CA1044858A - Dry strength paper and process therefor - Google Patents
Dry strength paper and process thereforInfo
- Publication number
- CA1044858A CA1044858A CA213,060A CA213060A CA1044858A CA 1044858 A CA1044858 A CA 1044858A CA 213060 A CA213060 A CA 213060A CA 1044858 A CA1044858 A CA 1044858A
- Authority
- CA
- Canada
- Prior art keywords
- paper
- copolymer
- salt
- alum
- dry strength
- 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
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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
-
- 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
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Paper (AREA)
Abstract
DRY STRENGTH PAPER AND PROCESS THEREFOR
ABSTRACT OF THE DISCLOSURE
Paper of dry strength is produced by forming an aqueous solution of papermaking cellulose fibers and adding thereto a 90:10 to 98:2 copolymer of acrylamide and maleic acid followed by addition of alum. The use of the acryla-mide-maleic acid copolymer allows production of paper at a much broader pH range towards the alkaline side which eli-minates the need for close control of pH and which sub-stantially reduces corrosion of the papermaking equipment.
ABSTRACT OF THE DISCLOSURE
Paper of dry strength is produced by forming an aqueous solution of papermaking cellulose fibers and adding thereto a 90:10 to 98:2 copolymer of acrylamide and maleic acid followed by addition of alum. The use of the acryla-mide-maleic acid copolymer allows production of paper at a much broader pH range towards the alkaline side which eli-minates the need for close control of pH and which sub-stantially reduces corrosion of the papermaking equipment.
Description
n.I~ C-1623 iO~
Th~ ~res~nt inv~n~ion rc~lates to l~ap~r havin~3 dry strcngth and proccss for its manufacturc which is char-acterized by th~ use of an anionic resin which is a co-polymer of acrylamide and maleic acid together with alum or another suitable metallic polyvalent salt. The copolymer of acrylamide and maleic acid is a dry strength additive which imparts a negligible amount of wet strength to the paper thus facilitating repulping thereof or making such paper available for particular applications where dry strength must predominate.
U. S. patent 2,884,057 defines dry strength of paper and paper which has a dry strength of about 10~ in excess of its normal strength as a result of resin treatment, is generally regarded as possessing a materially improved dry - 15 strength.
The art of making dry strength paper dates back to at least 1951 when the Azorlosa Canadian patent 477,265 issued. This patent discloses the use of a copolymer of acrylamide with acrylic or methacrylic acids together with alum. Pursuant to the Azorlosa's patent, paper of im-proved dry strength is manufactured by forming an aqueous suspension of cellulose papermaking fibers, adding thereto the anionic dry strength resin which is a copolymer of acrylamide with acrylic or methacrylic acids as well as alum, and sheeting the suspension. The resulting paper possesses much better dry strength than normal paper and possesses virtually no wet strength so that it can be easily repulped.
Th~ ~res~nt inv~n~ion rc~lates to l~ap~r havin~3 dry strcngth and proccss for its manufacturc which is char-acterized by th~ use of an anionic resin which is a co-polymer of acrylamide and maleic acid together with alum or another suitable metallic polyvalent salt. The copolymer of acrylamide and maleic acid is a dry strength additive which imparts a negligible amount of wet strength to the paper thus facilitating repulping thereof or making such paper available for particular applications where dry strength must predominate.
U. S. patent 2,884,057 defines dry strength of paper and paper which has a dry strength of about 10~ in excess of its normal strength as a result of resin treatment, is generally regarded as possessing a materially improved dry - 15 strength.
The art of making dry strength paper dates back to at least 1951 when the Azorlosa Canadian patent 477,265 issued. This patent discloses the use of a copolymer of acrylamide with acrylic or methacrylic acids together with alum. Pursuant to the Azorlosa's patent, paper of im-proved dry strength is manufactured by forming an aqueous suspension of cellulose papermaking fibers, adding thereto the anionic dry strength resin which is a copolymer of acrylamide with acrylic or methacrylic acids as well as alum, and sheeting the suspension. The resulting paper possesses much better dry strength than normal paper and possesses virtually no wet strength so that it can be easily repulped.
-2-~ jt~ ~.I. C-1623 It is a disadvanta-Je of the proces~, however, that the ~pcr is produc~d at the normal pl~ of alum solution, about 4.5. Paper produced at pH of 4.5 is significantly acid and undergoes acid tendering on aging. Moreover, paper-making systems operating at that pH cause a signi-ficant amount of corrosion to the apparatus under conditions of constant use. As a result, efforts have been made to discover means for increasing the operating pH of paper-making systems producing dry strength paper of the type just described without sacrifice of the dry strength de-veloped by the resin.
With the exceptions described in the herein-noted prior art, it has not been possible to increase the system pH beyond about 4,7-4.8 as the addition of alkali to give a higher pH causes the strengthening effect of the resin to disappear abruptly. Repeated laboratory tests have shown that the resin to cellulose bond is weak when formed at pH values in excess of about 4.7.
The close control of pH has been obviated by the in-vention described herein which allows manufacture of dry strength paper in a pH range of 4.5 to 6.5 without weaken-ing the resin to cellulose bond. This has been accom-plished by the use of anionic copolymer of acrylamide and maleic acid in conjunction with alum which fixes the co-polymer to the fibers. The unexpected advantàge of this invention is achieved if the resin is added to the paper fiber suspension before addition of alum.
The prior art describes manufacture of paper having substantial dry strength and negligible wet strength. The
With the exceptions described in the herein-noted prior art, it has not been possible to increase the system pH beyond about 4,7-4.8 as the addition of alkali to give a higher pH causes the strengthening effect of the resin to disappear abruptly. Repeated laboratory tests have shown that the resin to cellulose bond is weak when formed at pH values in excess of about 4.7.
The close control of pH has been obviated by the in-vention described herein which allows manufacture of dry strength paper in a pH range of 4.5 to 6.5 without weaken-ing the resin to cellulose bond. This has been accom-plished by the use of anionic copolymer of acrylamide and maleic acid in conjunction with alum which fixes the co-polymer to the fibers. The unexpected advantàge of this invention is achieved if the resin is added to the paper fiber suspension before addition of alum.
