CA1195049A - Wet strength resins - Google Patents
Wet strength resinsInfo
- Publication number
- CA1195049A CA1195049A CA000405084A CA405084A CA1195049A CA 1195049 A CA1195049 A CA 1195049A CA 000405084 A CA000405084 A CA 000405084A CA 405084 A CA405084 A CA 405084A CA 1195049 A CA1195049 A CA 1195049A
- Authority
- CA
- Canada
- Prior art keywords
- acid
- copolymer
- amide
- general formula
- web
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/20—Macromolecular organic compounds
- D21H17/33—Synthetic macromolecular compounds
- D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
- D21H17/42—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups anionic
- D21H17/43—Carboxyl groups or derivatives thereof
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
- D21C5/02—Working-up waste paper
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/20—Macromolecular organic compounds
- D21H17/33—Synthetic macromolecular compounds
- D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
- D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
- D21H17/45—Nitrogen-containing groups
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/64—Paper recycling
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31725—Of polyamide
- Y10T428/31779—Next to cellulosic
- Y10T428/31783—Paper or wood
Abstract
ABSTRACT OF THE DISCLOSURE
Water soluble wet strength resins containing maleamic acid and at least one other ethylenically unsaturated monomer, such as vinyl esters, olefins, acrylic and/or methyacrylic acids and/or their esters and/or their amindes are useful in the preparation of paper products having improved, off-machine dry strength and wet strength properties.
Water soluble wet strength resins containing maleamic acid and at least one other ethylenically unsaturated monomer, such as vinyl esters, olefins, acrylic and/or methyacrylic acids and/or their esters and/or their amindes are useful in the preparation of paper products having improved, off-machine dry strength and wet strength properties.
Description
WET STRENGTH RESINS
BACKG~OUND OF THE INVENTION
Field of the Invention The present invention relates 9 generally, to novel, wet strength resins; to a process for preparing said resins; to a process for treating paper with said resins to improve the off-machine wet strength and dry strength thereof; and to a paper product having improved wet and dry strength properties. More particularly this invention relates to wet strength resins containing maleamic acid and at least one other ethylenically unsaturated monomer, such as vinyl esters, oletins, acrylic and/or methyacrylic acids and/or their esters and/or their amides, and to paper with improved wet and dry strength properties which has been treated with said resins.
Description of the Prior Art In a conventional paper-makirlg operation cellulosic fibers are dispersed in water, drained on a wire screen, pressed into close physical contact and dried. The result is a paper sheet in which the individual fihers are held together by hydrogen bonds which give strength to the dry sheet. When the dry sheet is wet, these hydrogen bonds are broken and the paper loses most of its strength.
To prevent this loss of strength, various chemical treatments have been employed. Among the most successful treatments is the use of synthetic resins which, when added to the cellulosic fibers, either before or after a sheet is formed therefrom, and cured or polymerized, can significantly increase the wet strength of the sheet.
Most commonly used are the urea formaldehyde resins, the product of the condensation of urea and formaldehydeg and melamine-formaldehyde resins, the condensation product of melamine and formaldehyde. An outstanding disad~ant-age associated with the use of these resins is that if !~
~5~
they are not totally cured, a sheet treated with them can emit for~aldehyde or toxic aldehydic residues can remain in the sheet. Other resins useful in increasing the wet strength of cellulosic webs include polyamine-epihalohyd-rin resins, the condensation product of polyamines withepihalohydrins, glyoxalated polyacrylamide resins which are the products of the addition polymerization of N-glyoxalated acrylamide and at least one other ethyleni-cally unsaturated monomer and/or an ethylenically un-saturated basic nitrogen-containing monomer.
Recently, it has become deslrable to elirninate the use of formaldehyde-based wet strength resirls because of the known and suspected toxic effects of formaldehyde.
Formaldehyde-based resins, SllCh as urea-formaldehyde and melamine-formaldehyde resins, cure or crosslink by the formation of intermolecular rrlethyleneamide crosslinkages.
Formaldehyde is another product of this crosslinking reaction and can at any time be released during the production or use of products treated with formaldehy~e-based resins since the curing or crosslinking reactioncontinues for an extended period e~en at room temperature.
In order to circurnvent the possibility of exposure to formaldehyde~ this invention describes wet s~rength resins which are copolymers of ami.c acids. These resins function as wet strengthening agents by reaction with the cellulose molecules of a cellulosic web. The reaction takes p].ace between the pendent amide functionalities of the arnic acid portion of the copo]ymers and the hydroxyl groups of the cellulose molecules.
The general reaction between beta-amic acids and alcohols to form half-acid esters was descrlbed by Cuculo in a series of publications in the Textile Research Journal, Volume 41 pages 321-326; Volurne 41 pages 375-378;
volume 43 pages 283-293; volume 45 pages 314-316; volume 46 pages 393-397. These publications describe the pre-paration of half-acid esters of cellulose by the facile reaction of beta-amic acids and cellulosic hydro~yl groups.
U. S. Patent 315551585 describes the preparation of cellulose half-acid esters by reaction of beta-carbamyl or gamma-carbamyl acids with cellulose. The disclosure is concerned with modification of non-woven, cellulosic webs to yield disposable fabrics by the formation of cellulose half-acid esters through the reaction of the cellulosic fabric with a carbamyl substituted organic acid.
The use of salts of copolymers of maleic acid and an ethylenically unsaturated monomer fcr improving the wet strength of p`aper has been known since at least 1952.
