U.S. patent application number 11/322940 was filed with the patent office on 2007-07-05 for insulating paperboard.
Invention is credited to Donald D. Halabisky.
Application Number | 20070151687 11/322940 |
Document ID | / |
Family ID | 37943793 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151687 |
Kind Code |
A1 |
Halabisky; Donald D. |
July 5, 2007 |
Insulating paperboard
Abstract
An insulating paperboard contains at least one layer of
cellulose fibers. The one layer is at least partially composed of
crosslinked fibers and processed cellulosic fibers. The paperboard
provides sufficient insulation to provide a .DELTA.T across the
paperboard of at least 3.6.degree. C. at 0.5 mm. A hot cup may be
produced from the insulating paperboard.
Inventors: |
Halabisky; Donald D.;
(Tacoma, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Family ID: |
37943793 |
Appl. No.: |
11/322940 |
Filed: |
December 30, 2005 |
Current U.S.
Class: |
162/146 ;
162/142; 162/9; 428/340 |
Current CPC
Class: |
D21H 27/38 20130101;
D21H 27/10 20130101; D21H 15/00 20130101; Y10T 428/27 20150115 |
Class at
Publication: |
162/146 ;
162/009; 162/142; 428/340 |
International
Class: |
D21H 13/00 20060101
D21H013/00 |
Claims
1. An insulating paperboard comprising: at least one layer
comprising a mixture of crosslinked fibers and processed cellulosic
fibers, said crosslinked cellulosic fibers and said processed
fibers being present in an amount in said mixture from 35 to 60
percent of total dry weight of fibers of said at least one layer,
and wherein said paperboard being sufficiently insulating to
provide a .DELTA.T across said paperboard of at least 3.6.degree.
C. at a caliper of 0.5 mm, said paperboard having a density of less
than 0.5 g/cc, and a basis weight of from 200 gsm to 500 gsm, and
said caliper of said paperboard being greater than or equal to 0.5
mm.
2. The crosslinked fibers of claim 1 wherein said crosslinked
fibers are present in an amount of 30 to 70 percent of the total
dry weight of the mixture and the processed fibers are present in
an amount of 70 to 30 percent of the total dry weight of the
mixture.
3. The processed fibers of claim 2 wherein the processed fibers are
selected from the group consisting of chemically processed fibers,
mercerized fibers, mechanically processed fibers, chemimechanically
processed fibers, jet dried fibers, flash dried fibers and mixtures
thereof.
4. The fibers of claim 3 wherein the processed fibers are CTMP
fibers.
5. The fibers of claim 3 wherein the processed fibers are TMP
fibers.
6. The crosslinked fibers of claim 1 wherein the fibers are
selected from the group consisting of citric acid crosslinked
fibers, polyacrylic acid crosslinked fibers and polymaleic acid
crosslinked fibers.
7. The crosslinked fibers of claim 6 wherein the crosslinked fibers
are polyacrylic acid crosslinked fibers.
8. The crosslinked fibers of claim 6 wherein the crosslinked fibers
are citric acid crosslinked fibers.
9. The insulating paperboard of claim 1, wherein said paperboard
has a basis weight of from 250 gsm to 450 gsm.
10. The insulating paperboard of claim 1, wherein said paperboard
has a .DELTA.T of at least 3.6.degree. C. at a caliper of 0.5 mm
and a .DELTA.T of 9.8.degree. C. at a caliper of 1.15 mm, said
.DELTA.T being a substantially linear progression relative to
caliper in the range from below a .DELTA.T of 3.6.degree. C. to
above a .DELTA.T of 9.8.degree. C.
11. The insulating paperboard of claim 10, wherein said linear
progression extends from a .DELTA.T of 3.6.degree. C. to a .DELTA.T
of 9.8.degree. C.
12. The paperboard of claim 1 wherein the Taber stiffness is at
least 150 g-cm.
13. The paperboard of claim 1 wherein the ZDT is at least 180
kPa.
14. The insulating paperboard of claim 1, wherein said paperboard
is at least a two-ply board, said at least one ply containing said
crosslinked cellulosic fibers and processed cellulosic fibers.
Description
FIELD
[0001] The present application relates to an insulating paperboard,
and more particularly to an insulating paperboard containing
crosslinked cellulosic fibers and processed cellulosic fibers.
