CA2323341A1 - A paperboard container having enhanced grease resistance and rigidity and a method of making same - Google Patents
A paperboard container having enhanced grease resistance and rigidity and a method of making same Download PDFInfo
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- CA2323341A1 CA2323341A1 CA002323341A CA2323341A CA2323341A1 CA 2323341 A1 CA2323341 A1 CA 2323341A1 CA 002323341 A CA002323341 A CA 002323341A CA 2323341 A CA2323341 A CA 2323341A CA 2323341 A1 CA2323341 A1 CA 2323341A1
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Abstract
The invention is directed to a container press-formed of paperboard having a top surface that is substantially free of clay coating and that is disposed for contact with material to be contained and an opposed bottom surface, the container comprising a first functional coating material such as a latex dispersed in the paperboard forming a grease resistant surface. The invention also encompasses a method of manufacturing the press-formed paperboard container comprising before the container is press-formed the step of applying to the top surface of the paperboard that is substantially free of clay coating a first functional coating sufficient to form a grease resistant surface.
Description
A PAPERBOARD CONTAINER HAVING ENHANCED
GREASE RESISTANCE AND RIGIDITY
AND A METHOD OF MAKING SAME
Field of the Invention This invention pertains to press-formed paperboard containers, such as paper plates, paper trays, paper cups, and the like. In particular, this invention pertains to paperboard containers having enhanced rigidity and grease resistance and the method of making such containers.
Back_around of the Invention In the common process, paperboard web, after drying, is passed through a size press to apply starch sizing or other binders to both surfaces of the web.
After smoothing the surfaces, the web surface that will be used as the top or upper surface of a container, such as a plate or bowl, is coated with at least one coat of clay coating. The top layer or upper surface is then coated with at least one functional coating material that forms a barrier to moisture. Such a barrier is intended to prevent moisture from the food or drink placed in the container from wetting the paperboard. Many layers of functional coating material may be placed on the upper surface. In some products, the upper surface may also be printed. The printing ink is applied directly to the top clay coating and then is covered with one or more layers of functional heat releaselsealant coating material to preclude contact between the printing ink and food placed on or in the container. The coated paperboard is then rolled.
To form paperboard containers from the sized and coated paperboard stock, the paperboard web is moistened on the un-coated lower surface to achieve a predetermined level of moisture in the paperboard. The moisture content aids in deformation of the paperboard during press forming into the desired container shape. The moisture is generally added by a common device known as a flooded nip in amounts sufficient to achieve about 8-12 % moisture.
Since paperboard when dry contains about 3-6 % moisture, the flooded nip can add up to about 6% additional moisture. While water is a preferred moistening medium, some moistening solutions contain wax and surfactants, the former to act as a lubricant in the pressing operation and the latter to assist in moisture penetration. An available concentrate for a moistening solution is Velvetol~
sold by Rhone-Poulenc of Cranbury, NJ; it contains polyolefin wax and ethoxylated surfactant.
The moistened paperboard web may be rolled and cured for up to 24 hours after which it is die-cut into blanks having the shape and dimensions appropriate for the container to be made. Each blank is then fed into a die press in which mating dies, heat, and pressure work the paperboard blank to form it into the desired container.
Typically, grease resistance in paper plates is achieved primarily through the application of clay coatings over the porous fiber network at the board manufacturing facility. These coatings consist of various levels of fillers, pigments, binders, and other materials, that when combined, fill the voids in paperboard and form a smooth, printable surface. These coatings provide some degree of grease resistance which can be enhanced through the use of additional top functional coating materials such as polyvinyl acetate, sarans, and acrylics that are FDA approved for food contact. These coatings are referred to as releaselsealant coatings as they serve a dual function of improving release of the plate from the forming die, as well as enhancing grease and moisture resistance when applied over the clay coating. The grease resistence of prior art boards is still typically less than 50%. That is, typically half of the plate bottom will be grease stained. The paperboard for such generally accepted base materials is on the order of 160-200 pounds per 3,000 square foot ream.
The cost of clay coated paperboard economically interferes with entry into the light duty plate market segment with a grease resistant product.
Furthermore, feasible economic entry into this market would benefit from lightweight paperboard in the 100-140 pounds per 3,000 square foot ream as compared to the 160-200 pounds per 3,000 square foot ream paperboard that is
GREASE RESISTANCE AND RIGIDITY
AND A METHOD OF MAKING SAME
Field of the Invention This invention pertains to press-formed paperboard containers, such as paper plates, paper trays, paper cups, and the like. In particular, this invention pertains to paperboard containers having enhanced rigidity and grease resistance and the method of making such containers.
Back_around of the Invention In the common process, paperboard web, after drying, is passed through a size press to apply starch sizing or other binders to both surfaces of the web.
After smoothing the surfaces, the web surface that will be used as the top or upper surface of a container, such as a plate or bowl, is coated with at least one coat of clay coating. The top layer or upper surface is then coated with at least one functional coating material that forms a barrier to moisture. Such a barrier is intended to prevent moisture from the food or drink placed in the container from wetting the paperboard. Many layers of functional coating material may be placed on the upper surface. In some products, the upper surface may also be printed. The printing ink is applied directly to the top clay coating and then is covered with one or more layers of functional heat releaselsealant coating material to preclude contact between the printing ink and food placed on or in the container. The coated paperboard is then rolled.
To form paperboard containers from the sized and coated paperboard stock, the paperboard web is moistened on the un-coated lower surface to achieve a predetermined level of moisture in the paperboard. The moisture content aids in deformation of the paperboard during press forming into the desired container shape. The moisture is generally added by a common device known as a flooded nip in amounts sufficient to achieve about 8-12 % moisture.
Since paperboard when dry contains about 3-6 % moisture, the flooded nip can add up to about 6% additional moisture. While water is a preferred moistening medium, some moistening solutions contain wax and surfactants, the former to act as a lubricant in the pressing operation and the latter to assist in moisture penetration. An available concentrate for a moistening solution is Velvetol~
sold by Rhone-Poulenc of Cranbury, NJ; it contains polyolefin wax and ethoxylated surfactant.
The moistened paperboard web may be rolled and cured for up to 24 hours after which it is die-cut into blanks having the shape and dimensions appropriate for the container to be made. Each blank is then fed into a die press in which mating dies, heat, and pressure work the paperboard blank to form it into the desired container.
Typically, grease resistance in paper plates is achieved primarily through the application of clay coatings over the porous fiber network at the board manufacturing facility. These coatings consist of various levels of fillers, pigments, binders, and other materials, that when combined, fill the voids in paperboard and form a smooth, printable surface. These coatings provide some degree of grease resistance which can be enhanced through the use of additional top functional coating materials such as polyvinyl acetate, sarans, and acrylics that are FDA approved for food contact. These coatings are referred to as releaselsealant coatings as they serve a dual function of improving release of the plate from the forming die, as well as enhancing grease and moisture resistance when applied over the clay coating. The grease resistence of prior art boards is still typically less than 50%. That is, typically half of the plate bottom will be grease stained. The paperboard for such generally accepted base materials is on the order of 160-200 pounds per 3,000 square foot ream.
The cost of clay coated paperboard economically interferes with entry into the light duty plate market segment with a grease resistant product.
Furthermore, feasible economic entry into this market would benefit from lightweight paperboard in the 100-140 pounds per 3,000 square foot ream as compared to the 160-200 pounds per 3,000 square foot ream paperboard that is
-2-typically clay coated. Lightweight clay coated board volume is relatively nonexistent and where available sells at a premium price above conventional weight clay coated boards. Non clay coated lightweight board is abundantly available at low cost and is the primary choice among light duty plate producers who then produce plates with little or no grease resistance. Such lightweight board forms an inferior product since it does not provide an attractive level of plate rigidity. In addition, the clay coating on boards can be rather brittle and susceptible to pleat cracking which increases the difficulty in forming lightweight plates from clay coated boards where high forming pressures are used.
