Note: Descriptions are shown in the official language in which they were submitted.
The present invention is directed to a novel ~ethod for the
production of impregnated papers which can be carried out in
single operation on a paper making machine. Ihe improved
method can produce both smooth and creped papers in a similar
manner, and the resultant products are particularly useful as
substrates for masking and packlng tapes.
Impregnated papers have many commercial uses; for example,
cab]e and insulating papers for the electrical industry,
abrasive papers, high-grade wall papers, moisture resistent
shaped bodies and door elements in the construction and
furniture industries, decorative papers used in conjunction
with laminated pressed boards, and reinforcement elements for
foam structures and strips. One of the most important uses,
however, is as the substrate for pressure-sensitive adhesive
masses, especially those used as masking and packing tapes.
; .
In order that impregnated papers be satisfactory as
substrates for pressure-sensitive adhesive masses, it is
essential that the impregnating agent hold the fibers of the
paper together so that the finished paper exhibits sufficient
picking and splitting strengthO Since tapes of this character
are usually marketed in roll form, each adhesive coating is in
direct contact with the surface of the backing paper of the
adjacent layer of tape. Therefore, the picking and splitting
strength of this paper must meet stringent requirements to
prevent tearing or splitting when the tape is removed from the
roll.
~5~%
In addition to the foregoing reguirement, the support
material must also provide the necessary strength, elasticity,
and stretchability to permit the application of the tape around
corners, bends, and on irregular surfaces without tearing.
Moreover, the paper must also have substantial resistance to
both heat and water, since it will be subjected thereto during
use.
In the past, it has been customary ~o impregnate finished
papers having good absorption capacity (such as cellulose
papers) on special impregnating machines using solutions or
aqueous dispersions (latices) of preferably rubber-like
polymers or elastomers. The paper webs thus created are then
dried at elevated temperatures. Clearly, the impregnating and
drying of completed papers constitute additional operations,
with the attendant increase in cost. Moreover, of all the
conversion steps, the impregnation (whether the paper be smooth
or creped) is always the most time-consuming. Under normal
circumstance.,, the drying channel can be operated only at a
relatively low speed.
~20 A further factor is that, in the conventional method of
papermaking, a very high wet-strength sizing is usually
introduced. During the impregnation step which takes place
after the completion of the paper, this sizing tends to repel
the rubber particles and keep them away from the fibers. This
often leads to irregular distribution of the particles in the
paper.
~s~
Experi~ents have shown that, if the foregoing requirements
are to be satisfied, it is not possible to impregnate directly
on the papermak;ng machine because of the thermoplasticity and
the tackiness connected therewith. Generally, an attempt to do
so leads to the web sticking to and smearing on the hot
cylinders and/or the drying felts. The sticking causes the web
to tear, resulting in serious disturbances of - or breakdowns
in - the manufacturing process. This is especially true in the
case of thin papers.
An object of the present invention is, therefore, to
minimize sticking in the papermaking machine, and to eliminate
the expensive separate impregnating and drying steps which have
previously been applied to ready made papers.
It is a further object ~f the present invention to provide
a method which permits the production of impregnated papers,
whether smooth or creped, in a single operation on the usual
form of papermaking machine.
In practicing the present invention, it has been found that
these objects can be achieved by adding specific proportions of
~20 a certain mixture to the pulp or the moist paper with a defined
residual moisture content. In the case of thin papers, the
mixture can be added at a single point after the web has been
formed. As to heavier papers, the mixture is added in two
specific stages during the manufacturing process.
--4--
The mixture is usually in the form of an aqueous dispersion
and contains (a) a small amount of a silicone-free, adhesive
repellent surface-active agent, (b) an elastomer or rubber like
polymer as the principal component, and (c) a small amount of a
paper softener.
As a result of the addition of the foregoing mixture, it is
possible to produce impregnated smooth or creped papers having
the properties desired for use as the substrate for pressure
sensi~ive adhesive masses. Moreover, this can be accomplished
on a papermaking machine, in a single operation, while
minimizing or eliminating undesirable sticking of the paper web
on the hot cylinders or felts during the drying process.
