CA1048321A - Dense paper and method of manufacturing - Google Patents
Dense paper and method of manufacturingInfo
- Publication number
- CA1048321A CA1048321A CA76256508A CA256508A CA1048321A CA 1048321 A CA1048321 A CA 1048321A CA 76256508 A CA76256508 A CA 76256508A CA 256508 A CA256508 A CA 256508A CA 1048321 A CA1048321 A CA 1048321A
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- web
- weight
- impregnant
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Abstract
DENSE PAPER AND METHOD OF MANUFACTURING
Abstract of the Disclosure:
A dense paper comprising a web of cellulosic fibers and an impregnant dispersed throughout the web, the impregnant consisting essentially of a blend of a rigid polymeric material and an inorganic filler, in stated proportions, with the im-pregnant constituting a minor portion of the finished weight of the paper. A process for producing the paper is disclosed.
Abstract of the Disclosure:
A dense paper comprising a web of cellulosic fibers and an impregnant dispersed throughout the web, the impregnant consisting essentially of a blend of a rigid polymeric material and an inorganic filler, in stated proportions, with the im-pregnant constituting a minor portion of the finished weight of the paper. A process for producing the paper is disclosed.
Description
3~2~
Back~round of the Invention Papers of different densities have been provlded forvarious purposes. Low density paper~ are soft and porous and have high absorbency unless treated to reduce ab~orbency.
Medium density papers lnclude papers utilized for writing, printing and wrapping purposes as well as bags and linerboards.
Examples of high density papers include: gl~ssine paper, grease-proof paper, vege~able parchmen~ paper, vulcanized fiber paper and super-calendered paper.
An example of a dense writing psper is disclo~ed in my U.S. Patent No. 3,839,144. Al~hough that paper is dense and possesses excellent oil barrier properties, i.e. era~ability, ~ ;
among other properties, it has certain limitations For in-stance, the paper is not inexpensive to produce because it is manufactured from a furnish which is provided by heavily re-fining p~lp to a predetermined Schopper-Riegler freeness and adding certain quantities of unrefined pulp thereto, or by combining alpha or cot~on pulps wl~h ordinary pulps and heav~
ily reflning the combined pulp~, prlor to the applic~tion of the furnish to the screen of a paperm~king machlne. It has been found that w~ter drains relatively 810wly from such heav-ily-refined furni~hes 80 that it is v~ry diffieult to manufac-ture the desired dense paper at high machine speeds. Hence, it is more expensive to prvduce than o~her papers. Moreovex, there ls n limit on the maximum thick~ess of such a paper, and the necesslty o~ heavily refinlng the pulp al~o increases the manufacturln8 C08t of the paper.
Dense papers have certain deslrable properties, .,. , ., ~, .
including high ten3ile and burst (Mullen) strength~, improved folding endurance, improved lnterfiber bonding and delamination reslst3nce, solvent and oil penetration resistance, and good abra~ion resistance and rlgidity. On the o~her hand, dense papers have low tear strengths, brittleness, poor dlmenslonal stability and aging qualities and high manufacturing eostsO
For in~tance, vegetable parchment papers and paper~ manuf~c-tured by the so-called vulcanized fiber processes, although dense, have relatively low tear streng~h3, as do dense papers manu3ctured by super-calendering webs of medium density.
De~crip~ion of the Prlor Art In the papermaking art, papers of relatively low ~ -densities have been impregnated with polymeric resins. Such paper8, however~ usually have pre-impregnation denslties, ex~
pressed as the weight per mil of ~hickness (based on 500 sheets 24" x 36") of 6-7 lbs/mil and even as low as 5 lbs/mil. After impr~gnation, the paper~ are still relatively porous, even though the amount of resin impregnated m~y exceed 50% of the weight of the paper on a dry solids basic. Because of its ~:
porosity and low density, such a paper is not suitable for use a~ an erasable typing paper nor does it have solvent hol~-out propertie~.
The polymeric resins which h3ve been used a~ coat-ings and impregnants for low density papers have been relatively soft and elastic in nature, as distinguished from hard and inelastic polymeric re~in~. The Thermal Glass Transition Temperature (Tg) is a measure of the rigidity, or film stiff-ness of a polymeric resin. Thi~ is the ~emperature which cor-.; .
~ 3re~ponds to the temperature at which the resin forms a con-~inuous film. For instance, the gla~s ~r3nsi~ion temperature of relatively ~ot and elastic polymeric resin~ i8 le~s than about 0C. Rigid or stiff and inelastic polymers, on the other hand, have gla5s transition temperatures in excess of about 15C.
Pfipers of 8 lb~/mil or greater h~ve been impregnated with rigid polymeric m~teri~l~ and have been found to pos 3e~8 certain desirable characteristics. For instance, such papers have improved tensile and burst strength~, abra~ion resistance, re~istance to delamlnation, solvent and ~rease penetration resistance, and good fold endurance. On the other hand, such papers have certain undesirable characteri6tics which m~ke them unsuitable for use a~ typing papers or in application~
where den~e papers are de~ired. Such undesirable char~cter-istics include reduced tear ~trength, poor writing qualities, and increased brittlenes~. Since dense paper webs do not accept as much impregnant as porous paper webs, it is generally believed that incre~es in the physical properties of a paper due to impregnation may be realized only when ~he web is por-ou~ and the resin content of the fini~hed paper exceed~ about 5~h of its weight.
Te6ts have shown that the density of a p~per web prior to impregnation and the amount of resin impregnated in the web affect the reduction of tear strength which ~ccompan-ies impregnation of a paper with fl rigid polymer. For example, sheets of ba6e papers having various initial densities were impregn~ted with an aqueous disper~ion of ~ rigid homopolymer .. ..
.
32~polyvinyl acetate resin (PVAC) sold under the trade designa-tion VINAC 880 by Alr Products and Chemical Co. of Allentown, Pa, The dispersion contained 40% by weight of VINAC 880.
Impregnation was effected by dipping the sheets into the aque-ous dispersion and ~hen passing the sheets through squeeze rollers to remove excess impregnant. The sheets were dried for 4 minu~es each in a Williams pap~er sheet dryer at 220F.,
Back~round of the Invention Papers of different densities have been provlded forvarious purposes. Low density paper~ are soft and porous and have high absorbency unless treated to reduce ab~orbency.
Medium density papers lnclude papers utilized for writing, printing and wrapping purposes as well as bags and linerboards.
Examples of high density papers include: gl~ssine paper, grease-proof paper, vege~able parchmen~ paper, vulcanized fiber paper and super-calendered paper.
An example of a dense writing psper is disclo~ed in my U.S. Patent No. 3,839,144. Al~hough that paper is dense and possesses excellent oil barrier properties, i.e. era~ability, ~ ;
among other properties, it has certain limitations For in-stance, the paper is not inexpensive to produce because it is manufactured from a furnish which is provided by heavily re-fining p~lp to a predetermined Schopper-Riegler freeness and adding certain quantities of unrefined pulp thereto, or by combining alpha or cot~on pulps wl~h ordinary pulps and heav~
ily reflning the combined pulp~, prlor to the applic~tion of the furnish to the screen of a paperm~king machlne. It has been found that w~ter drains relatively 810wly from such heav-ily-refined furni~hes 80 that it is v~ry diffieult to manufac-ture the desired dense paper at high machine speeds. Hence, it is more expensive to prvduce than o~her papers. Moreovex, there ls n limit on the maximum thick~ess of such a paper, and the necesslty o~ heavily refinlng the pulp al~o increases the manufacturln8 C08t of the paper.
Dense papers have certain deslrable properties, .,. , ., ~, .
including high ten3ile and burst (Mullen) strength~, improved folding endurance, improved lnterfiber bonding and delamination reslst3nce, solvent and oil penetration resistance, and good abra~ion resistance and rlgidity. On the o~her hand, dense papers have low tear strengths, brittleness, poor dlmenslonal stability and aging qualities and high manufacturing eostsO
For in~tance, vegetable parchment papers and paper~ manuf~c-tured by the so-called vulcanized fiber processes, although dense, have relatively low tear streng~h3, as do dense papers manu3ctured by super-calendering webs of medium density.
De~crip~ion of the Prlor Art In the papermaking art, papers of relatively low ~ -densities have been impregnated with polymeric resins. Such paper8, however~ usually have pre-impregnation denslties, ex~
pressed as the weight per mil of ~hickness (based on 500 sheets 24" x 36") of 6-7 lbs/mil and even as low as 5 lbs/mil. After impr~gnation, the paper~ are still relatively porous, even though the amount of resin impregnated m~y exceed 50% of the weight of the paper on a dry solids basic. Because of its ~:
porosity and low density, such a paper is not suitable for use a~ an erasable typing paper nor does it have solvent hol~-out propertie~.
The polymeric resins which h3ve been used a~ coat-ings and impregnants for low density papers have been relatively soft and elastic in nature, as distinguished from hard and inelastic polymeric re~in~. The Thermal Glass Transition Temperature (Tg) is a measure of the rigidity, or film stiff-ness of a polymeric resin. Thi~ is the ~emperature which cor-.; .
~ 3re~ponds to the temperature at which the resin forms a con-~inuous film. For instance, the gla~s ~r3nsi~ion temperature of relatively ~ot and elastic polymeric resin~ i8 le~s than about 0C. Rigid or stiff and inelastic polymers, on the other hand, have gla5s transition temperatures in excess of about 15C.
Pfipers of 8 lb~/mil or greater h~ve been impregnated with rigid polymeric m~teri~l~ and have been found to pos 3e~8 certain desirable characteristics. For instance, such papers have improved tensile and burst strength~, abra~ion resistance, re~istance to delamlnation, solvent and ~rease penetration resistance, and good fold endurance. On the other hand, such papers have certain undesirable characteri6tics which m~ke them unsuitable for use a~ typing papers or in application~
where den~e papers are de~ired. Such undesirable char~cter-istics include reduced tear ~trength, poor writing qualities, and increased brittlenes~. Since dense paper webs do not accept as much impregnant as porous paper webs, it is generally believed that incre~es in the physical properties of a paper due to impregnation may be realized only when ~he web is por-ou~ and the resin content of the fini~hed paper exceed~ about 5~h of its weight.
Te6ts have shown that the density of a p~per web prior to impregnation and the amount of resin impregnated in the web affect the reduction of tear strength which ~ccompan-ies impregnation of a paper with fl rigid polymer. For example, sheets of ba6e papers having various initial densities were impregn~ted with an aqueous disper~ion of ~ rigid homopolymer .. ..
.
32~polyvinyl acetate resin (PVAC) sold under the trade designa-tion VINAC 880 by Alr Products and Chemical Co. of Allentown, Pa, The dispersion contained 40% by weight of VINAC 880.
Impregnation was effected by dipping the sheets into the aque-ous dispersion and ~hen passing the sheets through squeeze rollers to remove excess impregnant. The sheets were dried for 4 minu~es each in a Williams pap~er sheet dryer at 220F.,
2 minutes each side, After conditioning for several days, the basis weight and caliper of each sheet was measured, and the tear strength of each sheet be~ore and after impregnation was measured. The results are se~ forth below:
Initial PVAC in Impregnated Change in Sample _Density(lb/mil) Sheet (%) Densi~y Tear (7 A 5.5 48.5% 9.1 gain 20%
B 8.~ 41.5% 12.8 loss 33%
C 8~7 38.~%~7 12.~ l~ss ~3~0 D 9.3 42, l~/o 13 . 7 los8 37%
E 9.8 30.1% 13.3 loss 25%
From the above, it should be apparent that when dense papers are impregna~ed with rigid polymeric m~terials, they experien~e,signiiicant decreases in tear stren~th. This is unfortunate slnce other properties of paper, such as ten~ile and burst strength 9 abrasion re~istance, and delamination re-sistance are at their maximum when the paper is ~ense.
In U.S, patent 3,634~298 issued to R. A. Wamsley, et al~, there is disclosed a coating compo~ition for paper.
The composition includes a rigid polymeric ma~erial (having a glass transition temperature (Tg) in a range of about 85F~
to 110~.) blended with a clay slip. The composition is ap-plied as a coating onto a paper web to produce a high gloss paper.
L~ * Trade Mark Objects of the Invention With the foregoing in mind, it i~ a prim~ry object of the present inventlon to provide a novel paper h~ving the desirable physical properties of dense papers but wi~hout the unde~irable properties thereof.
It is another object of the present invention to provide de~e papers which ~re capable of being manufactured economically at relstively high papermaking machine speeds.
As another object, the present invention provides a novel den~e paper which is oil and solvent res~tant, re-sist~nt to tearing, abrasion resistant, and which has high fold~
ing endur~nce.
It is ano~her object of the present invention to provide a unique paper which is useful a~ a cover ~tock for books or as a carrier for release coatings, among other appli-cations.
