WO1996038296A1

WO1996038296A1 - Corrugated board manufacturing system and method

Info

Publication number: WO1996038296A1
Application number: PCT/US1996/007180
Authority: WO
Inventors: Gaylord Allin; John L. Childress; Thomas L. Benner; James Jones; Roy Gorham; Mark Gorham
Original assignee: Bell Packaging Corporation
Priority date: 1995-05-31
Filing date: 1996-05-29
Publication date: 1996-12-05

Abstract

The invention relates to a water and moisture resistant corrugated board (10) which is capable of being repulped and recycled. The invention includes an exterior coating (22) comprising (A) a prepolymer of a styrene-butadiene copolymer, and (B) a filler, such as TiO2 or barium sulfate; a medium coating (30, 32) having an emulsion of wax particles and a carrier; and an interior coating (20) comprising (A) a styrene-butadiene copolymer or a carboxylated styrene-butadiene copolymer and (B) a non-paraffinic wax, such as carnauba wax or polyethylene. The invention further relates to a cold set glue (18).

Description

CORRUGATED BOARD MANUFACTURING SYSTEM AND METHOD

Technical Field of the Invention

This invention relates to a water and moisture resistant corrugated board. More particularly, this invention relates to a water and moisture resistant corrugated board that can be repulped and recycled. Additionally, this invention relates to improvements in the manufacturing techniques for corrugated board.

Background of the Invention

Corrugated fiberboard ("board") containers are used in many high humidity bulk packaging applications, such as in the packaging of fresh produce items. To overcome the known impairment in the strength of corrugated board in high humidity service, it is known to treat such containers, or the corrugated board sheets or blanks from which the containers are formed, by impregnating them with a wax or wax-based material. However, wax treated containers cannot be repulped and recycled, and this requires that such containers be disposed of after use in an environmentally objectionable way, such as by incineration or disposition in a landfill. Such a method of disposition is also economically disadvantageous, since used corrugated containers that are suitable for repulping and recycling, such as those without wax treatment, have a significant resale value.

In addition to wax treated corrugated board not being repulpable or recyclable, these containers suffer from several other significant shortcomings. These wax treated products have a low strength to weight ratio as compared to the corrugated board of the present invention. This increases the manufacturing costs and distribution costs of these wax treated corrugated boards and the transportation costs of the finished products. Also with other water resistant corrugated boards, particularly those having wax based coatings, the corrugated board is not heat resistant, chemical resistant, blood resistant or grease and oil resistant. Further, wax based corrugated boards are not easily printable or gluable.

Wax based corrugated boards are not elastic and frequently crack when scores are made. A corrugated board produced in accordance with the present invention can be readily scored and otherwise fabricated to permit it to be formed into containers and other useful products. In that regard, it inherently solves a problem that was previously solved at substantial complexity and expense by the construction of U.S. Patent 3,523,058 (Shick) , the disclosure of which is hereby incorporated by reference.

Known corrugated boards are manufactured by a technique which includes hot set gluing. As compared with the method of the present invention which utilizes cold set gluing, hot set gluing results in higher equipment costs, higher operating costs, and a lower quality product due to warping which is a frequent result of hot set gluing.

Corrugated board products on the market have flute lines which inhibit printing on one or both sides of the corrugated board.

In the past, attempts have been made to repulp and recycle wax treated corrugated board. While some wax treated corrugated boards exhibited suitable repulping abilities, they produced hand sheets with unacceptable slide angle and water absorption properties, thus failing the criteria to serve as recyclable material.

Treated corrugated board containers are a practical and cost effective way to ship produce, meats, seafood and other items. However, the disposal of the treated corrugated board products, particularly wax coated corrugated board containers, by grocery stores and other end users has been a financial and environmental concern to the industry. It is desirable not only from an environmental standpoint, but also as a source of fiber for recycled paper, corrugated board and other products, to develop a corrugated board which may be repulped and recycled using standard, current mill technology.

There exists a need for a corrugated board that is water and moisture resistant and yet, can be easily made, repulped and recycled in contrast to boards waterproofed by wax. There further exists a need for a corrugated board which can be manufactured by cold set gluing techniques.

Summary of the Invention

According to the present invention there is provided a repulpable and recyclable corrugated board with satisfactory water and moisture resistance for use in high humidity packaging applications, such as in the packaging of fresh produce items. The corrugated board of the present invention utilizes a cold set glue, rather than conventional starch adhesives, to bond the interior and exterior liner boards to the flutes of a corrugated medium that is positioned therebetween. The liner boards of the corrugated board are coated, as by rod coating prior to processing on a corrugator, with FDA approved coatings. Further, the corrugated medium used in such corrugated board is coated, as by rod coating prior to processing on a corrugator, with an FDA approved coating.

The present invention provides a double-faced liner board, i.e., corrugated board, comprising an exterior liner board, a medium corrugated layer and an interior liner board, the exterior liner board having a coating comprising (A) an aqueous solution of a styrene-butadiene copolymer, and (B) a filler such as Ti0₂ or barium sulfate; the medium having an aqueous coating composition comprising:

(A) an emulsion of wax particles, and

(B) a carrier that is (1) a natural food gum, or

(2) a mixture of a styrene-acrylate copolymer with a crosslinker; and the interior liner board having a coating comprising (A) an aqueous solution of a styrene-butadiene copolymer, (B) an aqueous solution of a natural food gum and (C) a non-paraffinic wax, such as carnauba wax or polyethylene.

Accordingly, it is an object of the present invention to provide an improved water and moisture resistant corrugated board. More particularly, it is an object of the present invention to provide a corrugated board that can be repulped and recycled.

It is an object of the present invention to provide a corrugated board which weighs less and/or has a higher strength than comparable known corrugated board.

It is an object of the present invention to provide a cold set glue for corrugated board manufacturing which will bind the corrugated medium (flutes) to the interior and exterior liner boards without the hot plates and preheaters required in the prior art corrugators. It is further an object to provide water and moisture resistant corrugated board which is also heat resistant, chemical resistant, blood resistant and grease and oil resistant. It is an object of this invention to provide water and moisture resistant corrugated board which is elastic and does not crack during scoring which would inhibit the water resistant qualities of the final product. It is an object of this invention to provide a water and moisture resistant corrugated board which has printable and/or gluable surfaces, enabling the use of high resolution graphics. It is further an object to provide a new water and moisture resistant corrugated board, the coatings on which are in compliance with FDA regulations for contact with food and other products. It is still further an object to provide a water and moisture resistant corrugated board that exhibits good weatherability for outside storage applications.

