Note: Descriptions are shown in the official language in which they were submitted.
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ENHANCED EFFICACY OF FUNGICIDES IN PAPER AND PAPERBOARD
This patent claims priority from U.S. Provisional Patent Application
60/641,618, filed 05 January 2005.
Background of the Invention
Fungal growth is a serious threat to human health, and the potential costs for
remediation or replacement of contaminated building materials are
astronomical.
Fungal spores, released from surface growth, are well-recognized as allergens,
and
additional concerns have been raised due to toxic byproducts of at least one
species.
According to recent studies by Gomy et al., occupant exposure to various
health
problems, including those referred to as "sick building syndrome," is
increasing.
Further concern is being raised by human allergic responses, similar to that
observed
with fungal spores, to fungal fragments that can be released at much lower
humidity
levels (as low as 20%).
Paper and paperboard used in those building niaterials have been observed as
the sites for such fungal growth. Typical moisture in paper, paperboard, and
building
materials is sufficient to maintain growth. The cellulose of the paper and
paperboard,
along with the residual contaminants within the fiber web, offer a sufficient
food
source that is enhanced by other building product components such as starch
binders.
Since fungi can grow in temperatures from as low as 40 F to as high as 130 F,
most indoor conditions, as well as a large segment of outdoor conditions, will
easily
allow their growth. Although efforts have been made to use careful
construction
practices and humidity control to limit fitngal growth, fungi contamination
problems
have been observed in regions such as the Northeast U.S. where relative
humidity
rarely exceeds recommended maximums, and building materials were not exposed
to
the weather. Atmospheric fungal spores provide sufficient inoculation of fungi
to the
materials, and added moisture from condensation or water damage makes the
threat of
fungal contamination more likely.
Gypsum panels are used for drywall building products in heavy use for
residential, educational, and commercial buildings. Gypsum panels are used
primarily for interior wall and ceiling construction, and some specialty
panels are
used in exterior applications. Even though fungal contamination can come from
the
gypsum core, made of calcium sulfate hemihydrates, the primary location for
fungal
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growth on gypsum panels is the facing and backing paper that covers each side
of the
gypsum core. Once installed, gypsum panels can make treatment and/or
remediation
extremely difficult and expensive, as fungal contamination may be enclosed and
inaccessible.
Homeowners typically see fungal growth in closets, along baseboards and on
bathroom walls; removal of installed panels may reveal hidden growth on the
backside. Areas with even minor water damage or condensation are often heavily
contaminated. Growth is visible as dark green or black spots that can grow to
a
complete covering of the affected area. Many after-market treatments, usually
based
on chlorine bleach, lighten the spots. Such treatments tend to damage the
paint or
coating after multiple treatinents and do not prevent return of fungi.
Many efforts have been made to develop a method that controls fungal
growth. The patent literature describes different methods of treatment to
address this
problem:
U.S. Pat. No. 6,705,939 teaches design of air dehumidification systems to
control growth. However, as discussed above, regions of the U.S. where low
humidity
is the typical condition, such as the Northeast, have discovered serious
problems with
contamination. Additionally, new studies indicate that fungal fragments, which
are
potentially as allergenic as fungal spores, are more optimally released at
humidity
levels as low as 40%.
Other methods replace the cellulose paper facings with synthetic sheets,
attempting to eliminate potential fungal growth sites. U.S. Pat. Nos.
3,993,822 and
6,770,354 address the problem by replacing the paper coverings of the gypsum
board
with glass fiber. U.S. patent application 2003/0037502 teaches use of nonwoven
sheets and demands control of described fungal nutrients in the gypsum core to
prevent growth. These coverings are generally more expensive than paper
facings,
installation costs are higher, and they are difficult to paint or wallpaper.
Control of
fungal nutrients within the gypsum core remains difficult because of
inconsistent raw
material sources and the extreme flexibility exhibited by many fungal
organisms.
Therefore, as a result, this approach has not generated commercially viable
options.
