WO1996017789A1

WO1996017789A1 - Recyclable wax-coated containers

Info

Publication number: WO1996017789A1
Application number: PCT/US1994/014127
Authority: WO
Inventors: Jyh-Yee Lan; Teresa A. Krug
Original assignee: The Mead Corporation
Priority date: 1994-12-07
Filing date: 1994-12-07
Publication date: 1996-06-13
Also published as: AU1303995A

Abstract

A recyclable wax-coated paper product comprising a paper basestock coated with a wax composition comprising a mixture of a paraffin wax having a melting point of about 130 °F to 160 °F and a viscosity of about 10 to 200 cps at 10 °F above the melting points, a fatty acid having about 8 to 24 carbon atoms and a microcrystalline wax melting at a temperature less than about 180 °F and a method for recycling the containers prepared therefrom are disclosed.

Description

RECYCLABLE WAX-COATED CONTAINERS

Field of the Invention

The invention is directed to improved wax-coated containers and, more particularly, to wax-coated paperboard containers which are capable of being recycled under standard repulping conditions in a hydropulper without significantly increasing the repulping temperature or pH.

Background of the Invention

Wax-coated containers, particularly wax-coated corrugated paperboard containers have been used for years to ship and store fresh, perishable foods such as poultry, fish and meat. Typically, the containers are packed with crushed ice to keep the food cool during shipping and storage. The wax imparts water and moisture resistance to the containers. Examples of wax-coated or wax-impregnated paperboard containers are described in U.S. Patents

3,892,613 to McDonald et al.; 4,017,016 to Ivy; 4,126,225 to Hyland et al., and 4,948,033 to Halsell, II et al. As shown in Halsell, II et al., the paperboard may be impregnated with about 6 pounds per 1,000 square feet of a wax blend and then curtain coated with an additional 6.5 pounds per 1,000 square feet of wax blend.

Currently, wax-coated containers are not recycled for several reasons. In view of the large quantity of wax- coated containers which are used each year, it would be highly desirable to recycle the containers rather than to simply discard them. The reclamation of waste paper has been the subject of various patents and studies. For example, U.S. Patents 3,440,134 to Murphy, Jr., 4,347,009 to DeCuester et al.; 4,548,674 to Hageman et al.; and 4,737,238 to deRuvo, are related to methods for pulping waste paper and, particularly, used corrugated containers.

Several problems are inherent in recycling wax- coated containers. First, the purpose of the wax is to impart water and moisture resistance^' to the container and this property directly interferes with the essential property required in a recyclable container, namely, repulpability. Hence, it is necessary to remove the wax coating in the recycling process. Second, in removing the wax coating, a wax residue may remain on or contaminate the paper fibers. This residue weakens the strength of the recycled sheet because it prevents or reduces the amount of interfiber bonding such as hydrogen bonding which can be achieved in the sheet. Third, due to the high melting points of many of the waxes conventionally used in wax- coated containers, in order to remove the coating, it is necessary to modify the industry standard repulping conditions to use higher repulping temperatures. This can lead to increased energy costs which detracts from the profitability of recycling.

Presently used corrugated container boards are received at the pulping station in large bales. As a result of the difficulties involved in repulping wax-coated containers, if an inspection of the bales reveals the presence of an excessive amount of wax-containing board, the entire bale is discarded rather than repulped. While this may not represent a serious economic loss, it is certainly an important environmental concern. In order to recycle wax-coated containers, it would be desirable to design a wax coating which can be cleanly removed from the containerboard under conventional or industry standard repulping conditions of temperature and pH. Aluminum soaps have been proposed as a substitute for wax in recyclable wax-coated containers for this purpose, and the use of aluminum soaps in combination with fatty acids has also been considered. However, a hot dispersion technique and an alkaline pH are required to remove these coatings and there remains a need for a coating which is compatible with industry practice.

