U.S. patent application number 11/482702 was filed with the patent office on 2007-03-15 for use of non-thermosetting polyamidoamines as dry-strength resins.
Invention is credited to Mark T. Crisp, Willem Stevels.
Application Number | 20070056706 11/482702 |
Document ID | / |
Family ID | 37216077 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070056706 |
Kind Code |
A1 |
Crisp; Mark T. ; et
al. |
March 15, 2007 |
Use of non-thermosetting polyamidoamines as dry-strength resins
Abstract
The invention relates to a process for utilizing resins useful
for imparting dry-strength to paper without substantially
increasing the paper's wet-strength wherein the resins comprise
non-thermosetting crosslinked polyamidoamine-epihalohydrin resins.
The invention also relates to the paper produced containing the
resins.
Inventors: |
Crisp; Mark T.; (Leusden,
NL) ; Stevels; Willem; (Middelburg, NL) |
Correspondence
Address: |
Hercules Incorporated;Hercules Plaza
1313 North Market Street
Wilmington
DE
19894-0001
US
|
Family ID: |
37216077 |
Appl. No.: |
11/482702 |
Filed: |
July 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60698084 |
Jul 11, 2005 |
|
|
|
Current U.S.
Class: |
162/164.3 ;
162/164.6; 162/168.3 |
Current CPC
Class: |
C08G 73/0286 20130101;
D21H 17/11 20130101; D21H 17/55 20130101; D21H 17/56 20130101; D21H
21/18 20130101; D21H 17/54 20130101; D21H 25/005 20130101 |
Class at
Publication: |
162/164.3 ;
162/164.6; 162/168.3 |
International
Class: |
D21H 17/55 20060101
D21H017/55; D21H 17/52 20060101 D21H017/52 |
Claims
1. A process for manufacturing paper having dry strength comprising
the following steps, (a) forming an aqueous suspension of cellulose
fibers; (b) adding a non-thermosetting crosslinked
polyamidoamine-epihalohydrin resin to the aqueous suspension of
cellulose fibers; and (c) sheeting and drying the aqueous
suspension of cellulose fibers to form paper, wherein the
non-thermosetting crosslinked polyamidoamine-epihalohydrin resin
comprises a reaction product of a polyamidoamine and an
epihalohydrin and wherein the epihalohydrin to amine is in a ratio
of less than 0.10:1 on a molar basis and, and wherein the
polyamidoamine has a molecular weight as measured by its reduced
specific viscosity (RSV) of greater than 0.13 dL/g prior to
reaction with the epihalohydrin.
2. The process for manufacturing paper of claim 1, wherein the
polyamidoamine comprises a polyalkylene polyamine having at least
two primary amine groups and also at least one secondary and/or at
least one tertiary amine group.
3. The process for manufacturing paper of claim 2, wherein the
polyalkylene polyamine has two primary amine groups and also at
least one secondary and/or at least one tertiary amine group.
4. The process for manufacturing paper of claim 2, wherein the
polyamidoamine is selected from the group consisting of
diethylenetriamine (DETA), triethylenetetramine (TETA),
tetraethylenepentamine (TEPA), iminobispropylamine (IBPA),
N-methyl-bis-(aminopropyl)amine (MBAPA), bis-hexamethylenetriamine
(BHMT) and mixtures thereof.
5. The process for manufacturing paper of claim 2, wherein the
polyamidoamine is diethylenetriamine (DETA).
6. The process for manufacturing paper of claim 2, wherein the
polyamidoamine comprises a mixture of diethylenetriamine (DETA) and
triethylenetetramine (TETA).
7. The process for manufacturing paper of claim 2, wherein the
polyamidoamine comprises a mixture of diethylenetriamine (DETA) and
tetraethylenepentamine (TEPA).
8. The process for manufacturing paper of claim 1, wherein the
epihalohydrin is selected from the group consisting of
epichlorohydrin, epibromohydrin, epiiodohydrin, epifluorohydrin and
alkyl-substituted epihalohydrins.
9. The process for manufacturing paper of claim 1, wherein the
epihalohydrin is epichlorohydrin.
10. The process for manufacturing paper of claim 1, wherein the
polyamidoamine has a molecular weight as measured by its reduced
specific viscosity (RSV) of greater than 0.13 dL/g but less than
0.19 dL/g prior to reaction with the epihalohydrin.
11. The process for manufacturing paper of claim 8, wherein the
polyamidoamine has a molecular weight as measured by its reduced
specific viscosity (RSV) of greater than 0.15 dL/g but less than
0.18 dL/g prior to reaction with the epihalohydrin.
12. The process for manufacturing paper of claim 1, wherein the
epihalohydrin to amine is in a ratio in the range of about 0.01:1
to less than 0.10:1 on a molar basis.
13. The process for manufacturing paper of claim 11, wherein the
epihalohydrin to amine is in a ratio in the range of about 0.03:1
to about 0.08:1 on a molar basis.
14. The process for the manufacturing paper of claim 12, wherein
the epihalohydrin to amine is in a ratio in the range of about
0.05:1 to about 0.07:1 on a molar basis.
15. The process for the manufacturing paper of claim 6, wherein the
epihalohydrin to amine is in a ratio in the range of about 0.05:1
to about 0.07:1 on a molar basis, and wherein the epihalohydrin is
epichlorohydrin.
16. The process for manufacturing paper of any one of claim 1
wherein the non-thermosetting crosslinked
polyamidoamine-epihalohydrin resin is added to the aqueous
suspension of cellulose fibers in an amount based on about 0.1 to
2% dry-weight of the cellulose fibers.
