sign in sign up
<<
Home , Calender

US 20070137815Al (19) United States (12) Patent Application Publication (10) Pub. N0.: US 2007/0137815 A1 Shearer (43) Pub. Date: Jun. 21, 2007

(54) SMOOTH LOW (52) US. Cl...... 162/125; 428/340 (76) Inventor: Dwayne M. Shearer, Seattle, WA (US) (57) ABSTRACT Correspondence Address: WEYERHAEUSER COMPANY . INTELLECTUAL PROPERTY DEPT” CH 1J27 A paperboard product has at least tWo or three P1165‘. One of R0_ 9777 the pl1es has at least ‘25% by We1ght bulky cellulos1c ?bers. FEDERAL WAY, WA 98063 (Us) Another of the plies is an outer ply and has an outer surface having a Parker PrmtSurf measurement of between 3 and 6p. (21) APPL NO. 11/313,544 When measured at 10 kg/cm2 using a soft backing surface. The paperboard product has a density no greater than 0.5 (22) Filed; Dec_ 20, 2005 grams per cubic centimeter. An embodiment has a caliper in the range of 0.4 and 1.2 mm. An embodiment has a basis Publication Classi?cation Weight in the range of 200 to 500 grams per square meter. A method for making the paperboard product by passing the (51) Int. Cl. Web through a soft nip calender and an extended nip D21H 27/30 (2006.01) calender Which can be a shoe calender under conditions D21H 27/38 (2006.01) Which provide the surface and density properties. Patent Application Publication Jun. 21, 2007 US 2007/0137815 A1