BACKGROUND
[0002] Hot foods, particularly hot liquids, are commonly served and
consumed in disposable containers. These containers are made from a
variety of materials including paperboard and foamed polymeric
sheet material. One of the least expensive sources of paperboard
material is cellulose fibers. Cellulose fibers are employed to
produce excellent paperboards for the production of hot cups,
noodle cups, press-molded paperboard plates and bowls, and other
food and beverage containers. Conventional paperboard produced from
cellulosic fibers, however, is relatively dense, and therefore,
transmits heat more readily than, for example, foamed polymeric
material. Thus, hot liquids are often served in doubled cups of
conventional paperboard or in cups with sleeves.
[0003] It is desirable to possess an insulating paperboard produced
from cellulosic material that has good insulating characteristics,
that will allow the user to sense that food in the container is
warm or hot and at the same time will allow the consumer of the
food or beverage in the container to hold the container for a
lengthy period of time without the sensation of excessive
temperature. It is further desirable to provide an insulating
paperboard that can be tailored to provide a variety of insulating
characteristics so that the temperature drop across the paperboard
can be adjusted for a particular end use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] This application will become more readily appreciated and
understood by reference to the following detailed description, when
taken in conjunction with the accompanying drawings, wherein:
[0005] FIG. 1 is a schematic cross-sectional view of a two-ply
paperboard which can be constructed in accordance with the present
application;
[0006] FIG. 2 is an isometric view of a hot cup made from the
paperboard similar to that shown in FIG. 1 with a portion cut away;
and
[0007] FIG. 3 is an enlarged cross-sectional view of a portion of
the paperboard used to make the hot cup shown in FIG. 2.
DETAILED DESCRIPTION
[0008] Referring to FIG. 1, the substrate 10 for the insulating
paperboard 12 of the present application is produced in a
conventional manner from readily available fibers such as
cellulosic fibers. The paperboard of the present application can be
made in a single-ply, a two-ply construction, or a multi-ply
construction, as desired.
[0009] The distinguishing characteristic of the present application
is that at least one ply, 14, of the insulating paperboard, whether
a single-ply or a multiple-ply structure, contains a mixture of
crosslinked cellulosic fibers and processed cellulosic fibers in
addition to chemical pulp fibers. The mixture of crosslinked
cellulosic fibers and processed cellulosic fibers increase the
insulating characteristics of the board. As defined herein chemical
pulp fibers useable in the present application are derived
primarily from wood pulp and may be refined. Other sources such as
from kenaf and straw pulp may also be used. Suitable wood pulp
fibers for use with the application can be obtained from well-known
chemical processes such as the kraft and sulfite processes, with or
without subsequent bleaching. Softwoods and hardwoods can be used.
Details of the selection of wood pulp fibers are well known to
those skilled in the art. For example, suitable cellulosic fibers
(chemical pulp fibers) produced from southern pine that are useable
in the present application are available from a number of companies
including Weyerhaeuser Company under the designations C-Pine,
Chinook, CF416, FR416, and NB416. A bleached Kraft wet lap pulp,
KKT, Prince Albert Softwood and Grande Prairie Softwood, all
manufactured by Weyerhaeuser are examples of northern softwoods
that can be used. As used herein, processed cellulosic fibers
include fibers that are 1) chemically processed to change the
cellulose from Cellulose 1 to Cellulose 11, such as mercerized and
mercerized flash dried fibers in which the mercerization is
conducted as one stage in the bleaching process. Mercerized fibers
such as HPZ and mercerized flash dried fibers such as HPZ III, both
manufactured by Buckeye Technologies, Memphis Tenn., and
Porosinier-J-HP available from Rayonier Performance Fibers
Division, Jessup, Ga. are suitable for use in the present
application. These mercerized softwood pulps have an
.alpha.-cellulose purity of 95% or greater and are stiff fibers.
