JPS5941646B2 - Method for producing cationic starch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cationic starch.

Cationic starch has a wide range of uses; it is used as a sizing agent for warp threads in the textile industry, as a precipitant in wastewater treatment, and in the paper industry for the purpose of increasing paper strength, improving yield, and making neutral paper.

Cationic starch is made by reacting starch with a cationizing agent.

Various amine compounds are known as cationizing agents. There are two known methods for carrying out this reaction: a wet method in which the reaction is carried out in the presence of a large amount of water, and a dry method in which the reaction is carried out in the presence of a small amount of water. Among these methods, the wet method has the advantage that it is easy to obtain homogeneous cationic starch, but on the other hand, it requires a large amount of energy for dehydration or drying after the cationization reaction, and is therefore not advantageous. In order to improve this drawback, it has been proposed to further add alcohol or ketone to water as a solvent.

It is described in Japanese Patent Publication No. 36-18246. However, this method did not go beyond the wet method. This is because the total weight of alcohol or ketone and water is one and a half times as much as starch.
The result of mixing them is said to be a starch suspension, the alcohol or ketone is said to prevent the starch from swelling, and the reaction product is said to be filtered to remove impurities. Furthermore, at the time when Japanese Patent Publication No. 36-18246 was published, the dry method was not yet known. Therefore, the description in the above publication cannot be considered in connection with the dry method. Later, a dry method was proposed, but in the dry method, the reaction is carried out with an extremely low water content, for example, 25% by weight or less, so it does not require much energy for the dehydration or drying process after the reaction. It has advantages.

However, since the dry method is a heterogeneous reaction, the starch is locally denatured by the alkaline agent added as a reaction catalyst, and has the disadvantage that it is not possible to obtain uniform, high-quality cationic starch. Therefore, it was necessary to improve this point. The dry method is described, for example, in U.S. Pat. No. 412,756.
No. 3 (which corresponds to Japanese Unexamined Patent Publication No. 11983/1983).

This publication describes the general formula X-CH2-CH-(CH2)n-
A method is described in which a halohydrin represented by A is used as a cationizing agent and is reacted with starch in a dry state.

It is stated that according to this method, cationic starch can be easily obtained within a wide pH range from acidic to alkaline. The method also states that when adding the cationizing agent and reaction catalyst, they may be dissolved or dispersed in a liquid vehicle such as water, but even if water is used as the vehicle, the amount The amount must be less than 25% of the total amount. Therefore, even if such a vehicle is used, the cationization reaction is a heterogeneous reaction. Therefore, the addition of the reaction catalyst caused local deterioration of the starch, producing brown cationic starch particles, making it impossible to obtain cationic starch of uniform quality. The inventor discovered that when attempting to obtain cationic starch by a dry method, the presence of a small amount of alcohol such as methanol prevents local deterioration of the starch and produces uniform, high-quality cationic starch. It was discovered that starch can be obtained.

This invention was made based on such confirmation. This invention provides a method for producing cationic starch by reacting starch with a cationizing agent in the presence of an alkali and a small amount of water. Add the group monohydric alcohol and calculate the amount of alcohol and water relative to starch by weight of 4-85% each. and 5-35 weight? The present invention relates to a method for producing cationic starch, characterized in that the total amount of water and alcohol is 9 to 90% by weight, and the starch is reacted with a cationizing agent in this state.

The method of this invention is characterized in that an aliphatic monohydric alcohol having 1 to 10 carbon atoms is used. The aliphatic group in the alcohol may be linear or branched. The reason for choosing an aliphatic monohydric alcohol is that monohydric alcohol is effective in preventing local swelling of starch caused by alkali and water. This is also because monohydric alcohols have relatively low boiling points and are easily removed by evaporation together with water. Also, among aliphatic alcohols, we chose those with carbon numbers of 1 to 10 because carbon numbers of 11 to 10 were chosen.
If the temperature exceeds the limit, the effect of preventing local swelling of starch will be reduced, and the boiling point will become high, making it difficult to remove by evaporation. Alcohol is added at the same time as or before adding alkali.

Specifically, using caustic soda as the alkali,
When adding this to starch as a solid, alcohol is added to the starch in advance, and then caustic soda is added. Furthermore, when adding caustic soda as an aqueous solution, alcohol may be added to the starch before the addition, or alcohol may be added to the aqueous caustic soda solution. Alternatively, caustic soda may be dissolved in alcohol and added. The amount of alcohol added is limited.

