JP2008222794A - Method for preparing aqueous solution of cationic thermosetting resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a cationic thermosetting resin with an industrial advantage, wherein the cationic thermosetting resin is excellent in wet paper strength performance and contains <0.10% DCP that represents environmentally harmful AOX in resins. <P>SOLUTION: Into an aqueous solution of a particular polyamide-polyamine, 0.9-1.1 mol epihalohydrin (C) per 1 mol of secondary amino group in the compound is dropped at 10-35°C over 0.5-1.5 hr to carry out a primary reaction, provided that the concentration of the reactant of the polyamide-polyamine and epihalohydrin (C) in the aqueous solution is 30-70 wt.%. After dropping is completed, the aqueous solution is kept at the same concentration and kept warm at 10-35°C for 6-10 hr and subsequently diluted to reach a particular concentration range. A secondary reaction is carried out at a particular temperature until the aqueous solution comprising 25 wt.% reaction product achieves a viscosity of 100-1,000 mPa s at 25°C, and the pH of the resulting aqueous solution of the reaction product is adjusted to 1.5-4 at 25°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing an aqueous cationic thermosetting resin solution useful as a wet paper strength improver for paper. More particularly, the present invention relates to a method for producing a polyamide polyamine-epihalohydrin-based cationic thermosetting resin aqueous solution having a low content of an adsorbing organic halogen compound (hereinafter referred to as AOX) and excellent wet paper strength performance. It is.

The usefulness of polyamidepolyamine-epihalohydrin resin as a chemical for improving the strength of paper, particularly wet strength, is described in, for example, JP-A-56-34729 and is known. However, in the polyamide polyamine-epihalohydrin resin aqueous solution, as a by-product derived from epihalohydrin used as a raw material, AOX typified by 1,3-dichloro-2-propanol (hereinafter referred to as DCP) which is a kind of dihalohydrin. It is included. AOX is a substance that has received much attention in recent environmental protection due to its harmfulness to human bodies and the like, and its reduction is particularly desired.

Regarding the method for producing an aqueous solution of polyamidepolyamine-epihalohydrin resin having a low AOX content, for example, in the reaction between polyamidepolyamine and epihalohydrin, (I) production method through two-stage reaction (Patent Document 1) (II) two-stage reaction A manufacturing method in which a halogen group of a low molecular weight organic halogen compound is substituted by adding a nucleophilic substance containing a sulfur atom in the middle of the process (Patent Document 2), (III) An unreacted substance is added by adding a basic substance in the middle of a two-stage reaction Manufacturing method for enhancing the reactivity of epihalohydrin (Patent Document 3), (IV) Manufacturing method for adding an alcohol compound in the middle of a two-stage reaction (Patent Document 4), (V) Compound having a carboxyl group in the middle of a two-stage reaction (Patent Document 5), (VI) After the two-step reaction, the amine compound is further added to remove the low molecular weight organic halogen compound. Production method for carrying out the rogenation (Patent Document 6), or (VII) a method of contacting with an ion exchange resin (Patent Document 7), (VIII) a method of contacting with a carbon-based adsorbent (Patent Document 8), (IX) porous A method of contacting with a synthetic resin (Patent Document 9) has been proposed. However, the method (I) requires a very long reaction time, and the reduction of AOX is not sufficient. In each of the methods (II) to (VI), the addition of the drug and the reaction time are limited. I need. In each of the methods (VII) to (IX), the contact time with the adsorbent and the removal of the adsorbent are required. In any of the methods (I) to (IX), complexity in operability is unavoidable, excellent wet paper strength performance, and environmentally unfavorable AOX in a resin such as dihalohydrin. It has been desired to develop a method for industrially advantageously producing a polyamide polyamine-epihalohydrin resin having a DCP content of less than 0.10%.

