Note: Descriptions are shown in the official language in which they were submitted.
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-
-3-
.; .
~ 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
-4-
.. ..
.
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
-7-
.. . . .
-
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
-10-
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-
-15
* 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
-16
~ 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
-18-
.,
,. .. . . .
: ~ ` : : :: : :
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~
--20--
. :
~ . : . , , , . ., . :: . , .
:
:~: :
; : :
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,
-21-
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 ~ ~
--22--
: : ::. , '. ::~: : ;
: ': : '. '- : : : ' : ; . :
.
:
. ::. . ~ . : :
~ . : :
:. , , , . :`
.
, . ~
' . ' , ,
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~
--23--
.
, ' .: , , . . .. : . :
- ~ : :' ' .'. "
~ . , ,:. ,; . :
. ' ' , ,, , ., "' . ' ' '
'
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
-24-
* 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 #
-26-
.:
':' ~
'
- ' . ' ,
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 #
-28--
" : ' ' . '
.
.
~ 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.
~,'` .
':
, ::
-31-
~: 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
.
-32
' ''' -: .: : :
::: . .
: : ' '
':
~ 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
33-
'
was worn in the ~heet were counted. The re~ult~ ~re ~et :iEorth
in Table VIII .
'~ ~
,
. .
-34-
: '
' '
, ,:
.. . . .
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.
: ~
-37-
,
.
. : .
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~
--38-
.
. . .
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.
39