Processed fibers also include 2) mechanically and chemimechanically
treated fibers such as chemithermomechanical pulp fibers (CTMP),
bleached chemithermomechanical pulp fibers (BCTMP),
thermomechanical pulp fibers (TMP), refiner groundwood pulp fibers
and groundwood pulp fibers. Examples of these pulps are TMP
(thermomechanical pulp) made by Bowater, Greenville, S.C., a TMP
(thermomechanical pulp) made by Weyerhaeuser, Federal Way, Wash.,
made by passing wood chips through three stages of dual refiners,
and a CTMP (chemi-thermomechanical pulp) obtained from NORPAC,
Longview, Wash., sold as a CTMP NORPAC Newsprint Grade; the
brightness is from 53 to 75. Other processed fibers include jet
dried cellulosic fibers and treated jet dried cellulosic fibers
manufactured by the Weyerhaeuser Company by the method described in
U.S. application Ser. No. 10/923,447 filed Aug. 20, 2004. In this
method a slurry of pulp fibers is dewatered to a consistency of
approximately 34% and then passed through a jet drier having an
inlet temperature of approximately 190.degree. C. to 400.degree. C.
an outlet temperature of 50.degree. C. to 205.degree. C. and a
steam pressure of approximately 1082 kPa (157 psig). These fibers
are twisted kinked and curled. Additional processed fibers include
flash dried and treated flash dried fibers as described in U.S.
Pat. No. 6,837,970, Mixtures of processed fibers with crosslinked
cellulosic fibers can also be used.
[0010] The preferred bulky fibers for use in the invention are
crosslinked cellulosic fibers. Any one of a number of crosslinking
agents and crosslinking catalysts, if necessary, can be used to
provide the crosslinked fibers to be included in the layer. The
following is a representative list of useful crosslinking agents
and catalysts.
[0011] Suitable crosslinking agents include carboxylic acid
crosslinking agents such as polycarboxylic acids. Polycarboxylic
acid crosslinking agents (e.g., citric acid, propane tricarboxylic
acid, and butane tetracarboxylic acid) and catalysts are described
in U.S. Pat. Nos. 3,526,048; 4,820,307; 4,936,865; 4,975,209; and
5,221,285. The use of C.sub.2-C.sub.8 polycarboxylic acids that
contain at least three carboxyl groups (e.g., citric acid and
oxydisuccinic acid) as crosslinking agents is described in U.S.
Pat. Nos. 5,137,537; 5,183,707; 5,190,563; 5,562,740; and
5,873,979.
[0012] Polymeric polycarboxylic acids are also suitable
crosslinking agents. Suitable polymeric polycarboxylic acid
crosslinking agents are described in U.S. Pat. Nos. 4,391,878;
4,420,368; 4,431,481; 5,049,235; 5,160,789; 5,442,899; 5,698,074;
5,496,476; 5,496,477; 5,728,771; 5,705,475; and 5,981,739.
Polyacrylic acid and related copolymers as crosslinking agents are
described U.S. Pat. Nos. 5,549,791 and 5,998,511. Polymaleic acid
crosslinking agents are described in U.S. Pat. No. 5,998,511 and
U.S. Pat. No. 6,582,553.
[0013] Suitable specific crosslinking agents include polycarboxylic
acid crosslinking agents such as citric acid, tartaric acid, malic
acid, succinic acid, glutaric acid, citraconic acid, itaconic acid,
tartrate monosuccinic acid, maleic acid, polyacrylic acid,
polymethacrylic acid, polymaleic acid,
polymethylvinylether-co-maleate copolymer,
polymethylvinylether-co-itaconate copolymer, copolymers of acrylic
acid, and copolymers of maleic acid. Other suitable crosslinking
agents are described in U.S. Pat. Nos. 5,225,047; 5,366,591;
5,556,976; and 5,536,369.
[0014] Suitable crosslinking catalysts can include acidic salts,
such as ammonium chloride, ammonium sulfate, aluminum chloride,
magnesium chloride, magnesium nitrate, and alkali metal salts of
phosphorous-containing acids. In one embodiment, the crosslinking
catalyst is sodium hypophosphite.
[0015] The crosslinking agent is applied to the cellulosic fibers
as they are being produced in an amount sufficient to effect
intrafiber crosslinking. The amount applied to the cellulosic
fibers may be from about 1% to about 25% by weight based on the
total weight of fibers. In one embodiment, crosslinking agent in an
amount from about 4% to about 6% by weight based on the total
weight of fibers. Mixtures or blends of crosslinking agents and
catalysts can also be used.
[0016] In addition to fibrous materials, the paperboard of the
invention may optionally include a binding agent. Suitable binding
agents are soluble in, dispersible in, or form a suspension in
water. Suitable binding agents include those agents commonly used
in the paper industry to impart wet and dry tensile and tearing
strength to such products. Suitable wet strength agents include
cationic modified starch having nitrogen-containing groups (e.g.,
amino groups), such as those available from National Starch and
Chemical Corp., Bridgewater, N.J.; latex; wet strength resins, such
as polyamide-epichlorohydrin resin (e.g., KYMENE 557LX, Hercules,
Inc., Wilmington, Del.), and polyacrylamide resin (see, e.g., U.S.
