WATER-BASED BARRIER ADHESIVE

Abstract

The invention relates to a water-based barrier adhesive comprising: a polyurethane; at least one water-soluble polymer, wherein the water-soluble polymer comprises at least one hydroxyl group; and water; a barrier film comprising the same; a method for preparing the same; and the use thereof in food packaging.

Claims

1. A water-based barrier adhesive comprising: a polyurethane; at least one water-soluble polymer, wherein the water-soluble polymer comprises at least one hydroxyl group; and water.

2. The water-based barrier adhesive according to claim 1, wherein the water-based barrier adhesive comprises the polyurethane in an amount from 1 to 30 wt, with respect to the total weight of the water-based barrier adhesive.

3. The water-based barrier adhesive according to claim 1, wherein the water-based barrier adhesive comprises the at least one water-soluble polymer in an amount from 5 to 60 wt % with respect to the total weight of the water-based barrier adhesive.

4. The water-based barrier adhesive according to claim 1, further comprising at least one additive, in an amount from 0.1 to 10 wt % with respect to the total weight of the water-based barrier adhesive.

5. The water-based barrier adhesive according to claim 1, wherein the polyurethane and the at least one water-soluble polymer are contained in the water-based barrier adhesive in a weight ratio from 5:1 to 1:30.

6. The water-based barrier adhesive according to claim 1, wherein the polyurethane comprises a polyether urethane and an aliphatic polyester urethane.

7. The water-based barrier adhesive according to claim 1, wherein the water-soluble polymer is selected from the group consisting of polyvinyl alcohol, poly(ethylene vinyl alcohol), polyvinyl acetate, poly(ethylene vinyl acetate), cellulose acetate, and mixtures thereof.

8. The water-based barrier adhesive according to claim 1, wherein the water-based barrier adhesive further comprises a water-miscible solvent.

9. A barrier film comprising a substrate and a barrier adhesive layer coated on at least on surface of the substrate, wherein the barrier adhesive layer comprises the water-based barrier adhesive according to claim 1.

10. The barrier film according to claim 9, wherein the barrier adhesive layer coated on the substrate has a thickness of 0.1-10 μm.

11. The barrier film according to claim 9, wherein the water-based barrier adhesive is coated on the surface in an amount of 0.1-5 g/m.sup.2.

12. The barrier film according to claim 9, further comprising a laminate layer adjacent to the barrier adhesive layer, wherein the barrier adhesive layer is arranged between the laminate layer and the substrate.

13. The barrier film according to claim 9, wherein the substrate and/or the laminate layer comprises polyethylene, polypropylene or paper.

14. A method of producing a water-based barrier adhesive according to claim 1, the method comprising: providing an aqueous solution comprising the at least one water-soluble polymer; and mixing the aqueous solution with the polyurethane.

16. A method of packaging an item, the method comprising using the water-based barrier adhesive of claim 1 as a barrier adhesive layer for the packaging of the item.

17. The method of claim 16, wherein the item is food.

18. The method of claim 17, wherein the barrier adhesive layer reduces an oxygen transmission range and/or a water vapor transmission rate to the food.

Description

DETAILED DESCRIPTION

Materials

[0049] Polyurethane dispersion (PUD) has solid content of 32-35 wt %. Polyurethane consists of aliphatic polyether urethane and aliphatic polyester urethane with weight molecular weight of about 40,000 to 90,000 g/mol. The respective material used in the below examples was purchased from the DSM Coating Resins under the trade name of NeoRez™ and the Henkel Company under the trade name of LOCTITE™.

[0050] Polyvinyl alcohol (PVA) has a weight average molecular weight of 20,000 to 40,000 g/mol and a degree of hydrolysis of 96. The respective material used in the below examples was purchased from the FUJIFILM Wako Pure Chemical Corporation under the trade name of FujiFilm Wako™, the Kuraray Company under the trade name of Poval™ and Exceval™, the Mitsubishi Chemical Corporation under the trade name of GOHSENOL and the DENKA Company under the trade name of DENKAPOVAL.

