Sizing agents for paper

Details Sizing agents for paper Sizing agents for paper

1998-12-15

2001-10-30

Metzmaier, Daniel S. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S458000, C524S504000, C524S734000, C524S742000, C524S745000, C524S804000, C162S164500

Reexamination Certificate

active

06310132

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to aqueous emulsion polymers, to their use as surface sizing agents, and to processes for preparing the emulsion polymers.
The prior art has disclosed sizing agents based on aqueous emulsion polymers, but these are not satisfactory with respect to all of the requirements made of them.
Japanese Patent Application 58/115196 describes the use of aqueous dispersions of graft copolymers of acrylates and styrene on starch as sizing agents for paper, and European Patent Applications 257,412 and 276,770 claim graft copolymers of acrylates and acrylonitrile on starch which are likewise employed in the form of fine aqueous dispersions for sizing paper.
European Patent Application 276,770 also describes how, by adding from 0 to 3.0% by weight, based on the sum of the monomers employed, of low molecular mass emulsifiers such as sodium alkyl-sulfonate, sodium lauryl sulfate, or sodium dodecylbenzenesulfonate, it is possible to stabilize the emulsions claimed therein. However, a disadvantage is said to be that adding such an emulsifier impairs sizing and that the sizing agents are often associated with severe foaming.
Alternatively, European Patent Applications 331,066 and 400,410 disclose fine dispersions of sizing agents that have excellent performance properties and are obtained by emulsion polymerization of monomers such as acrylonitrile, butyl acrylate, or styrene, in the presence of polymeric anionic emulsifiers containing sulfonic acid groups (in the case of European Patent Application 331,066, based on maleic anhydride copolymers, and in the case of European Patent Application 400,410 based on polyurethanes with stellate branching). Sizing agent dispersions of this kind exhibit excellent performance properties, especially on neutral and chalk-containing papers. However, such dispersions have low stability to divalent and trivalent cations, such as Ca
2+
or Al
3+
. Under adverse conditions, this may sometimes result in precipitation on the sizing press and thus to a deterioration in their sizing effect.
It has surprisingly now been found that emulsion polymers based on starch graft copolymers and polymeric emulsifiers are of outstanding suitability as sizing agents that couple improved performance properties with high dispersion stability to divalent cations and an extremely low tendency to foam in use.
SUMMARY OF THE INVENTION
The present invention relates to aqueous emulsion polymers obtained by free-radically initiated addition polymerization of at least one monomer in the presence of (1) degraded starch and (2) at least one polymeric emulsifier selected from the group consisting of (i) sulfo-containing maleic anhydride copolymers and/or terpolymers, (ii) sulfo-containing oligourethanes having a branched molecular structure, and (iii) mixtures thereof.
DETAILED DESCRIPTION OF THE INVENTION
Particularly suitable polymeric emulsifiers from the series of sulfo-containing maleic anhydride copolymers and terpolymers are those of the formula (I)
in which
M represents a cation-forming radical (preferably H, Na, K, NH
4
, or R
3
NH
3
),
n represents 1 or 2,
R represents an aliphatic radical having 1 to 10 carbon atoms or an aromatic radical having 6 to 10 carbon atoms (preferably a radical derived from a C
1
-C
4
-alkane or from benzene, methylbenzene or naphthalene, especially —CH
2
CH
2
—),
R
1
represents H or CH
3
,
R
2
represents H, C
1
-C
6
-alkyl (preferably —CH
3
, —C
2
H
5
, —C
4
H
9
, —CH
2
—C(CH
3
)
3
), or phenyl,
R
3
represents a hydrocarbon radical of an amine,
R
4
represents H or CH
3
,
R
5
represents CH
3
or C
2
H
5
, and
x, y, and z are chosen such that the weight-average molecular weight (M,
−
w
) of the polymers of formula (I) is from 5,000 to 500,000 (preferably from 10,000 to 200,000) and the ratio of x:y:z is from 1:1:0 to 1:3:0.5.
