WO2000077300A1

WO2000077300A1 - Metallized paper with grease resistance

Info

Publication number: WO2000077300A1
Application number: PCT/US2000/040152
Authority: WO
Inventors: Terri R. Carvagno; Robert C. Erchinger; Mark T. Mcgarel; James P. Vanwinkle
Original assignee: Vacumet Corp
Current assignee: Vacumet Corp
Priority date: 1999-06-16
Filing date: 2000-06-07
Publication date: 2000-12-21
Anticipated expiration: 2001-12-16
Also published as: AU6120100A

Abstract

A decorative and functional substrate (10) consisting of a paper base sheet (11) coated with thermoplastic or thermoset material which provides grease resistance to the finished product. Grease resistance may be incorporated into one or more coatings (12, 14) between the paper (11) and the metal layer (16) and/or incorporated into the printable coating (18) applied on top of the metal layer (16). The grease resistant metallized paper may be used in labeling and packaging where grease and oil resistance are needed. Specifically, the metallized paper may be used in packaging for pet food bags of varying constructions and styles or it may be used in packaging chocolate. It may also be used in labels on industrial and consumer products where grease resistance is required.

Description

METALLIZED PAPER WITH GREASE RESISTANCE

FIELD OF THE INVENTION This invention relates to packaging materials, and more particularly to a packaging material having grease resistance.

BACKGROUND OF THE INVENTION

Grease resistant packaging with a metallic appearance has traditionally been obtained by several methods. One option is to apply a fluorochemical to the backside of the paper substrate and then print using metallic inks. The fluorochemicals and metallic inks are both expensive. Another option has been to laminate aluminum foil to the fluorochemical-treated paper or grease-resistant parchment and then print the foil using well-known techniques. This latter technique is popular for stick margarine wrap. Another option is to use aluminum foil wrap with an outer paper print ply or to use a paper-aluminum foil laminate. This technique is popular for chocolate bars and candies. Recently, a metallized fluorochemical-treated paper was introduced for use in the pet food market as an attractive, lower-cost, easier to handle option to foil. The use of fluorochemical- treated paper still makes this an expensive packaging material. It is an object of this invention to provide a lower-cost grease-resistant metallized packaging material.

SUMMARY OF THE INVENTION The metallized packaging material of the present invention has grease resistance provided by the coatings applied to the substrate. In general, the grease resistant packaging material comprises a paper substrate and at least one base coating layer overlying one surface of the paper substrate. A layer of metal is provided overlying the base coating layer or layers, and a top coating layer is provided overlying the metal layer. At least one of these coating layers is formed of a grease resistant polymeric coating formulation. For purposes of the present invention, a coating layer is considered "grease resistant" if it passes the Grease/Oil Penetration test as defined herein. The grease resistant coating formulation may suitably include an acrylic polymer and a polyethylene and/or polypropylene wax. Optionally, it may additionally include a fluorochemical additive. The grease resistant coating formulation may also be comprised of polyester polymers, polypropylene, polyethylene, or a polypropylene/polyethylene blend. The opposite side of the paper substrate may optionally have one or more coating layers, which may either be a grease resistant formulation or a non-grease resistant formulation. In accordance with one specific embodiment, a standard paper substrate is coated with two coatings prior to metallization. These coatings can be solvent- based and/or water-based. They can be the same or different in formulation. Grease resistance is incorporated into at least one of these coatings. A thin layer of aluminum is vacuum deposited (or can be processed as transfer metallization) onto these coatings. A top protective and printable coating is then applied. This top coating can be solvent-based and/or water-based. The top coating may also be grease resistant if the application requires it. The top coatings are typically vinyl-, olefin-, acrylic-, SBR or polyester-based, but other resin types are not excluded.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figure is a cross-section of a grease resistant sheet packaging material in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION A grease resistant sheet packaging material in accordance with the present invention is shown schematically in cross section in the drawing and is indicated generally by the reference character 10. It includes a paper substrate 11 with multiple coating layers overlying one surface of the paper substrate. The paper substrate 11 preferably has a basis weight of from about 20 to about 144 pounds per ream, and may be selected from any of a number of conventional paper types or grades, including coated or uncoated printing grade paper, bleached and unbleached kraft paper, hardwood pulp paper, softwood pulp paper, beater dyed paper, groundwood pulp paper and sulfite pulp paper. In the embodiment illustrated, the paper is a clay coated print grade paper.

One surface of the paper is coated with a first base coating layer 12, which may be applied as a solvent-based polymer solution or a water-based polymer dispersion. Suitable coating formulations for this first base coating layer include but are not limited to vinyl polymers, such as polyvinyl acetate, acrylic polymers, styrene-acrylic polymers, and styrene butadiene polymers. These coating formulations may or may not have resistance to grease and oils.