17. The process for manufacturing paper of claim 16, wherein the
non-thermosetting crosslinked polyamidoamine-epihalohydrin resin is
added to the aqueous suspension of cellulose fibers in an amount
based on about 0.15% dry-weight of the cellulose fibers.
18. Paper made by the process of any one of claims 1-18.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/698,084, filed Jul. 11, 2005, the entire
contents is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a process for manufacturing paper
using resin systems useful for imparting dry-strength to paper.
BACKGROUND OF THE INVENTION
[0003] It is well known to add certain resins to paper, usually
during the papermaking process, to improve dry-strength of the
resultant paper. It is also well known to add certain resins to
paper to improve wet-strength of the resultant paper. It is also
well known that certain additives increase both a paper's
wet-strength and dry-strength. However, it is not always desirable
that paper with increased dry-strength also exhibit an increased
wet-strength since increasing a paper's wet-strength makes paper
more difficult to repulp. If it is difficult for a paper product to
be repulped, the papermaker will find it difficult to reprocess the
material thereby increasing the amount of unusable waste associated
with the papermaking process.
[0004] Many polymers that improve a paper's dry-strength are
anionic under normal papermaking conditions, e.g., sodium
carboxymethylcellulose, carboxymethyl guar, and copolymers of
acrylamide and acrylic acid or sodium acrylate.
[0005] Alternatively, many cationic resins are used to improve a
paper's dry-strength, including glyoxalated cationic
poly(acrylamide)s, high molecular weight cationic polyacrylamides,
thermosetting polyamidoamine-epichlorohydrin resins and
poly(vinylamines). These resin are sometimes applied with anionic
co-factors such as poly(acrylamide-co-acrylic acid) or
carboxymethyl cellulose.
[0006] None of these anionic or cationic resins is universally
applicable and suffers from one or more of the following drawbacks:
low solids, significant levels of permanent wet strength, effective
over limited pH range, sensitivity to specific ions, subject to
hydrolysis under papermaking conditions or limited shelf-life.
There is a continued need for dry strength products addressing all
or most of these drawbacks.
[0007] In U.S. Pat. No. 5,338,406 to Smith, a dry-strength system
for a "water-soluble, linear, high molecular weight, low charge
density cationic polymer having a reduced specific viscosity
greater than two deciliters per gram (>2 dl/g) and a charge
density of 0.2 to 4 milliequivalents per gram" with "at least one
water-soluble, anionic polymer having a charge density less than 5
meq/g" is disclosed. The polyelectrolyte complex of Smith is useful
as an additive for providing dry-strength to all types of paper,
particularly for those papers which are produced using unbleached
pulp.
[0008] In U.S. Pat. No. 5,338,407 to Dasgupta, a process for
enhancement of paper dry-strength without reducing its softness is
disclosed. The process comprises adding a mixture of an anionic
carboxymethyl guar, carboxymethyl bean gum or carboxymethyl
hydroxyethyl guar with various cationic additives to a bleached
pulp furnish. The cationic additive may be a
polyamidoamine-epichlorohydrin resin. If the cationic additive is a
wet-strength resin, the paper's dry-strength is enhanced without
reducing its softness. Additionally, the wet-strength of the paper
is increased.
[0009] In Canadian Patent No. 1,110,019, "a process for
manufacturing paper having improved dry-strength which comprises
mixing an essentially alum-free pulp slurry with a water-soluble
cationic polymer and subsequently adding a water-soluble anionic
polymer to the essentially alum-free pulp slurry" is disclosed.
[0010] In addition to the above, polyamidoamine-epichlorohydrin
resins have been used extensively as wet-strength agents for paper.
Typically, these resins are prepared in a two-step process.
[0011] In a first step, a polyamidoamine prepolymer is prepared
from a diacid (e.g. adipic acid).and a polyamine (e.g.
diethylenetriamine).
[0012] In a second step, the polyamidoamine prepolymer is reacted
with epichlorohydrin in an amount equal to or greater than the
amount of secondary amine groups in the prepolymer. A small amount
of epichlorohydrin reacts to effect branching of the prepolymer,
accompanied by an increase in molecular weight. However, a majority
of the epichlorohydrin reacts with the prepolymer to give reactive
functional groups, specifically, either aminochlorohydrin or
azetidinium. It is well known to those skilled in the art of
papermaking that the above-described polyamidoamine-epichlorohydrin
resins may be used in combination with anionic acrylamides or
anionic cellulose derivatives. However, papers containing these
combinations exhibit increased wet-strength as well as increased
dry-strength, thereby making papers containing these combinations
difficult to repulp.
[0013] In U.S. Pat. No. 6,294,645 to Allen, et al., the disclosure
of which is incorporated herein by reference in its entirety, a
dry-strength system for paper comprising: a cationic component and
an anionic component is disclosed. In this dry-strength system, the
cationic component may comprise a cationic polyamidoamine
epihalohydrin polymer. When the cationic component comprises a
cationic polyamidoamine epihalohydrin polymer, an intralinker
comprises epihalohydrin. The epihalohydrin may be selected from the
group consisting of epichlorohydrin, epibromohydrin, epiiodohydrin,
epifluorohydrin and alkyl-substituted epihalohydrins. Preferably,
the epihalohydrin comprises epichlorohydrin
[0014] Additionally, it is well known that in manufacturing various
types of paper, namely creped paper products such as tissue
products, to use resins as creping adhesive chemicals. Rather than
adding the creping adhesive chemicals directly to paper, these
creping adhesive chemicals are typically sprayed directly onto a
surface of a rotating drying cylinder (creping drum) which adheres
a paper web as it is passed over the drying cylinder. The paper web
is removed and creped from the surface of the drying cylinder by
the use of a creping blade often called a doctor blade.