Production speed is increased and the quantity of wet strength
agent to be used can be reduced to abouL 50~/O of the usual
quantity-
More specifically, in the more common form of theinvention, the mixture is added to the fiber suspension or pulp
prior to sheet formation. The usual wet strength agents,
sizing agents, fillers, dyes, e~c~ may also be included. The
amount added is 1% to 12% by weight based on the dry fiber or
pulp. The composition of the mixture, based upon the dry
weight thereof, is
0.5% to 5.0% of a silicone free, adhesive repellent surface
active agent,
89.0% to 95.5% of an elastomer or rubber-like polymer, and
2.0% to 6O0% of a paper softener.
After the addition of the foregoing mixture, the paper web
is formed in the usual manner on the machine.` The web produced
,~ -5~
has a residual water content of 6% to 20~/o whell a second portion
of the mixture is applied thereto in such a quantity that, when
dried, the paper contains 7V/o to 60% by weight of the mixture.
Of course, if creped paper is desired, a known creping device
can be inserted in the papermaking machine in the usual manner.
It is, of course, generally known to acld various additives
to the pulp or the paper web by a number of di~ferent mean~.
These additives are introduced to the fiber suspension, the
moist paper web after formation, and the dried paper. Sizing
agents, for example, can be added to the pulp ("pulp sizing")
or to the finished paper ("surface sizing"~ by known
mechanisms, such as size presses, sprayers, or the like.
However, with the exception of the case of silicones, the
use of mixtures containing an adhesive repellent, surface
active agent to impregnate the paper has not been known. On
the contrary, those of ordinary skill in the art believed that
the presence of such materials would interfere with the
manufacturing process, even when only small amounts were
present, since such agents are preferably hydrophobic
substances. It was all the more surprising, therefore, that
the presence of a small amount of such an adhesive repellent
agent in the impregnating mixture in no way interferes with the
papermaking process and, additionally, provides great
advantages in that it suppresses the undesirable sticking of
the paper web durLng the drying procéss.
In British Pat:ent 922,828, there is disclosed a method of
treating papers, particularly parchment and waxed papers, with
a mixture of silicone rubber and silicone resin, to which other
. .
substances such as carboxyrnethyl cellulose or condensation
prod~cts of epichlorohydrin with aliphatic amines may be
added. However, because of their strong adhesive-rejecting
properties, such papers are useful as separators or
intermediate layers in connection with sticky substances or
pressure sensitive adhesives of various kinds. They are also
useful as intermediate supports for transferable adhesive
films, but in no way can they be used as a permanent support or
substrate Eor pressure sensitive adhesive masses. ~loreover,
]0 silicones cannot be used with ordinary papermaking machines
since they tend to deposit irreversibly on screens, felts,
etc., and cannot be removed therefrom. A further factor is
that, in the presence of silicones, it is not possible to crepe
the paper, as the scraper will not grip the siliconed surface.
There should also be mentioned in this connection
Applicants' earlier application DAS 2 809 422 relating to a
method for the production of a stretchable paper having nigh
picking and splitting strength. There is added to the fiber
suspension or pulp, in addition to other materials, a mixture
comprising a small quantity of a specific adhesive repellent
agent and a large quantity of synthetic rubber or resin. The
addition takes place prior to the breast box. The result is a
method for the production of speclal papers which can be used
advantageously to support highly adhesive, pressure sensitive
masses of high shearing and peeling strength. These are useful
for the production of heavy duty masking tapes, but are not the
result of an impregnation method. Hence, the problem se~ forth
and solved in thal: reference is not relevant to the present
situation.
-7-
5~
As the adhesive repellent, surface active agents of the
present invention, it has been found advantageous to use
organic compounds which contain, in the molecule (l) at least
one long chain alkyl or alkanoyl radical having 12 to 21 carbon
atoms and ~2) reactive polar groups. In particular, stearoyl
or stearyl groups exemplify the former, and carboxyl, nitrile,
amino, hydroxyl~ ketene, or acid anllydride groups exemplify the
latter.