In evaluating the process for making paperboard containers, the inventors have determined that application of a latex coating on the top or outermost upper surface of a coated web allows for replacement of at least some, and preferably all, of the layers of clay coating, while achieving both rigidity similar to that of much heavier paperboard, as well as enhanced grease resistance. Therefore, lightweight paperboard, i.e., less than 160 pounds per 3,000 square foot ream, can be used while achieving good grease resistance and the desired rigidity.
In addition, paperboard containers with superior grease resistance, as well as superior rigidity, can be manufactured by using this method with paperboards with weights in excess of 160 pounds per 3,000 square foot ream. In a more preferred embodiment of the present invention, a releaselsealant coating can be applied over the SBR latex coating.
The object of the invention, therefore, is to achieve enhanced container rigidity, as well as enhanced container grease resistance in an economical, lightweight plate by application of a functional coating material in place of the clay coating to a lightweight paperboard. In this application, the preferred functional coating used is an SBR latex. SBR latex is a synthetic binder produced via polymerization of styrene and butadiene monomers in a pressurized reaction with surfactants added for stability.
In evaluating the process for making paperboard containers, the inventors have determined that application of a latex coating on the top or outermost upper surface of a coated web allows for replacement of at least some, and preferably all, of the layers of clay coating, while achieving both rigidity similar to that of much heavier paperboard, as well as enhanced grease resistance. Therefore, lightweight paperboard, i.e., less than 160 pounds per 3,000 square foot ream, can be used while achieving good grease resistance and the desired rigidity.
In addition, paperboard containers with superior grease resistance, as well as superior rigidity, can be manufactured by using this method with paperboards with weights in excess of 160 pounds per 3,000 square foot ream. In a more preferred embodiment of the present invention, a releaselsealant coating can be applied over the SBR latex coating.
The object of the invention, therefore, is to achieve enhanced container rigidity, as well as enhanced container grease resistance in an economical, lightweight plate by application of a functional coating material in place of the clay coating to a lightweight paperboard. In this application, the preferred functional coating used is an SBR latex. SBR latex is a synthetic binder produced via polymerization of styrene and butadiene monomers in a pressurized reaction with surfactants added for stability.
-3-Summary of the Invention As embodied and broadly described herein, the invention is a container press-formed of paperboard having a top surface which is substantially free of clay coating and that is disposed for contact with material to be contained and an opposed bottom surface, the container comprising a paperboard layer, a size press coating layer on the top surface and a first functional coating material dispersed at the top surface size press coating layer, wherein the first functional coating is latex.
In preferred embodiments, a second functional coating material is disposed on the top surface in quantities sufficient to form a barrier to moisture.
The second layer can either be another layer of SBR or a releaselsealant layer.
If the second layer is SBR, a layer of releaselsealant coating should be applied over it. At higher levels of SBR application, the sealant qualities of: the releaselsealant coatings become less important than the release properties.
Preferably, the first functional coating material is a latex. In the presently preferred embodiment, the first functional coating material is Tykote~ Base I
distributed by Reichold, Inc. of Research Triangle Park, NC. The container of the invention preferably comprises first functional coating material at about pounds per 3,000 square foot ream of paperboard.
The invention further contemplates a method of making the container of the invention comprising the steps of forming the paperboard; applying first and second functional coating materials to the top surface size press layer;
cutting a blank for the container from the paperboard; and press-forming the blank at a predetermined temperature and pressure to form the container.
The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention.
In preferred embodiments, a second functional coating material is disposed on the top surface in quantities sufficient to form a barrier to moisture.
The second layer can either be another layer of SBR or a releaselsealant layer.
If the second layer is SBR, a layer of releaselsealant coating should be applied over it. At higher levels of SBR application, the sealant qualities of: the releaselsealant coatings become less important than the release properties.
Preferably, the first functional coating material is a latex. In the presently preferred embodiment, the first functional coating material is Tykote~ Base I
distributed by Reichold, Inc. of Research Triangle Park, NC. The container of the invention preferably comprises first functional coating material at about pounds per 3,000 square foot ream of paperboard.
The invention further contemplates a method of making the container of the invention comprising the steps of forming the paperboard; applying first and second functional coating materials to the top surface size press layer;
cutting a blank for the container from the paperboard; and press-forming the blank at a predetermined temperature and pressure to form the container.
The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention.
-4-Brief Description of the Drawings Figure 1 is a cross section of a paperboard container illustrating possible mechanisms by which the invention improves container rigidity and grease resistance.
Figure 2 is a cross section of a paperboard container illustrating possible mechanisms by which the invention improves container rigidity.
Figure 3 is a micrograph of a z-fold of a prior art paper board container.
Figure 4 is a micrograph of a z-fold of a paperboard container of the present invention.
Description of the Preferred Embodiment Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.
In accordance with the invention, the container is press-formed of paperboard having opposed top and bottom surfaces. As illustrated in Figure 1, the container 10 is press-formed from paperboard 12 having a top surface 14 and a bottom surface 16. The paperboard may be any cellulosic fiber web having weight and surface characteristics known to be useful for containers.
Preferably, the paperboard has a basis weight of 100-160 pounds per 3,000 square foot ream. It is more preferred that the paperboard have a basis weight of 130-140 pounds per 3,000 square foot ream, although the invention may provide improved grease resistance, improved rigidity, and other improved performance characteristics using paperboard at other weights.
In a traditional paperboard container, both top and bottom surfaces 14, 16 are size press coated. Although it is not conventional to apply size press coating to one side of the paperboard, it is not strictly necessary to apply coating to both.
For example, if only one side of the paperboard bears size press coating, the paperboard will often exhibit a tendency to curl. In addition, the paperboard will only achieve half the strength properties of a paperboard having a two-sided
Figure 2 is a cross section of a paperboard container illustrating possible mechanisms by which the invention improves container rigidity.
Figure 3 is a micrograph of a z-fold of a prior art paper board container.
Figure 4 is a micrograph of a z-fold of a paperboard container of the present invention.
Description of the Preferred Embodiment Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.
In accordance with the invention, the container is press-formed of paperboard having opposed top and bottom surfaces. As illustrated in Figure 1, the container 10 is press-formed from paperboard 12 having a top surface 14 and a bottom surface 16. The paperboard may be any cellulosic fiber web having weight and surface characteristics known to be useful for containers.
Preferably, the paperboard has a basis weight of 100-160 pounds per 3,000 square foot ream. It is more preferred that the paperboard have a basis weight of 130-140 pounds per 3,000 square foot ream, although the invention may provide improved grease resistance, improved rigidity, and other improved performance characteristics using paperboard at other weights.
In a traditional paperboard container, both top and bottom surfaces 14, 16 are size press coated. Although it is not conventional to apply size press coating to one side of the paperboard, it is not strictly necessary to apply coating to both.
For example, if only one side of the paperboard bears size press coating, the paperboard will often exhibit a tendency to curl. In addition, the paperboard will only achieve half the strength properties of a paperboard having a two-sided
-5-application. As depicted using dashed lines in Figure 1, the paperboard of the container can be divided roughly into three equal cross-sectional regions. The top region 20 proximate the top surface is defined by the depth of penetration of the upper size press coating from top surface 14. The bottom region 22 proximate the bottom surface is defined by the depth of size press coating penetration from the bottom surface 16. The middle region 24, sometimes called the fiber core, is defined between the top and bottom regions 20, 22.
In a preferred embodiment, approximately 5 - 8 pounds of size press coating are applied to each of the top and bottom layers per 3,000 square foot ream of paperboard. In a more preferred embodiment, 6.5 pounds of size press coating are applied to each of the top and bottom layers per 3,000 square foot ream of paperboard. In traditional paperboard, the size press coating is a starch or similar material. The size press coating layer is followed by application of one or more clay coating layers, as well as a sealant/release coating.
In the present invention, a container is press-farmed of paperboard having a top surface that is substantially free of clay coating. A paperboard is substantially free of clay coating for purposes of the present invention when it lacks a quantity of clay coating sufficient to materially enhance the barrier properties of the paperboard. Barrier properties are characterized by, for example, grease resistance. The mere presence of clay either in or as a layer with the coated paperboard of the present invention does not materially effect the paperboard of the present invention. For example, a paperboard could have a clay layer, but still require a layer of latex to materially enhance the barrier properties of the paperboard. Clay coating layers of up to, for example, two (2) pounds per 3,000 square foot ream of paperboard may be added to the paperboard without materially affecting barrier properties. Thus, containers having such structures are considered to be part of the present invention.