That is, alcohol should be in the range of 4-85% by weight relative to starch. Also, the amount of water present should be in the range of 5-35% by weight relative to starch. Moreover, the total amount of water and alcohol is 9-90% of starch.
weight? must be within the range. Since the method of this invention is premised on being a dry method, the amount of water present during the reaction must naturally be small.

If the amount of water is less than 5% by weight based on the starch, the reaction between the starch and the cationizing agent will not proceed smoothly. On the other hand, the amount of water is 35 weight? If the temperature exceeds the limit, the effect of preventing swelling caused by alcohol is reduced, the characteristics of the dry method are lost, and a large amount of energy is consumed to remove water from the produced cationic starch and dry it. For these reasons, in the method of this invention, the amount of water is 5 to 35% by weight. within the range of It goes without saying that this amount of water also includes the amount of water added together with the cationizing agent or alkali:
stomach. This amount also includes the amount of water already present in the starch. In the method of the present invention, the amount of alcohol is limited for the following reasons.

Alcohol has the effect of preventing starch from swelling locally due to water and alkali. Therefore, the required amount of alcohol increases approximately in proportion to the amount of water present in the reaction system. However, if the amount of alcohol is increased to 85% by weight or more based on the starch, removing the alcohol after the reaction becomes rather troublesome, but there is no practical advantage. Conversely, if the amount of alcohol is less than 4% by weight, the effect of preventing local swelling of starch due to water and alkali will be lost. Therefore, the amount of alcohol is
4-85 weight for starch? That is to say. Further, in the method of the present invention, it is necessary that the total amount of water and alcohol be 9 to 90% by weight based on the starch, and this is for the following reason. That is, if the total amount is less than 9% by weight, the respective effects of water and alcohol will be reduced, making it impossible to obtain a homogeneous product. Conversely, the total amount above is 90% by weight.
If the amount is more than 1, the characteristics of the dry process will be lost, and a large amount of energy will be required to remove water and alcohol from the produced cationic starch and to dry it. Also, 90
This is because all reactions can be carried out at less than % by weight. In the method of this invention, all conventional materials other than water and alcohol are used as they are.

That is, as the alkali, in addition to alkali metal hydroxides such as caustic soda and caustic potash, compounds that can be hydrolyzed to produce alkali hydroxides, such as soda carbonate, can also be used. In order for the alkali metal hydroxide to act as a catalyst for the cationization reaction, 0.0
15 to 0.2 mol is required. That is 0.0
This is because if it is less than 15 moles, the reaction efficiency will be reduced, and conversely, if it is more than 0.2 moles, the swelling suppressing effect due to alcohol will be reduced. The starch may be a treated product, generally referred to as processed starch, or may be an untreated starch.

Typical starches that can be used are potato, tapioca,
Corn, fractionated amylose, amicropectin, etc. In addition, etherified or esterified starches such as carboxymethyl starch, hydroxyethyl starch, and phosphate starch can also be used. Various known cationizing agents can also be used.

The cationizing agent can be said to be a reagent that reacts as starch to give an ether bond represented by the general formula.

However, in the above formula, R1 represents a straight chain or branched alkylene group or hydroxyalkylene group having 1 to 6 carbon atoms, and R2 and R3 are hydrogen or a straight chain or branched alkyl group having 1 to 4 carbon atoms. and R4 represents a straight chain or branched alkyl group having 1 to 4 carbon atoms. Also,
R3 and R4 may also be taken together to form a ring structure. Suitable examples of the ring structure include a pyrrole group,
These include a pyrrolidine group, a pyridine group, a piperidine group, and a morpholine group. Cationizing agents can be classified into primary amines, secondary amines, tertiary amines, and quaternary ammonium salts.

Among these, preferred are tertiary amines and quaternary ammonium salts. Examples of tertiary amines include 2-
Diethylaminoethyl chloride, 3-dibutylamino-1,2-epoxypropane, β-chloroethylmorpholine, chloromethylpyrrolidine, and the like can be used. In addition, examples of quaternary ammonium salts include, for example, 3-
Chloro-2-hydroxypropyltrimethylammonium chloride, 2,3-epoxypropyltrimethylammonium chloride, 4-chlorobutentriethylammonium chloride, 3-chloro-2-hydroxypropyltriethylammonium chloride, 3-chloro-propyl-(N-ethyl ) piperidine chloride, etc. can be used. However, chlor or chloride in the above compounds can be replaced with other halogens. The cationizing agent is obtained in the form of a powder or a 40-50% aqueous solution.