Pat. No. 3,556,932 and also the commercially available
polyacrylamide marketed by American Cyanamid Co., Stanford, Conn.,
under the trade name PAREZ 631 NC); urea formaldehyde and melamine
formaldehyde resins; and polyethylenimine resins. A general
discussion on wet strength resins utilized in the paper field, and
generally applicable in the present invention, can be found in
TAPPI monograph series No. 29, "Wet Strength in Paper and
Paperboard", Technical Association of the Pulp and Paper Industry
(New York, 1965).
[0017] Other suitable binding agents include starch, modified
starch, polyvinyl alcohol, polyvinyl acetate, polyethylene/acrylic
acid copolymer, acrylic acid polymers, polyacrylate,
polyacrylamide, polyamine, guar gum, oxidized polyethylene,
polyvinyl chloride, polyvinyl chloride/acrylic acid copolymers,
acrylonitrile/butadiene/styrene copolymers, and polyacrylonitrile.
Many of these will be formed into latex polymers for dispersion or
suspension in water.
[0018] Paperboard of the present application may have a broad set
of characteristics. For example, in one embodiment its basis weight
can range from about 200 gsm to about 500 gsm, in another
embodiment the basis weight ranges from 250 gsm to 400 gsm. In yet
another embodiment the basis weight of the paperboard is equal to
or greater than about 350 gsm. In one embodiment the insulating
paperboard has a density of less than 0.5 g/cc, in another
embodiment the density is from about 0.3 g/cc to about 0.45 g/cc,
and in another embodiment the density is from 0.35 g/cc to 0.40
g/cc.
[0019] When at least one ply of the paperboard contains a mixture
of crosslinked cellulosic fibers and processed cellulosic fibers in
accordance with the present application, advantageous temperature
drop characteristics can be achieved. These temperature drop
characteristics can be achieved by altering the amount of these two
fibers introduced into the paperboard, by adjusting the basis
weight of the paperboard, by adjusting the caliper of the
paperboard after it has been produced by running it, for example,
through nip rolls, and of course, by varying the number and
thickness of additional plies incorporated in the paperboard
structure. In one embodiment the paperboard has a caliper greater
than or equal to 0.5 mm, a basis weight equal to or greater than
200 gsm, and a density less than 0.5 g/cc. Insulating paperboard
properties are given in Table 1. TABLE-US-00001 TABLE 1 Insulating
Paperboard Properties % of Mixture Overall Taber Sample Basis Wt. %
Mixture Processed Crosslink Caliper Density, Bulk, ZDT Stiffness
.DELTA.T, No. Wt. g/m.sup.2 D. Fir Total, % Fiber Crosslink Level,
% (mm) g/cc cm.sup.3/g (kPa) (g-cm) .degree. C. 1 217.8 35 60 30 70
42 0.68 0.32 3.13 303.4 104.9 6.3 2 208.7 35 60 50 50 30 0.57 0.36
2.75 448.2 96.7 5.3 3 210.9 35 60 70 30 18 0.52 0.41 2.47 624.0
87.2 3.6 4 373.5 47.5 47.5 30 70 33.25 1.00 0.37 2.69 371.6 434.2
8.9 5 380.4 47.5 47.5 50 50 23.75 0.95 0.40 2.50 502.0 446.3 8.4 6
372.9 47.5 47.5 70 30 14.25 0.87 0.43 2.32 589.5 406.0 7.4 7 548 35
35 30 70 24.5 1.35 0.41 2.47 424.0 1062.2 12.2 8 552.2 35 35 50 50
17.5 1.29 0.43 2.34 466.1 974.1 10.9 9 539.9 35 35 70 30 10.5 1.13
0.48 2.1 678.5 968.7 9.8 10 216.4 35 60 30 70 42 0.78 0.28 3.63
179.3 115.7 8.8 11 217.2 35 60 50 50 30 0.73 0.30 3.38 207.5 109.9
8.0 12 216.4 35 60 70 30 18 0.71 0.30 3.3 255.1 113.0 7.3 13 389.2
47.5 47.5 30 70 33.25 1.13 0.34 2.91 206.9 332.3 11.3 14 392.6 47.5
47.5 50 50 23.75 1.09 0.36 2.77 281.3 413.7 10.6 15 390.9 47.5 47.5
70 30 14.25 1.06 0.037 2.72 359.9 444.6 9.3 16 559.2 60 35 30 70
24.5 1.4 0.40 5.50 337.9 859.5 12.5 17 565.9 60 35 50 50 17.5 1.4
0.41 2.47 353.7 938.4 11.7 18 565.5 60 35 70 30 10.5 1.34 0.42 2.36
428.9 822.2 11.4 Note: Samples 1-9, inclusive, contained CTMP
fibers as the processed fibers in the mixture with crosslinked
fibers and samples 10-18 contained TMP fibers as processed fibers
in the mixture with crosslinked fibers. All samples contain 5%
Lodgepole Pine, by total dry weight of fiber, refined to 50
CSF.
