NO790070L - PROCEDURE FOR SURFACE GLAPING OF PAPER - Google Patents

Description

The invention relates to a method for surface sizing of paper with an aqueous solution of a water-soluble salt of an anionic synthetic sizing agent and starch.

In order to reduce the rate of penetration of water and other liquids into paper in a certain way, it is necessary to glue the paper, i.e. partially hydrophobe it. Only after gluing can the paper be written on and pressed.

The gluing of paper and cardboard can take place using gluing agents which are either added to the paper pulp ("mass gluing") or which are applied to the finished paper tap using suitable application devices, such as glue presses or spray devices ("surface gluing"). The most famous mass adhesive, which also

today, what is used to the greatest extent is resin glue on a rosin basis. The gluing of paper produced in this way must be said to be very good, but the execution of the gluing is bound to the presence of a rather large amount of aluminum sulphate.

In addition to mass gluing, surface gluing has gained more and more popularity in recent times, since it is possible with suitable combinations of gluing agent and other finishing agents, in addition to the gluing of the paper, also at the same time to achieve other favorable properties for the paper, such as increased firmness and improvement of the printing properties of paper treated in this way. thus, for example, it is common to use aqueous solutions of water-soluble salts of anionic synthetic sizing agents, which also contain dissolved starch, for the surface sizing of paper. Until now, non-ionic or anionic starches have been used, e.g. starches produced by oxidative, thermal or enzymatic degradation. If these starches are not hardened using urea/formaldehyde or melamine/formaldehyde resins, they disintegrate when the excess is recovered and lead to a significant strain on the waste water.

The task of the invention is to improve the gluing effect of water-soluble salts of anionic synthetic gluing agents.

The task is solved in the manner described in the requirements, by

that the sizing agent solution contains 0.5 to 8% by weight of a cationic modified starch. Surprisingly, anionic synthetic sizing agent can be combined with cationically modified starch without precipitation forming. The mixture is stable and can be processed on the sizing press without difficulty. Gluing results are obtained that are far above those that can be obtained with mixtures of the same anionic synthetic gluing agent and anionic or neutral starch in accordance with the known technique. A further advantage of the method according to the invention is that it is possible to carry out a neutral bonding in the absence of alum and/or sodium aluminate.

Water-soluble salts of anionic synthetic surface sizing agents are commercially available. They consist of copolymers of ethylenically unsaturated, nonionic monomers with comonomers exhibiting an anionic group. Suitable non-ionic, ethylenically unsaturated monomers are, for example, olefins with 2 to 24 carbon atoms, styrene and styrene derivatives and vinyl ether. Of the non-ionic, ethylenically unsaturated monomers mentioned above, styrene and diisobutylene are particularly important. This group of monomers also includes esters and/or amides or imides of ethylenically unsaturated C₁ to C₂ mono- and/or dicarboxylic acids. This group of monomers which, when polymerized alone, form a hydrophobic polymer, is usually involved with up to approx. 40 to 95% by weight in the construction of the copolymer.

Monomers containing anionic groups are, for example, ethylenically unsaturated carboxylic acids with 3 to 6 carbon atoms, half-esters of maleic acid and fumaric acid as well as maleic anhydride.

Of the anionic monomers mentioned above, acrylic acid, methacrylic acid and maleic anhydride as well as half-esters of maleic acid with monohydric alcohols come into consideration. The anionic monomers may be present in the copolymer in an amount of 5 to 60, preferably 6 to 55, % by weight. The copolymer may optionally also contain further ethylenically unsaturated monomers. Suitable surface adhesives for paper are known, for example, from BRD patent document no.

2.040.692, BRD official publication no. 2.502.172, BRD official publication no. 1.546.411 and BRD official publication no. 2.361.544.

Cationic starches are also commercially available. Suitable are, for example, primary, secondary, tertiary or quaternary amine starch derivatives and other cationically modified nitrogen-substituted starch derivatives, such as cationic sulfonium and phosphonium starch derivatives. These products can be made from all kinds of starches, e.g. of starches from corn, potatoes, wheat and rice. Production of cationic starch derivatives is described, for example, in US patent no. 2,813,093 and iBRD publication no. 1,918,415. The nitrogen content of the modified cationic starches amounts to 0.05 to 1.5% by weight. The method according to the invention preferably uses the same starch derivatives that are offered on the market for surface impregnation of paper. The finished preparation solution contains 0.5 to 8, preferably 1 to 6, % by weight of a cationic starch.

The water-soluble salt of the anionic copolymer is obtained by neutralizing the carboxyl-group-containing copolymer with alkaline lye, ammonia and/or amines. This can be done by treating a copolymer melt with gaseous ammonia or amines and then dissolving the reaction product in water. However, an aqueous solution or suspension of the anionic copolymer can also be neutralized with aqueous lye, such as caustic soda or potassium hydroxide, or with aqueous ammonia or amines. The non-neutralized copolymer must not be water-soluble, but the salt of the copolymer, on the other hand. The copolymer does not need to be completely neutralized, in many cases a degree of neutralization of 70% of the carboxyl groups is sufficient. When it concerns copolymers containing maleic anhydride as anionic monomer, e.g. copolymers of styrene and maleic anhydride or diisobutylene and maleic anhydride (e.g. each in a 1:1 molar ratio), the anhydride group in the copolymer is cleaved during neutralization to form carboxylate groups. The molecular weight of the non-neutralized anionic copolymer is approx. 500 to 10,000. It was determined vapor pressure osmometrically in chloroform at a concentration of 0.1% by weight and a temperature of 37°C (Mechrolab osmometer).