U.S. Pat. No. 5,421,867, to Yeager et al. and assigned to CuCorp, Inc.,
suggests application of a fungicidal agent to cementious-based products. U.S.
Pat.
Nos. 3,918,891 and 3,998,944, to Long and assigned to United States Gypsum
Company, recommend application of fungicidal agent to the paper that covers
the
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3
gypsum core to improve gypsum board. The fungicidal agents discussed therein
are
water-soluble metal quinolate salts, more specifically a copper quinolate.
Sucli
preservatives are undesirable from an environmental perspective. Furthermore,
the
antifungal compositions discussed are quite specific in their application and
lack the
flexibility needed to handle the array of applications for gypsum products.
U.S. Pat. No. 6,440,365 discusses usage of hydrochloric acid and heat to
destroy growth after it occurs. This method may destroy the organisms, but it
also
damages cellulose fibers present in paper facings of gypsum board and
installed wood
components. Additionally, hydrochloric acid presents serious fume exposure
concerns for users, and a corrosion concern for surrounding materials.
Complete
removal from enclosed areas of existing buildings is difficult, causing
ongoing health
and corrosion concerns.
U.S. Pat. Nos. 5,338,345 and 5,882,731 teach the use of barrier coating to
prevent atmospheric fungi from reaching the board. However, growth of fungi
can
proceed unhindered within the core or under the surface of the board, in areas
where
the coating is thinned or damaged from long-term exposure to cleaning or
environmental stress.
U.S. Pat. Nos. 4,533,435 and 6,248,761 discuss using binders or
microencapsulation to help control the preservative application. U.S. Pat. No.
6,767,647 involves the use of more than one fungicide in the wallboard
manufacturing
process and U.S. patent application 20040005484A1 teaches methods that rely on
a
high amount of a water-soluble fungicide in the core and migration of the
preservative
from the core to treat the facing paper. Whether the problem is inability to
get
sufficient treatment at the critical points or an inconsistent treatment
throughout the
sheet, none of these have been able to provide desired levels of antifungal
protection
for the sheet or the finished building products of which it is a component.
Current efforts to treat paper and paperboard with fungicide primarily involve
coating operations with compositions that incorporate a preservative. Due to
several
challenges, coating application methods have had limited commercial success..
Some
of the challenges to effective coating operations include:
= required decrease in machine production speed and its associated increase in
costs or additional cost for off-machine coating
= increased cost for additional materials to serve as carriers and/or binders
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= difficulty in maintaining an even dispersion in the coating solution and
uniform application of the coating to the paper
= increased drying costs due to rewetting of the sheet
= increased complexity of paper manufacturing
= potential impact on other necessary machine additives or quality parameters
= loss of treatment through surface mechanical action (e.g. - sanding)
These challenges are especially difficult for fungicides with limited
solubility in
aqueous coating solutions.
A more desirable alternative to achieve an effective fungicidal preservative
application would be to add the preservative to the pulp slurry, at a wet-end
addition
point. The current use of fungicides in the wet-end of paper processing, has
generally
been limited to slime (deposit) control, rather than incorporation into the
finished
paper product. Due to challenges associated with obtaining good distribution
and
cost-effective levels of preservative, wet-end addition of fungicides into
paper
products used in building materials has never achieved commercial success.
Successful addition of a fungicide at the wet-end during paper processing
would
require a method of distributing a sufficient amount of the fungicide evenly
in the
pulp slurry. Having the fungicide distributed throughout the paper, preferably
attached to the paper fibers, should offer enhanced protection of the finished
paper or
paperboard under typical use conditions.
Chemistries for improved fiber and fines retention and drainage are known to
be useful additives to the wet-end of paper processing, and include
flocculants.
Polymer flocculants improve attachment of fibers and fines through their
relatively
high molecular weights to attract the cellulosic materials. In addition, such
flocculants typically have limited charge density to reduce negative impact of
charged
contaminants and use, the complex mechanical and hydraulic action of the paper
machine during processing to properly align the fibers to provide good
formation.