In a preferred embodiment, the top surface of the paperboard has no clay coating. As a replacement for some or all of the clay coating, a quantity of first
In a preferred embodiment, approximately 5 - 8 pounds of size press coating are applied to each of the top and bottom layers per 3,000 square foot ream of paperboard. In a more preferred embodiment, 6.5 pounds of size press coating are applied to each of the top and bottom layers per 3,000 square foot ream of paperboard. In traditional paperboard, the size press coating is a starch or similar material. The size press coating layer is followed by application of one or more clay coating layers, as well as a sealant/release coating.
In the present invention, a container is press-farmed of paperboard having a top surface that is substantially free of clay coating. A paperboard is substantially free of clay coating for purposes of the present invention when it lacks a quantity of clay coating sufficient to materially enhance the barrier properties of the paperboard. Barrier properties are characterized by, for example, grease resistance. The mere presence of clay either in or as a layer with the coated paperboard of the present invention does not materially effect the paperboard of the present invention. For example, a paperboard could have a clay layer, but still require a layer of latex to materially enhance the barrier properties of the paperboard. Clay coating layers of up to, for example, two (2) pounds per 3,000 square foot ream of paperboard may be added to the paperboard without materially affecting barrier properties. Thus, containers having such structures are considered to be part of the present invention.
In a preferred embodiment, the top surface of the paperboard has no clay coating. As a replacement for some or all of the clay coating, a quantity of first
-6-functional coating material 18 applied to the top surface during production of the container is sufficient to provide formation of a grease resistant barrier at the top surface. In a preferred embodiment, the first functional coating material is applied at a rate of 1-7 pounds per 3,000 square foot ream of paperboard. The actual preferred amount depends on board smoothness. The smoother the board, the less first functional coating is needed. In a more preferred embodiment, two layers of a first functional coating material are applied at a total rate of 1-7 pounds per 3,000 square foot ream of paperboard. In a still more preferred embodiment, more than two layers of a first functional coating material are applied, having a total rate of 1-7 pounds per 3,000 square foot ream of paperboard. If the board is very smooth, traditional hydrophilic coating methods may be used. In the case of rough board, it is preferred to use gravure coating methods with a smoothing bar. This is particularly desirable when there is no clay on the board.
Preferably, the first functional coating material is a styrene butadiene copolymer. In the preferred embodiment, the first functional coating material is primarily styrene butadiene rubber, specifically Tykote~ Base I distributed by Reichold, Inc. of Research Triangle Park, NC.
In traditional paperboard containers, the top surface 14 is often subject to printing. Generally, the clay coatings applied to a conventional paperboard, as discussed above, define a printing surface and provide partial grease resistance on the paperboard. Clay coatings add additional cost, as well as weight, to traditional paperboard containers. In addition, clay coatings are generally available on paperboards having heavy basis weights of 160-200 pounds per 3,000 square foot ream. Of note, in traditional paperboard containers, paperboards having basis weights of 160-200 pounds per 3,000 square foot ream are necessary to achieve the rigidity of the container desired by consumers. Furthermore, lightweight boards with the coatings of the present _7_ invention seem to be more tolerant of high forming pressures than lightweight clay coated boards.
In a preferred container of this invention, however, the size press coating layer of starch or similar material is of sufficient thickness to define a printing layer. In one embodiment of the preferred containers, the size press coating layer on the top surface is applied at a rate of approximately 6.5 Ibs per 3,000 square foot ream of paperboard. When a layer of this magnitude is applied, the size press substantially fills in the interstitial spaces in the rough paperboard surface providing a smoother upper surface for printing as compared to a similar paperboard having no size press coating layer. In this embodiment the size press coating is applied in a nip section wherein the size press coating is forced into the paperboard at the nip. Testing has shown that a large portion of the size press coating, however, remains impregnated in the paperboard such that the amount of size press coating contributing to a smoother surface on the upper layer is reduced. That is, if about 6.5 Ibs of size press coating is applied per 3,000 square foot ream of paperboard, approximately 75% is located beneath the surface of the paperboard, while only approximately 25% remains at the surface. The 75% of the size press coating located beneath the surface of the paperboard resides in the upper one-third of the paperboard total caliper. For purposes of this application, we will define this ratio of size press coating applied to size press residing beneath the surface of the paperboard as size press coating factor. Thus, using this method, the size press coating has a size press coating factor of about 1.33. While the printability of this embodiment is greater than a non clay coated board having a size press coating layer of 0-3 Ibs, per 3,000 square foot ream of paperboard, on the top layer, the printability is still inferior to that of a prior art clay coated board.
In a more preferred embodiment, printability approaching parity to that of a clay coated board is achieved in a non clay coated board at least as perceived by typical consumers. In this embodiment a film forming size press coating is _g_ applied to the paperboard. A film forming starch preferred in this embodiment has a much lower viscosity than a non-film forming starch applied at a size press nip. Starches typically applied at a size press nip typically have a high viscosity to more effectively impregnate the paperboard. One example of this type of size press coating is Cofilm, distributed by National Starch. In this method, the film forming starch is applied with a calendar box instead of in a typical size press nip. Using this method, it is preferred that approximately 1-6 Ibs of size press coating be applied to the 3,000 square foot per ream paperboard, with about half of the size press coating being applied to the top surface. Testing has shown that when using a film forming size press coating, only about 33% of the size press coating applied, impregnates the paperboard beneath the surface, thus achieving a coating size press coating factor of approximately 3.
Improved printability when using the film forming starch was shown in laboratory tests. In these tests, three different smoothness properties were tested: (1) Bendtsen Roughness; (2) Sheffield Roughness; and (3) Parker Print.
As shown below, better printability, indicated by lower numbers on each of the three factors, was seen in a paperboard coated with a film forming starch applied at a calendar box as compared to paperboard having starch applied at a size press coating. Lower numbers indicate a smoother surface.
Bendtsen Sheffield Sample Roughness Roughness Parker Print Standard Size Press 384 168 6.40 Film Forming Size 210 139 5.97 Press Thus, according to the present invention, less size press coating is used, while achieving a better printing surface. One drawback to this method is a reduction to the rigidity of the plate as compared to the method in which size press coating is deeply impregnated into the board. It should be noted, however, that as shown below, the plate rigidity of a paper plate of the preferred invention formed _g_ using this method can still be approximately equivalent to that found in the heavier clay coated paperboards.
The ink layer can be applied to the size press coating layer or to the latex layer. Thus, in one embodiment the ink is applied to the size press coating layer and the latex is then applied over the ink layer. In a second embodiment, the latex layer is applied to the size press coating and then the ink is applied to the latex layer. One example of ink used in this application is VMT Ink supplied by Progressive Inks of St. Louis, Mo.
The latex functional coating is applied after application of ink to the printing surface. When applying the functional latex coating, the latex appears to penetrate interstitial spaces in the size press coatings and the paperboard, thereby enhancing grease resistance and providing the container with increased rigidity. As seen in the examples below, the result is a 130-140 pound per 3,000 square foot ream paperboard container having a rigidity equivalent to a 160-pound per 3,000 square foot ream paperboard, with enhanced grease resistance. Thus, a desirable paperboard container is formed with an approximately 20% reduction in paperboard weight and, a corresponding 20%
reduction in paperboard cost. As well, a further reduction in weight is achieved as layers of clay coating are no longer necessary.
After the addition of the latex layer, one or more release/sealant coatings may be applied to further isolate the ink from contact with consumables. Thus, in a preferred embodiment, the container of the invention includes a second releaselsealant coating material on the top surface. Preferably, any known functional coating for the top surface of paperboard containers may be applied in any known manner. The second releaselsealant coating may be selected from food-safe polymers such as nitrocellulose, Saran and styrene acrylic acid copolymers, methyl cellulose, carboxymethyl cellulose acetate copolymer, vinyl acetate copolymer, styrene butadiene copolymer, and styrene-acrylic copolymer.