A further object of the present invention is to pro- : -vide an improved process for producing dense papers.
It is a more speclic object of the present inven-tion to provide an inexpensive dense p~per wh~ch has been im-pregnated with a sufficient quantity of a rigid polymeric mater-ia~ to provide oil and solvent resistance without Qignificantly reduclng its tear strength and abrasion resistance.
Summary of-5~c-l9~L~
According to the present invention, most of the dis-advantages which are associated with the impregnation uf a paper web with a ri8id polymer are ameliorated, and a dense paper having increased folding endurance, excellent oil bar---6~
.
32~
rier properties, good tear and burst strength~, as well as solvent penetration resi~tance and ~br~sion resifitance is pro-vided. To this end, i~ has been disc3vered that such proper~
tie~ are provided when a web of p~per having an uncfllendered dry density of ~bout 7~11 lbslmil i8 impregnated with an a~ue-ous disperslon consisting essentially of a rigid polymeric material and a mineral filler material blended together in prede~ermined proportions. The lmpregnant is dispersed ~hrough-out the thickness of the web, and preferably, the impregnant con~itut~s about 8.5 - 50% of ~he fini~hed weight of the paper~
The filler i5 in a range of 10-65% of the weight of the -lmpreg~
nant, and prefer~bly in a range of 20-65%. The polymer has a rigidity or film hardness as determined by its glasfi trans- ~ -ition temperature, of between 15-60C, and preferably between 22-44C. Preferred polymers include: polyvinyl acetate, poly- .
acrylate, and polyvinyl chloride. Preferr~d inorganic flllers include: clay, calcium carbon~te, mica and talc.
The paper of the present invention has certain pro-perties which are unexpected of an impregnated dense paper.
For instance, the paper of the present inventlon which has been impregnated with ~n e~tended-rigid polymer, h~s a fold~
ing endurance which is far superior to the olding endurance of a paper impregnated with a rigid polymer only. Impregnation of a dense base paper with a rigid polymer would normally significantly reduce the tear strength of the resulting paper.
However, a base paper impregnated according to the present invention surprisingly retains a significant amount of its tea:r strength while at the same time posseS5ing excellent oil .. . . .
-z~
barrier properties. Ey utilizing an impregn~nt which includes subs~ntl~l amounts of filler, ~he m~nllfacturing coYt of the paper i~ lowered by reducing the total amount of polymer re~uir-ed to provide the desired proper~ies, since the higher co~t polymer is repl~ced by lower cost filler~. However, even though the paper may be inexpensive to manufflcture, it has all ~ ;
of the de~irable properties of dense papers which are more expenslve to m~nufacture, It is desir~ble for the paper web ~o be impregnated as it advances in the papermaking proees~ ~uch a~ encountered in ~ Fourdrinier m~chine wherein a furnish of cellulosic paper~
making stock ls applied onto a moving wire and formed into a web beforQ being separated from the wire and dried. The im-pregnating step should occur after the web h~s formed and be-come coherent and at least par~ially dried, and the web may be impregnated after the paper ha~ been completely dried and rolled, for instanee as a subsequent po6t-manufacturing step.
Preferably, the psper web i8 impregnated at ~he size press o~ ::
a conventional papermalcing machine. It i~ necessary for the den6ity of the p~per web to be controlled in the c~stomary manner so that prior to impregnati~n its dry uncalendered density is in a range of 7-11 lbs/mil, ~d prefer3bly 8.5 -10.5 lb~/mil. The web is advanced through an aqueous di~per-sion which contains 12.5 - 40% by weight of the impregnant, and after impregnation, the web i~ heated to fuse the impregnant in the web. The impregnant m~y al~o be blended with the paper ~tock at the '~et end" of the m~chine before web form~-tio~, :
_~_ ' ~ -~04l~21 Description of the Pre~erred Embodimen~
In m~nufactur~ng paper according ~o the presen~
invention, ~he polymeric m~terial must have a predetermined minimum rigidity, i.e. brittleness or film stiffness which, as determined by its gla59 tran~ition temperature (Tg) must exceed about 15C. Rigid polymerie mater-lals capable of func-tioning qatisfactorily include: polyvinyl acetate copolymer latices such a~ RESYN 1105 and 1255 manufacture~ by National Starch and Chemic~l Corp. of New York~ N.Y , and VI~AC 880, ~ -a homopolymer, manufactured by ~ir Products and Che~icals Co.
* ~ .
Allentown, Pa. Suitable polyacrylate materials include RHOPl,aX
AC 201 and TR 407, manufactured by Rohm and Haas Company of Philadelphia, Pa. A suitable polyvinyl ch~oride material is *
GEON 35l manufactured by the B.F. Goodrich Chemical Company of Akron~ Ohio. Each of the aforementioned polymeric materi~
. .
is of ~he commercially-available grade and is sold for use in -~
papermaking applications~ It is noted that the polymeric mater ~ :
ials may be copol~mer~ or may include certain amounts of other polymers or mixtures of one another; however, as lon~ as the glas~ tran~ition temperature of the polymeric material is with-in the a~ore~aid range, satis~actory results should be real-iæed.
The in~rganic filler material which is blended with the rigid polymeric material to form the aqueous dispersion i8 preferably a finely-divided mineral filler of commercial grade~ which are sold ~or use in papermaking applications.
Pr~ r~d partLcle siæes ior the ~illers range between 2-5 microns. Examples of minerai fillers which have been ~ested * T:rade Mark A
, .~
and found s~tisfactory are kaolin clay, caleium carbonate mica, and ta lc .
The amount of impregnant eontained in the finished paper mu~t be within a predetermined range. For instanee, the impregn~nt should be between about 8.5% and ~bout 50%, by weight, of the total finished weight of the paper on a dry solids basis. If the amount of impregnant i~ below the lower limlt, the resulting paper has poor erasability. On the other hand, due to the density lim~tations of the base paper, it is difficult to impregnate the paper beyond the upper limi~
Preferably, the impregnan~ ls within a weight r~nge of about 15% to about ~OD~. The uncalendered finished density of the impregnated paper should be between ~bout lOo S and 14.0 lbslmil (500 sheets 24" x 36").
In order to provide the desired physical properties of the p~per of the present invention, it is necessary for the rigid poly~eric m~terial to be extended within prescribed limits : :
with one of the aforementloned mineral filler~ or b1ends thereoi.
For inst~nce, the filler should con~itute between about 10%
20 and about 65% of the solids weight of the im~regn~nt, and preerably, the filler m~terial should make up between about 20% and about 65% of the weight of the impregnant. The balance ~
o~ the welght o~ the impregn~nt is provided by the rigid resin, ~ :
so that ~he resin constitutes between 35% and 90% and prefera~
bly between 35% and 80% of the weigh~ of the impregnant. It has been found that as the percent:age of filler deexease~
below the lower llmlt of its preferred range the tear 8trength ~ .
of the p~per decrease~ significantly. On the other hand, as the percentage of filler increase~ above the upper limit of its preferred range the oll barrier and solvent resistance properties of the re~ulting paper tend to diminish.
The paper of the present invention is manufactured on a conventional papermaking machine, such a~ a Fourdrinier machine. In such a machine, a furnish of papermaking stock i8 laid on an ~dvancing wire scre2n~ and after the furnish has been formed into a web, the web is removed from the screen and passed over a series o heated drying roller~ ~o dry, It is customary for the web, when at least par~lally drled, to be subjected to further processing, including the application of siæing at a size press located downstream of the drying roller~
In manufacturing the paper of the present invention, it i~ desirable for the impregnating step to occur after the web has become coherent as by being at least ~ rtially dried.
Preferably, the web is impregnated at the size press; however, the impregnation step m~y occur at a later stage in the paper manufacturing process. As well known to those skilled in the art, two types of size presses are in wide~pread use in the papermaking industry, and either type m~y be utilized s~tis-factorily to effect impregnation of the paper m~de in accor-dance with the proces~ of the present invention. For ins~ance, there is the so-called horizontal ~ize pres~ and the 80-called vertical size press. In the horizontal size press, a pair of opposed rolls are mounted for rotaticn on horizont~lly-spaced ~-.
axes, and the paper web is advanced vertically d~wnward be-tween the rolls as they apply pre3~ure to opposite surfaces of the web. The impregnant forms a pool be~ween each side of the :, . , ~' . ~ . '. ; '. ' , .
~ ~ 4g~
paper web and the roll engaging that side. In the vertlcal size press, on the other hand, the rolls are mounted for ro-tfltion on ve~tically-space~ axes, and the p~per web advances - -:
horizontally between the rolls. The lower roll rotates in a trough, picks up the impregn~nt, and applies the same to ~he underside of the web9 while impregnant i~ flowed onto the upper-side of the paper web, for instance by pumplng the impregnant from a reservoir. In both types of apparatu~, pressures in a range of 50 - 250 pounds/linear inch ~re applied to the web as it advances between the rolls, and the rolls cooperate to force the impregnant into the web while removing excess lm- ;
pregnant from opposite surfaces of the web.
Regardles~ of the stage of the proce~s at which im-pregnation occurs, it is important or the resin-filler blend ts be dispersed throughout the thicknes~ of the web in order for the full advantages of the present invention to be real- ~
ized. The advantages cannot be realized if the blend is merely ~ ~-applied as a coating on the surface of the web, such as by ~n ~ ~ :
immer~ion roll and doctor system referred to in U.S. Patent
Initial PVAC in Impregnated Change in Sample _Density(lb/mil) Sheet (%) Densi~y Tear (7 A 5.5 48.5% 9.1 gain 20%
B 8.~ 41.5% 12.8 loss 33%
C 8~7 38.~%~7 12.~ l~ss ~3~0 D 9.3 42, l~/o 13 . 7 los8 37%
E 9.8 30.1% 13.3 loss 25%
From the above, it should be apparent that when dense papers are impregna~ed with rigid polymeric m~terials, they experien~e,signiiicant decreases in tear stren~th. This is unfortunate slnce other properties of paper, such as ten~ile and burst strength 9 abrasion re~istance, and delamination re-sistance are at their maximum when the paper is ~ense.
In U.S, patent 3,634~298 issued to R. A. Wamsley, et al~, there is disclosed a coating compo~ition for paper.
The composition includes a rigid polymeric ma~erial (having a glass transition temperature (Tg) in a range of about 85F~
to 110~.) blended with a clay slip. The composition is ap-plied as a coating onto a paper web to produce a high gloss paper.
L~ * Trade Mark Objects of the Invention With the foregoing in mind, it i~ a prim~ry object of the present inventlon to provide a novel paper h~ving the desirable physical properties of dense papers but wi~hout the unde~irable properties thereof.
It is another object of the present invention to provide de~e papers which ~re capable of being manufactured economically at relstively high papermaking machine speeds.
As another object, the present invention provides a novel den~e paper which is oil and solvent res~tant, re-sist~nt to tearing, abrasion resistant, and which has high fold~
ing endur~nce.
It is ano~her object of the present invention to provide a unique paper which is useful a~ a cover ~tock for books or as a carrier for release coatings, among other appli-cations.
A further object of the present invention is to pro- : -vide an improved process for producing dense papers.
It is a more speclic object of the present inven-tion to provide an inexpensive dense p~per wh~ch has been im-pregnated with a sufficient quantity of a rigid polymeric mater-ia~ to provide oil and solvent resistance without Qignificantly reduclng its tear strength and abrasion resistance.
Summary of-5~c-l9~L~
According to the present invention, most of the dis-advantages which are associated with the impregnation uf a paper web with a ri8id polymer are ameliorated, and a dense paper having increased folding endurance, excellent oil bar---6~
.
32~
rier properties, good tear and burst strength~, as well as solvent penetration resi~tance and ~br~sion resifitance is pro-vided. To this end, i~ has been disc3vered that such proper~
tie~ are provided when a web of p~per having an uncfllendered dry density of ~bout 7~11 lbslmil i8 impregnated with an a~ue-ous disperslon consisting essentially of a rigid polymeric material and a mineral filler material blended together in prede~ermined proportions. The lmpregnant is dispersed ~hrough-out the thickness of the web, and preferably, the impregnant con~itut~s about 8.5 - 50% of ~he fini~hed weight of the paper~
The filler i5 in a range of 10-65% of the weight of the -lmpreg~
nant, and prefer~bly in a range of 20-65%. The polymer has a rigidity or film hardness as determined by its glasfi trans- ~ -ition temperature, of between 15-60C, and preferably between 22-44C. Preferred polymers include: polyvinyl acetate, poly- .
acrylate, and polyvinyl chloride. Preferr~d inorganic flllers include: clay, calcium carbon~te, mica and talc.
The paper of the present invention has certain pro-perties which are unexpected of an impregnated dense paper.