l2 l4

10 Fig. 1

22 24 26

20 Fig. 2 US 2007/0137815 A1 Jun. 21, 2007

SMOOTH LOW DENSITY PAPERBOARD ment of betWeen 3 and 6p. at 108 Where 10 indicates a clamp force of 10 kilograms and S indicates the use of a soft [0001] This invention relates generally to a loW density backing to the tested paperboard. paperboard containing bulky ?bers and having a smooth surface. The invention also relates to the [0009] Paperboard of the present invention may have a board to achieve these results. broad set of characteristics. In one embodiment its basis Weight can range from 200 grams per square meter to 500 [0002] Hot foods, particularly hot liquids, are commonly grams per square meter. In another embodiment its basis served and consumed in disposable . These con Weight can range from 250 grams per square meter to 400 tainers are made from a variety of materials including grams per square meter. In another embodiment the basis paperboard and foamed polymeric sheet material. One of the Weight of the paperboard is equal to or greater than 250 least expensive sources of paperboard material is grams per square meter. To achieve the insulating charac ?bers. Cellulose ?bers are employed to produce excellent teristics of the present invention, the paperboard may have for the production of hot cups, paper plates, and a density of less than 0.5 g/cc. In another embodiment the other food and beverage containers. Conventional may be from 0.3 g/cc to 0.45 g/cc. In another board produced from cellulosic ?bers, hoWever, is relatively embodiment the density may be from 0.35 g/cc to 0.40 g/ cc. dense, and therefore, transmits heat more readily than, for In an embodiment of the present invention the caliper of the example, foamed polymeric sheet material. Thus, hot liquids paperboard is in the range of 0.4 to 1.2 mm after calendering. are typically served in double cups or in cups containing multiple plies of conventional paperboard. [0010] FIG. 1 is a schematic cross-sectional vieW of a tWo-ply paperboard. [0003] LoW density insulating paperboard contains ?bers Which have the purpose of reducing the temperature drop [0011] FIG. 2 is a schematic cross-sectional vieW of a across the paperboard. The paperboard Would be made into three-ply paperboard a Which maintains the heat of the contained [0012] The paperboard of the present invention has at least product and has an outer surface Which is at a temperature tWo plies. FIG. 1 illustrates a tWo-ply construction in Which that can be handled Without discomfort. The materials Within paperboard 10 has plies 12 and 14. FIG. 2 illustrates a the insulating paperboard may by their nature be lumpy and three-ply construction in Which the paperboard 20 has plies not smooth. This can provide a surface that is not smooth 22, 24 and 26. While the paperboard of the present invention and may be di?icult to use for some types of . may employ synthetic ?bers, it Would usually comprise all [0004] It is desirable to have a loW density paperboard that or substantially all cellulosic ?bers. has a smooth surface because the containers are used by [0013] The plies 12, 22 and 26 are of conventional hard retail outlets that desire to have a business name and logo on Wood or softWood cellulosic ?bers. They may be bleached or the container. The outlets may also Wish to have a statement unbleached. They may be made of chemical, mechanical, about the temperature of the contained product. A smooth chemimechanical or thermomechanical . surface is more useful for printing. [0014] The plies 14 and 24 contain bulky ?bers. The bulky [0005] A concern is hoW to maintain a loW density board ?bers increase the bulk density of the paperboard and thus While providing a smooth surface. Will the pressures the insulating characteristics. As used herein, bulky ?bers required to obtain a smooth surface increase the density are kinked, tWisted, curly, cellulosic ?bers. It is preferred, unacceptably? hoWever, that the ?bers be produced by intra?ber crosslink ing of the cellulosic ?bers as described in more detail beloW. [0006] An embodiment of this invention is a paperboard Conventional hardWood or softWood cellulosic ?bers may that has a loW density and a surface that is smooth. Another be used With the bulky ?bers in these plies. embodiment of this invention is a process for manufacturing a paperboard having a loW density and a surface that is [0015] Chemically crosslinked cellulosic ?bers are suit smooth. able for use as the bulky ?bers in paperboard. Any one of a number of crosslinking agents and crosslinking catalysts, if [0007] LoW density insulating paperboard may be in tWo necessary, can be used to provide the crosslinked ?bers to be or more plies. At least one of the plies contains both regular included in the layer. The folloWing is a representative list of chemical bleached, semi-bleached or unbleached pulp ?bers useful crosslinking agents and catalysts. and bulky ?bers. Bulky ?bers give the ply insulative quali ties because they provide bulk to the ply and create a loWer [0016] Suitable urea-based crosslinking agents include density ply. The purpose of these bulky ?bers is to provide substituted ureas, such as methylolated ureas, methylolated a greater temperature drop across the thickness of the cyclic ureas, methylolated loWer alkyl cyclic ureas, methy paperboard than Would be provided if bulky ?bers Were not lolated dihydroxy cyclic ureas, dihydroxy cyclic ureas, and used. Another of the plies is a surface ply Which does not loWer alkyl substituted cyclic ureas. Speci?c urea-based crosslinking agents include dimethyldihydroxy urea contain bulky ?bers and has a smooth outer surface. (DMDHU, 1,3-dimethyl-4,5-dihydroxy-2-imidaZolidinone), [0008] Bulky ?bers can be mechanically produced or can dimethyloldihydroxyethylene urea (DMDHEU, 1,3-dihy be produced by crosslinking the cellulosic ?bers. The bulky droxymethyl-4,5-dihydroxy-2 -imidaZolidinone), dimethylol ?bers create a rough surface on the paperboard. It is neces urea (DMU, bis[N-hydroxymethyl]urea), dihydroxyethyl sary to smooth the surface of the paperboard While main ene urea (DHEU, 4,5-dihydroxy-2-imidaZolidinone), dim taining the loW density of the paperboard. In an embodiment ethylolethylene urea (DMEU, 1,3-dihydroxymethyl-2-imi of the invention at least one surface of the paperboard is daZolidinone), and dimethyldihydroxyethylene urea smooth. In an embodiment of the invention at least one (DMeDHEU or DDI, 4,5-dihydroxy-1,3-dimethyl-2-imida surface of the paperboard has a Parker PrintSurf measure Zolidinone). US 2007/0137815 A1 Jun. 21, 2007