It is preferred that the second releaselsealant coating be applied at a rate of '/2 -1 pound per 3,000 square foot ream of paperboard. There may be a number of layers of second releaselsealant coating materials on the top surface of the container depending on the intended uses of the container and on whether the container's top surface is printed with an ink that must be isolated from contact with consumables.
In another embodiment, applicants have learned that paperboard plates having desirable rigidity and grease resistance can be formed using unbleached kraft paperboard. Environmentally conscious consumers often avoid the use of paper plates due to the harsh chemicals used to bleach the paperboard used in making paperboard plates. Applicants have found that an environmentally friendly paperboard plate, having the desired rigidity and grease resistance, can be made by using Tykote Base I as a functional coating. In this embodiment, an unbleached paperboard having a top layer of predominately hardwood fibers and a bottom layer of predominately softwood fibers has proven to be satisfactory.
In one commercially available grade of board, the top layer contains only a minor amount of softwood, on the of impurities in the pulp supply, while the other contains only minor amounts of hardwood. In this available grade, the predominately hardwood layer typically comprises around 10 - 30% of the board by volume. The predominately hardwood layer will most often comprise approximately 15% of the z-directional volume of the board, with the predominately softwood layer comprising the balance. While such a construction will form a paper plate, it has little or no grease resistance. Addition of about 1-7 pounds of Tykote Base I per 3,000 square foot ream of paperboard, as discussed above, provides the desired grease resistance. Moreover, the addition of the Tykote layer also increases the rigidity in the board. If the predominately hardwood layer comprises substantial proportions of softwoods, rather larger amounts of Tykote may be required to provide the desired barrier properties.
In accordance with the invention, a preferred method of manufacturing the press-formed container of the invention comprises, before press-forming the paperboard container having a size press coating, the step of applying to the top surface of paperboard a first functional coating to form a barrier to grease as well as to enhance rigidity, wherein the first functional coating is a latex, and wherein the first functional coating at least partially penetrates the size press coating.
After application of the first functional latex coating, at least one second releaselsealant coating may be applied.
Prior to pressing the containers, a moistening solution is applied to the bottom surface of the paperboard. The moistening solution used can be water or, preferably, a solution of 50 parts water and one part Velvetol~ as sold by Rhone-Poulenc of Cranbury, NJ. The moistening solution used, therefore, contains water, a surfactant, and a wax. , r The enhanced rigidity and grease resistance of lightweight paperboard containers made in accordance with the method of the invention was first confirmed in a laboratory evaluation. A comparison of paper plates made in accordance with the method of this invention having paperboard weights from 126 to 176 pounds per 3,000 square foot ream (samples 1 to 6) were compared with paper plates made with clay coated paperboard having a paperboard weight of 162 pounds per 3,000 square foot ream (sample 7), as well as with clay coated paper plates having a paperboard weight of 124 pounds per 3,000 square foot ream (sample 8). In addition, a non clay coated paper plate having a film forming starch applied and having a paperboard weight of 143 pounds per 3,000 square foot ream was also compared (sample 9). In the laboratory evaluation, the 126 and 176 pounds per 3,000 square foot ream non clay coated paperboards were coated with 13 pounds of size press per 3,000 square foot ream of paperboard (6.5 pounds per 3,000 square foot ream on each of the upper and lower surfaces), four layers of ink, approximately 2-3 pounds of Tykote Base I SBR latex per 3,000 square foot ream of paperboard, a barrier base release/sealant coating, and a barrier top releaselsealant coating. The 162 pounds per 3,000 square foot ream clay-coated paperboard had two layers of clay coating, four layers of ink, a barrier base releaselsealant coating, and a barrier top releaselsealant coating. Sample 8 had at least one layer of clay coating. Sample 9 was formed similarly to Samples 1-6 in that 2-3 pounds of Tykote Base I SBR latex was applied per 3,000 square foot ream of paperboard;
however, the board was coated with approximately 4-6 pounds of film forming size press per 3,000 square foot ream of paperboard (approximately 2-3 pounds per 3,000 square foot ream on each of the upper and lower surfaces).
The paperboards were then used to make 9" paper plates under standard press conditions. The paperboard was unrolled; no blocking (adhesive sticking) was encountered. Blanks were cut, scored and press-formed from the paperboard at 55 strokes per minute. The press temperature was 300°F.
The plates formed thereby were then tested for dry rigidity using the Plate Rigidity Tester, Model ML4431-2. The plate tester used conforms to the standard FSK
tester, except that it is modified to simulate how a consumer would hold the plate with one hand, whereas the thumb is placed on the upper surface brim area and the fingers are placed on the lower surface near the center of the plate. The following table provides the test results for the dry rigidity test.
Quantity Basis Weight Dry Mean Sample of Lbs13,000 Square Foot Ream Rigidity' Plates
Preferably, the first functional coating material is a styrene butadiene copolymer. In the preferred embodiment, the first functional coating material is primarily styrene butadiene rubber, specifically Tykote~ Base I distributed by Reichold, Inc. of Research Triangle Park, NC.
In traditional paperboard containers, the top surface 14 is often subject to printing. Generally, the clay coatings applied to a conventional paperboard, as discussed above, define a printing surface and provide partial grease resistance on the paperboard. Clay coatings add additional cost, as well as weight, to traditional paperboard containers. In addition, clay coatings are generally available on paperboards having heavy basis weights of 160-200 pounds per 3,000 square foot ream. Of note, in traditional paperboard containers, paperboards having basis weights of 160-200 pounds per 3,000 square foot ream are necessary to achieve the rigidity of the container desired by consumers. Furthermore, lightweight boards with the coatings of the present _7_ invention seem to be more tolerant of high forming pressures than lightweight clay coated boards.
In a preferred container of this invention, however, the size press coating layer of starch or similar material is of sufficient thickness to define a printing layer. In one embodiment of the preferred containers, the size press coating layer on the top surface is applied at a rate of approximately 6.5 Ibs per 3,000 square foot ream of paperboard. When a layer of this magnitude is applied, the size press substantially fills in the interstitial spaces in the rough paperboard surface providing a smoother upper surface for printing as compared to a similar paperboard having no size press coating layer. In this embodiment the size press coating is applied in a nip section wherein the size press coating is forced into the paperboard at the nip. Testing has shown that a large portion of the size press coating, however, remains impregnated in the paperboard such that the amount of size press coating contributing to a smoother surface on the upper layer is reduced. That is, if about 6.5 Ibs of size press coating is applied per 3,000 square foot ream of paperboard, approximately 75% is located beneath the surface of the paperboard, while only approximately 25% remains at the surface. The 75% of the size press coating located beneath the surface of the paperboard resides in the upper one-third of the paperboard total caliper. For purposes of this application, we will define this ratio of size press coating applied to size press residing beneath the surface of the paperboard as size press coating factor. Thus, using this method, the size press coating has a size press coating factor of about 1.33. While the printability of this embodiment is greater than a non clay coated board having a size press coating layer of 0-3 Ibs, per 3,000 square foot ream of paperboard, on the top layer, the printability is still inferior to that of a prior art clay coated board.
In a more preferred embodiment, printability approaching parity to that of a clay coated board is achieved in a non clay coated board at least as perceived by typical consumers. In this embodiment a film forming size press coating is _g_ applied to the paperboard. A film forming starch preferred in this embodiment has a much lower viscosity than a non-film forming starch applied at a size press nip. Starches typically applied at a size press nip typically have a high viscosity to more effectively impregnate the paperboard. One example of this type of size press coating is Cofilm, distributed by National Starch. In this method, the film forming starch is applied with a calendar box instead of in a typical size press nip. Using this method, it is preferred that approximately 1-6 Ibs of size press coating be applied to the 3,000 square foot per ream paperboard, with about half of the size press coating being applied to the top surface. Testing has shown that when using a film forming size press coating, only about 33% of the size press coating applied, impregnates the paperboard beneath the surface, thus achieving a coating size press coating factor of approximately 3.