Brief Description of the Drawings

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which: FIGURE 1 is a cross sectional view of a sheet of corrugated board according to the preferred embodiment of the present invention.

FIGURE 2 is a schematic representation of a corrugator which shows the equipment reductions which may be achieved with the inventive cold set gluing.

Detailed Description of Exemplary Embodiments

A section of a sheet of corrugated board is indicated generally by reference numeral 10 in the drawing, and the corrugated board 10 is made up of an interior, product containing sheet of liner board 12, an exterior sheet of liner board 14, and a corrugated sheet of corrugating medium 16 that is between and adhesively joined to the sheets of liner board 12, 14 at the tips of flutes 16a of the corrugated medium by an glue 18, whose composition will be hereinafter described in more detail.

The interior sheet of liner board 12 is coated on its interior, product contacting surface with a layer 20 of a coating composition that imparts moisture resistance to the liner board 12 and the corrugated board 10 incorporating the liner board 12. Likewise, the exterior sheet of liner board 14 is coated with a layer 22 of a composition that imparts moisture resistance to the liner board 14 and to the corrugated board 10 that incorporates the liner board 14. The coatings 20, 22 may be applied to the liner board sheets 12, 14 prior to the delivery to a commercial corrugator of the rolls from which such liner board sheets 12, 14 are taken, for example, by rod coating, or the coatings 20, 22 may be applied to the liner board sheets 12, 14 on a corrugator as part of the corrugating operation, but prior to the bonding of the corrugating medium 16 thereto, if so desired.

Further, the corrugated medium 16 is also provided with a coating of a moisture resistant composition which becomes impregnated into the corrugated medium as discussed below.

The moisture resistant coating layer 20 must be in compliance with the Food and Drug Administration regulations for use in food contact surfaces, if the corrugated board 10 is to be used in a food packaging operation, and the coating layer 20 preferably must not inhibit the repulping or recycling of the corrugated board 10 to avoid the need to dispose of the corrugated board 10, after its useful life is completed, by incineration or disposition in a landfill. While the coating layer 22 on the exterior liner board sheet 14 is not expected to be in direct contact with contents packaged in a container formed from the corrugated board 10, and, thus, need not necessarily be subject to Food and Drug Administration regulations, nevertheless there are Food and Drug Administration requirements for indirect components of a food container, and it is important that the coating layer 22 meet such requirements. Further, the coating layer 22 must not impede the repulping or recycling of the corrugated board 10. The coating layer 22 preferably has a white color, to permit appropriate graphics to be imparted thereto. It is also desirable that the coating layer 22 permit printing of the exterior liner board sheet or the gluing of labels thereon after the completion of the corrugating operation.

A. Interior Liner Board

The interior liner board coating composition is prepared by mixing the following ingredients in the approximate percents shown: Ingredients % by Weight

Styrene-butadiene copolymer aq. soln. 30-85 Natural Food Gum aq. soln. 10-30

Non-paraffinic Wax 1-10

The resulting compositions have a pH of about 8.5 to 9 and viscosity of about 12-13 (#3 Zahn) .

The "natural food gum" may include any of the commonly known food gums, including alkali metal alginate, carrageenan, guar gum, gum arabic, gum ghatti, gum karaya, gum tragacanth, locust bean gum, pectin, xanthan gum, tamarind gum, acacia gum, agar gum, carboxymethylcellulose (CMC) , and cesapectin.

The natural food gum, which is preferably an alkali metal alginate, serves as a thickener to thicken the water present and the overall coating composition. The alkali metal alginate solution is an aqueous solution which includes about 2 wt.% alkali metal alginate. The alkali metal alginate is preferably sodium alginate, although potassium and lithium can be used as the alkali metal. The percentage of the natural food gum, including sodium alginate, is generally set by that amount of the gum which results in a viscosity range of about 20 sec. to about 40 sec. (#3 Zahn) , preferably about 30 sec. (#3 Zahn) . The coating is preferably applied in a 36-40% solids concentration at the approximate coating weight of 3 pounds per MSF (thousand square feet) , when applied to a 69 pound kraft liner by a smooth rod in a rod coating operation. A cellulosic material, such liner board or a corrugated board formed therefrom, with such a coating has good chemical, blood, grease and oil resistance, as well as good water vapor transmission rate (WVTR, see discussion below) , it has good flexibility at scores, thus permitting fabrication of containers from the corrugated board, and it exhibits good heat resistance when applied before corrugation. The corrugated board to which it is applied is fully repulpable and recyclable. The interior coating composition is easily applied to a substrate such as a liner board. The composition can be applied rapidly and the resultant coating formed merely by heating the composition to about 110°F to 180°F or above to form the waterproof coating.

The thickness of the coating is generally about 0.2 to 30 mils and preferably about 1 to 5 mils.

The styrene-butadiene copolymer is preferably utilized in an aqueous solution. For a styrene-butadiene and water mixture which is about 50% water, the amounts of the aqueous copolymer in the interior coating composition is generally about 30 to 85 percent by weight, preferably about 65 to 75 percent by weight, and optimally, about 68 to 72 percent by weight. The amount of butadiene in the copolymer is generally about 25 to 40 percent by weight and preferably about 30 to 35 percent by weight. The optimum amount is generally about 32-33 percent by weight. A suitable pre-polymer of a styrene-butadiene copolymer for the interior coating composition is sold by BF Goodrich of Gastonia, NC (formerly sold by Rhone- Poulenc, Specialty Chemical Division) under the product name WRL 70631™, which contains about 50% water. This copolymer may be cured or crosslinked with, for instance, crosslinking agents such as acrylamides including N- methanol acrylamide.

The styrene-butadiene copolymer may be replaced, less preferably, with a carboxylated styrene-butadiene copolymer. The carboxylated pre-polymer can be cured or crosslinked with, for instance, crosslinking agents such as acrylamides including N-methanol acrylamide.