A second base coating layer 14 overlies the first base coating layer 12, and is formed of a coating formulation having resistance to grease and oils. Suitable coating formulations for this second base coating layer include but are not limited to vinyl polymers, such as polyvinyl acetate, acrylic polymers, styrene-acrylic polymers, styrene butadiene polymers, and polyester polymers. One preferred coating formulation comprises a water-based emulsion or dispersion of an acrylic polymer, together with polyethylene and polypropylene wax, and a silicone antifoam agent.

The coating formulations for base coating layers 12 and 14 may additionally include pigments or mineral fillers, such as, but not limited to, aqueous dispersions of clay, calcium carbonate or mica. Other additional components of the coatings may include thickening agents, defoaming or antifoaming agents, pigments, and crosslinking agents.

A metal layer 16 overlies and adheres to the second base coating layer 14. The metal layer 16 may be suitably applied by vacuum metallizing, although other conventional methods could also be employed, such as transfer metallization. The metal layer preferably has a thickness of at least 12 nm (optical density of 2.0) and may be formed of aluminum or other suitable metal. A top coat layer 18 overlies the metal layer 16. The top coat layer is also formed of a coating formulation having resistance to grease and oils. One preferred coating formulation comprises a water-based emulsion or dispersion of an acrylic polymer, together with polyethylene and polypropylene wax. The coating layers 12, 14 and 18 are each preferably applied at a coating weight within the range of from 0.5 to 15 grams per square meter, more preferably within the range from 0.7 to 5 grams per square meter.

The opposite side of the paper substrate 11 optionally has one or more coatings (not shown) overlying it. At least one of these coatings may be selected to have grease resistance. The coating may be applied as an extrusion coating or a solvent-based polymer solution or a water-based polymer dispersion. Suitable coating formulations include but are not limited to vinyl polymers, such as polyvinyl acetate, acrylic polymers, styrene-acrylic polymers, styrene butadiene polymers, polypropylene, polyethylene, or a polypropylene/polyethylene blend. Polymer formulations suitable for forming the grease resistant coating layer or layers include acrylic polymers or copolymers, preferably blended with one or more waxes selected from the group consisting of polyethylene wax, polypropylene wax, paraffin wax, and mixtures of these waxes. Other grease resistant polymer formulations may be ethyl acetate, polyesters, polyolefins, such as polypropylene, polyethylene or a polypropylene/polyethylene blend, which may suitably be applied by extrusion coating. Other grease resistant formulations may be based upon a polyester polymer or polymer blend or upon a styrene butadiene resin. Grease resistant additives including, but not limited to starches and fluorochemicals may be included in the coating formulation. In accordance with one specific embodiment, the coating composition used for the first base layer 12 is a polyvinyl acetate such as Sun Chemical CJX-4900 or CJX-6587. The second base layer 14 contains from about 15 to about 35 parts by weight of a styrene-acrylic polymer such as SC Johnson SCX-660 or SCX-1695 or Morton 61x105 or Cork FP6950 which have heat resistance built into the polymer structure, from about 0 to about 10 parts by weight of a polyethylene and/or a polypropylene wax such as SC Johnson Jonwax 22, 26, 28, 39 and 120, and from 0 to about 2 parts a fluorochemical such as 3M FC807 or FC845. Traditional additives for processability, well-known in the art, are also included in the formulation but are not essential to the grease resistance of the formulation. These components are dispersed in water to form a dispersion, preferably of about 20% to 30% solids. The coating composition used for the top coat layer 18 is similar, except that the fluorochemical is omitted. In another specific embodiment, the above-described formulation of the second base layer 14 is used for both the first and second base coat layers, 12 and 14. Another specific embodiment utilizes said formulation for both base coat layers, 12 and 14, and the top coat layer, 18. In another specific embodiment, a solvent-based polyvinyl acetate precoat

(Sun Chemical CJX-6587 or CJX-4900) is used for the first base layer 12, followed by a second base coat layer 14 of water-based polyester emulsion comprised of 20-25 parts of Eastman Eastek 1200 (31 126), 35-45 parts of Eastman Eastek 1300 (31281) and 0-5 parts Lawter Flexonic 600 wax. The grease-resistant topcoat layer 18 is comprised of 28-38 parts of Eastman Eastek 1200 (31126). In another specific embodiment, the first base coat layer 12 is a polypropylene/polyethylene blend extrusion coated onto the paper substrate 11. The second base coat layer 14 is omitted, and the metal layer 16 overlies and adheres to the first base coat layer 12. The top coat layer 18 is not grease resistant. In another specific embodiment, a grease resistant layer is coated onto the reverse side of the paper substrate 11. This grease resistant layer is comprised of 3-30 pounds per ream, more preferably 8-15 pounds per ream of a polypropylene/polyethylene blend that was extrusion coated onto the paper substrate. Base coating layers 12 and 14, metal layer 16 and top coating layer 18 are not grease resistant.