Summary of the Invention

It is a principal object of the present invention to provide a wax composition which can be used in wax-coated paper products such as wax-coated paperboard useful in making wax-coated containers and, more particularly, corrugated paperboard containers, and which is compatible with industry standard recycling procedures. The wax-coated paperboard of the present invention is designed to be repulped using a hydropulper at a temperature greater than about 130°F and preferably about 140 to 145°F and pH equal to or greater than about 6.5.

It is another object of the present invention to provide a wax-coated paperboard which can be used in wax- coated corrugated containers which is compatible with industry standard recycling procedures and which yields a recycled sheet which exhibits good strength.

The wax-coated products in accordance with the present invention are prepared using a was composition which comprises a paraffin wax having a melting point of about 130 to 160^CF and a viscosity of 20 to 200 cps at 10^βF above its melting point, a fatty acid having about 8 to 24 carbon atoms, and microcrystalline wax which melts at a temperature less than about about 180°F and preferably less than 160°F. This composition is desirable for use in making wax-coated paper products for two reasons in particular. First, it can be removed from the basestock in a hydropulper under standard operating procedures such that the fiber in the basestock can be recycled, and, second, its viscosity is such that the wax can be applied to the basestock by spray coating. Many previous wax coatings are too viscous to be applied by spray coating and are applied by curtain coating or other techniques such as immersion or impregnation. The higher viscosities and coating techniques associated with previous coatings have resulted in higher coat weights than are often necessary for satisfactory product performance and often unnecessarily add to the cost of the wax-coated product. Other objects and advantages of the present invention will become apparent from the following description and the appended claims.

Detailed Description of the Invention

The present invention is principally directed to wax-coated containers prepared from paperboard. However, those skilled in the art will appreciate that the invention may be useful in preparing any wax-coated paper product where ease of recyclability is desired including milk containers. The containers of the invention are designed primarily for use in shipping and storing perishable food items such as poultry, meat and fish. The containers of the present invention are conventional with the exception of the wax coating and the coating technique.

The wax composition used in the present invention incorporates a paraffin (macrocrystalline) wax having a melting point of about 130 to 160°F and preferably about 140°F, a viscosity of about 10 to 200 and preferably about 20 cps at 10°F above the melting point and is preferably ash-free, i.e., contains little or no fillers. The paraffin wax is preferably further characterized as comprising a mixture of paraffins ranging from about 20 to 45 carbon atoms and preferably about 20 to 40 carbon atoms with at least about 60 wt. % of the mixture containing waxes having about 25 to 32 carbon atoms and more preferably 26 to 30 carbon atoms. Suitable waxes include Ecco Wax 244 commercially available from Eastern Color and Chemical Company, Providence, RI, and Boler Wax 1977. A particularly preferred wax is Ecco Wax 244. The wax may be used alone but it is preferably used in combination with a fatty acid. The wax composition further includes a wax which is characterized as a microcrystalline wax which is flexible and melts at a temperature less than about 180^βF. This wax is selected such that it is compatible with the paraffin wax and the temperatures used in the hydropulper. The microcrystalline wax used in the preferred embodiment has a wide melting range from about 85°F to 160^βF. Preferably no more than about 15% of the wax, still more preferably no more than about 10% and most preferably no more than about 5-6% of the wax melts at a temperature less than about 100°F. If the wax contains substantially higher amounts of these low melting components, blocking may occur. The wax may be further characterized in that no more than about 10% and preferably no more than about 4-5% of the wax melts at a temperature greater than about 150^βF. Most preferably, about 75% to 90% of the microcrystalline wax melts in the range of about 100^βF to 150°F. One example of a useful microcrystalline wax is Bowax 1018. Other microcrystalline waxes which melt in about the same temperature range as the paraffin wax described above should also be useful in the present invention.