Improved printability when using the film forming starch was shown in laboratory tests. In these tests, three different smoothness properties were tested: (1) Bendtsen Roughness; (2) Sheffield Roughness; and (3) Parker Print.
As shown below, better printability, indicated by lower numbers on each of the three factors, was seen in a paperboard coated with a film forming starch applied at a calendar box as compared to paperboard having starch applied at a size press coating. Lower numbers indicate a smoother surface.
Bendtsen Sheffield Sample Roughness Roughness Parker Print Standard Size Press 384 168 6.40 Film Forming Size 210 139 5.97 Press Thus, according to the present invention, less size press coating is used, while achieving a better printing surface. One drawback to this method is a reduction to the rigidity of the plate as compared to the method in which size press coating is deeply impregnated into the board. It should be noted, however, that as shown below, the plate rigidity of a paper plate of the preferred invention formed _g_ using this method can still be approximately equivalent to that found in the heavier clay coated paperboards.
The ink layer can be applied to the size press coating layer or to the latex layer. Thus, in one embodiment the ink is applied to the size press coating layer and the latex is then applied over the ink layer. In a second embodiment, the latex layer is applied to the size press coating and then the ink is applied to the latex layer. One example of ink used in this application is VMT Ink supplied by Progressive Inks of St. Louis, Mo.
The latex functional coating is applied after application of ink to the printing surface. When applying the functional latex coating, the latex appears to penetrate interstitial spaces in the size press coatings and the paperboard, thereby enhancing grease resistance and providing the container with increased rigidity. As seen in the examples below, the result is a 130-140 pound per 3,000 square foot ream paperboard container having a rigidity equivalent to a 160-pound per 3,000 square foot ream paperboard, with enhanced grease resistance. Thus, a desirable paperboard container is formed with an approximately 20% reduction in paperboard weight and, a corresponding 20%
reduction in paperboard cost. As well, a further reduction in weight is achieved as layers of clay coating are no longer necessary.
After the addition of the latex layer, one or more release/sealant coatings may be applied to further isolate the ink from contact with consumables. Thus, in a preferred embodiment, the container of the invention includes a second releaselsealant coating material on the top surface. Preferably, any known functional coating for the top surface of paperboard containers may be applied in any known manner. The second releaselsealant coating may be selected from food-safe polymers such as nitrocellulose, Saran and styrene acrylic acid copolymers, methyl cellulose, carboxymethyl cellulose acetate copolymer, vinyl acetate copolymer, styrene butadiene copolymer, and styrene-acrylic copolymer.
It is preferred that the second releaselsealant coating be applied at a rate of '/2 -1 pound per 3,000 square foot ream of paperboard. There may be a number of layers of second releaselsealant coating materials on the top surface of the container depending on the intended uses of the container and on whether the container's top surface is printed with an ink that must be isolated from contact with consumables.
In another embodiment, applicants have learned that paperboard plates having desirable rigidity and grease resistance can be formed using unbleached kraft paperboard. Environmentally conscious consumers often avoid the use of paper plates due to the harsh chemicals used to bleach the paperboard used in making paperboard plates. Applicants have found that an environmentally friendly paperboard plate, having the desired rigidity and grease resistance, can be made by using Tykote Base I as a functional coating. In this embodiment, an unbleached paperboard having a top layer of predominately hardwood fibers and a bottom layer of predominately softwood fibers has proven to be satisfactory.
In one commercially available grade of board, the top layer contains only a minor amount of softwood, on the of impurities in the pulp supply, while the other contains only minor amounts of hardwood. In this available grade, the predominately hardwood layer typically comprises around 10 - 30% of the board by volume. The predominately hardwood layer will most often comprise approximately 15% of the z-directional volume of the board, with the predominately softwood layer comprising the balance. While such a construction will form a paper plate, it has little or no grease resistance. Addition of about 1-7 pounds of Tykote Base I per 3,000 square foot ream of paperboard, as discussed above, provides the desired grease resistance. Moreover, the addition of the Tykote layer also increases the rigidity in the board. If the predominately hardwood layer comprises substantial proportions of softwoods, rather larger amounts of Tykote may be required to provide the desired barrier properties.
In accordance with the invention, a preferred method of manufacturing the press-formed container of the invention comprises, before press-forming the paperboard container having a size press coating, the step of applying to the top surface of paperboard a first functional coating to form a barrier to grease as well as to enhance rigidity, wherein the first functional coating is a latex, and wherein the first functional coating at least partially penetrates the size press coating.
After application of the first functional latex coating, at least one second releaselsealant coating may be applied.
Prior to pressing the containers, a moistening solution is applied to the bottom surface of the paperboard. The moistening solution used can be water or, preferably, a solution of 50 parts water and one part Velvetol~ as sold by Rhone-Poulenc of Cranbury, NJ. The moistening solution used, therefore, contains water, a surfactant, and a wax. , r The enhanced rigidity and grease resistance of lightweight paperboard containers made in accordance with the method of the invention was first confirmed in a laboratory evaluation. A comparison of paper plates made in accordance with the method of this invention having paperboard weights from 126 to 176 pounds per 3,000 square foot ream (samples 1 to 6) were compared with paper plates made with clay coated paperboard having a paperboard weight of 162 pounds per 3,000 square foot ream (sample 7), as well as with clay coated paper plates having a paperboard weight of 124 pounds per 3,000 square foot ream (sample 8). In addition, a non clay coated paper plate having a film forming starch applied and having a paperboard weight of 143 pounds per 3,000 square foot ream was also compared (sample 9). In the laboratory evaluation, the 126 and 176 pounds per 3,000 square foot ream non clay coated paperboards were coated with 13 pounds of size press per 3,000 square foot ream of paperboard (6.5 pounds per 3,000 square foot ream on each of the upper and lower surfaces), four layers of ink, approximately 2-3 pounds of Tykote Base I SBR latex per 3,000 square foot ream of paperboard, a barrier base release/sealant coating, and a barrier top releaselsealant coating. The 162 pounds per 3,000 square foot ream clay-coated paperboard had two layers of clay coating, four layers of ink, a barrier base releaselsealant coating, and a barrier top releaselsealant coating. Sample 8 had at least one layer of clay coating. Sample 9 was formed similarly to Samples 1-6 in that 2-3 pounds of Tykote Base I SBR latex was applied per 3,000 square foot ream of paperboard;
however, the board was coated with approximately 4-6 pounds of film forming size press per 3,000 square foot ream of paperboard (approximately 2-3 pounds per 3,000 square foot ream on each of the upper and lower surfaces).
The paperboards were then used to make 9" paper plates under standard press conditions. The paperboard was unrolled; no blocking (adhesive sticking) was encountered. Blanks were cut, scored and press-formed from the paperboard at 55 strokes per minute. The press temperature was 300°F.
The plates formed thereby were then tested for dry rigidity using the Plate Rigidity Tester, Model ML4431-2. The plate tester used conforms to the standard FSK
tester, except that it is modified to simulate how a consumer would hold the plate with one hand, whereas the thumb is placed on the upper surface brim area and the fingers are placed on the lower surface near the center of the plate. The following table provides the test results for the dry rigidity test.
Quantity Basis Weight Dry Mean Sample of Lbs13,000 Square Foot Ream Rigidity' Plates
7 67 162 175
8 10 124 98
9 20 143 -191 'Grams per'/:' deflection The test data summarized in the table above establishes that removal of the clay coating and application of a Tykote Base I to the upper surface of a lightweight paperboard achieves at least equivalent dry rigidity as a more expensive heavier weight paperboard having two layers of clay coatings.