A suitable carboxylated styrene-butadiene latex is sold by Reichhold Chemical, Research Triangle Park, N.C. as TYLAC® Resin Emulsion 97422-02. In general, the carboxylated copolymer is made by reaction with an unsaturated carboxylic acid such as aleic acid or methacrylic acid. The non-paraffinic wax is preferably polyethylene or carnauba wax. The polyethylene is a liquid (non-solid) low molecular weight polyethylene having a molecular weight of about 1000 to about 2500. EMULSION 260™ (Chemical Corp. of America, Rutherford, N.J.) can be used. The liquid carnauba wax helps give the resultant coating body, and the wax is commercially available as AS35-3 (Chemical Corp. of America, Rutherford, N.J.). Other suitable non-paraffin waxes include other polyolefin based waxes and plant based waxes. Paraffinic waxes are to be avoided, as known coatings using paraffinic waxes either alone or in combination with polymers result in "greasy" surfaces which are generally unprintable and ungluable, i.e., for labels. The coating as described does not result in a "greasy" surface.

The following illustrates the interior liner board coating compositions. Example 1 An aqueous coating composition was prepared by mixing the following ingredients in the approximate percents: Ingredients % by Weight

Styrene-butadiene copolymer aq. soln. 70 Sodium Alginate aq. Soln. 20

Carnauba Wax 5

Polyethylene Wax 5 The resulting composition had a pH of about 8.5 to 9 and viscosity of about 12-13 (#3 Zahn)

The composition was applied to a liner board substrate to form, when heated, a waterproof coating. The coating was repulpable and recyclable.

Example 2 A composition was made as in Example 1 except that a carboxylated styrene-butadiene (33% butadiene) copolymer was used instead of the styrene-butadiene copolymer. Substantially equivalent results were obtained.

B. Exterior Liner Board

The coating 22 that is applied to the exterior liner board 14 comprises: about 40 wt.% to about 80 wt.% of an aqueous solution of a pre-copolymer of styrene-butadiene or carboxylated styrene-butadiene; and about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of Ti0₂ at about the same weight percent filler, and combinations thereof;

The coating is preferably applied in a 60-66% solids concentration at the approximate rate of 4 pounds per MSF to 69 pound liner board, is gluable and printable after application, and has very good weatherability for applications requiring outdoor storage. It has very good chemical, blood, oil and grease resistance, and it does not crack when scored, which enhances the moisture vapor transmission resistance properties of the final product container. Further, the corrugated board 10 is fully repulpable and recyclable when such a coating composition is used for the exterior coating layer 22. With the post-printability and the white coloration of the coating 22, a container fabricated from the corrugated board 10 can be readily printed on, in a single or in multiple colors, to meet the graphics needs or desires of customers.

The exterior coating composition is easily applied to a substrate such as a liner board. The composition can be applied rapidly and the resultant coating formed merely by heating the composition to about 110°F to 180°F or above to form the waterproof coating.

The exterior coating composition can be used advantageously as an exterior coating of a double faced liner board, the composition being waterproof and being recyclable in contrast to wax coatings. The thickness of the coating is generally about 0.2 to 30 mils and preferably about 1 to 5 mils. The coatings are measured for waterproof qualities by standard ASTM tests and TAPPI tests including the Cobb test. A lower Cobb value such as 10 to 30 is generally preferred.

Moisture resistant tests are described in the Gotoh U.S. Patent No. 4,117,199 (Oji Paper Company, Ltd.). The patent is incorporated by reference.

The styrene-butadiene copolymer is preferably utilized in an aqueous solution. For a styrene-butadiene and water mixture which is about 50% water, the amounts of the copolymer in the exterior layer coating composition is generally about 40 to 80% by wt. , preferably about 50 to 70% by wt. , and optimally, about 56 to 62% by wt. The amount of butadiene in the copolymer is generally about 5 to 40 percent by weight and preferably about 30 to 35 percent by weight. The optimum amount is generally about 32 - 33 percent by weight.

The fillers, Ti0₂, barium sulfate, and other fillers which have a suitable WVTR (described below) are generally about 20 - 400 mesh and preferably 200 to 325 mesh in diameter. The amount of the filler in coating 22 is generally about 20 wt.% to about 60 wt.%, preferably about 30 wt% to about 50 wt.%, and optimally about 38 wt.% to about 42 wt.%.

The water vapor transmission rate (WVTR) of a sheet material is the mass of water vapor transmitted from one face of a specimen to the other under given steady conditions. The standard unit is g/m²/day and for this method, the specimen has an atmosphere approaching 0% RH on one face and 90% RH on the other, at a temperature of 37.8°C (100°F) . The water vapor transmission rate may be calculated as follows:

WVTR, g/m² • day = 24x/A where x = weight gained per unit of time, g y = time for the gain of x, h

A = exposed areas of specimen, m²

The quantities x and y can be derived conveniently from a plot of weight gain in grams vs. elapsed time in hours. This WVTR is a standard TAPPI test, TAPPI T 464 om- 90, "Gravimetric determination of water vapor transmission rate of sheet materials at high temperature and humidity", said test and testing procedure being incorporated by reference.

For water and moisture resistant corrugated board, it is desired to have as low a WVTR as is possible.

Titanium dioxide and barium sulfate have been found to have acceptable WVTRs. With an exterior coating that has about 40 wt.% Ti0₂, experiments on exterior liner boards show this coating composition has an acceptable WVTR of about 5 g/m²/day. Generally, the lower the wt.% Ti0₂ or barium sulfate, the lower the WVTR. With coatings having fillers other than Ti0₂ and barium sulfate, it is preferable to have a WVTR of less than about 1.1 times titanium dioxide's WVTR at about equal weight percentages of the fillers in their respective coatings. The fillers provide the exterior coating with heat resistance which may be desired from a manufacturing point, i.e., the desired ability to withstand high drying or glue setting temperatures, or an end-use point, i.e., the service the corrugated board container is used in. Generally, the more filler, the more heat resistant the exterior coating is.

