JPS621403B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is an economically advantageous manufacturing method in which an aqueous acrylamide polymer solution is reacted with an alkali hypohalite and a caustic alkali to perform the so-called Hofmann reaction, and then the polymer layer is separated and directly dried to form a powder. It is related to. Many prior art techniques have been disclosed regarding the Hoffman reaction of acrylamide polymers. Schiller
[USP 2729560 (1956)] set the molar ratio of amide group to halogen or alkali hypohalite or caustic alkali to 1:0.8:1.6 to 1:2:4, and then neutralized with acid to precipitate a polymer. After dehydration with an organic solvent such as methanol or acetone, it is dried and powdered, and it has been shown that this powdered polymer is soluble in hot water and dilute acids. Sugiura et al.
72 , 1926 (1969)] reacted an aqueous polyacrylamide solution with an alkaline bromine solution, and obtained the best results when the molar ratio of amide group:bromine:sodium hydroxide was 1:1:6.5, and precipitated acetone. It is used as an agent. Also, Senju etc. [Paper Paper Technology Association Magazine]
30 , 392 (1976), JP-A-51-122188] shows the advantage of carrying out the Hofmann reaction at low temperatures. In addition, many other technologies have been disclosed, such as Yoshii et al. (Japanese Patent Publication No. 46-29441), Suzuki et al. [Journal of the Japan Society of Wood Science 23 , 204, (1977)], Ariyoshi et al. Although it is known to exhibit excellent performance as an internal additive during paper making such as paper strength enhancers, aqueous properties improvers, filler retention agents, etc., there are actually polyacrylamide-based Hoffmann reactants on the market. are only one or two cases. The present inventor has discovered that as a cationic polymer electrolyte,
As a result of various investigations into why the extremely useful polyacrylamide-based Hofmann reaction product has been difficult to commercialize, it has been found that it has various deficiencies. In other words, the Hofmann reaction of polyacrylamide systems must be carried out in an aqueous solution state and at a relatively low polymer concentration, which increases transportation costs when commercialized, and as disclosed in the prior art, carbamoyl groups: When the Hofmann reaction is carried out at a molar ratio of alkali hypohalite and caustic alkali of 1:1:2, a considerable decrease in viscosity is inevitable even in low-temperature reactions, and a sufficient effect is obtained when a high molecular weight is required. I can't. In order to avoid a decrease in viscosity, the ratio of carbamoyl group: alkali hypohalite: caustic alkali can be obtained by reducing the charging ratio of alkali hypohalite to 1:0.5:1, but in this case, the ratio of alkali hypohalite to caustic alkali is 1:0.5:1. If the aqueous solution remains alkaline, the remaining carbamoyl groups will undergo hydrolysis, resulting in significant deterioration of the effect. Even when this is neutralized with acid and stored at pH 7.5 to 8.0, a decrease in cationic active groups is observed as measured by colloid titration.
If the pH is further lowered, it becomes cloudy and the polymer separates over time, making it unusable as a polymer electrolyte. As mentioned above, it has been found that it is extremely difficult to commercialize polyacrylamide-based Hoffmann reactant aqueous solutions due to the disadvantages of decreased viscosity, polymer precipitation, and decreased amino groups.