U.S. Patent 2,621,169 granted December 9, 1952 to Robin-ette et al discloses that ammonium salts of copolymers of styrene and maleic anhydride have utility in improving the wet strength of paper (without specifically teaching ho~/ such improvement is obtained). Robinette et al em-phasize however that care must be taken in preparing the polymeric compositions of their invention to avoid the formation of amides. Thus the prior art as represented by U.S. Patent 2,621,169 teaches away from the present inven-tion wherein it has been found that resins containing mal.eamic acid impart wet strength to paper.
U.S. Patent 3,017,291 granted January 16, 1962 to Mci.aughlin et al describes the use of emulsion copolymers containi.ng an acid such as maleic or aconitic, and their salts, as wet strength resins. This patent at Column 1, lines 36-39 contains the naked suggestion that salts of partial amides, such as the salt of maleamic acid, can be produced by neutrallzation of the emulsion copolymers of the patented invention with ammonia and amines. While there is no subsequent enabling disclosure or teaching in respect of such salts merely named by McLaughlin et all neutralization, as normally understood by one of ordinary skill in the art and in accordance with the disclosure o~
an antecedent patent assigned to the same assignee, U.S.
Patent 2,999,038, at Column 2, lines 50-54, means that aqueous alkali, particularly ammonia, is added to the copolym~r. The resulting compound, in the case hypothe-sized by McLaughlin et al would contain the diammonium salt of maleic acid, not the salt of a half acid, half amide characteristic of a salt of maleamic acid.
SUMMARY OF THE INVENTION
It is the teaching of this invention that water soluble copolymers containing the half acid, half amide structure of amic acids can be used to increase the wet strength o~ paper. These copolymers comprise A) a half-acid, hal-amide corresponding to the following general formula NH - C - R - C - O
BACKG~OUND OF THE INVENTION
Field of the Invention The present invention relates 9 generally, to novel, wet strength resins; to a process for preparing said resins; to a process for treating paper with said resins to improve the off-machine wet strength and dry strength thereof; and to a paper product having improved wet and dry strength properties. More particularly this invention relates to wet strength resins containing maleamic acid and at least one other ethylenically unsaturated monomer, such as vinyl esters, oletins, acrylic and/or methyacrylic acids and/or their esters and/or their amides, and to paper with improved wet and dry strength properties which has been treated with said resins.
Description of the Prior Art In a conventional paper-makirlg operation cellulosic fibers are dispersed in water, drained on a wire screen, pressed into close physical contact and dried. The result is a paper sheet in which the individual fihers are held together by hydrogen bonds which give strength to the dry sheet. When the dry sheet is wet, these hydrogen bonds are broken and the paper loses most of its strength.
To prevent this loss of strength, various chemical treatments have been employed. Among the most successful treatments is the use of synthetic resins which, when added to the cellulosic fibers, either before or after a sheet is formed therefrom, and cured or polymerized, can significantly increase the wet strength of the sheet.
Most commonly used are the urea formaldehyde resins, the product of the condensation of urea and formaldehydeg and melamine-formaldehyde resins, the condensation product of melamine and formaldehyde. An outstanding disad~ant-age associated with the use of these resins is that if !~
~5~
they are not totally cured, a sheet treated with them can emit for~aldehyde or toxic aldehydic residues can remain in the sheet. Other resins useful in increasing the wet strength of cellulosic webs include polyamine-epihalohyd-rin resins, the condensation product of polyamines withepihalohydrins, glyoxalated polyacrylamide resins which are the products of the addition polymerization of N-glyoxalated acrylamide and at least one other ethyleni-cally unsaturated monomer and/or an ethylenically un-saturated basic nitrogen-containing monomer.
Recently, it has become deslrable to elirninate the use of formaldehyde-based wet strength resirls because of the known and suspected toxic effects of formaldehyde.
Formaldehyde-based resins, SllCh as urea-formaldehyde and melamine-formaldehyde resins, cure or crosslink by the formation of intermolecular rrlethyleneamide crosslinkages.
Formaldehyde is another product of this crosslinking reaction and can at any time be released during the production or use of products treated with formaldehy~e-based resins since the curing or crosslinking reactioncontinues for an extended period e~en at room temperature.
In order to circurnvent the possibility of exposure to formaldehyde~ this invention describes wet s~rength resins which are copolymers of ami.c acids. These resins function as wet strengthening agents by reaction with the cellulose molecules of a cellulosic web. The reaction takes p].ace between the pendent amide functionalities of the arnic acid portion of the copo]ymers and the hydroxyl groups of the cellulose molecules.
The general reaction between beta-amic acids and alcohols to form half-acid esters was descrlbed by Cuculo in a series of publications in the Textile Research Journal, Volume 41 pages 321-326; Volurne 41 pages 375-378;
volume 43 pages 283-293; volume 45 pages 314-316; volume 46 pages 393-397. These publications describe the pre-paration of half-acid esters of cellulose by the facile reaction of beta-amic acids and cellulosic hydro~yl groups.
U. S. Patent 315551585 describes the preparation of cellulose half-acid esters by reaction of beta-carbamyl or gamma-carbamyl acids with cellulose. The disclosure is concerned with modification of non-woven, cellulosic webs to yield disposable fabrics by the formation of cellulose half-acid esters through the reaction of the cellulosic fabric with a carbamyl substituted organic acid.
The use of salts of copolymers of maleic acid and an ethylenically unsaturated monomer fcr improving the wet strength of p`aper has been known since at least 1952.
