100:48 1f 25.05 — 0.89 57* 5.9* 6.1* 15050 13 252 100:48 1g 25.60 — 0.85 52* 5.0* 5.3* 10825 13 255 100:50 2a 8.11 0.27 0.07 63* 7.4* 6.8* 4425 13 246 100:48 2b 0.86 0.10 51* 7.6* 6.2* 9500 13 229 100:55 2c 1.84 0.14 0.06 65* 7.2* 6.9* 3750 13 244 100:50 2d 0.53 0.07 38** 1.7** 1.2** 3900 13 212 100:50 2e 6.45 0.27 0.10 74* 7.9* 6.1* 8425 13 248 100:50 2f 0.20 0.17 33** 3.2** 3.1** 6250 12 246 100:48 *Tearing or breaking of the material **Separation at the boundary surface of the adhesive (adhesive separation) ***25000 mPas after 12 min. Measurement discontinued after 20 min. and 100000 mPas.

(26) The results indicate that the PAA values in the case of the binder system according to the invention subside more quickly than in the corresponding reference system, which contained no alkoxylated diamine in the curing agent (Examples 1b, 1c, and 1d vs. Example 1a. Examples 2b and 2c vs. Example 2a).

(27) The use of triethanolamine in the curing agent causes no reduction in the PAA values in comparison to the reference (Example 1g vs. Example 1a).

(28) The use of triisopropanolamine in the curing agent causes the PAA values to subside more quickly in comparison to the reference (Example 2e vs. Example 2a), but the effect is far less pronounced than when using alkoxylated diamines (Example 2e vs. Examples 2b and 2c).

(29) It was furthermore shown that the use of tin-based catalysts causes a somewhat faster reduction in PAA values, but also causes an increase in viscosity, which corresponds to a shorter pot life (see Example 1e vs. Example 1a). Furthermore, the use of tin compounds in food packaging poses a health concern.

(30) As was the case for the tin-based catalysts, the use of amine catalysts likewise caused a higher viscosity and a shorter pot life. Furthermore, no acceleration in the reduction of PAA values was observed (see Example 1f vs. Example 1a).

(31) Like the formulations according to the invention, binder systems using polyether polyols producible by alkoxylating monoamines exhibit rapidly subsiding PAA values as well as low viscosities, but the bond strength values are lower (Example 2d vs. 2b and 2c).

(32) Similar results were seen in binder systems in which the resin comprised an isocyanate-terminated prepolymer produced from a tertiary amine-initiated polyether polyol. Rapidly subsiding PAA values and low viscosities comparable to those in the formulations according to the invention were determined in this case as well, but the bond strength values were poorer (Example 2f vs. Examples 2b and 2c). Furthermore, a resin featuring such prepolymers exhibits diminished storage stability because the tertiary amino groups in the polymer backbone of the isocyanate-terminated polyurethane prepolymer catalyze the isocyanate groups. Autocatalytic activity having a negative effect on stability is thus detected in the prepolymers. This is based on the observation that, following not more than four weeks of storage in a closed container, these prepolymers were solid.