In another specific embodiment, base coating layer 12 is a water-based, grease resistant dispersion comprised of 25-75 parts, preferably 45-55 parts, Dow 681 (a SBR resin), 5-50 parts, preferably 20-30 parts Grain Processing Corporation Coatmaster^® K580 starch, and 0-75 parts, preferably 20-30 parts, Kaowhite clay slurry, plus additives known in the art for stabilization. The second base coating layer 14 and the top coat layer 18 are not grease resistant.

Grease resistance may be measured using the 3M Kit test. This involves exposing the substrate to solutions containing varying amounts of castor oil, heptane and toluene. This test is generally published under the designation TAPPI UM557, incorporated herein by reference. To determine the grease resistance rating of a particular coating layer, the procedure is run on an individual coating layer formed of the polymeric coating composition. The grease resistance rating of the overall coated substrate is determined by conducting the same procedure on the coated substrate.

The test is as follows:

3M (Minnesota Mining and Manufacturing Co., St. Paul, Minn.) provides a kit for conducting the test. The kit includes twelve small bottles for use during testing and equipped with droppers or rods for application of solutions to the substrate to be tested. Also needed for conducting the test is absorbent cotton or tissue and a stopwatch or timer.

The bottles contain three reagents (Castor Oil, C.P. Grade; Toluene, C.P. Grade; and Heptane, C.P. Grade) in varying proportions.

Mixtures of these reagents are prepared according to the table above. The reagents should be measured individually, rather than by addition since there will be loss of volume upon mixing. Store these in the labeled stock bottles. As required, fill each dropping bottle with the appropriate Kit Number reagents from the stock bottles. Five representative specimens of suitable size (at least 2 by 2 inches or 5 by 5 cm) are obtained. Each test specimen is placed on a clean flat surface, test side up, being careful not to touch the area to be tested. From a height of about one inch (2.5 cm), a drop of test solution from one of the Kit Number testing bottles is dropped onto the specimen. Start a stopwatch as the drop is applied. After 15 seconds, remove the excess fluid with a clean swatch of absorbent cotton or tissue and immediately examine the wetted area for damage/smearing/softening. Failure (i.e. staining or lack of grease resistance) is evidenced by a pronounced darkening of the specimen caused by penetration, even in a small area, under the drop. Repeat the procedure as required, making sure that drops from other Kit Number bottles fall in untouched areas.

Results are reported as the Kit Rating, which is the highest numbered solution that stands on the surface of the specimen for 15 seconds without causing failure. The average Kit Rating of five specimens is reported to the nearest whole number.

This same procedure can also be used to test for resistance to a particular oil or greasy substance. If an oil or greasy substance is being tested, zero damage is considered a pass. A substrate is required to be undamaged by kit solutions 1 through 7 or undamaged by the particular oil or greasy substance tested in order to be considered "grease resistant" according to this test procedure. In many cases, at least one of the coating layers in the overall coated substrate is undamaged by all twelve solutions. This superior performance indicates that these metallized papers should be suitable for use in other applications where grease resistance is needed, such as oil can labels, margarine wrap, other food wrap, personal care product labels, etc. It is postulated that the high acid number of some of these polymers results in a very polar, high energy surface that renders the coating highly lipophobic. A preferred test for assessing the performance of the grease resistant packaging materials of the present invention is the Grease/Oil Penetration test. The procedure is as follows:

Cut one (1) sample 4" x 4" and fold through the center parallel to the MD direction and coated (printed side down) to give the sample a preliminary light crease. The preliminary crease should be only 1/2" from the top of the sample.

Lay the sample on the glass plate and push the roller (Creasing Roller, HR-100 4.5 lb. PSTC approved) over the crease, being careful not to exert any additional pressure. The speed of your roller should be one linear inch per second for any of the creases. Unfold the sample and pull roller back over the crease. Now fold a new crease at 90° to the first crease, but with the reverse side inward. Again push the roller over the crease; unfold and pull the roller back over the crease. Place the grid printed sheet on top of the unprinted sheet and place these on the backup plate. Put a 4" x 4" sample metallized side down on each grid backup sheet, and place a 3" diameter metal ring on each sample. Place the oil to be tested in the center of the sample.