Sample 1, having a paperboard weight of 126 pounds per 3,000 square foot ream with no clay coating and coated with Tykote Base I achieves a substantially equivalent dry rigidity as compared to a 162 pound per 3,000 square foot ream clay coated paperboard (Sample 7). The data also shows that paper plates made with heavier paperboards, 136 to 176 pounds per 3,000 square foot ream, achieve substantially higher rigidity than paper plates fabricated with a clay coated board. Sample 9, the non clay coated paperboard with film forming starch, shows that when higher quality printing is desired, lightweight paperboard paper plates can be manufactured while still maintaining adequate rigidity. In comparing Sample 9 to Sample 3, wherein both paperboards had a weight of 143 pounds per 3,000 square foot ream, there is approximately a 10% reduction in rigidity when using the film forming size press. This reduction is due, as noted above, to the absence of size press coating imbedded in the paperboard of Sample 3. A comparison of Sample 8 (124 pounds per 3,000 square foot ream clay coated paperboard) to Sample 1 (126 pounds per 3,000 square foot ream non clay coated paperboard) shows the substantial improvement in rigidity by adding a first functional layer of Tykote Base I in the absence of clay coating.
In the table below, the 162 pound per 3,000 square foot ream clay coated plates (Sample 1 ), the 126 pound per 3,000 square foot ream non clay coated plates (Sample 2), and the 162 pound per 3,000 square foot ream noncoated plates (Sample 3) were also tested for wet rigidity using the same tester as used to determine dry rigidity. A wet rigidity test differs from a dry rigidity test. in that prior to testing the rigidity of the plate, a heated substance, such a$ baked beans r heated to 150°F, is placed on the eating surface for 10 minutes, then removed.
Of note, wet rigidity is generally more important to the consumer than dry rigidity, as paper plates are often used to contain wet products such as baked beans. The following table provides the test results.
Quantity Base Weight Wet Mean Sample of Lbs13,000 Square Foot ReamZ
Plates Rigidity zGrams per %4' deflection The test data, summarized in the table above, establishes that a non clay coated lightweight paperboard paper plate, coated with Tykote Base I, achieves superior wet rigidity as compared to a heavyweight clay coated paperboard paper plate.
Similar improvements using unbleached paperboard have also been observed. Using identical test methodology as described above, unbleached, non clay coated paperboard having two layers of top release/sealant coatings (Sample 1 ) was compared with unbleached paperboard having a 2 - 4 pounds of Tykote Base I per 3,000 square foot ream layer of paperboard and one layer of top releaselsealant coating. As shown in the table below, paper plates formed from the same basis weight unbleached paperboard having a Tykote Base I
layer exhibited greater dry rigidity and wet rigidity as compared to paper plates formed of unbleached paperboard having no Tykote layer.
Quantity Dry Mean Wet Mean Visual Grease Sample of Plates Rigidity Rigidity Failure 1 30 123 106 1-2%
2 30 112 83 100%
3Grams per %4' deflection A visual grease failure test was performed on various plates to determine the amount of penetration of grease through the top layer of the paper plates.
In the visual grease plate failure test, a 3 mm layer of dyed oil, heated to approximately 150°F, is placed in the upper surface of a plate for 20 minutes.
The oil is then removed and the plates are observed on the reverse side or back to determine the percentage on the bottom surface area of the plate that has been penetrated by the dye. Sample 1 was a 136 pound per 3,000 square foot ream paperboard having a 2-3 pounds of Tykote Base I layer (per 3,000 square foot ream) and one layer of top releaselsealant coating. Samples 2-5 were commercially available paper plates having paperboard weights of approximately 180 pounds per 3,000 square foot ream, an undetermined number of clay coating layers, an undetermined number of layers of top functional coatings, and at least two layers of ink. Samples B, R, I, and A are competitive products currently available from a variety of manufacturers.
BASIS WEIGHT VISUAL GREASE
SAMPLE LBS13,000 Square Foot FAILURE
Ream 1 136 0%
B 183 50%
R 186 100%
I 175 100%
A 180 100%
The above results indicate an enhanced grease resistance achieved by applying Tykote to the top surface of the paperboard as compared torcommercial paperboards having clay coating. And, as such, the above results establish that a lightweight plate can be fabricated having at least equivalent rigidity and enhanced grease resistance as compared to a heavier weight commercial paperboard plate, at a substantially reduced cost.
Testing of the invention suggests that the overall rigidity of a paperboard plate is not only related to shape, board physical properties, and forming efficiencies, but is also related to the rigidity of the pleats found around the edges of the plate. Pleats are formed in the shape of a "z" fold around the edges of the plate when the paperboard is press formed, as shown in Fig. 2. The rigidity of the pleats in a conventional plate is largely due to the repair of the internal delineation caused by the scoring process with contribution from bonding of adjacent surfaces. As shown in Fig. 2, when the pleats are formed, portions of the top surface are folded back on themselves, and portions of the bottom surface are likewise folded back on themselves. When the plates are press formed, heat is transferred into the paperboard from the heated dies. Not wishing to be bound by theory, this heat can activate the cross linking of compatible materials in the surface layers, allowing the surfaces to rebond.
In prior art paperboard plates, the top surface is coated with size press, followed by two layers of clay coating and releaselsealant coatings. The bottom surface of the paperboard is coated only with size press. Therefore, when a "z"
fold is formed, a release/sealant coating bond is formed on the top surface, while a size press coating to size press coating bond is formed on the lower surface.
Laboratory testing has shown that the bonds formed on the bottom surface are substantially stronger than those formed on the top surface, thereby indicating that the combination of clay coating and releaselsealant coating inhibits bonding.
This is expected, as release/sealant coating is a material that one of ordinary skill in the art would not expect to bond to itself. Size press coating, on the other hand, is soluble and rebonds to itself, causing increased strength in the pleat bonds, which results in increased plate rigidity from the pleats. Thus, removal of the clay coating from the top surface apparently allows for increased bonding and, hence, a more rigid plate.
Figures 3 and 4 depict micrographs taken of the fold in a paperboard plate having clay coating and a paperboard plate without clay coating. As noted in comparing the two figures, on the upper surface of the plate having the clay coating do not appear to be bonded to each other (Fig. 3). On the other hand, (as shown in Figure 4), bonding is complete on both the upper and lower surfaces.
However, as noted above, the removal of the clay coating leaves the paperboard plate with little or no grease resistance. The addition of a latex first coating, such as Tykote, to the paperboard not only restores the grease resistance lost by removal of the clay coating, but enhances the plate's rigidity as compared to plates having clay coating. Moreover, the rigidity of the Tykote coated plate is greater than those plates having no clay coating and no Tykote.
The following table compares pleat tensile strength in lightweight paperboard plates having no clay coating with heavyweight paperboard pleats having clay coating. Sample 1 is a 126 pound per 3,000 square foot ream paperboard with no clay coating and no Tykote Base I. Sample 2 is a 126 pound per 3,000 square foot ream paperboard with no clay coating, but with a Tykote Base I upper layer. Sample 3 is a 162 pound per 3,000 square foot ream paperboard with clay coating. The tensile strength of the pleats was tested using an Instron~ testing machine and image analysis techniques. Sample pleats were preconditioned and conditioned according to TAPPI standards. The pleats were then cut from the plates using a razor blade. Although a quarter inch sample is desired, the true width of each sample is measured so that accurate load (Id/in of pleat) can be calculated. Dots are inked on the edges of the sample on opposite sides of the pleat to provide reference marks to measure displacement. The samples are then pulled using an Instron~ set with a crosshead speed of 0.025 in/min. Two video cameras are used to record the testing and provide input to the image analysis. One camera shows the sample under tension while the other camera provides the load values from the Instron~.
The two camera inputs are combined using a picture in picture function. The video is then played through a digitizing function and OptimasT"' image analysis software is used to track the movement of the dots.
Quantity Basis Weight Sample of Pleats Lbs13,000 Spuare Foot ReamPleat Strength 1 11 126 10.6 2 10 126 14.0 3 12 162 4.7 ° Pounds of force The results show that the clay coating appears to inhibit the strength of the pleat.
In addition, the results indicate an even greater improvement in pleat strength when using Tykote Base I as an upper layer.
Therefore, application of Tykote allows for the use of light weight paperboard and removal of the clay coatings, achieving a less expensive light weight paperboard plate having equivalent rigidity and enhanced grease resistance.
It is understood that the invention is not confined to the particular construction and arrangement of parts and the particular processes described herein but embraces such modified forms thereof as come within the scope of the following claims.
