WO2007140009A2

WO2007140009A2 - Repulpable moisture vapor barrier

Info

Publication number: WO2007140009A2
Application number: PCT/US2007/012640
Authority: WO
Inventors: Krishnan Venkataram; Baker Lee
Original assignee: Dow Reichhold Specialty Latex, Llc
Priority date: 2006-05-26
Filing date: 2007-05-29
Publication date: 2007-12-06

Abstract

Repulpable moisture vapor barriers are disclosed. The moisture vapor barriers are essentially devoid of wax, and include a resin latex and an un-modified component having a crystalline platelet structure. The compositions can optionally include a hydrophobic component other than wax. Suitable resin latexes include polystyrene, styrene-acrylonitrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterborne polyurethanes, alkyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolyrners thereof. The component having a crystalline platelet structure can be suspended in means for suspending the component, such as fully hydrolyzed polyvinyl alcohol.

Description

REPULPABLE MOISTURE VAPOR BARRIER

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a moisture vapor barrier, and more particularly a moisture vapor barrier for paper and paperboard.

Fibrous substrates such as paper are widely used in packaging operations. Such fibrous substrates can be in sheet and roll form, and can be paper, paperboard, preformed paper containers, fabric and other fiber-based materials. Typically, fibrous substrates are subject to poor resistance to water vapor, gases, oil, solvents and greases. To improve the water vapor barrier resistance the fibrous substrates have been coated with a wide variety of compositions particularly when the substrates are used for food packaging.

Various coatings of this type are described in U.S. Pat. No. 3,632,424 to Graham et al. Of particular interest is the use of a wax or waxes incorporated into a latex and applied to a fibrous substrate as a coating. The physical phenomenon accounting for the good moisture vapor barrier properties of wax-coated paper is that the wax tends to migrate to the film surface to form a continuous wax layer. In laminating operations, however, this barrier layer can be interrupted; for example, such layers are susceptible to creases. Creases substantially reduce the water vapor resistance properties.

Additionally, the presence of wax makes recycling (repulping) of the fibrous substrate difficult. A conventional repulping operation typically comprises mixing water and the fibrous substrate, and the fibers are separated via mechanical action. The slurry may then be passed through screens and centrifugal cleaners to remove non-fibrous contaminants such as glass, metal, plastic, dirt, and other unwanted solid materials. In such repulping operations, the wax will separate and float to the surface of the repulping vessel. After waste paper is repulped, it is formed into paper or paperboard on the moving wire of a fourdrinier machine or on the cylinders of a cylinder machine, pressed and dried to remove the remaining water. If the separated wax is inadvertently incorporated into a paper sheet, the wax will appear as a grease spot, and coating and printing can be adversely affected. Various coatings of this type are also described in U.S. Pat. No. 5,897,411 to Stark et al. In these coatings, hydrophobically-modified mica or other hydrophobically-modified crystalline platelet structures were incorporated into a latex and applied to a fibrous substrate as a coating. This required a modification step before the coating was prepared.

It would be advantageous to have water-resistant coatings that do not require the presence of wax, and thus obviates the problem associated with wax during repulping operations, and that further do not require pre-modification of crystalline platelet structures in order to provide a moisture vapor layer to a fibrous substrate. It would also be advantageous to have fibrous substrates provided with such a moisture vapor layer applied thereto, particularly in a manner that permits the coatings to be printed, coated and bonded (e.g., using adhesive or glue) to another similar or dissimilar substrate.

SUMMARY OF THE INVENTION

Repulpable moisture vapor barriers, and fibrous substrates coated with the repulpable moisture vapor barriers, are disclosed. The barriers are formed from a coating composition that includes a resin latex and a component having a crystalline platelet structure, e.g., mica, clay, talc, kaolin, silica and the like. In one embodiment, the coating compositions further include a hydrophobic agent.

Suitable resin latexes include polyacrylic acid, polystyrene, styrene- acrylonitrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterborne polyurethanes, alkyl acrylates, vinyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolymers thereof.