[0017] Suitable crosslinking agents also include dialde (see, e.g., US. Pat. No. 3,556,932 and also the commercially hydes such as C2-C8 dialdehydes (e.g., glyoxal), C2-C8 available polyacrylamide marketed by American Cyanamid dialdehyde acid analogs having at least one aldehyde group, Co., Stanford, Conn., under the trade name PAREZ 631 and oligomers of these aldehyde and dialdehyde acid ana NC); urea formaldehyde and melamine formaldehyde res logs. Other suitable crosslinking agents include aldehyde ins; and polyethylenimine . A general discussion on and urea-based formaldehyde addition products, glyoxal resins utiliZed in the paper ?eld, and generally adducts of ureas and glyoxal/cyclic urea adducts. applicable in the present invention, can be found in TAPPI [0018] Other suitable crosslinking agents include carboxy monograph series No. 29, “Wet Strength in Paper and lic acid crosslinking agents such as polycarboxylic acids. Paperboard”, Technical Association of the Pulp and Paper Polycarboxylic acid crosslinking agents include citric acid, Industry (New York, 1965). propane tricarboxylic acid, and butane tetracarboxylic acid) [0026] Other suitable binding agents include starch, modi and catalysts. C2-C9 polycarboxylic acids that contain at ?ed starch, polyvinyl alcohol, polyvinyl acetate, polyethyl least three carboxyl groups (e.g., citric acid and oxydisuc ene/acrylic acid copolymer, acrylic acid , polyacry cinic acid) are also suitable as crosslinking agents. late, polyacrylamide, polyamine, guar gum, oxidiZed [0019] Polymeric polycarboxylic acids are also suitable , , polyvinyl chloride/acrylic crosslinking agents. Polyacrylic acid and related copolymers acid copolymers, acrylonitrile/butadiene/ styrene copoly may be used as crosslinking agents. Polymaleic acid may be mers, and polyacrylonitrile. Many of these Will be formed used as a crosslinking agent. into latex polymers for dispersion or suspension in Water. [0020] Speci?c suitable polycarboxylic acid crosslinking [0027] The insulative ?bers may be blended With other agents include citric acid, tartaric acid, malic acid, succinic cellulosic ?bers Which have lesser insulative properties. acid, glutaric acid, citraconic acid, itaconic acid, tartrate Although available from other sources, these other ?bers are monosuccinic acid, maleic acid, polyacrylic acid, poly derived primarily from Wood pulp. Suitable Wood pulp methacrylic acid, polymaleic acid, polymethylvinylether-co ?bers for use With the invention can be obtained from maleate copolymer, polymethylvinylether-co-itaconate Well-knoWn chemical processes such as the kraft and sul?te copolymer, copolymers of acrylic acid, and copolymers of processes, With or Without subsequent bleaching. The pre maleic acid. ferred pulp ?ber is produced by chemical methods. Recycled or secondary Wood pulp ?bers, and bleached and unbleached [0021] Suitable crosslinking catalysts can include acidic Wood pulp ?bers can be used. SoftWoods and hardwoods can salts, such as ammonium chloride, ammonium sulfate, alu be used. Details of the selection of Wood pulp ?bers are Well minum chloride, magnesium chloride, magnesium nitrate, knoWn to those skilled in the art. These ?bers are commer and alkali metal salts of phosphorous-containing acids. In cially available from a number of companies, including one embodiment, the crosslinking catalyst is sodium hypo Weyerhaeuser Company, the assignee of the present inven phosphite. tion. For example, suitable cellulose ?bers produced from [0022] The crosslinking agent is applied to the cellulosic southern pine that are usable With the present invention are ?bers as they are being produced in an amount suf?cient to available from Weyerhaeuser Company under the designa affect intra?ber crosslinking. The amount applied to the tions CF4l6, NF405, PL416, FR516, and NB416. These are cellulosic ?bers may be from about 1% to about 25% by the same ?bers that Would be used in plies 12, 22 and 26. Weight based on the total Weight of ?bers. In one embodi [0028] Paperboard of the present invention may have a ment, crosslinking agent in an amount from about 4% to broad set of characteristics. In one embodiment its basis about 6% by Weight based on the total Weight of ?bers. Weight can range from 200 grams per square meter to 500 Mixtures or blends of crosslinking agents and catalysts can grams per square meter. In another embodiment its basis also be used. Weight can range from 250 grams per square meter to 400 [0023] The insulative ?bers may also be mechanically grams per square meter. In another embodiment the basis pulped ?bers, thermomechanical pulped ?bers, chemither Weight of the paperboard is equal to or greater than 250 momechanically pulped ?bers or combinations of these. grams per square meter. To achieve the insulating charac teristics of the present invention, the paperboard may have [0024] Insulating ?bers, for the most part, are not smooth. a density of less than 0.5 g/cc. In another embodiment the They often are curled and tWisted. They have a tendency to density may be from 0.3 g/cc to 0.45 g/cc. In another provide an uneven surface to the loW density insulative embodiment the density may be from 0.35 g/cc to 0.40 g/ cc. paperboard. [0029] In a tWo-ply structure, for example, the ?rst ply [0025] In addition to ?brous materials, the paperboard of may contain 100% non-bulky ?bers by Weight While the the invention may optionally include a binding agent. Suit second ply may in one embodiment contain from 25% to able binding agents are soluble in, dispersible in, or form a 100% bulky ?bers by Weight and in another embodiment suspension in Water. Suitable binding agents include those from 30% to 70% bulky ?bers by Weight. In a three-ply agents commonly used in the paper industry to impart Wet layer, for example, the bottom and top plies may comprise and dry tensile and tearing strength to such products. Suit 100% of non-bulky ?bers by Weight While the middle ply able Wet strength agents include cationic modi?ed starch contains in one embodiment from about 25% to about 100% having nitrogen-containing groups (e.g.,. amino groups), bulky ?ber by Weight and in another embodiment from such as those available from National Starch and Chemical about 30% to about 70% bulky ?bers by Weight. Corp., BridgeWater, N.J.; latex; Wet strength resins, such as polyamide-epichlorohydrin (e.g., KYMENE 557LX, [0030] In each of these embodiments it is desired to have Hercules, Inc., Wilmington, Del.), and polyacrylamide resin a surface Which is smooth and printable. The surface Would US 2007/0137815 A1 Jun. 21, 2007