[0015] Creping adhesive chemicals which are widely used include
polyvinyl alcohols, poly(ethylene vinyl acetate) copolymers,
polyvinyl acetate, polyacrylates and thermosetting cationic
polyamides which comprise the water-soluble reaction products of an
epihalohydrin and a polyamide containing secondary amino groups.
These chemicals may be used alone or in combination with each other
in order to achieve the desired effect.
[0016] In U.S. Pat. No. 5,234,547 to Knight, et al. discloses a
method of creping a paper which comprises applying a synthetic
anionic polymer to the creping drum prior to the application of the
paper web to be creped. The polymers used are (meth)acrylate
polymers and especially polymers of acrylic or methacrylic
acid.
[0017] EP-A-0 063 301 relates to water-soluble polymers obtainable
by reacting an optionally modified polyamidoamine and/or
polyureaamine with a bifunctional dihaloalkylene derivative. This
document further discloses the use of said polymers as creping
additives in the manufacture of creped paper. The creping additives
are preferably applied on the paper sheet prior to the contact with
the heated surface of the creping drum.
[0018] EP-A-0 739 709 discloses a composition for creping fibrous
web comprising a polyamine/epihalohydrin resin creping adhesive and
a creping release agent that is a plasticizer for the
polyamine/epihalohydrin resin.
[0019] Most of these creping adhesive chemicals and particularly
those polyamides become crosslinked by the input of thermal energy
and dehydration which occur on the surface of the drying
cylinder.
[0020] EP 0 856 083 B1, the disclosure of which is incorporated
herein by reference in its entirety, discloses a method of creping
a paper which comprises applying directly to the surface of the
creping drum a water-soluble, non-thermosetting polyamidoamine or
modified polyamidoamine which is crosslinked with an
epihalohydrin.
[0021] It would be desirable to provide a process for imparting dry
strength to paper which uses readily available creping adhesive
chemicals as a dry strength resin. It is also desirable to obtain a
dry strength resin for which anionic co-factors are not a
prerequisite. Furthermore, it is desirable to obtain a dry strength
resin which is available at favorable solids levels with good
stability and limited levels of permanent wet strength, whilst
providing dry strength over a range of practical conditions.
SUMMARY OF THE INVENTION
[0022] The invention relates to a process for manufacturing paper
having dry strength comprising the following steps: forming an
aqueous suspension of cellulose fibers; adding a non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin to the aqueous
suspension of cellulose fibers; and sheeting and drying the aqueous
suspension of cellulose fibers to form paper. The non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin comprises a reaction
product of a polyamidoamine and an epihalohydrin and wherein the
epihalohydrin to amine is in a ratio of less than 0.10:1 on a molar
basis, preferably, the epihalohydrin to amine is in a ratio in the
range of about 0.01:1 to less than about 0.10:1 on a molar
basis.
[0023] In producing the non-thermosetting crosslinked
polyamidoamine-epihalohydrin resin, of use in manufacturing paper,
the polyamidoamine has a molecular weight as measured by its
reduced specific viscosity (RSV) of greater than 0.13 dL/g prior to
reaction with the epihalohydrin.
[0024] The polyamidoamine of use in forming the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resins comprises a
polyalkylene polyamine having at least two primary amine groups and
also at least one secondary and/or at least one tertiary amine
group. The polyamidoamine may be selected from the group consisting
of diethylenetriamine (DETA), triethylenetetramine (TETA),
tetraethylenepentamine (TEPA), iminobispropylamine (IBPA),
N-methyl-bis-(aminopropyl)amine (MBAPA), bis-hexamethylenetriamine
(BHMT) and mixtures thereof. Preferably, the polyamidoamine is
diethylenetriamine (DETA).
[0025] The epihalohydrin of use in forming the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resins comprises a
epihalohydrin selected from the group consisting of
epichlorohydrin, epibromohydrin, epiiodohydrin, epifluorohydrin and
alkyl-substituted epihalohydrins. Preferably, the epihalohydirn is
epichlorohydrin.
DETAILED DESCRIPTION OF THE INVENTION
[0026] This invention pertains to a method for providing
dry-strength to paper while not substantially increasing the
paper's wet-strength and comprises a non-thermosetting crosslinked
polyamidoamine-epihalohydrin resin. The non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin comprises a reaction
product of an epihalohydrin with a water-soluble polyamidoamine
comprised of a dicarboxylic acid and a polyamine containing
secondary and/or tertiary amines. The epihalohydrin and amine are
reacted with one another in a ratio. This ratio expressed on a
molar basis of less than 0.10:1 on a molar basis of epihalohydrin
to amine. The amines of the reaction product may be either
secondary or tertiary amines. Preferably, the ratio of
epihalohydrin to amine is in the range of about 0.01:1 to less than
about 0.10:1 on a molar basis.
[0027] One aspect of the invention pertains to dry-strength systems
in which a water-soluble polyamidoamine's molecular weight, as
measured by the polyamidoamine's RSV, is of greater than 0.13 dL/g
prior to reaction with the epihalohydrin. Preferably, the
polyamidoamine's RSV is greater than 0.13 dL/g but less than 0.19
dL/g prior to reaction with the epihalohydrin. More preferably, the
polyamidoamine's RSV is greater than 0.15 dL/g but less than 0.18
dL/g prior to reaction with the epihalohydrin.