Sample 1, having a paperboard weight of 126 pounds per 3,000 square foot ream with no clay coating and coated with Tykote Base I achieves a substantially equivalent dry rigidity as compared to a 162 pound per 3,000 square foot ream clay coated paperboard (Sample 7). The data also shows that paper plates made with heavier paperboards, 136 to 176 pounds per 3,000 square foot ream, achieve substantially higher rigidity than paper plates fabricated with a clay coated board. Sample 9, the non clay coated paperboard with film forming starch, shows that when higher quality printing is desired, lightweight paperboard paper plates can be manufactured while still maintaining adequate rigidity. In comparing Sample 9 to Sample 3, wherein both paperboards had a weight of 143 pounds per 3,000 square foot ream, there is approximately a 10% reduction in rigidity when using the film forming size press. This reduction is due, as noted above, to the absence of size press coating imbedded in the paperboard of Sample 3. A comparison of Sample 8 (124 pounds per 3,000 square foot ream clay coated paperboard) to Sample 1 (126 pounds per 3,000 square foot ream non clay coated paperboard) shows the substantial improvement in rigidity by adding a first functional layer of Tykote Base I in the absence of clay coating.
In the table below, the 162 pound per 3,000 square foot ream clay coated plates (Sample 1 ), the 126 pound per 3,000 square foot ream non clay coated plates (Sample 2), and the 162 pound per 3,000 square foot ream noncoated plates (Sample 3) were also tested for wet rigidity using the same tester as used to determine dry rigidity. A wet rigidity test differs from a dry rigidity test. in that prior to testing the rigidity of the plate, a heated substance, such a$ baked beans r heated to 150°F, is placed on the eating surface for 10 minutes, then removed.
Of note, wet rigidity is generally more important to the consumer than dry rigidity, as paper plates are often used to contain wet products such as baked beans. The following table provides the test results.
Quantity Base Weight Wet Mean Sample of Lbs13,000 Square Foot ReamZ
Plates Rigidity zGrams per %4' deflection The test data, summarized in the table above, establishes that a non clay coated lightweight paperboard paper plate, coated with Tykote Base I, achieves superior wet rigidity as compared to a heavyweight clay coated paperboard paper plate.
Similar improvements using unbleached paperboard have also been observed. Using identical test methodology as described above, unbleached, non clay coated paperboard having two layers of top release/sealant coatings (Sample 1 ) was compared with unbleached paperboard having a 2 - 4 pounds of Tykote Base I per 3,000 square foot ream layer of paperboard and one layer of top releaselsealant coating. As shown in the table below, paper plates formed from the same basis weight unbleached paperboard having a Tykote Base I
layer exhibited greater dry rigidity and wet rigidity as compared to paper plates formed of unbleached paperboard having no Tykote layer.
Quantity Dry Mean Wet Mean Visual Grease Sample of Plates Rigidity Rigidity Failure 1 30 123 106 1-2%
2 30 112 83 100%
3Grams per %4' deflection A visual grease failure test was performed on various plates to determine the amount of penetration of grease through the top layer of the paper plates.
In the visual grease plate failure test, a 3 mm layer of dyed oil, heated to approximately 150°F, is placed in the upper surface of a plate for 20 minutes.
The oil is then removed and the plates are observed on the reverse side or back to determine the percentage on the bottom surface area of the plate that has been penetrated by the dye. Sample 1 was a 136 pound per 3,000 square foot ream paperboard having a 2-3 pounds of Tykote Base I layer (per 3,000 square foot ream) and one layer of top releaselsealant coating. Samples 2-5 were commercially available paper plates having paperboard weights of approximately 180 pounds per 3,000 square foot ream, an undetermined number of clay coating layers, an undetermined number of layers of top functional coatings, and at least two layers of ink. Samples B, R, I, and A are competitive products currently available from a variety of manufacturers.
BASIS WEIGHT VISUAL GREASE
SAMPLE LBS13,000 Square Foot FAILURE
Ream 1 136 0%
B 183 50%
R 186 100%
I 175 100%
A 180 100%
The above results indicate an enhanced grease resistance achieved by applying Tykote to the top surface of the paperboard as compared torcommercial paperboards having clay coating. And, as such, the above results establish that a lightweight plate can be fabricated having at least equivalent rigidity and enhanced grease resistance as compared to a heavier weight commercial paperboard plate, at a substantially reduced cost.
Testing of the invention suggests that the overall rigidity of a paperboard plate is not only related to shape, board physical properties, and forming efficiencies, but is also related to the rigidity of the pleats found around the edges of the plate. Pleats are formed in the shape of a "z" fold around the edges of the plate when the paperboard is press formed, as shown in Fig. 2. The rigidity of the pleats in a conventional plate is largely due to the repair of the internal delineation caused by the scoring process with contribution from bonding of adjacent surfaces. As shown in Fig. 2, when the pleats are formed, portions of the top surface are folded back on themselves, and portions of the bottom surface are likewise folded back on themselves. When the plates are press formed, heat is transferred into the paperboard from the heated dies. Not wishing to be bound by theory, this heat can activate the cross linking of compatible materials in the surface layers, allowing the surfaces to rebond.
In prior art paperboard plates, the top surface is coated with size press, followed by two layers of clay coating and releaselsealant coatings. The bottom surface of the paperboard is coated only with size press. Therefore, when a "z"
fold is formed, a release/sealant coating bond is formed on the top surface, while a size press coating to size press coating bond is formed on the lower surface.
Laboratory testing has shown that the bonds formed on the bottom surface are substantially stronger than those formed on the top surface, thereby indicating that the combination of clay coating and releaselsealant coating inhibits bonding.
This is expected, as release/sealant coating is a material that one of ordinary skill in the art would not expect to bond to itself. Size press coating, on the other hand, is soluble and rebonds to itself, causing increased strength in the pleat bonds, which results in increased plate rigidity from the pleats. Thus, removal of the clay coating from the top surface apparently allows for increased bonding and, hence, a more rigid plate.
Figures 3 and 4 depict micrographs taken of the fold in a paperboard plate having clay coating and a paperboard plate without clay coating. As noted in comparing the two figures, on the upper surface of the plate having the clay coating do not appear to be bonded to each other (Fig. 3). On the other hand, (as shown in Figure 4), bonding is complete on both the upper and lower surfaces.
However, as noted above, the removal of the clay coating leaves the paperboard plate with little or no grease resistance. The addition of a latex first coating, such as Tykote, to the paperboard not only restores the grease resistance lost by removal of the clay coating, but enhances the plate's rigidity as compared to plates having clay coating. Moreover, the rigidity of the Tykote coated plate is greater than those plates having no clay coating and no Tykote.
The following table compares pleat tensile strength in lightweight paperboard plates having no clay coating with heavyweight paperboard pleats having clay coating. Sample 1 is a 126 pound per 3,000 square foot ream paperboard with no clay coating and no Tykote Base I. Sample 2 is a 126 pound per 3,000 square foot ream paperboard with no clay coating, but with a Tykote Base I upper layer. Sample 3 is a 162 pound per 3,000 square foot ream paperboard with clay coating. The tensile strength of the pleats was tested using an Instron~ testing machine and image analysis techniques. Sample pleats were preconditioned and conditioned according to TAPPI standards. The pleats were then cut from the plates using a razor blade. Although a quarter inch sample is desired, the true width of each sample is measured so that accurate load (Id/in of pleat) can be calculated. Dots are inked on the edges of the sample on opposite sides of the pleat to provide reference marks to measure displacement. The samples are then pulled using an Instron~ set with a crosshead speed of 0.025 in/min. Two video cameras are used to record the testing and provide input to the image analysis. One camera shows the sample under tension while the other camera provides the load values from the Instron~.
The two camera inputs are combined using a picture in picture function. The video is then played through a digitizing function and OptimasT"' image analysis software is used to track the movement of the dots.
Quantity Basis Weight Sample of Pleats Lbs13,000 Spuare Foot ReamPleat Strength 1 11 126 10.6 2 10 126 14.0 3 12 162 4.7 ° Pounds of force The results show that the clay coating appears to inhibit the strength of the pleat.
In addition, the results indicate an even greater improvement in pleat strength when using Tykote Base I as an upper layer.