JP-A-2-170825 JP-A-6-220189 Japanese Patent Laid-Open No. 6-1842 JP 2001-048881 A JP 2003-231751 A JP-A-11-166034 Japanese Patent Laid-Open No. 10-152556 JP 2000-136245 A Japanese Patent Laid-Open No. 2004-51742

The present invention relates to a polyamide polyamine-epihalohydrin resin having an excellent wet paper strength performance and containing less than 0.10% of AOX, for example, DCP, which is a kind of dihalohydrin, in an environmentally undesirable resin. It aims at providing the method of manufacturing industrially advantageous.

As a result of intensive studies to solve the above problems, the present inventors have


I) (A) Aliphatic dicarboxylic acid compound and (B) polyalkylene polyamine at a molar ratio of 1: 1.0 to 1.2, the viscosity at 25 ° C. of a 50 wt% aqueous solution of the resulting polyamide polyamine is 400 Heat condensation to ˜1000 mPa · s to produce a polyamide polyamine,
II) Next, the concentration of the reaction product of (C) epihalohydrin, which is 0.9 to 1.1 mole times the secondary amino group in the polyamide polyamine, is 30 to 70% by weight of the polyamide polyamine and (C) epihalohydrin. In the aqueous solution of polyamide polyamine to be dropped at a temperature of 10 to 35 ° C. in the range of 0.5 to 1.5 hours, and after the completion of dropping, the primary reaction is performed at the same temperature for 6 to 10 hours,
III) Next, a product diluted with water so as to have a concentration of 5% or more lower than that of the primary reaction and expressed as a concentration of 20% by weight or more at a temperature of 25 to 70 ° C. The secondary reaction is carried out until the viscosity at 25 ° C. of the weight% aqueous solution reaches 100 to 1000 mPa · s, and
IV) By adjusting the aqueous solution of the obtained reaction product so that the pH at 25 ° C. is 1.5 to 4, the generated AOX can be reduced, and further the aqueous solution is used as a wet paper strength agent. As a result, the present inventors have found that it has excellent wet paper strength performance, and completed the present invention.

According to the production method of the present invention, the content of AOX in an environmentally unfavorable resin, for example, DCP, which is one of dihalohydrins, is less than 0.10% because of the production method of the present invention. A polyamide polyamine-epihalohydrin resin having a high molecular weight can be industrially advantageously produced.

The present invention will be specifically described below.
In the present invention, a polyamide polyamine is first produced by a condensation reaction of (A) an aliphatic dicarboxylic acid compound and (B) a polyalkylene polyamine. The (A) aliphatic dicarboxylic acid compound in the present invention is a generic term for an aliphatic compound having two carboxyl groups in its molecule and an amine-reactive derivative thereof. In addition to a free acid, its esters and Acid anhydrides and the like are also included. Representative examples of such aliphatic dicarboxylic acid compounds include free dicarboxylic acids such as malonic acid, succinic acid, glutamic acid, adipic acid, and sebacic acid, their lower alkyl esters, and their acid anhydrides. Can be mentioned. These aliphatic compounds may be used alone or in combination of two or more. Furthermore, you may use together with these aliphatic dicarboxylic acid type compounds other dicarboxylic acid type compounds, such as an aromatic type, in the range which does not inhibit the effect of this invention.

The (B) polyalkylene polyamine in the present invention is an aliphatic compound having two primary amino groups and at least one secondary amino group in the molecule, specifically, diethylenetriamine, triethylenetetramine. Tetraethylenepentamine and iminobispropylamine may be used alone or in combination of two or more. In addition, aliphatic diamines such as ethylenediamine and propylenediamine can be used in combination with the polyalkylenepolyamine as long as the effects of the present invention are not impaired.

In the polyamidation reaction of (A) an aliphatic dicarboxylic acid compound and (B) polyalkylene polyamine in the present invention, (B) is reacted in the range of 1.0 to 1.2 mol per 1 mol of (A). Let In this case, aminocarboxylic acids can be used in combination as long as the performance of the water-soluble resin obtained by the present invention is not impaired. Examples of aminocarboxylic acids include aminocarboxylic acids such as glycine, alanine, and aminocaproic acid and ester derivatives thereof, and lactams such as caprolactam.