In the case of an aqueous solution, it may be used as it is or may be diluted with alcohol. Even in the case of powder, it can be used as it is, dissolved in alcohol, or diluted.
The amount of the cationizing agent added is determined depending on the desired degree of substitution. In the method of this invention, the reaction efficiency is approximately constant depending on the type of starch used as the raw material, but the range is approximately 7.
0-90% by weight In the method of this invention, the mixture obtained by addition is heated as necessary in order to allow the cationization reaction to proceed smoothly.

Heating is in the range of 40-100°C, preferably 50-80°C
range. When heated in this manner, the cationization reaction is usually completed within 1 to 24 hours, and under favorable conditions 3 to 10 hours, during which time cationic starch is produced. The production mechanism of cationic starch is as follows.

For example, when 3-chloro-2-hydroxypropyltrimethylammonium chloride is used as the cationizing agent, the reaction with starch can be expressed by the following chemical formula. The reaction thus results in the production of equimolar hydrochloric acid as the cationizing agent.

Therefore, the alkali metal hydroxide is consumed not only for catalytic action but also for neutralizing the generated hydrochloric acid. The amount required for neutralization is equimolar to the cationic agent. The cationic starch obtained by the method of this invention can be used as it is, but it can also be purified by neutralizing the alkali remaining therein and further removing alcohol and water. In some cases, this is further decomposed to lower the viscosity and used as a low-viscosity cationic starch. In the method of this invention, when starch is reacted with a cationizing agent in the presence of an alkali, a small amount of alcohol is present in addition to a large amount of water. Since it acts as a medium, local deterioration of starch, especially the formation of brownish cationic starch, is eliminated, and high-quality cationic starch can be obtained.

Moreover, alcohol can be easily removed together with water by vacuum suction or the like. Therefore, by adding alcohol, the cationization reaction can be carried out uniformly. In short, the method of this invention has the advantage that homogeneous cationic starch can be easily produced. In connection with the inventive process described above, an advantageous process has been found for further decomposing the cationic starch obtained therein to a low viscosity.

Conventionally, in order to reduce the viscosity of cationic starch, the cationic starch was made into a slurry and treated with an oxidizing agent, particularly sodium hypochlorite, or an inorganic acid such as sulfuric acid.

However, it is not advantageous to use a wet method in the form of a slurry. Therefore, it is possible to use a dry method, but if you try to make a product with a low viscosity by a dry method using sodium hypochlorite, the reaction equipment will be severely corroded and the cationic starch will be locally denatured. It is not possible to obtain a low viscosity product. On the other hand, if an inorganic acid such as sulfuric acid or hydrochloric acid is used, a low viscosity can be obtained by a dry method. However, when an inorganic acid is used, it is difficult to control the amount added, temperature, and time, and there are also disadvantages in that it increases the amount of salts as by-products in the product. Therefore, there was room for further improvement in making cationic starch low in viscosity. However, when hydrogen peroxide is added to the mixture containing alcohol and alkali obtained by the method of the present invention and heated, the mixture can easily have a desired low viscosity depending on the amount of hydrogen peroxide added. It has been found that cationic starch can be obtained.

The invention based on this knowledge will be referred to as the second invention herein, but the second invention further decomposes the cationic starch obtained by adding alcohol by the method of the first invention with hydrogen peroxide to reduce the This is a method for producing viscous cationic starch. In other words, the second invention is a method for producing cationic starch by reacting starch with a cationizing agent in the presence of an alkali and a small amount of water. By adding 1 to 10 aliphatic alcohols, the amount of alcohol and water relative to starch is 4-85% by weight, respectively. and 5-35% by weight, and the total amount of water and alcohol is 9-90% by weight, and the reaction is carried out with a cationizing agent, and then hydrogen peroxide is added and reacted to convert the cationic starch into a low-viscosity The present invention relates to a method for producing cationic starch.

The lower viscosity of cationic starch is due to α-
This is thought to occur due to cleavage and decomposition of 1,4-glucoside bonds.

