U.S. patent application number 09/463208 was filed with the patent office on 2001-07-26 for whitened polymers and the use thereof in coating slips for coating substrates.
Invention is credited to ECKSTEIN, UDO, FELDHUES, ULRICH, GEIGER, HANS-PETER, HUNKE, BERNHARD, KORTE, SIEGFRIED, ROICK, THOMAS, SACKMANN, GUNTER.
Application Number | 20010009938 09/463208 |
Document ID | / |
Family ID | 7836869 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009938 |
Kind Code |
A1 |
ECKSTEIN, UDO ; et
al. |
July 26, 2001 |
WHITENED POLYMERS AND THE USE THEREOF IN COATING SLIPS FOR COATING
SUBSTRATES
Abstract
The present invention relates to polymers whitened with optical
brighteners obtained by (a) emulsion polymerization of
acrylonitrile with or without a comonomer in the presence or
absence of a graftable substrate, and (b) addition of an optical
brightener before, during, or after the emulsion
polymerization.
Inventors: |
ECKSTEIN, UDO; (KOLN,
DE) ; KORTE, SIEGFRIED; (ODENTHAL, DE) ;
FELDHUES, ULRICH; (MOUNT PLEASANT, SC) ; GEIGER,
HANS-PETER; (ROSRATH, DE) ; HUNKE, BERNHARD;
(EITORF, DE) ; ROICK, THOMAS; (LEVERKUSEN, DE)
; SACKMANN, GUNTER; (LEVERKUSEN, DE) |
Correspondence
Address: |
BAYER CORPORATION
100 BAYER ROAD
PITTSBURGH
PA
15205-9741
US
|
Family ID: |
7836869 |
Appl. No.: |
09/463208 |
Filed: |
February 28, 2000 |
PCT Filed: |
July 14, 1998 |
PCT NO: |
PCT/EP98/04355 |
Current U.S.
Class: |
524/86 ;
428/512 |
Current CPC
Class: |
Y10T 428/31935 20150401;
Y10T 428/31902 20150401; Y10T 442/2582 20150401; C08F 291/00
20130101; C08F 291/00 20130101; Y10T 428/31906 20150401; Y10T
442/2861 20150401; D21H 21/30 20130101; Y10T 442/2779 20150401;
Y10T 442/2787 20150401; C08F 220/44 20130101; C08F 220/44 20130101;
D21H 19/58 20130101; Y10T 428/31899 20150401 |
Class at
Publication: |
524/86 ;
428/512 |
International
Class: |
C08K 005/34; B32B
023/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 1997 |
DE |
197 32 032.5 |
Claims
What is claimed is:
1. A polymer whitened by means of optical brighteners and
obtainable by emulsion polymerization of acrylonitrile with or
without comonomers, in the presence or absence of graftable
substrates, with addition of an optical brightener before, during
or after the emulsion polymerization.
2. The whitened polymer as claimed in claim 1, which is in the form
of its aqueous dispersion.
3. The whitened polymer as claimed in claim 1, which has an average
particle size of <1 .mu.m, in particular 50-800 nm, preferably
50-500 nm.
4. The whitened polymer as claimed in claim 1, wherein comonomers
used are nonionic comonomers from the group consisting of alkyl
esters of acrylic and methacrylic acid, preferably C.sub.1-C.sub.8
alkyl esters, and also ethoxylated and propoxylated esters of
acrylic and methacrylic acid, styrene and .alpha.-methylstyrene,
and derivatives thereof, vinyl carboxylates, preferably vinyl
acetate, conjugated dienes such as butadiene or isoprene,
methacrylonitrile, vinyl chloride and vinylidene chloride, N-alkyl-
and N-aryl-substituted maleimides, and also hydrophilicizing
comonomers such as acrylamides and methacrylamides, acrylic and
methacrylic acid, N-vinylamides such as, for example,
1-vinyl-2-pyrrolidone, and/or ionic comonomers from the group
consisting of vinylsulfonic acid and its salts, methallylsulfonic
acid and also allylsulfonic acid and salts thereof, styrenesulfonic
acid and its salts, (2-acrylamido-2-methyl)-propanesulfonic acid,
its esters and its salts, (3-sulfopropyl)-acrylic acid and its
salts, (3- sulfopropyl)acrylic esters and also alkyl esters and
oxyalkyl esters of said vinylic sulfonic acids.
5. The whitened polymer as claimed in claim 1, wherein
polymerization is carried out in the presence of graftable
substrates which are polymeric emulsifiers containing sulfonic acid
groups and from the group consisting of compounds of the formulae I
and II 13in which M denotes a cation-forming radical, preferably H,
Na, K, NH.sub.4, R.sub.3NH.sub.3, n denotes 1 or 2, R denotes a
hydrocarbon chain having 1 to 10 carbon atoms or an aromatic
radical having 6 to 10 carbon atoms, preferably
--(CH.sub.2).sub.2NH(CH.sub.2).sub.2-- or a radical derived from a
C.sub.1-C.sub.4 alkane or from benzene, methylbenzene or
naphthalene, R.sub.1 denotes H or --CH.sub.3, R.sub.2 denotes H,
C.sub.1-C.sub.16 alkyl, preferably --CH.sub.3, --C.sub.2H.sub.5,
--C.sub.4H.sub.9, --CH.sub.2--C(CH.sub.3).sub.3,
--C.sub.14H.sub.29, --C.sub.16H.sub.33 or phenyl, R.sub.3 denotes a
hydrocarbon radical of an amine, and x, y are chosen such that the
average molecular weight M.sub.w of the polymers (I) and (II) is
from 2000 to 500,000, preferably from 5000 to 100,000, and the
ratio x:y=from 1:4 to 1:1, preferably from 1:3 to 1:1, and also the
oligourethanes disclosed in EP-A-400 410, p. 7, which are used for
the free-radically initiated emulsion polymerization.