For instance, the paper of the present inventlon which has been impregnated with ~n e~tended-rigid polymer, h~s a fold~
ing endurance which is far superior to the olding endurance of a paper impregnated with a rigid polymer only. Impregnation of a dense base paper with a rigid polymer would normally significantly reduce the tear strength of the resulting paper.
However, a base paper impregnated according to the present invention surprisingly retains a significant amount of its tea:r strength while at the same time posseS5ing excellent oil .. . . .
-z~
barrier properties. Ey utilizing an impregn~nt which includes subs~ntl~l amounts of filler, ~he m~nllfacturing coYt of the paper i~ lowered by reducing the total amount of polymer re~uir-ed to provide the desired proper~ies, since the higher co~t polymer is repl~ced by lower cost filler~. However, even though the paper may be inexpensive to manufflcture, it has all ~ ;
of the de~irable properties of dense papers which are more expenslve to m~nufacture, It is desir~ble for the paper web ~o be impregnated as it advances in the papermaking proees~ ~uch a~ encountered in ~ Fourdrinier m~chine wherein a furnish of cellulosic paper~
making stock ls applied onto a moving wire and formed into a web beforQ being separated from the wire and dried. The im-pregnating step should occur after the web h~s formed and be-come coherent and at least par~ially dried, and the web may be impregnated after the paper ha~ been completely dried and rolled, for instanee as a subsequent po6t-manufacturing step.
Preferably, the psper web i8 impregnated at ~he size press o~ ::
a conventional papermalcing machine. It i~ necessary for the den6ity of the p~per web to be controlled in the c~stomary manner so that prior to impregnati~n its dry uncalendered density is in a range of 7-11 lbs/mil, ~d prefer3bly 8.5 -10.5 lb~/mil. The web is advanced through an aqueous di~per-sion which contains 12.5 - 40% by weight of the impregnant, and after impregnation, the web i~ heated to fuse the impregnant in the web. The impregnant m~y al~o be blended with the paper ~tock at the '~et end" of the m~chine before web form~-tio~, :
_~_ ' ~ -~04l~21 Description of the Pre~erred Embodimen~
In m~nufactur~ng paper according ~o the presen~
invention, ~he polymeric m~terial must have a predetermined minimum rigidity, i.e. brittleness or film stiffness which, as determined by its gla59 tran~ition temperature (Tg) must exceed about 15C. Rigid polymerie mater-lals capable of func-tioning qatisfactorily include: polyvinyl acetate copolymer latices such a~ RESYN 1105 and 1255 manufacture~ by National Starch and Chemic~l Corp. of New York~ N.Y , and VI~AC 880, ~ -a homopolymer, manufactured by ~ir Products and Che~icals Co.
* ~ .
Allentown, Pa. Suitable polyacrylate materials include RHOPl,aX
AC 201 and TR 407, manufactured by Rohm and Haas Company of Philadelphia, Pa. A suitable polyvinyl ch~oride material is *
GEON 35l manufactured by the B.F. Goodrich Chemical Company of Akron~ Ohio. Each of the aforementioned polymeric materi~
. .
is of ~he commercially-available grade and is sold for use in -~
papermaking applications~ It is noted that the polymeric mater ~ :
ials may be copol~mer~ or may include certain amounts of other polymers or mixtures of one another; however, as lon~ as the glas~ tran~ition temperature of the polymeric material is with-in the a~ore~aid range, satis~actory results should be real-iæed.
The in~rganic filler material which is blended with the rigid polymeric material to form the aqueous dispersion i8 preferably a finely-divided mineral filler of commercial grade~ which are sold ~or use in papermaking applications.
Pr~ r~d partLcle siæes ior the ~illers range between 2-5 microns. Examples of minerai fillers which have been ~ested * T:rade Mark A
, .~
and found s~tisfactory are kaolin clay, caleium carbonate mica, and ta lc .
The amount of impregnant eontained in the finished paper mu~t be within a predetermined range. For instanee, the impregn~nt should be between about 8.5% and ~bout 50%, by weight, of the total finished weight of the paper on a dry solids basis. If the amount of impregnant i~ below the lower limlt, the resulting paper has poor erasability. On the other hand, due to the density lim~tations of the base paper, it is difficult to impregnate the paper beyond the upper limi~
Preferably, the impregnan~ ls within a weight r~nge of about 15% to about ~OD~. The uncalendered finished density of the impregnated paper should be between ~bout lOo S and 14.0 lbslmil (500 sheets 24" x 36").
In order to provide the desired physical properties of the p~per of the present invention, it is necessary for the rigid poly~eric m~terial to be extended within prescribed limits : :
with one of the aforementloned mineral filler~ or b1ends thereoi.
For inst~nce, the filler should con~itute between about 10%
20 and about 65% of the solids weight of the im~regn~nt, and preerably, the filler m~terial should make up between about 20% and about 65% of the weight of the impregnant. The balance ~
o~ the welght o~ the impregn~nt is provided by the rigid resin, ~ :
so that ~he resin constitutes between 35% and 90% and prefera~
bly between 35% and 80% of the weigh~ of the impregnant. It has been found that as the percent:age of filler deexease~
below the lower llmlt of its preferred range the tear 8trength ~ .
of the p~per decrease~ significantly. On the other hand, as the percentage of filler increase~ above the upper limit of its preferred range the oll barrier and solvent resistance properties of the re~ulting paper tend to diminish.
The paper of the present invention is manufactured on a conventional papermaking machine, such a~ a Fourdrinier machine. In such a machine, a furnish of papermaking stock i8 laid on an ~dvancing wire scre2n~ and after the furnish has been formed into a web, the web is removed from the screen and passed over a series o heated drying roller~ ~o dry, It is customary for the web, when at least par~lally drled, to be subjected to further processing, including the application of siæing at a size press located downstream of the drying roller~
In manufacturing the paper of the present invention, it i~ desirable for the impregnating step to occur after the web has become coherent as by being at least ~ rtially dried.
Preferably, the web is impregnated at the size press; however, the impregnation step m~y occur at a later stage in the paper manufacturing process. As well known to those skilled in the art, two types of size presses are in wide~pread use in the papermaking industry, and either type m~y be utilized s~tis-factorily to effect impregnation of the paper m~de in accor-dance with the proces~ of the present invention. For ins~ance, there is the so-called horizontal ~ize pres~ and the 80-called vertical size press. In the horizontal size press, a pair of opposed rolls are mounted for rotaticn on horizont~lly-spaced ~-.
axes, and the paper web is advanced vertically d~wnward be-tween the rolls as they apply pre3~ure to opposite surfaces of the web. The impregnant forms a pool be~ween each side of the :, . , ~' . ~ . '. ; '. ' , .
~ ~ 4g~
paper web and the roll engaging that side. In the vertlcal size press, on the other hand, the rolls are mounted for ro-tfltion on ve~tically-space~ axes, and the p~per web advances - -:
horizontally between the rolls. The lower roll rotates in a trough, picks up the impregn~nt, and applies the same to ~he underside of the web9 while impregnant i~ flowed onto the upper-side of the paper web, for instance by pumplng the impregnant from a reservoir. In both types of apparatu~, pressures in a range of 50 - 250 pounds/linear inch ~re applied to the web as it advances between the rolls, and the rolls cooperate to force the impregnant into the web while removing excess lm- ;
pregnant from opposite surfaces of the web.
Regardles~ of the stage of the proce~s at which im-pregnation occurs, it is important or the resin-filler blend ts be dispersed throughout the thicknes~ of the web in order for the full advantages of the present invention to be real- ~
ized. The advantages cannot be realized if the blend is merely ~ ~-applied as a coating on the surface of the web, such as by ~n ~ ~ :
immer~ion roll and doctor system referred to in U.S. Patent
3,634,298, for applying a coating onto a web. In sueh a ~y~tem ;~
the lower periphery of a roll rotates in a trough containing ~:
coating, and the upper periphery engages the underside of the advancing web. Thu~, the roll pick~-up the coating from the trough a~d applies it onto the underside of the web. The thick-ness of the coating i8 controlled by passing the coated web over a doctor blade downstream of the roll to allow only a certain amount of coatlng to remain on the under~urface of ~'~
the web.
. -~2-~a~3~
Tne reRin filler blend may even be admixed with the paper stock before applicatlon o ~he furni~h on~o the wire screen.
In order to ensure di~persion of the blend through-out the web, there are certain conditions which must be ob-served in the manuf~cturing proces~. For instance, prior to impregnation, the dry uncalendered density of the web must be controlled so that it is in a range of between 7 and about 11 lbs/mil. The density may be controlled by a v~riety of tech-niques, all of whieh are well known to tho~e skilled in the art.The control of the pre-i~pregn~tion den~ity i8 importan~, be-cause when the dry unc~lendered density is below 7 lb~imil, the resulting paper is too porous. On the other hand, when the dry uncalendered density is about 11 lbs/mil, the web i~
incapable of absorbing ~ ~uffieient amount of impregnant to provide the desired properties.
Another important step in the manufacture of the ~ ..
paper of the present invention is the nece3sity of contro;lling the aunt of solids present in the aqueou~ dispersion through ~:
20 which the web i5 passed. For in~t~nce, ~he solids content, which includes the combined weight of the rigid polymeric material and filler, should be in a range of between about 12.5% and about 60~/o of the tot~l weight of the dispersio~
If the combined weight is below ~he lower limit, webs within the above-stated den~ity r~nge (7-11 lbs/mil) do not acquire a ~ufficient amount of impregn~nt to provide the desired result~
On the other hand, if the percentage i9 ~bove the upper limit, :
the dispersion tends to become viscous and the resin-flller -13- :
:~ .
~ 4 ~ ~ Z ~
blend tends to coat the surface of paper web~ having den~ities clo5e to the 11 lb~/mil upper limit rather than to impregnate the Qame.
The paper web is sub~ected to a heating step after impregnation to fuse the lmpregnant in the paper. In the con-ventional papermaking process, the web is heated to a temper-ature of about 100C. to dry the same so that rigid polymers which have glass transition temperatures in excess of that temperature would not provide s~tisfactory results. Preerably, the upper limit for the glass transition temperature vf rigid polymeric materials employed in the present invention i9 les~
than about 60C.
Certain advantages are realized in manufacturing pa~
per according to this process. For inst3nce, the use of a rigid polymeric impregn~nt heavil~ extended w~th flllers tends to kill the tackiness of the impregnant and renders the drying drums easier to clean. ;~
Summ~rY of th~ Ex~mples The importance of the aforementioned factors in the manufacture of the p3per of the present invention should be-come apparent from the following example~. In brief, Exanples I and II demonstrate the permissible degree of exten~ion of a rigid polymeric material with a mineral iller. In Example III, the importance of the rigidity of the polymer i~ set forth. The types of fillers which are required to provide satisfactory results are exemplified in Example IV. The nece~-si~y of controlling the pre-impregnatlon density of the paper web ls set forth in Example V. The amount of impregnant which , ~14-3~
is re~uired to provide the desired properties is presented in Example VI, The types of rigid poly~eric materials which are required are demonstrated in Example VII. Example VIII demon-strates the abrasion resistance properties of the paper of the present invention. Example IX demonstrates the properties of a paper impregnated with a composition according to the pre-sent invention as compared with a paper coated with the same composition.
~For the purpose of determining the limits ~f ~ e permissible extensîon of the resîn with a minera~ filler, sheets of unsized paper m~de from a blend of 5~% bleached hard-wood kra~t and 50% bleached Northern kraft were used as base p~pers. The basis weight oft~ paper was 51.8 Ibs., which is the weight of 500 sheets measur ~ng 24" x 36". The caliper or thlckness of a single ~heet oE the pape~ wa~ .OOSS" (5.5 mils). Since the density of a paper may be conveniently ex~
pressed as lts weight per mil of ~hickness, the density of the base paper was 51.8 lbs/5.5 mil, or approxim~tely 9.4 lbs/milO
The impregnant was prepared by dispersing fi~ely ground calcium carbonate powder having ~ particle size of about 2 m~crons in water and agitating the same. A finely di~ided rigid polyvinyl ace~ate emulsion was blended with the aqueous dlspersion so ~ :
that the total solids content of the resin and filler wa~ 4~%
by weight of the dispersion~ The cal~ium carbonate which wa~
used is sold under the trade designation CAMEL WHITE by the ~ar~y T. Campbell Sons CoO, Towson, Maryland. The polyvinyl acetate emulsion which was used is sold under the ~r~de des^lg-* Trade Mark ' ~ 3 nation VINAC 880 by ~he Air Products ~nd Chemical Company, Allentown, Pa.