Particularly suitable compounds are:
N,N'-diacyl compounds of polyalkylene polyamines with
long-chain hydrocarbon radicals, in particular those containing
at least one unreacted secondary amino group, such as
N,N'-distearoyl dipropylene triamine and N,N'-dipalmitoyl
triethylene tetramine;
polyvinyl carbamates, such as
polyvinyl-N-octadecyl carbamate and polyvinyl-N-pentadecyl
carbamate;
triethanolamine monostearyl carbamate;
glycerin monostearyl carbamate;
pentaerythritol monostearyl carbamate;
triethanolamino monostearate;
triethanolamino monopalmitate;
triethanolamino monooleate;
glycerin monostearate;
reaction products of stearyl isocyanate with urea or melamine
resins or with tr:iethanolamine;
low molecular polybutadienes containing hydroxyl groups which,
are fully or part:ially reacted with stearyl isocyanate;
copolymers resulting from emulsion polymerization of maleic
acid monoamides or maleic acid monoesters having long-chain
~ s~
h rocarbon rad;cals with ~tyrene or its derivatives, the
copolymers additionally may contain crosslinkin~ components
with reactive functional groups or carboxyl groups;
copolymers of butadiene with no more than 3()% styrene in
which are incorporated 2 - 20% maleic acid monoamides or
monoesters;
complex compounds of stearic acid with basic chromium
chloride (Werner complexes); and
polytetrafluoroethylene.
The percentage of surface active agent in the impregnating
mixture is 0.5 to 5% by weight, preferably 1% to 3% by weight.
These percentages are based on the solids in the total
composition of the mixture.
Since the Eoregoing substances are only slightly soluble in
organic solvents, and are virtually insoluble in water, they
are advantageously dispersed in water with the aid of suitable
emulsifiers. It may also be found useful to adsorb these
substances on highly dispersed silica or other customary finely
divided fillers. These dispersions (whether adsorbed or not)
are stirred into an aqueou.s dispPrsion of an elastomer or
rubber-like polymer to produce the impregnating mixture of the
present invention. In particular, mixtures of non-ionic and
anionic emulsifiers in a 1:1 ratio have been found suitable.
More specifically, aromatic polyglycol ethers, alkyl
sulfonates, or alkylaryl sulfonates can be used. In
particular, nonyl phenol poly~,lycol ether is desirable.
The elastomer or rubber-like polymer is present in the
mixture in an amount of 89.0% to 95.5% by weight, based on the
wei~ht of solids in the total mixture. It forms the main
component and may advantageously comprise:
butadiene styr~ene copolymers with a styrene content of ?3
to 55%,
_9_
}
butadiene-acrylonitrile copolymers having a Mooney
viscosity of about 40 to 160, preferably between 65 and 85,
terpolymers of butadiene, styrene and acrylonitrile,
acrylic acid butyl ester-acrylic acid copolymers or
5 mixtures thereof,
aqueous acrylate copolymer dispersions containing a small
quantity of acrylic and/or methacrylic acid and up to 15%
acrylonitrile,
aqueous acrylate copolymers dispersions having butadiene
10 acrylonitrile and/or acrylic acid esters, polyvinyl acetate,
polyvinyl chloride or polyvinylidene chloride as a component
thereof; e.g. mixtures of butadiene-acrylonitrile co- or
ter-polymers with polyvinyl acetate; as well as polyurethane
latices and polychloroprene dispersions.
Among butadiene acrylonitrile or butadiene-styrene
copolymers there may be used also relatively low molecular
sticky types in the form o their latices.
The paper softeners constitute the third component of the
mixture and are present in an amount of 2% to ~% by weight,
20 preferably 3% to 4% by weight, based on the amount of solids in
the total mixture. Glycols and triethanolamine have been found
particularly suitable. Depending upon the type and quantity of
the addition, this preferably water soluble component provides
a degree of hydrophilia in the finished paper. This
25 characteristic is of importance for subsequent treatment steps.