Ti0₂ used as a filler provides a white, opaque exterior liner board appearance. Barium sulfate provides a clearer, duller white appearance. Preferably, the exterior coating includes about 1 wt.% to about 12 wt.% glycerine. The higher percentages are less preferred as drying time is increased. Preferably, the exterior coating includes about 1 wt.% to about 4 wt.% glycerine; optimally, about 2 wt.% glycerine.

The exterior layer coating pre-polymer can be cured or crosslinked with crosslinking agents such as acrylamides including N-methanol acrylamide.

A suitable pre-polymer of the styrene-butadiene copolymer is the same copolymer used in the interior coating composition, WRL 706S1™, sold by BF Goodrich.

The following examples illustrate the exterior coatings.

Example 3 An aqueous composition was prepared by mixing the following ingredients in approximate percents by weight: Ingredients % bv Weight

Butadiene-styrene copolymer aq. emulsion 44

Ti0₂ 30 Glycerin 2

Water £4

100 The viscosity of the composition was about 9.5 (No. 3 Zahn) and the pH was about 10.1. The composition was applied to a substrate to form, when heated, a waterproof coating. The coating was repulpable and recyclable. Subsequent testing showed that the presence of the additional water was less desired as it served to increase drying time.

Example 4 A composition was made as set forth in Example 3 except that it included 1 to 20% by weight of additional ingredients including calcium stearate, a wetting agent, and potassium phosphate, a defoamer.

Results similar to that of the composition and coating of Example 3 were obtained.

C. Medium The corrugated medium 16 is formed by a process comprising:

(a) coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of a carrier selected from the group comprising an aqueous solution of a natural food gum and a mixture comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bismaleimide, polyimide, melamine/formaldehyde, polyester, urethane, urea, urea/formaldehyde, and mixtures thereof; (b) heating the coated uncorrugated medium to a temperature of at least about 135°F; and

(c)corrugating the medium. It is believed that upon heating, the medium coating either absorbs or moves by capillary action or sublimes into the fiber medium and impregnates the fiber medium (see impregnation indicated at reference no. 34) , with the coating composition passing into and/or through pores contained in the fiber medium.

When the wax particle emulsion is combined with the aqueous solution of a natural food gum, the resulting medium has improved moisture resistance with no appreciable stiffening or strengthening of the corrugated board. With this combination coated on a medium, the coated medium is heated to at least about 135°F; the temperature generally correlating with the melt point of the particular wax chosen, taking into account the melting point influencing effects of the other ingredients present.

When the styrene-acrylate and crosslinker, either alone or in combination with the wax particle emulsion or other compounds, is used as the medium coating, the resulting medium has improved water resistance and the overall corrugated board has improved strength and stiffness. The crosslinker may be any suitable crosslinker including epoxy, phenolic, bismaleimide, polyimide, melamine/formaldehyde, polyester, urethane, urea, urea/formaldehyde, and mixtures thereof. The preferred crosslinker is a melamine-formaldehyde pre-polymer. The crosslinker is initiated in any suitable way, preferably by heating to at least about 160°F. The styrene-acrylate and crosslinker is preferably used in combination with about 40 wt.% to about 98 wt.% of a wax particle emulsion.

The styrene-acrylate and crosslinker impregnated fiber medium adds strength to the corrugated medium, resulting in a stronger, stiffer corrugated board. The additional strength provided by the styrene-acrylate and crosslinker impregnated flutes can advantageously be used to reduce the overall weight of a container as compared with a known container of the same strength or provide additional strength as compared with a known container of the same weight.

Thus, the medium coating can be adjusted as desired to meet specific requirements. If just moisture resistance is desired, the wax particle emulsion and aqueous solution of a natural food gum carrier may be chosen. If additional strength is desired for a corrugated board, a styrene-acrylate copolymer and crosslinker may be chosen.

When using 69 pound liner board sheets for the liner board layers 12, 14, the corrugated medium is preferably of 33 pound weight. The corrugating medium 16 is coated, either by rod coating prior to the delivery to the corrugator of a roll from which such corrugated medium 16 is to be formed or on the corrugator as part of the corrugating operation. The coating preferably is a 50- 60% solids concentration used in the approximate amount of 3 pounds per MSF. Corrugated medium materials and the corrugated board formed therefrom coated with such coatings have good water and heat resistance, they meet FDA requirements for indirect materials for use in food containers, they are gluable and they are repulpable and recyclable.

The wax particles in the medium coating composition are generally about 0.1 to 150 microns and preferably 1 to 100 microns in diameter. The amount of wax is generally about 40 to 98 percent by weight of the composition and preferably about 50 to 75 percent by weight, the optimum amount for most applications being about 65 to 75 percent by weight. A suitable wax particle emulsion is AQUABEAD 325-E™ wax (65 percent total paraffin solids) from Micro Powders Inc., Tarrytown, N.Y.

Suitable carriers for the medium coating are aqueous solutions of natural food gums, preferably, an aqueous solution of a alkali metal alginate (most preferably sodium alginate) and a mixture of a styrene-acrylate copolymer and crosslinker selected from the group comprising epoxy, phenolic, bismaleimide, polyimide, melamine/formaldehyde, polyester, urethane, urea, urea/formaldehyde, and mixtures thereof, preferably, a water-soluble melamine-formaldehyde prepolymer. The carrier is generally about 2 to 40 percent by weight, preferably 10 to 35 percent by weight; and more preferably 22 to 32 percent by weight of the composition. A suitable styrene-acrylate copolymer is P-158™ copolymer from Emulsion Systems Inc., Boca Raton, FL. P-158™ includes about 49% water.

In the medium coating composition, a suitable melamine/formaldehyde prepolymer is CYMEL 303™, a hexamethoxymethylmelamine material, which may be purchased from Cytec Industries, Inc., Wallingford, CT. Generally, the melamine-formaldehyde prepolymer is present as about 1 wt.% to about 5 wt.% of the overall coating, preferably about 1 wt.% to about 2 wt.% of the overall composition. Generally, the viscosity of the medium coating composition at 78-82°F is about 13.5 to 15.5 sec (#3 Zahn) and the pH is about 8.9 to 9.2.

The water resistance and other properties were measured by standard ASTM or TAPPI test methods including the Cobb test. The low Cobb values of 0.1 to 35 obtained are generally under 30 and preferably under 15. The following illustrate aqueous medium coating compositions.

