Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-01-19
2001-10-30
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S304000, C526S311000, C526S312000, C526S318000, C526S318400, C526S318410, C526S318420, C526S320000, C526S321000, C526S323200, C526S329200, C526S333000, C526S347000
Reexamination Certificate
active
06310159
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention refers to low foaming paper sizing compositions comprising a copolymer bearing specific hydrophobic substituents.
Sizing is a technique which renders paper resistant to the penetration of fluids. A paper may be sized to a variety of degrees and to a variety of purposes. Thus, writing paper is sized to prevent the spread of ink while milk carton stock is sized to prevent any fluid flow through the carton walls and edges.
Sizing can be applied to paper as either a post-production operation or as a portion of a paper making process itself. Surface size is applied to typically in the paper making process after the paper sheet has been formed and dried but not passed through a calendar stack.
Surface treatment is applied by paper makers for a variety of reasons all related in some way to improve quality control of the paper. The sizing effect translates into higher penetration time values and moreover correlates to less feathering and reduced lateral spread of printing inks producing improved imaging and contrast.
Anionic copolymers, i.e., &agr;-olefin/unsaturated carboxylic acid-copolymers and in particular styrene/(meth)acrylic acid copolymers have been known for a long time as paper surface sizing agents, as described in DE-A-2117682, DE-A-233354713, DE-A-2421826 and DE-A-2502172.
The anionic styrene/(meth)acrylic acid and/or styrene maleic anhydride based copolymers are very hydrophilic. Hence, they are highly surface-active and, as a consequence, air is entrained into their solutions which then promotes the formation of foam in the paper making process. This results in an in homogeneous sizing. DE-A-3224528 discloses the use of polysiloxanes as additives for anionic surface sizing agents in order to reduce their foaming. Unfortunately these additives are not very stable in the aqueous polymer solution and separate into a second layer within a short time, often within weeks or even a couple of days. As a result their ability to reduce the foam level of the paper sizing composition is lost.
In EP-A-238968 also the problem of air entrainment in paper sizing compositions comprising copolymers based on maleic anhydride and diisobutylene is addressed. The solution suggested in EP-A-238968 to solve this problem is to provide a paper sizing composition comprising a copolymer of a vinyl monomer and maleic anhydride whereby 3 to 20 mole percent of the anhydride groups are bi-esterified with linear, branched or cyclic C
1
-C
12
alcohols, the copolymer may also contain structural units derived from maleic esters, or half-esters esterified with the above-mentioned alcohols. Unfortunately the bi-esterification is a time-consuming process, for example, batch time of 12 hours and the presence of an acid catalyst in order to achieve a reasonable conversion and bi-esterification of the polymer is required rendering the production of this copolymer expensive.
DE-A-3742330 mentions among other advantages, a reduced foam level of the paper sizing compositions which comprises styrene/methacrylic acid copolymers containing as a third component, long-chain aliphatic methacrylates. However, preparation of long-chain aliphatic acrylates is not cost effective and yields insufficient reduction of the foam level of a paper sizing composition.
From WO 95/11341, the use of styrene/(meth)acrylic acid/half-esters of maleic anhydride are known. Maleic half-esters are esterified with alcohols having the following structure CH
3
—[(CH
2
)
n
—O]
m
—(CH
2
)
0
—OH. Particularly preferred is the half-ester of 2-(n-butoxy)ethyl alcohol. The copolymers are said to result in better sizing properties. A reduction of the foam level is not mentioned.
U.S. Pat. No. 5,237,024 discloses polymers of alkenyl aromatic monomers and alkyl half-esters of maleic anhydride with primary or secondary C
1
-C
18
alcohols having a high weight average molecular weight of above 110,000 Daltons. The high molecular weight provides suitable film forming properties for paper sizing.
In view of the deficiencies of the prior art, an object of the present invention is to provide a paper sizing composition exhibiting low foaming without compromising paper sizing properties that can be easily produced at low costs. This object has been attained by a paper surface sizing composition comprising a copolymer having:
a) structural units derived from ethylenically unsaturated hydrocarbons;
b) structural units derived from monomers selected from esters of ethylenically unsaturated mono-carboxylic acids, half-esters of ethylenically unsaturated dicarboxylic acids, allylethers and vinylethers and mixtures thereof bearing a substituent R linked to the oxygen atom of either the ester groups or the ether groups that is at each occurrence selected from:
(i) polyalkyleneoxide groups corresponding to the formula:
wherein R
1
is independently at each occurrence selected from hydrogen and C
1
-C
4
alkyl, R
2
is C
1
-C
44
hydrocarbyl, t is 0 or 1 and m is an integer in the range of 5-200 with the proviso that if R
2
is C
1
-C
5
alkyl, the polyalkyleneoxide group does not contain more than 50 weight percent ethyleneoxide moieties based on the weight of the polyalkyleneoxide group; and
(ii) groups corresponding to the formula:
wherein t is 0 or 1 and Q is a polysiloxane residue, whereby the substituents R of said half-esters are additionally selected from
(iii) C
1
-C
24
alkyl, with the proviso that if R comprises C
1
-C
9
alkyl, at least 1 mole percent of the substituents R of said half-esters are selected from substituents (i) and (ii); optionally
c) structural units derived from ethylenically unsaturated monomers selected from mono-carboxylic acids as well as salts and amides thereof, dicarboxylic acids as well as salts, amides and half-amides thereof and cyclic anhydrides and imides of dicarboxylic acids and mixtures thereof; and optionally
d) structural units derived from alkyl or amino-substituted alkyl acrylates of methacrylates
with the proviso, that if no structural units c) are present, the structural units b) are derived from monomers selected from half-esters of ethylenically unsaturated dicarboxylic acids.
The paper sizing composition of the present invention combines satisfactory paper sizing properties hydrophobicity and printability with a low air entrainment due to incorporation of certain specified hydrophobic residues whereby these desired properties can already be achieved at a low level of incorporation of hydrophobic residues. Thus, the copolymers of the present invention are not only highly effective, but they can also be produced at considerably lower costs in comparison to the cited prior art products.
The copolymer of the present invention is composed of at least 2 different types of structural units as defined above.
The structural units a) preferably correspond to the Formula I:
wherein R
4
is selected from C
1
-C
8
alkyl and substituted and non-substituted aryl and R
5
, R
6
and R
7
are independently at each occurrence selected from hydrogen and C
1
-C
4
alkyl.
The selection of specific olefinic starting materials for the production of the copolymer is not critical. But for reasons of ease of production and availability of starting materials, styrene and diisobutylene are the preferred monomers used to provide for the structural units corresponding to Formula I. The most preferred olefinic monomer used in the preparation of the copolymer of the present invention is styrene.
The structural units b) of the copolymer of the present invention preferably correspond to the formulae:
wherein R
8
and R
9
are independently at each occurrence selected from hydrogen and C
1
-C
4
alkyl, R
10
is selected from hydrogen and C(O)X; X is independently at each occurrence selected from OA and NR
11
2
, whereby A is selected from hydrogen, ammonium, alkyl ammonium, alkanol ammonium and
1
n
·
Mn
+
whereby M is a metal having the valence n, and R
11
is selected from hydrogen, alkyl and aryl; p is 0 or 1, and R
12
, R
13
and R
4
are independently at each
Carlsson Roger
Eiffler Jurgen
Hermanns Jürgen
Oliver Stephen
Pezzuto Helen L.
The Dow Chemical Company
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