6. The whitened polymer as claimed in claim 1, wherein the optical
brightener is selected from the group consisting of 14in which
R.sub.4 denotes ethyl or phenyl, and An.sup..theta. represents an
anion, or 15in which X represents CH or N, An.sup..theta.
represents an anion, R.sub.5 represents CH.sub.3 or
CH.sub.2--C.sub.6H.sub.5, and R.sub.6 represents H or
SO.sub.2--CH.sub.3, or 16in which R.sub.7 represents NH.sub.2,
CH.sub.3, C.sub.2H.sub.4--OH,
NH--C.sub.3H.sub.6--N(CH.sub.3).sub.2,
CH.sub.2--CH(CH.sub.3)--N(CH.sub.3).sub.2,
C.sub.2H.sub.4--CONH--C.sub.2H- .sub.4--N(CH.sub.3).sub.2,
C.sub.2H.sub.4--O--CH(CH.sub.3)--CH.sub.2--N(CH- .sub.3).sub.2,
NH--C.sub.3H.sub.6--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
C.sub.2H.sub.4--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
C.sub.2H.sub.4--CONH--C.sub.2H.sub.4--N(CH.sub.3).sub.3.sup.+An.sup..thet-
a., CH.sub.2--CH(CH.sub.3)--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
C.sub.2H.sub.4--O--CH(CH.sub.3)--CH.sub.2--N(CH.sub.3).sub.3.sup.+An.sup.-
.theta., where An.sup..theta. represents an anion, preferably the
anion of a mineral acid or --O.sub.3SOCH.sub.3 or 17in which
R.sub.8 denotes H or CH.sub.3, or 18in which R.sub.9 represents
CH.sub.3,
CH.sub.2C(CH.sub.3).sub.2--CH.sub.2--N(CH.sub.3).sub.3.sup.+An.sup..theta-
. or 19where An.sup..theta. denotes the anion of a mineral acid or
--O.sub.3SOCH.sub.3.
7. An aqueous dispersion containing more than 30% by weight, in
particular from 31 to 65% by weight, based on the dispersion, of a
polyacrylonitrile and/or acrylonitrile copolymer whitened by means
of optical brighteners.
8. An aqueous dispersion containing 1-65 % by weight of whitened
polymer as claimed in claim 1, and 1-15 % by weight of
surface-active substances, based on whitened polymer.
9. An acrylonitrile homo- or copolymer whitened by means of optical
brighteners and emulsion-polymerized in the presence of at least
one polymeric emulsifier from the group consisting of compounds of
the formulae I and II 20in which M denotes a cation-forming
radical, preferably H, Na, K, NH.sub.4 or R.sub.3NH.sub.3, n
denotes 1 or 2, R denotes a hydrocarbon chain having 1 to 10 carbon
atoms or an aromatic radical having 6 to 10 carbon atoms,
preferably --(CH.sub.2).sub.2NH(CH.s- ub.2).sub.2-- or a radical
derived from a C.sub.1-C.sub.4 alkane or from benzene,
methylbenzene or naphthalene, R.sub.1 denotes H or --CH.sub.3,
R.sub.2 denotes H, C.sub.1-C.sub.16 alkyl, preferably --CH.sub.3,
--C.sub.2H.sub.5, --C.sub.4H.sub.9, --CH.sub.2--C(CH.sub.3).sub.3,
--C.sub.14H.sub.29, --C.sub.16H.sub.33 or phenyl, R.sub.3 denotes a
hydrocarbon radical of an amine, and x, y are chosen such that the
average molecular weight M.sub.w of the polymers (I) and (II) is
from 2000 to 500,000, preferably from 5000 to 100,000, and the
ratio x:y=from 1:4 to 1:1, preferably from 1:3 to 1:1 or in the
presence of the oligourethanes disclosed in EP-A-400 410, p. 7.
10. An aqueous coating slip comprising whitened polymer as claimed
in at least one of claims 1, 7 and 9, inorganic pigment, and
binder(s).
11. The use of an aqueous coating slip as claimed in claim 10 to
coat substrates.
12. The use as claimed in claim 11 to coat paper, photographic
paper, paperboard, wood, polymer films, textiles or stone.
13. A substrate coated with an aqueous coating slip as claimed in
claim 10.
Description
[0001] The invention relates to whitened polyacrylonitriles and
acrylonitrile copolymers, especially as aqueous dispersions, to
coating slips comprising them, and to their use for coating a wide
variety of substrates.
[0002] In addition to the customary white pigments, especially
china clay and calcium carbonate, the coating slips generally
include anionic whiteners for the purpose of optical brightening,
examples being those of the bis-triazinyl-aminostilbene-disulfonic
acid type. These whiteners, however, lead only to highly
unsatisfactory white effects and to very low grayness limits
(=whitener concentration at which further addition of whitener
produces no increase, or even a decrease, in whiteness).
Furthermore, the whitener types referred to possess inadequate
lightfastness in the coating slips.
[0003] DE-A-195 00 195 describes how whitened, finely divided
polymer materials affixed with brighteners suitable for the polymer
material can be used as powders or as dispersions for whitening
paper coating slips based on synthetic binders. This method is
still in need of improvement, however, in terms of the rheological
properties when the whitened polymer powder is used, or in terms of
the solids contents of their dispersions.
[0004] The preparation of whitened coatings on various substrates,
especially on coated papers and cards with high whiteness, a high
grayness limit and good lightfastness, is a difficult problem which
has not been solved satisfactorily to date.
[0005] It has now been found, surprisingly, that when specific
whitened polymers are used in coating slips, they give the coatings
produced therewith on a wide variety of substrates very high
whitenesses, high grayness limits, high lightfastnesses, and high
bleedfastnesses.
[0006] The invention therefore provides polyacrylonitriles or
acrylonitrile copolymers, referred to below simply as polymers,
which are whitened by means of optical brighteners and are
obtainable by emulsion polymerization of acrylonitrile with or
without comonomers, in the presence or absence of graftable
substrates, with the addition of an optical brightener before,
during or after the emulsion polymerization.
[0007] In one preferred embodiment the polymers of the invention
are in the form of their aqueous dispersions.
[0008] The aqueous polymer dispersion contains preferably:
[0009] a) 1-65% by weight, in particular 10-55% by weight, of
polymer of the invention, based on the dispersion, and
[0010] b) 1-15% by weight, in particular 5-10% by weight, of
surface-active substances, based on polymer of a).
[0011] The aqueous polymer dispersion may additionally include
customary additives such as preservatives, preferably from 0 to 15%
by weight, based on the polymer of component a).
[0012] Suitable surface-active substances are preferably anionic
and/or nonionic surfactants.