[0051] Poly(acrylic acid) (PAA) has an viscosity average molecular weight (Mv) of 300,000 to 500,000 Daltaon, Brookfield viscosity of 100 to 3,000 cP and glass transition temperature of 100 to 110 degree Celsius. The respective material used in the below examples was purchased from the Sigma Aldrich company.

Measurement Methods

Particle Size

[0052] Particle size (=particle diameter) and specific surface area were measured by Zetasizer Nanoseries model S4700 (Malvern Instrument, UK) with dilution of sample in deionized water at concentration ca. 0.001 to 0.003 wt %, dispersant refractive index 1.33 and particle refractive index 1.56.

Viscosity

[0053] Solution viscosity was measured by Brookfield viscometer at 25° C. with needle NO. 18, torque value more than 90% and speed 14-30 rpm.

Molecular Weight

[0054] The number average molecular weight (Mn), the weight average molecular weight (Mw), and The Z-average molecular weight (Mz) were evaluated by Gel Permeation Chromatography (GPC) using THF system, flow rate 1.00 mL/min, injection value 100 μL, detector temperature 35° C., column temperature 35° C., and sample concentration 1.999, 4.001, 5.999 mg/mL.

Oxygen Transmission Rate

[0055] The oxygen transmission rate (OTR) (cc/m2/day) was measured at the temperature of 23° C. and 0% relative humidity (% RH) using an oxygen transmission rate analyser (OX-TRAN®, 2/21 MT) according to ASTM D3985.

Water Vapor Transmission Rate

[0056] The water vapor transmission rate (WVTR) (g/m2/day) was measured at the temperature of 38° C. and 90% RH using a water vapor permeation analyser (Systech Illinois, 7002) according to ASTM F1249.

Initial Tack by Tape

[0057] The initial tack was determined by the tape test according to ASTM F 2296. Briefly, the transparent tape was placed on the coated film. After ensuring a good contact between the tape and the coated film, the tape was removed rapidly by hand. The removed tape and the coated film was then visually inspected.

Adhesion Strength

[0058] The adhesion strength (N/15 mm) was measured with a universal testing machine (UTM) at an applied load of 100 N and a peeling speed of 254 mm/min. The sample width was fixed constant at 15 mm.

Film Appearance

[0059] The film appearance was visually observed and also analyzed under scanning electron microscope (SEM).

Preparation of the Water-Based Adhesive

Comparative Example 1

[0060] PVA solution was prepared by dissolving PVA in water at temperature of 90-95° C. Then it was cooled down to at ambient temperature with stir speed about 300 to 800 rpm under ambient atmosphere for about 1 to 2 hours.

Comparative Example 2

[0061] PAA solution was prepared by dissolving PAA in water at temperature of 90-95° C. Then it was cooled down to at ambient temperature with stir speed about 300 to 800 rpm under ambient atmosphere for about 1 to 2 hours.

Comparative Example 3

[0062] The PVA solution and PAA solution prepared in comparative example 1 and 2 was mixed at part ratio shown in Table 1.

Examples 4, 5, 6 and 7

[0063] PVA solution was prepared by dissolving PVA in water or water-methanol mixing at temperature of 90-95° C. Then it was cooled down to at ambient temperature with stir speed about 300 to 800 rpm under ambient atmosphere for about 1 to 2 hours.

[0064] PUD was slowly added into PVA for about 10 to 30 mins and then kept continuously stirring from 3-5 hours until uniform PUD-PVA solution was obtained.

[0065] The ratio of PVA and PUD are shown in Table 1 as part ratio.

Film Preparation

Sample 1a to 7a

[0066] Biaxially oriented polypropylene (BOPP) commercially available at thickness of about 20 μm were coated with the barrier adhesive prepared as mentioned above using a versatile coating machine (VCML, RK Printcoat Instruments) at the coating weight of less than 3.0 gsm or thickness of about 1-2 μm.

[0067] Comparative sample 1a, 2a, 3a, 4a, 5a, 6a and 7a are prepared by using Comparative sample 1, 2, 3, 4, 5, 6 and 7 respectively.