Example 5 A formulation providing a waterproof coating was prepared from a composition as follows:

Ingredient % by Weight

Wax particle emulsion 71.5

Sodium Alginate aq. soln. 24

The composition formed a coating on a liner board that was waterproof.

Example 6

Ingredient % by Weight

Wax particle emulsion 68.4 Styrene acrylic prepolymer 26.5

Melamine/formaldehyde prepolymer 5.0

The composition was applied to a substrate to form a waterproof coating.

D. Cold Set Glue

When the layers 12, 14, 16 are treated with moisture resistant coatings, as herein described, they generally cannot be readily bonded or adhered to one another by the use of conventional starch adhesives of the type widely used in manufacturing conventional corrugated board. The traditional starch based glues formerly used in corrugated board manufacturing have been found unsuitable for use with the coated liner boards of the present invention. It is believed that the starch based adhesives are unacceptable due to their high water content, of which the water cannot evaporate in the standard corrugated board manufacturing techniques due to the water and moisture resistant properties of the coated liner boards of the present invention and, due to the water resistant coatings, water does not carry the starch adhesive into the liner board fiber. In unsuccessful experiments with the coated liner boards of the present invention, starch based adhesives did not set properly using standard corrugated board manufacturing techniques, resulting in easy delamination of the liner board from the corrugated medium. However, it was discovered that such coated liner boards and medium layers could be readily joined by an inventive cold set glue, comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

The vinyl acetate-ethylene copolymer used as a cold set glue has significant advantages over known vinyl acetate adhesives whose use is known in fields other than corrugated board manufacturing. As compared with a vinyl acetate adhesive, the vinyl acetate-ethylene copolymer cold set glue has significant advantages, including it provides improved set speed, wet tack, water resistance, and the dried adhesive is flexible while retaining good tensile strength. These advantages and properties of the vinyl acetate-ethylene copolymer make it a well-suited adhesive for use in corrugated board manufacturing, particularly for use as a glue 18 in cold set gluing tips of flutes 16a to liner boards 12,14.

A cold set glue suitable for use in joining moisture treated corrugated medium to moisture resistant liners, as heretofore described, is a liquid adhesive sold by Sonoco Products Company of Hartsville, South Carolina under the designation CD 46-33. A water diluted version of this product is designated 9E 117-18. Such an adhesive is a white, water borne, resin based adhesive. This adhesive has good roll coating properties, and sets up quickly with minimum heat. A dried glue line with such an adhesive is somewhat flexible and as meets FDA regulation CFR 29, paragraph 175.105. Such an adhesive has a total solids composition of approximately 43.0%, a pH of 5.2, with good mechanical stability and fair water resistance. While the use of cold set glue is particularly applicable to the coated or treated liner boards as described herein, it is also useful in uncoated or untreated liner boards used in making untreated corrugated board. The use of cold set glue is advantageous as the current standard corrugation process utilizes a heating section normally employing hot plates which, after the joining of the interior liner board, the corrugated medium, and the exterior liner board, is heated to temperatures of about 350°F and above to set and dry the adhesive between the tips of the flute on the corrugated medium and the exterior liner board. This post-joining heating to cure this glued surface significantly increases the cost of the machinery required for producing corrugated board. Thus, with the use of cold set glue, this heating section is not required, dramatically reducing the cost of corrugated board manufacturing equipment which utilizes cold set glue.

Additionally, cold set gluing has the advantage of producing straight corrugated board as compared with the warped corrugated board which is often produced via traditional hot set gluing techniques using hot plates. Further, cold set glue has the advantage of reducing flute lines, even with regard to larger sized flutes. It is known to produce smaller, closer spaced flutes to reduce the detrimental effects of flute lines. However, smaller, closer spaced flutes have the disadvantage of increasing the amount of medium used. Thus, the use of cold set glue reduces flute lines and reduces the amount of medium used in known techniques for reducing flute lines.

Example 7 Various samples of 69 pound liner board, including untreated control samples and samples treated with the interior and exterior coatings were tested for various properties, with the following results:

CD Ring Crush ("RC") (lbs/6 inches)

Control Interior Exterior

Sample Uncoated Coating Coating RC-Average 169.7 170.8 169.7 RC-Sigma 10.7 3.1 9.7 RC-Range 37.9 9.1 32.7

Basis Weight (Actual lbs. /MSF)

Control Interior Exterior

Sample Uncoated Coating Coating Weight 70.0 69.0 71.7

Gurlev Porosity (Seconds/lOOcc)

Control Interior Exterior

Sample Uncoated Coating Coating Average 31.2 148.7 >1000 Sigma 1.0 9.7 Range 2.3 22.9

Thirty Minute COBB (grams/100cm2)

Control Interior Exterior

Sample Uncoated Coating Coating Average 126 59 32

The very substantial increase in the Gurley Porosity test results for the coated samples relative to the uncoated control samples, and the very substantial reduction in the Thirty Minute COBB test results for the coated samples relative to the uncoated, control samples, are indicative of a very substantial improvement in the water and moisture resistance.

Example 8 A corrugated board was produced on a commercial corrugator at rates of 250 ft./minute and 280 ft./minute from a single facer 69 pound kraft liner board sheet precoated with the interior coating, a double facer 69 pound kraft liner board sheet precoated with the exterior coating and a 33 pound corrugated medium sheet precoated with the medium coating. The sheets were adhered together with the diluted Sonoco cold set adhesive 9E 117-18, after purging the starch adhesive previously used from the system. The corrugated board produced at 250 ft./minute had very good fibre pull adhesion, and it was observed as being better formed than conventional corrugated board with better adhesion than conventional, starch adhered corrugated board. At a production speed of 280 ft./minute, the board showed signs of adhesive bond failure, due to the poor flow characteristics of the cold set adhesive at higher flow rates.