The paper sheets were dipped in the dispersion, and after withdrawal were passed through rubber rollers where ~he excess was squee ed from the sheets. The impregnated sheets were then dried for 4 minutes at 220F., 2 minutes for each side in a Willi~ms paper sheet dryer. The shee~s were per-mitted to condition (cure) for several days before being t~st-ed. The te~r, Mullen and fold tests were conducted according to TAPPI standard procedures identified in Table I. The oil barrier properties were determined by typing a character on the paper with a commercial portable typewriter and observing the difficulty or e~se with which the character ~ould be removed by rubbing with a pencil eraser. Since inks in conventional typewriter ribbons contain substantial amounts of non~drying oil~, there is a direct correlation between the erasability of a p~per and its oil barrier properties. A determination of "excellent" meant that essentially all of the character was erased with a few rubs A rating of "good" meant that ~he character rem~ining after a few rubs was ob~ervable but not apparent to the naked eye after another character was typed over the erased character. A rating of "fair" meant that erasure was acceptable. A rating of "poor" indicated unsa~-isfactory erasure.
The solvent resi~tance properties of the sheets were determined by placing a drop of dyed (purple) toluene on the ~urface of e~ch sheet and allowing it to contact;a predeter-mined area for 30 seconds. The drop of toluene was then wiped ~ 3 away with a paper towel, and the area was rubbed with another paper towel saturated with undyed toluene. This cause~ the dye remaining on the surface to be removed so that the amount of penetration of the p~qper may be determined by ob~erving the presence of the remainlng purple dye. A rating of "good"
meant thflt there had been penetration at several points but that the degree of staining was light and less than about 50%
of the test area. A rating of "fair" meant that light stain^
ing had occurred over most of the test area. A rating of 1'poor" meant that the entire test area beeame darkly stained, A rating of "none" was given if the stain completely penetrated to the back of the paper ~heet.
The re~ults of the tests are set forth in Table I.
It is noted that the notation XD means that the test was con-ducted in the cross machlne direction of the paper. The units of measure9 as well as the identifying numbers on the standard test procedures employed in the various examples are set forth in Table I. ~:
-17- :
.
, . ~- ~ ", .. .
332~
U~
IJ IJ
n~ ~ ~ ~ ~ ,~
,, ~ ~ ~ ,, ~1~rl UOUVUO
o ~ X ~ X X X o ~ o V~ ~ ~ ~ ~ ~ ~ ~ ~ Z
.,~
~ ~ ~ ,, P~
o X X ~ X o o O~ rl ~ U~
V ,~
o~ 1 4 V ~ oo U~
t, o ~,~ ,~ o P~ o ~ ~ ~ o ~ o ,~ a ~d '' o ,1 ~ In 1~ ~~ t~ ~
oo a~ ~ o ~o~ o~
~ o o rO~ ~~ I 0 0 0 0 0 0 0 u ~ ¢ I ~E~
~ ~P o O O o O O O
P; ~ Oh O
U~ # ~J
., ,. .. . . .
: ~ ` : : :: : :
33~ 1~
In the above table, lt may be observed that a paper ~heet prior to trea~men~ ~sample H) h~d a tear s~rength of 147 grams. A similar sheet which had been impregnated with a lOOV/o solution of polyvinyl acetate (sample A) had a tear ~trength of 80 grams. However, lt should be noted ~hat when the impregnant had been extended with calcium carbonate in the range of between 10-70% aQ indicated by samples B-G, the tear strengths of the sheets decrea~ed, but not ~o the same degree a8 W~S observed when the impregnant wa~ 100% polyvinyl acetate.
The oil barrier ~nd ~olvent resistance propertie~ were retained ~:
even though the impregnant had been extended up to about 70%
of its weight with calcium carbonate. Mo~eover, it is nated that the fold endurance of ~he extended-resin impregnant was greater than that measured when the impregnant was 100% poly-vinyl acetate.
EXAMPLE XI
The test procedure described above with respect to Example I W~5 repeated; however, kaolin cl~y wa~ employed a~
a mineral filler in place of the calcium carbonate. The clay utili~ed is sold under the trade designation HYD~APRINT by the J. M. Huber Co~poration, Huber, Georgia. The results of the tests are summ~rized in Table II.
-19- ;
2~
a~ ~, V ~ U V
1:1 R R R R R
a) ~ a~
~ V
o ~J a) ~ ~ ~
V V V U
~X ~X
~q ~
~ Q~
V S~ V ....
5~ ~ a~
~ ~1:4 'I ~ ~ ~
~ V ~1 V V U o P~ ~~,~ X X X O
~ v O ~
~ V
E~ P~ ~ ~ ~ a~
~o C~
~) ~
oo a) _, ~1 ~
o ~ or~ ~ ~
E~ X o~ ~ ~ ,1 ~_ ~1 C~ -.' rl ~
V ~ o O o td ~ ~I GO r~
P;
(~ O o o o ~1 U~
. :
~ . : . , , , . ., . :: . , .
:
:~: :
; : :
From ~he oregoing tests, it ~hould be apparent th~t kaolin clay and calcium carbonate have sub~tantially the same effect as fillers on the proper~ies of a base paper ~hen blend-ed with a rigid polymerlc material and impregnated in the base paper.
EXAMPLE III
For the purpose of demonstrating the importance of impregnatin~ the paper web with a polymer of a predetermined rigidity, the base paper of Example I was impregnated with a series of polymer-filler blends differing only in the thermal glass transition temperature (Tg) of the polymer. As noted heretofore, the Tg is a mea~ure of the rigidity or film stiff~
ness of a polymeric material. In the example, the polymer was extended with calcium carbonate, 60% polymer aRd 40% calcium carbonate.
The re~ults are set forth below in Table III, 2~
a) ~ ~ .~
a) J~
a~ ~ ~ ,4 h oU) ~OOoo oU
U~ ~ O O o O O O X
p:; Z; C~
J- ~ ~ ' ', ~ ~ ~ C g ~t; ~rl ~ ~ ~_ 0~ H h ~t J O O ~: O O
~1~ ~ O XXOO OO
.Z ~ O P~ ~ Z ~!) C~
~d ~1 J 0 4~ p~ r~ o u~
O ~ ~ rl ~ ~ r~
.IJ t~ ~
~ r-l J~ ., t~ O h ~ l ~ ~ a~ ~ ~ ~ ~ .
E~ ~ ~ ~
u~ ,q ~1 ~ ~ pO~
HC!~ U ~ ~~ r-l H~ U O E~ O ~ cn ~ O 1 C~ _ +
~d E~ ~) -J a~ ~ o~ o ~ ~
P ~0 ¢ ~ # rl ~1 co O ~ ~ ~ u~
a~
~rl h , I L~
O
~O ~ J-~I ~
~:J ~1 d td t:O ~ i~ ~ ~ ~1 ~ c~
r~ ~ ~ ~D ~ 00 ~ cr ~1 ~i H
~0 P~ u~
aJ
a) u, o o u~ ~I t) ~/ ~ ~ ¢ u~ .
~d c) o7~1 ~ o o d ~ X X X X X 1:
rl ~ a e S~ ~d ,~ ~ ~
~ t~ ~ :~ td ~ ~o ~ ~o ~ ~o o ~ ~
: : ::. , '. ::~: : ;
: ': : '. '- : : : ' : ; . :
.
:
. ::. . ~ . : :
~ . : :
:. , , , . :`
.
, . ~
' . ' , , 32~
a U
~ ,~
? u~
~rl ~ ~ ~
~ ~
V~ ~ 0 0 ~0 ~ ,, ~ 0 h U h a) ~ V . ~ h al ~0 ~I 0 '0 0 g - a) a~ O P~ 4 æ
E~ v o ~ ~ ~
V U O ~ ~ I~ ~ 00 ~01 a~
~q ~d ~1 .V ~_ ~1 ~0 ~ i~ O n ~ ~ `V Oe ~
H t~ O
~1 ~1 h ~¦
~1 ~1 c~a~ b~ O ~1 ~ ~ ~d E~`--X P ~0 ~ C~ 0~ 0~ ~:
~O I ~00 0~ O O ~D
E~ '~
P~ ~rl V V
rl ~ # ~î
~rl p r-l ~rl ~rl Ot'~) I~
v o tT~ l ~ .
~ rdl ~ ~ ~J
r-l ~ ~ _~
~ ~rVI JJ
~.~ 1~
O F4 1~0 r-l 1~ ~ ~.
~ i~ O~ r~
V
a~
r-l ~ Il~ ~ d tl) V U~ r-l ~ r~
~rl~ l ~i a a d a r~ :
rl .~ ~r ~1 V r l g ~S ~ ~;
~O~ ~0 ~ 1:4 C~
.
, ' .: , , . . .. : . :
- ~ : :' ' .'. "
~ . , ,:. ,; . :
. ' ' , ,, , ., "' . ' ' ' ' 32~
Referxing to the above data, it can be seen that a sheet of paper impregnated with a polyvlny3. acetate having a Tg of 16~C. has fair oil barrier properties and air solvent resistance~ On the other hand, ~ sheet of paper impregnated with a polyacrylate havlng a Tg of 101C.+ does not have any oil barrier propertles or solvent resistance. Accordingly, it should be apparent that a satisfactory polymeric material should have a rigidity, iOe., Tg which is within this range, about 15C. to about 100C., and preferably the Tg shnuld not exceed about 60C.- (See Table VIII regarding a polyvinyl chloride having a Tg of 60C. ? if satisfactory results are to be ensured.
The preferable Tg range is between 22C. and 44C. to ensure fuslon of the polym~r at conventional papermaking processing ~æ~peratures.
EXAMPLE IV
The types o~ mineral fillers employed as extenders have ~l important bearing on the properties of the impregnated ~ :
paper~ This shoul{' be apparent ~rom the present example wherein the base paper of Example- I was impregnated with the polyvinyl aeetate which had been blended with a series of different mineral ~ille~s. Each blend consisted of 40% filler and 60%
polyvlnyl acetate on a dry solids weighL basis. The c~lcium carbonate and clay were the same as employ~d in previous exam~
ples; the talc which was e~ployed is sold under the trade designation MISTRON VAPOR by the United Sierra Division, Cypress ~i~e~, Trenton, New Jersey; the mica is sold under the trade * ~ .
de~ignation DAVENITE MICA P-12 by the Hayden Mica Co., o Wil- -mington, Massachusetts; and the diatom~ceous earth is sold * Trad~ Mark A
, : ' ' " ' ' :
`~J ~ 3Z ~ :
under the trade designa~ion of CELLITE by Johns-Manville Cor-poration, New York9 New York. Each of the aforementi~ned fillers i5 of a commercial grade and quality normally u~i.lized In papermaking applications, having partlcle sizes in the 2-5 micron range.
The result~ of the test are set forth in Table IV.
* Trade Mark ~ .
-~5- :~
A
. ~. ~ . ~. .
.
832~
~U ~ ~ U
U
~u ~u~u ~u ~u .~ ~ ~ ,...
~ n u u u ~ u h O ~r~ ~ O
u~ ~n p~ X~ 1 X F40 ~U rlJ
~rl h ~U ~ 1 ~ h O h O O O OO O
h r J X ~ O OO O
~rn ~rî ,1 oo ~ ~J
h r ~
H.,1r J *
~11:4'~U 'O ~ ~1 u~
~ 0 ¢ o 4~ ~ N
i~ O H ~ ~ ~U') ~t ~ N N
tl~`~ h ~
P ~ ~ ~ O ~ or~ $, o E~ '~
P~
~:
O
a P~ r~
~o ~n F3 h ~u ~ ~ NN ~1 E~i ~ ~
H
. ~ r_ C~,~ .
~U ~ H ~ N N
~ ~ ~ ~ ~ 'O
H aJ
?~ (U
o ~1 aJ :
W ~1 p~ Z ,~
D Z; C.) ~ t #
.:
':' ~
' - ' . ' , From the above ~a~le, it should be ~pparent that calcium carbonate, clay, talc, and: mica prnvide ~atisfaetory fillers; where~s, di~tomaceous earth i8 unsa~i~factory because the resulting paper provLdes poor oil barrier p~operties ~nd poor solvent resistance.
EXAMPLE V
__ The importance of controlling the density of the paper web prior to impregnation is illustrated in the pre~ent example, An aqueous dispersion of polyvinyl acetate and cal-cium carbonate W~5 prepared as in Exa~ple I. The polyner-filler blend constituted 40% of the weight of the di~per~ion, ~ ~
and the ratio of polymer to filler wa~ 60/40 on ~ weight basis. ~:
A series of s~eets of unsized paper of different densities were dipped into the dispersion, and the excess impregnant was removed from the sheets by passing them through rubber rollers and blotting the surface of the sheets with paper towe~s to ensure t~e removal of excess impregnant from the ~urf~ce of the sheets. The sheet~ were thereafter dried for 4 minutes ~t 220~., conditioned for several d~ys, ~nd tested a~ noted heretofore. For comparison purposes, a dispersion was prepared i;
wherein only polyv~nyl acetate wa~ present at 40% by ~eight ~olids, and a second ~et of base papers were similarly impre~-nated. As ~ urther compari~on, plain paper which had not bee~
impregnated was al~e tested.