[0013] Preferred surface-active substances are the graftable
substrates of types I to III below, preferably those of types I and
II, and, in particular, those of type I.
[0014] Examples of suitable preservatives are methyl- and
chloromethyl-isothiazolin-3-one, benzisothiazolin-3-one, or
mixtures thereof.
[0015] The polymers of the invention are preferably finely divided
and in particular have an average particle size (measured by the
method of laser correlation spectroscopy) of <1 .mu.m,
preferably 50-800 nm, in particular 50-500 nm, and, with particular
preference, 50-400 nm.
[0016] The polymers preferably contain 50 or more mol-% of
acrylonitrile units. Examples of suitable comonomers are nonionic
and/or ionic-ethylenically unsaturated comonomers.
[0017] Preferred nonionic comonomers are alkyl esters of acrylic
and methacrylic acid, preferably C.sub.1-C.sub.8 alkyl esters, and
also ethoxylated and propoxylated esters of acrylic and methacrylic
acid, styrene and .alpha.-methylstyrene and their derivatives,
vinyl carboxylates, preferably vinyl acetate, conjugated dienes
such as, for example, butadiene or isoprene, methacrylonitrile,
vinyl chloride and vinylidene chloride, N-alkyl and
N-aryl-substituted maleimides, and also hydrophilicizing comonomers
such as acrylamides and methacrylamides, acrylic and methacrylic
acid, N-vinylamides, such as, for example,
1-vinyl-2-pyrrolidone.
[0018] Examples of suitable ionic comonomers are vinylsulfonic acid
and its salts, methallylsulfonic acid and also allylsulfonic acid
and salts thereof, styrenesulfonic acid and its salts,
(2-acrylamido-2-methyl)-prop- anesulfonic acid, its esters and its
salts, (3-sulfopropyl)-acrylic acid and its salts,
(3-sulfopropyl)-acrylic esters, and also the alkyl esters and
oxyalkyl esters of said vinylic sulfonic acids.
[0019] Particularly preferred comonomers are alkyl acrylates,
styrene, and butadiene/styrene mixtures. Preferably, however, it is
also possible to operate with acrylonitrile as sole monomer.
[0020] In one preferred embodiment the whitened polymers of the
invention are obtainable by emulsion polymerization in the presence
of graftable substrates. These graftable substrates are preferably
polymeric emulsifiers containing sulfonate groups. Particularly
suitable are polymers of types I and II, which preferably have
average molecular weights of M.sub.w>5000 g/mol. Likewise
preferred are poly- and oligourethanes of type III, which
preferably have an average molecular weight of >1000 g/mol.
[0021] The emulsifier of type I corresponds to the formula (I) and
that of type II to the formula (II) 1
[0022] in which
[0023] M denotes a cation-forming radical, preferably H, Na, K,
NH.sub.4 or R.sub.3NH.sub.3,
[0024] n denotes 1 or 2,
[0025] R denotes a hydrocarbon chain having 1 to 10 carbon atoms or
an aromatic radical having 6 to 10 carbon atoms, preferably
--(CH.sub.2).sub.2NH(CH.sub.2).sub.2-- or a radical derived from a
C.sub.1-C.sub.4 alkane or from benzene, methylbenzene or
naphthalene,
[0026] R.sub.1 denotes H or --CH.sub.3,
[0027] R.sub.2 denotes H, C.sub.1-C.sub.16 alkyl, preferably
--CH.sub.3, --C.sub.2H.sub.5, --C.sub.4H.sub.9,
--CH.sub.2--C(CH.sub.3).sub.3, --C.sub.14H.sub.29,
--C.sub.16H.sub.33 or phenyl,
[0028] R.sub.3 denotes a hydrocarbon radical of an amine, and
[0029] x, y are chosen such that the average molecular weight
M.sub.w of the polymers (I) and (II) is from 2000 to 500,000,
preferably from 5000 to 100,000, and the ratio x:y=from 1:4 to 1:1,
preferably from 1:3 to 1:1.
[0030] Particularly preferred emulsifiers are those of the formulae
(I) and (II), in which
[0031] 1A) R.sub.1=CH.sub.3 and
R.sub.2=--CH.sub.2--C(CH.sub.3).sub.3 or
[0032] 2A) R.sub.1=CH.sub.3 and R.sub.2=CH.sub.3 or
[0033] 3A) R.sub.1=H and R.sub.2=C.sub.6H.sub.5,
[0034] where in each case
[0035] R=--CH.sub.2CH.sub.2--,
[0036] M=Na,
[0037] n=1 and
[0038] x: y=from 1:1.0 to 1:1.1.
[0039] Very particular preference is given to the emulsifier of the
type 1A).
[0040] Emulsifiers of the formulae I and II are known, for example,
from EP-A 590 460.
[0041] Emulsifiers of the type III are the oligourethanes known
from EP-A 400 410 which are used in connection with the
free-radically initiated emulsion polymerization for preparing
surface sizing agents for paper.
[0042] Particular preference is given as emulsifiers of the type
III to the oligourethanes specified on p. 7 of EP-A 400 410,
especially those obtainable by reacting a macrodiol and an
oligoisocyanate having an NCO functionality of >2.
[0043] A macrodiol is, for example, a polyester of adipic acid,
hexanediol, neopentyl glycol having an average molecular weight
M.sub.w=1700 g/mol. The oligoisocyanate is, for example, a
hexamethylene diisocyanate (HDI) based trimer of the isocyanate
type (f=3) and higher molecular mass oligomers (f=3) derived
therefrom.
[0044] At medium and high molecular weights, suitable linear and
branched polyacrylonitriles and acrylonitrile copolymers exhibit
intrinsic viscosities (measured in dimethylformamide at 20.degree.
C.) of [.eta.]=from 0.5 to 10.0 dl/g, preferably of [.eta.]= from
1.0 to 5.0 dl/g. High molecular mass products exhibit heightened
long-chain branching.
[0045] Preferred polymers are those modified by strongly acidic
groups. Preferred strongly acidic groups are sulfonate groups, the
amount of strongly acidic groups being preferably 50-500,
particularly 100-500, milliequivalents/kg of polymer.
