JPH03213597A - Production of paper having improved horizontal rule fracture - Google Patents

Abstract

PURPOSE:To obtain the title paper having compression strength in drying and burst strength free from horizontal rule fracture, adding ampholytic graft starch polymer to pulp slurry and making paper. CONSTITUTION:Pulp slurry is blended with preferably 0.1-3wt.% (calculated as solid content based on per dried pulp weight) ampholytic graft starch polymer to pulp slurry and made into paper to give the objective paper. The polymer is preferably a graft starch polymer obtained by polymerizing 10-80 pts.wt. monomer mixture comprising 30-96mol (meth)acrylamide, 4-50mol% alpha,beta-unsaturated carboxylic acid (salt) and 0-20mol% cationic monomer in an aqueous solution containing 20-90 pts.wt. cationic starch.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing paper, and more particularly, the present invention relates to a method for producing paper, and more particularly, by adding an amphoteric grafted starch polymer to a pulp slurry, the dry compressive strength and bursting strength of paper can be improved. This invention relates to a method for producing paper that has excellent strength and other strengths and does not cause creases along the lines.

[Prior Art] Various papermaking additives have been used in the papermaking process for the purpose of improving paper quality. Examples include water-soluble natural polymer substances such as starch and modified starch, polyacrylamide and its derivatives, polyamide polyamine-epichlorohydrin resin, melamine and urine formaldehyde resin, and various other water-soluble synthetic polymer substances.

Although starch-based additives are inexpensive, they have a poor paper strength enhancement effect per amount used, so they must be used in large amounts. As a result, starch-based additives must be dissolved by steaming before use. ,
Recently, synthetic polymer additives have become mainstream due to their workability.

A typical synthetic polymer additive is polyacrylamide, and various anionically modified, cationically modified, or amphotericly modified polyacrylamide additives are used. When producing corrugated board paper with excellent strengths such as compressive strength and bursting strength, polyacrylamide additives are used in most cases. However, although polyacrylamide-based additives have excellent performance as paper strength enhancers, it has been pointed out that they have drawbacks such as being susceptible to line cracking and being expensive.

Grafted starch polymers have been proposed as additives that have both the characteristics of polyacrylamide-based additives and starch-based additives. For example, Japanese Patent Publication No. 38-17051 teaches a papermaking additive made by polymerizing an unsaturated amide and an unsaturated carboxylic acid in the presence of a water-dispersible polysaccharide. Also, in Japanese Patent Publication No. 50-12481, water-soluble polysaccharides,
A mixture of a grafted starch polymer obtained by polymerizing acrylamide and an unsaturated carboxylic acid in the presence of at least one water-dispersible polysaccharide or its derivative, and a specific copolymer containing acrylamide as the main monomer component. A paper strength enhancer consisting of Further, JP-A-58-41998 describes a paper strength enhancer obtained by polymerizing a polymerizable vinyl monomer in an aqueous solution of a water-soluble polysaccharide.

Furthermore, JP-A-61-211319 discloses that a water-soluble graft copolymer made from cationic starch, nonionic monomer, and cationic monomer is effective as a dry strength improver for paper. Something is taught. And, JP-A-6
No. 3-219696 discloses a papermaking additive in which a monomer mixture consisting of dialkylaminoalkyl (meth)acrylamide, (meth)acrylic acid, and (meth)acrylamide is polymerized in an aqueous solution containing starch. is proposed.

By the way, as measures to prevent ruled line cracking, measures have been taken such as adjusting the blending ratio of pulp and the degree of beating, and increasing the water content in the paper. In addition, overdrying is prevented by spraying water during the production of corrugated cardboard sheets or applying steam during the production of boxes. In addition, chemicals that impart water retention properties to paper, such as higher alcohols such as ethylene glycol, polyethylene glycol, and glycerin, are also applied. However, the use of these higher alcohols is problematic in that it reduces the quality of paper.

[Problem to be solved by the invention] It goes without saying that all paper is required to have general strength, but it is important that ruled line cracks do not occur in corrugated base paper, white paperboard, etc. used for packaging. This is a requirement.