Additionally, it may be advantageous to coat the flute surface of the interior liner board and the exterior liner board for water or moisture resistance (see coatings 30, 32) . Such a coating is desired when, there is a possibility that water or moisture could enter an open fluted end and thus absorb into the interior and exterior liner boards from the fluted side. It has been found that a mixture of about 4 wt.% Rhone Poulenc MANILOX X-196 and about 4 wt.% MANILOX X-197, with the remainder water provides a suitable water and moisture resistant coating for the flute surfaces of the interior and exterior liner board. This coating is preferably applied to the interior and exterior liner boards before the drying step at about 110°F to about 180°F, as discussed herein. This combination has been found to suitably bind with the cold set glue as discussed herein. A suitable lap glue for forming corners and sealed edges of the interior and exterior coated liner boards is Sonoco's water base adhesive containing poly(vinyl acetate) CD 47-91 (Sonoco Products Company, Hartsville, S.C.) The corrugated board of the present invention may be manufactured as follows. First, the interior and exterior coatings, as described above, are preferably coated on liner board and dried at about 110° F to about 180° F. Likewise, the medium coating, as described above, is coated on a sheet of uncorrugated medium and dried at about 110° F to about 180° F. (These sheets may less preferably be coated just prior to the corrugation and/or adhesion steps.) These sheets are supplied on rolls as is known in the art to a corrugator which may be a Langston, Mitsubishi or similar corrugator as known to those of skill in the art.

The manufacturing improvements and equipment reductions which may be achieved with the inventive cold set gluing may be seen with reference to FIGURE 2, a schematic representation of a corrugator having the following components: interior liner board roll 41, corrugating medium roll 42, exterior liner board roll 43, preheaters 44, pressure roll 45, corrugating rolls 46, roll applicators for applying glue 47, hot plates 48, cooling section 49, splitting and scoring section 50, cutoff section 51, single facer section 52, double facer section 53 and medium pre-conditioner 54. Thus, it can be seen with cold set glue used in glue applicators 47, with the cold set glue not requiring heated liner boards or heated single facer liner (heat supplied by preheaters 44) , heated medium sheets (heat supplied by medium pre- conditioner 54) , or post-heating after glue application (heat supplied by hot plates 48) , that a significant amount of the equipment, including the preheaters 44, hot plates 48 and cooling section 49 (see dotted lines on FIGURE 2) may be eliminated, thus significantly reducing the equipment costs and simplifying the corrugated board manufacturing technique.

In medium pre-conditioner 54, the medium sheet may be preheated to about 330°F which causes the medium coating to absorb or move via capillary action into the medium as described above and open pores on the medium surface for the cold set glue. While this preheating causes the coating on the flute sheet to absorb or move via capillary action into the medium, its primary purpose is tQ open the pores in the medium surface for the application of the glue (either hot set or cold set) . With known corrugated board manufacturing techniques, the preheaters were required for the hot set glue which adhered the flutes to the interior liner board. However, with the cold set glue of the present invention, this preheating step in pre-conditioner 54 is not required if an alternate means for opening pores in the medium surface is available. One such alternate means for opening the pores in the medium surface is to steam the medium sheet instead of heating it with preheaters.

Steam opens the pores and is believed suitable with the inventive cold set glue of the present invention. "Steaming", i.e., contacting the medium sheet with steam, generally involves contacting the medium sheet with steam at, or slightly above atmospheric pressure. Preferably, the steam temperature is at least about 240°F. A suitable apparatus to accomplish this steaming step is the GAYLORD SHOWER, available from Bell Packaging Corp., Dallas, Texas. Thus, the cold set glue of the present invention provides for a corrugated board manufacturing technique which does not require preheaters 45 or hot plates 48 (see discussion above) , and the corrugated board manufacturing technique may be completed at about ambient temperature. This significantly reduces equipment and operational cost. With the present inventive cold set glue, after the flutes are adhered to the interior liner board, an applicator 47 is used to apply the cold set glue to the tips of the flutes for adhesion to the exterior liner board. This technique requires no further heating with hot plates 48 or cooling (see cooling section 49) as is currently done with known manufacturing techniques, and this equipment may be eliminated from a corrugated board manufacturing plant.

The cold set glue of the present invention has a higher solids content (generally about 35 wt.% to about 60 wt.% solids) than the starch based adhesives previously used (generally about 20-25 wt.% solids). Due to this higher percent solids, it was determined that a thinner adhesive film performed better. With conventional starch based adhesives, an adhesive layer of about .012 in. was suitable. However, with the cold set glue of the present invention, an adhesive film of about .006 in. is desired. As such, an applicator roll having 25 cells/sq. in. is preferred over the currently known and generally used applicator rolls having 10 cells/sq. in.

Thus, the method of manufacturing using the cold set glue of the present invention includes the vinyl acetate and ethylene co-polymer based adhesive as described above, a lower temperature, which not only saves equipment costs, but also provides a better adhesion, and a new applicator to optimally apply a thinner film of the inventive cold set glue, which is preferred due to the higher solids content of the inventive cold set glue. While the interior coating, the exterior coating, the fluting treatment and the cold set adhesive are optimally designed to be used together to provide a water and moisture resistant, stiff and strong corrugated board for use in containers, these individual treatment steps and gluing procedures can be used individually, depending upon the needs of a particular corrugated board or container. For example, as previously stated, the cold set glue and gluing process may be used in uncoated or untreated corrugated board. Also, where an untreated corrugated board is desired to be stiffer and stronger, the fluting treatment may be used with or without the coatings and cold set glue to provide a stronger and stiffer corrugated board or a lower weight corrugated board of comparable strength to known corrugated board. Further, where just interior water and/or moisture resistance is required, the interior coating can be used without the other coating treatments and gluing procedures. Still further, the exterior coating may be used alone or in combination with any of the other coatings treatment or gluing procedures in applications where only exterior moisture protection is required.