[0028] In one embodiment of the invention, the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin may be a crosslinked
polyamidoamine epihalohydrin polymer where the epihalohydrin is
selected from the group consisting of epichlorohydrin,
epibromohydrin, epiiodohydrin, epifluorohydrin and
alkyl-substituted epihalohydrins. Preferably a crosslinked
polyamidoamine comprises epichlorohydrin polymer where the
epihalohydrin is epichlorohydrin.
[0029] The non-thermosetting crosslinked
polyamidoamine-epihalohydrin is a reaction product of a water
soluble polyamidoamine comprised of a dicarboxylic acid and a
polyamine with secondary and/or tertiary amines present in the
polyamidoamine, and an epihalohydrin. The RSV of the water soluble
polyamidoamine is greater than 0.13 dL/g prior to reaction with the
epihalohydrin.
[0030] In this embodiment of the invention, the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin comprises
poly(adipic acid-co-diethylenetriamine) reacted with
epichlorohydrin at a mole ratio of less than 0.10 moles of
epihalohydrin per mole of amine, preferably at a mole ratio of less
than 0.08 moles of epihalohydrin per mole of amine, alternatively
at a mole ratio of less than about 0.07 moles of epihalohydrin per
mole of amine. In this embodiment of the invention, the
polyamidoamine is poly(adipic acid-co-diethylenetriamine). In this
embodiment, the polyamidoamine's molecular weight is controlled by
regulating the amount of condensation water removed during the
reaction of the dibasic acid and the polyamine.
[0031] The non-thermosetting crosslinked
polyamidoamine-epihalohydrin is synthesized by first producing a
polyamidoamine and subsequently alkylating and crosslinking the
polyamidoamine with epihalohydrin, preferably epichlorohydrin. The
polyamidoamines useful in the method of the present invention are
prepared by the condensation of aliphatic, cycloaliphatic,
araliphatic or heterocyclic (preferably aliphatic) polyamines
containing at least two amino groups, at least one of which must be
a primary amino group, with a saturated or unsaturated aliphatic or
aromatic (preferably aliphatic) dicarboxylic acid having from 2 to
12 carbon atoms or their functional equivalents, preferably having
from 3 to 10 carbon atoms or their functional equilivalents. The
dicarboxylic acids and dicarboxylic acid derivatives of use in
producing the polyamidoamine comprise two amidization reactive
carboxyl (i.e., --COOH) groups. Suitable dicarboxylic acids for use
in producing the polyamidoamine include the C.sub.2-C.sub.12
dicarboxylic acids. Particular dicarboxylic acids which are
suitable include oxalic, malonic, succinic, glutaric, adipic,
pimelic, suberic, azelaic, sebacic, maleic, fumaric, itaconic,
phthalic, isophthalic, and terephthalic acids.
[0032] Suitable dicarboxylic acid derivatives for producing the
polyamidoamine include dicarboxylic acid esters and dicarboxylic
acid halides. Preferred derivatives are the esters.
[0033] Dicarboxylic acid esters which may be used include esters of
the C.sub.2-C.sub.12 dicarboxylic acids, and especially the
C.sub.1-C.sub.3 diesters of these acids. Particular diesters which
are suitable include dimethyl adipate, dimethyl malonate, diethyl
malonate, dimethyl succinate, and dimethyl glutarate.
[0034] The preferred dicarboxylic acid is adipic acid. Examples of
functional equivalents of dicarboxylic acids include dicarboxylic
acid halides. Appropriate dicarboxylic acid halides include adipoyl
chloride, glutaryl chloride, and sebacoyl chloride.
[0035] Alternatively, a corresponding diester may be used instead
of the above mentioned dicarboxylic acids in the formation of the
polyamidoamine. When a diester is used instead of dicarboxylic
acid, prepolymerization can be conducted at a lower temperature,
specifically, about 110.degree. C. and at atmospheric pressure. In
this case, the byproduct is an alcohol with the type of alcohol
dependent upon the identity of the diester. For instance, where a
dimethyl ester is employed the alcohol byproduct will be methanol,
while ethanol will be the byproduct obtained from a diethyl
ester.
[0036] The polyamine comprising a polyalkylenepolyamine, may be
selected from the group consisting of diethylenetriamine (DETA),
triethylenetetraamine (TETA), and tetraethylenepentamine (TEPA),
Iminobispropylamine (IBPA), N-methyl-bis-(aminopropyl)amine
(MBAPA), bis-hexamethylenetriamine (BHMT) and mixtures thereof. The
polyamine is charged into a reaction vessel having sufficient
mixing. While the polyamine is being mixed, the dicarboxylic acid
is added to the reaction vessel over a period of time. Over this
period of time, the temperature of the reactants is allowed to rise
and is maintained below about 125.degree. C. during this stage of
the reaction. The temperature of the reactants is then raised to
about 170.degree. C. and an amount of water contained in the
reactants is driven off. At this stage in the reaction,
polymerization to polyamidoamine is essentially complete. The
aqueous polyamidoamine solution is to have an RSV of greater than
0.13 dL/g at this stage of the process.
[0037] An amount of water is added to the reactor, and the
resultant polyamidoamine is stirred until it dissolves in the
water. The amount of water added to the reactor is not critical to
the process.