As a result of intensive research in order to supply polyacrylamide-based Hoffmann reactants in a more economical manner without quality deterioration, the present inventors found that alkali hypohalite or A Hofmann reaction is carried out using a substance capable of forming this and a smaller amount of caustic alkali than the theoretical amount, and after the reaction, neutralization is carried out with hydrochloric acid, which is a monobasic acid, to bring the pH of the polymer aqueous solution to 5 or less,
As time passes, the polymer is allowed to settle, and the supernatant liquid is removed by a method such as decantation, and the water in the polymer layer is further synergized, resulting in a water content of 80% by weight (wet base) or less (hereinafter referred to as water content). (all expressed on a wet basis) Preferably, after concentrating to 70% by weight or less, drying directly with a drum dryer etc. evaporates the water in a short time and powders it, which dissolves in cold water and becomes a powder. The present invention was achieved based on the finding that a Hofmann reaction product of an acrylamide polymer of stable quality without loss of amino groups can be obtained by storing it in a vacuum. Although there are examples of prior art that have gone as far as powdering, they all use water-absorbing organic solvents such as methanol and acetone, so if they are to be industrialized, not only the initial cost but also the running cost will be high. It seems that industrialization has not been carried out because it has become too much and lacks competitiveness as a product. According to the technology of the present invention, the use of organic solvents is not required at all and the production method is energy-saving, so dimethylaminoethyl methacrylate-based polymer electrolytes and polyacrylamide aminomethyl, which are currently commercialized as cationic polymer electrolytes, are used. It can be said that the product is fully competitive in terms of price with chemical products. In carrying out the present invention, it is necessary to explain it in more detail. Polymers that can be used in the present invention include acrylamide,
It is a copolymer of methacrylamide or a copolymer thereof, or a monomer copolymerizable with these, and contains at least 50 mol% of acrylamide or methacrylamide. Monomers that can be copolymerized with these include acrylonitrile, (meth)acrylic acid, (meth)acrylic acid esters, styrene, vinyl acetate, vinylpyridine, vinylpyrrolidone, (meth)acrylamide N-substituted products, etc. . The Hofmann reaction of polyacrylamide using sodium hypochlorite and caustic soda is expressed as a reaction equation. The molar ratio of carbamoyl group: alkali hypohalite: caustic alkali is 1:1:2, and in fact, in the prior art, it is also 1:1:2 or 1:1:2.
As mentioned above, the alkali hypohalite is equimolar to the carbamoyl group, and the caustic alkali is generally used in an amount twice or more than twice the mole of the alkali hypohalite. As a result of intensive research on this Hofmann reaction, the present inventor found that the alkali hypohalite is 0.5 to 1 or less, preferably 0.6 to 0.8, per 1 carbamoyl group, and the caustic alkali is 1.4 to 1 per 1 carbamoyl group. Only when the Hofmann reaction was carried out in the range of 2, no significant decrease in viscosity was observed, and the precipitation of the polymer after neutralization with acid took a relatively short time.Moreover, by leaving the separated polymer layer at a low temperature, Furthermore, it was found that a polymer that can be easily concentrated to synergate water can be obtained. As for the reaction temperature, the method proposed by Senju et al. of carrying out the reaction at a low temperature is a good method to avoid side reactions, but this Hofmann reaction generates too much reaction heat and cannot be fully controlled, making it difficult to industrialize. is not realistic. Rather, by keeping the reaction initiation temperature as low as possible, allowing the reaction to occur under strong stirring, and even if the system temperature reaches 40°C or higher, it can be neutralized within a short time to shorten the reaction time. Methods that avoid reactions are more realistic and easier to industrialize. It is not necessary to be involved in low-temperature reactions because the reaction product obtained at high temperature for a short time has a lower amination rate by a few percent compared to the reactant at low temperature for a long time, but there is no big difference in performance. There isn't. The phenomenon in which the acid-neutralized product of the Hoffmann reaction product of an acrylamide polymer precipitates from an aqueous solution is due to the formation of a polymer complex of carboxyl groups and amino groups generated as a result of hydrolysis of carbamoyl groups with caustic alkali during the Hoffmann reaction. Although this can be explained as the precipitation of the polymer, the salting out effect due to the salt by-produced in the Hofmann reaction is also considered to be a major contributor to the precipitation of this polymer. More interestingly, the phenomenon of salt dissolution can also be observed depending on the type of salt and the concentration of the salt. For example, the precipitated polymer is completely dissolved in a saturated aqueous solution of ammonium chloride, ammonium sulfate, or the like. The polymer is also affected by the type of acid used for neutralization. Polymers neutralized using dibasic or higher polyhydric acids such as sulfuric acid, oxalic acid, and phosphoric acid are insoluble in water after drying, but are soluble in aqueous solutions such as hydrochloric acid, common salt, and ammonium chloride. be. Furthermore, even if a salt consisting of divalent or higher anion groups, such as sodium sulfate, is added to the aqueous polymer solution after neutralization with a monobasic acid such as hydrochloric acid, the polymer becomes insoluble if the added amount of the salt exceeds a certain amount. Based on these facts, when carrying out the present invention, monobasic acids are the most preferable acids to use, and hydrochloric acid is the best in terms of cost, but the polymer after drying becomes water-insoluble. It is also possible to use sulfuric acid etc. in combination to the extent that it is not necessary. Furthermore, when the pH of the aqueous polymer solution during neutralization is neutral or alkaline, gelation occurs due to intermolecular crosslinking during drying, and a water-soluble polymer cannot be obtained. If the pH of the aqueous polymer solution is 5 or less, it is possible to obtain a powdered polymer that does not undergo gelation during drying or deterioration during storage, but it is not possible to reduce the pH to 2 or less. The pH of the polymer aqueous solution should be set to 5 because it is economically disadvantageous and also undesirable from the standpoint of equipment corrosion.
