Anionic paper surface sizing agent

Paper surface sizing agents based on aqueous solutions ofcopolymers of maleic acid anhydride and dicyclopentadiene, which are further reacted after preparation to produce the half amides with ammonia, or primary or secondary aliphatic amines.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for the sizing of paper surfaces 
by use of a statistical copolymer of maleic acid anhydride and 
dicyclopentadiene and to the reaction products of these copolymers. 
2. Description of the Prior Art 
It is generally known to size paper in the pulp form by use of rosin soaps 
and aluminum ions. Besides of the known sizing agents based on rosin 
derivatives other solutions or dispersions of polymer compositions have 
been utilized for the sizing of paper. The advantage of such synthetic 
agents arises from the fact that they can also be brought to the already 
finished paper surface, while a normal resin glue with aluminum ions 
precipitates on the paper fibers. 
The utilization of synthetic polymer sizing agents allows paper sizing 
without addition of metal salts. As examples of such sizing agents are 
solutions or dispersions of statistical copolymers of unsaturated 
carboxylic acids and their derivatives with specific ethylenic unsaturated 
compounds. The degree of sizing of these, state of the art copolymer-sized 
papers, is not always in accord with the technical requirements, as for 
example in the sizing of presized paper pulp. 
It is known from DT-OS 1621693 that copolymers containing succinic acid 
imide groups can be used for the sizing of paper surfaces, wherein said 
copolymers contain vinylogous compounds as comonomers. As a possible 
vinylogous compound is mentioned, among others dicyclopentadiene. In order 
to make these copolymers soluble for the paper sizing, they have to be 
reacted with ammonia, bases or amines. This treatment with base, causes 
the formation of a variety of undesired derivatives becasue of the imide 
group content of the copolymer. 
By the above mentioned method, it is necessary in order to form the imide 
groups, either to transform maleic acid anhydride into maleic acid imide 
or to form the imide groups from a copolymer composed of maleic acid 
anhydride and vinylogous compounds. Because of industrial interest it is 
desirable to simplify the preparation of the paper sizing agents 
containing copolymers and also based on a need for better reproducibility, 
to keep the number of the above mentioned derivatives obtained upon 
solution, under strict control. 
SUMMARY OF THE INVENTION 
It is thus an object of the invention to produce anionic surface sizing 
agents based on aqueous solutions of statistical maleic acid anhydride 
copolymers wherein said copolymers are prepared from maleic acid anhydride 
and dicyclopentadiene. 
This and other objects of the invention as will hereinafter become clear, 
have been achieved by the surprising discovery that copolymers of maleic 
acid anhydride and dicyclopentadiene, which do not contain an imide 
structure, --and thereby save during their preparation, one or more 
steps--are highly usable paper sizing agents, comparable or even superior 
in efficiency and strength to the above mentioned agents and which can be 
used for unsized as well as presized paper pulp as excellent sizing 
agents. The utilization of such copolymers as paper sizing agents is until 
now unknown. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The statistical copolymers of the present invention can be obtained by a 
known method, in that the polymerization is carried out by suspension-or 
solution polymerization in aliphatic or aromatic hydrocarbons, such as for 
example toluene or xylene, in alcohols, such as for example ethylene 
glycol or ethyl glycol, or in ethers, such as for example ethylene glycol 
dimethyl ether or dioxane, at temperatures between 60.degree. and 
150.degree. C., preferentially between 70.degree. and 90.degree. C., in 
the presence of radical initiators. As initiators it is possible to use 
azo compounds, peroxides or hydroperoxides, such as for example azo 
bisisobutyronitrile, di-benzoyl-peroxide or di-tert-butyl-peroxide. The 
initiators are used preferentially in amounts of from 2 to 6% by weight of 
the comonomers. 