The re~ults of the te~ts ~re set forth below ln Table V. ~ .
~7 ~ . . ............. . .
,, . ~. .
3~
~ l C) h S~
Z ~ C~ W
~: ¢ O P
al p h p~
~0 ~ ~( 1` ~ ~I r~ oo O
O O ~ ~ O ~ ~ O U~
~Ll F4--~ ~
a) ,1::
~ ~ri S~ _~
U~ ~ (~ ~ ~00 1~ 0 ~ O
~O
~ ~ ~ r~
td ~ ~ ~ O ~1 ~ ~ a~
0 4~ ~ ~ I I U~
~ _~ ~1 ~1 ~I
¢ h ~ ,~ ~ ~ ~ o :~ E~
_~ ~ ~ O ~ I~ U~ ,1 ~ ~ o ~ ~ ~ ~ O ~ ~ co ~ ~, o 8 ~1 ~3 ~ ~ ~ ~ ~ ~n ~ ~I ~ oo :q ~ ~ # c!
h ~c E~ O ~ h h O ~1 ~rl ~; ~4 1~1 ~ ~1 ~ ~1 1~1 C~ IY h h ~ 4 3 ~11 R
'O ~ X l U~ o o ~ o ~ ~I 0 ~ ~ ~ O ~ ~ ~ ~ ~1 o ~3 o~
P~
H l X ~.
to 0 J- a h J- 00 u ) 1` u~
CO ~r) O cn o ~3 U~ ~o 1~ oO o~ a~ ~ o ~ ~ ~D ~ ,1 ~ a) ~4 O h h to 'O
~1 ~ O r~
_ o ,i ~ I g _ ~ ~ ~ ~ ~ V~
h ~ Z
t~l ¢ ~ ~ ~ ~ ~ 1~ 5: H
P~ ~t #
" : ' ' . ' .
.
~ 3~
From the above table, it Yhould be apparent that the minimum uncalendered density of the paper web prior to impregnation should be greater ~han the 6,9 lbs/mil as in s~mple B. The maxlmum uncalendered impregnation den~ity should not exceed the 11.0 lbs/mil value as in sample I. It i8 noted that even though sample B contained 48.5% impregnant, it was unsatisfactory from an oil barrier stflndpoint. Although sam-ple J had excellent oil barrier properties, i~ acquired 9.1%
of impregnant but posse~sed very l~w tear strength, It is:~
further noted that each of the papers which was ~atisfactory had a finished uncalendered density in excess of 10.5 lbs/mil and less th~n about 14.0 lbs/mil.
EXAMPLE VI
The amount of polymer-filler impregnant which is necessary to provide a satisfactory paper is e~emplified in the present example wherein a b~se paper fabricated from Nor~
thern bleached kraft pulp and containing approximately 5% tit-anium dioxide was employed. Although the paper wa~ unsized there was a slight sizing effect due to some re~idual pit~h; ` :~
however, this was not believed sufficient to have prevented penetration of the impregnant into the interior of the sheet.
The basis weight of the paper was 34.6 lbs (24" x 36" ~ 500 sheets). The s~mples were prepared as set forth in Example V;
however, the solids content of the impregnant was varled from :~
~0% to 40%.
The results of the test are ~et forth in Table VI. ::
- 29- :
,. . . ~ . ~ , .
: ~ -v~
~l cJ ~ ~ ou~ o o o S~ ~ ~ ~1 ~ ~ ~ ~
~ro g H U~ t~
., d ~q ~ ~1 ~1 ~1 ~n ~1 ~ ~~o a~ ~,~ o ~d O ~C O O O
, O ~
o r~ 0~ ~ I 00 ~ ~ ~ ~ ~D
',i ~ E~
H ¦ O ~.
~ d ¢ r~
E-l t3 ~. o ~_ ~ CO o ~ ,~
~!
d o ~ ~ ~
~ ~ ~ ~ , .
.~ ~ ~ ~ ~ ~ I~ o U~ ~ o ,.
Q~ ~ i O O O ~i t~
~ ~ a ~ ,~
h ~
a) h a a~
r~ ~ O O ~1 ~D O
~ a ~O,; u~ ~ O O ,~
r~ r~ ~ ~ ~ O
h a) c~ aJ
td b a) ~ o . .
~ ¢ ~C,) 1~ I I 'X ' .. '1' V~ ,~
. _30_ . . .
:,.. ' , ~ " . ' ' :
: , , - . . :
. . ' : ~,, ': :, , '::, :
:.
- ' ' ~ ' , " ', ' ':
~' :, ' : ', :' : ' ~
~ 3~
From ~he above d~t~, it should be apparen~ that a signiflcant improvement in oil barrier p~operties and ~olding endurance properties occurs when the polymer-filler impregnant constitutes between about 6-10%, or about 8.5% of the weight of the sheet (sample B~ with highly desirable proper~ies re-sulting when the impregn~nt is in 3 range between 15-25% of the weight of the ~heet, as indicated in samples D and E, and up to ~bout 48% as indic~ted in Example I (page 19, infra). ~;
EXAMPLE VII
In order to demon~trate the different types of rigid polymerlc m~terials which m~y be employed ~atisfactor;ly in m~nu~cturing paper of the present invention, sheets of the ~::
base paper of Example I were impregnated with a polymer-filler dispersion having ~ ~olid~ content of 40% by weight, with the weight ratio of polymer to filler being 60% to 40%. The filler was calcium carbon3te, and the polymers included: RHOPLEX
AC-201, a polyacrylate em~lsion n~nufactured by Rohm & Haas Co., Philadelphia, Pa.; and GEON 351, a polyvinyl chloride emulsion m~nufactured by the B.F. Goodrich Chemic~l Co., Akron, Ohio.
The test results are sumN~rized below in Table VII.
~,'` .
':
, ::
~: K
I~ a) ? ~ U ~ ~1 O O ~rl 0 I #
~rl 0 ~ ~ W ~ P~
O a~
a ¦
U) ~1 ~ O ~ O
~ ~ ~ ~ r~
h d ~1 ~ :
U~ (IJ 0 ~ ~3 ~ X ~ ~o ~ oo a~
~ P E~ ; ~
P ' ~ K
~ t~ 00 ~
o ~ a) tO~rl o o ~ c~ , O 0 ~ 0 ~:: Ei ~') ~ ~ ~`i :
? H ~ ~1 ~1 ~1 ~1 E~ 5~
H O O I ~ ¦
~1 0 t~ O C~ ~ ~ I~ O O C~l a0 ~ c~
d ~ I ~ ~ ~t `;t `;J
o ~ o~ .
~,~ ~0~ .
~ ~:1 ~ C~ .
~? E~ ?. ::
a~ l o o o o X'01~ ' a~ o o o ~1 ;~ .,~ .,1 P~
dP~; ~1 o ~:1 h o al o ~0 a~ ?. ~ ~ ~?. ~ a ~ 4~
hO h ~h~
Ei E~ 0 0 ~ h? 5 1 ~c1 X ~ ~4 H~ ~ O P~ ~1 ;~ O ?. O d a O 0 0 0 0 O~C OrC V ~1 ~
P~ o ,, J-l ~ h d a) , Or ) ~ d d d o h ~1 -- ~`1 ~1 0 d a~ 1 X g X ~1 ~ X O P~ c~ O h h 0 ~J
t~ 1:~1 0 0 ~1 ~`I ~1 P~ ~, O
~1 ~`1 c~ ~1 d ~ `1 ~/13 ~3 d 11 11 h ~ o ¢ ~ o ¢ æ u~ z u~ H H p ~1 P~
E3 0 ~ 1 1 1 #
H 1:~ K ~i ~ ~ ~1~`J * K
.
' ''' -: .: : :
::: . .
: : ' ' ':
~ 3~2~
From the above data, i~ should be apparent that an impregnant consisting of a rigid polyacrylflte material extended with calcium carbonate has substan~ially the same effect on a base paper a~ a rigid polyvinyl ac~tate and calcium carbon-ate impregn~nt (compare Tables I and VII). It is n~ ed that :
similar results are obtained when the impregnant consists of a blend of polyvinyl chloride extended wi~h calcium carbonate; ~ :
however, the solvent resistance and oil barrier properties of the impregnated paper are actually higher with the extend~d lmpregnant than with the unextended impregnant. Accordingly, it ~hould be app3rent that beneficial results can be arhieved ~' only by employing certain ~ypes of rigid polymeric materials such as polyvinyl acetate, polyacrylate, and polyvinyl chloride.
EXAMPLE VIII
The paper of the present invention has good abrasion ~ :
resistance even though the impregnant blend is ex~ended with slgnificant percentages of filler and even though considerably less than half of the weight of the paper is provided by the impregnant. In determining the abraslon resistance of the paper of the present invention, sheets of the base paper ofExample I we~e impregnated with various rigid polymers and polymer-filler blends in accordance with the procedure of Example I. The polyvinyl acetate polymer was VINAC 880; the poly~crylate polymer was RHOPLEX 407; and the polyvinyl chlor-ide was GEON 351, The sheets were subjected to the Tabor Abrasion Test according to TAPPI Stan~ard procedures (TAPPI
T 476 t~-63). An H-18 abraslve wheel was utilized in the test, and the number of cycles of rotation of the wheel until a hole ' was worn in the ~heet were counted. The re~ult~ ~re ~et :iEorth in Table VIII .
'~ ~
, . .
: ' ' ' , ,:
.. . . .
33;~
~, d O
I~ C~l O U~ ~ ~ O .' ~i 1~ o ~t '' "
~ ' .~
H . .
.,1 ~ a) ~ a) h H¢ 0~ F4 O
t~d X o o o o o o ~ o E-~ toto o ~ o o o u~ ~o~
0~ P;
O g O
O rd Q~
tU tl) t~ a~ a) O ~J
u c~ U ~ a~ rC ~ r~
¢ ¢
~ ~ ~ ~ ~ ~ ~ ~ ?~
tl~ ~ ~ t~
~ o o o o o o o o o ~:
~, -35 ..... .
,~ ' , , , ' . - . , .
:, ~ 3 2 ~
From the above data, i~ should be apparent tha~ ~he abrasion reslstance of a paper sheet which ha~ been impregna-~ed with a blend of a rigid polyvinyl acetate and a mineral filler s~ch as calclum carbonflte, is only slightly less (530 cysle~) than a paper sheet impregnated with polyvinyl acetate only ~600 cycles). A sheet impregnated wi~h polyvinyl acet~e extended wi~h clay in the stated propor~ions has even greater abrasion resistance than does a sheet impregnated with poly-vinyl acetate only, A sheet impregnated with a polyacrylate m~terial extended with calcium carbonate also has a higher abrasion resistance than does a sheet impregnated only with the polyacrylate, The abrasion resistance of a sheet i~reg- ~ -nated with a filler-extended blend of polyvinyl chloride has :~ :
slightly greater abrasion resistance ~400 cycles) than does a simil~r sheet impregnated with the polyvinyl chloride only. :~
EXAMPLE IX
The paper of the present invention must be impreg-nated with the above~noted dispersion; it cannot be produced merely by applying the dispersion as a co~ting. To demonstra~e thi~, sheets of a base paper having a basis weight of 54.1 lbs (500 sheets 24" x 36") and a caliper of 5O5 mil~, were im-pregnated and coa~ed with the polymer-filler compositionO For example, a sheet of base paper was impregnated with the compo-sition described in Example I and another sheet of the base ~:
p~per was coated wi~h the same composition in the manner des-cribed in Example I of U.S. Patent 3,634,298, except that Virlac 880 polyvlnyl acetate having a Tg of 31C. was substi- ~
tuted for the polymer ~ynthesized :Ln Example I of the patent ~.:
-36~
' ~' ... . .
3;2~
to form the aqueous clay-polymer dispersion. The dispersion comprised 55%, by weight, of ~he clay-polymer blend in a ratio ; ;-of 83% clay to 17% polymer, The resulting di~persion was ap-plied to one side of ~he ba3e paper as a coating, using a Meyer bar, as described in Example I of ~ patent. The coated paper was thereafter dried for one minute at 300F.
The coated and impregnated papers were later tested for tear, burst and fold properties, and the results of the tests are set forth in Table IX.
: ~
, .
. : .
3~1 R
r1 ~
t.) t~ R
a ~ R
e u~ o O o e ~ U~ ~
.
~0 ~ ~ `D 0 ~0 a~ ~.C
~1 , .
~ O
~ . . ~ `J ~
O ~ ~ 0 0~ U~
~, ~ ~ ~, R
c~
o~ ~ o :~
X
e u~
E~
~ P~
~ e ~ ~ ~
~O
R ~ ~ ~ ,1 ~1 ..