[0020] In another embodiment the paperboard exhibits a .DELTA.T of
at least 3.6.degree. C. at a caliper of 0.5 mm. In another
embodiment the paperboard exhibits a .DELTA.T of at least
9.8.degree. C. at a caliper of at least 1.15 mm. The relationship
of .DELTA.T (as defined below) to caliper is a linear one between
the caliper of 0.5 mm and 1.15 mm and continues to be linear with a
reduction in the caliper below 0.5 mm or an increase above 1.15
mm.
[0021] These temperature values are based on a linear regression
equation of caliper versus .DELTA.T using the values for caliper
and .DELTA.T for samples 1-9 in Table 1. Upper and lower confidence
limits can be calculated for each point on the regression line from
the data given in Table 1. The statistical parameters are given in
Table 2. TABLE-US-00002 TABLE 2 Regression Statistics Multiple R
.999 R Square .98 Lower Upper Coefficients 95.0%* 95.0%* Intercept
-0.32 -1.55 0.9 X Variable 9.06 7.8 10.3 *Confidence Limits
[0022] Using the coefficients established in Table 2 above, the
following relationships in Table 3 can be established for the
.DELTA.T at different caliper levels for samples 1-9, inclusive.
TABLE-US-00003 TABLE 3 .DELTA.T At Various Caliper Levels Based On
Regression Line Caliper .DELTA.T, .degree. C. LCL UCL 0.2 1.5 0 3.0
0.3 2.4 .8 4.0 0.4 3.3 1.6 5.0 0.5 4.2 2.4 6.1 0.6 5.1 3.1 7.1 0.7
6 3.9 8.1 0.8 6.9 4.7 9.2 0.9 7.8 5.5 10.2 1 8.7 6.3 11.2 1.1 9.6
7.0 12.3 1.2 10.5 7.8 13.3 1.25 11.4 8.6 14.3 LCL, Lower 95%
Confidence Limit UCL, Upper 95% Confidence Limit
[0023] Tables 4 represents the regression statistics for samples
10-18 in which TMP was used in the mixture with crosslinked fiber
and Table 5 represents the .DELTA.T values at various caliper
levels using the coefficients and confidence limits established in
Table 4. TABLE-US-00004 TABLE 4 Regression Statistics Multiple R
0.95 R Square .91 Lower Upper Coefficients 95.0%* 95.0%* Intercept
3.48 1.54 5.41 X Variable 6.19 4.43 7.94 *Confidence Limits
[0024] TABLE-US-00005 TABLE 5 .DELTA.T At Various Caliper Levels
Based On Regression Line Caliper .DELTA.T, .degree. C. LCL UCL 0.2
4.7 2.4 7 0.3 5.3 2.9 7.8 0.4 5.9 3.3 8.6 0.5 6.6 3.8 9.4 0.6 7.2
4.2 10.2 0.7 7.8 4.6 11 0.8 8.4 5.1 11.8 0.9 9 5.5 12.5 1 9.7 6
13.3 1.1 10.3 6.4 14.1 1.2 10.9 6.9 14.9 1.25 11.5 7.3 15.7 LCL,
Lower 95% Confidence Limit UCL, Upper 95% Confidence Limit
[0025] The paperboard of the application can be a single-ply
product. When a single-ply product is employed, the low density
characteristics of the paperboard of the present application allows
the manufacture of a thicker paperboard at a reasonable basis
weight. Using a mixture of the crosslinked cellosic fibers and
processed cellulosic fibers of the present application, an
insulating paperboard having the same basis weight as a normal
paperboard can be made. This effectively allows the manufacture of
insulating paperboard on existing paperboard machines with minor
modifications and minor losses in productivity. Moreover, a one-ply
paperboard has the advantage that the whole structure is at a low
density. Alternatively, the paperboard of the application can be
multi-ply product, and include two, three, or more plies.