The third component of the wax composition is the fatty acid. Useful fatty acids are saturated or unsaturated fatty acids having about 8 to 22 carbon atoms. Examples of fatty acids useful in the invention include stearic acid, palmitic acid, myristic acid, lauric acid, capric acid, caprylic acid, arachidic acid, behenic acid, oleic acid, linoleic acid, etc. The preferred fatty acids include stearic acid, palmitic acid and myristic acid. Most preferably, the fatty acid is stearic acid.

The amount of the fatty acid will vary with the amount of water resistance desired in the product and its repulpability. The upper limit on the amount of fatty acid contained in the wax composition is dependent upon the water resistance desired. As the concentration of the fatty acid increases the water resistance of the coating tends to be reduced. For most applications, the wax composition may contain up to about 30% fatty acid, preferably about 5 to 20% and most preferably about 10%.

The fatty acid is believed to function as a wax- compatible soap precursor which forms a salt of the fatty acid upon the addition of a base such as an alkali or alkaline earth metal hydroxide or salt to adjust the pH during the repulping of the corrugated paperboard containers in the hydropulper. It is theorized that some of the wax used in carrying out the invention when used in conjunction with the fatty acid during repulping produces small wax particles which become interspersed among the fibers and acts as an internal sizing agent in the recycled sheet. It is further theorized that other conventional waxes which fall outside the above characterization description provide larger particles which may interfere with fiber-to-fiber bonding or hydrogen bonding and therefore reduce the strength of the repulped product.

It has been found that the particular wax material present in the highest concentration in the composition dictates the melting point of the composition. For example, in a composition containing 60% Ecco wax 244 having a melting point of about 140°F, 30% Bowax 1018 having a melting point of about 160°F, and 10% fatty acid, the observed melting point of the composition is at or near 140^βF, i.e., the melting point of the Ecco wax which is present in the composition at the higher concentration. It is believed that the wax present in the highest concentration may behave as a solvent for the wax present in the lesser concentration and that the melting point of the composition is determined similar to the melting point of other solutions as contrasted with other mixtures which yield melting points which are closer to the average melting point of the constituents.

In formulating the wax compositions of the present invention, the paraffin wax will be present in an amount greater than the amount of the microcrystalline wax.

Typically, the paraffin wax is present in an amount greater than 50%, preferably about 55-60% and most preferably about 60%. A highly preferred wax composition is one which contains about 60% Ecco wax 244, 25 to 35% Bowax 1018 and 5 to 15% fatty acid.

The containers of the present invention are typically paperboard made up of two sheets of liner board having a corrugated media sandwiched therebetween. In preparing a wax-coated container, the corrugated media is usually impregnated with the wax composition by immersing the media in a bath of the melted wax and the liner board is usually coated on one or both sides with the wax composition. Previously, wax coatings have typically been applied to the liner board using a curtain coater, however, due to the low viscosity of the wax composition of the present invention, it may be preferred to use a spray coating technique. Spray coating may enable coating of both sides of the basestock simultaneously and also enable the use of lesser amounts of the coating thereby providing an economical advantage over the prior art coatings. Additives which increase the viscosity of the wax may also be employed if it is desired to use curtain coating.

Typically, the wax-containing composition is applied at an average amount of about 5 pounds per 1,000 square feet. More precisely, the internal corrugated media is impregnated with the wax composition at a coat weight of about 3 to 5 pounds per 1,000 square feet and the interior liner of the corrugated media is generally coated with the wax composition at a coat weight of about 5 to 6 pounds of wax composition per 1,000 square feet. The coat weight is typically a function of a cost versus^' water-resistance balance.

The wax composition used in the present invention in coating the corrugated paperboard containers is especially attractive because, unlike prior waxes, it allows the wax-coated container to be recycled using a hydropulper at standard pulping conditions which include a temperature of about 130 to 160°F and a neutral or alkaline pH (e.g., greater than about 6.5). Any alkaline pH can be used to repulp the container, however, for compatibility with industrial operations, a pH of less than about 9.0 is preferred and a pH of less than about 8.0 is most preferred. Excellent results have been achieved with a wax composition of Ecco Wax 244 and stearic acid at a pH of 6.5. Removal of the wax is evident when the repulping water turns milky.