Fixatives, as compared to flocculants, are much more compact in size, have
relatively
high charge densities, are typically cationic, and are lower in molecular
weight. A
wide variety of both organic and inorganic molecules has been used to fix dye,
pitch,
size, stickies particles, and anionic trash. However, fixative use has not
previously
included the attachment of preservatives for enhancement of their application
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,
efficiency, proximity to the fiber and dispersion throughout the sheet, and
finished
goods effectiveness.
U.S. Pat. No. 4,443,222 teaches that a preservative can be permanently
attached to a textile fiber through usage of a water-soluble compound, urea,
and a
non-reversible, heat-generated reaction. However, this type of permanent
attachment
reduces the effectiveness of many preservatives by binding up the active
antimicrobial
sites.
U.S. Pat. Nos. 6,680,127 and 6,773,822 and W02004/076770A1 all deal with
application to paper of a preservative that is cationic. Such preservatives
have a
natural affinity toward the anionic fibers and fines. The use of cationic
preservatives,
however, has not been a commercial success, due to either limited kill
efficiency
against fungi or the challenge of getting enough preservative into the sheet
to be
effective..
Summary of the Invention
This invention is a method for making a fungal-resistant paper or paperboard
sheet, particularly for use in building materials. The method includes adding
a
hydrophobic fungicide and a specific cationic fixative in a controlled manner
to pulp
slurry during manufacture of the paper or paperboard, as opposed to a surface
coating,
addition after sheet formation, or with an off-machine application. Addition
to the
pulp slurry is often referred to as addition to the wet end of a paper-making
process.
The method of this invention further includes processing the pulp slurry in a
paper
machine to create a finished sheet.
Selection of feed points for the fungicide and cationic fixative need to be
optimally chosen based upon individual paper machine system flow, available
options
for injection, potential for improved mechanical distribution and mixing, and
locations of other potentially influencing additives. In one embodiment of
this
invention, the cationic fixative is added, either neat or diluted, directly to
the higher
concentration pulp slurry, often referred to as thick stock, in the machine
chest,
allowing distribution throughout the slurry and activation of the fiber before
addition
of the fungicide. The hydrophobic fungicide is then added into the main stock
flow
prior to the fan pump or pumps to allow for adequate distribution and mixing.
In
another embodiment, especially useful for some types of cylinder paper
machines, the
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cationic fixative is added directly to the machine vats, while the hydrophobic
fungicide is added indirectly to the stock return loop, which is then recycled
back into
the main pulp slurry flow. One skilled in the art may optimize the method of
this
invention for a particular paper machine system design. This invention allows
for a
pre-activation of the fiber by the fixative followed by a more even
distribution of the
fungicide.
Paper or paperboard made by the process of the invention exhibits the
following benefits not presently found in fungicide-treated papers currently
available
in the marketplace:
= Reduced fungal growth because of an improved, even treatment.
= Reduced application requirements or increased application efficiency of
fungicide due to the synergy exhibited.
= Better product control.
= Reduced waste of materials.
= Reduced cost of production.
= Reduced potential for human exposure to suspected triggers of respiratory
illness and infection.
Detailed Description of the Invention
This invention is a method for making a fungal-resistant paper sheet for use
in
building materials. The method includes adding a hydrophobic fungicide and a
cationic fixative to a paper slurry during manufacture of the paper or
paperboard, and
processing the paper slurry in a paper machine to create a sheet. Addition to
the paper
slurry is often referred to as addition to the wet end of a paper-making
process.
The hydrophobic fungicide suitable for use in this invention must possess
several qualities. It must have extremely limited water solubility to prevent
its
leaching after installation and reduce the threat of environmental or human
exposure.
A preferred water solubility is less than 0.3 g/L at 25 C, and a more
preferred water
solubility is less 0.05 g/L at 25 C. The preservative must be temperature-
stable
against both the conditions of the paper machine dryer section and the
building
product manufacturing process (such as the gypsum board kilns). The
preservative
must be considered safe for humans, especially due to the higher risk for
exposure of
children in homes and schools. The preservative application must be cost-
effective
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enough to be practical. The preservative must provide a sufficient and
consistent
level of protection throughout the sheet to help prevent fungal growth.