The prior art describes manufacture of paper having substantial dry strength and negligible wet strength. The
-3-.I. C-1623 ~.orlos~ C~lnLdian pat~nt h~s alrcady bcen mcntioned. This patent describes and claims the use of a copolymer of acrylamide or methacrylamide with acrylic or methacrylic acids followed by addition o~ alum to the aqueous suspen-sion. In view of the fact that the acrylic acids described in the A~orlosa patent are structurally similar to maleic acid in that they contain a vinyl group and one carboxyl group, as illustrated below:
CH2 = CR - COOH HOOC - CH = C~I - COO~i acrylic type acid maleic acid one might be tempted to conclude that substitution of such acids as itaconic, maleic and fumaric for the acrylic type acid would be obvious especially in view of the known fact that such acids are known to copolymeriæe with acrylamide.
Such a conclusion of obviousness would be unfounded since ~ no attempt has been made to study the effect of a dual `; carboxy moiety on dry and wet strength of paper. The ad-vantage achieved by the use of the acrylamide-maleic acid copolymer is unexpected since it allows pH in the paper-making system to vary over a range from 4.5 to 6.5 without detriment to the dry strength of paper. To put importance of this two-point spread in perspective, attention is directed to lines 54 to 57 in col. 1 of the Reynolds et al U. S. patent 3,269,891 where it is noted that the invention described therein permits the pH in the papermaking system to be increased by half of a pH unit.
With respect to the Azorlosa patent, i~ is here pointed out that a minor amount of polyacrylamide can be hydrolyzed to yield carboxyl groups which would make it resemble a
CH2 = CR - COOH HOOC - CH = C~I - COO~i acrylic type acid maleic acid one might be tempted to conclude that substitution of such acids as itaconic, maleic and fumaric for the acrylic type acid would be obvious especially in view of the known fact that such acids are known to copolymeriæe with acrylamide.
Such a conclusion of obviousness would be unfounded since ~ no attempt has been made to study the effect of a dual `; carboxy moiety on dry and wet strength of paper. The ad-vantage achieved by the use of the acrylamide-maleic acid copolymer is unexpected since it allows pH in the paper-making system to vary over a range from 4.5 to 6.5 without detriment to the dry strength of paper. To put importance of this two-point spread in perspective, attention is directed to lines 54 to 57 in col. 1 of the Reynolds et al U. S. patent 3,269,891 where it is noted that the invention described therein permits the pH in the papermaking system to be increased by half of a pH unit.
With respect to the Azorlosa patent, i~ is here pointed out that a minor amount of polyacrylamide can be hydrolyzed to yield carboxyl groups which would make it resemble a
-4-.
, lt)4~ . I. C-1623 l~oly.lcryl~midc--c~ c~ylic ~cid. ~low~v~r, ur.d~r our poly-mcrization conditions, the amount of carboxylic acid group~
produced by hydrolyQis ~hould be no more than about 1%.
~mount of acrylic acid used in Azorlosa copolymer i5 between 1 and 25~, pref~rably 5 to 12%, whereas amount of maleic acid used in the acrylamlde-maleic acid copolymer oP our invention is from 3 to 15%, preferably from S to 10%.
~nounts here given are based on the total weight of the monomers. Therefore, even if there were a minor amount of hydrolyzed acrylamide in the acrylamide-acrylic acid copolymer of the Azorlosa's patent, this amount would be insignificant for the purpose described herein.
The principal discovery in the Reynolds et al patent 3,269,891 relates to the use of a buffer to fix the anionic dry strength resin. As far as the anionic dry strength resin is concerned, Reynolds et al did not disclose any novel polymer other than a generalization of what has been reported in Azorlosa's Canadian patent 477,265. Reynolds et al demon-strated that the use of Azorlosa's anionic polymer fixed on the fiber with alum to confer dry strength required a care-fully controlled pH of about 4.5 and the addition of alkali to give a pH higher than 4.7-4.8 caused the strengthening effect of the resin to dlsappear abruptly. Reynolds et al's invention relates to the manufacture of paper of improved dry strength by use of an anionic polymer fixed on the fiber with alum in the presence of a buffer so that the resin re-tains its high efficiency up to a pH of about 5.5 so that accurate control of pH is no longer necessary. The buffer is a non-chelating acid having an ionization constant between _5_ ... . ~ . - . ~.
, :. :
- 1()4~
.LO 4 and 10 6 and a salt of such acid with a strong base.
Davlson patent 3,049,469 discloses a process for making paper having wet and dry strength by impregnating cellulosic fibers disposed in an aqueous suspension first with a cationic thermo-setting polyamide-epichlorohydrin resin and then with an acrylic resin. Davison's objectives are achieved without the use of alum.
In one particular aspect the present invention provides process for the manufacture of paper of improved dry strength and negligible wet strength without the use of a buffer and without a water-soluble non-thermosetting cationic resin comprising the steps of forming an aqueous suspension at pH of about 5 to 7 of paper making fibers containing a dry strength additive and a fixing agent selected from the group consisting of polyvalent metal salts and mixtures thereof, and sheeting the suspension to form the paper, the . . .
additive consists essentially of an anionic copolymer of acrylamide ` ~; and maleic acid or its anhydride in respective mol ratio of from - 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient amount to affix the copolymer to the fibers.
In another aspect the present invention provides paper com-posed of cellulose fibers and being devoid of a buffer and a water-soluble non-thermosetting cationic resin having deposited thereon a fixing agent selected from the group consisting of polyvalent metal salts and being bonded with a dry strength additive consistin~ essen-tially of an anionic copolymer of acrylamide and maleic acid or its anhydride in respective mol ratio of from 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient A ~ -6-C
mount to affix the copolymer to the fibers.