It is a good idea to keep it between ~3. When the pH of the Hoffmann reaction product aqueous solution of an acrylamide polymer is made acidic, the reduced viscosity at a concentration of 0.1% by weight (hereinafter all concentrations are expressed as weight%) increases from 6 to 6.
If a polymer with a molecular weight of 7 or higher is used, the polymer will separate during neutralization, but if the polymerization degree is lower than this, it will become slightly cloudy during neutralization, but it can be stored at low temperatures. If left for 2 to 3 hours, the polymer will settle and the upper layer will become a nearly clear water layer. When this aqueous layer is poured into methanol, it becomes cloudy, indicating that a very small amount of polymer remains in the upper layer without settling. When this layer-separated polymer layer is taken out, the water content is around 80% by weight, and although it is possible to dry it with a drum dryer, etc., this polymer can further release water by simply leaving it at a low temperature. By applying shearing force or syneresis, water can be synercised in a shorter time and it is possible to easily concentrate the water content to about 70%, so it is better to concentrate using this method as much as possible to make drying work easier. This method is preferable because it requires less water to be removed and is more energy-saving. Further, this concentration can be performed more effectively by adding a small amount of common salt. This polymer with a water content of around 70% is gel-like at low temperatures and has no fluidity, but it becomes fluid when heated, so when it is granulated and subjected to methods such as fluidized bed drying or band drying, the particles adhere to each other. It is difficult to dry them together. However, if you take advantage of the characteristic that it becomes fluid when heated and dry it in a drum dryer or film state, it can be dried in a relatively short time if the thickness is 3 mm or less, and especially if it is 1 mm or less, it will dry in a few minutes. Time is enough,
Furthermore, it has become possible to produce a polymer powder with good solubility even when using a drying temperature of 140 to 150°C. Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. [Example 1] 710 g of acrylamide polymer aqueous solution with a reduced viscosity of 3.8 at 0.1% (71 g as acrylamide)
Take it in a beaker and cool it to 4℃, separately.
435 g (0.7 mol) of a 12% aqueous solution of NaOCl and 83.4 g (1 mol) of a 48% aqueous solution of caustic soda were mixed and cooled.
The acrylamide polymer aqueous solution taken in a beaker and kept at 5° C. was vigorously stirred while being cooled from the outside, and a mixed solution of sodium hypochlorite and caustic soda was added thereto. As stirring continued, after an induction period of 1 to 2 minutes, the temperature rapidly rose due to the heat of reaction, and external cooling was not enough, and the system temperature reached 42°C 15 minutes after the start of the reaction. After that, the temperature gradually decreased and reached 20°C after 30 minutes. 35 for this thing
After adding 3 g of % sodium bisulfite and stirring, hydrochloric acid was added to adjust the pH of the system to 4.8. This aqueous polymer solution was slightly cloudy but homogeneous.
This aqueous polymer solution was stored in a refrigerator at 4° C. overnight to cause layer separation into a cloudy polymer layer and a translucent aqueous layer containing a small amount of a polymer with a molecular weight similar to that of an oligomer. The water layer was removed by decantation, a portion of the polymer layer was taken out, and the water content was measured and found to be 80.2%. If the remaining polymer is cooled externally to prevent the temperature from rising and is slowly stirred, water will be synergized and the water content will increase.
