U.S. patent application number 11/170415 was filed with the patent office on 2006-12-28 for method for treating secondary fiber to achieve wet strength while retaining repulpability.
Invention is credited to Jeffrey E. Mayovsky, David W. Park, William A. White.
Application Number | 20060289140 11/170415 |
Document ID | / |
Family ID | 37565900 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060289140 |
Kind Code |
A1 |
Park; David W. ; et
al. |
December 28, 2006 |
Method for treating secondary fiber to achieve wet strength while
retaining repulpability
Abstract
A method for treating secondary fiber to achieve wet strength
while retaining repulpability is provided. In an embodiment, the
method involves supplying a first line of secondary fiber which
represents a total supply of secondary fiber. The method has a
further step of removing a portion of the total supply of secondary
fiber in the first line and transporting the portion into a second
line. The second line is treated with a cationic resin treatment. A
third line supplies virgin fiber. The third line and the first line
are combined. Next, the treated secondary fiber in the second line
is combined with the mixed contents of the first line and third
line. Separation of the virgin fiber line from the secondary fiber
line at initial stages of the process lowers cationic demand for
the system, and reduces an amount of resin required to treat the
system.
Inventors: |
Park; David W.; (Puyallup,
WA) ; Mayovsky; Jeffrey E.; (Puyallup, WA) ;
White; William A.; (Idabel, OK) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Family ID: |
37565900 |
Appl. No.: |
11/170415 |
Filed: |
June 28, 2005 |
Current U.S.
Class: |
162/183 ;
162/147; 162/158; 162/164.3; 162/164.6 |
Current CPC
Class: |
D21C 5/00 20130101; D21H
11/14 20130101; D21H 11/20 20130101; D21C 9/002 20130101 |
Class at
Publication: |
162/183 ;
162/147; 162/158; 162/164.3; 162/164.6 |
International
Class: |
D21H 23/02 20060101
D21H023/02; D21H 17/00 20060101 D21H017/00 |
Claims
1. A method for treating fiber comprising the steps of: supplying a
first line of secondary fiber which represents a total supply of
secondary fiber; removing a portion of the total supply of
secondary fiber in the first line and transporting the portion into
a second line wherein a remainder of the total supply of secondary
fiber remains in the first line; treating the second line with a
cationic resin treatment; supplying a third line having virgin
fiber; combining the remainder of secondary fiber in the first line
and the virgin fiber in the third line; and adding the treated
secondary fiber in the second line to the combined first line and
third line.
2. The method of claim 1 wherein a mix time for the cationic resin
treatment is in a range from 30 seconds to 90 seconds.
3. The method of claim 1 wherein a mix time when the second line is
added to the combined first line and third line is in a range from
1 minute to 3 minutes.
4. The method of claim 1 wherein the cationic resin treatment
includes use of a cationic polyamide-epichlorohydrin resin to treat
the secondary fiber in the second line.
5. The method of claim 1 wherein the first line and third line are
mixed in a blend chest.
6. The method of claim 1 wherein the second line is added to the
combined first line and third line at a blend chest pump.
7. A method for treating fiber comprising: supplying a first line
of secondary fiber; supplying a second line of secondary fiber;
treating the second line with a cationic treatment; supplying a
third line having virgin fiber; combining the secondary fiber in
the first line and the virgin fiber in the third line; and adding
the treated secondary fiber in the second line to the combined
first line and third line.
8. The method of claim 7 wherein the first line and the second line
are separate.
9. The method of claim 7 wherein the second line is supplied by
removing a portion of the secondary fiber from the first line.
10. The method of claim 7 wherein the secondary fiber in the second
line is provided from a furnish which is separate from a furnish
used to supply the first line.
11. The method of claim 7 wherein a mix time for the cationic resin
treatment is in a range from 30 seconds to 90 seconds.
12. The method of claim 7 wherein a mix time when the second line
is added to the combined first line and third line is in a range
from 1 minute to 3 minutes.
13. A paper product prepared by a process comprising: supplying a
first line of secondary fiber which represents a first portion of a
total supply of secondary fiber; supplying a second line of
secondary fiber which represents a second portion of the total
supply of secondary fiber; treating the second line with a cationic
resin treatment; supplying a third line having virgin fiber;
combining the secondary fiber in the first line and the virgin
fiber in the third line; adding the treated secondary fiber in the
second line to the combined first line and third line; sheeting
contents of the combined first, second and third lines; and drying
the contents of the combined first, second and third lines.
14. The paper product of claim 13 wherein the second line is
supplied by removal of secondary fiber from the first line.
15. The paper product of claim 13 wherein the cationic resin
treatment includes use of a cationic urea-formaldehyde to treat the
secondary fiber in the second line.