Our method for manufacturing paper of high dry strength but of low wet strength includes forming an aqueous suspension of cellu-lose papermkaing fibers and adding thereto an aqueous solution of acrylamide-maleic acid resin followed by addition of alum of another polyvalent metallic salt. ~mount of the resin used may vary from 0.1 to 2.0~ depending on the required dry strength and the type of papermaking system whereas amount of the alum used is in the range of 1 to 3~. Amount of alum less than 1% or more than 3~ generally have an adverse effect on efficiency of the dry strength resin.
Amounts are given on the basis of dry weight of the fibers. The resin and alum are used in ~ to 5~ aqueous solutions. The reagents may be added at any convenient point in the papermaking system. In practice, the resin is most advantageously added to the papermaking fibrous suspension in the beater and the alum is most advantageously added as near to the wire as possible, for example at the fan pump, sufficient time being preferably allowed in each instance for the added reagent to become uniformly distributed through the suspension before the next reagent is added.
; 20 The mol ratio of acrylamide to maleic acid in the copolymer is in the range of from 90:10 to 98:2, preferably A -6a_ jc/ ~.,.~, ~ R.I. C-1623 Y5:5. ~ e resin suita~le for ou~ pur~ose has molecular w~ ht, as repr~sented by intrinsic viscosity (measured in 0.l N NaCl solution at 25C) in the range of from 0.5 dl/g to 6.0 dl/g, preferably from l.0 dl/g to l.5 dl/g. In place of alum, other polyvalent metallic salts can be used such as aluminum chloride or aluminum nitrate.
Ou~ process has the advantage over the prior art in that a specific resin can be used in a much wider pH range of 4.5 to 6.5 than was hitherto possible which obviates the necessity for close p~i control. ~urthermore, the use of a third component such as a thermosettin~ or nonthermosetting polyamide, or the use of a buffer, is not necessary. The application of the acrylamide-maleic acid copolymer as a dry strength additive is preferably carried out by adding the polymer at a suitable point to the paper stock after completion of major refining. Sufficient alum must be added after the addition of the resin in order to fix the resin onto the fibers. ~he adjustment of pH can be made after all these additions have been completed if a certain pH value is desired. When the resin and alum is added in this preferred order, the efficiency of the resin to strengthen paper is not adversely affected by a pH change in the range of 4.5 to 6.5.
If the alum is added before the resin, efficiency of the resin will be more affected by the change of pH.
Outline of the preparation of a 95:5 mol ratio acryla-mide-maleic acid copolymer is given below:
, . . .
1~4~ R.l. C-1623 Renct.~ntfi Y. by we1~ht lA Water (heel) 43.00 A lB Sequestrene NA-22 0.01*
2 Wntér 20.00 3 Acrylamide 18.51 4 Water (at 130-140F or 55-60C) 8.27 Maleic anhydride 1.35 6 Ammonia solution 26~e 0.75 7 Water 4.80 8 Potassium Persulfate 0.06 9 Water 3.20 Potassium Persulfate 0.05 100 . OOX
*The amount of Sequestrene NA-22 used is generally less than 0.01%
and is preferably about 0.005X.
Procedure:
(A) Charge reactor with (lA) and (lB).
Set reflux to full return snd heat to reflux.
~20 (B) Prepare a solution by dissolving ~3) in (2) in a container of suitable volume.
(C) Prepare a solution by dissolving (5) in hot water (4) in a lined container.
(D) Make up the monomer mixture by adding solution (C) to solution (B).
(E) Add (6) to monomer mixture (D) in small in-crements whlle mixing and measuring the pH
so that it can be adJusted to pH ~ 3Ø
Record the final pH.
:, ' , '' : ' ' ., : ~ ~.
~ .I. G-1623 (F) Preyare the catalyst solution by di~solvinc~ (8) in (7) in a lined container.
(G) If the heel t~mperatur~ reached 212F or 100C
start feeding the monomer mixture (D-~) and initiator (~). Feeding should be completed in 90 minutes and reflux must be maintained. If reaction mixture cooled below boiling point and stop~ed re-fluxing both monomer and catalyst feeds must be halted until reflux is restored. Measure and record the Brookfield viscosity in every 15 mins. using the LVF 4 spindle at 95C (203F).
(H) When two-thirds of the monomer and initiator is fed into the reactor prepare the booster initiator solution by dissolving (lO) in (9) in a lined con-LS tainer that was used to prepare (F).
(I) When monomer and initiator feeding is completed ` ' start feeding the booster catalyst. Feeding should ` be completed-in 60 minutes under refluxing. When -~ completed measure and record viscosity under con-ditions described in (G).
(J) When feeding the booster catalyst is complete, main-tain reactor at reflux for an additional 3 hr. period.
` Continue measuring the viscosity in every hour.
(K) Cool resin to 100F or 40C, take a one quart sample and drum off. Measure the pH and Brookfield viscosity of the product at 250C (77F).
_9_ .l. C-lfi23 e fin-l] pro~ucL1on sllot~ ve tlle follow~ng l)roper~:ics:-~ solld = 20% + 1%
Viscosity ~ 400-800 cps. (Brookfield LVY, Splndle #4, at 30 rpm, 90C~
or 1000-2000 Cp9 (Brookfleld, Spindle #4 at 12 rpm, 25C) p~ = 4.8 to 5.4 Weight per gallon, 25C. ~ 10.75 (Imperial gallon) 8.96 (U.S. gallon) Our invention will now be more particularly described with reference to the following examples whlch constitute speciflc embodiments and are not to be construed as limi-tations thereof. Unless otherwise stated, percentages are based on the dry weight of the fibers.
~15 EXAMPLE 1 Copolymerization of Acrylamide and Maleic Acid, 95:5 mol ratio `
3.4 grams of maleic anhydride were dissolved in 50 ml of distilled water (Solution A); and 46.6 grams of purified 20 - acrylamide were dissolved in 400 grams of distilled water (Solution B). Solution (A) was added to Solution (B) to form Solution (C); the pH after mixing was 2.30. This mixture, Solution (C), was degassed and placed in a one liter, 3-necked flask equipped with a stirrer, a nitrogen .2S inlet, a thermometer, and sampling device and a reflux con-denser After nitrogen was bubbled through this mixture for 15 minutcs, and the Solution (C) was cooled to 10C, an .:
` --10--.