The interior and exterior coatings may be used on cellulosic fibrous substrates other than corrugated board to provide an inexpensive product with a high degree of waterproofing, including without limitation, water resistant paper, detergent boxes, cereal boxes, meat, poultry and/or produce packaging, mailboxes, cat boxes, dog houses, fibre drums, outdoor storage containers, cable wrap, concrete forms, rail box car liners, lumber wraps, casket liners, outdoor speaker backing, portable shelters, including ice fishing shanties, temporary restrooms and car and boat covers, and outdoor realtor signs. Such cellulosic fibrous substrate, non-corrugated board articles produced with the interior and exterior coatings will have the same advantages as the coated interior and exterior surfaces of corrugated board, including water and moisture resistance, improved crush strength, resistance to heat, chemicals, blood, grease and oil, scorable, and printable and gluable surfaces, while still being repulpable and recyclable. Corrugated boards made with the coatings and techniques disclosed herein solve the problems mentioned above, providing water and moisture resistant corrugated boards that can be repulped and recycled. The present invention provides corrugated boards which weighs less and/or have a higher strength than comparable known corrugated board, particularly for the inventive water resistant corrugated board in comparison with wax coated corrugated board. Also provided are water and moisture resistant corrugated boards which are also heat resistant, chemical resistant, blood resistant and grease and oil resistant.

The present invention provides water and moisture resistant corrugated board which is elastic and does not crack during scoring which would inhibit the water resistant qualities of the final product. This invention provides a water and moisture resistant corrugated board which has printable and/or gluable surfaces, including surfaces without or with reduced flute lines. The present invention provides a water and moisture resistant corrugated board, the coatings on which are in compliance with FDA regulations for contact with food and other products.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A corrugated board, comprising: an interior liner board; an exterior liner board; a corrugated medium adhesively joined to the interior liner board and the exterior liner board, the corrugated medium being formed by a process comprising:

(a) coating at least a first side of an uncorrugated medium with a coating comprising: about 2 wt.% to about 40 wt.% of a carrier comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bixmaleimide, polyimide, melamine/formaldehyde, polyester, urethanes, urea, urea/formaldehyde, and mixtures thereof;

(b) initiating crosslinking of the styrene- acrylate copolymer;

(c) corrugating the medium.

2. The corrugated board of claim 1, wherein the coating further comprises: about 40 wt.% to about 98 wt.% of a wax particle emulsion;

3. The corrugated board of claim 1, wherein step (b) comprises heating the uncorrugated medium to a temperature of at least about 160°F.

4. The corrugated board of claim 2, wherein the coating comprises: about 65 wt.% to about 75 wt.% of a wax particle emulsion; about 10 wt.% to about 35 wt.% of a carrier comprising a styrene-acrylate pre- copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bixmaleimide, polyimide, melamine/formaldehyde, polyester, urethanes, urea, urea/formaldehyde, and mixtures thereof.

5. The corrugated board of claim 1, wherein the corrugated medium is formed by a process further comprising steaming the medium with steam.

6. The method of claim 1, wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

7. A method of manufacturing corrugated board, comprising:

(a) selecting an interior liner board sheet, an exterior liner board sheet and a medium sheet; (b) corrugating the medium sheet to form flutes;

(c) applying a glue to the flutes, the glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn; and (d) contacting the interior liner board and the exterior liner board with the glue on the flutes to form the corrugated board.

8. The method of claim 7, wherein, after contacting the exterior liner board with the glue on the flutes, the temperature is maintained at about ambient temperature to about 150°F.

9. The method of claim 7, further comprising the step of steaming the medium sheet prior to corrugating the medium sheet.

10. The method of claim 7, further comprising the steps of: coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of a carrier comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bixmaleimide, polyimide, melamine/formaldehyde, polyester, urethanes, urea, urea/formaldehyde, and mixtures thereof; initiating crosslinking of the styrene-acrylate copolymer.

11. The method of claim 10, wherein the initiating crosslinking step comprises heating the uncorrugated medium to a temperature of at least about 160°F.

12. A corrugated board, comprising: an interior liner board; an exterior liner board; a corrugated medium adhesively joined to the interior liner board and the exterior liner board, the corrugated medium being formed by a process comprising:

(b) heating the coated uncorrugated medium to a temperature of at least about 160°F;

(c) corrugating the medium; wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

13. The corrugated board of claim 12, wherein the coating further comprises about 40 wt.% to about 98 wt.% of a wax particle emulsion.

14. The corrugated board of claim 13, wherein the crosslinker is melamine/formaldehyde.

15. A recyclable corrugated board, comprising: a water resistant, repulpable interior liner board, having an interior surface, the interior surface having an interior coating comprising: about 30 wt.% to about 85 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 10 wt.% to about 30 wt.% of an aqueous solution of a natural food gum; about 1 wt.% to about 10 wt.% of a non- paraffinic wax selected for the group comprising carnauba wax, polyethylene, plant based waxes, polyolefin based waxes, and mixtures thereof; an exterior liner board; and a corrugated medium adhesively joined to the interior liner board and the exterior liner board.

16. The corrugated board of claim 15, wherein the interior coating comprises about 65 wt.% to about 75 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene.

17. The corrugated board of claim 15, wherein the natural food gum is an alkali metal alginate.

18. The corrugated board of claim 17, wherein the alkali metal alginate is sodium alginate.

19. The corrugated board of claim 15, wherein the exterior liner board has an exterior surface, the exterior surface having an exterior coating comprising: about 40 wt.% to about 80 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a

WVTR of less than about 1.1 times the WVTR of Ti0₂ at about the same weight percent filler, and combinations thereof.

20. The corrugated board of claim 15, wherein the corrugated medium is formed by a process comprising: (a) coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of a carrier selected from the group comprising an aqueous solution of a natural food gum and a mixture comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bixmaleimide, polyimide, melamine/formaldehyde, polyester, urethanes, urea, urea/formaldehyde, and mixtures thereof; (b)heating the coated uncorrugated medium to a temperature of at least about 135°F; (c) corrugating the medium.

21. The corrugated board of claim 20, wherein the corrugated medium is formed by a process further comprising steaming the medium with steam.

22. The method of claim 15, wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

23. A recyclable corrugated board, comprising: a water resistant interior liner board; a water resistant, repulpable exterior liner board having an exterior surface, the exterior surface having an exterior coating comprising: about 40 wt.% to about 80 wt.% of a an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of Ti0₂ at about the same weight percent filler, and combinations thereof; a corrugated medium adhesively joined to the interior liner board and the exterior liner board.

24. The corrugated board of claim 23, wherein the exterior coating further comprises about 1 wt.% to about 12 wt.% glycerine.