~J
a~ ~a c~ ~1 u~ ~ ~ :
~1 ~
u I I
a`e rl .~ d ~ o e O ~ ~ .
~ ~.~ ~ , .
~, e u~ e ~ O
~d ~ 4 H d F~
.
. . .
From the foregoing table, i~ may be seen ~h~t impreg~ -nation decreased ~eflr strength about 13% while coating lncreased tear strength by about 12~/o~ Impregnation more than doubled burst strength while coating only increa~ed burst strength by about 50%. In the fold test, impregnation con~iderably more th3n doubled the fold endurance (even at the lower 10-20% rela-tive humidity) whereas coating actually decreased the fold endurance by about 30%. The delamination resistance of the coated paper w~s the same as ~he base paper; however, the de- :
l~mination resistance of the impregnated paper mea~ured in excess of 800 grams/inch, at which point the paper actually : ~ears and does not delamina~e. Hence, from the foregoing data, it should be app~rent for the polymerqfiller blend must be impreg~ated in the paper web r~ther than merely being applied on the surface as a coating, In view of the foregoing description and examples, it should be apparent that the present invention provide~ a novel :
dense paper which possesses the desirable properties of den~e papers without the unde~lrable properties thereof rendering ~ -the paper useful in many applications. Moreover, ~he dense papers of the present invention are capable of being manuf~c- ;
tured economically at relatively high paperm~king machine speeds.
Accordingly, while a preferred embodiment of the present invention has been described in detail, various modi fications, alteration~ or changes m~y be m~de without departing from the spirit and ~cope of the present invention as deined in ~he appended claims.
the lower periphery of a roll rotates in a trough containing ~:
coating, and the upper periphery engages the underside of the advancing web. Thu~, the roll pick~-up the coating from the trough a~d applies it onto the underside of the web. The thick-ness of the coating i8 controlled by passing the coated web over a doctor blade downstream of the roll to allow only a certain amount of coatlng to remain on the under~urface of ~'~
the web.
. -~2-~a~3~
Tne reRin filler blend may even be admixed with the paper stock before applicatlon o ~he furni~h on~o the wire screen.
In order to ensure di~persion of the blend through-out the web, there are certain conditions which must be ob-served in the manuf~cturing proces~. For instance, prior to impregnation, the dry uncalendered density of the web must be controlled so that it is in a range of between 7 and about 11 lbs/mil. The density may be controlled by a v~riety of tech-niques, all of whieh are well known to tho~e skilled in the art.The control of the pre-i~pregn~tion den~ity i8 importan~, be-cause when the dry unc~lendered density is below 7 lb~imil, the resulting paper is too porous. On the other hand, when the dry uncalendered density is about 11 lbs/mil, the web i~
incapable of absorbing ~ ~uffieient amount of impregnant to provide the desired properties.
Another important step in the manufacture of the ~ ..
paper of the present invention is the nece3sity of contro;lling the aunt of solids present in the aqueou~ dispersion through ~:
20 which the web i5 passed. For in~t~nce, ~he solids content, which includes the combined weight of the rigid polymeric material and filler, should be in a range of between about 12.5% and about 60~/o of the tot~l weight of the dispersio~
If the combined weight is below ~he lower limit, webs within the above-stated den~ity r~nge (7-11 lbs/mil) do not acquire a ~ufficient amount of impregn~nt to provide the desired result~
On the other hand, if the percentage i9 ~bove the upper limit, :
the dispersion tends to become viscous and the resin-flller -13- :
:~ .
~ 4 ~ ~ Z ~
blend tends to coat the surface of paper web~ having den~ities clo5e to the 11 lb~/mil upper limit rather than to impregnate the Qame.
The paper web is sub~ected to a heating step after impregnation to fuse the lmpregnant in the paper. In the con-ventional papermaking process, the web is heated to a temper-ature of about 100C. to dry the same so that rigid polymers which have glass transition temperatures in excess of that temperature would not provide s~tisfactory results. Preerably, the upper limit for the glass transition temperature vf rigid polymeric materials employed in the present invention i9 les~
than about 60C.
Certain advantages are realized in manufacturing pa~
per according to this process. For inst3nce, the use of a rigid polymeric impregn~nt heavil~ extended w~th flllers tends to kill the tackiness of the impregnant and renders the drying drums easier to clean. ;~
Summ~rY of th~ Ex~mples The importance of the aforementioned factors in the manufacture of the p3per of the present invention should be-come apparent from the following example~. In brief, Exanples I and II demonstrate the permissible degree of exten~ion of a rigid polymeric material with a mineral iller. In Example III, the importance of the rigidity of the polymer i~ set forth. The types of fillers which are required to provide satisfactory results are exemplified in Example IV. The nece~-si~y of controlling the pre-impregnatlon density of the paper web ls set forth in Example V. The amount of impregnant which , ~14-3~
is re~uired to provide the desired properties is presented in Example VI, The types of rigid poly~eric materials which are required are demonstrated in Example VII. Example VIII demon-strates the abrasion resistance properties of the paper of the present invention. Example IX demonstrates the properties of a paper impregnated with a composition according to the pre-sent invention as compared with a paper coated with the same composition.
~For the purpose of determining the limits ~f ~ e permissible extensîon of the resîn with a minera~ filler, sheets of unsized paper m~de from a blend of 5~% bleached hard-wood kra~t and 50% bleached Northern kraft were used as base p~pers. The basis weight oft~ paper was 51.8 Ibs., which is the weight of 500 sheets measur ~ng 24" x 36". The caliper or thlckness of a single ~heet oE the pape~ wa~ .OOSS" (5.5 mils). Since the density of a paper may be conveniently ex~
pressed as lts weight per mil of ~hickness, the density of the base paper was 51.8 lbs/5.5 mil, or approxim~tely 9.4 lbs/milO
The impregnant was prepared by dispersing fi~ely ground calcium carbonate powder having ~ particle size of about 2 m~crons in water and agitating the same. A finely di~ided rigid polyvinyl ace~ate emulsion was blended with the aqueous dlspersion so ~ :
that the total solids content of the resin and filler wa~ 4~%
by weight of the dispersion~ The cal~ium carbonate which wa~
used is sold under the trade designation CAMEL WHITE by the ~ar~y T. Campbell Sons CoO, Towson, Maryland. The polyvinyl acetate emulsion which was used is sold under the ~r~de des^lg-* Trade Mark ' ~ 3 nation VINAC 880 by ~he Air Products ~nd Chemical Company, Allentown, Pa.
The paper sheets were dipped in the dispersion, and after withdrawal were passed through rubber rollers where ~he excess was squee ed from the sheets. The impregnated sheets were then dried for 4 minutes at 220F., 2 minutes for each side in a Willi~ms paper sheet dryer. The shee~s were per-mitted to condition (cure) for several days before being t~st-ed. The te~r, Mullen and fold tests were conducted according to TAPPI standard procedures identified in Table I. The oil barrier properties were determined by typing a character on the paper with a commercial portable typewriter and observing the difficulty or e~se with which the character ~ould be removed by rubbing with a pencil eraser. Since inks in conventional typewriter ribbons contain substantial amounts of non~drying oil~, there is a direct correlation between the erasability of a p~per and its oil barrier properties. A determination of "excellent" meant that essentially all of the character was erased with a few rubs A rating of "good" meant that ~he character rem~ining after a few rubs was ob~ervable but not apparent to the naked eye after another character was typed over the erased character. A rating of "fair" meant that erasure was acceptable. A rating of "poor" indicated unsa~-isfactory erasure.
The solvent resi~tance properties of the sheets were determined by placing a drop of dyed (purple) toluene on the ~urface of e~ch sheet and allowing it to contact;a predeter-mined area for 30 seconds. The drop of toluene was then wiped ~ 3 away with a paper towel, and the area was rubbed with another paper towel saturated with undyed toluene. This cause~ the dye remaining on the surface to be removed so that the amount of penetration of the p~qper may be determined by ob~erving the presence of the remainlng purple dye. A rating of "good"
meant thflt there had been penetration at several points but that the degree of staining was light and less than about 50%
of the test area. A rating of "fair" meant that light stain^
ing had occurred over most of the test area. A rating of 1'poor" meant that the entire test area beeame darkly stained, A rating of "none" was given if the stain completely penetrated to the back of the paper ~heet.
The re~ults of the tests are set forth in Table I.
It is noted that the notation XD means that the test was con-ducted in the cross machlne direction of the paper. The units of measure9 as well as the identifying numbers on the standard test procedures employed in the various examples are set forth in Table I. ~:
-17- :
.
, . ~- ~ ", .. .
332~
U~
IJ IJ
n~ ~ ~ ~ ~ ,~
,, ~ ~ ~ ,, ~1~rl UOUVUO
o ~ X ~ X X X o ~ o V~ ~ ~ ~ ~ ~ ~ ~ ~ Z
.,~
~ ~ ~ ,, P~
o X X ~ X o o O~ rl ~ U~
V ,~
o~ 1 4 V ~ oo U~
t, o ~,~ ,~ o P~ o ~ ~ ~ o ~ o ,~ a ~d '' o ,1 ~ In 1~ ~~ t~ ~
oo a~ ~ o ~o~ o~
~ o o rO~ ~~ I 0 0 0 0 0 0 0 u ~ ¢ I ~E~
~ ~P o O O o O O O
P; ~ Oh O
U~ # ~J
., ,. .. . . .
: ~ ` : : :: : :
33~ 1~
In the above table, lt may be observed that a paper ~heet prior to trea~men~ ~sample H) h~d a tear s~rength of 147 grams. A similar sheet which had been impregnated with a lOOV/o solution of polyvinyl acetate (sample A) had a tear ~trength of 80 grams. However, lt should be noted ~hat when the impregnant had been extended with calcium carbonate in the range of between 10-70% aQ indicated by samples B-G, the tear strengths of the sheets decrea~ed, but not ~o the same degree a8 W~S observed when the impregnant wa~ 100% polyvinyl acetate.
The oil barrier ~nd ~olvent resistance propertie~ were retained ~:
even though the impregnant had been extended up to about 70%
of its weight with calcium carbonate. Mo~eover, it is nated that the fold endurance of ~he extended-resin impregnant was greater than that measured when the impregnant was 100% poly-vinyl acetate.
EXAMPLE XI
The test procedure described above with respect to Example I W~5 repeated; however, kaolin cl~y wa~ employed a~
a mineral filler in place of the calcium carbonate. The clay utili~ed is sold under the trade designation HYD~APRINT by the J. M. Huber Co~poration, Huber, Georgia. The results of the tests are summ~rized in Table II.
-19- ;
2~
a~ ~, V ~ U V
1:1 R R R R R
a) ~ a~
~ V
o ~J a) ~ ~ ~
V V V U
~X ~X
~q ~
~ Q~
V S~ V ....
5~ ~ a~
~ ~1:4 'I ~ ~ ~
~ V ~1 V V U o P~ ~~,~ X X X O
~ v O ~
~ V
E~ P~ ~ ~ ~ a~
~o C~
~) ~
oo a) _, ~1 ~
o ~ or~ ~ ~
E~ X o~ ~ ~ ,1 ~_ ~1 C~ -.' rl ~
V ~ o O o td ~ ~I GO r~
P;
(~ O o o o ~1 U~
. :
~ . : . , , , . ., . :: . , .
:
:~: :
; : :
From ~he oregoing tests, it ~hould be apparent th~t kaolin clay and calcium carbonate have sub~tantially the same effect as fillers on the proper~ies of a base paper ~hen blend-ed with a rigid polymerlc material and impregnated in the base paper.
EXAMPLE III
For the purpose of demonstrating the importance of impregnatin~ the paper web with a polymer of a predetermined rigidity, the base paper of Example I was impregnated with a series of polymer-filler blends differing only in the thermal glass transition temperature (Tg) of the polymer. As noted heretofore, the Tg is a mea~ure of the rigidity or film stiff~
ness of a polymeric material. In the example, the polymer was extended with calcium carbonate, 60% polymer aRd 40% calcium carbonate.
The re~ults are set forth below in Table III, 2~
a) ~ ~ .~
a) J~
a~ ~ ~ ,4 h oU) ~OOoo oU
U~ ~ O O o O O O X
p:; Z; C~
J- ~ ~ ' ', ~ ~ ~ C g ~t; ~rl ~ ~ ~_ 0~ H h ~t J O O ~: O O
~1~ ~ O XXOO OO
.Z ~ O P~ ~ Z ~!) C~
~d ~1 J 0 4~ p~ r~ o u~
O ~ ~ rl ~ ~ r~
.IJ t~ ~
~ r-l J~ ., t~ O h ~ l ~ ~ a~ ~ ~ ~ ~ .