:`' ' - ` ~
"`
- ` ,, ~' ;~ ' ' ~ -- ' ' ' ~' . ' ~
lO~ t~
l n l l l ;I L O I III I X L ~ O 1~ I ~1 I n I n 1~ () . () l g r ;l m ~ O r ;I m m o ll l u m p ~ r -I ~ ~ c ~n (1 0 . 004 ~ r nm~: o f (N~ ) 2~()4 F h 2 ch~lr~e~l. Thc ~olutlon w~s llcld at 14 to 18~C tlll lt renched a Brook~ield vlHcosity of 65,000 (LVF Spindle ~
4, 6 rpm, at 20C) and sufflcient water WaA added to dllute the solution to about 5% solld. Addltlonal inltlator con-talning 0.1 gr~m o~ ammonlllm persulfate, and 0.04 gram of (NH4)2SO4 FeSO4 6H20) was charged. The fiolution was then heated to about 70C and held there for one hour.
The product has the followlng properties:
pH = 2.30 % solid ~ 5.21~
Viscosity ~ (Brookfield LVF 4/6 rpm, 20C) 62,000 cps.
Effec~lveness of this resin as in dry strength additive to paper remained unchanged over a pH range of 4.5 to 6.5.
Copolymerization of Acrylamide-Acrylic Acid, 90:10 Mol Ratio To a reactor similar to Example 1, 1934.0 grams of water was used as solvent, a monomer mixture containing 622.0 grams of acrylamide, 54.8 grams of acrylic acid, 168.4 grams of 10% NaOH, and 182 grams of water was allowed to react with a catalyst mixture containing 1.3 grams of ammonium per-sulfate in 198 grams of water at refluxing temperature by feeding.
The product has the following properties:
% solid: 15.8%
Brookfield Viscoslty: (LVF Spindle No. 4 at 12 rpm, 25C) 8,300 Cp8 .
.
' ,, ., ' . ~'' ' ~ R . I . C-1623 F.ffcctiv~ness of thls resln 1R A dry strenp,th addltlve to paper droppcd substantin]ly at pll hlg)lcr than about 4.5.
EX~MPLE 3 Preparation of Acrylic Acid-Acrylamide Co~olymer accor(lin~ to Canadian ratent 477,265 An acrylamide-acrylic acid copolymer was prepared accord-in8 to Canadian patent No. 477,265 and different from a feeding procedure as described in Example 2. Thus, 45.0 grams of acrylamide and 5.1 grams of acrylic acid are dis-solved in 2,450 grams of distilled water. 0.5 grams of potassium persulfate is added to the solution which is then degassed under vacuum and allowed to stand in the absence of air for 7 days at room temperature.
The product has the following propertie~:
% Solid: 2.53%
Brookfield Viscosity: (LVF Spindle No. 4 at 60 rpm 25C) 1,780 cps.
pH: 3.4 Evaluation of Dry Strength Addit_ve The effect of additive on the strength of paper can be evaluated generally according to the following procedure.
A chosen pulp, and sometimes a blend of chosen pulps, at 2S 1.6% consistency was beaten to a desired Canadian Standard Freeness. This slurry was diluted to a consistency of 0.25% and the pll was ad~usted to the desired value with N/l aqueous solution of either sulfuric acid or sod1um hydroxlde. -12-~, - ~
:
:;
rO O)~l~ lit~ r ~t~k ~ TY~ 2.n ml ~f ;l 0.625X
~ ;olut~ (l m~x~l f~r ] m~ lt~. Whil~
m~xln~, 10.0 ml of a 0.75~ nqueous sollltion of fllum wns addcd, and the pH was nd~usted to the deslred vnlue while continued the mixing for 4 more minutes. Thls ~qlurry was emptied into a Williams sheet mold previously fllled up to about 3/4 full with water and thc water was drained. The wet hands2leet while stlll resting on the screen w~s covered with a blotter (supplied by Domtnr Pulp and Paper Company and fitted Tappi specification) and then placed in a Williams sheet press for 1-2 seconds at 10-20 psl pressure.
The handsheet was removed from the press and screen; ad-hering to the blotter, and was then covered with another blotter and pressed in the Williams Sheet Press for 3 minutes at 100 psi. After pressing, the sheet together wlth the original blotter was dried in an Emerson Speed drier (model 10) for 3 minutes at 240F with the blotter side up.
The sheet was then conditioned at room temperature and about 50% humidity overnight.
:
The paper sheet was cut into 15 mm wide strips with a Thwing-Albert JDC-15 sample cutter, and tested on a Thwing-Albert Electro-Hydraulic tensile tester. Average of nine tests was reported for tensile test.
Bursting strength was tested by the use of a B. F. Perkins hand-driven Mullen Tester and an average of eighteen values was reported.
An example of a hardwood bleached sulfite pulp prepared pursuant to this invention is as follows:
T~.I. C-1623 l'urnish: Weyerhauser IIardwood Bl~ache~ Sulite C.S.F.: 560 ml Resin Level: 0.5%
Alum: 3.0 p~ of pulp Order of Addition: Resin, Alum, pH ad~ustment with dil. sulfuric acid or sodium hydroxide solution.
The following results were obtained:
Dry Tensile (lb/15mm) Resin/pH 7.0 6.0 4.5 Control (1) 3.52 3.92 3.77 Acrylamide-maleic acid (Ex. 1) 5.87 6.02 5.12 Acrylamide-acrylic acid (Ex. 2) 5.25 5.33 6.16 Mullen (psi) ; Resin/pH 7.0 6.0 4.5 :
Control 2.47 2.82 2.65 Acrylamide-maleic acid (Ex. 1) 8.42 8.56 6.64 Acrylamide-acrylic acid (Ex. 2) 5.22 5.57 8.98 ~1) Paper without the treatment with resin or alum.