U.S. Patent 2,621,169 granted December 9, 1952 to Robin-ette et al discloses that ammonium salts of copolymers of styrene and maleic anhydride have utility in improving the wet strength of paper (without specifically teaching ho~/ such improvement is obtained). Robinette et al em-phasize however that care must be taken in preparing the polymeric compositions of their invention to avoid the formation of amides. Thus the prior art as represented by U.S. Patent 2,621,169 teaches away from the present inven-tion wherein it has been found that resins containing mal.eamic acid impart wet strength to paper.
U.S. Patent 3,017,291 granted January 16, 1962 to Mci.aughlin et al describes the use of emulsion copolymers containi.ng an acid such as maleic or aconitic, and their salts, as wet strength resins. This patent at Column 1, lines 36-39 contains the naked suggestion that salts of partial amides, such as the salt of maleamic acid, can be produced by neutrallzation of the emulsion copolymers of the patented invention with ammonia and amines. While there is no subsequent enabling disclosure or teaching in respect of such salts merely named by McLaughlin et all neutralization, as normally understood by one of ordinary skill in the art and in accordance with the disclosure o~
an antecedent patent assigned to the same assignee, U.S.
Patent 2,999,038, at Column 2, lines 50-54, means that aqueous alkali, particularly ammonia, is added to the copolym~r. The resulting compound, in the case hypothe-sized by McLaughlin et al would contain the diammonium salt of maleic acid, not the salt of a half acid, half amide characteristic of a salt of maleamic acid.
SUMMARY OF THE INVENTION
It is the teaching of this invention that water soluble copolymers containing the half acid, half amide structure of amic acids can be used to increase the wet strength o~ paper. These copolymers comprise A) a half-acid, hal-amide corresponding to the following general formula NH - C - R - C - O
2 ~, 11 O O
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenical.ly unsaturated monomer.
These water soluble amic acid copolymers can be prepared by reacting an anhydride-containing precursor copolymer with ammonla, namely by adding it to aqueous ammotlia, thereby yroducing an amic aci.d-containing co-polymer. The resulting amic acid copolymer solution can then be applied to a cellulosic web, such as paper, by a ~ariety of methods including coating, spraying, printing and the like. The amic acid copolymers useful in this invention can also be prepared by copolymerizing an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated monomer. I'he cellulosic webs, such as paper, treated with resins as described in this invention have off-machine wet tensi.les, improved dry tensiles, and improved broke recovery after the finishing operationO
If it is desired tha.t the copolymer be substantive to cellulose, copolymers can ~e made by reacting an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated monomer and at least one other ethylenically unsatura~ed basic nitrogen-containing monomer. The basic nitrogen-containing monomer will impa.rt a cationic character to the copolymer which makes it attràctive to anionic cellulose fibers for deposition in the wet end of a paper machine. Suitable examples o the other ethylenically unsaturated, basic nitrogen-con-taining monomer include N,N - dimethylaminoethylmethacry-late, N,N - diethylaminoethylmethacrylate~ N,N - dimethyl-aminaethylacrylate, N,N - diethylaminoethylacrylate, 2-vinylpyridine, 4-vinylpyridine, and N-(t-butyl)-aminoethyl-methacrylate.
The ethylenically unsaturated amic acid useful in synthesizi~lg these cellulose-substantive polymers are polymerizable compounds of the following general formula:
NH2 ~ C - R - C - ORl .
Il 11 O O
wherein R is a hydrocarbon chain containing a multiple bond capable of radical polymerization and Rl, is H, alkyl or alkenyl~ The amount of the amic acid which can be used along with the other monomeric species to make up the desired a-nic acid copolymer must be chosen so as to render the resulting copolymer water soluble.
Depending upon the nature of the other comonomers, this amount can range from 5% to 50% by weight of the co-polymer.
5~
The other ethylenically unsaturated monomers useful in synthesizing the deslred amic acid precursor polymer include acrylic and/or methacrylic acids and/or their esters, amides, substituted amides, and nitriles. Also use~ul are esters of vinyl alcohol, vinyl ethers and ke-tones, acrolein, styrene and substituted styrenes, vinyl pyridines, ethylene, butadiene, maleic, fumaric and itaconic acids and esters and substituted amides 9 poly-merizable derivatives of allyl alcohol, vi.nylacetic acid and the like.
The wet strength resins as described in this disclosure may be applied to cellulosic webs, such as paper, by any conventional technique for applying a polymer to a cell~llosic web. In the case where the web is already formed, the polymer or resin may be applied by coating, printing, or spraying. In the case of addition to cellulosic fibers prior to web formation~ the resin, if it bears a net positive charge, can be added to a slurry of fibers, as in the wet end of a paper machine. The net positi~e charge on the resin renders it substantive to cel].ulose. The amount of resin added to the web can vary, depending upon the degree of wet strength desired. The preferred amount of resin to be applied is in the range of 0.1 to 5% based upon weight of fiber. The curing or 2S crosslinking reaction can be accelerated by the addition of mirleral acids or salts of acids such as ammonlum~
ma~lleSiUIIl, zinc and tin chlorides, nitrates or sulfates~
The increase in wet tenslle of cellulosic webs treated with the resins as described in this invention is due to the crosslinkin~ of the amic acid copolymer molecules with the cellulosic substrate.