The polyamidation reaction is carried out under heating, and the temperature at that time is usually 100 to 250 ° C, preferably 130 to 200 ° C. And reaction is continued until the viscosity in 25 degreeC when making the production | generation polyamide polyamine into a 50 weight% aqueous solution becomes 400-1000 mPa * s. If the viscosity at the end of the polyamidation reaction is lower than 400 mPa · s, the cationic thermosetting resin aqueous solution as the final product does not exhibit a sufficient wet paper strength improving effect, and if it exceeds 1000 mPa · s, the final product In many cases, the stability of the resin deteriorates and gelation occurs.

In the polyamidation reaction between (A) an aliphatic dicarboxylic acid compound and (B) a polyalkylene polyamine, sulfuric acid or sulfonic acids can be used as a catalyst. Examples of sulfonic acids include benzenesulfonic acid and paratoluenesulfonic acid. The acid catalyst is preferably used in the range of 0.005 to 0.1 mol, more preferably in the range of 0.01 to 0.05 mol, relative to 1 mol of the polyalkylene polyamine.

The polyamide polyamine thus obtained is then subjected to reaction with (C) epihalohydrin in aqueous solution. Examples of the (C) epihalohydrin used here include epichlorohydrin (ECD) and epibromohydrin. Industrially, epichlorohydrin is preferable.

The reaction between the polyamide polyamine and (C) epihalohydrin is performed in two stages, a primary reaction and a secondary reaction. The primary reaction is performed in an aqueous solution having a reactant concentration of 30 to 70% by weight, preferably 30 to 60% by weight. If the concentration of the reactant in the primary reaction is too low, the progress of the reaction is remarkably slow or no reaction occurs at all. On the other hand, if the concentration of the reactant in the primary reaction is higher than 70% by weight, the reaction progresses too quickly and the viscosity is remarkably increased. In some cases, the reaction is difficult to control. This primary reaction is carried out at a temperature in the range of 10 to 35 ° C., and the molar ratio of (C) epihalohydrin to secondary amino groups in the polyamide polyamine (hereinafter referred to as “epihalo ratio”) is 0.9 to 1. The range is 1, preferably 0.95 to 1.05. If the reaction temperature is too higher than 35 ° C. or the epihalo ratio is larger than 1.1, the content of AOX in the final resin is increased, and the object of the present invention is not sufficiently achieved. On the other hand, when the epihalo ratio is less than 0.9, the processing performance as a wet paper strength agent of the final product is deteriorated.

Under the above conditions, the time during which (C) epihalohydrin is dropped into the polyamide polyamine aqueous solution at a temperature of 10 to 35 ° C. is 0.5 to 1.5 hours, preferably 0.75 to 1.5 hours. It is. When the dropping time is longer than 1.5 hours, the content of AOX in the polyamidepolyamine-epihalohydrin resin as the final product increases.
On the other hand, since the reaction heat between polyamide polyamine and (C) epihalohydrin is large, if the dropping time is shorter than 0.5 hours, it is difficult to control the temperature in the system, which causes a problem in terms of safety and disaster prevention.

(C) As a primary reaction after dropping epihalohydrin, the temperature is kept in the range of 10 to 35 ° C. for 6 to 10 hours. At that time, if the heat retention temperature is lower than 10 ° C., the reaction of epihalohydrin in the system is slow, and epihalohydrin is reacted. Therefore, the content of AOX, which is the object of the present invention, can be sufficiently reduced without increasing the heat retention time. It will not be achieved. In addition, when the incubation time is shorter than 6 hours, a large amount of unreacted epihalohydrin remains during the primary reaction, and the reduction in the content of AOX cannot be sufficiently achieved. On the other hand, if the heat retention temperature is higher than 35 ° C. or the heat retention time exceeds 10 hours, the thickening during the secondary reaction is fast and the reaction cannot be controlled.