[0046] The incorporation of strongly acidic groups into the
copolymer can take place, for example:
[0047] a) by using the above-described graftable emulsifiers
containing sulfo groups,
[0048] b) by using comonomers containing sulfonic acid groups
and/or sulfonate groups, preferably the abovementioned
ionic-ethylenic comonomers, and/or
[0049] c) by the free-radical initiator components, preferably by
using the initiator system: persulfate/sulfite.
[0050] The amount of graftable substrates, especially of the
abovementioned emulsifiers, which is preferably used for the
emulsion polymerization is 2-20% by weight, preferably 2-10% by
weight, based on the total amount of monomers to be
polymerized.
[0051] The polymers obtained in the presence of graftable
substrates, especially their dispersions, include not only homo-
and/or copolymers of the acrylonitriles used for the polymerization
and/or mixtures thereof with other monomers, preferably including
fractions of graft polymer of the monomers used onto the polymeric
emuslifiers, but also fractions of the ungrafted, graftable
substrates, especially of the polymeric emulsifiers.
[0052] Based on the amount of emulsifier used, preferably 50 or
more mol-% is grafted. Depending on the chosen polymerization
conditions such as temperature, initiator system and nature of the
comonomers, the grafting yield when using the polymeric emulsifiers
specified as preferred is from 50 to 80 mol-%.
[0053] Particularly suitable optical brighteners are those commonly
used in the textiles sector for whitening polyacrylonitrile.
Particular preference is given to neutral brighteners, but
especially cationic brighteners. Particularly suitable are optical
brighteners which on the corresponding fiber material in the
textiles sector have lightfastnesses of at least 4 as determined in
accordance with the xenon test in accordance with the method by way
of the guidelines determining colorfastness properties in
accordance with DIN 54 004. Particularly advantageous for this
application are all brighteners having lightfastnesses of 5-7.
[0054] Brigheners used with preference for the polymer dispersions
are compounds of the formula: 2
[0055] in which
[0056] R.sub.4 denotes ethyl or phenyl, and
[0057] An.sup..theta. represents an anion,
[0058] or 3
[0059] in which
[0060] X represents CH or N,
[0061] An.sup..theta. represents an anion,
[0062] R.sub.5 represents CH.sub.3 or CH.sub.2--C.sub.6H.sub.5,
and
[0063] R.sub.6 represents H or SO.sub.2--CH.sub.3,
[0064] or 4
[0065] in which
[0066] R.sub.7 represents NH.sub.2, CH.sub.3, C.sub.2H.sub.4--OH,
NH--C.sub.3H.sub.6--N(CH.sub.3).sub.2,
CH.sub.2--CH(CH.sub.3)--N(CH.sub.3- ).sub.2,
[0067] C.sub.2H.sub.4--CONH--C.sub.2H.sub.4--N(CH.sub.3).sub.2,
C.sub.2H.sub.4--O--CH(CH.sub.3)--CH.sub.2--N(CH.sub.3).sub.2,
NH--C.sub.3H.sub.6--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
C.sub.2H.sub.4--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
[0068]
C.sub.2H.sub.4--CONH--C.sub.2H.sub.4--N(CH.sub.3).sub.3.sup.+An.sup-
..theta.,
CH.sub.2--CH(CH.sub.3)--N(CH.sub.3).sub.3.sup.+An.sup..theta.,
C.sub.2H.sub.4--O--CH(CH.sub.3)--CH.sub.2--N(CH.sub.3).sub.3.sup.+An.sup.-
.theta.,
[0069] where An.sup..theta. represents an anion, preferably the
anion of a mineral acid or --O.sub.3SOCH.sub.3 or 5
[0070] in which
[0071] R.sub.8 denotes H or CH.sub.3,
[0072] or 6
[0073] in which
[0074] R.sub.9 represents CH.sub.3,
CH.sub.2C(CH.sub.3).sub.2--CH.sub.2--N-
(CH.sub.3).sub.3.sup.+An.sup..theta. or 7
[0075] where An.sup..theta. denotes an anion, preferably the anion
of a mineral acid or --O.sub.3SOCH.sub.3.
[0076] Preferred polyacrylonitriles or acrylonitrile copolymers of
the invention are whitened with optical brighteners of the formula
(1), (2) or (3), especially (1) or (2).
[0077] The emulsion polymerization generally takes place such that
acrylonitrile and/or its mixtures with the comonomers and, if
desired, graftable substrates in the presence of emulsifiers are
polymerized in aqueous emulsion, using free-radical initiators, in
a manner known per se.
[0078] Suitable initiators are persulfates, hydrogen peroxide and
various other organic peroxides which decompose below 100.degree.
C., and also the redox systems which respond in the temperature
range from 20 to 100.degree. C., such as, for example,
H.sub.2O.sub.2/Rongalit, H.sub.2O.sub.2/thioglycol and t-butyl
hydroperoxide/ascorbic acid. Particularly advantageous is the
system persulfite/SO.sub.2, which is active at temperatures of
40-70.degree. C. and which, by virtue of the incorporation of
sulfonate and sulfate end groups, increases the level of acidic
groups present.
[0079] Particularly preferred emulsifiers are the above-described
polymeric emulsifiers, containing sulfonic acid groups, of the
formulae (I) to (III).
[0080] To conduct the emulsion polymerization it is preferred to
include all or some of an aqueous solution of the emulsifier,
preferably of the polymeric emulsifier described above, in the
initial charge and then to add the monomers and the initiator
gradually, for example over 2 to 6 hours, preferably separately. In
the case where some of the emulsifier is included in the initial
charge, the remainder can then be metered in gradually, for example
over 2 to 6 hours, together with the monomers and the initiator,
preferably in separate streams. Alternatively, it is possible to
add the emulsifier, initiator and the monomers separately and
continuously throughout the polymerization period and to include
only water in the initial charge.
[0081] It is also possible to operate batchwise, in which case, for
example, emulsifier, monomer mixture and initiator are introduced
together and this charge is then heated, for polymerization, to the
desired polymerization temperature.
[0082] Depending on the decomposition characteristics of the
initiators used, the emulsion polymerization is conducted at
temperatures from 20 to 100.degree. C., preferably in the range
from 40 to 80.degree. C.
[0083] The product of the polymerization reaction comprises
generally finely divided aqueous polymer emulsions which are free
from precipitated coagulum.