The polymerization of these monomers to yield water soluble copolymers can be accomplished by well known polymerization techniq~les as described in such chemistry .~19 S04L9 texts as POLY~R SYNTHESIS, Volume I, II, and III, by Stanley P~. Sandler and Wolf Karo, Academic Press, New York and London, (1974), and PREPARATIVE METHODS OF
POLYMER CHFMISTRY, second edition, by Wayne R. Sorenson and Tod W. Campbell, Interscience Pub].ishers (John Wiley & Sons), New York (1968)o Thus various aspects of this invention are as follows:
A wet strength resin comprising a wa-ter soluble copolymer comprised of A) a half-acid, half-amide corresponding to the following general formula:
NH2 ~ C - R - C - OR
1~ 11 O O
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
A cellulo~ic fibrous web treated with a wet strength resin comprising a water soluhle copolymer o~
comprised A) a half-acid, half-amide corresponding to the following ~eneral formula:
NH - C - R - C - OR
2 ll l O O
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at lea~t one other ethylenicallv unsaturated monomer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymer composition of this in~ention is a water soluble addition copolymer of an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated 30 monomer. Preferably, the e-thylenically unsaturated amic acid is - 7a -(I) maleamic acid, (Z)-4-amino-4-oxo-2-butenoie acid H H
NH -C-C=C-C-OH
O O
(II) fumaramic acid, (E)-4-amino-4-oxo-2-butenoic acld NH2-C-c=c_c_oH
Il 1 11 O ~I O
or (III) itaconamic acid, 4-amino-4-oxo-2-methylene butanoic acid NH -C-C-C-C-OH
2 ll I ll O H
Among the other ethylenically unsaturated monomers useful in this invention are the vinyl esters of aliphatic acids which have one to ten carbon atoms. The preferred vinyl ester is vinyl acetate especially when used with esters of acrylic or methacrylic acids. The acrylate and methacrylate esters o alkyl and cycloalkyl alcohols having one to twenty carbon atoms are most efficacious in forming useful copolymers with vinyl acetate. The preerred esters of nlethacryllc acid are methyl, ethyl, n-propyl, n-butyl, iso-butyl, 2-ethylhe.Yyl esters. The preferred esters of acrylic acid are methyl, ethyl, n-propyl, n-butyl, iso-butylg 2-ethyl hexyl with n-butyl being the nnost preferred.
Most preferably the copolymer is composed of 80-98%
by weight acrylamide, 1-10% by weight N,N-dimethylamino-ethyl methacrylate, and 1-10% maleamic acid. The pre-~erred copolymer is prepared by the addition polymeriza-tion of the respective monomers by a standard method as outlined ln the chemistry texts aforementioned.
Another preerred method of making a copolymer as described in this invention is to transform an existing copolymer into an amic acid copolyme~. T~is is done by adding an anhydride-containing copolymer to aqueous ammonia to form an amic acid copolymer.
Thus the copolymers of this invention are also formed as the products of the reaction of an anhydride-containing copolymer and aqueous ammonia. These anhydride-containing copolymers have a general formula -comonomer-anhydride-comonomer-anhydride-comonomer-anhydride-The anhydride-containing copolymer as described by the above general formula is the product of the addition polymerization reaction of an ethylenically unsaturated, polymeri.zable anhydride and at least or-e other ethyleni-cally unsaturated monomer.
The ethylenically unsaturated, polymerizable an-hydride used to synthesize the anhydride-containing copolymer is a cyclic anhydride containi.ng a poly-merizable multiple bond capable of radical polymeri-zation. Most preferrably the cyclic anhydride ismaleic anhydride or itaconic anhydride.
Among the other ethylenically unsaturated monomers used to make the anhydride-containing copolymer are the vinyl esters of aliphatic acids which have one to ten carbon atoms; alkyl vinyl ethers which ha~e alkyl groups ~5~
composed of from one to ten carbon atoms and whose alkenyl groups are composed of from one to ten carbon atoms;
alkenes; and alkadienes which have from one -to ten carbon atoms.
The preferred vinyl esters of aliphatic acids are vinyl acetate and vinyl propionate. The preferred alkyl vinyl ethers are methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether and propyl vinyl ether. The preferred alkene and/or alkadiene are ethylene, propylene, l-butene, 2-butene and 1,3-butadiene.
In order to describe the present inventiorl so that it may he more clearly understood, the following examples are set forth. These examples are set forth ;orimarily for the purpose of illustration, and any specific enumera-tion of detail contained therein should not be interpreted as a limitation on the concept of this invention.
Example 1 Into a 500 ml reaction flask equipped with a mechani-cal stirrer, thermometer, and addition funnel were placed 82.0 grams of water and 8.4 grams of 29% aqueous ammonia (0.143 moles). To the ammonia solution is added lOg of a maleic anhydride methyl vinyl ether copolymer (l:l mole ratio) (commercial product trademark Gantre~-AN 119, GAF
Corp.) in small increments while maintaining a reaction temperature of 65C. After all the copolymer has been added, the solution was removed from the reactor and dil.uted with l:L33.6 grams of water.
Example 2 Into a 500 ml reaction flask equipped with a mechanical stirrer, thernometer and addition funnel were placed, 304 grams of water and 46 grams of 29% aqueous ammonia (0.785 moles). To this solution is added 50 grams of a maleic anhydride-ethylene copolymer (1:1 mole ratio) (commercial product trademark EMA 1103, Monsanto, Inc.) in small increments while maintaining the reaction tempera-ture of 65Cn After all the copolymer has been added, the solution is cooled to room teniperature.
Example 3 The following tables illustrate the properties achieved by utilizing the resins prepared in the above examples. Approximately 100 grams of the solution from Example 1 is placed in the container so as to form a saturation bath. All the data presented was obtained from filter paper sheets (Whatman ChroTnatography Paper #4) measuring approximately 9" MD (machine direction) x7.5" CD
(cross dire~tion) are immersed in the saturation bath.