have a Parker PrintSurf (TAPPI Test Method T 555 om-04) across the Width of the paper. In the soft nip calender the of betWeen 3 and 6p. at a clamping pressure of 10 kg/cm2 and paperboard Will be exposed to a heated surface having a using a soft backing sheet. temperature of 120° C. to 160° C. and be under a linear load of 40 to 150 N/mm. [0031] It is understood that TAPPI test method T-555 is a recognized method of measuring surface smoothness. It is [0040] Extended nip calendering uses an endless band/belt also understood that Collaborative Testing Services, Inc., over a backing roll to provide support for the paper Web that 21331 Gentry Drive, Sterling, Va. 20166 has over the years is pressed against a heated cylinder. A variation to this checked variations in the readings among a population of concept, shoe calendering, uses a shoe instead of a roll as a Parker PrintSurf test machines using a clamping pressure of backing for the paperboard. The backing shoe provides 10 kg/ cm and a standard test sample and have found longer nip Widths and hence an increased dWell time. In variations of as much as +1p. from a mean measurement. either con?guration the nip Would have a Width of 6 to 12 cm Therefore the measurement of betWeen 3 and 6 p. as used here for best results. In the calender the paperboard Will be and in the claims is a mean measurement and the actual exposed to a heated surface having a temperature of 180° C. measurement Would be betWeen 3 and 6u11u. to 250° C. and be under a linear load of 100 to 300 N/mm. [0032] The paperboard of the present invention can be [0041] In the folloWing examples, the paperboard Was formed using conventional machines includ formed at a forming pilot facility, and calendered at a ing, for example, Rotoformer, Fourdrinier, inclined Wire calendering pilot facility. The paperboard Was three-ply Delta former, and tWin-Wire forming machines. having bulky ?ber in the center ply. The paperboard had [0033] A multi-ply paperboard may be made by using 20% of its ?ber in each of the outer plies and 60% of its ?ber multiple headboxes arranged sequentially in a Wet-forming in the center ply. The bulky ?ber Was 50% of the Weight of the center ply. The bulky ?ber Was chemically intra?ber process, or by a ba?‘led headbox having the capacity of crosslinked cellulose ?ber Which used bleached chemical receiving and then laying multiple pulp fumishes. In a cellulosic Wood pulp as its starting material. The ?ber in the multi-ply construction the printing surface ply may be of outer plies and the remainder of the ?ber in the center ply other ?bers and the non printing ply of a tWo ply construc Was bleached chemical cellulosic Wood pulp. tion or a middle ply of a three or more ply construction may be of insulative ?bers or a blend of insulative ?bers and other ?bers. [0034] Multilayer basestock can Basis Calendered Softnip Softnip Shoe Shoe PPS be formed on a papermachine capable of producing multi Weight Caliper Temp Load Temp Load 10S layer product. The papermachine can be a conventional Ex. g/m2 mm ° C. N/mm ° C. N/mm [1 Fourdrinier machine ?tted With multiple head . Each 1 392 1.12 140 60 210 150 5.43 of the plies Would be placed on the Fourdrinier machine by 2 392 1.12 140 60 210 250 4.24 one of the headboxes to form a multiply Web. Vacuum Would 3 392 1.09 140 120 210 150 5.22 be applied to remove Water from the Web. The Web Would 4 392 1.09 140 120 210 250 4.06 then be pressed in a conventional press section to remove additional Water. [0042] The foregoing invention has been described in [0035] The paperboard Web Would then be dried. The conjunction With a preferred diment and various alterations dried Web may then optionally pass through a siZe press of and variations thereof. One of ordinary skill Will be to the puddle or metering type, or a blade coater, Where substitute equivalents in the disclosed invention Without additional chemicals may be applied to the Web. departing from the broad pts imparted herein. It is therefore [0036] Materials that can be added at the siZe press are intended that the present invention be limited by the de? starch, polyvinyl alcohol, pigments such as calcium carbon nition contained in the appended claims ate or clay, or lubricants that are compatible With the starch and other binders. The Web then passes through another dryer section. 1. A paperboard product comprising at least tWo plies [0037] When bulky ?bers are used in paperboard in accor said paperboard product having a density no greater that dance With the present invention, it has been found that the paperboard exiting the papermaking machine can be com 0.5 grams per cubic centimeter, pressed to varying degrees. In one embodiment of the one of said plies comprising a least 25% by Weight bulky present invention the caliper of the paperboard is in the cellulosic ?bers, range of 0.4 to 1.2 mm after calendering. another of said plies being an outer ply and having an [0038] FolloWing the siZe press treatment and drying, the outer surface having a Parker PrintSurf measurement of paperboard is passed through a calender station. In the betWeen 3 and 6p. When measured at 10 kg/cm2 using a calender station the paperboard is calendered ?rst With a soft soft backing surface. nip calender and then With an extended nip or shoe calender. 2. The paperboard product of claim 1 in Which said [0039] In soft nip calendering the Web is pressed against a paperboard product has a caliper in the range of 0.4 and 1.2 hot surface in a nip by a roll that has a resilient cover. The mm. resilient cover gives the paper a longer dWell time in the nip 3. The paperboard product of claim 1 in Which said compared to hard nips and also alloWs the smoothness paperboard product has a basis Weight in the range of 200 to and gloss development to occur at relatively uniform density 500 grams per square meter. US 2007/0137815 A1 Jun. 21, 2007