[0038] An amount of the aqueous polyamidoamine solution is charged
into a reaction vessel and diluted with water. The total aqueous
polyamidoamine solution is not critical. An amount of an
epihalohydrin, preferably epichlorohydrin, is charged into the
reaction vessel to provide a reaction solution having a
concentration of about 30% by weight total solids
(polyamidoamine+epihalohydrin). The temperature of the reactants is
raised to about 45.degree. C. to about 70.degree. C., preferably
about 52.degree. C. to about 62.degree. C., more preferably about
57 to about 58.degree. C. The viscosity of the solution is
monitored. When a viscosity is achieved which is indicative of the
desired level of reaction of the polyamidoamine with the
epihalohydrin, the reaction is stopped by diluting the polymer with
cold water. Alternatively, the reaction can be stopped through the
adjustment of the pH of the solution with a mineral acid to a pH of
about 3.5. The final solids of the resultant crosslinked solution
is from about 5% to about 30% by weight, preferably about 10% to
25% by weight, more preferably about 15% to about 18% by
weight.
[0039] To increase the molecular weight of the crosslinked
polyamidoamine-epihalohydrin resin, it is preferred to react the
polyamidoamines or modified polyamidoamines with a
substoichiometric amount of epihalohydrin. By using a
substoichiometric amount, it is ensured that the epihalohydrin
completely reacts with the polyamidoamine or the modified
polyamidoamine so that no further crosslinking can take place under
elevated temperature conditions. To produce the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resins of the present
invention wherein a substoichiometric amount of epihalohydrin is
used, the epihalohydrin to amine is in a ratio in the range of
about 0.01:1 to less than 0.10:1 on a molar basis, preferably in a
ratio in the range of about 0.03:1 to about 0.08:1 on a molar
basis, more preferably in a ratio in the range of about 0.05:1 to
about 0.07:1 on a molar basis.
[0040] In case of incomplete reaction of the epihalohydrin or use
of more than substoichiometric amounts of epihalohydirn, any
functional groups which remain after crosslinking and can result in
further crosslinking under the elevated temperature conditions can
be "neutralized" by reacting the crosslinked polyamidoamine or
modified polyamidoamine with suitable agents. Any remaining free
epoxy functionality of the epihalohydrin, which could lead to
further crosslinking, can e.g. be removed by reacting the
crosslinked polyamidoamine or modified polyamidoamine with an amine
or ammonia.
[0041] As stated earlier, preferably, the polyamidoamines useful in
the method of the present invention are obtained by the
condensation of a dicarboxylic acid and an amine containing two
primary amino groups and at least one secondary amino group, e.g.,
diethylenetriamine. The condensation results in polyamidoamines
which contain about ten dicarboxylic acid derived units and the
corresponding amount of amine derived units. In order to increase
the molecular weight by crosslinking, the condensation product is
reacted with an epihalohydrin, preferably epichlorohydrin. However,
in contrast to the preparation of resins conventionally used as wet
strength agents, the epihalohydrin is used in substoichiometric
amounts to make sure that no free reactive functionality is
included in the crosslinked polyamidoamine which would make it
crosslinkable and thus thermosetting.
[0042] Indeed it is already known to use crosslinked
polyamidoamines or modified polyamidoamines which are useful in the
present invention as adhesion-improving agents in paper creping for
direct application to the surface of the drying cylinder or as
retention aids in the paper making process. However, such
adhesion-improving agents or retention aids have never been used to
provide dry strength to paper.
[0043] In the prior art, many modifications of thermosetting
polyamidoamines useful as wet strength agents or non-thermossetting
polyamidoamines useful as retention aids or as adhesion-improving
agents for paper creping are described. All of these modified
polyamidoamines are also useful in the method of the present
invention as long as they are non-thermosetting, i.e. crosslinking
of the polyamidoamines has been effected by the use of
substoichiometric amounts of epihalohydrin or any functional
crosslinkable groups remaining after crosslinking have been
"neutralized" (see above). Examples for modifications of
polyamidoamines are disclosed in U.S. Pat. No.4,501,862,
incorporated herein by reference in its entirety, DE-A-33 23 732.
U.S. Pat. No. 4,673,729, incorporated herein by reference in its
entirety, DE-C-24 34 816, DE-A-18 02 435, and EP-A-74 588.
Preferred modified polyamido amines are disclosed in DE-A-34 21
557. These are polyamidoaminepolyamines formed by transamidation of
polyamidoamines with polyamines which are obtainable by reacting
under substantially anhydrous conditions and at elevated
temperatures of at least 150.degree. C.
[0044] The preparation of the polyamidoamines or modified
polyamidoamines useful in the method of the present invention is
well known to a person of ordinary skill and described in detail in
the prior art such as the prior art documents cited above.
[0045] Gelling and thermosetting of polyamidoamine resins result
from the presence of reactive epihalohydrin functionality. Both
gelling and thermosetting entail the formation of intermolecular
connections between discrete resin molecules. Gelling and
thermosetting are caused by reaction between reactive epihalohydrin
functionality and epihalohydrin reactive amine groups of different
resin molecules; the reactive epihalohydrin functionality
crosslinks the different molecules, and these molecules accordingly
form an interconnected structure which is insoluble.
[0046] Particularly in the case of a thermosetting resin, the act
of heating and/or drying the resin hardens it, as well as rendering
it insoluble. In the prior art, resin solutions are acid
stabilized, so that heating will not gel or thermoset the
resin.