After saturation, the sheets are squeezed through a laboratory wringer, dried overnight at room temperature and cured for 3 minutes at 300F (149C). Some of these sheets are then tested for increases in wet and dry tensiles relative to untreated controls. The results are depicted in Table I. The remainder of the treated sheets are allowed to stand at room temperature for an extended period and tested for wet tensile clevelopment through natural aging. The results are shown in Table II.
In the tables which follows, the amounts o resin applie.d to the sheet is expressed under the column "% Addition" as a percent by weight of the sheet. Tensile .~5 measurements were obtained on a Thwing r~lbert Tensile Tester in accordance with TAPPI Standard Number T 456m-49.
Tensile was measured cross direction for a dry strip (CDT) and a wet strip (CDWT). All tensile values are reported as pounds/inch. These values may be converted to the standard metric unit of grams per 15 millimeters by multiplying by 268.4.
~5~
Table I
Cured Tensiles Treatment % ddition CDWT CDT
Example l 1.8 5.33 11.1 Example 2 1.7 6.47 13.16 Control 0.0 0.0 6.7 Table II
Wet Tensile Increase as a Functiorl of Time -Example I Treatment - 1.8% Addition Time After Treatment CDWT CDT
12 ho~rs 0.2 9.0 1 week 2.00 9.1 2 weeks 2.2 9.0
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenical.ly unsaturated monomer.
These water soluble amic acid copolymers can be prepared by reacting an anhydride-containing precursor copolymer with ammonla, namely by adding it to aqueous ammotlia, thereby yroducing an amic aci.d-containing co-polymer. The resulting amic acid copolymer solution can then be applied to a cellulosic web, such as paper, by a ~ariety of methods including coating, spraying, printing and the like. The amic acid copolymers useful in this invention can also be prepared by copolymerizing an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated monomer. I'he cellulosic webs, such as paper, treated with resins as described in this invention have off-machine wet tensi.les, improved dry tensiles, and improved broke recovery after the finishing operationO
If it is desired tha.t the copolymer be substantive to cellulose, copolymers can ~e made by reacting an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated monomer and at least one other ethylenically unsatura~ed basic nitrogen-containing monomer. The basic nitrogen-containing monomer will impa.rt a cationic character to the copolymer which makes it attràctive to anionic cellulose fibers for deposition in the wet end of a paper machine. Suitable examples o the other ethylenically unsaturated, basic nitrogen-con-taining monomer include N,N - dimethylaminoethylmethacry-late, N,N - diethylaminoethylmethacrylate~ N,N - dimethyl-aminaethylacrylate, N,N - diethylaminoethylacrylate, 2-vinylpyridine, 4-vinylpyridine, and N-(t-butyl)-aminoethyl-methacrylate.
The ethylenically unsaturated amic acid useful in synthesizi~lg these cellulose-substantive polymers are polymerizable compounds of the following general formula:
NH2 ~ C - R - C - ORl .
Il 11 O O
wherein R is a hydrocarbon chain containing a multiple bond capable of radical polymerization and Rl, is H, alkyl or alkenyl~ The amount of the amic acid which can be used along with the other monomeric species to make up the desired a-nic acid copolymer must be chosen so as to render the resulting copolymer water soluble.
Depending upon the nature of the other comonomers, this amount can range from 5% to 50% by weight of the co-polymer.
5~
The other ethylenically unsaturated monomers useful in synthesizing the deslred amic acid precursor polymer include acrylic and/or methacrylic acids and/or their esters, amides, substituted amides, and nitriles. Also use~ul are esters of vinyl alcohol, vinyl ethers and ke-tones, acrolein, styrene and substituted styrenes, vinyl pyridines, ethylene, butadiene, maleic, fumaric and itaconic acids and esters and substituted amides 9 poly-merizable derivatives of allyl alcohol, vi.nylacetic acid and the like.
The wet strength resins as described in this disclosure may be applied to cellulosic webs, such as paper, by any conventional technique for applying a polymer to a cell~llosic web. In the case where the web is already formed, the polymer or resin may be applied by coating, printing, or spraying. In the case of addition to cellulosic fibers prior to web formation~ the resin, if it bears a net positive charge, can be added to a slurry of fibers, as in the wet end of a paper machine. The net positi~e charge on the resin renders it substantive to cel].ulose. The amount of resin added to the web can vary, depending upon the degree of wet strength desired. The preferred amount of resin to be applied is in the range of 0.1 to 5% based upon weight of fiber. The curing or 2S crosslinking reaction can be accelerated by the addition of mirleral acids or salts of acids such as ammonlum~
ma~lleSiUIIl, zinc and tin chlorides, nitrates or sulfates~
The increase in wet tenslle of cellulosic webs treated with the resins as described in this invention is due to the crosslinkin~ of the amic acid copolymer molecules with the cellulosic substrate.