The finished adhesive solution usually contains 0.3 to 5, preferably 1 to 2, wt.% of the water-soluble salt of an anionic copolymer and 0.5 to 8, preferably 1 to 6, wt.% of a cationically modified starch. However, it is also possible to use several different copolymers as adhesives. the preparation solution is applied to paper in the glue press. In addition, other application methods also come into consideration, e.g. spraying, impregnation by dipping methods, casting or application in the water scraper at the calender. The entire gluing effect of the mixtures used according to the invention is achieved directly after drying the paper.

The invention is further explained with the help of the following examples. The parts given in the examples are parts by weight and the percentages given are based on the fabric weight. The gluing degree of the paper was measured according to Cobb (DIN 53/32 - 1 min.) and by means of the ink-swimming test, whereby a test ink according to DIN 53 126 was used, whereby the time in minutes until 50% ink penetration was determined.

The K value of the anionic copolymer was determined by

H. Fikentscher, Cellulose-Chemie 13, 58-64 and 71-74 (1932), in 0.5% dimethylformamide solution at 20°C, and thus K == k • 10"^.

Example 1

As test paper, a wood-free, unglued paper with 14% ash and 1% alum is used. The basis weight of the paper is 70 g/m 2. It is impregnated in a laboratory foulard, which corresponds to a glue press, with the preparation solutions specified below. In accordance with the invention, the preparation solutions ia to Ic are used, each of which contains dissolved 6% of a cationically modified starch (starch for surface impregnation from the company Roquette National chimie, Lille). Hereby, preparation solution la contains 1.0; Ib 1.5 and Ic 2.0% of an anionic adhesive (I) which is the ammonium salt of a statistical solution copolymer of 65% styrene and 35% acrylic acid. The K-value of the copolymer is 32 and the degree of neutralization is 90%. The solids absorption of the paper is, based on the weight of the dried paper, 85 in 5%.

For comparison, the comparison preparation solutions Ib and Ic are prepared, which respectively contain 1.5 and 2.0% of adhesive I, and which each contain dissolved 6% of an oxidatively built-up anionic starch common in the trade. the paper is impregnated with the same amount as the amount of the adhesive mixtures Ia to Ic used according to the invention. The results are summarized in the following table.

Example 2

Example 1 is repeated with the exception that a copolymer of 65% styrene, 20% acrylic acid and 15% maleic anhydride is used as anionic synthetic adhesive (II). The copolymer has a number-average molecular weight of 1900, and it is 100% neutralized.

in the same way as in example 1, comparative preparations Ilb and lic are prepared from adhesive II and anionic starch. The results are summarized in the following table:

Example 3

By means of this example, it is shown that it is achieved

an improvement in the gluing effect also by partial replacement of anionic starch in the gluing agent preparations with cationic starch. The adhesive agent I described in example 1 is prepared with the

mixtures of cationic starch (in accordance with example 1) and commercially common anionic starch specified in the following table, to preparation solutions, which are then tested with regard to their gluing effect in accordance with example 1. Each preparation contains 1.5% of gluing agent I , and the float absorption makes up 90%. The following results are thereby achieved:

Example 4

From a 30% aqueous solution of the adhesive I described in example 1, by mixing different amounts of 10% cationic modified starch according to example 1, the following mixtures are prepared, and the stability of the mixtures is assessed. After storage for 7 days at a temperature of 60°C, the mixtures are now unchanged. The following mixtures were investigated:

This example shows that aqueous solutions of anionic sizing agent of cationic starch do not precipitate.

Example 5

In order to demonstrate the superiority of mixtures of anionic adhesive and cationic starch also in a neutral adhesive, i.e. in the absence of alum, a 1.5% aqueous solution of the adhesive II described in example 2 according to the invention and 6%, based on the finished preparation solution, of the cationic starch specified in example 1. With this sizing agent solution, a wood-free offset paper, which was not pre-glued in the pulp, which contained 18% ash (half of each of kaolin and calcium carbonate) and which had a basis weight of 75 g/m 2 , was impregnated in the sizing press on a experimental paper machine with a speed of 80 m/min. (flow absorption 65%). The Cobb value (1 min.) was 25, and the ink swimming time until 50% penetration was 6 minutes.

A preparation solution prepared for comparison, which only differed from the one mentioned above in that instead of cationic starch, the same amount of an anionically modified commercial starch was used, gave in the gluing test under the same conditions as above a Cobb value (1 min.) of 81 and an ink swimming time of up to 50% penetration in just 1/2 minute..

Claims (3)

1. Process for surface gluing of paper with an aqueous solution of a water-soluble salt of an anionic synthetic adhesive and starch, characterized in that an adhesive solution containing 0.5 to 8% by weight of a cationic modified starch is used. 2. Process according to claim 1, characterized in that an anionic synthetic adhesive is used which is made up of 40 to 95% by weight olefin with 2 to 24 carbon atoms, styrene or styrene derivatives, esters, amides and/or imides of ethylenically unsaturated CU - to C^- carboxylic acids and 60 to 5% by weight ethylenically unsaturated C^ - to C^ - carboxylic acids, half-esters of maleic acid or fumaric acid or maleic anhydride. 3. Method according to claims 1 and 2, characterized in that copolymers of styrene or diisobutylene are used with acrylic acid, methacrylic acid, maleic acid and/or maleic anhydride.