Hydrophobic agents that can be added to the coating composition include fluorochemicals and fluoropolymers, including fluorinated telomere and oligomers; silicones, functionalized silicones (e.g., ether, amino epoxy, etc), silanes and siloxanes; hydrocarbon polymers, including polyolefϊns such as polyethylene and polypropylene, fatty acids and modified fatty acids (e.g. fatty esters, fatty amides, and salts of fatty acids, such as calcium stearate); fatty alcohols; fats; lipids; oils; styrene maleic anhydride polymers; and hybrids of the above (e.g., hydrocarbon/flourocarbon polymers). In one embodiment, the crystalline platelet structure is suspended in means for suspending, such as a hydrophilic polymer. Representative hydrophilic polymers include highly carboxylated polymers, including polycarboxylated acrylics such as Morcryl® 132, colloids, cellulosics, starches, polyethylene oxide, polyethylene glycol, and fully hydrolyzed polyvinyl alcohol.

The moisture vapor barrier composition of the present invention is applied to a variety of fibrous substrates, and particularly paper. The term "paper" includes paper of all weights and types, paperboard including Fourdrinier cylinders or other types, coated paper, printed paper and the like. The resulting fibrous substrate has excellent moisture vapor properties. Additionally, the fibrous substrate can be repulped without the problems associated with wax coatings during repulping process.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the repulpable moisture vapor barrier composition described herein is suitable for use with various fibrous substrates, and particularly paper. The moisture vapor barrier comprises a resin latex and an un-modified crystalline platelet structure, and optionally includes a hydrophobic component.

Suspending Means

In one embodiment, the unmodified crystalline platelet structure is suspended in a suspending means, such as a hydrophilic polymer. Representative hydrophilic polymers include highly carboxylated polymers, including polycarboxylated acrylics such as Morcryl® 132, colloids, cellulosics, starches, polyethylene oxide, polyethylene glycol, and fully hydrolyzed polyvinyl alcohol. The suspending means, in addition to facilitating the application of the coating, does not adversely affect the water resistant properties of the barrier.

Crystalline Platelet Structures

Although the Applicants do not wish to be bound by one theory, Applicants believe that the crystalline platelet structure is aligned in the barrier resulting in a tortuous path for any moisture to go through the barrier. This results in the barrier properties being a bulk property rather than a surface property such as is present in wax-coated paper or in the use of wax dispersion in a latex. Moreover, such a structure is less susceptible to interruption of the barrier such as caused by creasing or lamination to another layer. Additionally, it is believed that the component having a crystalline platelet structure has a high aspect ratio, and can be fully dispersed on recycling.

Suitable components having a crystalline platelet structure are mica, talc, silica, clay, and kaolin. Mica is a preferred component. The mica employed in the present invention may be a natural mica such as muscovite, paragonite, phlogopite, biotite, and Syrian mica, or a synthetic mica such as fluorine-contained phlogopite, fluorine/silicone-contained mica, and taeniolite. The resin is typically present in an amount ranging from about 20 to 85 parts of the crystalline platelet structure, such as mica, preferably 30 to 45 parts based on 100 parts of resin. Additionally, the component preferably has a particle size of less than 100 μm.

In one embodiment, around 25 to around 35 parts by weight of the mica is used, for example, around 30 parts by weight. At higher levels, there may be a dropoff of the MVTR values than when resin alone is used, and this tends to provides poor results. When uncoated paper is used, the results are even worse.

Resin Latexes

Suitable resin latexes include polyacrylic acid, polystyrene, styrene- acrylonirrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterborne polyurethanes, alkyl acrylates, vinyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolymers thereof. The resin latex typically comprises from about 60 to 80 percent by weight, preferably about 60 to 75 percent by weight of the barrier composition, although conventionally formulations are based on 100 parts of resin. The resin may also include additional comonomers such as monocarboxylic acid monomers, dicarboxylic acid monomers, unsaturated monocarboxylic ester monomers (e.g., acrylates and methacrylates), acrylamide- based monomers, half esters of unsaturated dicarboxylic acid monomers including mono esters of maleic acid or fumaric acid (e.g., monomethyl maleate), and blends and mixtures thereof. Representative resins include styrene acrylates and a styrene butadiene blend having a small amount of monomethyl maleate.

Means for Suspending the Crystalline Platelet Structures The means for suspending the crystalline platelet structure is used at an amount of about 0.5 to about 3 parts by weight, such as between about 1 to about 2 parts by weight, including about 1.5 parts by weight, based on 100 parts of resin. The means for suspending must be capable of suspending the crystalline platelet structure, while not adversely affecting the moisture barrier properties of the overall barrier composition. A particularly suitable means for suspending is a highly carboxylated polymer such as Morcryl® 132.

