CA1090511A

CA1090511A - Method for controlling canadian standard freeness in fiber slurry beater addition

Info

Publication number: CA1090511A
Application number: CA251,067A
Authority: CA
Inventors: Vincent M. Rasicci; Paul A. Clotz
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1975-05-02
Filing date: 1976-04-26
Publication date: 1980-12-02
Also published as: NL7604592A; FR2350423A1; BE841583A; DE2619310A1; JPS51136905A; FI761279A; FR2350423B1

Abstract

METHOD FOR CONTROLLING CANADIAN
STANDARD FREENESS IN FIBER
SLURRY BEATER ADDITION

ABSTRACT OF THE DISCLOSURE
In the preparation of beater saturated fiber sheet materials in which polymers in latex form are incorporated into water dispersions of the fibers and deposited thereon, the Canadian standard freeness is readily controlled by adding to the fiber furnish, before addition of the polymer latex, a small amount of a water soluble anionic polymer or water-soluble salt thereof.

Description

1~90511 This invention relates to the preparation of fiber sheets.
Polymeric latexes have been used for years in making improved fiber sheet materials, more recently and efficiently by incorporating the polymers onto the fibers by the so-called wet-end or beater addition that includes methods of incorpor-ating polymeric latex into, and deposition of polymers there-on, beaten pulp or fibers in water before sheet formation. In many processes the polymer latex is added to the fiber slurry and then precipitated or coagulated. With many fibers includ-ing paper making fibers and other non-woven making fibers including synthetic polymeric fibers, a coagulating agent is j required. However, with asbestos fibers, normally no coagu-lant is required. One well known method used in the beater addition industry is described in U.S. Patent 2,759,813 and is based on use of sodium citrate and sodium lignosulfonate solutions. In U.S. Patent 3,748,223 there i8 described an improved method for incorporating latex polymer into fibers in water dispersions by using in the polymer latex an anionic water soluble polymer such as polyacrylic acid. The objective in this patent was to improve deposition of polymers in the fibers. In all of these processes, control of the Canadian standard freenes~ is important and improvements as to this variable are desired.
In accordance with this invention the Canadian standard freeness, particularly with asbestos fiber finish, is easily controlled by adding to the fiber furnish prior to adding the polymer latex, a small amount of an anionic water-soluble polymer and thereafter adding the polymer latex.
According to the invention there is provided in the process for preparing fiber sheets having polymer latex particles deposited on the fibers wherein synthetic polymeric ~, B' 1 ~
;

latice~ are added to fiber slurrie~ or dispersion by the wet-end addition before formation of a sheet therefrom by coagulation, the improvement comprising adding to said di~persion, before adding said polymeric latex, greater than 0.01 to less than 5 parts per 100 weight part~ of fiber of an anionic water-soluble hydrophilic polymer having a molecular weight greater than about 1000.
By mean-~ of this improvement, the Canadian ~tandard freenes~ can be controlled linearly in a range of Canadian ~tandard freene~s value~ from about 800 down to about 200 or les~ with de~irable ,

-2 _ . .:

~(~9OSll drainage rates. The process is applicable to any latex used in fiber beater addition applications.
DETAILED DESCRIrrlON
-In the practice of the invention the improvement is read~ly obtained by first preparing the fiber water blend in a beater or refiner to break down the fiber bundles, diluting the furnish to the requlred consistency, adding the anionic water soluble polymer, adding the latex binder and forming the sheet.
The fibers are prepared in accordance with the usual beater saturation technique and the fibers will be taken up in water 80 as to form a slurry having about 0.5 to 3% consis-tency, more preferably about 1.5 to 2.5%. In the case of asbestos the fibers are placed in a beater to break up the fiber bundles as well as to decrea~e the size and this may also be done with a rerlner. Fibers treated ln accordance with the invention include, for example, a~bestos ribers and cellulo_ic fibers, including wood fiber, rag fiber, polyacrylo-nitrile fibersl pQlyester, viscose fibers, nylon J cotton, Kraft and sulfite and the like normally used to make paper or felted products. As has been stated, in the case of asbestos fibers normally no additional precipitation or coagulation agent is required to be added after the latex binder has been added to the furnish. However, it may be necessary to add alum to other fiber slurries after adding the anionic water Roluble polymer and latex binder. ~he invention is of parti-cular utillty ln controlling the Canadian freeness of treated asbestos dispersions.
The lncorporation Or synthetic polymer latices into fibrous slurries or dispersions be~ore formatlon of a sheet therefrom i6 by wet-end or beater addition. This technique is used to incorporate in the fiber sheet from less than 1 to more than 50% polymer content, depend~ng on the end use of the sheet. Controlled deposition of the latex particles is obtained by the addition of a coagulant such as papermaker~s alum in water solution to most fibers other than asbestos.
This improvement, use of anionic, water-soluble, hydrophilic po}ymers as polyacrylic acid, can be applied to a variety of techniques lncluding direct addition, the inverted method, the Armstrong method, continuous addltion, and the like.
In direct addition, for example, after the flurnish has been beaten to the desired degree of freeness, the pH of the pulp furnish may be ad~usted to between 8.5 and 9.0 with alkali if an alkaline latex is to be added. The latex is ~added to the pulp furnish and is dispersed by operating the beater. The latex may be diluted before addition. After the latex has been dispersed, a 1 to 10% solution of a coagulant, for example, alum, is added to coagulate the latex polymor which is deposited on the fibers. In the case of asbestos pulp, however, alum i8 not required. In the inverted method the furnish 18 beaten to the desired freeness, the p~ is re-duced to 4.5 using alum and dilute latex is added thereto.
The Armstrong method is described in U.S. patents 2,375,245 and 2,613,190. In tho continuous method the furni~h is pre-pared, the pH reduced to 4.5 with alum and the latex is added after the ~urnish lea~es the beater. It i8 understood by tho&e skilled in the art that in commerclal methods Or latex wet-end addition, the latex is normally added as dilute as possible at a point o~ maximum agitation, in the range of about 10 to 60~ total solids. In each case the anionic poly-mer is added prior to the latex addition.
This invention may be applied to sny synthetic poly-mer latex used in wet-end addition to flbrous slurries, and improvement will be obtained thereby both in the process and resulting sheet product, particularly in more camplete deposi-tion and clear serum. These include vinylidene monomers con-taining at least one C~' group as vinyl ch~oride, styrene, vinyl acetate, vinylidene chloride, acrylic ester, con~ugated diene and like polymer and copolymer latices, as is well known in the art, particularly latices of elastomeric polymers. Such latices include, for example, latices of alkyl acrylate poly-mers and copolymers, polychloroprene, copolymers of butadiene and acrylonitrile, butadiene and methyl methacrylate, butadiene and vinylldene chloride, butadiene and styrene, vinyl chloride polymer latices including copolymers of vinyl chloride and 5 to 40 parts Or copolymerized alkyl acrylates and the like.
Typical useful latices are describea in "Synthetic Rubber", Whitby, 1954 and "Poly~er P;rocesses", Schildknecht, 1956.