[0047] In contrast, the non-thermosetting crosslinked
polyamidoamine-epihalohydrin resin of the present invention is
non-gelling. With substantially all of the epihalohydrin already
reacted to link polyamidoamines, the dearth of reactive
epihalohydrin functionality precludes, or at least greatly limits,
reaction between the discrete resin molecules. The
non-thermosetting crosslinked polyamidoamine-epihalohydrin resin
can accordingly be redissolved after drying and/or heating.
[0048] The process for manufacturing paper comprises three
principal steps: (1) forming an aqueous suspension of cellulose
fibers; (2) adding a strengthening additive; and (3) sheeting and
drying the fibers to form paper.
[0049] The step of forming an aqueous suspension of cellulosic
fibers is performed by conventional means, such as known
mechanical, chemical and semi-chemical, etc., pulping processes.
Alternatively, a suspension may be formed by repulping paper or
paperboard. After the mechanical grinding and/or chemical pulping
step, the pulp may be washed to remove residual pulping chemicals
and solubilized wood components. These steps are well known, as
described in, e.g., Casey, Pulp and Paper (New York, Interscience
Publishers, Inc. 1952).
[0050] The step of adding the strengthening additive, e.g. a
non-thermosetting crosslinked polyamidoamine-epihalohydrin resin is
carried out according to conventional means through direct addition
to the papermaking system. Previously, resins having similar
chemistries as the non-thermosetting crosslinked
polyamidoamine-epihalohydrin resins of use in the present invention
had been applied directly to the surface of a creping drum rather
than to the wet end of the papermaking system.
[0051] The step of sheeting and drying of the fibers to form paper
is carried out according to conventional means, such as those
described in Casey, Pulp and Paper, cited above.
[0052] The preferable level of addition of the non-thermosetting
crosslinked polyamidoamine-epihalohydrin resin is about 0.1 to 2%
based on the dry-weight of the pulp.
[0053] The process for manufacturing paper having dry strength may
also comprise use of additives, such as a crosslinked starch. The
crosslinked starch may be added at a level of about 0.1 5% to about
2.0% by weight of the paper, preferably about 0.25% to about 1.5%
by weight of the paper, more preferably about 0.5% to about 1.25%
by weight of the paper. The crosslinked starch may be any
crosslinked starch used in the paper-making process. The
crosslinked starch may be selected form the group consisting of
potato starch, tapioca starch, wheat starch, corn starch and other
crosslinked starches derived from waxy maize. Crosslinked starches
of use in the instant invention are described in U.S. Pat. No.
4,643,801 incorporated herein by reference in its entirety.
[0054] The process for manufacturing paper having dry strength of
the invention may also comprise use of a wet-strength resin. The
wet-strength resin may be added at such levels to the paper so as
not to significantly increase the paper's wet-strength. The process
for manufacturing paper having dry strength of this invention may
also be used to enhance the dry-strength of wet-strengthened
papers. A wet-strength resin can then be added to at such levels to
provide only the needed amount of wet-strength, and the
non-thermosetting crosslinked polyamidoamine-epihalohydrin resin
used in this invention can be used to increase the dry-strength
without further increasing the wet-strength. Some examples of
wet-strength resins available from Hercules Incorporated are
Kymene.RTM.557H resin, Kymene.RTM.736 resin, Kymene.RTM.450 resin,
Kymene.RTM.557LX resin and Kymene.RTM. Plus resin. The wet-strength
resin may be added at a level of about 0.025% to about 1.5% by
weight of the paper, preferably about 0.05% to about 1.0% by weight
of the paper, more preferably about 0.075% to about 0.75% by weight
of the paper. Polyamidoamine epichlorohydrin ("PAE") resins are the
most preferred wet-strength resins. Most preferred is
Kymene.RTM.557H resin, in which adipic acid is reacted with
diethylenetriamine (DETA) to form a polyamidoamine that is
alkylated and crosslinked with epichlorohydrin to form a PAE resin,
namely, adipic acid-DETA polyamidoamine epichlorohydrin.
Alternatively, the wet-strength resin may comprise an
aldehyde-functionalized starch or a glyoxal-modified polyacrylamide
resin.
[0055] The process for manufacturing paper having dry strength of
the invention may also comprise use of a retention aid. The
retention aid may be a high molecular weight polyacrylamide or a
high molecular weight flocculent. Alternatively, the retention aid
may be poly(ethyleneoxide). Alternatively, the retention aid may be
a microparticulate retention aid. The microparticulate retention
aid may be selected from the group consisting of bentonite and
colloidal silica. Alternatively, the microparticulate retention aid
may comprise a synthetic polymeric microparticle.
[0056] The process for manufacturing paper having dry strength of
the invention may also comprise use in paper which contains a
highly crosslinked material for charge control or for fine particle
retention. The highly crosslinked material for charge control may
be selected from the group consisting of alum, polyaluminum
chloride, poly(diallyldimethylammonium) chloride,
poly(dialkylamine-epichlorohydrin) and polyethyleneimine.
[0057] Other additives useful in the papermaking process of this
invention include sizes, defoamers, fillers, wetting agents,
optical brighteners, inorganic salts, etc.
[0058] The process for manufacturing paper having dry strength of
the invention is of utility in manufacturing many types of paper.
The process for manufacturing paper having dry strength of the
invention is of particular utility in manufacturing papers selected
from the group consisting of bleached board, linerboard,
corrugating medium, newsprint, printing and writing paper, tissue
and towel. The process for manufacturing paper having dry strength
of the invention is preferably used in the manufacture of recycled
liner board and recycled corrugating medium.