The above results unequivocally illustrate the advantage which is obtained by the use of acrylamide-maleic acid copolymer in the manufacture of paper as opposed to an acrylamide-acrylic acid copolymer. The tensile strength for our resin actually increased considerably from 5.12 at _14-.: , '~.
-:
~ R.I. C--1623 pl~ .5 to 6.02 at pH of 6.0 ~nd then (~ecLined to 5.87 ~t pH of 7Ø In the acrylamide-acrylic acid copolymer, the tensile strength declined from 6.16 at pll of 4.5 to 5.33 at pH of 6.0 and further to 5.25 at pH of 7Ø The effect of the p~l on the bursting strength was even more impressive, as the above-tabulated results indicate.
EXA~PLE S
Further tests were conducted to determine burst strength and tensile strength of the resins prepared in Examples 1 and 3 as well as on paper made without any resin or alum and paper made without resin but with alum. The procedure followed and amounts of ingredients are set forth in Example 3. The results, set forth below, confirm conclusions made earlier.
Burst Strength (psi) Resin/pH 4.0 4.5 5.0 5.5 6.5 Control (1) 7.237.82 7.227.60 8.00 Alum (2) 8.538.74 9.429.82 10.78 Ex. 3 16.8214.00 13.9913.24 13.10 Ex. 1 17.5219.91 21.2618.84 18.96 Tensiie Strength (lb/15mm) Resin/pH 4.0 4.5 5 5.5 6.
Control (1) 5.605.90 5.90`5.60 5.90 Alum ~2) 6.006.10 6.306.40 6.80 Ex. 3 8.2 7.5 7.5 7.0 7.37 Ex. 1 8.519.16 9.229.10 8.83 R. I . C-1623 lt)~8~
(1) ~a~)er without the treatment with re~;in or alum (2) Paper treated with ~6 alum but no rcsin.
.:~
: '` " .
~6 _ .
' . ' ' ' . ' , ' . . : . , .
. .
,. ~ . .
.
- -. ~, ' . . :
,,; .,.
, lt)4~ . I. C-1623 l~oly.lcryl~midc--c~ c~ylic ~cid. ~low~v~r, ur.d~r our poly-mcrization conditions, the amount of carboxylic acid group~
produced by hydrolyQis ~hould be no more than about 1%.
~mount of acrylic acid used in Azorlosa copolymer i5 between 1 and 25~, pref~rably 5 to 12%, whereas amount of maleic acid used in the acrylamlde-maleic acid copolymer oP our invention is from 3 to 15%, preferably from S to 10%.
~nounts here given are based on the total weight of the monomers. Therefore, even if there were a minor amount of hydrolyzed acrylamide in the acrylamide-acrylic acid copolymer of the Azorlosa's patent, this amount would be insignificant for the purpose described herein.
The principal discovery in the Reynolds et al patent 3,269,891 relates to the use of a buffer to fix the anionic dry strength resin. As far as the anionic dry strength resin is concerned, Reynolds et al did not disclose any novel polymer other than a generalization of what has been reported in Azorlosa's Canadian patent 477,265. Reynolds et al demon-strated that the use of Azorlosa's anionic polymer fixed on the fiber with alum to confer dry strength required a care-fully controlled pH of about 4.5 and the addition of alkali to give a pH higher than 4.7-4.8 caused the strengthening effect of the resin to dlsappear abruptly. Reynolds et al's invention relates to the manufacture of paper of improved dry strength by use of an anionic polymer fixed on the fiber with alum in the presence of a buffer so that the resin re-tains its high efficiency up to a pH of about 5.5 so that accurate control of pH is no longer necessary. The buffer is a non-chelating acid having an ionization constant between _5_ ... . ~ . - . ~.
, :. :
- 1()4~
.LO 4 and 10 6 and a salt of such acid with a strong base.
Davlson patent 3,049,469 discloses a process for making paper having wet and dry strength by impregnating cellulosic fibers disposed in an aqueous suspension first with a cationic thermo-setting polyamide-epichlorohydrin resin and then with an acrylic resin. Davison's objectives are achieved without the use of alum.
In one particular aspect the present invention provides process for the manufacture of paper of improved dry strength and negligible wet strength without the use of a buffer and without a water-soluble non-thermosetting cationic resin comprising the steps of forming an aqueous suspension at pH of about 5 to 7 of paper making fibers containing a dry strength additive and a fixing agent selected from the group consisting of polyvalent metal salts and mixtures thereof, and sheeting the suspension to form the paper, the . . .
additive consists essentially of an anionic copolymer of acrylamide ` ~; and maleic acid or its anhydride in respective mol ratio of from - 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient amount to affix the copolymer to the fibers.
In another aspect the present invention provides paper com-posed of cellulose fibers and being devoid of a buffer and a water-soluble non-thermosetting cationic resin having deposited thereon a fixing agent selected from the group consisting of polyvalent metal salts and being bonded with a dry strength additive consistin~ essen-tially of an anionic copolymer of acrylamide and maleic acid or its anhydride in respective mol ratio of from 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient A ~ -6-C
mount to affix the copolymer to the fibers.
Our method for manufacturing paper of high dry strength but of low wet strength includes forming an aqueous suspension of cellu-lose papermkaing fibers and adding thereto an aqueous solution of acrylamide-maleic acid resin followed by addition of alum of another polyvalent metallic salt. ~mount of the resin used may vary from 0.1 to 2.0~ depending on the required dry strength and the type of papermaking system whereas amount of the alum used is in the range of 1 to 3~. Amount of alum less than 1% or more than 3~ generally have an adverse effect on efficiency of the dry strength resin.
Amounts are given on the basis of dry weight of the fibers. The resin and alum are used in ~ to 5~ aqueous solutions. The reagents may be added at any convenient point in the papermaking system. In practice, the resin is most advantageously added to the papermaking fibrous suspension in the beater and the alum is most advantageously added as near to the wire as possible, for example at the fan pump, sufficient time being preferably allowed in each instance for the added reagent to become uniformly distributed through the suspension before the next reagent is added.