[0084] Thus with the process of emulsion polymerization it is
possible, for example, to produce the whitened polymers of the
invention as aqueous dispersions in the case of acrylonitrile
homopolymers, preferably with solids contents of up to 45% by
weight, and, in the case of acrylonitrile copolymers, preferably
with solids contents of up to 65% by weight.
[0085] The resulting dispersions are extremely stable to additions
of electrolyte, to temperature effects, and to the action of shear
forces.
[0086] The optical brightener can be applied to the polymer
particles, for example, in accordance with the methods described in
DE-A-195 00 195. The process of the invention has the particular
feature that a suitable optical brightener is added before, during
or after the emulsion polymerization.
[0087] In one particularly preferred embodiment the brightener,
preferably a water-soluble cationic brightener, alone or in
combination with further optically brightening compounds, is mixed
into the aqueous dispersions of the polymers containing strongly
acidic groups, and is then caused to attach to the polymer
particles at elevated temperature. If desired, further auxiliaries
are used.
[0088] The attachment of the optical brightener preferably takes
place above the hydrothermal softening temperature (TgH.sub.2O) of
the polymer, preferably at 25-150.degree. C., in particular at
50-100.degree. C. This takes place largely with retention of the
original particle size distribution of the emulsion polymers.
[0089] It is advantageous to cause the optical brighteners to act
on the dispersion comprising emulsion polymers, which still
contains residual monomers. Subsequently, the monomers are
separated off, preferably by distillation. It has been found that,
in the case of this preferred attachment variant, the takeup
capacity on the one hand and the attachment rate of the brightener
on the other hand are increased.
[0090] The amount of the optical brighteners used, based on the
polymer, is guided by the desired brightener effect and is
preferably 0.1-2% by weight of brightener, based on the polymer
solids fraction in the dispersion.
[0091] The invention additionally provides aqueous dispersions
containing more than 30% by weight, especially 31-65% by weight
and, with particular preference, 40-65% by weight, based on the
dispersion, of a whitened polyacrylonitrile and/or acrylonitrile
copolymer. This aqueous dispersion of the invention contains
preferably 1-15% by weight, especially 2-10% by weight and, with
particular preference, 5-10% by weight of at least one
surface-active substance, based on whitened polymer. The preferred
embodiments of these dispersions in terms of polymer,
surface-active substances and possible further additives correspond
to those for the abovementioned dispersions. The polymer is
preferably obtained by the method of emulsion polymerization, in
particular in accordance with the process described above.
[0092] The aqueous polymer dispersions of the invention may include
as further additives, like additives already described above to the
whitened, finely divided polymer dispersions used in accordance
with the invention, in the stated amounts, examples being
surface-active substances, preservatives, etc.
[0093] The invention additionally provides acrylonitrile homo-
and/or copolymers whitened with optical brighteners, said polymers
having been emulsion-polymerized in the presence of at least one
polymeric emulsifier of the formulae I to III.
[0094] The preferred embodiments correspond to those indicated
above.
[0095] The whitened polymers of the invention, especially in the
form of their aqueous dispersions, can be used without further
treatment or purification or can be admixed with pigments and/or
further auxiliaries.
[0096] The invention additionally provides aqueous coating slips
having a solids content of 25-80% by weight, especially 50-70% by
weight, and containing:
[0097] 30-70, preferably 40-60% by weight of at least one inorganic
pigment, based on the solids content,
[0098] 10-50% by weight of whitened polyacrylonitrile and/or
acrylonitrile copolymer, based on the inorganic pigment, and
[0099] 5-15% by weight of at least one binder, based on the
inorganic pigment.
[0100] The polymer of the invention or the dispersion of the
invention comprising a whitened polymer is preferably employed in
the coating slips of the invention.
[0101] The coating slips of the invention may also include wet
strength agents, dispersants and, if desired, further
additives.
[0102] Suitable inorganic pigments are preferably clay, kaolin,
barium sulfate, satin white, silica, alumina, aluminum silicate,
titanium dioxide, talc, chalk and mixtures thereof.
[0103] These pigments are preferably used in the form of an aqueous
slurry.
[0104] Examples of suitable binders are those based on polymeric
binding agents, such as, for example, butadiene-styrene,
styrene-butyl acrylate, acrylonitrile-butadiene-styrene,
styrene-butadiene-alkyl acrylate, alkyl acrylate,
acrylonitrile-alkyl acrylate, acrylonitrile-styrene, ethylene-vinyl
chloride, and ethylene-vinyl acetate copolymers and also the
homopolymers polyethylene, polyvinyl chloride, polyvinylidene
chloride, polyvinyl acetate, and polyaddition compounds such as
polyurethanes.
[0105] Also outstandingly suitable, however, are natural binding
agents such as, for example, starch, degraded starch, alginates and
proteins, such as gelatin, casein and soy protein, for example.
Sodium carboxymethylcellulose, polyvinyl alcohol, and synthetic,
acrylate-based thickeners are also suitable. Examples of suitable
dispersants are sodium polyacrylates, sodium polyphosphate and
sodium citrate.
[0106] The coating slips per se into which the polymers of the
invention, or the dispersions of the invention comprising whitened
polymers, can be incorporated are known and are described, for
example, in J. P.Casey "Pulp and Paper", Chemistry and Chemical
Technology, 2nd Ed. Vol. III, pp. 1648-1649 and McGraw-Hill "Pulp
and Paper Manufacture", 2nd and 5th Ed. Vol. II, p. 497.
[0107] The invention additionally provides for the use of such
coating slips to coat substrates.
[0108] Examples that may be mentioned of substrates suitable for
coating are:
[0109] Paper, such as coated paper, photographic paper, etc.,
paperboard, wood, polymer films, textiles and also nonwoven
materials and building materials such as stone, plaster, etc. The
abovementioned coating slips are preferably used to coat coated
papers, photographic papers, and paperboard.
[0110] With the coating slip of the invention it is possible to
coat paper and paperboard with the customary coating apparatus: for
example, with an air knife, a coating knife, a brush, a roller, a
knife coater, a rod or any other coating apparatus common in the
paper industry.
[0111] The coating slips of the invention can be used in particular
for coating paper, especially for chromoprints, art prints/picture
prints, offset prints, gravure prints, and paperboard.