That is, when a box is manufactured by adding ruled lines to a paper sheet, the front side is likely to break and so-called ruled line cracking occurs, but boxes with ruled line cracking have a reduced strength and a significant loss in commercial value. By the way, among the so-called line cracks, in mild cases only a "cracking" occurs on the front side of the paper, but in severe cases, the cracks can extend to the back side of the paper and even cause the entire layer to crack. Furthermore, cracks in ruled lines are not limited to the front side of the paper; cracks also rarely occur on the back side of the paper when adding ruled lines to the paper or when folding it backwards when assembling a box. do not have.

Line cracks in corrugated cardboard sheets occur both in the horizontal ruled lines perpendicular to the corrugations and in the vertical ruled lines parallel to the corrugated sheets, but in terms of the frequency at which cracks occur, thick liners are more likely to cause cracks than thin liners. It is also said that this phenomenon is more likely to occur with multi-sided corrugated cardboard than with double-sided corrugated cardboard.

There are various possible causes of broken lines, but one of the main ones is moisture in the paper.

As for corrugated cardboard sheets, in general, when the water content is low, cracks are likely to occur, and therefore, during periods of low humidity such as winter, the sheets become overdried and the occurrence of cracks is promoted. Therefore, there is a desire in the industry to develop a chemical that can effectively prevent line cracking without damaging paper quality.

[Means for Solving the Problems] As a result of extensive research into means for effectively preventing creases in paper lines, the present inventors added an amphoteric grafted starch polymer to pulp slurry and began papermaking in a conventional manner. It has been found that by drying, it is possible to produce paper that has excellent general strength upon drying and is free from line cracks.

The amphoteric grafted starch polymer used here has the following properties: (a) (meth)acrylamide (l)) α,β-unsaturated carboxylic acid and/or or a salt thereof (c) It has been found that an amphoteric grafted starch polymer obtained by polymerizing a monomer mixture consisting of a cationic monomer is suitable.

The specific configuration of the present invention will be explained in detail below.

In the present invention, cationic starch refers to starch derived from corn, wheat, potato, rice, tapioca, etc., containing primary, secondary, and tertiary amino groups and quaternary ammonium groups. A substance containing at least one kind of basic nitrogen selected from the group consisting of: Basic nitrogen content is 0.3
The basic nitrogen is preferably a quaternary ammonium group, and the starch is most preferably tapioca starch.

There are two methods for producing cationic starch containing quaternary ammonium groups: a wet method using an aqueous medium and a dry method using a solid-gas phase reaction. According to the above, cationic starch can be produced by reacting a cationizing agent consisting of a reaction product of dialkylamine or trialkylamine and epichlorohydrin with starch in an aqueous medium in the presence of an alkali. .

Viscosity of 20 to 200 centipoise (at 25°C, 10%
Aqueous solution) is most suitable as an aqueous solution containing cationic starch to be used when obtaining the amphoteric grafted starch polymer of the present invention.

If the viscosity of the aqueous solution is less than 20 centipoise, the product, the zwitterionic grafted starch polymer, will not be able to fully exhibit the desired effect, and if the viscosity is more than 200 centipoise, the oral stability of the product will decrease. do.

Examples of α,β-unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, fumaric acid,
Citraconic acid and the like can be used, among which acrylic acid and methacrylic acid are preferred.

Furthermore, as the salts of the above carboxylic acids, alkali salts such as sodium salts and potassium salts, and ammonium salts can be used.

Cationic monomers include mono- or di-alkylaminoalkyl acrylate, mono- or di-alkylaminoalkyl methacrylate, mono- or di-alkylaminoalkylacrylamide, mono- or di-alkylaminoalkylmethacrylamide, vinyl pyridine,
Examples include vinylimidazole, mixtures thereof, and quaternary ammonium salts thereof.

When producing the amphoteric graft starch polymer of the present invention, in an aqueous solution containing 20 to 90 parts by weight of the cationic starch described in 1. (a) (meth)acrylamide 30 to 96 mol% (b
) α,β-unsaturated carboxylic acid and/or its salt 4 to 50 mol% (c) Cationic monomer It is preferable to polymerize 10 to 80 parts by weight of a monomer mixture consisting of 0 to 20 mol%. . In this case, the polymerization initiator is hydrogen peroxide,
Any redox initiator consisting of peroxides such as ammonium persulfate, potassium peroxide, ammonium hydroperoxide, or a combination of these peroxides and a reducing agent, as well as 2,2 azobis(aminopropane) hydrochloride. Water-soluble azo initiators and the like can be used.