E~ ~ ~ ~
u~ ,q ~1 ~ ~ pO~
HC!~ U ~ ~~ r-l H~ U O E~ O ~ cn ~ O 1 C~ _ +
~d E~ ~) -J a~ ~ o~ o ~ ~
P ~0 ¢ ~ # rl ~1 co O ~ ~ ~ u~
a~
~rl h , I L~
O
~O ~ J-~I ~
~:J ~1 d td t:O ~ i~ ~ ~ ~1 ~ c~
r~ ~ ~ ~D ~ 00 ~ cr ~1 ~i H
~0 P~ u~
aJ
a) u, o o u~ ~I t) ~/ ~ ~ ¢ u~ .
~d c) o7~1 ~ o o d ~ X X X X X 1:
rl ~ a e S~ ~d ,~ ~ ~
~ t~ ~ :~ td ~ ~o ~ ~o ~ ~o o ~ ~
: : ::. , '. ::~: : ;
: ': : '. '- : : : ' : ; . :
.
:
. ::. . ~ . : :
~ . : :
:. , , , . :`
.
, . ~
' . ' , , 32~
a U
~ ,~
? u~
~rl ~ ~ ~
~ ~
V~ ~ 0 0 ~0 ~ ,, ~ 0 h U h a) ~ V . ~ h al ~0 ~I 0 '0 0 g - a) a~ O P~ 4 æ
E~ v o ~ ~ ~
V U O ~ ~ I~ ~ 00 ~01 a~
~q ~d ~1 .V ~_ ~1 ~0 ~ i~ O n ~ ~ `V Oe ~
H t~ O
~1 ~1 h ~¦
~1 ~1 c~a~ b~ O ~1 ~ ~ ~d E~`--X P ~0 ~ C~ 0~ 0~ ~:
~O I ~00 0~ O O ~D
E~ '~
P~ ~rl V V
rl ~ # ~î
~rl p r-l ~rl ~rl Ot'~) I~
v o tT~ l ~ .
~ rdl ~ ~ ~J
r-l ~ ~ _~
~ ~rVI JJ
~.~ 1~
O F4 1~0 r-l 1~ ~ ~.
~ i~ O~ r~
V
a~
r-l ~ Il~ ~ d tl) V U~ r-l ~ r~
~rl~ l ~i a a d a r~ :
rl .~ ~r ~1 V r l g ~S ~ ~;
~O~ ~0 ~ 1:4 C~
.
, ' .: , , . . .. : . :
- ~ : :' ' .'. "
~ . , ,:. ,; . :
. ' ' , ,, , ., "' . ' ' ' ' 32~
Referxing to the above data, it can be seen that a sheet of paper impregnated with a polyvlny3. acetate having a Tg of 16~C. has fair oil barrier properties and air solvent resistance~ On the other hand, ~ sheet of paper impregnated with a polyacrylate havlng a Tg of 101C.+ does not have any oil barrier propertles or solvent resistance. Accordingly, it should be apparent that a satisfactory polymeric material should have a rigidity, iOe., Tg which is within this range, about 15C. to about 100C., and preferably the Tg shnuld not exceed about 60C.- (See Table VIII regarding a polyvinyl chloride having a Tg of 60C. ? if satisfactory results are to be ensured.
The preferable Tg range is between 22C. and 44C. to ensure fuslon of the polym~r at conventional papermaking processing ~æ~peratures.
EXAMPLE IV
The types o~ mineral fillers employed as extenders have ~l important bearing on the properties of the impregnated ~ :
paper~ This shoul{' be apparent ~rom the present example wherein the base paper of Example- I was impregnated with the polyvinyl aeetate which had been blended with a series of different mineral ~ille~s. Each blend consisted of 40% filler and 60%
polyvlnyl acetate on a dry solids weighL basis. The c~lcium carbonate and clay were the same as employ~d in previous exam~
ples; the talc which was e~ployed is sold under the trade designation MISTRON VAPOR by the United Sierra Division, Cypress ~i~e~, Trenton, New Jersey; the mica is sold under the trade * ~ .
de~ignation DAVENITE MICA P-12 by the Hayden Mica Co., o Wil- -mington, Massachusetts; and the diatom~ceous earth is sold * Trad~ Mark A
, : ' ' " ' ' :
`~J ~ 3Z ~ :
under the trade designa~ion of CELLITE by Johns-Manville Cor-poration, New York9 New York. Each of the aforementi~ned fillers i5 of a commercial grade and quality normally u~i.lized In papermaking applications, having partlcle sizes in the 2-5 micron range.
The result~ of the test are set forth in Table IV.
* Trade Mark ~ .
-~5- :~
A
. ~. ~ . ~. .
.
832~
~U ~ ~ U
U
~u ~u~u ~u ~u .~ ~ ~ ,...
~ n u u u ~ u h O ~r~ ~ O
u~ ~n p~ X~ 1 X F40 ~U rlJ
~rl h ~U ~ 1 ~ h O h O O O OO O
h r J X ~ O OO O
~rn ~rî ,1 oo ~ ~J
h r ~
H.,1r J *
~11:4'~U 'O ~ ~1 u~
~ 0 ¢ o 4~ ~ N
i~ O H ~ ~ ~U') ~t ~ N N
tl~`~ h ~
P ~ ~ ~ O ~ or~ $, o E~ '~
P~
~:
O
a P~ r~
~o ~n F3 h ~u ~ ~ NN ~1 E~i ~ ~
H
. ~ r_ C~,~ .
~U ~ H ~ N N
~ ~ ~ ~ ~ 'O
H aJ
?~ (U
o ~1 aJ :
W ~1 p~ Z ,~
D Z; C.) ~ t #
.:
':' ~
' - ' . ' , From the above ~a~le, it should be ~pparent that calcium carbonate, clay, talc, and: mica prnvide ~atisfaetory fillers; where~s, di~tomaceous earth i8 unsa~i~factory because the resulting paper provLdes poor oil barrier p~operties ~nd poor solvent resistance.
EXAMPLE V
__ The importance of controlling the density of the paper web prior to impregnation is illustrated in the pre~ent example, An aqueous dispersion of polyvinyl acetate and cal-cium carbonate W~5 prepared as in Exa~ple I. The polyner-filler blend constituted 40% of the weight of the di~per~ion, ~ ~
and the ratio of polymer to filler wa~ 60/40 on ~ weight basis. ~:
A series of s~eets of unsized paper of different densities were dipped into the dispersion, and the excess impregnant was removed from the sheets by passing them through rubber rollers and blotting the surface of the sheets with paper towe~s to ensure t~e removal of excess impregnant from the ~urf~ce of the sheets. The sheet~ were thereafter dried for 4 minutes ~t 220~., conditioned for several d~ys, ~nd tested a~ noted heretofore. For comparison purposes, a dispersion was prepared i;
wherein only polyv~nyl acetate wa~ present at 40% by ~eight ~olids, and a second ~et of base papers were similarly impre~-nated. As ~ urther compari~on, plain paper which had not bee~
impregnated was al~e tested.
The re~ults of the te~ts ~re set forth below ln Table V. ~ .
~7 ~ . . ............. . .
,, . ~. .
3~
~ l C) h S~
Z ~ C~ W
~: ¢ O P
al p h p~
~0 ~ ~( 1` ~ ~I r~ oo O
O O ~ ~ O ~ ~ O U~
~Ll F4--~ ~
a) ,1::
~ ~ri S~ _~
U~ ~ (~ ~ ~00 1~ 0 ~ O
~O
~ ~ ~ r~
td ~ ~ ~ O ~1 ~ ~ a~
0 4~ ~ ~ I I U~
~ _~ ~1 ~1 ~I
¢ h ~ ,~ ~ ~ ~ o :~ E~
_~ ~ ~ O ~ I~ U~ ,1 ~ ~ o ~ ~ ~ ~ O ~ ~ co ~ ~, o 8 ~1 ~3 ~ ~ ~ ~ ~ ~n ~ ~I ~ oo :q ~ ~ # c!
h ~c E~ O ~ h h O ~1 ~rl ~; ~4 1~1 ~ ~1 ~ ~1 1~1 C~ IY h h ~ 4 3 ~11 R
'O ~ X l U~ o o ~ o ~ ~I 0 ~ ~ ~ O ~ ~ ~ ~ ~1 o ~3 o~
P~
H l X ~.
to 0 J- a h J- 00 u ) 1` u~
CO ~r) O cn o ~3 U~ ~o 1~ oO o~ a~ ~ o ~ ~ ~D ~ ,1 ~ a) ~4 O h h to 'O
~1 ~ O r~
_ o ,i ~ I g _ ~ ~ ~ ~ ~ V~
h ~ Z
t~l ¢ ~ ~ ~ ~ ~ 1~ 5: H
P~ ~t #
" : ' ' . ' .
.
~ 3~
From the above table, it Yhould be apparent that the minimum uncalendered density of the paper web prior to impregnation should be greater ~han the 6,9 lbs/mil as in s~mple B. The maxlmum uncalendered impregnation den~ity should not exceed the 11.0 lbs/mil value as in sample I. It i8 noted that even though sample B contained 48.5% impregnant, it was unsatisfactory from an oil barrier stflndpoint. Although sam-ple J had excellent oil barrier properties, i~ acquired 9.1%
of impregnant but posse~sed very l~w tear strength, It is:~
further noted that each of the papers which was ~atisfactory had a finished uncalendered density in excess of 10.5 lbs/mil and less th~n about 14.0 lbs/mil.
EXAMPLE VI
The amount of polymer-filler impregnant which is necessary to provide a satisfactory paper is e~emplified in the present example wherein a b~se paper fabricated from Nor~
thern bleached kraft pulp and containing approximately 5% tit-anium dioxide was employed. Although the paper wa~ unsized there was a slight sizing effect due to some re~idual pit~h; ` :~
however, this was not believed sufficient to have prevented penetration of the impregnant into the interior of the sheet.
The basis weight of the paper was 34.6 lbs (24" x 36" ~ 500 sheets). The s~mples were prepared as set forth in Example V;
however, the solids content of the impregnant was varled from :~
~0% to 40%.
The results of the test are ~et forth in Table VI. ::
- 29- :
,. . . ~ . ~ , .
: ~ -v~
~l cJ ~ ~ ou~ o o o S~ ~ ~ ~1 ~ ~ ~ ~
~ro g H U~ t~
., d ~q ~ ~1 ~1 ~1 ~n ~1 ~ ~~o a~ ~,~ o ~d O ~C O O O
, O ~
o r~ 0~ ~ I 00 ~ ~ ~ ~ ~D
',i ~ E~
H ¦ O ~.
~ d ¢ r~
E-l t3 ~. o ~_ ~ CO o ~ ,~
~!
d o ~ ~ ~
~ ~ ~ ~ , .
.~ ~ ~ ~ ~ ~ I~ o U~ ~ o ,.
Q~ ~ i O O O ~i t~
~ ~ a ~ ,~
h ~
a) h a a~
r~ ~ O O ~1 ~D O
~ a ~O,; u~ ~ O O ,~
r~ r~ ~ ~ ~ O
h a) c~ aJ
td b a) ~ o . .
~ ¢ ~C,) 1~ I I 'X ' .. '1' V~ ,~
. _30_ . . .
:,.. ' , ~ " . ' ' :
: , , - . . :
. . ' : ~,, ': :, , '::, :
:.
- ' ' ~ ' , " ', ' ':
~' :, ' : ', :' : ' ~
~ 3~
From ~he above d~t~, it should be apparen~ that a signiflcant improvement in oil barrier p~operties and ~olding endurance properties occurs when the polymer-filler impregnant constitutes between about 6-10%, or about 8.5% of the weight of the sheet (sample B~ with highly desirable proper~ies re-sulting when the impregn~nt is in 3 range between 15-25% of the weight of the ~heet, as indicated in samples D and E, and up to ~bout 48% as indic~ted in Example I (page 19, infra). ~;
EXAMPLE VII
In order to demon~trate the different types of rigid polymerlc m~terials which m~y be employed ~atisfactor;ly in m~nu~cturing paper of the present invention, sheets of the ~::
base paper of Example I were impregnated with a polymer-filler dispersion having ~ ~olid~ content of 40% by weight, with the weight ratio of polymer to filler being 60% to 40%. The filler was calcium carbon3te, and the polymers included: RHOPLEX
AC-201, a polyacrylate em~lsion n~nufactured by Rohm & Haas Co., Philadelphia, Pa.; and GEON 351, a polyvinyl chloride emulsion m~nufactured by the B.F. Goodrich Chemic~l Co., Akron, Ohio.
The test results are sumN~rized below in Table VII.
~,'` .