The impregnating mixture of the present invention is
preferably used in the form of a 20% to 55% aqueous
dispersion. The preferred range is 33% to 42~to~ The dispersion
~t -10- ` '
~ 5~
may include, for modificc3tion of its properties in known
manner, minor quantities of additional substances. ~nong these
are viscosity regulators; such as polyacrylamides,
polyvinylalcohols, and polyvinylpyrrolidone. In addition,
precondensates such as water soluble urea or melamine
formaldehyde resins containing free reactive groups may be
included. More specifically, methylol ureas, methylol
melamines, ~nd methylol acrylamide fall into this categoryO
The selection of these individual components is generally
known in the artO The object is to obtain a relatively sof~,
pliable paper which can be slightly crosslinked in a subsequent
reaction to obtain the required stiffness and strength values
in both the lengthwise and crosswise directions. IE the paper
is to be used as a substrate for pressure sensitive masking
tape, it must be flexible and soft, coatable, and impervious to
coating agents, solvents, and dispersions. Since such tape is
used by painters and lacquerers, it must have all of these
properties in order to prevent leakage and, in addition, it
should be as thin as possible.
. .
The fiber suspension or pulp should preferably consist of
pure cellulose and advantageously it should be comminuted to
between 18 and 38 SR. In the form of the invention in which
the mixture is added in two parts, the first addition is
; advantageously carried out after the beating operation. An
amount o 1% to ].2% by weight, preferably 2% to 4% by weight,
based on the dry fiber or pulp is introduced.
- 1 1-
When makin~ a lightweight paper having a weight oi up to
approximately 80g/m2 the addition of a portion of the
impregnating mixture to the pulp before sheet formation can be
omitted. In that case, the entire quantity of the mixture is
added to the paper web (which has a residual water content of
6% to 20%~ by means of, for example, a sizing press.
To further modify the properties of the paper, small
amounts of customary additives such as sizing agents, natural
resin soap (sodium resinate), alum, waxes, starch, animal
glues, and caseln may be added. In addition, fillers such as
alumina, chalk, metal oxides or salts, etc., as well as dyes
may also be introduced. It is preferable to add these
materials to the fiber suspension or pulp.
The wet strength agent is preferably added to the iber
suspension or pulp in the form of an aqeuous dispersion before
the breast box, but after the admixture of 0.~% to 0.5% alum.
The latter activates the fibers and catalyzes the bonding o
the resin thereto. The wet strength agent, in a preferred form
of the invention, comprises melamine or urea formaldehyde
resins containing methylol groups and having a crosslinking
action at elevated temperature. When using the impregnating
mixture of the present invention, the amount of wet strength
agent can be reduced by more than half, as compared with the
quantity which would normally be used; for example, 2.4% can be
used instead of 6.5%, based on the dry fiber or pulp.
The exaet quantities - as well as the ratios - of the
substances to be added depend upon the web velocity in the wet
section and on the throughput of the substances per unit time.
These amounts can be easily determined by a simple trial on the
part of the person of ordinary skill.
If the paper is to be creped, this can be done on the wet
roll with a thin, sharp scraper. This portion of the process
can be carried out, at the earliest, at the point when the
paper web being formed has sufficient strength to withstand the
high stresses of this process. The fineness of the creping is
governed primarily by the thickness of the scraper; the thinner
the scraper, the finer will be the creping. It also depends
upon the temperature of the creping cylinder, the speed
thereof, as well as the position of the scraper relative to the
cylinder surface. As an alternative to wet creping, the
creping can be carried out on the finished paper product, after
rewetting.
After removal from the creping cylinder, the web containing
the additives enters the drying section of the papermaking
machine. At this point, steam is driven off the web by the hot
drying cylinders producing a residual water content of the web
of 6% to 20%9 preferably 8% to 12%. An additional portion of
the impregnating mixture is introduced by means of a suitable
device; e.g. a sizing press. The amount used is such that the
web, after drying will contain 7% to 60% by weight, preferably
15% to 40~/O by weight, of the mixture, based on the dry paper.
It has been found advantageous to operate with a 40% bath of
the impregnating mixture at a running spead of 120 meters per
-13-
minute. For example, there is ob~ained a 70 gram paper from a
sh~et weight of 50 grams plus 20 ~rams of i~pregnating mixture
addition. This would correspond to a mixture content of about
28.5%.