Moreover, the consumption of the charged (C) epihalohydrin can also be used as a measure for the end of the primary reaction. The consumption of the charged epihalohydrin can be determined as the difference between the charged epihalohydrin amount and the remaining unreacted epihalohydrin amount by measuring the amount of unreacted epihalohydrin remaining in the reaction system. As a standard of consumption of epihalohydrin charged at that time, it is 98% or more, and the primary reaction is completed at that stage. The amount of unreacted epihalohydrin and the amount of other AOX can be measured, for example, by gas chromatography.

In the production method of the present invention, the specific polyamide polyamine is converted to 0.9 to 1.1 mol times of the secondary amino group in the polyamide polyamine by reacting (C) epihalohydrin with (C) epihalohydrin. It is dripped in the range of 0.5-1.5 hours at the temperature of 10-35 degreeC in the aqueous solution of the polyamide polyamine used as a physical concentration of 30-70 weight%, and is made to react at the same temperature for 6-10 hours after completion | finish of dripping. Thus, although the specific structure is unknown, it is presumed that a polyamide polyamine-epihalohydrin reactant with reduced AOX can be obtained.

After completion of the primary reaction, water is added to the reaction system to dilute it so that it is lower by 5 points or more in terms of the weight% concentration of the reaction product than at the time of the primary reaction, but the concentration is 20% by weight or more. For example, when the primary reaction is performed at a reactant concentration of 30% by weight, the concentration is 20 to 25% by weight. For example, when the primary reaction is performed at a reactant concentration of 70% by weight, 20% is obtained. Diluted to a concentration of ~ 65 wt%. When the reactant concentration is lower than 20% by weight, in the subsequent secondary reaction,
The viscosity at 25 ° C. of a 25% by weight aqueous solution of the product does not reach 100 mPa · s. If the reactant concentration is not lower by 5 points or more in terms of the weight% concentration of the reactant than at the time of the primary reaction, the viscosity increases in the secondary reaction and the reaction cannot be controlled.

After diluting the reaction system in this way, the temperature is further maintained, and a crosslinking reaction between the polyamide polyamines to which epihalohydrin has been added is carried out (secondary reaction). The temperature in the secondary reaction is in the range of 25 to 70 ° C. This secondary reaction is continued until the viscosity at 25 ° C. when the resin content of the reaction product is 25% by weight is 100 to 400 mPa · s, preferably 200 to 275 mPa · s. When the viscosity of the 25% by weight aqueous solution at the end of the secondary reaction is lower than 100 mPa · s, the effect of enhancing the wet paper strength of the resin as the final product is not sufficient, and when it exceeds 400 mPa · s, the stability of the aqueous resin solution In addition, when added to the pulp slurry during the papermaking process, strong foaming is caused, which not only makes the papermaking work difficult, but also impairs the paper texture.

After completion of the secondary reaction, after diluting with water if necessary, in order to stop the reaction, for example, an acid such as hydrochloric acid, sulfuric acid, phosphoric acid, formic acid or acetic acid is added to adjust the pH to 1.5 to 4. It adjusts and obtains the cationic thermosetting resin aqueous solution which is a target object.

The aqueous cationic thermosetting resin solution of the present invention imparts a wet paper strength enhancing effect on paper equal to or higher than that of a polyamide polyamine-epihalohydrin resin produced by a conventionally known method, and is a low molecular organic halogen compound. Is extremely excellent in that it has an extremely low content and excellent stability. As used herein, AOX includes dihalohydrins (eg, DCP) and monohalohydrins (eg, 3-halo-1,2-propanediol) that are derived from epihalohydrins and formed by side reactions. For example, when epichlorohydrin, which is one of epihalohydrins, is used as a raw material, DCP and 3-chloro-1,2-propanediol may be generated by side reactions. In the reaction employed in the present invention, dihalohydrin is particularly likely to remain as an impurity. According to the present invention, even if such a dihalohydrin or even a monohalohydrin is produced, the content of these low molecular organic halogen compounds is low. Can be kept in value.