; 20 The mol ratio of acrylamide to maleic acid in the copolymer is in the range of from 90:10 to 98:2, preferably A -6a_ jc/ ~.,.~, ~ R.I. C-1623 Y5:5. ~ e resin suita~le for ou~ pur~ose has molecular w~ ht, as repr~sented by intrinsic viscosity (measured in 0.l N NaCl solution at 25C) in the range of from 0.5 dl/g to 6.0 dl/g, preferably from l.0 dl/g to l.5 dl/g. In place of alum, other polyvalent metallic salts can be used such as aluminum chloride or aluminum nitrate.
Ou~ process has the advantage over the prior art in that a specific resin can be used in a much wider pH range of 4.5 to 6.5 than was hitherto possible which obviates the necessity for close p~i control. ~urthermore, the use of a third component such as a thermosettin~ or nonthermosetting polyamide, or the use of a buffer, is not necessary. The application of the acrylamide-maleic acid copolymer as a dry strength additive is preferably carried out by adding the polymer at a suitable point to the paper stock after completion of major refining. Sufficient alum must be added after the addition of the resin in order to fix the resin onto the fibers. ~he adjustment of pH can be made after all these additions have been completed if a certain pH value is desired. When the resin and alum is added in this preferred order, the efficiency of the resin to strengthen paper is not adversely affected by a pH change in the range of 4.5 to 6.5.
If the alum is added before the resin, efficiency of the resin will be more affected by the change of pH.
Outline of the preparation of a 95:5 mol ratio acryla-mide-maleic acid copolymer is given below:
, . . .
1~4~ R.l. C-1623 Renct.~ntfi Y. by we1~ht lA Water (heel) 43.00 A lB Sequestrene NA-22 0.01*
2 Wntér 20.00 3 Acrylamide 18.51 4 Water (at 130-140F or 55-60C) 8.27 Maleic anhydride 1.35 6 Ammonia solution 26~e 0.75 7 Water 4.80 8 Potassium Persulfate 0.06 9 Water 3.20 Potassium Persulfate 0.05 100 . OOX
*The amount of Sequestrene NA-22 used is generally less than 0.01%
and is preferably about 0.005X.
Procedure:
(A) Charge reactor with (lA) and (lB).
Set reflux to full return snd heat to reflux.
~20 (B) Prepare a solution by dissolving ~3) in (2) in a container of suitable volume.
(C) Prepare a solution by dissolving (5) in hot water (4) in a lined container.
(D) Make up the monomer mixture by adding solution (C) to solution (B).
(E) Add (6) to monomer mixture (D) in small in-crements whlle mixing and measuring the pH
so that it can be adJusted to pH ~ 3Ø
Record the final pH.
:, ' , '' : ' ' ., : ~ ~.
~ .I. G-1623 (F) Preyare the catalyst solution by di~solvinc~ (8) in (7) in a lined container.
(G) If the heel t~mperatur~ reached 212F or 100C
start feeding the monomer mixture (D-~) and initiator (~). Feeding should be completed in 90 minutes and reflux must be maintained. If reaction mixture cooled below boiling point and stop~ed re-fluxing both monomer and catalyst feeds must be halted until reflux is restored. Measure and record the Brookfield viscosity in every 15 mins. using the LVF 4 spindle at 95C (203F).
(H) When two-thirds of the monomer and initiator is fed into the reactor prepare the booster initiator solution by dissolving (lO) in (9) in a lined con-LS tainer that was used to prepare (F).
(I) When monomer and initiator feeding is completed ` ' start feeding the booster catalyst. Feeding should ` be completed-in 60 minutes under refluxing. When -~ completed measure and record viscosity under con-ditions described in (G).
(J) When feeding the booster catalyst is complete, main-tain reactor at reflux for an additional 3 hr. period.
` Continue measuring the viscosity in every hour.
(K) Cool resin to 100F or 40C, take a one quart sample and drum off. Measure the pH and Brookfield viscosity of the product at 250C (77F).
_9_ .l. C-lfi23 e fin-l] pro~ucL1on sllot~ ve tlle follow~ng l)roper~:ics:-~ solld = 20% + 1%
Viscosity ~ 400-800 cps. (Brookfield LVY, Splndle #4, at 30 rpm, 90C~
or 1000-2000 Cp9 (Brookfleld, Spindle #4 at 12 rpm, 25C) p~ = 4.8 to 5.4 Weight per gallon, 25C. ~ 10.75 (Imperial gallon) 8.96 (U.S. gallon) Our invention will now be more particularly described with reference to the following examples whlch constitute speciflc embodiments and are not to be construed as limi-tations thereof. Unless otherwise stated, percentages are based on the dry weight of the fibers.
~15 EXAMPLE 1 Copolymerization of Acrylamide and Maleic Acid, 95:5 mol ratio `
3.4 grams of maleic anhydride were dissolved in 50 ml of distilled water (Solution A); and 46.6 grams of purified 20 - acrylamide were dissolved in 400 grams of distilled water (Solution B). Solution (A) was added to Solution (B) to form Solution (C); the pH after mixing was 2.30. This mixture, Solution (C), was degassed and placed in a one liter, 3-necked flask equipped with a stirrer, a nitrogen .2S inlet, a thermometer, and sampling device and a reflux con-denser After nitrogen was bubbled through this mixture for 15 minutcs, and the Solution (C) was cooled to 10C, an .:
` --10--.
:`' ' - ` ~
"`
- ` ,, ~' ;~ ' ' ~ -- ' ' ' ~' . ' ~
lO~ t~
l n l l l ;I L O I III I X L ~ O 1~ I ~1 I n I n 1~ () . () l g r ;l m ~ O r ;I m m o ll l u m p ~ r -I ~ ~ c ~n (1 0 . 004 ~ r nm~: o f (N~ ) 2~()4 F h 2 ch~lr~e~l. Thc ~olutlon w~s llcld at 14 to 18~C tlll lt renched a Brook~ield vlHcosity of 65,000 (LVF Spindle ~
4, 6 rpm, at 20C) and sufflcient water WaA added to dllute the solution to about 5% solld. Addltlonal inltlator con-talning 0.1 gr~m o~ ammonlllm persulfate, and 0.04 gram of (NH4)2SO4 FeSO4 6H20) was charged. The fiolution was then heated to about 70C and held there for one hour.