':
, ::
~: K
I~ a) ? ~ U ~ ~1 O O ~rl 0 I #
~rl 0 ~ ~ W ~ P~
O a~
a ¦
U) ~1 ~ O ~ O
~ ~ ~ ~ r~
h d ~1 ~ :
U~ (IJ 0 ~ ~3 ~ X ~ ~o ~ oo a~
~ P E~ ; ~
P ' ~ K
~ t~ 00 ~
o ~ a) tO~rl o o ~ c~ , O 0 ~ 0 ~:: Ei ~') ~ ~ ~`i :
? H ~ ~1 ~1 ~1 ~1 E~ 5~
H O O I ~ ¦
~1 0 t~ O C~ ~ ~ I~ O O C~l a0 ~ c~
d ~ I ~ ~ ~t `;t `;J
o ~ o~ .
~,~ ~0~ .
~ ~:1 ~ C~ .
~? E~ ?. ::
a~ l o o o o X'01~ ' a~ o o o ~1 ;~ .,~ .,1 P~
dP~; ~1 o ~:1 h o al o ~0 a~ ?. ~ ~ ~?. ~ a ~ 4~
hO h ~h~
Ei E~ 0 0 ~ h? 5 1 ~c1 X ~ ~4 H~ ~ O P~ ~1 ;~ O ?. O d a O 0 0 0 0 O~C OrC V ~1 ~
P~ o ,, J-l ~ h d a) , Or ) ~ d d d o h ~1 -- ~`1 ~1 0 d a~ 1 X g X ~1 ~ X O P~ c~ O h h 0 ~J
t~ 1:~1 0 0 ~1 ~`I ~1 P~ ~, O
~1 ~`1 c~ ~1 d ~ `1 ~/13 ~3 d 11 11 h ~ o ¢ ~ o ¢ æ u~ z u~ H H p ~1 P~
E3 0 ~ 1 1 1 #
H 1:~ K ~i ~ ~ ~1~`J * K
.
' ''' -: .: : :
::: . .
: : ' ' ':
~ 3~2~
From the above data, i~ should be apparent that an impregnant consisting of a rigid polyacrylflte material extended with calcium carbonate has substan~ially the same effect on a base paper a~ a rigid polyvinyl ac~tate and calcium carbon-ate impregn~nt (compare Tables I and VII). It is n~ ed that :
similar results are obtained when the impregnant consists of a blend of polyvinyl chloride extended wi~h calcium carbonate; ~ :
however, the solvent resistance and oil barrier properties of the impregnated paper are actually higher with the extend~d lmpregnant than with the unextended impregnant. Accordingly, it ~hould be app3rent that beneficial results can be arhieved ~' only by employing certain ~ypes of rigid polymeric materials such as polyvinyl acetate, polyacrylate, and polyvinyl chloride.
EXAMPLE VIII
The paper of the present invention has good abrasion ~ :
resistance even though the impregnant blend is ex~ended with slgnificant percentages of filler and even though considerably less than half of the weight of the paper is provided by the impregnant. In determining the abraslon resistance of the paper of the present invention, sheets of the base paper ofExample I we~e impregnated with various rigid polymers and polymer-filler blends in accordance with the procedure of Example I. The polyvinyl acetate polymer was VINAC 880; the poly~crylate polymer was RHOPLEX 407; and the polyvinyl chlor-ide was GEON 351, The sheets were subjected to the Tabor Abrasion Test according to TAPPI Stan~ard procedures (TAPPI
T 476 t~-63). An H-18 abraslve wheel was utilized in the test, and the number of cycles of rotation of the wheel until a hole ' was worn in the ~heet were counted. The re~ult~ ~re ~et :iEorth in Table VIII .
'~ ~
, . .
: ' ' ' , ,:
.. . . .
33;~
~, d O
I~ C~l O U~ ~ ~ O .' ~i 1~ o ~t '' "
~ ' .~
H . .
.,1 ~ a) ~ a) h H¢ 0~ F4 O
t~d X o o o o o o ~ o E-~ toto o ~ o o o u~ ~o~
0~ P;
O g O
O rd Q~
tU tl) t~ a~ a) O ~J
u c~ U ~ a~ rC ~ r~
¢ ¢
~ ~ ~ ~ ~ ~ ~ ~ ?~
tl~ ~ ~ t~
~ o o o o o o o o o ~:
~, -35 ..... .
,~ ' , , , ' . - . , .
:, ~ 3 2 ~
From the above data, i~ should be apparent tha~ ~he abrasion reslstance of a paper sheet which ha~ been impregna-~ed with a blend of a rigid polyvinyl acetate and a mineral filler s~ch as calclum carbonflte, is only slightly less (530 cysle~) than a paper sheet impregnated with polyvinyl acetate only ~600 cycles). A sheet impregnated wi~h polyvinyl acet~e extended wi~h clay in the stated propor~ions has even greater abrasion resistance than does a sheet impregnated with poly-vinyl acetate only, A sheet impregnated with a polyacrylate m~terial extended with calcium carbonate also has a higher abrasion resistance than does a sheet impregnated only with the polyacrylate, The abrasion resistance of a sheet i~reg- ~ -nated with a filler-extended blend of polyvinyl chloride has :~ :
slightly greater abrasion resistance ~400 cycles) than does a simil~r sheet impregnated with the polyvinyl chloride only. :~
EXAMPLE IX
The paper of the present invention must be impreg-nated with the above~noted dispersion; it cannot be produced merely by applying the dispersion as a co~ting. To demonstra~e thi~, sheets of a base paper having a basis weight of 54.1 lbs (500 sheets 24" x 36") and a caliper of 5O5 mil~, were im-pregnated and coa~ed with the polymer-filler compositionO For example, a sheet of base paper was impregnated with the compo-sition described in Example I and another sheet of the base ~:
p~per was coated wi~h the same composition in the manner des-cribed in Example I of U.S. Patent 3,634,298, except that Virlac 880 polyvlnyl acetate having a Tg of 31C. was substi- ~
tuted for the polymer ~ynthesized :Ln Example I of the patent ~.:
-36~
' ~' ... . .
3;2~
to form the aqueous clay-polymer dispersion. The dispersion comprised 55%, by weight, of ~he clay-polymer blend in a ratio ; ;-of 83% clay to 17% polymer, The resulting di~persion was ap-plied to one side of ~he ba3e paper as a coating, using a Meyer bar, as described in Example I of ~ patent. The coated paper was thereafter dried for one minute at 300F.
The coated and impregnated papers were later tested for tear, burst and fold properties, and the results of the tests are set forth in Table IX.
: ~
, .
. : .
3~1 R
r1 ~
t.) t~ R
a ~ R
e u~ o O o e ~ U~ ~
.
~0 ~ ~ `D 0 ~0 a~ ~.C
~1 , .
~ O
~ . . ~ `J ~
O ~ ~ 0 0~ U~
~, ~ ~ ~, R
c~
o~ ~ o :~
X
e u~
E~
~ P~
~ e ~ ~ ~
~O
R ~ ~ ~ ,1 ~1 ..
~J
a~ ~a c~ ~1 u~ ~ ~ :
~1 ~
u I I
a`e rl .~ d ~ o e O ~ ~ .
~ ~.~ ~ , .
~, e u~ e ~ O
~d ~ 4 H d F~
.
. . .
From the foregoing table, i~ may be seen ~h~t impreg~ -nation decreased ~eflr strength about 13% while coating lncreased tear strength by about 12~/o~ Impregnation more than doubled burst strength while coating only increa~ed burst strength by about 50%. In the fold test, impregnation con~iderably more th3n doubled the fold endurance (even at the lower 10-20% rela-tive humidity) whereas coating actually decreased the fold endurance by about 30%. The delamination resistance of the coated paper w~s the same as ~he base paper; however, the de- :
l~mination resistance of the impregnated paper mea~ured in excess of 800 grams/inch, at which point the paper actually : ~ears and does not delamina~e. Hence, from the foregoing data, it should be app~rent for the polymerqfiller blend must be impreg~ated in the paper web r~ther than merely being applied on the surface as a coating, In view of the foregoing description and examples, it should be apparent that the present invention provide~ a novel :
dense paper which possesses the desirable properties of den~e papers without the unde~lrable properties thereof rendering ~ -the paper useful in many applications. Moreover, ~he dense papers of the present invention are capable of being manuf~c- ;
tured economically at relatively high paperm~king machine speeds.
Accordingly, while a preferred embodiment of the present invention has been described in detail, various modi fications, alteration~ or changes m~y be m~de without departing from the spirit and ~cope of the present invention as deined in ~he appended claims.
Claims (15)
1. A dense paper comprising a web of cellulosic fibers having an impregnant dispersed throughout the web, said web containing from about 8.5% to about 50%, by weight, of the impregnant, based on the dry weight of the fibers, and said impregnant consisting essentially of from about 35% to about 90% of a rigid polymeric material and from about 10% to about 65% of an inorganic filler, said percentages of polymeric material and filler being by weight based on the weight of said impregnant.
2. The paper according to claim 1 wherein said poly-mer has a glass transition temperature in a range of between about 15°C. to about 60°C.
3. The paper according to claim 2 wherein said glass transition temperature is in a range of between about 22°C. to about 44°C.
4. The paper according to claim 1 wherein said paper has a finished uncalendered density of at least about 10.5 lbs/mil and less than about 14.0 lbs/mil based on 500 sheets 24" x 36".
5. The paper according to claim 1 wherein said im-pregnant is in a range of between about 15% to about 40% of the finished weight of said paper.
6. The paper according to claim 1 wherein said filler is in a range of between about 20% to about 65% of the weight of said impregnant.
7. The paper according to claim 1 wherein said poly-meric material is selected from the group of polymeric mater-ials consisting of: polyvinyl acetate, polyacrylate, and poly-vinyl chloride or mixtures thereof.
8. The paper according to claim 7 wherein said selected polymeric material includes copolymers and homopoly-mers thereof.
9. A paper according to claim 1 wherein said filler is selected from the group of minerals consisting of: clay, calcium carbonate, mica, and talc or blends thereof.
10. A process for manufacturing dense paper compris-ing the steps, performed in the following sequence, of:
advancing a web of paper having a dry uncalendered density between opposite surfaces in a range of between about 7 to about 11 lbs/mil;
impregnating the advancing web by applying to both of said surfaces an excess amount of an aqueous dispersion containing a blend of a rigid polymeric material and an inorganic filler, said blend consisting essentially of from about 35 to about 90%
of said polymeric material and from about 10 to about 65% of said inorganic filler, said percentages being by weight based on the weight of the blend, said rigid poly-meric material having a glass transition temperature in a range of between about 15 to about 60° C., and passing said advancing web between opposed squeeze rolls to ensure penetration of said web by said dispersion and to remove excess disper-sion from said surfaces; and heating said web after it passes between said rolls and said excess dispersion has been removed to fuse said blend in said web in a range of between about 8.5% to about 50%, by weight, of the blend, said weight being based on the dry weight of the web.
advancing a web of paper having a dry uncalendered density between opposite surfaces in a range of between about 7 to about 11 lbs/mil;
impregnating the advancing web by applying to both of said surfaces an excess amount of an aqueous dispersion containing a blend of a rigid polymeric material and an inorganic filler, said blend consisting essentially of from about 35 to about 90%
of said polymeric material and from about 10 to about 65% of said inorganic filler, said percentages being by weight based on the weight of the blend, said rigid poly-meric material having a glass transition temperature in a range of between about 15 to about 60° C., and passing said advancing web between opposed squeeze rolls to ensure penetration of said web by said dispersion and to remove excess disper-sion from said surfaces; and heating said web after it passes between said rolls and said excess dispersion has been removed to fuse said blend in said web in a range of between about 8.5% to about 50%, by weight, of the blend, said weight being based on the dry weight of the web.
11. The process according to claim 10 wherein said polymeric material of said blend is selected from the group of materials consisting of polyvinyl 2cetate, polyacrylate 9 ~nd polyvinyl chloride.
12. The proce~s according to claim 10 wherein said inorganic filler is selected from the group of fillers consist-ing of clay9 calcium carbonate, mica~ and talc.
13. The process according to claim 10 wh~rein s~id aqueou~ dispersion contains between about 12.5 and 60%, by weight, of said blend, ba~ed on the total weight o said di9 persion.
14. The process according to cl~im 10 wherein the density of said paper web prior to impregnation with said~blend is in ~ range of between about 8.5 to about 10~5 lbs./mil.
15. The process according to clal~ 10 wherein said web prior to impregnation is ~ubstantially free of sizing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA76256508A CA1048321A (en) | 1976-07-07 | 1976-07-07 | Dense paper and method of manufacturing |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA76256508A CA1048321A (en) | 1976-07-07 | 1976-07-07 | Dense paper and method of manufacturing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048321A true CA1048321A (en) | 1979-02-13 |
Family
ID=4106387
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA76256508A Expired CA1048321A (en) | 1976-07-07 | 1976-07-07 | Dense paper and method of manufacturing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1048321A (en) |
-
1976
- 1976-07-07 CA CA76256508A patent/CA1048321A/en not_active Expired
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