The heat treatment in the drying section of the paper-
making machine causes the impregnating mixture to precipitate
from the dispersion in a finely divided state. The other high
molecular sizing substances which are present are slightly
crosslinked under the action of the heat, and they, to~ether
with the impregnating mixture, are anchored to the fibers. In
this manner, it is possible to produce a suita'ble paper usin~ a
much smaller quantity of rubber than woukl otherwise be
possible under the prior art methods. At the same time, tne
undesirable sticking and smearing of the hot cylinders and
felts in the drying section is prevented, even at relative'ly
high temperatures (115 to 130C~. Moreover, high running
speeds of more than 100 meters per minute at a web width of
over 2 meters can be obtained, without any tearing of ~he paper
~ we'b.
:`
By the use of the present method, impregnated smooth and
creped papers can be produced in a simple manner, wit~out the
necessity of the additional process steps which would otherwise
be necessary. The papers can be used as substrates for th'e''
usual pressure sensitive adhesive tapes~ especially masking and
packing tapesO
The following examples will serve to illustrate the present
invention.
-14-
Example 1
1000 kg cellulose consisting of 690 kg conifer cellulose
(500 kg highly bleached pine sulfate cellulosel long fiber,
extra absorbent, and 190 kg unbleached pine sulfate cel]ulose),
280 kg deciduous cellulose ~140 kg birch sulfate cellulose and
140 kg beech sulfate cellulose) and 30 kg hydroxyethyl
cellulose ("Cellusize", Union Carbide) were beaten in the
beater to a degree of comminution oE 33~SR and diluted with
water to a concentration of 0.5~/O.
An impregnating mixture was prepared from the following
substances, based on 1000 kg cellulose and 400 kg of solids in
the impregnating mixture.
Solids Total
(kg) ~kg) (aq.
dispersion)
Mixture of acrylic acid butyl ester-
acrylic acid copolymer and poly-
butadiene styrene ("Butofan DS
3255 X", çxperimental product of
BASF) - 50% 355.55 711.12
Triethanolamine monostearate -
10% 13.33 133.33
Polyethylene glycol of
Average Mol. Wt. 570-630
("Polydiol 600", Hoechst~ 6.67 6.67
triethanolamine 6.67 6.67
Foam inhibitor
("Nopco NDW", Nopco Chem.) 0.89 3.89
-15-
,..
Melamine formaLdehyde pre-
condensate ("Maprenal MF 900",
Hoechst) 16.45 16.45
p-Toluene sulfonic acid - 1% 0.44 44.44
5 Water, desalinated 191.55
400.00 1111.12
Solids content of the dispersion: 36%
After beating, 20 kg of the solicl impregnating mixture were
added to the fiber suspension which contains, based on the
solid components of the total composition, 89% by weight
elastomer, 3.3~/O by weight triethanolamino monostearate, and
3.3% by weight paper softener, in the form of 55.5 kg of a 36%
aqueous dispersion. Immediately thereafter, a mixture of 35A kg
of a urea-formaldehyde resin ("Urecoll KL", BASF~ and 6 kg
aluminum sulfate/sulfuric acid in the form of a 10% aqueous
solution of pH 2.0 - 3.0 were added as the wet strength agent
by means of a proportioning pump.
Thereafter, the mass was made into a paper web using a
conventional papermaking machine over a screen section and wet
press section (sheet formation, draining, drying). Th~e screen
water had a pH value of 4.5 to 5Ø At a dry weight of about
38 to 42%, the web was creped by means of an apparatus
consisting of a creping cylinder and scraper; the temperature
after the creping cylinder rose to 105 to 125C.
As a residual water content of the paper web of about ~ to
12%, the entire remainder of the impregnating mixture (380 kg
referred to solids) was then incorporated in the paper web in
the form of the 36% aqueous dispersion, using a sizing press.
* denotes trade marks
t~ -16-
In the subsequent drying section, the support material wau
brought to a temperature between 90 and 135C. at a machine
speed of about 100 m/min. The prevailing residual moisture oX
the impregnated paper was 4.5 to 5.5U/o.
There was obtained a crepe paper having a sheet weight of
100 g/m2 (~ 2) and an elongation of 15%, which was highly
suitable as a substra~e for the produc~ion of pressure-
sensitive adhesive masking tapes.