16. The paper product of claim 13 wherein a mix time when the
second line is added to the combined first line and third line is
in a range from 1 minute to 3 minutes.
17. The paper product of claim 13 wherein a mix time for the
cationic resin treatment is in a range from 30 seconds to 90
seconds.
18. The paper product of claim 13 wherein the cationic resin
treatment includes use of a compound selected from the group
consisting of: cationic polyamide-epichlorohydrin resins, cationic
urea-formaldehyde (UF) and melamine-urea-formaldehyde (MUF)
condensation products.
19. The paper product of claim 13 wherein the second line is added
to the combined first line and third line at a blend chest
pump.
20. The paper product of claim 13 wherein the secondary fiber in
the second line is provided from a furnish which is separate from a
furnish used to supply the first line.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to a method for treating
fiber. More specifically, the method involves treating all or a
portion of a secondary fiber line prior to combination with a
virgin fiber line.
BACKGROUND OF THE INVENTION
[0002] Paper mills through the country are presently using
increasing amounts of secondary fiber in their products. This has
in part resulted from more efficient collection of waste paper
products, e.g., by businesses and by curbside recycling, and in
part from improved technology-that has enabled acceptable primary
products to be made from what were formerly waste products. An
additional impetus has come following the realization that well
over half of the volume of waste going into municipal landfills was
paper-based. Many customers and consumers now demand paper products
with a significant amount of post-consumer recycled fiber.
[0003] Unfortunately, each time cellulosic fibers are recycled
there is some loss in strength. This is in part due to fiber
breakage and cutting during the repulping process and from
subsequent refining. In part it is due to the inherent nature of
the fiber itself. Fiber once dried from an aqueous system suffers a
morphological change that affects subsequent fiber-to-fiber
bonding. For any given paper type; e.g., papers of identical basis
weight and additives, products made from recycled fiber of the same
type will typically be approximately 30% lower in selected strength
properties than the same product made from virgin fiber. Some mills
may compensate by making products of higher basis weight, by using
additives to increase lost strength, by increased refining, or by
some combination of these methods. The result is a higher cost
product that is often less competitive with a similar product made
from primarily virgin fiber.
[0004] Certain additives are commonly used to augment wet and dry
strength. Cationic starches have long been used in linerboard to
increase dry strength. Small quantities; e.g., 0.1-0.7%, of
cationic polyamide-epichlorohydrin reaction products (PAE resins)
are well known to increase both wet and dry strengths. They are
routinely used in products such as facial tissues and paper towels.
They are also used in a small percentage of the linerboard used for
the manufacture of wet strength-type corrugated board products.
Tissue and towels normally do not enter the recycle stream,
although much of the wet strength corrugated board does. There it
presents a problem because of less than desired repulpability. This
is normally tolerable since typically not more than about 1% or 2%
of the corrugated board produced for the marketplace has received
this type of wet strength treatment. However, if significantly
larger quantities of PAE treated products were in the recycle waste
stream from screening, repulped fiber would increase substantially
and production rates would be adversely affected. Thus, despite
their known efficiency at increasing both dry and wet strength, PAE
resins have been very selectively used only for specific products
where their poor repulpability does not present a significant
problem.
[0005] In addition, it is generally known that virgin fiber, when
exiting a digester or similar system, may have a high anionic
charge. This is due in part to the byproducts that accompany the
virgin fiber, such as, for example, sulfides, lignon fragments,
methanol and other negatively charged anions. Considerable amounts
of resin are therefore necessary to treat a line containing
secondary fiber and virgin fiber because the cationic resin reacts
with the anionic byproducts. Accordingly, a need exists for a
method for treating secondary fiber to achieve wet strength while
retaining repulpability. A further need exists for a method for
treating secondary fiber which requires reduced levels of resin
treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The embodiments of the present invention are described in
detail below with reference to the following drawings.
[0007] FIG. 1 is a diagram of a system for fiber treatment in an
embodiment of the present invention;
[0008] FIG. 2 is a chart of reject comparison for products
manufactured via a conventional method and products manufactured
via at least one of the methods of the present invention; and
[0009] FIG. 3 is a diagram of a system for fiber treatment in an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The present invention provides a method for treating fiber
to achieve wet strength while retaining repulpability and/or
recyclability. In an embodiment, a paper-making process is
provided. The process has a first flow line which contains
secondary fiber in the form of, for example, old corrugated
containerboard ("OCC"). Secondary fiber may be defined as fiber
which has been dried at least once. In an embodiment, a portion of
this line is separated into a second line and is treated with
cationic resin. A third, and separate, line contains virgin fiber.