The polymerization of these monomers to yield water soluble copolymers can be accomplished by well known polymerization techniq~les as described in such chemistry .~19 S04L9 texts as POLY~R SYNTHESIS, Volume I, II, and III, by Stanley P~. Sandler and Wolf Karo, Academic Press, New York and London, (1974), and PREPARATIVE METHODS OF
POLYMER CHFMISTRY, second edition, by Wayne R. Sorenson and Tod W. Campbell, Interscience Pub].ishers (John Wiley & Sons), New York (1968)o Thus various aspects of this invention are as follows:
A wet strength resin comprising a wa-ter soluble copolymer comprised of A) a half-acid, half-amide corresponding to the following general formula:
NH2 ~ C - R - C - OR
1~ 11 O O
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
A cellulo~ic fibrous web treated with a wet strength resin comprising a water soluhle copolymer o~
comprised A) a half-acid, half-amide corresponding to the following ~eneral formula:
NH - C - R - C - OR
2 ll l O O
wherein Rl is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at lea~t one other ethylenicallv unsaturated monomer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymer composition of this in~ention is a water soluble addition copolymer of an ethylenically unsaturated amic acid and at least one other ethylenically unsaturated 30 monomer. Preferably, the e-thylenically unsaturated amic acid is - 7a -(I) maleamic acid, (Z)-4-amino-4-oxo-2-butenoie acid H H
NH -C-C=C-C-OH
O O
(II) fumaramic acid, (E)-4-amino-4-oxo-2-butenoic acld NH2-C-c=c_c_oH
Il 1 11 O ~I O
or (III) itaconamic acid, 4-amino-4-oxo-2-methylene butanoic acid NH -C-C-C-C-OH
2 ll I ll O H
Among the other ethylenically unsaturated monomers useful in this invention are the vinyl esters of aliphatic acids which have one to ten carbon atoms. The preferred vinyl ester is vinyl acetate especially when used with esters of acrylic or methacrylic acids. The acrylate and methacrylate esters o alkyl and cycloalkyl alcohols having one to twenty carbon atoms are most efficacious in forming useful copolymers with vinyl acetate. The preerred esters of nlethacryllc acid are methyl, ethyl, n-propyl, n-butyl, iso-butyl, 2-ethylhe.Yyl esters. The preferred esters of acrylic acid are methyl, ethyl, n-propyl, n-butyl, iso-butylg 2-ethyl hexyl with n-butyl being the nnost preferred.
Most preferably the copolymer is composed of 80-98%
by weight acrylamide, 1-10% by weight N,N-dimethylamino-ethyl methacrylate, and 1-10% maleamic acid. The pre-~erred copolymer is prepared by the addition polymeriza-tion of the respective monomers by a standard method as outlined ln the chemistry texts aforementioned.
Another preerred method of making a copolymer as described in this invention is to transform an existing copolymer into an amic acid copolyme~. T~is is done by adding an anhydride-containing copolymer to aqueous ammonia to form an amic acid copolymer.
Thus the copolymers of this invention are also formed as the products of the reaction of an anhydride-containing copolymer and aqueous ammonia. These anhydride-containing copolymers have a general formula -comonomer-anhydride-comonomer-anhydride-comonomer-anhydride-The anhydride-containing copolymer as described by the above general formula is the product of the addition polymerization reaction of an ethylenically unsaturated, polymeri.zable anhydride and at least or-e other ethyleni-cally unsaturated monomer.
The ethylenically unsaturated, polymerizable an-hydride used to synthesize the anhydride-containing copolymer is a cyclic anhydride containi.ng a poly-merizable multiple bond capable of radical polymeri-zation. Most preferrably the cyclic anhydride ismaleic anhydride or itaconic anhydride.
Among the other ethylenically unsaturated monomers used to make the anhydride-containing copolymer are the vinyl esters of aliphatic acids which have one to ten carbon atoms; alkyl vinyl ethers which ha~e alkyl groups ~5~
composed of from one to ten carbon atoms and whose alkenyl groups are composed of from one to ten carbon atoms;
alkenes; and alkadienes which have from one -to ten carbon atoms.
The preferred vinyl esters of aliphatic acids are vinyl acetate and vinyl propionate. The preferred alkyl vinyl ethers are methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether and propyl vinyl ether. The preferred alkene and/or alkadiene are ethylene, propylene, l-butene, 2-butene and 1,3-butadiene.
In order to describe the present inventiorl so that it may he more clearly understood, the following examples are set forth. These examples are set forth ;orimarily for the purpose of illustration, and any specific enumera-tion of detail contained therein should not be interpreted as a limitation on the concept of this invention.
Example 1 Into a 500 ml reaction flask equipped with a mechani-cal stirrer, thermometer, and addition funnel were placed 82.0 grams of water and 8.4 grams of 29% aqueous ammonia (0.143 moles). To the ammonia solution is added lOg of a maleic anhydride methyl vinyl ether copolymer (l:l mole ratio) (commercial product trademark Gantre~-AN 119, GAF
Corp.) in small increments while maintaining a reaction temperature of 65C. After all the copolymer has been added, the solution was removed from the reactor and dil.uted with l:L33.6 grams of water.
Example 2 Into a 500 ml reaction flask equipped with a mechanical stirrer, thernometer and addition funnel were placed, 304 grams of water and 46 grams of 29% aqueous ammonia (0.785 moles). To this solution is added 50 grams of a maleic anhydride-ethylene copolymer (1:1 mole ratio) (commercial product trademark EMA 1103, Monsanto, Inc.) in small increments while maintaining the reaction tempera-ture of 65Cn After all the copolymer has been added, the solution is cooled to room teniperature.
Example 3 The following tables illustrate the properties achieved by utilizing the resins prepared in the above examples. Approximately 100 grams of the solution from Example 1 is placed in the container so as to form a saturation bath. All the data presented was obtained from filter paper sheets (Whatman ChroTnatography Paper #4) measuring approximately 9" MD (machine direction) x7.5" CD
(cross dire~tion) are immersed in the saturation bath.
After saturation, the sheets are squeezed through a laboratory wringer, dried overnight at room temperature and cured for 3 minutes at 300F (149C). Some of these sheets are then tested for increases in wet and dry tensiles relative to untreated controls. The results are depicted in Table I. The remainder of the treated sheets are allowed to stand at room temperature for an extended period and tested for wet tensile clevelopment through natural aging. The results are shown in Table II.