25. The corrugated board of claim 24, wherein the exterior coating comprises: about 50 wt.% to about 70 wt.% of an aqueous solution of pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 30 wt.% to about 50 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of

Ti0₂ at about the same weight percent filler, and combinations thereof; and about 1 wt% to about 4 wt.% glycerine.

26. The corrugated board of claim 23, wherein the interior liner board has an interior surface, the interior surface having an interior coating comprising: about 30 wt.% to about 85 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 10 wt.% to about 30 wt.% of an aqueous solution of a natural food gum; and about 1 wt.% to about 10 wt.% of a non- paraffinic wax selected for the group consisting of carnauba wax, polyethylene, plant based waxes, polyolefin based waxes, and mixtures thereof.

27. The corrugated board of claim 23, wherein the corrugated medium is formed by a process comprising: (a) coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of a carrier selected from the group comprising an aqueous solution of a natural food gum and a mixture comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bismaleimide, polyimide, melamine/formaldehyde, polyester, urethanes, urea, urea/formaldehyde, and mixtures thereof; (b) heating the coated uncorrugated medium to a temperature of at least about 135°F; (c) corrugating the medium.

28. The corrugated board of claim 27, wherein the corrugated medium is formed by a process further comprising steaming the medium with steam.

29. The method of claim 23, wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

30. A corrugated board, comprising: an interior liner board; an exterior liner board; a corrugated medium adhesively joined to the interior liner board and the exterior liner board, the corrugated medium being formed by a process comprising:

(a) coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of an aqueous solution of a natural food gum carrier;

(b) heating the coated uncorrugated medium to a temperature of at least about 135°F; (c) corrugating the medium.

31. The corrugated board of claim 30, wherein the coating comprises: about 65 wt.% to about 75 wt.% of a wax particle emulsion; about 10 wt.% to about 35 wt.% of an aqueous solution of a natural food gum carrier;

32. The corrugated board of claim 30, wherein the natural food gum is an alkali metal alginate.

33. The corrugated board of claim 32, wherein the alkali metal alginate is sodium alginate.

34. The corrugated board of claim 30, wherein the corrugated medium is formed by a process further comprising steaming the medium with steam.

35. The corrugated board of claim 30, wherein the interior liner board has an interior surface, the interior surface having an interior coating comprising: about 30 wt.% to about 85 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 10 wt.% to about 30 wt.% of an aqueous solution of a natural food gum; and about 1 wt.% to about 10 wt.% of a non- paraffinic wax selected for the group consisting of carnauba wax, polyethylene, plant based waxes, polyolefin based waxes, and mixtures thereof.

36. The corrugated board of claim 30, wherein the exterior liner board has an exterior surface, the exterior surface having an exterior coating comprising: about 40 wt.% to about 80 wt.% of an aqueous solution of pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; and about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of

Ti0₂ at about the same weight percent filler, and combinations thereof.

37. The method of claim 30, wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

38. A recyclable corrugated board, comprising: a water resistant, repulpable interior liner board, having an interior surface, the interior surface having an interior coating comprising: about 30 wt.% to about 85 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 1 wt.% to about 10 wt.% of a non- paraffinic wax selected for the group comprising carnauba wax, polyethylene, plant based waxes, polyolefin based waxes, and mixtures thereof; a water resistant, repulpable exterior liner board having an exterior surface, the exterior surface having an exterior coating comprising: about 40 wt.% to about 80 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of Ti0₂ at about the same weight percent filler, and combinations thereof; a corrugating medium adhesively joined to the interior liner board and the exterior liner board, the corrugated medium being formed by a process comprising: (a) coating at least a first side of an uncorrugated medium with a coating comprising: about 40 wt.% to about 98 wt.% of a wax particle emulsion; about 2 wt.% to about 40 wt.% of a carrier selected from the group comprising an aqueous solution of an natural food gum and a mixture comprising a styrene-acrylate pre-copolymer and a crosslinker selected from the group comprising epoxy, phenolic, bismaleimide, polyimide, melamine/formaldehyde, polyester, urethane, urea, urea/formaldehyde, and mixtures thereof;

(b) heating the coated uncorrugated medium to a temperature of at least about 135°F;

(c) corrugating the medium.

39. The corrugated board of claim 38, wherein the interior coating further comprises about 10 wt.% to about 30 wt.% of an aqueous solution of a natural food gum.

40. The corrugated board of claim 38, wherein the interior liner board has a first flute surface and the exterior liner board has a second flute surface and the first and second flute surfaces are coated with a moisture resistant coating.

41. The corrugated board of claim 38, wherein the corrugated medium is formed by a process further comprising steaming the medium with steam.

42. The method of claim 38, wherein the corrugated medium is adhesively joined to at least one of the interior liner board and the exterior liner board by a glue comprising: about 60 wt.% to about 95 wt.% of a copolymer of vinyl acetate and ethylene having less than about 0.5 wt.% vinyl acetate monomer, and about 5 wt.% to about 35 wt.% water; said glue having a viscosity of about 15 sec. to about 20 sec. as measured by #3 Zahn.

43. A water resistant coated article, comprising: a cellulosic fibrous substrate, having an interior surface and an exterior surface, an interior coating on the interior surface, the interior coating comprising: about 30 wt.% to about 85% of an aqueous solution of pre-copolymer of styrene-butadiene or carboxylated styrene-butadiene; about 1 wt.% to about 10 wt.% of a non- paraffinic wax selected for the group consisting of carnauba wax, polyethylene, plant based waxes, polyolefin based waxes, and mixtures thereof; and an exterior coating on the exterior surface, the exterior coating comprising: about 40 wt.% to about 80 wt.% of an aqueous solution of a pre-copolymer of styrene- butadiene or carboxylated styrene-butadiene; about 20 wt.% to about 60 wt.% of a filler selected from the group comprising titanium dioxide, barium sulfate, fillers which have a WVTR of less than about 1.1 times the WVTR of Ti0₂ at about the same weight percent filler, and combinations thereof.

44. The coated article of claim 43, wherein the interior coating further comprises about 10 wt.% to about 30 wt.% of an aqueous solution of a natural food gum.

45. The coated article of claim 44, wherein the natural food gum is an alkali metal alginate.

46. The coated article of claim 43, wherein the exterior coating further comprises about 1 wt.% to about 12 wt.% glycerine.