Further, according to the present invention, a cationic thermosetting resin aqueous solution having such excellent properties can be obtained without requiring a complicated operation such as addition of a drug. Furthermore, the method of the present invention is effective even when the concentration of the final product is low. For example, even when the concentration of the resin aqueous solution of the final product is about 10 to 20% by weight, it can be stored in a stable state. . When the resin concentration of the final product is low, it is preferable to adjust the pH to a relatively high value, for example, pH 2 to 4.

The aqueous resin solution obtained by the method of the invention is used not only as a wet paper strength improver for paper, but also as a filler yield improver added during the paper making process, and a drainage used to improve paper making speed. It can also be used as an improver or a precipitation flocculant for removing fine particles contained in sewage such as factory effluent.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these. The% and amount ratios in the examples are by weight unless otherwise stated. The viscosity is a value measured with a Brookfield viscometer.

(Production example of polyamide polyamine)
In a four-necked flask equipped with a thermometer, Liebig condenser and stirring rod, 300 g (2.91 mol) of diethylenetriamine, 21.5 g of water, 403.6 g (2.76 mol) of adipic acid and 8.8 g of 71% sulfuric acid (0.06 mol) was added, the temperature was raised to 145 ° C., and the mixture was refluxed for 1 hour, and then reacted at 140 to 160 ° C. for 12 hours while draining water. Thereafter, 588.7 g of water was gradually added to obtain an aqueous solution of polyamide polyamine. This polyamide polyamine aqueous solution had a solid content of 50.7% and a viscosity at 25 ° C. of 550 mPa · s.

(Production example of polyamidoamine-epichlorohydrin resin aqueous solution)
Into a four-necked flask equipped with a thermometer, a reflux tube and a stirring rod, water 266 was added so that the reactant concentration would be 45% in 700 g of the polyamidopolyamine aqueous solution obtained above (1.7 mol as a secondary amino group). 0.7 g was charged, and 155.9 g (1.7 mol (epihalo ratio: 1.0)) of epichlorohydrin was added dropwise at 30 ° C. over 1 hour, and the mixture was kept at the same temperature for 6 hours. At this point, analysis by gas chromatography revealed that the epichlorohydrin conversion was 98.4%. Thereafter, 898.1 g of water was added, the mixture was kept warm at 35 to 50 ° C. to increase the viscosity, and then cooled. Thereafter, 50.9 g of 71% sulfuric acid and 52.0 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 25%, a viscosity of 230 mPa · s (25 ° C.), and a pH of 3.0.

In a four-necked flask equipped with a thermometer, a reflux tube and a stirring rod, the reaction solution concentration is 45% in 730 g of the polyamidopolyamine aqueous solution obtained in Example 1 (1.8 mol as a secondary amino group). 284.3 g of water was charged, and 170.7 g of epichlorohydrin (1.9 mol (epihalo ratio: 1.05)) was added dropwise at 20 ° C. over 1 hour, and then kept at 20 to 35 ° C. for 6 hours. Thereafter, 851.7 g of water was added, and the mixture was kept warm at 35 to 50 ° C. to increase the viscosity, and then cooled. Thereafter, 50.4 g of 71% sulfuric acid and 87.3 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 26%, a viscosity of 180 mPa · s (25 ° C.), and a pH of 2.7.

(Comparative Example 1)
In a four-necked flask equipped with a thermometer, a reflux tube and a stirring rod, the reaction product concentration becomes 45% in 251.6 g (0.6 mol as a secondary amino group) of the polyamide polyamine aqueous solution obtained in Example 1. In this way, 109.7 g of water was charged, and 66.9 g (0.7 mol (epihalo ratio: 1.2)) of epichlorohydrin was added dropwise at 30 ° C. over 3 hours, and then kept at the same temperature for 4 hours. Thereafter, 122.4 g of water was added and the mixture was kept warm at 35 to 50 ° C. to increase the viscosity, and then 169.1 g of water was added and cooled. Thereafter, 19.4 g of 71% sulfuric acid and 32.6 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 27%, a viscosity of 120 mPa · s (25 ° C.), and a pH of 2.3.