In the tables which follows, the amounts o resin applie.d to the sheet is expressed under the column "% Addition" as a percent by weight of the sheet. Tensile .~5 measurements were obtained on a Thwing r~lbert Tensile Tester in accordance with TAPPI Standard Number T 456m-49.
Tensile was measured cross direction for a dry strip (CDT) and a wet strip (CDWT). All tensile values are reported as pounds/inch. These values may be converted to the standard metric unit of grams per 15 millimeters by multiplying by 268.4.
~5~
Table I
Cured Tensiles Treatment % ddition CDWT CDT
Example l 1.8 5.33 11.1 Example 2 1.7 6.47 13.16 Control 0.0 0.0 6.7 Table II
Wet Tensile Increase as a Functiorl of Time -Example I Treatment - 1.8% Addition Time After Treatment CDWT CDT
12 ho~rs 0.2 9.0 1 week 2.00 9.1 2 weeks 2.2 9.0
3 weeks 2.5 8.9
Claims (20)
1. A wet strength resin comprising a water soluble copolymer comprised of A) a half-acid, half-amide corres-ponding to the following general formula:
wherein R1 is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
wherein R1 is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
2. The resin according to claim 1 wherein the half-acid, half-amide corresponding to the general formula is maleamic acid.
3. The resin according to claim 1 wherein the half-acid, half-amide corresponding to the general formula is fumaramic acid.
4. The resin according to claim 1 wherein the half-acid, half-amide corresponding to the general formula is itaconamic acid.
5. The resin according to claim 1 wherein the other ethylenically unsaturated monomer comprises a vinyl ester of an aliphatic acid having one to ten carbon atoms.
6. The resin according to claim 5 wherein said monomer is vinyl acetate.
7. The resin according to claim 6 wherein the copolymer further includes esters of acrylic or methacrylic acids.
8. The resin according to claim 1 wherein the co polymer comprises an ethylenically unsaturated, basic nitrogen containing monomer.
9. The resinaccording to claim 1 wherein the half-acid, half-amide comprises from 1 to 10% by weight of the copolymer.
10. A cellulosic fibrous web treated with a wet strength resin comprising a water soluble copolymer comprised of A) a half-acid, half-amide corresponding to the following general formula:
wherein R1 is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
wherein R1 is H, alkyl or alkenyl and R is a hydrocarbon chain which has radically polymerized with B) at least one other ethylenically unsaturated monomer.
11. The web in accordance with claim 10 wherein said copolymer is present in an amount equal to 0.1 to 5% based on the weight of the fiber in the web.
12. The web according to claim 10 wherein the half-acid, half-amide corresponding to the general formula is maleamie acid.
13. The web according to claim 10 wherein the half acid, half-amide corresponding to the general formula is fumaramic acid.
14. The web according to claim 10 wherein the half-acid, half-amide corresponding to the general formula is itaconamic acid.
15. The web according to claim 10 wherein the other ethylenically unsaturated monomer comprises a vinyl ester of an aliphatic acid having one to ten carbon atoms.
16. The web according to claim 15 wherein said monomer is vinyl acetate.
17. The web according to claim 16 wherein the copolymer further includes esters of acrylic or metha-crylic acids.
18. The web according to claim 10 wherein the half-acid, half-amide comprises from 1 to 10% by weight of the copolymer.
19. The web according to claim 12 wherein the half-acid, half-amide comprises from 1 to 10% by weight of the copolymer.
20. The web according to claim 10 wherein the copolymer comprises an ethylenically unsaturated, basic nitrogen containing monomer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US286,078 | 1981-07-24 | ||
| US06/286,078 US4391878A (en) | 1981-07-24 | 1981-07-24 | Wet strength resins |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195049A true CA1195049A (en) | 1985-10-08 |
Family
ID=23096975
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000405084A Expired CA1195049A (en) | 1981-07-24 | 1982-06-14 | Wet strength resins |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4391878A (en) |
| JP (1) | JPS5825312A (en) |
| CA (1) | CA1195049A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6264791B1 (en) | 1999-10-25 | 2001-07-24 | Kimberly-Clark Worldwide, Inc. | Flash curing of fibrous webs treated with polymeric reactive compounds |
| US6322665B1 (en) | 1999-10-25 | 2001-11-27 | Kimberly-Clark Corporation | Reactive compounds to fibrous webs |
Families Citing this family (26)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5160789A (en) * | 1989-12-28 | 1992-11-03 | The Procter & Gamble Co. | Fibers and pulps for papermaking based on chemical combination of poly(acrylate-co-itaconate), polyol and cellulosic fiber |
| US5049235A (en) * | 1989-12-28 | 1991-09-17 | The Procter & Gamble Company | Poly(methyl vinyl ether-co-maleate) and polyol modified cellulostic fiber |