The invention is illustrated in more detail by the following non-limiting examples.

Example 1

Two sheets of corrugated liner board were prepared by hand-drawdown using the following compositions: (1) 60% Ecco Wax 244, 30% Bowax 1018 and 10% stearic acid, and (2) 80% Ecco Wax 244 and 20% stearic acid. The compositions were allowed to set and then evaluated for the properties shown in Table 1. WVTR and Fiber Recovery were measured in a conventional manner.

Boat soak was evaluated by accurately cutting and weighing an 8 inch square sample from the coated corrugated board. The sample was then scored 1 1/2 inches from the four edges as well as diagonally from the corners to the scores, folded into a bellows tray, placed in water and then filled with 1 inch of water. The sample coated with the E/F formulation was so brittle that the corrugated sample broke along the fold lines. After 72 hours, the sample was removed and a 4" x 4" specimen was cut, using a template, from the bottom of the boat and weighed to determine the % water pick-up.

Cleanness was evaluated by sandwiching each of the hand sheet between two sheets of blotter paper and heating to 250^PF. The surface of the sheets were then visually inspected for wax deposits.

The results are shown in Table 1 below.

T A B L E I

Tesc -TVTR Boat Soaking, % Fiber Rec. , % Cleanness (g/100 in ^J/24th) (Corrugated) System 15 Min. 30 Min. BS-15 ! AS-15

Target 1 7% >Θ0V >80. Clean ! Clean Volume

Co p No. 1 0.5 7% 93.3 94.7 Clean ' Clean

Cotnp No. 2 0.7 12%* 94.3 97.6 Clean ! Clean

The corrugated board broke along the fold liner.

It will be recognized by those skilled in the art that changes may be made to the above-described embodiments of the invention without departing from the broad inventive concepts thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover all modifications which are within the scope and spirit of the invention as defined by the appended claims. What is claimed is:

Claims

1. A recyclable wax-coated paper product comprising a paper basestock coated with a wax composition comprising a mixture of a paraffin wax having a melting point of about 130^*F to 160^*F and a viscosity of about 10 to 200 cps at 10^*F above the melting points, wherein said paraffin wax is a mixture of paraffins ranging from about 20 to 45 carbon atoms with at least about 60 weight percent of said paraffins ranging from about 25 to 32 carbon atoms, about 5 to 30% of a fatty acid having about 8 to 22 carbon atoms, and a microcrystalline wax melting at a temperature less than about 180^*F.

2. The paper product of claim 1 wherein said paraffin wax is a mixture of paraffins ranging from about 20 to 40 carbon atoms with at least about 60 weight percent of said paraffins ranging from about 26 to 30 carbon atoms.

3. The paper product of claim 1 wherein said fatty acid is selected from the group consisting of stearic acid, palmitic acid and myristic acid.

4. The paper product of claim 1 wherein said paraffin wax has a melting point of about 140^*F and a viscosity of about 20 cps at 10^*F above its melting point.

5. The paper product of claim l wherein said paper product is paperboard and said paperboard includes a liner board which is coated with said wax composition at a coat weight of about 3 to 6 pounds per 1,000 square feet.

6. The paper product of claim 5 wherein said paperboard includes a corrugated media impregnated with said wax composition in an amount of about 2 to 5 pounds per 1,000 square feet.

7. The paper product of claim 1 wherein said wax-coated paper product is recyclable in a hydropulper at a temperature sufficient to remove said wax composition from said container and at a pH greater than about 6.5.

8. The paper product of claim 1 wherein said paraffin wax is present in said wax composition in an amount greater than the amount of said microcrystalline wax.