Paperboard that includes more than a single-ply can be made by
combining the plies either before or after drying. Multi-ply
paperboard can be made by using multiple headboxes arranged
sequentially in a wet-forming process, or by a baffled headbox
having the capacity of receiving and then laying multiple pulp
furnishes. The individual plies of a multi-ply product can be the
same or different.
[0026] The paperboard of the present application can be formed
using conventional papermaking machines including, for example,
Rotoformer, Fourdrinier, inclined wire Delta former, and twin-wire
forming machines.
[0027] In one embodiment when a single-ply paperboard is used in
accordance with the present application, it is homogeneous in
composition. The single ply, however, may be stratified with
respect to composition and have one stratum enriched with
crosslinked cellulosic fibers and processed cellulosic fibers and
another stratum enriched with cellulosic fibers (chemical pulp
fibers) to provide a smooth, denser, less porous surface.
[0028] It is most economical to produce a composition paperboard
that is homogeneous where the crosslinked cellulosic fibers and
processed cellulosic fibers are uniformly mixed with the cellulosic
fibers. In one embodiment the crosslinked cellulosic fibers and
processed cellulosic fibers are present in the insulating ply or
layer in an amount from about 35% to about 60% of the total dry
weight of the cellulosic fiber. In another embodiment they are
present in an amount of from 45% to about 55%. of the total dry
weight of the cellulosic fiber. In a two-ply structure, for
example, the first ply may contain 100% cellulosic fibers while the
second ply may contain from 25% to 70% crosslinked cellulosic
fibers and processed cellulosic fibers. In another embodiment the
second ply may contain from 35% to 60% crosslinked cellulosic
fibers and processed cellulosic fibers. In one embodiment, in a
three-ply layer, the bottom and top layers may comprise 100% of
cellulosic fibers while the middle layer may contain from about 25%
to about 70% of crosslinked cellulosic fibers and processed
cellulosic fibers. In another embodiment, in a three ply layer, the
middle layer may contain from about 35% to about 60% of crosslinked
celluosic fibers and processed cellulosic fibers.
[0029] The paperboard of the present application has a broad set of
strength properties. For example, in one embodiment the Taber
stiffness ranges from about 90 g-cm to about 1000 g-cm. In another
embodiment the Taber stiffness ranges from about 150 to about 500
g-cm and in yet another embodiment the Taber stiffness ranges from
about 200 to about 400 g-cm. Taber stiffness was determined by
TAPPI T-489.
[0030] In converting operations of a conventional board to the cup,
a minimum Z-direction tensile (ZDT) is necessary for proper rim or
top curl formation so that delamination does not occur during this
process. In one embodiment ZDT ranges from about 180 kPa to 450
kPa, in another embodiment the ZDT ranges from about 300 kPa to
about 400 kPa. ZDT was determined by TAPPI T-541.
[0031] Sheet bulk was determined by TAPPI T-411.
[0032] The paperboard of the present application can be utilized to
make a variety of structures, particularly containers, in which it
is desired to have insulating characteristics. Referring to FIG. 2,
one of the most common of these containers is the ubiquitous hot
cup utilized for hot beverages such as coffee, tea, and the like.
Other food service items that could benefit from improved
insulating properties such as noodle cups, and press-molded plates
and bowls can also incorporate the paperboard of the present
application. Also, carry-out containers conventionally produced of
paperboard or of foam material can also employ the paperboard of
the present application. As shown in FIGS. 2 and 3, a hot cup type
container produced in accordance with the present application may
comprise one or more plies 22 and 24, one of which, in this
instance, 24, contains crosslinked cellulosic fibers and processed
cellulosic fibers. In this embodiment the crosslinked cellulosic
fibers and the processed cellulosic fibers are in the interior ply
24. A liquid impervious backing 26 is preferably laminated to the
interior ply. The backing may comprise, for example, a variety of
thermoplastic materials, such as polyethylene. It is preferred that
the paperboard used in the bottom of the cup contain no crosslinked
cellulosic fibers or processed cellulosic fibers.