| US5763044A (en) * | 1995-11-22 | 1998-06-09 | The Procter & Gamble Company | Fluid pervious, dispersible, and flushable webs having improved functional surface |
| US6689378B1 (en) | 1999-12-28 | 2004-02-10 | Kimberly-Clark Worldwide, Inc. | Cyclodextrins covalently bound to polysaccharides |
| US6683129B1 (en) * | 2000-03-31 | 2004-01-27 | National Starch And Chemical Investment Holding Corporation | Salt sensitive aqueous emulsions |
| EP1632440A1 (en) | 2004-08-26 | 2006-03-08 | Weyerhaeuser Company | Cup made from an insulating paperboard |
| US20060144537A1 (en) | 2004-12-30 | 2006-07-06 | Schwonke Paul A | Paperboard |
| US7381298B2 (en) * | 2004-12-30 | 2008-06-03 | Weyerhaeuser Company | Process for making a paperboard from a high consistency slurry containing high levels of crosslinked cellulosic fibers |
| US20080156857A1 (en) | 2006-12-28 | 2008-07-03 | Weyerhaeuser Co. | Method For Forming A Rim And Edge Seal For An Insulating Cup |
| MX2012009810A (en) | 2010-02-26 | 2012-09-12 | Procter & Gamble | Fibrous structure product with high wet bulk recovery. |
| TWI454490B (en) | 2011-12-30 | 2014-10-01 | Ind Tech Res Inst | Copolymer and method for forming the same |
| CN103183776B (en) * | 2011-12-30 | 2015-08-12 | 财团法人工业技术研究院 | Multipolymer and forming method thereof |
| JP5843620B2 (en) * | 2012-01-11 | 2016-01-13 | 株式会社クラレ | Crosslinkable composition comprising vinyl alcohol polymer having primary amino group |
| US9458574B2 (en) | 2012-02-10 | 2016-10-04 | The Procter & Gamble Company | Fibrous structures |
| TWI469996B (en) * | 2013-10-11 | 2015-01-21 | Univ Nat Taipei Technology | Temperature and ph both sensitive copolymer and method for making the same |
| US9458297B2 (en) | 2014-06-30 | 2016-10-04 | Weyerhaeuser Nr Company | Modified fiber, methods, and systems |
| US10132042B2 (en) | 2015-03-10 | 2018-11-20 | The Procter & Gamble Company | Fibrous structures |
| US20160136013A1 (en) | 2014-11-18 | 2016-05-19 | The Procter & Gamble Company | Absorbent articles having distribution materials |
| US10517775B2 (en) | 2014-11-18 | 2019-12-31 | The Procter & Gamble Company | Absorbent articles having distribution materials |
| US10765570B2 (en) | 2014-11-18 | 2020-09-08 | The Procter & Gamble Company | Absorbent articles having distribution materials |
| EP3023084B1 (en) | 2014-11-18 | 2020-06-17 | The Procter and Gamble Company | Absorbent article and distribution material |
| EP3178458A1 (en) | 2015-12-08 | 2017-06-14 | The Procter and Gamble Company | Absorbent articles with distribution system |
| EP3178457A1 (en) | 2015-12-08 | 2017-06-14 | The Procter and Gamble Company | Absorbent articles with distribution system |
| US10156042B2 (en) | 2015-12-29 | 2018-12-18 | International Paper Company | Modified fiber from shredded pulp sheets, methods, and systems |
| WO2017156203A1 (en) | 2016-03-11 | 2017-09-14 | The Procter & Gamble Company | A three-dimensional substrate comprising a tissue layer |
| US11408129B2 (en) | 2018-12-10 | 2022-08-09 | The Procter & Gamble Company | Fibrous structures |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2621169A (en) * | 1948-12-18 | 1952-12-09 | Publicker Ind Inc | Process for preparing ammonium salts of copolymer compositions |
| US2999038A (en) * | 1958-01-24 | 1961-09-05 | Rohm & Haas | Method of producing wet-strength papers |
| NL241114A (en) * | 1958-07-10 | |||
| BE586294A (en) * | 1959-01-06 | |||
| US3442698A (en) * | 1966-02-04 | 1969-05-06 | Monsanto Co | Cellulosic webs treated with a derivative of an alkyl vinyl ether/maleic anhydride interpolymer |
| US3555585A (en) * | 1968-05-03 | 1971-01-19 | Du Pont | Process for forming cellulose half-acid esters |
| JPS5124086A (en) * | 1974-08-23 | 1976-02-26 | Tokyo Shibaura Electric Co | Keikomakuno keiseihoho |
| JPS5124088A (en) * | 1974-08-23 | 1976-02-26 | Tokyo Shibaura Electric Co | KANKYUYOHIMAKUKEISEIHOHO |
| JPS5280677A (en) * | 1975-12-26 | 1977-07-06 | Toshiba Corp | Method for coating bulb with fluorescent film |
| US4061465A (en) * | 1976-04-02 | 1977-12-06 | The United States Of America As Represented By The Secretary Of Agriculture | Creasable durable press textiles from methylol reagents and half amides or half salts of dicarboxylic acids |
| NL7607788A (en) * | 1976-07-14 | |||
| DE2936518A1 (en) * | 1979-09-10 | 1981-03-26 | Cassella Ag, 60386 Frankfurt | STORAGE-STABLE ACRYLATE-MODIFIED MELAMINE RESIN, ITS PRODUCTION AND USE |
-
1981
- 1981-07-24 US US06/286,078 patent/US4391878A/en not_active Expired - Fee Related
-
1982
- 1982-06-14 CA CA000405084A patent/CA1195049A/en not_active Expired
- 1982-07-21 JP JP57125965A patent/JPS5825312A/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6264791B1 (en) | 1999-10-25 | 2001-07-24 | Kimberly-Clark Worldwide, Inc. | Flash curing of fibrous webs treated with polymeric reactive compounds |
| US6322665B1 (en) | 1999-10-25 | 2001-11-27 | Kimberly-Clark Corporation | Reactive compounds to fibrous webs |
Also Published As
| Publication number | Publication date |
|---|---|
| US4391878A (en) | 1983-07-05 |
| JPS5825312A (en) | 1983-02-15 |
| JPH0474480B2 (en) | 1992-11-26 |
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