The product has the followlng properties:
pH = 2.30 % solid ~ 5.21~
Viscosity ~ (Brookfield LVF 4/6 rpm, 20C) 62,000 cps.
Effec~lveness of this resin as in dry strength additive to paper remained unchanged over a pH range of 4.5 to 6.5.
Copolymerization of Acrylamide-Acrylic Acid, 90:10 Mol Ratio To a reactor similar to Example 1, 1934.0 grams of water was used as solvent, a monomer mixture containing 622.0 grams of acrylamide, 54.8 grams of acrylic acid, 168.4 grams of 10% NaOH, and 182 grams of water was allowed to react with a catalyst mixture containing 1.3 grams of ammonium per-sulfate in 198 grams of water at refluxing temperature by feeding.
The product has the following properties:
% solid: 15.8%
Brookfield Viscoslty: (LVF Spindle No. 4 at 12 rpm, 25C) 8,300 Cp8 .
.
' ,, ., ' . ~'' ' ~ R . I . C-1623 F.ffcctiv~ness of thls resln 1R A dry strenp,th addltlve to paper droppcd substantin]ly at pll hlg)lcr than about 4.5.
EX~MPLE 3 Preparation of Acrylic Acid-Acrylamide Co~olymer accor(lin~ to Canadian ratent 477,265 An acrylamide-acrylic acid copolymer was prepared accord-in8 to Canadian patent No. 477,265 and different from a feeding procedure as described in Example 2. Thus, 45.0 grams of acrylamide and 5.1 grams of acrylic acid are dis-solved in 2,450 grams of distilled water. 0.5 grams of potassium persulfate is added to the solution which is then degassed under vacuum and allowed to stand in the absence of air for 7 days at room temperature.
The product has the following propertie~:
% Solid: 2.53%
Brookfield Viscosity: (LVF Spindle No. 4 at 60 rpm 25C) 1,780 cps.
pH: 3.4 Evaluation of Dry Strength Addit_ve The effect of additive on the strength of paper can be evaluated generally according to the following procedure.
A chosen pulp, and sometimes a blend of chosen pulps, at 2S 1.6% consistency was beaten to a desired Canadian Standard Freeness. This slurry was diluted to a consistency of 0.25% and the pll was ad~usted to the desired value with N/l aqueous solution of either sulfuric acid or sod1um hydroxlde. -12-~, - ~
:
:;
rO O)~l~ lit~ r ~t~k ~ TY~ 2.n ml ~f ;l 0.625X
~ ;olut~ (l m~x~l f~r ] m~ lt~. Whil~
m~xln~, 10.0 ml of a 0.75~ nqueous sollltion of fllum wns addcd, and the pH was nd~usted to the deslred vnlue while continued the mixing for 4 more minutes. Thls ~qlurry was emptied into a Williams sheet mold previously fllled up to about 3/4 full with water and thc water was drained. The wet hands2leet while stlll resting on the screen w~s covered with a blotter (supplied by Domtnr Pulp and Paper Company and fitted Tappi specification) and then placed in a Williams sheet press for 1-2 seconds at 10-20 psl pressure.
The handsheet was removed from the press and screen; ad-hering to the blotter, and was then covered with another blotter and pressed in the Williams Sheet Press for 3 minutes at 100 psi. After pressing, the sheet together wlth the original blotter was dried in an Emerson Speed drier (model 10) for 3 minutes at 240F with the blotter side up.
The sheet was then conditioned at room temperature and about 50% humidity overnight.
:
The paper sheet was cut into 15 mm wide strips with a Thwing-Albert JDC-15 sample cutter, and tested on a Thwing-Albert Electro-Hydraulic tensile tester. Average of nine tests was reported for tensile test.
Bursting strength was tested by the use of a B. F. Perkins hand-driven Mullen Tester and an average of eighteen values was reported.
An example of a hardwood bleached sulfite pulp prepared pursuant to this invention is as follows:
T~.I. C-1623 l'urnish: Weyerhauser IIardwood Bl~ache~ Sulite C.S.F.: 560 ml Resin Level: 0.5%
Alum: 3.0 p~ of pulp Order of Addition: Resin, Alum, pH ad~ustment with dil. sulfuric acid or sodium hydroxide solution.
The following results were obtained:
Dry Tensile (lb/15mm) Resin/pH 7.0 6.0 4.5 Control (1) 3.52 3.92 3.77 Acrylamide-maleic acid (Ex. 1) 5.87 6.02 5.12 Acrylamide-acrylic acid (Ex. 2) 5.25 5.33 6.16 Mullen (psi) ; Resin/pH 7.0 6.0 4.5 :
Control 2.47 2.82 2.65 Acrylamide-maleic acid (Ex. 1) 8.42 8.56 6.64 Acrylamide-acrylic acid (Ex. 2) 5.22 5.57 8.98 ~1) Paper without the treatment with resin or alum.
The above results unequivocally illustrate the advantage which is obtained by the use of acrylamide-maleic acid copolymer in the manufacture of paper as opposed to an acrylamide-acrylic acid copolymer. The tensile strength for our resin actually increased considerably from 5.12 at _14-.: , '~.
-:
~ R.I. C--1623 pl~ .5 to 6.02 at pH of 6.0 ~nd then (~ecLined to 5.87 ~t pH of 7Ø In the acrylamide-acrylic acid copolymer, the tensile strength declined from 6.16 at pll of 4.5 to 5.33 at pH of 6.0 and further to 5.25 at pH of 7Ø The effect of the p~l on the bursting strength was even more impressive, as the above-tabulated results indicate.