Examples of
suitable fungicides include: diiodomethyl-p-tolylsulfone (DIMTS), zinc
pyrithione,
thiabendazole, 3-iodo-2-propynyl butylcarbamate, dichloro-
octylisothiazolinone, o-
phenylphenol, bromonitrostyrene, and 2-(thiocyanomethylthio) benzothiazole.
Table 1 gives approximate values of some low-solubility fungicides.
Table 1.
Water Solubility
Fungicide /L
diiodometh I- -tol Isulfone DIMTS 0.0001 (25 C
zinc pyrithione 0.02 (20 C
Thiabendazole 0.03 (20 C
3-iodo-2- ro n I butylcarbamate (IPBC) 0.156 (20 C
Dichloro-oct lisothiazolinone (DCOIT) 0.002
o- hen I henol (OPP) 0.20 (20 C
bromonitrostyrene (BNS) 0.128 (est.)
2-(thiocyanomethylthio) benzothiazole
(TCMTB) 0.033
A preferred fungicide for use in the present invention is diiodomethyl-p-
tolylsulfone, known by several names including P-Tolyl diiodomethyl sulfone
and
DIMTS (CAS Registry No. 020018-09-1). A preferred formulation of diiodomethyl-
p-tolylsulfone for use in this invention is commercially available from The
Dow
Chemical Company of Midland, MI as FUNGI-BLOCKTM fungicidal agent, which
contains approximately 40 wt. % DIMTS. The primary challenge to application of
this material is to achieve a consistent and cost-efficient treatment. The
haphazard
entrapment of water-insoluble preservative particles in an application on its
own
leaves lower sheet concentrations and inconsistent results. The complex
environment
of paper manufacturing can lead to inefficient attachment of the preservative
or
uneven treatment of the whole sheet. Voids in the microenvironment of an
inconsistently treated sheet allow fungi to "take root" at multiple points,
allowing
growth over the surface until it becomes completely covered.
Preferably, the active fungicide is added at amount equal to at least 0.02
pound
active fungicide per ton dry fiber produced, more preferably, when the active
fungicide is diiodomethyl-p-tolylsulfone, between about 2.0 pounds and 10.0
pounds
DIMTS per ton dry fiber produced, most preferably between about 2.0 and 3.2
pounds
DIMTS per ton dry fiber produced.
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The cationic fixative is chosen to provide the optimum concentration of
hydrophobic fungicide in the finished sheet and the best results with respect
to
antifungal treatment. The cationic fixative is chosen from the group
consisting of
cationic homopolymers and copolymers of polyacrylamides, polyamines,
polyDADMACs, polyguanidines, polyethyleneimines, cellulosic ethers, starches,
aluminum-based coagulants, iron-based coagulants, modified clays, modified
talcs,
silica microparticle systems, and combinations thereof, more preferably a
polyamine.
The fixative can be fed ahead of, together with, or after the addition of the
diiodomethyl-p-tolylsulfone. However, we have found that the fixative works
well
when added before the fungicide. Dosage ratios of cationic fixative-to-
fungicide can
be from 1:35 to 15:1 parts by weight, more preferably 1:35 to 2.5:1. In
particularly
preferred embodiments, the cationic fixative is fed at a cationic fixative-to-
fungicide
ratio from about 1:3.5 to 1:0.8.
Some fixatives of the present invention may be selected from paper processing
products referred to as coagulants. Even though coagulants are frequently used
in
paper manufacturing, their use has been completely unrelated to attachment of
preservatives to fibers. Coagulants have been used exclusively to improve
drainage,
assist in fiber and fines retention, and to reduce problems with anionic trash
(organic
contaminants).