Hydrophobic Agents

In addition to the latex and mica or other crystalline platelet structure, the compositions can also include a hydrophobic agent. Hydrophobic agents that can be added to the coating composition include fluorochemicals and fluoropolymers, including fluorinated telomere and oligomers; silicones, functionalized silicones (e.g., ether, amino epoxy, etc), silanes and siloxanes; hydrocarbon polymers, including polyolefins such as polyethylene and polypropylene, fatty acids and modified fatty acids; fatty alcohols; fats; lipids; oils; styrene maleic anhydride polymers; and hybrids of the above (e.g., hydrocarbon/flourocarbon polymers). Another representative hydrophobic agent is SMA® 2625 by Sartomer, a partially esterified, low molecular weight styrene maleic anhydride polymer.

The hydrophobic agent is used at an amount of about 0.5 to about 2 parts by weight, such as between about 0.75 to about 1.5 parts by weight, including about 1 part by weight, based on 100 parts of resin.

As used herein, the term "modified fatty acids" specifically includes esters, amides, and salts of fatty acids, including calcium stearate and calcium salts of other fatty acids. Optional Components

The barrier composition may also include a number of other components such as biocides, defoamers, pigments, thickeners, crosslinking agents, flame retardants, catalysts, dispersing agents, wetting agents, and the like.

The following examples illustrate specific embodiments of the present invention. In the examples and throughout the specification, all parts and percentages are by weight, unless otherwise indicated

EXAMPLES

Example 1: Representative Coating Formulation:

In this representative example, the formulation contains the following:

Synthemul® 18106 (DRSL) - styrene acrylic binder chosen for barrier & UV stable properties.

Unmodified Mica (GA Industrial Minerals) - for moisture and oil/grease barrier properties. Barrier properties tend to drop gradually at levels below 35%, then fall dramatically at levels below 25%.

Zinc Ammonium Carbonate ("ZAC") - crosslinker that interacts with the styrene acrylic polymer chain, reduces blocking potential.

Morcryl® 132 (Rohm & Haas) - a mid range molecular weight, solid grade, styrene/acrylic resin, used to help pigment wetting, helps keep the mica in suspension. Potential crosslinking with ZAC.

Bostex 732R (Akron Dispersions) - antioxidant package, for heat and color stability.

Uvitex® OB (Ciba) - fluorescent optical brightener for bluish whitening effects.

Tinuvin® 477 (Ciba)- experimental aromatic UV absorber.

TiO₂ - opacity and whiteness/brightness.

Alcogurn® VEP-I (Alco) - sodium polyacrylate thickener - gives compound some body, helps slow mica settling.

Blue pigment - extremely small amount, used to shift the final coating color away from yellowish tint

The amounts of the components are provided in Table 1, below: Table 1

Example 2: Application of the Coating to an FSK Laminate

A laminate of bleached kraft paper, fiberglass scrim, and aluminum foil was prepared, for use in imparting ignition resistance to fiberglass pipe jacketing and to serve as a moisture barrier. The FSK laminate was wrapped in such a way that the paper side was exposed to the elements.

The composition provided in Example 1 was applied to the FSK laminate. When applied, the composition holds out moisture on levels equal to a plastic laminate, while allowing for tape adhesion. The barrier coating was effective down to 32⁰F at adhering tape.

While various embodiments have been disclosed and described herein, it will be appreciated that various changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention, as defined in the following claims.

Claims

1. A repulpable moisture vapor barrier for paper and paperboard devoid of wax and consisting essentially of a resin latex and an unmodified crystalline platelet structure.

2. The repulpable moisture vapor barrier of claim 1 wherein the unmodified crystalline platelet structure is selected from the group consisting of mica, talc, silica, clay and kaolin.

3. The repulpable moisture vapor barrier according to claim 1 wherein the resin latex is selected from the group consisting of latexes of polyacrylic acid, polystyrene, styrene-acrylonitrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterborne polyurethanes, alkyl acrylates, vinyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolymers thereof.

4. The repulpable moisture vapor barrier according to claim 1 wherein the resin latex includes a comonomer selected from the group consisting of monocarboxylic acid monomer, dicarboxylic acid monomers, unsaturated monocarboxylic ester monomers, acrylamide-based monomers, half esters of unsaturated dicarboxylic acid monomers, and blends and mixtures thereof.