4. The paperboard product of claim 1 in Which the density 12. The paperboard product of claim 10 in Which said of said paperboard product is betWeen 0.3 and 0.45 grams paperboard product has a basis Weight in the range of 200 to per cubic centimeter. 500 grams per square meter. 5. The paperboard product of claim 4 in Which said 13. The paperboard product of claim 10 in Which the paperboard product has a caliper in the range of 0.4 and 1.2 density of said paperboard product is betWeen 0.3 and 0.45 mm. grams per cubic centimeter. 6. The paperboard product of claim 4 in Which said 14. The paperboard product of claim 13 in Which said paperboard product has a basis Weight in the range of 200 to paperboard product has a caliper in the range of 0.4 and 1.2 500 grams per square meter. mm. 7. The paperboard product of claim 1 in Which the density 15. The paperboard product of claim 13 in Which said of said paperboard product is betWeen 0.35 and 0.4 grams paperboard product has a basis Weight in the range of 200 to per cubic centimeter. 500 grams per square meter. 8. The paperboard product of claim 7 in Which said 16. The paperboard product of claim 10 in Which the paperboard product has a caliper in the range of 0.4 and 1.2 density of said paperboard product is betWeen 0.35 and 0.4 mm. 9. The paperboard product of claim 7 in Which said grams per cubic centimeter. paperboard product has a basis Weight in the range of 200 to 17. The paperboard of claim 16 in Which said paperboard 500 grams per square meter. product has a caliper in the range of 0.4 and 1.2 mm. 10. The paperboard product of claim 1 further comprising 18. The paperboard product of claim 16 in Which said at least three plies, and said one of said plies comprises a paperboard product has a basis Weight in the range of 200 to center ply. 500 grams per square meter. 11. The paperboard product of claim 10 in Which said paperboard product has a caliper of 0.4 and 1.2 mm. * * * * *