(Comparative Example 2)
In a four-necked flask equipped with a thermometer, a reflux tube and a stir bar, the reactant concentration is 45% in 700 g of the polyamidopolyamine aqueous solution obtained in Example 1 (1.7 mol as a secondary amino group). 266.7 g of water was charged, and 155.9 g (1.7 mol (epihalo ratio: 1.0)) of epichlorohydrin was added dropwise at 30 ° C. over 2 hours, and then kept at the same temperature for 6 hours. At this time, analysis by gas chromatography revealed that the conversion of epichlorohydrin was 98.1%. Thereafter, 898.1 g of water was added, the mixture was kept warm at 35 to 50 ° C. to increase the viscosity, and then cooled. Thereafter, 51.9 g of 71% sulfuric acid and 53.8 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 26%, a viscosity of 210 mPa · s (25 ° C.), and a pH of 3.0.

(Comparative Example 3)
In a four-necked flask equipped with a thermometer, a reflux tube and a stir bar, the reactant concentration is 45% in 700 g of the polyamidopolyamine aqueous solution obtained in Example 1 (1.7 mol as a secondary amino group). 266.7 g of water was charged, and 155.9 g (1.7 mol (epihalo ratio: 1.0)) of epichlorohydrin was added dropwise at 30 ° C. over 3 hours, and then kept at the same temperature for 6 hours. At this time, analysis by gas chromatography revealed that the conversion of epichlorohydrin was 98.1%. Thereafter, 898.1 g of water was added, the mixture was kept warm at 35 to 50 ° C. to increase the viscosity, and then cooled. Thereafter, 52.8 g of 71% sulfuric acid and 55.6 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 25%, a viscosity of 230 mPa · s (25 ° C.), and a pH of 3.0.

(Comparative Example 4)
In a four-necked flask equipped with a thermometer, a reflux tube and a stirring rod, the reaction solution concentration is 45% in 670 g of the polyamidopolyamine aqueous solution obtained in Example 1 (1.6 mol as secondary amino group). 260.9 g of water was charged, and 156.7 g (1.7 mol (epihalo ratio: 1.05)) of epichlorohydrin was added dropwise from 20 ° C. over 1 hour, and then kept at 20 to 35 ° C. for 4 hours. Thereafter, 516.3 g of a reaction mass was collected, 377.3 g of water was added, and the mixture was kept at 35 to 50 ° C. to increase the viscosity, and then cooled. Thereafter, 21.3 g of 71% sulfuric acid and 36.9 g of water were added to obtain a polyamide polyamine-epichlorohydrin resin aqueous solution having a solid content concentration of 26%, a viscosity of 170 mPa · s (25 ° C.), and a pH of 2.7.

(Comparative Example 5)
In a four-necked flask equipped with a thermometer, a reflux tube and a stir bar, the reaction product concentration is 45% in 100 g of the polyamidopolyamine aqueous solution obtained in Example 1 (0.24 mol as secondary amino group). 39.2 g of water was charged, and 22.3 g of epichlorohydrin (0.24 mol (epihalo ratio 1.0)) was added dropwise at 40 ° C. over 1 hour. Then, it gelled when it was kept at the same temperature for 2 hours.

(Comparative Example 6)
In a four-necked flask equipped with a thermometer, a reflux tube and a stir bar, the reaction product concentration is 45% in 100 g of the polyamidopolyamine aqueous solution obtained in Example 1 (0.24 mol as secondary amino group). 39.2 g of water was charged, and 22.3 g (0.24 mol (epihalo ratio 1.0)) of epichlorohydrin was added dropwise at 30 ° C. over 1 hour. Then, it gelled when it was kept at the same temperature for 20 hours.