Virgin fiber may be defined as a predominance of cellulosic fiber
which has never been dried after a pulping process. The virgin
fiber line is combined with the untreated secondary fiber in the
first flow line. The treated portion is then recombined with the
mixed product of the first line and the virgin fiber line. Products
made from the combined flow lines demonstrate wet strength as well
as sufficient repulpability. Moreover, separation of the virgin
fiber from the secondary fiber provides the system with less
cationic demand. Accordingly, less resin is required to treat the
secondary fiber.
[0011] Referring now to the drawings wherein like numerals refer to
like parts, FIG. 1 illustrates a system 2 which may be used to
produce a base sheet having a first line 4 into which is fed
secondary fiber in the form of, for example, untreated OCC from a
supply or furnish 6. A flow rate extending from the furnish 6 may
be in a range from 2500 gpm to 4500 gpm. Moreover, the secondary
fiber supplied may represent 10-40% of the total fiber in the
system. At point 8, line 4 may be split into separate lines wherein
the line 4 is untreated and wherein the line 12 is treated with a
cationic resin treatment at a point 14. The resin may be provided
from a supply 15. A flow rate for the line 12 may be in a range
from 500 gpm to 3000 gpm. Examples of resins which may be utilized
are cationic polyamide-epichlorohydrin (PAE) resins, as well as
cationic urea-formaldehyde (UF) and melamine-urea-formaldehyde
(MUF) condensation products. In an embodiment, the OCC and/or other
secondary fiber which has been drawn off from line 4 is treated
with, for example, KYMENE.RTM.. A mix time for the cationic
treatment may be in a range from 30 seconds to 90 seconds.
[0012] The treated secondary fiber travels along line 16 to a blend
chest pump 18 at a flow rate in a range from 1500 gpm to 2000 gpm.
Approximately 20-30% of the total flow exiting the blend chest pump
18 consists of treated secondary fiber. More specifically, the
total flow exiting the blend chest pump 18 may include untreated
secondary fiber and/or treated secondary fiber and/or virgin fiber.
Of this total flow, 10-40% may be treated secondary fiber; 5-50%
may be untreated secondary fiber; and 60-90% may be virgin
fiber.
[0013] A virgin fiber furnish 20 provides a line 22 of virgin fiber
to the blend chest 10 at a flow rate in a range from 5400 gpm to
7500 gpm. More specifically, the virgin fiber supplied may
represent 60-90% of the total fiber in the system. At the blend
chest 10, the virgin fiber may be mixed with the untreated
secondary fiber flowing from the line 4. The mix time for the
virgin fiber and the untreated secondary fiber is in a range from 5
minutes to 20 minutes. Next, the combined virgin fiber and
untreated secondary fiber is mixed with the treated secondary fiber
line 16 at the blend chest pump 18. A mix time for the combination
of the lines 4, 12 and 22 is in a range from 1 minute to 3 minutes.
The entire mixture may then be transferred to a system 24 for
drying and/or pressing and/or other finishing activities.
[0014] In an embodiment, the line 12 of secondary fiber which is
treated may be supplied by an independent stream rather than split
from the line 4. In an embodiment, a furnish used to supply the
line 12 may be different than a furnish used to supply the
secondary fiber in the line 4. The independent line may be treated
with cationic resin prior to combination with the secondary fiber
line 4 and the virgin fiber line 22 in a manner similar to that
described above. Flow rates may be adjusted to create the system
parameters outlined above. For example, the flow rate of the
independent line may be adjusted wherein the treated secondary
fiber accounts for 20-30% of the total fiber exiting the blend
chest pump 18. In another embodiment, a single line of secondary
fiber may be supplied. This line may be treated with a cationic
resin treatment and combined with virgin fiber. In this embodiment,
the virgin fiber line may be combined with only treated secondary
fiber.
[0015] EXAMPLE 1, illustrated in FIG. 3, describes an embodiment of
the present invention in which fiber was treated to provide a
product having wet strength and adequate repulpability. More
specifically, in the example below, the objective was to produce
paper with wet strength, and normal repulpablility. To achieve
this, 15% to 25% of the furnish was treated with a strong dose of
wet strength resin. The treated portion gave the sheet 50% to 70%
of the strength found in a normal wet strength sheet. The sheet was
considered repulpable because only 20% of the sheet was treated
with wet strength resin. It should be understood that, although
EXAMPLE 1 describes an embodiment in which all of the secondary
fiber is treated, this should not be construed to limit any
embodiments in which a portion of the total amount of secondary
fiber used is untreated.
EXAMPLE 1
[0016] In this embodiment, top sheet wet strength was added to a
top tickler pressure relief line 40 using AMRES.RTM.. A tank 41
provides a supply of virgin fiber for the top ply of product. In a
first step, the air was bled from the pressure relief line 40 at a
point 42. This was performed by opening a pressure control valve 44
to 50% output. This is the pressure relief line 40 from the top
tickler outlet 46. Next, isolation valves 45 on each side of an
automatic pressure relief valve 44 were opened.