This invention is particularly adapted to use of latices containing polymers of butadiene or alkyl acrylates and copolymers thereo~. AlXyl acrylate polymers are valuable ln provlding lmproved *lbrous artlcles containing the alkyl acrylate polymers dispersed thereon. Since some alkyl acry-lates have some water solubility, polymerization thereo* to form laticeæ may be conducted in the preæence Or minimum amounts of surrace active agents. More dif*iculty has been experienced in adequately deposlting low surrace active-containing or nonionic emulsirier-containing latices on fibrous materials in aqueous suspenslon than with latices containing larger amounts of ionic sur*ace active agents. Such polymers include homo-and copolymers o~ alkyl acrylates wherein the alkyl groups of ssters of acrylic acid contain ~rom 1 to 8 carbon ~toms. Im-proved polymer latlces are prepared *rom copolymers of alkyl acrylates and butadlene with vinylidene moncoe rs contalning terminal CH2C gFoups; including particl~larly, monomers such as styrene, a-methyl styrene, acrylonitrile, mothacrylonitrile, 1~90511 ethyl methacrylate, butyl methacrylate, methyl ethacrylate, acrylic acid, itaconic acid, vinyl chloride, vinylidene chlor-ide, vi~yl acetate and the like. Such polymers may also in-clude cure sites generally supplied by chlorine-containing monomeræ as vinyl chloroacetate, chloropropyl acrylate, chloroethyl vinyl ether, vinyl benzyl chloride and other known comonomeræ.
Excellent results are obtained with latices of buta-diene alkyl acrylates containing reactive monomers, for exam-ple, acrylamide and methacrylamide, t-butyl acrylamide, octyl acrylamide and diacetone acrylamide, N-alkylol amideæ as N-methylol acrylamide and N-methylol methacrylamide, N-alkoxy-alkyl acrylamldes includlng for example, N-ethoxy methacryl-amide and N-butoxy methacrylamide, a,~-unsaturated carboxylic acids containlng 3 to 8 carbon atQms including, ror example, acrylic acid and methacrylic acld, dicarboxylic acids as itaconlc acid, and the llke. Normally, at least about 0.2~
of the~e camonomer~ are used. Useful are copolymers of ethyl, methyl and butyl acrylate containing about one part each Or at least tWQ such cQmonomers ~or example, N-butoxymethyl acryl-amide and acrylamide, N-methylol acrylamide and acrylamide, N-methylol acrylamido and methacrylamide, N-methylol acrylamide and acrylic acld and the like. m e total of such monQmers normally being less than about 10% of the copolymer.
The anlonic polymers include polyacrylic acids hav-ing molecular weights greater than about 1,000, as ~pO0, and as high as about 3,000,000. Polymers of average numbor mole-cular weights of about 5,000 to 300,000 normally wlll be used.
The polyacrylic acld is used in amounts from 0.035 to 1.0 part per 100 parts o~ ~ibers. Usually no more than about 1 w~lght part per 100 weight parts of ~iber i~ required but larger amounts a~ 3 to 5 parts may be usod. Excellent results have 1C~90 5 11 been obtained when the concentration is about 0.1 - 0.5 part.
While amounts as low as 0.001 to 0.01 show improved results, larger amounts as 0.03 and higher usually provide better results both in the process and resultlng product. Other poly-meric ~ acids may be used so long as they are water-soluble including, for example, polymethacrylic acid, polyitaconic acid and the like. Copolymers of such acids also may be used so long as the copolymer is water soluble. These polymers may contain other vinylidene monomers containing at least one terminal CH2'~ group copolymerized therewith so long as the copolymer or the salt thereof is water soluble. &ch materials contain greater than 60 weight percent acid and less than 40 weight percent other copolymerizable monomers as monovinylidene materlals as alkyl acrylates and the like. Alkali metal water-soluble salts as sodium polyacrylate may be used and ammonium polyacrylate.
The coagulants, if used, in addition to the pre-ferred alum, include water-soluble polyvalent metal salts used in the art such as potasslum sulfate, magnesium sulfate and the like.
The Canadian standard freeness value is a measure of the ease with which water passes through fibers whlle they are being formed into a wet mat on a perforated plate. The Canadian Standard Freeness Tester consists of an upper con-tainer of l liter capacity which holds the fiber-water slurry, a perforated plate at the bottom, a bottom cover, a hinged top and a petcock for air admission. When the bottom cover i~
dropped and the petcock is opened, the water draining from the fibers in the upper container drops into a funnel type recep-tacle with an overflow outlet in the side and flows through a standard orifice in the bottom. If the water drains into the funnel from the ribers at a rate greater than can be handled ~090511 by the standard outlet, the excess flows through the overflow tube and is collected ~n a graduated cylinder. The volume of this overflow meaeured in milliliters is known as the Canadian standard freeness value.
EXAMPLE I
To demonstrate the practice of the invention, asbes-tos fibers and water were blended in a beater and diluted to a furnish consistency of 2~. Varying amounts of 0.5~ water solution of sodium polyacrylate having a molecular weight of about 180,000 to 220,000 was added to the furnish. A polymer latex diluted to a conce~tratlon of 20% of a copolymer o~ about 33~ acrylonitrile and 67~ butadlene was then added to the ~urnish. The concentration of polymer in the latex on a dry basis normally will be varled from about 10 to 30%, more pre-~erably 15 to 25~. The amount of sodium polyacrylate, prec~pl-tation time, Canadlan standard freeness, drain and sheet thickness, den~ity, dry tensile and amount Or ~odium polyacry-late are set forth ~n data table I.