Place the sample assembly in a 60° C oven for 24 hours. Remove the sample from the oven and count the percent of the grid area that is stained by oil. Less than or equal to 2% staining is considered a pass.

The various above-described embodiments of grease resistant packaging materials according to the present invention will pass this test with a variety of oily or greasy substances, including corn oil, chocolate oil, automotive grease, caulk, 10W-40 automotive oil, spearmint oil, and dishwashing liquids such as Ajax^®.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED IS:

1. A grease resistant packaging material comprising a paper substrate; at least one base coating layer overlying one surface of the paper substrate; a layer of metal overlying said at least one base coating layer; and a top coating layer overlying the metal layer, wherein at least one of said coating layers is formed of a grease resistant polymeric coating formulation.

2. A material as defined in claim 1 , wherein said at least one coating layer has a grease resistance Kit Rating of at least 7 according to the TAPPI

UM557 test method.

3. A material as defined in claim 1 , wherein said at least one coating layer is undamaged by an oil or greasy substance selected from the group consisting of corn oil, chocolate oil, automotive grease, caulk, automotive lubricating oil, spearmint oil, and dishwashing liquids when applied according to the procedures of the Grease/Oil Penetration test method.

4. A material as defined in claim 1, wherein said at least one base coating includes a first said base coating layer carried by said one surface of the paper substrate and a second said base coating layer carried by said first base coating layer and said layer of metal, said second base coating layer having a grease resistance Kit Rating of at least 7 according to the TAPPI UM557 test method.

5. A material as defined in claim 4, wherein said first base coating layer also has a grease resistance Kit Rating of at least 7.

6. A material as defined in claim 4, wherein said top coating layer also has grease resistance Kit Rating of at least 7.

7. A material as defined in claim 4, wherein said first base coating layer is comprised of polyolefins.

8. A material as defined in claim 7, wherein said first base coating layer is comprised of polypropylene, polyethylene, or a polypropylene/polyethylene blend.

9. A material as defined in claim 1 , wherein said at least one base coating layer includes a first base coating layer carried by said one surface of the paper substrate and a grease resistant second base coating layer carried by said first base coating layer, said second base coating layer being formed from a grease resistant formulation including an acrylic polymer and a polyethylene wax.

10. A material as defined in claim 9, wherein said grease resistant formulation additionally includes a fluorochemical.

11. A material as defined in claim 1 , wherein said grease resistant coating formulation comprises an acrylic polymer and a wax selected from the group consisting of polyethylene wax, polypropylene wax, paraffin wax, and mixtures of these waxes.

12. A material as defined in claim 1, wherein said grease resistant coating formulation comprises an acrylic polymer and polyethylene wax and is approved for FDA direct or indirect food contact.

13. A material as defined in claim 1 , wherein said grease resistant coating formulation comprises an acrylic polymer, polyethylene wax and paraffin wax and is approved for FDA direct or indirect food contact.

14. A material as in claim 1, additionally including at least one coating on the surface of said paper substrate opposite said one surface.

15. A material as defined in claim 14, wherein at least one coating on said opposite surface of the paper substrate is grease resistant.

16. A material as defined in claim 15, in which said at least one grease resistant coating is comprised of polypropylene, polyethylene, or a polypropylene/polyethylene blend.

17. A material as defined as in claim 1, wherein said grease resistant coating formulation comprises a polyester polymer or polymer blend.

18. A material as defined as in claim 1, wherein said grease resistant coating formulation comprises a styrene butadiene resin and starch.

19. A material as defined as in claim 1, wherein said grease resistant coating formulation comprises a styrene butadiene resin, starch and pigment.

20. A material as defined in claim 19, wherein said grease resistant formulation additionally includes a fluorochemical.

21. A material as defined as in claim 1 , wherein said grease resistant coating formulation comprises an acrylic resin and starch.

22. A grease resistant packaging material comprising a paper substrate; a first base coating layer carried by one surface of the paper substrate; a second base coating layer carried by said first base coating layer, said second base coating layer comprising a grease resistant polymeric coating formulation having a grease resistance Kit Rating of at least 7 according to the TAPPI UM557 test method, a layer of metal carried by said at least one base coating layer; and at least one top coating layer overlying the metal layer.

23. A grease resistant packaging material comprising a paper substrate; a first base coating layer carried by one surface of the paper substrate; a second base coating layer carried by said first base coating layer, said second base coating layer comprising an acrylic polymer and a wax selected from the group consisting of polyethylene wax, polypropylene wax, paraffin wax, and mixtures of these waxes, a layer of metal carried by said at least one base coating layer, and a top coating layer overlying the metal layer.