When polymerizing the above monomer mixture, if the amount of cationic starch in the aqueous solution exceeds the above range, the paper strength enhancing effect will not be sufficient, and if it is below, the ruled line Cracking cannot be satisfactorily prevented. and,
In the monomer mixture, even if the amount of α, β-unsaturated carboxylic acid or its salt exceeds the range specified in 1.
The intended purpose of the present invention cannot be fully achieved.

0 The amphoteric grafted starch polymer of the present invention is usually produced in the form of an aqueous dispersion with a solid content concentration of about 10 to 20% by weight. 0.01-5% of the pulp dry weight, preferably 0.01% to 5% of the pulp dry weight.
By adding it to the raw pulp slurry in an amount corresponding to 1 to 3%, making paper and drying it in a conventional manner, it is possible to produce paper that has excellent general strengths and is almost free from creases.

Such excellent effects can be obtained due to the balance between the cationic groups of the cationic starch and the anionic groups of the α,β-unsaturated carboxylic acid. It is presumed that this is because the hydroxyl groups of starch or the amide groups of (meth)acrylamide form hydrogen bonds with the hydroxyl groups of pulp fibers, resulting in strong adhesive strength as a whole. Furthermore, the zwitterionic grafted starch polymer of the present invention imparts sufficient water retention to paper (
It is presumed that since the NJ can be applied, line cracking is prevented even in a low-humidity environment, and this fact can be easily understood from the reference examples described later.

Examples of preparing the amphoteric grafted starch polymer used in the present invention and examples of the present invention are shown below.

Preparation Example 1 200 g of a 20% concentration cationic tapioca starch (nitrogen content 0.41%, 10% concentration viscosity 75 centipoise, at 25 °C) aqueous solution, cooked at 90-100 °C;
A mixture of 89.9 g of 40% acrylamide, 5.06 g of 80% acrylic acid, and 162 g of water was adjusted to pH 5.5 using a 10% aqueous potassium hydroxide solution. Add 4% ammonium persulfate (APS) aqueous solution to this solution at a temperature of 50°C.
ml and 4ml of 2% sodium bisulfite (SBS) aqueous solution
1 was added, and the reaction was carried out at a temperature of 60 to 70°C for 3 hours.

Thereafter, 72 g of additional water was added to obtain the amphoteric grafted starch polymer shown in Table 1.

Preparation Example 2 20% cationic tapioca starch 240g (nitrogen content 0.40%, 10% concentration viscosity 50 centipoise, at 25°C) 2 40% acrylamide 63.8g80
%acrylic acid 8.1g water
145g2%APS
3.5m12%SB
3 3.5ml additional water
A zwitterionic grafted starch polymer was prepared in the same manner as in Preparation Example 1 using a 60 g formulation.

Preparation Example 3 20% cationic tapioca starch 320g (nitrogen content 0.42%, 10% concentration viscosity 35 centipoise, at 25°C) 40% acrylamide 27.9g80
%acrylic acid e, oeg water
203g2%APS
3m12%SB8
3ml additional water
A zwitterionic grafted starch polymer was prepared in the same manner as in Preparation Example 1 using 66 g of the formulation.

3 Preparation Example 4 20% cationic tapioca starch 120g (nitrogen content 0.38%, 10% concentration viscosity 150 centipoise, at 25°C) 40% acrylamide 125.8g8
0% acrylic acid 7.09g water
204 g2%A
PS 5.5m12%S
B 8 5.5ml additional water
A zwitterionic grafted starch polymer was prepared in the same manner as in Preparation Example 1 using 72 g of the formulation.

Preparation Example 5 240 g of 20% cationic tapioca starch (nitrogen content 0.4%, 10% concentration viscosity 50 centipoise,
(at 25°C) 40% acrylamide 64.1. g
80% acrylic acid 3.82g Dimethylaminopropylacrylamide 3.31g4 Water 1.46g
2% APS 5m1
A zwitterionic grafted starch polymer was prepared in the same manner as in Preparation Example 1 using a recipe of 2% SB3, 5 ml of additional water, and 76 g.