~ ~o h h o~I ~) ~
~o~,~ o :~ ~ ~ O ~I ~I N N t--O~ ~IC~
O 0 ,Q000000 oo~l~iNN
~t'O~ ~.
1 0 ~

~1 O O O 0 00 0 ~æ~ou~
ul . i-1~5 N ~t~) ~1~ ~N ~I N
~; ~ ~1 ~ CU N N N ~1~1 ~I C~ l N
h E~
~ ~$
O U~ ~ O
~n o~ ...... .... I
O ~ ID 0~0~0~-- o~0aD~a) ~0~ ~D~O~O~O~O~O

¢
~A ~J ~ 0 ~1 N ~ ~i ~i ~i ~i N ~i ~J r~ ~1 O
H N ~ ~ ~r)~r) ~) ~n ~ ~) t~) ~ t~) ~ O . ~..
a3 _ .,~ ~ . ~0 InN O~OD O ~D ~ ll~tr~ 0~ ~1 ~0 CD O~N ~
.,1 E~ .

g~ ~ ~ o ~i~N ~æ oa~ O ~ 0~ ~ -CJ~ 11~ N N ~D~O~D t~t~ ~ t--1 Q~-~.rl~l l l l b ~EI~NNCUNN ~) p C~ ¦~ ~I N ~ ~1 ~I CU ~ ~ N
.
~a I ~ O
oo ~1 ~ O h ~ O ~ C V~ :~
~ ~0 ~ ~ U~ ~ , ID
~ ~ ~ " 8 h o t~ 9~ ~ t . o . o o o ~1 A
~ A ~ O P~ Q ~ ~1 : ~
..

<D N
b 3i~ o ~
~ ~ ~;

1C~D5 1 ~
It is obvious that in accordance with the improved process of this invention, that without sacrificing drain time at the same freeness, good freeness control is obtained st a decreased cost compared to other systems used in this process.
Important from an environmental standpoint, the sodium poly-acrylate is removed from the water with the ribers, whereas with the salts as sodlum citrate and diammonium ethylene-diamlne tetraacetic acid, these materials remain in the water and present a disposal problem. One disadvanta~e to the salts remaining ln the water 18 if, as ln many paper blends, the water must be recycled, such salt as sodium cltrate will cause a drlft ln productlon rreeness control. When thl~ Example was repeated with a latex of a copolymer of a ma~or proportion Or n-butyl acrylate and about equal parts of acrylonltrlle, acrylamide and N-methylol acrylamide9 with an inltlal Canadian standard ~reeness of 750, ~ith the sodlum polyacrylate of the Example I, a C~F range of 750 to 160 was obtalned.
EXAMPLE II
To demonstrate the advantages in adding the sodium polyacrylate to the furnish and then addlng the polymer latex, rather than adding the sodlum polyacrylate in the latex, two experiment~ were run. In the flrst experiment the sodlum poly-acrylate in amount of 0.5~ was added to the furni~h and then the latex of Example I and the Canadian standard ~reeness determined against the m~llillters as 0.5~ sodlum polyacrylate.
For comparlson, the equlvalent amount of sodlum polyacrylate was added to the same latex as in Example I, and the Canadlan standard freeness determined. The data are as rollows:

109(~511 Vol CFS
c c Sodium polyacrylate 0 780 added to rurnlsh 15 560 ~o 290 Sod~um polyacrylate 0 780 added in latex 15 600 : 10 20 480 EXAMPLE III
: Another series of demonstration runs with asbestos ~iber dispersions ~ollowing the procedure of ExampleI, and using a polymer latex containing a copolymer of 67~ butadiene, 33% acrylonitrile, this latex had a Canadian standard free-ness value, when run without the polymeric polyacrylic acld, of 780. As in Example I, 20~ polymer binder add on was used.
In the table following there i8 shown the nature of the poly-acrylic acid, whether it is the free acid or salt, and the molecular weight. In the table also are shown the volumes o~ 0.5% solution, the polyacrylic acid in water used, the precipitation time in minutes, the Canadian standard freeness (CSF) value and drain time in seconds.
Precipi-tation Drain - cc time CSF time (PA) minutes ml seconds Polyacrylic acid o 2 780 6 Molecular weight 10 2 590 19 80,000-110,000 15 2 410 2 Potassium salt o~ 0 2 780 6 80,000-110,000 10 2 580 16 molecular weight 15 2 400 32 - polyacrylic acid 20 2 270 59 Polyacrylic acid with 0 2 780 6 about 5,000 10 2 540 21 molecular weight 15 2 440 31 Preeipi-tation Drain cc time CSF time (PA) minutes ml seeonds Potassium salt of 0 2 780 6 5,000 molecular 10 2 640 12 weight polyacrylic 15 2 ~50 19 acid 20 2 400 33 - Polyacrylic acid 0 2 780 6 Moleeular weight 10 2 640 12 220,000-250,000 15 2 ~50 19