[0017] A 1.5'' flush valve 48 was opened on the pressure relief
line 40 just above an entry point in the machine chest pump suction
50. This was performed for a duration sufficient to bleed the air
from a pressure recirculation line 52. The isolation valve 45 from
the top tickler pressure relief valve 44 was opened at the top
machine chest pump suction 50. A 250 to 300 gpm difference was
established between the top basis weight flow and the top tickler
flow. The valve 56 on the wet strength resin addition point 58 was
opened. A 2#/ton wet strength addition was then established. The
top tickler power was minimized as shear may reduce wet strength
resin efficiency. The wet strength addition set point was increased
to 6#/ton at a point in the process which was 2 reels before
starting the order. Wet strength addition was adjusted to control
test. The virgin fiber in this process was delivered to a blend
chest 47.
[0018] Base sheet wet strength resin was added before the OCC
refiner 60. To this end, the total OCC flow from a tank 61 was set
at 20% of the base basis weight flow (1600 to 1900 gpm). The OCC
flow controller (not shown) was set to manual because the wet
strength resin may negatively influence the flow indication. The
flow indicator (not shown) from the OCC refiner 60 can be used for
control. As shown in the FIGURE, treated secondary fiber and virgin
fiber are mixed in a blend chest 65. The base blend chest level set
point was reduced to meet the residence time requirement in the
chest because excessive mix time may reduce wet strength resin
efficiency. The valve 62 on the wet strength resin addition point
was then opened. A 2#/ton wet strength addition was then
established.
[0019] The wet strength addition set point was increased to 6#/ton
at a point 2 reels before starting the order. Wet strength addition
was adjusted to control test. The system was then flushed. To this
end, the wet strength addition rate was reduced to 2#/ton. The
suction valve (not shown) on the wet strength supply tank (not
shown) was then closed. Next, the flush water valve (not shown) was
opened for sufficient time to flush the system of resin. The wet
strength pump (not shown) was stopped after the flush was complete.
The isolation valves (not shown) at the base and top addition
points were closed when the flush was complete.
[0020] FIG. 2 illustrates a chart of a comparison of product
rejects based on conventional methods of paper manufacturing and
methods of the present invention. In the embodiments of the present
invention, a portion of secondary fiber is treated with cationic
resin prior to combination with virgin fiber. In the FIGURE, the
square-shaped symbols represent a percentage of rejects for a set
of rolls which were produced. The diamond-shaped symbols represent
an amount of resin used per ton to treat the system. Each
diamond-shaped symbol corresponds to each square-shaped symbol, as
they represent a trial collectively. From the FIGURE, it can be
seen that those products in which a portion of secondary fiber was
treated prior to combination with virgin fiber provided less
rejects. Thus, these embodiments demonstrated greater repulpability
on average. Moreover, the products of the present invention
required less resin, on average, in comparison to conventional
products. This is due to the separation of the virgin fiber line
from the secondary fiber line. This separation may prevent any
possible reaction between the anionic byproduct associated with the
virgin fiber and any cationic resin added to the system to treat
the secondary fiber. For example, in conventional systems, a line
combining secondary fiber and virgin fiber may have a charge of
0.3-3.0 meq/L. However, in the present invention, a secondary fiber
line, prior to combination with the virgin fiber, may have a charge
in a range from 0.1-1.0 meq/L. Accordingly, less resin is necessary
to treat the secondary fiber.
[0021] Table 1 shows data in a comparison between products prepared
using conventional methods (denoted "WS") and products prepared
using at least one of the methods of the present invention (denoted
Reels 1, 2 and 3). TABLE-US-00001 TABLE 1 Unit Reel 1 Reel 2 Reel 3
WS Basis Weight Lbs/MSF 57.0 56.6 56.8 56.1 Caliper Points 15.6
15.2 15.5 15.0 Density kg/m.sup.3 705.5 719.5 705.4 722.3 Mullen
Lbs/In.sup.2 120.9 124.2 112.4 127.4 Mullen Wet Lbs/In.sup.2 39.7
40.7 41.4 39.4 Repulpability - Rejects % 5.5 4.7 6.2 28.6 STFI - CD
Lbs/In 33.9 36.6 35.7 31.5
[0022] As can be seen in the table, the method of the present
invention enables wet strength grade products. Moreover, the
present invention allows for greater repulpability, as evidenced by
the considerably fewer percentage of rejects.
[0023] While the embodiments of the invention have been illustrated
and described, as noted above, many changes can be made without
departing from the spirit and scope of the invention. Accordingly,
the scope of the invention is not limited by the disclosure of the
embodiments. Instead, the invention should be determined entirely
by reference to the claims that follow.
* * * * *