[0112] The aqueous coating slips used in accordance with the
invention can comprise additional dispersants and/or emulsifiers
and also customary anionic or cationic and/or nonionic
surface-active substances, as are described, for example, in DE-A-
2 334 769, pp. 8-10 (corresponds to GB-A-1 417 071). Preference is
given in this context to anionic and/or nonionic surfactants.
[0113] The aqueous coating slips of the invention can be used, for
example, as topcoats. A particular advantage of this use in
accordance with the invention lies in the very high gloss and
extraordinary smoothness of the coated papers obtained in this
case.
[0114] The invention additionally provides the substrates,
especially papers, coated with the coating slips of the
invention.
[0115] The invention is illustrated using the following examples.
The parts indicated in the examples are parts by weight; the
percentages, unless stated otherwise, likewise relate to the weight
of the substances employed.
EXAMPLES
EXAMPLE 1
[0116] 100 g of a fine acrylonitrile copolymer dispersion (solids
content (SC): 48.6% of polymer, average particle size: about 140
nm; [.eta.].sub.DMF=3.1 dl/g; polymer-bound sulfonate group
content: 120 meq./kg), containing 55.4% of an acrylonitrile-methyl
acrylate copolymer (in the proportion of 55/45) and 4.6% of a
polymeric emulsifier of type 1A that is grafted therewith (average
molar weight M.sub.w: 20,000 g/mol; [.eta.].sub.DMF=3.1 dl/g), were
treated for 20 minutes at 90.degree. C. with a) 0.1, b) 0.2, and c)
0.4% of the optical brightener, based on polymeric solids fraction,
of the formula 8
[0117] Sieving was carried out at 60.degree. C. to remove a little
sieve residue (8 mm). The whitened, fine polymer dispersion present
was coated onto base paper using a manual knife coater (coat
weight: about 15 g/m.sup.2). The coated papers exhibit the
following whitenesses:
1 TABLE 1 Whitener based on Whiteness Example 1 polymer in % Berger
CIE none 85.3 84.3 a) 0.1 112.6 112 b) 0.2 126.2 123.6 c) 0.4 131.3
126.4
[0118] The Berger whiteness is calculated in accordance with the
formula of Berger.
W=Ry+3(Rz-Rx)
[0119] Rx, Ry and Rz are the readings from a three-filter
photometer
[0120] A. Berger, Wei.beta.gradformeln und ihre praktische
Bedeutung [whiteness formulae and their practical significance]
Die Farbe 8 (1956) 4/6, 187-202
[0121] The CIE method was proposed in 1986 by the Commission
intemationale de l'clairage.
[0122] The evaluation of whiteness, Colorimetry Second Edition,
Publication CIE No. 15.2 (1986) pp. 36-38.
EXAMPLE 2
[0123] 100 g of a fine acrylonitrile copolymer dispersion (SC: 40%
of polymer, average particle size: about 480 nm; polymer-bound
sulfonate group content: 340 meq/kg), containing 51% of an
acrylonitrile-methyl acrylate-sodium styrene sulfonate copolymer
(in the proportion of 53.5/44.5/2.0) and 9% of a polymeric
emulsifier of type 1A which is grafted therewith (having an average
molar weight M.sub.w: 20,000 g/mol, [.eta.].sub.DMF=1.7 dl/g), were
treated for 2 hours at room temperature and 1 h at 70.degree. C.
with a) 0.1, b) 0.2, c) 0.4 and d) 0.8% of the optical brightener,
based on polymeric solid fraction, from Example 1. Sieving was
carried out at room temperature to remove a little sieve residue (8
mm). The resulting whitened, fine dispersion was coated onto base
paper using a manual knife coater (coat weight: about 15
g/m.sup.2). The coated papers were exposed at a distance of about
15 cm using the daylight fluorescent lamp Sylvania Daylight F 20
W/DRS for 72 h, and exhibited the following whitenesses before and
after exposure:
2 TABLE 2 Decrease in whiteness Brightener CIE whiteness due to
Example in %, based on before after exposure 2) polymer exposure
exposure (difference) none 80.6 80.3 0.3 a) 0.1 121.9 122.3 0 b)
0.2 129.1 129.0 0.1 c) 0.4 143.6 143.1 0.5 d) 0.8 148.2 147.4 0.8
e) 1 150 148.9 1.1
[0124] The resulting stable, whitened polymer dispersion showed
excellent white effects with high lightfastnesses, as a topcoat,
and, moreover, was easy to incorporate into paper coating
slips.
EXAMPLE 3
[0125] 100 g of a fine acrylonitrile copolymer dispersion (SC: 35%
of polymer, average particle size: about 720 nm; polymer-bound
sulfonate group content: 340 meq/kg), containing 51% of an
acrylonitrile-methyl acrylate-sodium styrenesulfonate copolymer (in
the proportion of 53.5/44.5/2.0) and 9% of a polymeric emulsifier
of type 1A which is grafted therewith (having an average molar
weight M.sub.w: 20,000 g/mol, [.eta.].sub.DMF=1.8 dl/g), were
treated for 2 hours at room temperature and 1 hour at 70.degree. C.
with a) 0.1, b) 0.2 and c) 0.4% of the optical brightener, based on
polymeric solid fraction, of the formula 9
[0126] The resulting whitened, fine dispersion was coated onto base
paper using a manual knife coater (coat weight: about 30
g/m.sup.2). The subsequent daylight exposure took place as
described in Example 2. The coated papers exhibited the following
whitenesses before and after exposure.
3 TABLE 3 Decrease in Brightener CIE whiteness whiteness Example in
%, based on before after due to 3) polymer exposure exposure
exposure none 83.4 83.1 0.3 a) 0.1 118.1 115.6 2.5 b) 0.2 124.9
120.1 4.8 c) 0.4 132 122.8 9.2
EXAMPLE 4
[0127] A reactor equipped with stirrer and four metering devices
was charged under a nitrogen blanket with 650 parts by weight of
deionized water, 105 parts by weight of the polymeric emulsifier
from Example 1 and 7.4 parts by weight of sodium styrene-sulfonate.