Therefore, it is thought that the greater the amount of decomposition accelerator added to the starch weight, the more the viscosity will be lowered. When this decomposition is carried out using hydrogen peroxide, it is advantageous because the decomposition is less dependent on temperature and time, and the degree of viscosity reduction is solely determined by the amount of hydrogen peroxide added. Depending on the amount of hydrogen peroxide added, cationic starch
Although it has been stated that the viscosity decreases almost quantitatively, this cannot be true between cationic starches with different types of cationic groups or between cationic starches with different degrees of substitution by cationic groups.

For example, between cationic starches with different types of cationic groups, even if the same amount of hydrogen peroxide is added, the degree of viscosity reduction will differ. Furthermore, even if the cationic groups are the same, if the degree of substitution by the cationic groups is low, a larger amount of hydrogen peroxide is required to bring about the same level of viscosity reduction. However, between cationic starches having the same type of cationic group and the same degree of substitution by the cationic group, the viscosity decreases almost quantitatively depending on the amount of hydrogen peroxide added. This is extremely advantageous in reducing the viscosity.
In other words, by measuring the relationship between the amount of hydrogen peroxide added and the resulting low viscosity through preliminary experiments, it is possible to know the amount of hydrogen peroxide necessary to obtain the desired low viscosity based on this. By adding this amount, a desired low viscosity product can be obtained. The amount of hydrogen peroxide added is 0.0 per mole of starch.
Conveniently it is within the range of 1 to 0.2 mol.
Low viscosity using hydrogen peroxide has other advantages as well.

After lowering the viscosity with hydrogen peroxide,
The point is that no consideration is required regarding hydrogen peroxide residue. That is, there is an advantage that there is no need to remove the reaction product of hydrogen peroxide at all.
In the method of the first invention described above, what is produced is cationic starch, and the cationic starch contains an alkali catalyst and small amounts of water and alcohol.

Since this alkali promotes the activation of hydrogen peroxide, and water and alcohol help disperse hydrogen peroxide, in the end, the product obtained in the first invention allows hydrogen peroxide to smoothly lower the viscosity of cationic starch. Moreover, it is suitable for progressing evenly.
Moreover, the viscosity reduction progresses quantitatively depending on the amount of hydrogen peroxide added. In this respect, the method of the second invention, which utilizes the results of the first invention, shows significant advantages. In addition, in the method of the second invention, heating may be performed in order to promote decomposition by hydrogen peroxide. Heating is preferably in the range of 40 to 100°C. The reaction time with hydrogen peroxide does not need to be strictly controlled. The viscosity reduction is usually completed within 30 minutes to 24 hours. This reaction is preferably carried out in a jacketed pressure vessel equipped with a stirrer. After the viscosity reduction reaction is completed, water and alcohol still remain in addition to the alkali used as a catalyst for the cation reaction.

Therefore, first, in order to remove the alkali, acid is used to neutralize it. Next, while stirring the whole mixture, the pressure is reduced and suction is applied.
Then, the remaining water and alcohol are volatilized, and dry, low-viscosity cationic starch is obtained. The low-viscosity cationic starch thus obtained is a uniform powder with no coloration, and is of good quality with good stability in an aqueous solution and excellent properties. Next, the method of the present invention will be explained in more detail with reference to Examples and Comparative Examples.

However, the term "parts" hereinafter simply means parts by weight.
In addition, the water content of the cationic starch obtained in the example, P
The degree of H1 substitution, gelatinization start temperature, viscosity, etc. are shown, and the measurement methods thereof are as follows unless otherwise specified. Moisture content: Place in a dryer at 105°C, and determine the weight loss when it reaches a constant weight as water content.

The PH value of a 5% by weight suspension is measured using a PH meter.

Degree of substitution Determined by measuring the amount of nitrogen.

That is, thoroughly wash with 70V/V% methyl alcohol,
After drying, the gel tar is decomposed and steam distilled.

Gelatinization start temperature Determined by amylograph method.

That is, 8W/V using a Brabender type 1 rotational viscometer.
Determined from the amylogram of the % solution.

Viscosity 5 weight? Liquid or 10 weight? After gelatinizing the liquid at 96℃,
Example 1: A 51-volume stainless steel pressure-resistant container with a stirrer and a jacket capable of circulating the heating medium. In a container, add 1000 parts of corn starch (moisture content: 13.5%)
) and sealed.