[0059] The method for the determination of a material's reduced
specific viscosity (RSV) is as follows:
Reduced Specific Viscosity
[0060] The reduced viscosity of a 2% solution of polymer in 1 N
ammonium chloride is determined at 25.0.degree. C. by means of a
Ubbelohde viscometer and a Brinkmann Viscotimer. Flow times of a 2%
polymer solution and a pure solvent are measured and the relative
viscosity (Nrel) calculated. The reduced viscosity is calculated
from the relative viscosity. This method is based on ASTM D446.
Apparatus Used to Determine RSV:
[0061] (1) Ubbelohde Viscometer tubes, No. 1, with Viscometer
Constant C=0.01--available from Visco Systems, Yonkers, N.Y., or
Schott, Hofheim, Germany, or Brinkmann Instruments. [0062] (2)
Brinkmann Viscotimer C--available from Brinkmann Instruments Inc.,
Cantiague Rd., Westbury, N.Y. 11590. [0063] (3) Ubbelohde
Viscometer Support--ibid., Cat. No. 21-00-032-9. [0064] (4)
Constant temperature water bath maintained at 25+/-0.1.degree. C.
Cooling capability (cold water or ice pack) may be necessary to
maintain constant temperature. An ASTM 45.degree. C. thermometer
should be used to monitor the temperature near the viscometer tube
mounting location. [0065] (5) Volumetric flask, 50 mL, Class A.
[0066] (6) Beaker, 10 mL. [0067] (7) ASTM 45 C. thermometer,
calibrated, designed for measurements at 25.degree. C. with 0.05
degree divisions--available from VWR Scientific, Cat. No.
61118-923, or equivalent. [0068] (8) Source of vacuum--Preferably a
water aspirator for cleaning of viscometers. [0069] (9) Filter or
Stainless Steel Screen, ca. 100 mesh. Reagents Used to Determine
RSV: [0070] (1) Ammonium chloride, granular. ACS reagent grade.
[0071] (2) Solvent (1 N ammonium chloride). Add 53.5+/-0.1 g of
NH.sub.4 Cl to a 1-liter volumetric flask, dilute to volume with
distilled water and mix. Ammonium Chloride Flow Measurement:
[0072] The ammonium chloride flow time should be measured once per
day that Polymer RV measurements are made. This value should be
used in the RV calculation. [0073] (1) The viscometer is mounted in
the 25.degree. C. constant temperature bath in a vertical position
and allowed to equilibrate for at least 15 minutes. The bath must
be at 25+/-0.1.degree. C. [0074] (2) The viscometer is filled with
ammonium chloride solvent, through tube "L", so that the level of
liquid falls between the marks on bulb "A". The viscometer is
placed in the constant temperature bath and is allowed to stand for
at least 5 minutes in order to reach the correct temperature.
[0075] (3) The Ubbelohde viscometer is connected to the Viscotimer
with the attached tubing. The Viscotimer is turned on and is
allowed to run. [0076] (4) Measurements are recorded at least 3
flow times. The average of three measurements that agree within 0.2
seconds is calculated If after 4 measurements, agreement is not
reached, the viscometer tube is cleaned and the flow is measured 3
times again. [0077] (5) The viscometer is then cleaned and dried.
Polymer Flow Measurement:
[0078] The following procedure is used: [0079] (1) Determine the
total solids content of the polymer. [0080] (2) Calculate the
amount of polymer required for 1.000+/-0.020 g of solids using
Equation 1. [0081] (3) Weigh, to the nearest 0.0001 g, the
appropriate amount of sample, calculated in Step 2, into a 50 mL
volumetric flask. Alternately, the sample can be weighed into a
small beaker and quantitatively transferred to the 50 mL volumetric
flask with 4 or 5 washings of ammonium chloride solution. [0082]
(4) Add 20-25 mL of 1 N ammonium chloride to the flask and gently
swirl until the sample has completely dissolved. Then add ammonium
chloride solution to within 1/4 ''of the mark. [0083] (5) Place the
flask and contents in the 25.degree. C. constant temperature bath
and allow the temperature to equilibrate for at least 15 minutes.
[0084] (6) (6) Mount the viscometer in the 25.degree. C. constant
temperature bath in a vertical position and allow it to equilibrate
for at least 15 minutes. The bath must be at 25+/-0.1.degree. C.
[0085] (7) Slowly make up to the volume mark with more solvent and
finally mix to obtain complete homogeneity. This will give a
2.000+/-0.040% solution. Calculate the actual concentration to the
Polymer solution, to the nearest 0.001 g/100 mL. [0086] (8) After
equilibration of the polymer solution and adjustment to volume at
25.degree. C., filter the solution through a 100 mesh stainless
steel screen or comparable pore size filter. [0087] (9) Fill the
viscometer through tube "L" so that the level of liquid falls
between the marks on bulb "A". Place the viscometer in the constant
temperature bath and allow to stand for at least 5 minutes in order
to reach the correct temperature. [0088] (10) Connect the Ubbelohde
viscometer to the Viscotimer with the attached tubing. Turn the
Viscotimer on and allow it to run. [0089] (11) Measure and record
at least 3 flow times. Calculate the average of three measurements
that agree within 0.2 seconds. If after 4 measurements, agreement
is not reached, clean the viscometer tube and measure the flow
times again. Prepare a fresh solution if agreement still cannot be
obtained. [0090] (12) Clean the viscometer immediately after use.
[0091] (13) Calculate the relative viscosity (Nred) of the polymer
using Equation 3 and the reduced viscosity (Nred) using Equation 4.