The polymers (I) in which the ratio of x:y:z is 1:1:0 are known (cf., e.g., German Patent Application 3,344,470, European Patent Application 331,066) or they can be prepared as described in European Patent Application 331,066.
The polymers (I) in which the ratio of x:y:z is 1:1:0.1 to 1:3:0.5 are novel and are likewise a subject of the present invention. The novel polymers (I) can be prepared in analogy to the known polymers (I).
Particularly suitable polymeric emulsifiers from the series of sulfo-containing oligourethanes having a branched molecular structure are those containing on average per molecule at least 2.2 terminal sulfonic acid groups (sulfo groups).
Suitable oligourethanes have an average molecular weight, calculable from the stoichiometry of the starting material, of less than 30,000 (preferably from 1,500 to 20,000) and have a branched molecular structure. This means that the components used in their preparation include those having a functionality of more than two for the purposes of the isocyanate addition reaction. Suitable oligourethanes, moreover, have terminally incorporated sulfonate groups, at least 2.2 such terminal sulfonate groups being present on average per molecule.
Preferred oligourethanes have a content of terminally incorporated ionic groups of from 7.3 to 400 (particularly from 11 to 300) milliequivalents per 100 g.
The oligourethanes are prepared by the known methods of polyurethane chemistry. Starting materials for their preparation are
(a) organic polyisocyanates, preferably of the molecular weight range from 168 to 1,000;
(b) organic compounds having isocyanate-reactive groups and a molecular weight ranging from 60 to 10,000 (preferably from 62 to 3,000), and
(c) structural components having at least one isocyanate-reactive group and sulfonic acid groups as well as salts thereof.
Examples of suitable polyisocyanates (a) are 4,4′-diisocyanato-diphenylmethane, 2,4- and/or 2,6-diisocyanatotoluene, 4,4′-diisocyanato-dicyclohexylmethane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI), 1,6-diisocyanatohexane (HDI), polyisocyanates containing isocyanurate groups, such as the polyisocyanate consisting essentially of N,N′,N″-tris-(6-isocyanatohexyl) isocyanurate alone or together with its higher homologues and obtainable by trimerization of some of the isocyanate groups of HDI, polyisocyanates containing urethane groups, such as the reaction product of 1 mol of trimethylol-propane with 3 mol of IPDI or with 3 mol of 2,4-diisocyanatotoluene, and biuret polyisbcyanates, such as the biuret polyisocyanate based on HDI and consisting essentially of N,N′,N″-tris-(6-isocyanatohexyl)biuret and its higher homologues. Any desired mixtures of such polyisocyanates can likewise be used as component (a) in preparing the oligourethanes. Moreover, the structural components (a) include, for example, (a1) polyisocyanates containing acylurea groups of the general formula
The structural components (a1) are prepared in analogy to the teaching of German Patent Application 2,436,741 by partial carbodiimidization of the isocyanate groups of organic polyisocyanates and addition of organic carboxylic acids onto the resulting carbodiimide-modified polyisocyanates. Typical examples of suitable structural components (a1) are diisocyanates of the general formula
which are prepared by reacting, in a first stage, all or some of the carbodiimide groups of diisocyanatocarbodiimides of the general formula
with carboxylic acids of the general formula
R′—COOH
alone or in the presence of an appropriate solvent at temperatures from 25 to 100° C.
In these formulas,
R′ represents an organic radical (preferably a saturated or unsaturated aliphatic hydrocarbon radical having 1 to 35 carbon atoms, an aryl radical having 6 to 10 carbon atoms, or an araliphatic radical having 7 to 10 carbon atoms), it being possible for different radicals R′ to be present alongside one another when two or more radicals R′ exist in the same molecule,
R
6
represents a divalent hydrocarbon radical with or without urethane, ester, and/or ether groups, as can be obtained by removing the terminal isocyanate groups fr

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