Therefore, application of Tykote allows for the use of light weight paperboard and removal of the clay coatings, achieving a less expensive light weight paperboard plate having equivalent rigidity and enhanced grease resistance.
It is understood that the invention is not confined to the particular construction and arrangement of parts and the particular processes described herein but embraces such modified forms thereof as come within the scope of the following claims.
Claims (43)
1. A container press-formed of paperboard having a top surface which is substantially free of clay coating, said top surface being disposed for contact with material to be contained, said paperboard having an opposed bottom surface, the container comprising a size press layer on the top surface and on the bottom surface, and a layer of first functional coating material at the top surface size press coating, wherein the first functional coating is a latex.
2. The container of claim 1 wherein the first functional coating material consists essentially of styrene butadiene rubber latex.
3. The container of claim 1 wherein the first functional coating material is Tykote~ Base I.
4. The container of claim 1 also including additional layers of release/sealant coating materials on the top surface.
5. The container of claim 1 wherein the amount of the first functional coating material dispersed at the top surface size press coating is about one (1) pound per 3,000 square foot ream of paperboard.
6. The container of claim 1 wherein the amount of the first functional coating material dispersed at the top surface size press coating is up to about seven (7) pounds per 3,000 square foot ream of paperboard.
7. The container of claim 1 wherein the basis weight of the paperboard is 100 - 160 pounds per 3,000 square foot ream.
8. The container of claim 1 wherein the basis weight of the paperboard is 130 - 140 pounds per 3,000 square foot ream.
9. The container of claim 1 wherein the basis weight of the paperboard is greater than 160 pounds per 3,000 square foot ream.
10. The container of claim 1 having an ink layer on the top surface size press coating.
11. The container of claim 1 having an ink layer on the first functional surface.
12. The container of claim 1 manufactured using the steps of:
a. applying the first functional coating material to the top surface size press coating;
b. cutting a blank for the container from the paperboard; and c. press-forming a pre-moistened blank at a predetermined temperature and pressure to form the container.
a. applying the first functional coating material to the top surface size press coating;
b. cutting a blank for the container from the paperboard; and c. press-forming a pre-moistened blank at a predetermined temperature and pressure to form the container.
13. The container of claim 1 manufactured using the steps of:
a. forming the paperboard;
b. applying size press coating to each surface of the paperboard;
c. applying the first functional coating material to the top surface size press coating;
d. applying a second release/sealant coating material to the top surface of the paperboard;
e. cutting a blank for the container from the paperboard; and f. press-forming a pre-moistened blank at a predetermined temperature and pressure to form the container.
a. forming the paperboard;
b. applying size press coating to each surface of the paperboard;
c. applying the first functional coating material to the top surface size press coating;
d. applying a second release/sealant coating material to the top surface of the paperboard;
e. cutting a blank for the container from the paperboard; and f. press-forming a pre-moistened blank at a predetermined temperature and pressure to form the container.
14. The container of claim 13 further comprising the step of applying an ink layer to the top surface size press coating.
15. The container of claim 13 further comprising the step of applying an ink layer to the first functional coating material..
16. The container of claim 1 wherein the container is a plate.
17. The container of claim 1 wherein the container is a tray.
18. In a method of manufacturing a press-formed paperboard container having a top surface which is substantially free of clay coatings, said top surface being disposed for contact with material to be contained, said paperboard having an opposed bottom surface comprising the steps of applying a size press coating on the top surface and the bottom surface, applying latex solids to the size press coating on the top surface, wherein the latex solids at least partially penetrate the size press coating.
19. The method of claim 18 wherein the latex is essentially styrene butadiene rubber.
20. The method of claim 18 wherein the latex is Tykote~ Base I.
21. The method of claim 18 wherein the container is press formed at a temperature of about 300° F.
22. A container press-formed of paperboard having a top surface which is substantially free of clay coating, said top surface being disposed for contact with material to be contained, said paperboard having an opposed bottom surface, the container comprising a layer of first functional coating material at the top surface, wherein the first functional coating is a latex.
23. The container of claim 22 wherein the first functional coating material consists essentially of styrene butadiene rubber latex.
24. The container of claim 22 wherein the first functional coating material is Tykote~ Base I.
25. The container of claim 22 also including additional layers of release/sealant coating materials on the top surface.
26. The container of claim 22 wherein the amount of the first functional coating material dispersed at the top surface is about one (1) pound per 3,000 square foot ream of paperboard.
27. The container of claim 22 wherein the amount of the first functional coating material dispersed at the top surface is up to about seven (7) pounds per 3,000 square foot ream of paperboard.
28. The container of claim 22 wherein the basis weight of the paperboard is 100 - 160 pounds per 3,000 square foot ream.
29. The container of claim 22 wherein the basis weight of the paperboard is 130 - 140 pounds per 3,000 square foot ream.
30. The container of claim 22 wherein the basis weight of the paperboard is greater than 160 pounds per 3,000 square foot ream.
31. The container of claim 22 wherein the paperboard is unbleached.
32. The container of claim 22 having at least on size press coating layer.
33. The container of claim 22 having an ink layer on the first functional surface.
34. The container of claim 22 manufactured using the steps of:
a. applying the first functional coating material to the top surface;
b. cutting a blank for the container from the paperboard;
and c. press-forming the pre-moistened blank at a predetermined temperature and pressure to form the container.
a. applying the first functional coating material to the top surface;
b. cutting a blank for the container from the paperboard;
and c. press-forming the pre-moistened blank at a predetermined temperature and pressure to form the container.
35. The container of claim 34 further comprising the step of applying an ink layer to the top surface size press coating
36. The container of claim 22 manufactured using the steps of:
a. forming the paperboard;
b. applying the first functional coating material to the top surface of the paperboard;
c. applying a second release/sealant coating material to the top surface of the paperboard;
d. cutting a blank for the container from the paperboard; and e. press-forming the pre-moistened blank at a predetermined temperature and pressure to form the container.
a. forming the paperboard;
b. applying the first functional coating material to the top surface of the paperboard;
c. applying a second release/sealant coating material to the top surface of the paperboard;
d. cutting a blank for the container from the paperboard; and e. press-forming the pre-moistened blank at a predetermined temperature and pressure to form the container.
37. The container of claim 22 wherein the container is a plate.
38. The container of claim 22 wherein the container is a tray.
39. In a method of manufacturing a press-formed paperboard container having a top surface which is substantially free of clay coating, said top surface being disposed for contact with material to be contained, said paperboard having an opposed bottom surface, comprising the steps of applying latex solids to the top surface, wherein the latex solids partially penetrates the top surface.
40. The method of claim 39 wherein the latex is essentially styrene butadiene rubber.
41. The method of claim 39 wherein the latex is Tykote R Base I.
42. The method of claim 39 wherein the container is press formed at a temperature of about 300° F.
43. The method of claim 39 wherein the paperboard is unbleached.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41885199A | 1999-10-15 | 1999-10-15 | |
| US09/418,851 | 1999-10-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2323341A1 true CA2323341A1 (en) | 2001-04-15 |
Family
ID=23659806
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002323341A Abandoned CA2323341A1 (en) | 1999-10-15 | 2000-10-16 | A paperboard container having enhanced grease resistance and rigidity and a method of making same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2323341A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018081764A1 (en) | 2016-10-31 | 2018-05-03 | Sun Chemical Corporation | Grease, oil, and water resistant coating compositions |
| US11555276B2 (en) | 2017-04-28 | 2023-01-17 | Sun Chemical Corporation | Heat sealable barrier coating |
-
2000
- 2000-10-16 CA CA002323341A patent/CA2323341A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018081764A1 (en) | 2016-10-31 | 2018-05-03 | Sun Chemical Corporation | Grease, oil, and water resistant coating compositions |
| US11242461B2 (en) | 2016-10-31 | 2022-02-08 | Sun Chemical Corporation | Grease, oil, and water resistant coating compositions |
| US11555276B2 (en) | 2017-04-28 | 2023-01-17 | Sun Chemical Corporation | Heat sealable barrier coating |
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| EEER | Examination request | ||
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