Example 2
In the manner described in Example 1, an im~regnated crepe
paper weighing 7~ g/m2 was produced for the manuLacture o~
masking tapes;
I Cellulose charge 1000 kg cellulose consisting of:
560 kg pine sulfate cellulose, long fiber, extra absorbent,
bleached
200 kg pine sulfate cellulose, unbleached
240 kg eucalyptus cellulose
Degree of Comminution: 19 SR
II Wet strength agent (added before breast box)
12 kg urea formaldehyde resin
("Urecoll KL" BASF)
(as l~/o solution
0.5 kg alum/su].furic acid
.
lll SheeC fo~m~tion, draining, dLying, creping
IV At 6 to 9% residual water content of the web:
Addition of the impregnating mixture stated below
(impregnating formula) by means of sizin~ press.
V Drying and smoothing of the impregnated crepe paper
between felt and cylinders after the si~ing press at
temperatures between 105 and 135C.
Impregnating formula:
Total Solids
(kg) (kg)
(aq.dispersion)
Butadiene-acrylonitrile latex
("Synthomer~8155", Synthomer Chemie)
50% 80.00 40.00
Plasticizer-free copolymer of
acrylic acid esters with vinyl -
compounds ("Acronal~500 D", BASF)
50% 70.00 35.00
Emulsion on basis of distearoyl-
dipropylene triamine - 20% 10.00 2.00
Triethanolamine - 100% 1.50 1.50
~I Polyethylene glycol of Average
Mol.Wt. 570-630 (I'Polydiol 600", - I
Hoechst~ 1.20 1.20
Foam inhibitor ("Nopco~NDW",
Nopco Chem.) 0.30 0.30
Water, desalinated 37.00
..
` 200.00 80.00
lo Solids content of the dispersion: ¦
40%
~o t-~s ~ de ~k
-18-
;
The residual moisture of the impregnated paper was adjusted to
the tolerance as in Example 1.
There was obtained a crepe paper having a sheet weight of
70 (+ 2) g/m , which showed rupture load value of 36 N/cm at
15% elongation.
Example 3
As in Example l, an impregnated paper thermostable to about
180C was produced:
I Cellu]ose charge
700 kg pîne su]fate cellulose, long fiber, extra
I absorbent, bleached
220 kg pine sulfate cellulose, unbleached
80 kg acrylic acid ester copolymer ("Basoplast~k
580 D", BASF) = 160 kg 50% dispersion
2 kg triethanolamino monostearate
Degree of Comminution: 22 SR
II Wet strength agent (added before breast box)
12 kg urea-formaldehyde
resin ("Urecoll KL", BASF) ( 10% solution
0.5 kg alum/sulfuric acid
III Sheet formation, draining, drying
IV At 10 to 12% residual water content of the web:
An impregnating mixture of the compo6ition listed below was
added, using a sizing press.
e ~ e ~
-19-
V Drying, crosslinking and smoothing of the impregnated paper
between felt and cylinders after the sizing press at
temperatures between 105 and 135~C.
Impregnating formula: SolidsTotal (kg)
(kg)(aq.dispersion)
Butadiene-acrylonitrile latex,
35%, with 33% acrylonitrile and
4% methacrylic acid 70.00200.00
("Perbuna~N Latex 3460 M", Bayer)
Emulsion sn basis of polyvinyl-
stearyl carbamate - 20% 2.00 lO.00
Triethanolamine 1.50 1.50
Low Visc. olyvinyl alcohol
("Polyviol~ 05/140", Wacker-Chemie~ 6.00 6.00
Polyethylene glycol ("Polydiol 600",
Hoechst) 1.20 1~20
Defoamer ~'Nopco NDW'I, Nopco Chem.) 0.30 0.30
81.0021g.00
Solids content of the dispersion:
37%
An impregnated smooth paper having a sheet weight of
go g/m2 was made.
While only a limited number of specific embodiments of the
present invention have been expressly described, it is,
nonetheless, to be broadly construed, and not to be limited
except by the character of the c]aims appended hereto.
With regard to component (b) as a general principle all
latices of elasl:omers - and rubber-like polymer types commonly
used in papermaking processes are suitable in practicing the
~30 present invention.
s t r~
-20