EXA~PLE S
Further tests were conducted to determine burst strength and tensile strength of the resins prepared in Examples 1 and 3 as well as on paper made without any resin or alum and paper made without resin but with alum. The procedure followed and amounts of ingredients are set forth in Example 3. The results, set forth below, confirm conclusions made earlier.
Burst Strength (psi) Resin/pH 4.0 4.5 5.0 5.5 6.5 Control (1) 7.237.82 7.227.60 8.00 Alum (2) 8.538.74 9.429.82 10.78 Ex. 3 16.8214.00 13.9913.24 13.10 Ex. 1 17.5219.91 21.2618.84 18.96 Tensiie Strength (lb/15mm) Resin/pH 4.0 4.5 5 5.5 6.
Control (1) 5.605.90 5.90`5.60 5.90 Alum ~2) 6.006.10 6.306.40 6.80 Ex. 3 8.2 7.5 7.5 7.0 7.37 Ex. 1 8.519.16 9.229.10 8.83 R. I . C-1623 lt)~8~
(1) ~a~)er without the treatment with re~;in or alum (2) Paper treated with ~6 alum but no rcsin.
.:~
: '` " .
~6 _ .
' . ' ' ' . ' , ' . . : . , .
. .
,. ~ . .
.
- -. ~, ' . . :
,,; .,.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for the manufacture of paper of improved dry strength and negligible wet strength without the use of a buffer and without a water-soluble non-thermosetting cationic resin comprising the steps of forming an aqueous suspension at pH of about 5 to 7 of paper making fibers containing a dry strength additive and a fixing agent selected from the group consisting of polyvalent metal salts and mixtures thereof, and sheeting the suspension to form the paper, the additive consists essentially of an anionic copolymer of acrylamide and maleic acid or its anhydride in respective mol ratio of from 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient amount to affix the copolymer to the fibers.
2. Process of Claim 1 including the step of first adding the copolymer to the suspension with mixing followed by the step of adding the salt which is selected from the group con-sisting essentially of alum, aluminum chloride, aluminum nitrate and mixtures thereof; amount of the copolymer being from 0.1 to 2% and amount of the salt being from 1 to 3%, both amounts are based on the weight of dry fibers.
3. Process of Claim 2 wherein the salt is alum, the copolymer has an intrinsic viscosity of from 0.5 to 6 dl/g measured in a 0.1N NaCl solution at 25°C and the suspension has a pH in the range of up to 6.5.
4. Process of Claim 3 wherein the copolymer and the salt are in 0.5 to 5% solids aqueous solutions when added to the suspension, the copolymer solution being acidic.
5. Process of Claim 2 wherein mol ratio of acryla-mide to maleic acid or its anhydride in the copolymer is about 95:5.
6. Process of Claim 2 wherein pH of the suspension is in the range of up to 6.5.
7. Paper composed of cellulose fibers and being devoid of a buffer and a water-soluble non-thermosetting cationic resin having deposited thereon a fixing agent selected from the group consisting of polyvalent metal salts and being bonded with a dry strength additive consisting essentially of an anionic copolymer of acrylamide and maleic acid or its anhydride in re-spective mol ratio of from 90:10 to 98:2 which is used in sufficient amount to impart to the paper improved dry strength and negligible wet strength whereas the salt is used in sufficient amount to affix the copolymer to the fibers.
8. Paper of Claim 7 wherein the salt is selected from the group consisting of alum, aluminum chloride, aluminum nitrate and mixtures thereof, amount of the copolymer is from 0.1 to 2% and amount of the salt is from 1 to 3%, both amounts being based on the weight of dry fibers.
9. Paper of Claim 8 wherein the salt is alum and the copolymer has an intrinsic viscosity of from 0.5 to 6 dl/g measured in a 0.1 N NaCl solution at 25°C.
10. Paper of Claim 9 wherein mol ratio of acrylamide to maleic acid or its anhydride is about 95:5.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA213,060A CA1044858A (en) | 1974-11-05 | 1974-11-05 | Dry strength paper and process therefor |
| GB972776A GB1540133A (en) | 1974-11-05 | 1976-03-11 | Dry strength paper and process therefor |
| FR7611587A FR2348999A1 (en) | 1974-11-05 | 1976-04-20 | PAPER RESISTANT TO DRY STATE AND PROCESS FOR ITS PREPARATION |
| US05/683,581 US4088530A (en) | 1974-11-05 | 1976-05-06 | Dry strength paper and process therefor |
| AU19326/76A AU502378B2 (en) | 1974-11-05 | 1976-11-05 | Dry strength paper |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA213,060A CA1044858A (en) | 1974-11-05 | 1974-11-05 | Dry strength paper and process therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044858A true CA1044858A (en) | 1978-12-26 |
Family
ID=4101543
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA213,060A Expired CA1044858A (en) | 1974-11-05 | 1974-11-05 | Dry strength paper and process therefor |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU502378B2 (en) |
| CA (1) | CA1044858A (en) |
| FR (1) | FR2348999A1 (en) |
| GB (1) | GB1540133A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5049235A (en) * | 1989-12-28 | 1991-09-17 | The Procter & Gamble Company | Poly(methyl vinyl ether-co-maleate) and polyol modified cellulostic fiber |
| 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 |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA826107A (en) * | 1969-10-28 | J. Jursich Myron | Papermaking process |
-
1974
- 1974-11-05 CA CA213,060A patent/CA1044858A/en not_active Expired
-
1976
- 1976-03-11 GB GB972776A patent/GB1540133A/en not_active Expired
- 1976-04-20 FR FR7611587A patent/FR2348999A1/en active Granted
- 1976-11-05 AU AU19326/76A patent/AU502378B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU502378B2 (en) | 1979-07-26 |
| AU1932676A (en) | 1978-05-11 |
| FR2348999B1 (en) | 1983-12-09 |
| GB1540133A (en) | 1979-02-07 |
| FR2348999A1 (en) | 1977-11-18 |
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