.DELTA.T Test Procedure
[0033] Paperboard thermal performance is determined in a test unit
that models the heat transfer through a paper cup. A box of
plexiglass measuring 10.times.10.times.10 cm interior dimensions
has a sample opening of 8.2 cm by 8.2 cm in one side. A gasket of
surgical tubing is attached to the box around the perimeter of the
8.2 cm.times.8.2 cm opening. A 10 cm.times.10 cm sample of
paperboard is laminated on one surface with 10 cm wide 3 M Tartan
3765 packaging tape. Alternatively, polyethylene may be extruded
onto the surface of the board. The paperboard sample is mounted
onto the apparatus covering the sample opening with the sealed face
toward the interior. A separate piece of plexiglass (with the same
outside dimensions as the box and a hole 8.2 cm.times.8.2 cm cut
out) is clamped over the paperboard sample to hold it firmly
against the box. The box is filled with hot water at a temperature
of 96.1.degree. C. (205.degree. F.) through a small opening in the
top of the box so that the water is in full contact with the
sample. A small stir bar is inserted into the box and the assembly
is then placed on a stir plate to permit stirring during the
measurement phase. A K type thermocouple is inserted into the hot
water through the small opening in the box top and an infra-red
thermometer IRCON Inc. Modline Series 3400 Radiation Thermometer,
set to measure at 0.96 emissivity is aimed at the outside center of
the paperboard sample at a 29.7 cm distance and the IR radiation
measured. A data logger, (HP34970A Data Acquisition/Switch Unit
capturing the mVdc response from the radiation thermometer adjusted
by a gain of 30.0 and an offset of 100 and the mVdc response from
the thermocouple but does not adjust it) records the temperature of
both the inside water (from the thermocouple inserted into the
water) and the outside surface of the sample (from the infrared
radiation thermometer gun) from which the temperature drop
(.DELTA.T) can be calculated. When the water temperature reaches
85.degree. C. (185.degree. F.), the data capture is halted. The
difference between the inside water temperature and the outside
paperboard temperature is calculated for each data point captured
by the data logger. A linear regression analysis is performed on
the data for .DELTA.T (inside water temperature minus outside wall
temperature) versus inside water temperature and, from the
regression, the .DELTA.T at 87.8.degree. C. (190.degree. F.) is
determined. The linear regression analysis is run from the point of
maximum outside wall temperature to a point on the curve that
corresponds to an internal water temperature of 85.degree. C.
(185.degree. F.). .DELTA.T is the difference in temperature between
the water temperature of 87.8.degree. C. (190.degree. F.) and the
corresponding outside wall temperature of the paperboard on the
test unit.
[0034] Insulating paperboard with varying compositions of
crosslinked fiber and processed cellulosic fibers, basis weight and
other properties, shown in Table 1, were made by methods similar to
those represented in Examples 1 and 2 by substituting the
appropriate amount of fiber and additives.
EXAMPLE 1
[0035] This method is representative of making a 350 gsm board in
which 60% of the total dry weight of the fiber mixture is made up
of a 50/50 blend of crosslinked fiber and Bowater TMP fiber. In all
cases, dry weight of fiber means the fibers were dried at
105.degree. C. for one hour. Other paperboards, shown in Table 1,
of various basis weights and various levels of crosslinked fibers
and processed fiber levels can be made with adjustment to the
appropriate amounts and weights of fiber and other additives. In
all samples shown in Table 1 the bleached Douglas Fir component was
refined to 510 CSF; Lodgepole Pine (refined to 50 CSF) was added to
all samples at a level of 5% of total dry fiber weight. All samples
had 10% by weight PVOH added on the total fiber dry weight. Other
additive levels are given in this Example and in Example 2.
[0036] TMP (from Bowater), 19.43 g fiber (43.2% consistency), 57.7
g Douglas Fir refined to 510 CSF (29.1% consistency), 9.03
crosslinked fiber (93.0% consistency), 70.7 g Lodgepole Pine
refined to 50 CSF (2.5% consistency), and 3.54 g polyvinylalcohol
(Celvol 165SF PVOH, available from Celanese, Dallas Tex.), 100%
solids, were disintegrated for 5 minutes in a British
Disintegrator. The mixture was diluted to 4 L with deionized water
and adjusted to a pH of 7.2-7.4 using NaHCO.sub.3. The equivalent
of 1 g/kg (2 lb/T) Kymene and 0.13 g/kg (0.26 lb/T) of
Perform-PC8138 (both available from Hercules, Wilmington, Del.)