Sample 5b, 5c and 5d.

[0068] The sample 5a was then laminated with cast polypropylyne (cPP) film having thickness 40 μm, linear low density polyethylene (LLDPE) having thickness of 80 μm, or BOPP film having thickness 20 80 μm. The adhesive curing was done by keeping the laminated film at the temperature of 50° C. for at least 24 h.

[0069] From Table 1, it can be seen Sample 4 to 7 show much better OTR value than all comparative examples 1 to 3. In addition when PVA content is increased that relative to the reducing of PU content, the OTR value tends to evidently increase as shown in Sample 4 and 5. However, with too much increasing of PVA content leads to reduce of initial tack and adhesion strength of barrier adhesive or coating on that coated film substrate as shown in Sample 5 and 6. Besides, the adhesive compositions and barrier film performance of semi-water based barrier adhesive is shown in Sample 7, which is design to improve the drying performance of adhesive solution during lamination or coating processes and residual carrier solvent on the barrier film with remaining in the barrier property compared with our original water based barrier adhesive.

TABLE-US-00001 TABLE 1 The varied compositions, properties and comparative sample are shown in Table 1. Comparative Comparative Comparative Sample Sample Sample Sample Composition Unit Sample 1 Sample 2 Sample 3 4 5 6 7 PU Part — — — 1  1 1  1 PAA Part 1 1 — — — — PVA Part — 1 2.22 0.09 4.54 13.64 4.54 Water Part 9 9 21.22 2.54 27.79 79.30 20.06 Methanol Part — — — — — — 7.73 Comparative Cmnparative Comparative Sample Sample Sample Sample Barrier Film Sample 1a Sample 2a Sample 3a 4a 5a 6a 7a Film BOPP BOPP BOPP BOPP BOPP BOPP BOPP structure* (20 um) (20 um) (20 um) (20 um) (20 um) (20 um) (20 um) OTR cc/m2/day >2,000 >2,000 >2,000 209-251 <0.1 <0.1  1-30 WVTR g/m2/day 6.63-8.32 7.07-7-16 6.89-7.22 7.69-7.89 6.16-6.29 643-6.52 6.39-6.80 Initial tack by AF MF AF MF MF AF MF tape** Adhesion (N/15 mm) n/d n/d n/d n/d n/d n/d n/d Film Hazy Clear Hazy Clear Clear Clear Clear appearance *Film references of BOPP (20 um) and CPP (40 um) have a value of ≥2,000 cc/m2/day in the OTR and 8 to 11 g/m2/day in the WVTR **MF is material failure/film (substrate) tearing that means it can reach to the maximum adhesion on that coated film, AF is adhesion failure/delamination that means adhesion of that adhesive or coating has not sufficient adhesive strength on that coated film substrate and it need to improve as being the adhesive function.

TABLE-US-00002 TABLE 2 The properties of laminated films with different film structures are shown in Table 2. Laminated Film PP PE Film Properties Sample 5b Sample 5c Sample 5d Film structure BOPP (20 μm)// BOPE (30 μm)// BOPE (30 μm)// cPP (40 μm) LLDPE (80 μm) LLDPE (80 μm) Coated ~1-2  ~1-2  ~2-3  thickness (μm) Coating weight 1.2-1.5 1.2-1.4 2.2-2.4 (gsm) OTR <0.1 <0.1 <0.1 (cc/m.sup.2/day) WVTR 2.3-3.6 3.1-3.3 2-4 (g/m.sup.2/day) Adhesion 3-4 3-4 3-4 (N/15 mm) Failure mode MF MF MF Film Clear Clear Clear appearance ***MF is material failure/film tearing, AF is adhesion failure/delamination

[0070] Table 2 shows that the laminated film samples 5b, 5c and 5d provide excellent OTR and WVTR values. In addition, these structure comprise more than 90% polyolefin which provides recyclability and makes the materials suitable for packaging especially food packaging.

[0071] The features disclosed in the foregoing description and in the dependent claims may, both separately and in any combination thereof, be material for realizing the aspects of the disclosure made in the independent claims, in diverse forms thereof.