After conditioning at 60.degree. C., 4 parts by weight of iron(II)
sulfate * 7H.sub.2O (0.1% strength) were added in order to activate
free-radical polymerization, and the following solutions were
metered in at a uniform rate over the course of 5 hours:
[0128] Feed 1: 610 parts by weight of acrylonitrile 499 parts by
weight of methyl acrylate
[0129] Feed 2: 370 parts by weight of deionized water 1.85 parts by
weight of butyl acrylate
[0130] Feed 3: 370 parts by weight of deionized water 1.40 parts by
weight of Rongalit.RTM. C (NaSO.sub.2--CH.sub.2--OH *
2H.sub.2O)
[0131] Feed 4: 370 parts by weight of deionized water 14.80 parts
by weight of sodium styrenesulfonate
[0132] Following the end of the metered additions reaction was
continued for 1 hour. This gave an emulsion (SC: 39.5%) containing
51% of an acrylonitrile-methyl acrylate-sodium styrenesulfonate
copolymer (in the proportion of 53.5/44.5/2.0) and 9% of a
polymeric emulsifier of type 1A grafted therewith and having an
average molar weight M.sub.w: 20,000 g/mol; [.eta.].sub.DMF=1.75
dl/g. The polymer-bound sulfonate group content is about 340 meq/kg
of polymer.
[0133] For whitening, in each case 500 parts by weight of the
emulsion polymer, which still contained residual monomers, were
treated at 60.degree. C. for 1.5 h with an aqueous solution (15%
strength) of the optical brightener from Example 1 in an amount of
a) 0.2%, b) 0.4% and c) 0.8%, based on the polymeric solids
fraction. Thereafter, the residual monomer fractions were removed
by vacuum distillation with the addition of 50 parts by weight of
water. Subsequently, the final filtration through a filter cloth
with a mesh size of 30 .mu.m gave the whitened emulsion polymers.
The solids content and the average particle size (determined by
laser correlation spectroscopy) of the white pigment/polymer
dispersions obtained in this way were as follows:
4TABLE 4 Example Brightener in %, Average particle size 4 based on
polymer SC in % (nm) a) 0.2 43.8 542 b) 0.4 38.6 252/239 c) 0.8 37
256
[0134] The whitened, fine dispersions a)-c) obtained in this way
were coated onto base paper using a manual knife coater (coat
weight: about 20 g/m.sup.2). The whitenesses of the coated papers
were as follows:
5 TABLE 5 Example Optical brightener in % Whiteness 4) based on
polymer Berger CIE none 82 81.3 a) 0.2 131.4 130.2 b) 0.4 150.5
146.76 c) 0.8 162.4 153.9
[0135] The resulting stable, whitened polymer dispersion was easy
to incorporate into paper coating slips and exhibited excellent
white effects with high lightfastnesses, even when added in large
amounts.
EXAMPLE 5 (not in accordance with the invention)
[0136] An unwhitened paper coating slip having a solids content of
about 60% by weight, whose pH was adjusted to 9 using sodium
hydroxide solution, was prepared by stirring together
[0137] 60 parts of calcium carbonate pigment (chalk HC 90)
[0138] 40 parts of kaolin pigment (china clay SPS)
[0139] 0.25 parts of a dispersant based on Na salt of a
polycarboxylic acid
[0140] 10 parts of a commercial 50% polymer dispersion based on
styrene-butadiene-acrylic acid copolymer (Baystal.RTM. P from
Bayer) (corresponding amounts of an acrylate-containing copolymer
(Acronal.RTM. 320 D from BASF) gave the same result)
[0141] 0.75 parts of polyvinyl alcohol
[0142] 66 parts of water.
EXAMPLE 6
[0143] For each 1 kg of the pigmented coating slip of Example 5, a)
0.025%, b) 0.05%, c) 0.1%, d) 0.2%, and e) 0.3% of a comparative
brightener, based on the solids content of the coating slip of
Example 5, of the formula 10
[0144] which is commonly used in paper coating slips, was added and
incorporated.
[0145] In a second series of tests, f) 10%, g) 20%, h) 40% and i)
80% (amount based on solids) of the pigment dispersion (SC: 38.6%)
of Example 4b) were incorporated into this coating slip.
[0146] To prepare the coated papers, the coated slips 6a)-e) (not
in accordance with the invention) and 6f)-i) (Inventive Examples)
are applied to base paper with the aid of a manual knife coater or
an experimental coating unit and are dried at 80.degree. C.
[0147] Table 6 shows the CIE whiteness of the papers following
production and drying.
6 TABLE 6 Comparative optical brightener, based on solids content
of the coating slip of Example 5 CIE Example (in % by weight)
whiteness 5) -- 69.0 6a) 0.025 78.0 6b) 0.05 82.4 6c) 0.1 88.2 6d)
0.2 91.2 6e) 0.3 91.3 6f) 0.016 78.7 6g) 0.032 83.9 6h) 0.064 90.2
6i) 0.128 97.2
[0148] The papers coated with the coating slips 6f)-i) (Inventive
Examples) exhibited very high gloss and good smoothness in
comparison to the papers coated with 6a)-e) (brighteners).
EXAMPLE 7
[0149] Base paper was precoated with a pigmented coating slip as in
Example 5, without whitener, with an application of about 16
g/m.sup.2. Subsequently, the dispersion of Example 4b) was coated
as topcoat with an application of 8 g/m.sup.2. The comparison used
for a brightened coat was Example 6d). The lightfastnesses were
determined in the xenon test in accordance with the guidelines for
the determination of colorfastnesses in accordance with DIN 54
004.
7 TABLE 7 Drop in whiteness CIE whiteness after after exposure 4 h
of Example Pigmented slip before 1 h 2 h 4 h exposure 5) without 69
66 67.5 67.6 1.4 brighteners 6d) 0.2% by weight 91.2 83.7 82 75.2
16 comparative brightener 7) Precoat of 5) and 127.3 121.7 121.3
118.9 8.1 whitened polymer dispersion (coat weight 8 g/m.sup.2)
[0150] The coat furnished in this way exhibited not only high
whiteness and excellent lightfastness but also high gloss and high
smoothness.
EXAMPLE 8
[0151] Base paper was precoated with an application of about 16
g/m.sup.2 of the following pigment slip
[0152] 100 parts of calcium carbonate pigment (chalk HC 90)
[0153] 7 parts of starch
[0154] 0.25 parts of a dispersant based on Na salt of a
polycarboxylic acid (Polysalz.RTM. S from BASF)
[0155] 5 parts of a commercial 50% polymer dispersion based on
styrene-butadiene-acrylic acid copolymer (Baystal.RTM. P from
Bayer) and
[0156] 72 parts of water (about 60% SC; pH: 8.8-9).