The polyamide polyamine-epichlorohydrin resin aqueous solutions obtained in Examples 1 and 2 and Comparative Examples 1 to 4 were evaluated as follows. The results are shown in Table 1.

(DCP content)
Quantified by gas chromatography. % In Table 1 is the content in an aqueous solution.

(Storage stability)
The obtained aqueous solution was judged from the properties after standing at 50 ° C. for 2 weeks.
○: Little change in viscosity. X: Gelation or a significant decrease in viscosity.

(Wet paper strength)
Using the aqueous solutions obtained in Example 1, Example 2, and Comparative Examples 1 to 4, the following papermaking tests were performed. The wet tensile strength of the obtained paper was measured according to ISO 1924 / 1-1992, and the results are shown in Table 1 as the wet tear length.

(Paper making conditions)
Pulp used: N-BKP / L-BKP = 1/1
Beating degree: 400cc
Resin addition amount: 0.6% (resin solid content versus pulp dry weight)
Heat treatment condition: 110 ° C., 4 minutes, papermaking average rice basis weight: 60 g / m ²

Claims (4)

I) (A) Aliphatic dicarboxylic acid compound and (B) polyalkylene polyamine at a molar ratio of 1: 1.0 to 1.2, the viscosity at 25 ° C. of a 50 wt% aqueous solution of the resulting polyamide polyamine is 400 Heat condensation to ˜1000 mPa · s to produce a polyamide polyamine,
II) Next, the concentration of the reaction product of (C) epihalohydrin, which is 0.9 to 1.1 mole times the secondary amino group in the polyamide polyamine, is 30 to 70% by weight of the polyamide polyamine and (C) epihalohydrin. In the aqueous solution of polyamide polyamine to be dropped at a temperature of 10 to 35 ° C. in the range of 0.5 to 1.5 hours, and after the completion of dropping, the primary reaction is performed at the same temperature for 6 to 10 hours,
III) Next, a product diluted with water so as to have a concentration of 5% or more lower than that of the primary reaction and expressed as a concentration of 20% by weight or more at a temperature of 25 to 70 ° C. The secondary reaction is carried out until the viscosity at 25 ° C. of the weight% aqueous solution reaches 100 to 1000 mPa · s, and
IV) A method for producing a cationic thermosetting resin aqueous solution, wherein the aqueous solution of the obtained reaction product is adjusted to have a pH of 1.5 to 4 at 25 ° C. I) (A) Aliphatic dicarboxylic acid compound and (B) polyalkylene polyamine at a molar ratio of 1: 1.0 to 1.2, the viscosity at 25 ° C. of a 50 wt% aqueous solution of the resulting polyamide polyamine is 400 Heat condensation to ˜1000 mPa · s to produce a polyamide polyamine,
II) Next, the concentration of the reaction product of (C) epihalohydrin, which is 0.9 to 1.1 mole times the secondary amino group in the polyamide polyamine, is 30 to 70% by weight of the polyamide polyamine and (C) epihalohydrin. In the aqueous solution of polyamide polyamine to be dropped at a temperature of 10 to 35 ° C. in the range of 0.5 to 1.5 hours, and after the completion of dropping, the primary reaction is performed at the same temperature for 6 to 10 hours,
III) Next, a product diluted with water so as to have a concentration of 5% or more lower than that of the primary reaction and expressed as a concentration of 20% by weight or more at a temperature of 25 to 70 ° C. The secondary reaction is carried out until the viscosity at 25 ° C. of the weight% aqueous solution reaches 100 to 1000 mPa · s, and
IV) A cationic thermosetting resin obtained by adjusting the aqueous solution of the obtained reaction product so that the pH at 25 ° C. is 1.5 to 4. A wet paper strength enhancer comprising the cationic thermosetting resin according to claim 2 as an effective component. A paper comprising the wet paper strength enhancer according to claim 3.