were added from 1% solutions each, and mixed for 2 minutes. AKD
(alkyl ketene dimer available from Hercules, Inc., Wilmington,
Del.) at 2 g/kg (4 lb/T) and 4.25 g/kg (8.5 lb/Ton) starch (Sta-Lok
300, available from Tate-Lyle, Decatur Ill.) were each added and
the mixture stirred for two minutes. A 31.75.times.31.75 cm forming
wire (155 mesh) was placed in the bottom of a Noble & Wood
12.5'' by 12.5'' handsheet mold, the slurry poured into the sheet
mold, diluted to 35 liters with deionized water and mixed with a
plunger. The slurry was then drained, dewatered by using blotters
with even hand pressing until the sheet reached a consistency of
approximately 20%. The sheet was removed from the screen and
blotted further to approximately 30% solids. Blotters were placed
on each side of the sample, the sample placed between damp felts
and then passed through a press at 137.8 kPa (20 psi) to further
dewater the sample. The solids content at this point was
approximately 40%. The resulting sheet was placed on a drum dryer,
(surface temperature of 121.degree. C.), between two dry blotters
and allowed to dry for 10 minutes. The sample was then inverted and
allowed to dry an additional 10 minutes. The sample was conditioned
in a 50% Relative Humidity room for a minimum of 4 hours prior to
testing.
EXAMPLE 2
[0037] This method is representative of making a 200 gsm board in
which 60% of the total dry weight of the fiber mixture is made up
of a blend of 42% crosslinked fiber and 18% Bowater TMP fiber.
Other paperboards, shown in Table 1, of various basis weights and
processed fiber levels can be made with adjustment to the
appropriate amounts and weights of fiber and other additives. In
all samples shown in Table 1 the bleached Douglas Fir component was
refined to 510 CSF; Lodgepole Pine, refined to 50 CSF, was added to
all samples at a level of 5% by weight of total dry fiber. All
samples had 10% by weight PVOH added on the total fiber dry
weight.
[0038] CTMP, 8.35 g fiber (43.5% consistency), 24.3 g Douglas Fir
refined to 510 CSF (29.1% consistency), 9.1 g crosslinked fiber
(93.0% consistency), 40.5 g Lodgepole Pine refined to 50 CSF (2.5%
consistency), and 2.02 g polyvinylalcohol (Celvol 165SF PVOH,
available from Celanese, Dallas Tex.), 100% solids, were
disintegrated for 5 minutes in a British Disintegrator. The mixture
was diluted to 4 L with deionized water and adjusted to a pH of
7.2-7.4 using NaHCO.sub.3. The equivalent of 1 g/kg (2 lb/T) Kymene
and 0.13 g/kg (0.26 lb/T) of Perform-PC8138 (both available from
Hercules, Wilmington, Del.) were added from 1% solutions each, and
mixed for 2 minutes. AKD (alkyl ketene dimer available from
Hercules, Inc., Wilmington, Del.) at 2 g/kg (4 lb/T) and 4.25 g/kg
(8.5 lb/Ton) starch (Sta-Lok 300, available from Tate-Lyle, Decatur
Ill.) were each added and the mixture stirred for two minutes. A
31.75.times.31.75 cm forming wire (155 mesh) was placed in the
bottom of a Noble & Wood 12.5'' by 12.5'' handsheet mold, the
slurry poured into the sheet mold, diluted to 35 liters with
deionized water and mixed with a plunger. The slurry was then
drained, dewatered by using blotters with even hand pressing until
the sheet reached a consistency of approximately 20%. The sheet was
removed from the screen and blotted further to approximately 30%
solids. Blotters were placed on each side of the sample, the sample
placed between damp felts and then passed through a press at 137.8
kPa (20 psi) to further dewater the sample. The solids content at
this point was approximately 40%. The resulting sheet was placed on
a drum dryer, (surface temperature of 121.degree. C.), between two
dry blotters and allowed to dry for 10 minutes. The sample was then
inverted and allowed to dry an additional 10 minutes. The sample
was conditioned in a 50% Relative Humidity room for a minimum of 4
hours prior to testing.
[0039] The foregoing application has been described in conjunction
with a preferred embodiment and various alterations and variations
thereof. One of ordinary skill will be able to substitute
equivalents in the disclosed application without departing from the
broad concepts imparted herein. It is therefore intended that the
present application be limited only by the definition contained in
the appended claims.
* * * * *