Calculation: 100/TS=Ws Eq(1) where: [0092] TS=% total solids of
Polymer [0093] Ws=weight of sample required for 1.000+/-0.020 g of
solids (Ws.times.TS)/50=Cp Eq(2) where: [0094] Ws=actual weight of
Polymer sample [0095] TS=% total solids of Polymer [0096] 50=mL of
diluted Polymer solution [0097] Cp=concentration of Polymer
solution, g/l 100 mL t.sub.s/t.sub.o=Nrel Eq(3) where: [0098]
t.sub.s=average flow time of the 2% sample solution at 25.degree.
C. sec. [0099] t.sub.o=average flow time of the solvent at
25.degree. C., sec. [0100] Nrel=relative viscosity (Nrel-1)/Cp=RSV
Eq(4) where: [0101] Nrel=relative viscosity [0102] Cp=concentration
of the polymer solution in grams of polymer solids per 100 mL of
solution. [0103] RSV=reduced specific viscosity Note: Carry out
this value to the nearest 0.001 unit.
[0104] The tensile tests were determined using TAPPI test method
T494. The Mullen burst was determined using TAPPI test method T807.
The Ring Crush was determined using TAPPI test method T818, and the
Scott Bond was determined using TAPPI Method T569.
[0105] The following examples will serve to illustrate the
invention, parts and percentages being by weight unless otherwise
indicated.
EXAMPLES
Example 1
[0106] A non-thermosetting crosslinked polyamidoamine was prepared
in two steps.
[0107] In the first step, a mixture of adipic acid,
triethylenetetramine (TETA) and diethylene triamine (DETA) was
condensed at elevated temperature to a low molecular weight
poly(amidoamine) and diluted to a 35% solids solution in water (RSV
0.17 dL/g).
[0108] In a second step, this polymer was crosslinked using a
substoichiometric amount of epichlorohydrin to obtain a
non-thermosetting resin as a 24% solids solution in water (RSV 0.39
dL/g) (Resin A1).
[0109] Paper of 115 g/m.sup.2 was made on a model papermaking
machine using re-dispersed commercial neutral recycled linerboard
furnish, with conductivity controlled at 2000 micro Siemens per
centimeter and pH of 7. Resin A1 was added at several addition
levels to the furnish. The properties of the dried paper were
compared to an untreated control. Properties studied included dry
tensile (MD and CD), Ring crush resistance (MD and CD), and Mullen
burst strength.
[0110] In Table 1, the results of this Example are shown.
Properties determined in MD and CD directions are expressed as
their geometric mean (or breaking length for dry tensile). The
Table shows dry strength properties of paper prepared with several
additional levels of Resin A1 to the papermachine wet end.
TABLE-US-00001 TABLE 1 Resin A1 Mullen Burst Addition Breaking GM
Ring Crush index Level (%) length (km) (kN/m) (kPa*m.sup.2/g) 0
(untreated 3.43 0.86 1.61 control) 0.1 3.79 0.91 1.85 0.2 3.88 0.93
1.88 0.4 3.73 0.93 1.81
[0111] Table 1 shows Resin A1 provides dry strength improvements at
commercially useful addition levels.
Example 2
[0112] As in the method of Example 1, non-thermosetting crosslinked
polyamidoamine resin was prepared in two steps.
[0113] In the first step, a mixture of adipic acid,
triethylenetetramine (TETA) and diethylene triamine (DETA) was
condensed at elevated temperature to a low molecular weight
poly(amidoamine) and diluted to a 35% solids solution in water (RSV
0.17 dL/g).
[0114] In a second step, this polymer was crosslinked using a
substoichiometric amount of epichlorohydrin to obtain a
non-thermosetting crosslinked polyamidoamine resin as a 25% solids
solution in water (RSV 0.39 dL/g) (Resin A2).
[0115] In a similar way, resins were made based on the use of DETA
and a mixture of TEPA (tetraethylenepentamine) and DETA to provide
after crosslinking respectively Resin B at 15% solids and Resin C
at 24.1% solids.
[0116] Paper of 115 g/m.sup.2 was made on a model papermaking
machine using re-dispersed commercial neutral recycled linerboard
furnish, with conductivity controlled at 2000 micro Siemens per
centimeter and a pH of 7. Resins A2, B and C were added at several
addition levels and the properties of the dried paper were compared
to the untreated control. Properties studied included dry tensile
(MD and CD), Ring crush resistance (MD and CD), and Mullen burst
strength, wet tensile and Scott internal bond.
[0117] In Table 2, the results of this study are shown at a dose
level of 0.15%, as obtained by averaging the results at 0.10, 0.15
and 0.20%. Properties determined in MD and CD direction are
expressed as their geometric mean (or breaking length for dry
tensile. TABLE-US-00002 TABLE 2 Breaking GM Ring Crush Scott Bond
Wet Tensile Resin length (km) (kN/m) (J/m.sup.2) (kN/m) None 4.09
1.39 250 0.20 (untreated control) Resin A2 4.17 1.42 280 0.29 Resin
B 4.28 1.44 300 0.36 Resin C 4.34 1.42 299 0.30
[0118] Clearly, Resins A, B and C provide dry strength improvements
over the untreated control at a commercially useful addition
levels.
[0119] It is not intended that the examples presented here should
be construed to limit the invention, but rather, they are submitted
to illustrate some of the specific embodiments of the invention.
Various modifications and variations of the present invention can
be made without departing from the scope of the appended
claims.
* * * * *