Preparation Example 6 20% cationic potato starch 240g (nitrogen content 0.4%, 10% concentration viscosity 50 centipoise, at 25°C) 40% acrylamide 63.8g80
%acrylic acid 8.1g water
145g2%AP
S 3.5m12%S
B 8 3.5ml additional water
An amphoteric grafted starch polymer was prepared in the same manner as in Preparation Example 1 using the formulation of eog.

5 Preparation Example 7 20% cationic corn starch 240g (nitrogen content 0.4%, 10% concentration viscosity 50 centipoise, at 25°C) 40% acrylamide 63.8g80
%acrylic acid 8.1g water
145g2%AP
S 3.5m12%S
B 8 3.5ml additional water
An amphoteric grafted starch polymer was prepared in the same manner as in Preparation Example 1 using the formulation of eog.

Examples 1 to 7 Coropar 5S-40 (synthetic sizing agent, concentration 40%, manufactured by Seiko Kagaku Kogyo ■) was added to a pulp slurry of N-U K P (c, S, P, 490 ml) at a rate of 0.3 based on the weight of the pulp. %
, 1.5% by weight of sulfuric acid based on the weight of the pulp was added, and then 0.5% of the amphoteric grafted starch polymer obtained in the previous preparation example was added and thoroughly mixed. Each of the prepared pulp slurries thus obtained was processed into 6 sheets with a basis weight of 200 by a TAPPI standard sheet machine.
It was made into paper equivalent to g/rd, pressed at 3.5 kg/rrf' for 5 minutes, and then dried at 105°C for 4 minutes.

The humidity of each of the handmade papers thus obtained was adjusted and subjected to a paper quality test. The test results are shown in Table 2.

Comparative Example 1 The same procedure as described above except that Star Gum Δ-15 (anionic polyacrylamide paper strength agent, concentration 15%, manufactured by Seiko Kagaku Kogyo ■) was used instead of the amphoteric grafted starch polymer used in the example. Hand-made paper was obtained using the same procedure as in the example. A paper quality test was also conducted on this handmade paper. The results are also listed in Table 2.

Comparative Example 2 Star gum A-15 was added at 0.35% by weight of pulp in place of the amphoteric grafted starch polymer used in the example.
Star Gum AD-X (cationic paper strength agent, concentration 10%)
A hand-made paper was obtained in the same manner as in the previous example, except that the same amount of <01-5% of the same amount of <01-5% of the same amount of <0.01-5% of the same amount was added. A paper quality test was also conducted on this handmade paper. The results are also listed in Table 2.

7 The paper quality test method is as follows.

Specific bursting strength: According to JIS P-8112.

Specific compressive strength: According to JIS P-8126.

Ruled line cracking test: A piece of measurement paper (basis weight 200g/ry1') was stored in a constant temperature and humidity chamber (manufactured by Yamato Scientific Co., Ltd.) at a specified temperature and humidity for 24 hours, then a ruled line was drawn, and the percentage of the broken part was determined by bending it. is expressed as a percentage.

Reference Example The paper pieces obtained in Example 1 and Comparative Example 1 were stored in a constant temperature and humidity chamber at a predetermined temperature and humidity for 24 hours, and then the grain weight and moisture content of the paper were measured. Table 2 shows the results.

(The following is a blank space) 8 [Effects of the Invention] According to the method of the present invention, by adding a specific amphoteric grafted starch polymer to pulp slurry and making paper in a conventional manner, compressive strength and bursting strength upon drying can be improved. It is possible to produce paper that has excellent properties and is substantially free from line cracks.

Claims (1)

[Scope of Claims] 1. A method for producing paper with improved crease cracking, which comprises adding an amphoteric grafted starch polymer to pulp slurry before papermaking. 2. Zwitterionic grafted starch polymer is cationic starch 2
In an aqueous solution containing 0 to 90 parts by weight, (a)(
meth)acrylamide 30-96 mol% (b) α,β-
A grafted starch polymer obtained by polymerizing 10 to 80 parts by weight of a monomer mixture consisting of 4 to 50 mol% of an unsaturated carboxylic acid and/or its salt (c) 0 to 20 mol% of a cationic monomer. 2. The method of claim 1.