3 2 310 55 Potassium salt of 0 2 780 6 220,000-250,000 10 2 640 14 molecular weight 15 2 530 20 . polyaerylie aeid 20 2 360 42 Further tests were run with 0.25 weight péreent polyaerylie aeid and the potassium salt thereor.
The re~ults are shown below:
Polyaerylie aeld 0 2-1/2 780 6 Moleeular weight 10 2-1/2 720 9 about 5,000 15 2 650 12 Potassium salt of 0 2-1/2 780 6 5,000 molecular 10 2-1~2 690 12 weight polyacrylie. 15 2 610 15 acid 20 2 560 19 Other advantage~ aecruing to the novel proeess ln aecordanee with thls invention, as eompared to the known use of polyaeryllc aeid ln latex, i8 that with some latlee6, particularly those using ~atty aeld or rosin aeld-based emul-sifiers, may present stablllty problems when polyaerylie aeid or sodium polyaerylate are added thereto, and speeial preeau-tions may have to be taken to prevent 1088 Or polymer by form-ation of eoagulum. Thls problem 18 eliminated by adding thepolyaerylle ae~d or salt thereof to the furnish berore addl-tlon of the latex.

1~90511 A further advantage of this invention is the flexi-bility one has as compared to addition of the anionic control agent in the latex. This being a loæs of flexibillty. For example, only one gauge or density type of sheet could be made from a latex containing a given amount of the anionic addi-tive; and thus, to obtain different gauge sheets each latex has to be compounded separately. In accordance with this inven-tion t~e Canadian freeness related to the gauge or density of the deslred sheet is readily obt&ined by varying the addition of the polyacrylic acid or salt thereof to the furnish, so that the same latex may be used regardless of the gauge sheet desired. In any event, it will be understood that once the polymer is deposited on the fiber particles, a sheet of the coated flber i8 then readily formed on conventional paper making equipment such a8 a cylinder machine or Fourdrinier wire.
As has been noted, the invention is of particular - utility with asbestos rurnish where problems have been previ-ously observed in treating such materials with polymer latices because of the presence ln the rurnish of substantial amounts of metal ions. The art has tried many techniques to meet this problem a6 it relates to control Or the Canadian standard freeness. In comparison to these processes, the process of the present inventlon provides superior freeness control as shown by the examples and greater rlexibility as to choice o~
binders. A particular adYantage is that the polyacid or alkali metal salt thereo~ are all that is reguired, no other addi-tional ingred1ents being necessary. It was surprising to ~ind that a combination Or sodium polyacrylate and ethylenediamine tetraacetic acid was c pletely unsatisractory. For example, a 5% solution did not drop the Canadian standard freeness below 500 cc.

lC~90 5 11 Fiber sheet formed in accordance with this invention with the above latex composition have good appearance and drainage rate, there ls no sticking to screen or felt; the dry sheets have good tensile strength. Tho unusually wide Canadian freeness range of CFS of from about 800 to 200 in a single latex with desirable drainage rates is readlly obtained when the latex used demonstrates a CSF value greater than about 600 in the absence of the anionic additive.

.

- 14 _

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the process for preparing fiber sheets having polymer latex particles deposited on the fibers wherein syn-thetic polymeric latices are added to fiber slurries or dis-persion by the wet-end addition before formation of a sheet therefrom by coagulation, the improvement comprising adding to said dispersion, before adding said polymeric latex, greater than 0.01 to less than 5 parts per 100 weight parts of fiber of an anionic water-soluble hydrophilic polymer having a molecular weight greater than about 1000.

2. The process of claim 1, wherein said anionic water-soluble hydrophilic polymer is added in amounts from about 0.05 to less than 1 weight part and the anionic polymer is selected from the group consisting of water-soluble polymers of acrylic acid, methacrylic acid, itaconic acid and water-soluble salts thereof.

3. The process of claim 2, wherein the anionic polymer is polyacrylic acid or an ammonium or alkali metal salt thereof having a molecular weight in the range of about 2,000 to 300,000 present in amount from about 0.035 to 1 weight part per 100 weight parts of fiber.

4. The process of claim 3, wherein said fiber slurry is an asbestos fiber slurry.

5. The process of claim 4, wherein the latex con-tains a butadiene polymer.

6. The process of claim 5, wherein the polymer is a copolymer of butadiene-acrylonitrile.

7. The process of claim 5, wherein the polymer is a copolymer of butadiene-styrene.

8. The process of claim 4, wherein the latex con-tains a polymer of an alkyl acrylate.

9. The process of claim 4, wherein the anionic poly-mer is sodium polyacrylate.

10. The process of claim 8, wherein the alkyl acrylate is ethyl acrylate.

11. The process of claim 4, wherein the latex con-tains a polymer of vinyl chloride.