Next, the air in the reaction vessel was removed using a vacuum pump, and then 110 parts of a 15% by weight solution of sodium hydroxide in methyl alcohol was injected through a valve while stirring. Further, while stirring was continued, 80 parts of a 50% by weight aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added thereto, and the mixture was heated through a jacket to bring the internal temperature to 65 DEG C., and reacted for 4 hours. After that, the pressure inside the container was reduced using a vacuum pump, and then 90°C was used for neutralization.
13.3 parts by weight of acetic acid was sprayed and stirred for 15 minutes for neutralization. Thereafter, the pressure inside the container was reduced again using a vacuum pump, the internal temperature was raised to 80° C., water and alcohol were removed, and the container was dried. What was obtained was a uniform powdery cationic starch. This cationic starch contains 12.5% water by weight, has a pH of 6.5, a degree of substitution of 0.029, a gelatinization initiation temperature of 64°C, and a viscosity of 6200 cps at 5% concentration at 65°C. It was in good condition.

Example 2 1000 parts of the same corn starch as in Example 1 was placed in the same container as in Example 1, and the air in the container was removed.

Thereafter, 150 parts of 2-ethylhexanol was injected, and while stirring, 48 parts of solid sodium hydroxide was added, followed by 300 parts of a 50% by weight aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride. , heating from the jacket to bring the internal temperature to 65℃,
The cationization reaction was carried out for 5 hours. After reaction, 90% by weight
26.7 parts of acetic acid was injected, and drying was continued in the same manner as in Example 1.

The resulting product is a homogeneous powdered cationic starch;
All products passed through a 100 mesh sieve. This cationic starch weighs 13.0? of water, pH is 6.5, and degree of substitution is 0.

114, gelatinization initiation temperature 5 was 34°C, and the viscosity at 5% concentration at 65°C was 2200 cps, which was good.

Comparative Example 1 This comparative example differs from Example 1 only in that 2-ethylhexanol is not used.
It was treated in exactly the same manner as 2.

The resulting cationic starch weighs 13.0? of water, the pH was 6.5, the degree of substitution was 0.085, the gelatinization initiation temperature was 38°C, and the viscosity at 5% concentration at 65°C was 1520 cps.

The cationic starch obtained in this comparative example has a lower degree of substitution and a higher gelatinization initiation temperature than that obtained in Example 2. This shows that the reaction is not progressing. Also, when this cationic starch 1009 was passed through a 100 mesh sieve, 21.29% remained without passing through the sieve. Therefore, we separated those that passed through the sieve and those that did not and examined their properties, and found that those that passed had a pH of 60, a degree of substitution of 0,098, and uniform particles. Those that did not pass had a pH of 11.
9. The degree of substitution was 0.020, the particles were swollen and granular, and the product was found to be non-uniform. Example 3 In the same container as in Example 1, potato starch (moisture content 14.
5%), 1,000 parts were added, the mixture was sealed, and the air was evacuated.

Then, while stirring the inside of the container, add 50% of sodium hydroxide.
0 weight? An alcoholic sodium hydroxide aqueous solution prepared by diluting 33 parts of the aqueous solution with 50 parts of isopropyl alcohol was injected, and then 80 parts of a 50% by weight aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was injected and stirred. He continued.

At that time, the mixture was heated with a jacket to bring the internal temperature to 60°C, and the cationization reaction was carried out for 5 hours. After the reaction, 13.8 parts of 90% by weight acetic acid was injected for neutralization, and then dried in the same manner as in Example 1 to obtain cationic starch.

The obtained cationic starch was a uniform powder with no coloration.

This cationic starch contains 14.0% water and has a pH of 6.
．． 5, the degree of substitution was 0,034, and the gelatinization start temperature was 53.
At 5% concentration, the viscosity at 65°C is 3600.
It was cps. Example 4 In the same container as Example 1,
1000 parts of hydroxypropylated corn starch (moisture content 12.5%) with a degree of substitution of 0.05 was added, sealed, and evacuated.