5. The repulpable moisture vapor barrier according to claim 1, further consisting essentially of a hydrophobic agent other than wax.

6. The repulpable moisture vapor barrier according to claim 5, wherein the hydrophobic agent is selected from the group consisting of fluorochemicals, fluoropolymers, silicones, functionalized silicones, silanes, siloxanes, hydrocarbon polymers, fatty acids, modified fatty acids, fatty alcohols, fats, lipids, oils, styrene maleic anhydride polymers, and hybrids of the above.

7. A fibrous substrate coated with the repulpable moisture vapor barrier of claim 1.

8. A repulpable moisture vapor barrier for paper and paperboard devoid of wax and consisting essentially of a resin latex selected from polyacrylic acid, acrylonitrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterborne polyurethanes, alkyl acrylates, vinyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolymers thereof, and

20 to 80 parts by weight based on 100 parts of resin latex of an unmodified crystalline platelet structure.

9. The repulpable moisture vapor barrier of claim 8 wherein the unmodified crystalline platelet structure is selected from the group consisting of mica, tale, silica, clay and kaolin.

10. The repulpable moisture vapor barrier according to claim 9 wherein the unmodified crystalline platelet structure is mica.

1 1. The repulpable moisture vapor barrier according to claim 20 wherein the mica includes 0.5 to 3.0 parts by weight of means for suspending the mica.

12. The repulpable moisture vapor barrier according to claim 11 wherein the means for suspending the mica is a highly carboxylated polyacrylic acid.

13. The repulpable moisture vapor barrier according to claim 8 wherein the resin latex includes a comonomer selected from the group consisting of monocarboxylic acid monomer, dicarboxylic acid monomers, unsaturated monocarboxylic ester monomers, acrylamide-based monomers, half esters of unsaturated dicarboxylic acid monomers, and blends and mixtures thereof.

14. The repulpable moisture vapor barrier according to claim 8, further consisting essentially of a hydrophobic agent other than wax.

15. The repulpable moisture vapor barrier according to claim 14, wherein the hydrophobic agent is selected from the group consisting of fluorochemicals, fluoropolymers, silicones, functionalized silicones, silanes, siloxanes, hydrocarbon polymers, fatty acids, modified fatty acids, fatty alcohols, fats, lipids, oils, styrene maleic anhydride polymers, and hybrids of the above.

16. A fibrous substrate coated with the repulpable moisture vapor barrier of claim 8.

17. A repulpable moisture vapor barrier for paper and paperboard devoid of wax and consisting essentially of a resin latex and mica.

18. The repulpable moisture vapor barrier according to claim 17 wherein the mica is suspended in means for suspending the mica.

19. The repulpable moisture vapor barrier according to claim 18 wherein the means for suspending the mica is a fully hydrolyzed polyvinyl alcohol.

20. The repulpable moisture vapor barrier according to claim 17 wherein the resin latex is selected from the group consisting of latexes of polyacrylic acid, polystyrene, styrene-acrylonitrile, styrene-acrylonitrile-butadiene, styrene acrylates, styrene-butadiene, carboxylated styrene butadiene, polyvinyl chloride, polyvinyl acetate, waterbome polyurethanes, alkyl acrylates, vinyl acrylates, polyvinylidene chloride, ethyl vinyl chloride, and copolymers and terpolymers thereof.

21. The repulpable moisture vapor barrier according to claim 17 wherein the resin latex includes a co-monomer selected from the group consisting of monocarboxylic acid monomer, dicarboxylic acid monomers, unsaturated monocarboxylic ester monomers, acrylamide-based monomers, half esters of unsaturated dicarboxylic acid monomers, and blends and mixtures thereof.

22. The repulpable moisture vapor barrier according to claim 21, further consisting essentially of a hydrophobic agent other than wax.

23. The repulpable moisture vapor barrier according to claim 22, wherein the hydrophobic agent is selected from the group consisting of fluorochemicals, fluoropolymers, silicones, functionalized silicones, silanes, siloxanes, hydrocarbon polymers, fatty acids, modified fatty acids, fatty alcohols, fats, lipids, oils, and hybrids of the above.

24. A fibrous substrate coated with the repulpable moisture vapor barrier of claim 17.