We have found that fixatives selected from polyamines work well in this
invention. Polyamines have shorter chain lengths, especially in comparison
with
flocculants, and higher charge densities. Polyamines tightly bind any
attracted
particles to each other or to fiber. This tight binding provides polyamine
with the
lowest application dosage requirement to meet demand. Polyamines also provide
a
broader operating window in order to successfully make the mold-resistant
material.
Polyamines used in papermaking are generally obtained from condensation
reactions
between epichlorohydrin and dimethylamine (known commonly as EPI-DMA
polyamines). With any overdose of polyamine, agglomeration of anionic
particles
can occur (instead of attachment to the fiber, particles attach to each other)
and an
uneven distribution can result. Also, with the tendency for overdose comes the
possibility to convert the system from anionic to cationic, leading to a
"reverse"
dispersion. This is more likely to occur with an overdose of the larger
molecular
weight flocculants.
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The selection of cationic fixative and levels that work best with a paper
slurry
can be optimized by one skilled in the art. Some of the application variables
that will
change the effectiveness of the fixative include, but are not limited to,
system flows,
raw materials (especially the fiber source), specific machine layout and
components,
percentage closure (percentage of excess water and stock not removed from the
mill
as waste), other additives present, feed location, feed method (e.g.,
continuous, slug),
system temperatures, operating parameters (e.g., speed, drying capacity), and
so forth.
Following the processing of the pulp slurry into a sheet of paper, the paper
may be secondarily treated with a biocide to provide additional resistance to
microbial
growth. The paper sheet inay be treated in any of the means known in the art,
such as
with a surface treatinent or coating at the size press, calendar stack, water
box, or off-
machine. In addition, other treatments known in the art, such as treating the
paper for
moisture resistance and strength enhancement, may be done to improve the
usefulness
of the paper as a construction material.
Examples
TAPPI test (T-487) was used to evaluate fungal growth on paper made with
fungicides and fixatives added to the pulp. A 40% DIMTS formulation was used
in
the test. Values presented below are converted to an "as active" basis.
Experiments
were performed using six various cationic coagulants and two flocculants.
Example 1
The fixative was added to an aliquot of paper stock at variable doses. A 40%
concentration of DIMTS was then added at a dose of 2 pounds per ton of active
ingredient. The water was drained from the stock and the resulting paper mat
was
blotted, couched, and dried to form a paper sheet.
Paper without fixative retained about 400 ppm of DIMTS while paper with the
fixative retained up to 750 ppm of DIMTS. Antifungal efficacy testing of the
paper
found that when the polyamine was dosed as a fixative at 1.2 pounds per ton or
greater, the paper was mold-resistant, with a 2 pound per ton dose of DIMTS.
The cationic polyamine used was a medium molecular weight polyamine.
Examples include Aquaserv AQ-294 from Aquaserv and Agefloc A50 from Ciba.
The cationic flocculant used was a very high molecular weight cationic
polyacrylamide with a charge density = 23% (w/w). Cationic polyacrylamides
used
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,
in papermaking are typically copolymers of acrylamide and various cationic
substituents. Examples include Aquaserv AQ-330 from Aquaserv and Drenafloc
402C from Europolimeri. When the flocculant was applied as a fixative with a 2
pound per ton dose of DIMTS, some of the paper samples supported mold growth
while others were resistant.
Table 2 indicates fungal growth on paper, where "0" indicates no growth; "1"
indicates 25% coverage of the surface with fungal growth; "2" indicates 50%
coverage; "3" indicates 75% coverage; "4" indicates 100% coverage. Three
sample
results are presented for each mixture.