9. The paper product of claim 8 wherein said wax composition comprises greater than 50% of said paraffin wax, about 25 to 35% of said microcrystalline wax, and about 5 to 15% of a fatty acid selected from the group consisting of stearic acid, palmitic acid and myristic acid.

10. The paper product of claim 1, wherein said paper product is a corrugated paperboard container.

11. The paper product of claim 10 wherein said fatty acid is stearic acid.

12. The paper product of claim 11 wherein said microcrystalline wax melts in the range of about 85 to 160'F.

13. The paper product of claim 12 wherein at least about 75% to 90% of said microcrystalline wax malts in the range of about 100^*F to 150^*F.

14. The paper product of claim 5 wherein said liner of said paperboard is spray coated with said wax composition at a coat weight of about 3 to 6 pounds per 1,000 square feet.

15. The paper product of claim 5 wherein the wax composition is applied to said liner board using a curtain coater.

16. The paper product of claim 15 wherein said wax composition further contains a viscosity increasing additive.

17. A recyclable wax coated container comprising a paper basestock coated with a wax composition consisting essentially of a paraffin wax ranging from about 20 to 45 carbon atoms with at least about 60 weight percent of said paraffin wax ranging from about 25 to 32 carbon atoms said paraffin wax having a melting point of about 130^*F to 160^*F and a viscosity of about 10 to 200 cps at 10^*F about the melting point; a microcrystalline wax melting at a temperature less than about 180^*F, wherein no more than about 15% of said microcrystalline wax melts at less than about 100^*F, and about 5 to 30% of a fatty acid having about 8 to 22 carbon atoms, wherein said paraffin wax is present in said composition in an amount greater than the amount of microcrystalline wax.

18. A recyclable container having improved flexibility and watertight integrity wherein said container comprises paperboard coated or impregnated with a wax composition comprising:

(1) about a 60% paraffin wax having a melting point of about 140^*F and a viscosity of about 20 cps at 10^*F above its melting point, said paraffin wax comprising a mixture of paraffins ranging from about 20 to 40 carbon atoms with at least about 60% of said paraffins ranging from about 26 to 30 carbon atoms;

(2) about 30% microcrystalline wax having a melting range of about 85 to 160^*F wherein at least about 75% to 90% of said microcrystalline wax melts in the range of about 100'F to 150^*F; and

(3) about 10% stearic acid, said container being recyclable in a hydropulper at a temperature of about 140 to 160^*F and a pH of about 6.5 to 9.

19. A method for recycling a paperboard container coated with a wax composition wherein said wax composition comprises a mixture of a paraffin wax having a melting point of about 130 to 160^*F, and a viscosity of about 10 to 200 cps at 10^*F, above the melting point, said paraffin wax being a mixture of paraffins ranging from about 20 to 45 carbon atoms with at least about 60% of said paraffins ranging from about 25 to 32 carbon atoms, a fatty acid having about 8 to 22 carbon atoms and a microcrystalline wax having a melting range of about 85^*F to 160^*F comprising repulping said wax-coated container in a hydropulper at a temperature of about 140 to 160^*F and a pH of about 6.5 to 9.0.

20. The method of claim 19 wherein said wax-coated container is repulped in the presence of an alkali or alkaline earth metal hydroxide or salt to convert said fatty acid to a soap, said soap being capable of emulsifying said wax.

21. The method of claim 19 wherein said wax composition comprises:

(1) greater than 50% paraffin wax having a melting point of about 140^*F and a viscosity of about 20 cps at 10^*F above its melting point, said paraffin wax comprising a mixture of paraffins ranging from about 20 to 40 carbon atoms with at least about 60% of said paraffins ranging from about 26 to 30 carbon atoms;

(2) about 25% to 35% microcrystalline wax having a melting range of 85 to 160'F, wherein at least about 75% to 90% of said microcrystalline wax melts in the range of about 110"F to 150^*F; and

(3) about 5% to 15% stearic acid.