It was possible to concentrate to a concentration of 68.8%. This polymer was dried to a thickness of about 0.3 mm in a drum dryer at an internal temperature of 140°C, and the dried product was pulverized to obtain a polyacrylamide Hoffmann reaction product in powder form. This powder polymer was dissolved in water and colloid titration was performed, and the amount of cations was 5.23 m ^e q/1 g of powder polymer.
(m ^eq is milliequivalent) The amount of anion was 0.46 ^m eq/1 g of powdered polymer. In addition, after storing this powder polymer in a constant temperature bath at 55℃ for 21 days, it was dissolved in water and measured by colloid titration. The amount of cations was 5.22 m ^e q/1 powder polymer.
g, the amount of anions was 0.44 ^m eq/g of powdered polymer, and almost no deterioration was observed during storage. [Example 2] Table 1 shows the results of a series of tests conducted using the same polymer as used in Example 1 and varying the loading ratio of sodium hypochlorite and caustic soda to polyacrylamide. Ta. The reaction method was carried out in the same manner as in Example 1, and the pH of the system was adjusted to 4±1 using hydrochloric acid for neutralization.

[Example 3]

80g of acrylamide, 20g of acrylonitrile,
Pour 900g of deionized water into a beaker, introduce nitrogen and bring the temperature of the system to 30°C, and add 0.08 ammonium persulfate.
When 0.08 g of sodium hydrogen sulfite was added, polymerization started, and the polymerization was completed after 8 hours. According to the infrared absorption spectrum, this polymer
There was a nitrile absorption at 2240 cm ^-1 , indicating that it was an acrylamide-acrylonitrile copolymer. The viscosity of this polymer was measured using a Bruckfield viscometer and was found to be 10,800 centipoise (measurement temperature: 25°C). Take 500 g of this polymer in a beaker and cool it to 0°C. Separately, 250 g of NaOCl 12% aqueous solution and 48%
Mix and cool 55 g of caustic soda aqueous solution to -10°C. The aqueous polymer solution taken in a beaker was vigorously stirred while being cooled from the outside, and a mixed solution of sodium hypochlorite and caustic soda was added. As stirring continued, after an induction period of 2 to 3 minutes, the temperature rapidly increased due to the heat of reaction, and 20 minutes after the start of the reaction, the temperature of the system reached 35°C, after which the temperature gradually decreased until 45°C. After a few minutes, the temperature dropped to 15°C. After adding and mixing 2 g of sodium bisulfite, the mixture was neutralized with hydrochloric acid to bring the pH of the system to 4.5. When this polymer was placed in a refrigerator at 4°C, it phase-separated into a polymer layer and an aqueous layer after 2 hours. When the polymer layer was taken out and the moisture content of a portion thereof was measured, it was found to be 79.8%. When 20 g of common salt was added and mixed to 200 g of this polymer with a water content of 79.8%, water was further synercised and the water content of the polymer was concentrated to 65.2%. This polymer was applied to a thickness of approximately 1 mm on a polyester film (trade name Diafoil) and dried in a ventilation dryer at an internal temperature of 90°C for 25 minutes to obtain a dried polymer in the form of a film. . This polymer was pulverized to obtain a powdered polymer. Dissolve this powdered polymer in water,
As a result of colloid titration, the amount of cations was 4.72 m ^e
q/1g of powder polymer, the amount of anions is 0.41m ^e q/
The amount of powdered polymer was 1 g.

Claims (1)

[Claims] 1. In an aqueous polymer solution containing at least 50 mol% of acrylamide and methacrylamide, a molar ratio of 1 to 1 carbamoyl group to alkali hypohalite or a substance capable of forming this is 0.5 or more.
1.0 or less, and a caustic alkali is reacted with 1.4 or more and 2 or less of alkali hypohalite to perform the so-called Hofmann reaction, and then an acid is added to the system.
Reduce the pH to 5 or less, separate the polymer layer and water layer, and reduce the water content in the polymer layer to 80% by weight (wet base).
1. A method for producing a powder of a Hofmann reaction product of an acrylamide-based polymer, which is characterized in that the powder is made into a powder by directly drying it to remove moisture.