TABLE 2
DOSAGE SCREENING
DIMTS (2 #/ton) with: Week 1 Week 2 Week 3
Blank 4,4,4 4,4,4 4,4,4
No fixative 1,2,2 4,4,4 4,4,4
Polyamine (0.4#/ton) 0,0,0 1,1,0 3,3,2
Polyamine (0.8#/ton) 0,0,0 1,0,1 3,3,3
Polyamine (1.2#/ton) 0,0,0 0,0,0 0,0,0
Polyamine (1.6#/ton) 0,0,0 0,0,0 0,0,0
Polyamine (2.0#/ton) 0,0,0 0,0,0 0,0,0
Polyamine (3.0#/ton) 0,0,0 0,0,0 0,0,0
Polyamine (4.0#/ton) 0,0,0 0,0,0 0,0,0
Cationic flocculant (0.5#/ton) 0,0,0 0,0,0 0,0,0
Cationic flocculant (1.0#/ton) 0,0,0 0,1,1 2,3,3
Cationic flocculant (1.5#/ton) 0,0,0 0,0,0 3,4,3
Cationic flocculant (2.0#/ton) 0,0,0 0,0,0 0,0,0
Cationic flocculant (3.0#/ton) 0,0,0 0,0,0 1,0,1
Cationic flocculant (4.0#/ton) 0,0,0 F 1,1,0 4,4,2
Example 2
Paper samples were made to test the order of addition of DIMTS and
polyamine, using similar conditions to Example 1. In Table 3, adding polyamine
at
1# /ton ahead of the DIMTS addition prevented growth for all three weeks.
However,
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adding 5#/ton of polyamine before adding the DIMTS resulted in microbial
growth at
2 weeks. Using the reverse order, adding the DIMTS before adding polyamine at
5#
per ton resulted in microbial growth in one sample at week 3.
Table 3 also shows the results of experiments conducted on other potential
fixatives. These coagulants include
polyDADMAC (diallyldimethylammonium chloride) similar to Aquaserv AQ-
299 (estimated MW = 150,000),
DADMAC-acrylamide copolymer similar to Aquaserv AQ-365 (estimated
MW = 1,000,000),
polyguanidine (branched) similar to Aquaserv AQ-651 (estimated MW =
25,000),
polyguanidine (unbranched) similar to Aquaserv AQ-366 (estimated MW =
25,000),
aluminum chlorohydrate (ACH) similar to Aquaserv AQ-292, and
a very high molecular weight anionic polyacrylamide similar to Aquaserv AQ-
367.
TABLE 3
u _.
FIXATIVE SCREENING
DIMTS (2 #/ton) with: Week 1 Week 2 Week 3
Blank 4,4,4 4,4,4 4,4,4
No fixative 0,0,0 1,0,1 3,0,1
Polyamine (1#/ton) 0,0,0 0,0,0 0,0,0
Polyamine (5#/ton) 0,0,0 2,3,3 3,4,4
Polyarnine (5#/ton) - reverse order 0,0,0 0,0,0 0,1,0
DADMAC-acrylamide copolymer 0,0,0 3,1,1 4,2,2
PoIyDADMAC 0,0,0 0,3,0 1,4,0
ACH 0,0,0 1,3,3 1,4,4
Polyguanidine - branched 0,0,0 3,2,3 4,3,4
Polyguanidine - straight chain 0,0,0 0,2,0 0,3,0
Cationic flocculant 0,0,0 3,2,2 3,2,2
Anionic flocculant 0,0,0 2,0,2 2,0,3
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Addition of a polyamine ahead of the DIMTS at reasonable levels
(expectations of 0.5 - 1.5 #/ton) seems to enhance the antifungal benefits.
However, a
relatively high dose of polyamine, ahead of the DIMTS feed, does not lead to
improved antifungal performance and can actually decrease the efficacy of the
treatment when compared to paper made without any fixative.
Example 3
Similar experiments were conducted using a cationic and an anionic
flocculant, typical of those used on recycle furnish paper machines. Using a
dosage at
the same level as the polyamine, the results for the cationic flocculant were
less
effective than those of the anionic flocculant. We infer that molecular weight
is more
of a factor for the flocculants than is charge density (the anionic performed
better).
The inconsistent results observed within each grouping of flocculants may be
associated with a tendency of them to form three-dimensional, compact
structures.
These structures may serve to entrap the DIMTS particles, reducing the
preservative's
ability to interact with target organisms. Alternatively, the flocculants
might simply
agglomerate those DIMTS particles.