While stirring inside the container, add 50% by weight of sodium hydroxide.
An alcoholic sodium hydroxide aqueous solution prepared by diluting 45 parts of the aqueous solution with 80 parts of isobutyl alcohol was injected. Subsequently, a 50% by weight 70% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride
of the mixture and continued stirring. At this time, the container was heated with a jacket to maintain the internal temperature of the container at 65° C., and a cationic reaction was carried out for 4 hours and 30 minutes. After the reaction was completed, 20 parts of 90% by weight acetic acid was injected for neutralization, and then the mixture was dried in the same manner as in Example 1 to obtain cationic starch.

The obtained cationic starch was a uniform powder without coloring.

This cationic starch contains 13.5% water and 6.5% water content.
The degree of substitution is 0.039, the gelatinization start temperature is 45°C, and the viscosity at 5% and 65°C is 5400 cps.
It was hot. Example 5 In the same container as in Example 1, 1000 parts of corn starch (moisture content: 13.570) was sealed and evacuated.

While stirring inside the container, add 50% by weight of sodium hydroxide.
72 parts of the aqueous solution was injected with an alcoholic sodium hydroxide aqueous solution diluted with 72 parts of methyl alcohol.

Subsequently, a solution of 50 parts of 2-diethylaminoethyl chloride hydrochloride dissolved in 50 parts of methyl alcohol was injected, and stirring was continued. At this time, the inner temperature of the container was maintained at 60° C. by heating through a jacket, and a cationic reaction was carried out for 5 hours. 90 weight after the reaction? 26.7% of acetic acid was injected to effect neutralization, and then the internal temperature was brought to 8'C, water and alcohol in the container were removed by suction using a vacuum pump, and cationic starch was obtained by drying.

The obtained cationic starch was a uniform powder without coloring.

This cationic starch contains 12.0% water and 6.5
, the substituent is 0.032, the gelatinization initiation temperature is 66°C, and the viscosity at 5% and 65°C is 6700 cp.
It was s. Example 6 In this example, a cationization reaction was carried out as described in Example 3, followed by a viscosity reduction reaction with hydrogen peroxide.

After carrying out the cationization reaction as in Example 3, the pressure inside the container was reduced using a vacuum pump and 35% by weight hydrogen peroxide was sprayed before neutralization with acetic acid.

After that, the temperature was maintained at 65°C, but the amount of hydrogen peroxide added and the reaction time were changed, and the following 4 batches, 6A, 6B, 6
Experiments C and 6D were conducted. The reaction conditions for each are shown in Table 1 below. After the viscosity-lowering reaction was completed, 13.3 parts of 90% by weight acetic acid was sprayed to effect neutralization and the viscosity-lowering reaction was completed.

Thereafter, the internal temperature was raised to 80° C., water and alcohol were removed by suction using a vacuum pump, and the product was dried. The reaction product was a uniform powder without coloring. The viscosity of this powder was measured at 30 rpm at a concentration of 10% and a temperature of 65°C.
It was ps. Example 7 In this example, a cationization reaction was carried out using corn starch as a raw material.

In each case of Examples 1, 2, 4 and 5, the viscosity-lowering reaction was subsequently carried out with hydrogen peroxide without neutralization with acetic acid. Hydrogen peroxide with a concentration of 35% was used, 15 parts of hydrogen peroxide was added, a viscosity reduction reaction was carried out at the same temperature as the canonization reaction for 2 hours, and each batch was converted to 7A, 7B, 7C and 7D. And so.

Claims (1)

[Claims] 1. A method for producing cationic starch by reacting starch with a cationizing agent in the presence of an alkali and a small amount of water,
At the same time as or before adding the alkali to the starch, add an aliphatic monohydric alcohol having 1 to 10 carbon atoms so that the amounts of alcohol and water relative to the starch are 4-85% by weight and 5-35% by weight, respectively. , and a method for producing cationic starch, characterized in that the total amount of water and alcohol is 9-90% by weight, and starch is reacted with a cationizing agent under this condition. 2. A method for producing cationic starch by reacting starch with a cationizing agent in the presence of an alkali and a small amount of water,
At the same time as or before adding the alkali to the starch, add an aliphatic alcohol having 1 to 10 carbon atoms so that the amount of alcohol and water in the starch is 4-85% by weight and 5-35% by weight, respectively, A method for producing cationic starch, characterized in that the total amount of water and alcohol is 9 to 90% by weight, the reaction is carried out with a cationizing agent, and then hydrogen peroxide is added and the reaction is carried out.