In order to make the copolymers of the present invention, which contain 
anhydride groups, soluble in water, it is necessary to transform them with 
bases into their salts. It is, according to this invention, not necessary 
to neutralize all carboxyl groups, since in general a neutralization 
degree of about 80%--relative to the total carboxylic acid content--is 
sufficient. As cations, it is possible to use ammonium and/or mono-, di-or 
trialkyl ammonium with up to 6 carbon atoms as well as alkali metal ions. 
It is therefore possible to use the copolymers of the present invention in 
the form of their reaction products with ammonia or primary aliphatic or 
aromatic amines, as for example ethylamine or aniline, or secondary amines 
as for example diethylamine, morpholine or pyrrolidine and/or aliphatic 
alcohols. 
These reaction products have excellent paper sizing properties. 
The quantity of copolymers of the present invention necessary for the paper 
sizing is between 0.01 and 3, preferentially between 0.1 and 1% by weight, 
relative to the paper weight. 
The paper sizing agent copolymers of the present invention can be used for 
the paper sizing with various anionic strengtheners in combination. The 
thus obtained sizing liquor can be reacted if necessary with customary 
additives. The work-up can be carried out according to well known 
techniques used in the manufacture of paper.

The following examples are intended merely to describe specific embodiments 
of the present invention and are not to be construed as a limitation of 
the scope thereof. 
EXAMPLE 1 
Sizing Agent I 
Maleic acid anhydride is polymerized with dicyclopentadiene in a molar 
ratio of 1:1 in toluene as solvent and in the presence of benzoyl peroxide 
as initiator. After ending the polymerization, the product was filtered 
and dried of the remaining toluene. The recovered white powder had a 
softening point of higher than 270.degree. C. 
Sizing Agent II 
Maleic acid anhydride and dicyclopentadiene are polymerized following the 
method of I. In order to convert the resulting copolymer into the half 
amide, gaseous ammonia was introduced into the polymerizate suspension, 
until the necessary nitrogen value was reached. After evaporation of the 
remaining solvent, a white powder was obtained with a softening point 
higher than 270.degree. C. 
Sizing Agent III (comparative) 
A copolymer of maleic anhydride and styrene according to the state of the 
art, was prepared as the half amide as a comparison substance. 
The sizing agents I to III were combined with an anionic corn starch, 
commercially available under the trademark "Amisol 5591", into a 10% 
sizing liquor. The solid contents of sizing agent to starch was 1.5:8.5. 
This liquor was applied by means of a labor sizing press onto a sample of 
80 g of unsized paper, so that the amount of sizing agent corresponds to 
0.6% of the paper weight. The drying of the paper in the sizing press 
followed at 140.degree. to 160.degree. C. in about 5 seconds. The obtained 
sizing values are described in Table 1. 
Table 1 
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With- 
Sizing Agent I II III out 
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Water absorption (DIN 53 132) sec 
30 10 &lt;1 &lt;1 
g/m.sup.2 20 12 10 89 
Sizing Degree (DIN 53 145) sec. 
&gt;1800 1160 157 &lt;1 
Absorption Height, 10 min. 
3 &lt;1 8 44 
(DIN 35 106)mm 
Surface Strength 18 16 14 11 
(Dennison-Test) 
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The efficiency of the sizing agents of the present invention is 
overwhelmingly clear. 
EXAMPLE 2 
In analogy to Example 1, the sizing agents I-III were formulated into 
sizing liquors, and applied on a labor sizing press, with the difference 
that as paper, was utilized a pulp which was presized with 0.8% resin 
size. The obtained sizing values are contained in Table 2. The advantage 
of the sizing agents I and II with respect to the comparative agent III is 
clearly recognizable. 
Table 2 
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With- 
Sizing Agent I II III out 
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Water absorption (DIN 53 152) sec 
300 300 300 300 
g/m.sup.2 25 25 25 27 
Sizing Degree (DIN 53 145) sec 
&gt;1800 924 461 418 
Absorption Height, 10 min. 
&lt;1 &lt;1 &lt;1 &lt;1 
(DIN 53 106)mm 
Surface Strength 
(Dennison-Test) 18 16 13 13 
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