[0157] a) without whitener, b) with 0.1% and c) with 0.2% of the
comparative brightener from Example 6 (based in each case on the
solids content of the coating slip).
EXAMPLE 9
[0158] The precoated papers produced in accordance with Examples
8b) and c) with brightener were furnished with a topcoat of the
following composition:
[0159] 80 parts of calcium carbonate pigment (chalk HC 90)
[0160] 20 parts of kaolin pigment (china clay SPS)
[0161] 0.25 parts of a dispersant based on Na salt of a
polycarboxylic acid (Polysalz.RTM. S from BASF)
[0162] 10 parts of a commercial 50% polymer dispersion based on
styrene-butadiene-acrylic acid copolymer (Baystal.RTM. P from Bayer
) (the same result was also obtained with an acrylate-containing
copolymer (Acronal.RTM. 320 D from BASF)
[0163] 0.75 parts of polyvinyl alcohol and
[0164] 66 parts of water (SC: 60%, pH: 9)
[0165] and also a) 0.25%, b) 0.5%, and c) 1% of the comparative
brightener from Example 6 (based in each case on the solids content
of the coating slip) (about 8-12g/m.sup.2 coat weight).
EXAMPLE 10
[0166] In a second series of experiments, the paper precoated in
accordance with Example 8a) without brightener was coated with a
topcoat of the following composition
[0167] a) 100 parts of a dispersion in accordance with Example
4b)
[0168] 20 parts of precipitated calcium carbonate (PCC)
[0169] 0.25 parts of Polysalz.RTM. S; BASF
[0170] 0.2 parts of polyvinyl alcohol and
[0171] 59 parts of water SC: about 50%
[0172] or
[0173] b) 100 parts of a dispersion in accordance with Example
4b)
[0174] 40 parts of precipitated calcium carbonate (PCC)
[0175] 0.25 parts of Polysalz.RTM. S
[0176] 0.2 parts of polyvinyl alcohol and
[0177] 18 parts of water SC: about 50%.
[0178]
[0179] The papers furnished in accordance with Examples 9 and 10
were subsequently exposed at a distance of about 15 cm for 5 days
using the daylight fluorescent lamp Sylvania Daylight F 20 W/DRS.
The whitenesses of the coated papers before and after exposure were
as follows.
8 TABLE 8 CIE whiteness Drop in Precoat Topcoat Before After
whiteness Example Example exposure exposure due to exposure 8b) 9a)
95.3 77.6 17.7 9b) 96.7 76.8 19.9 9c) 99.5 74.2 25.3 8c) 9a) 95.6
76.9 18.7 9b) 97.4 76.4 21 9c) 99.1 73.9 25.2 8a) 10a) 135 132.9
2.1 8a) 10b) 135.4 132.9 2.5
EXAMPLE 11
[0180] Pigmented ink-jet coat:
[0181] Using a manual knife coater or an experimental coating unit,
the following paper coating slip (pigmented slip)
[0182] 100 parts of a whitened polymer dispersion in accordance
with Example 4b)
[0183] 11.4 parts of precipitated silica or silica hydrogel
[0184] 1 part of polyvinyl alcohol (e.g., Mowiol.RTM. 28-99 or
2-88, from Hoechst)
[0185] 1 part of cationic additive (e.g., Additol.RTM. VXT 3529,
from Hoechst)
[0186] 50 parts of water
[0187] having a solids content of 30% and a pH of about 6 was
applied to base paper (coat weight: 10-12 g/m.sup.2). Drying gave
color-printable papers of excellent quality with a high CIE
whiteness of 136.7, which are outstandingly suitable for colored
and black ink-jet printing.
EXAMPLE 12
[0188] In the same way as described in Example 2, the untreated
polymer dispersion was treated at 98.degree. C. for 20 minutes with
a) 0.2%, b) 0.4%, c) 0.8% and d) 1% (based in each case on polymer)
of the optical brightener of the formula 11
[0189] The coating of the whitened polymer dispersions prepared in
this way on base paper was subsequently exposed at a distance of
about 15 cm for 5 days using the daylight fluorescent lamp Sylvania
Daylight F 20 W/DRS. The whitenesses of the coated papers before
and after exposure were as follows.
9 TABLE 9 Brightener in % by weight CIE whiteness Drop in Example
based on Before After whiteness 9) polymer exposure exposure due to
exposure none 80.6 80.3 0.3 a) 0.2 141 143.3 0 b) 0.4 146 146.7 0
c) 0.8 145 144.9 0.1 d) 1 144.4 142.8 1.6
[0190] The maximum white yield was achieved with a whitener
concentration of just 0.4%. The drop in whiteness due to exposure
was within the error margin of the measuring instinuent.
EXAMPLE 13
[0191] Following the procedure described in Example 2 but adding,
instead of the brightener from Example 1, a) 0.1%, b) 0.2%, c) 0.4%
and d) 0.8% by weight, based in each case on polymeric solids
fraction, of the optical brightener of the formula 12
[0192] followed by workup as described, likewise gave a polymer
dispersion suitable for the brightening of the paper coating slips.
The whitened, fine polymer dispersion thus obtained was coated onto
base paper using a manual knife coater (coat weight: about 15
g/m.sup.2). The coated papers were exposed at a distance of about
15 cm for 72 h using the daylight fluorescent lamp Sylvania
Daylight F 20 W/DRS and gave the following whitenesses before and
after exposure:
10 TABLE 10 Brightener in % by weight CIE whiteness Drop in Example
based on Before After whiteness 10) polymer exposure exposure due
to exposure none 80.6 80.3 0.3 a) 0.1 115.8 114.3 1.5 b) 0.2 144.7
143.5 1.2 c) 0.4 148.6 145.1 3.5 d) 0.8 154.8 152.3 2.5
[0193] As a topcoat, in a mixture with precipitated calcium
carbonate, the resulting stable white pigment-polymer dispersion
showed excellent white effects and was also easy to incorporate
into paper coating slips. The high gloss and high smoothness of the
coats are noteworthy.
* * * * *