JPS62240306A - Production of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a highly water-absorptive resin economically in high safety under extremely mild conditions, by polymerization, using an initiator consisting of sulfur-contg. reducing agent and oxidizing agent, of acrylic acid followed by treatment with additional oxidizing agent. CONSTITUTION:The objective resin can be obtained by polymerization, using an initiator consisting of (A) a sulfur-contg. reducing agent (e.g. sodium sulfite, sodium dithionite) and (B) an oxidizing agent (e.g. peroxodisodium sulfate, per-oxodiammonium sulfate) so as to be 0.01-0.1pt.wt. per 100pts.wt. of the monomer charged, of said reducing and oxidizing agents, respectively of acrulic acid with a neutralization degree by monovalent cation 30-100 (pref. 70-95)% followed by treatment with 0.001-0.5pt.wt. based on 100pts.wt of the monomer charged of an additional oxidizing agent. USE:Paper diapers, sanitary products, carriers for chromatography, etc.

Description

[Detailed description of the invention] Industrial application fields> The present invention relates to a method for producing a water absorbent resin.

More specifically, the present invention relates to a method for producing a water-absorbing resin having excellent manufacturing safety and high water-absorbing capacity.

<Problems to be solved by conventional techniques and inventions> In recent years, water-absorbing resins with high water-absorbing and water-retaining abilities have been used for disposable diapers, sanitary products, culture media for microorganisms and plants, carriers for liquid chromatography, etc. There is. As a type of such water-absorbing resin, a crosslinked polyacrylic acid metal salt type is widely used.

This acrylic acid metal salt-based water absorbent resin is
・After adding a polymerization initiator to an aqueous solution of an alkali metal salt such as potassium acrylate or potassium acrylate and polymerizing it,
Manufactured by removing moisture. In this case, as a polymerization initiator, for example, a periiQ acid salt such as sodium persulfate or sodium persulfate, a redox catalyst consisting of a combination of an oxidizing agent and a reducing agent (for example, the persulfur F[[salt and monovalent copper ions, hydrogen peroxide, divalent iron ions, etc.), but when these persulfates or redox catalysts are used as initiators, the polymerization reaction is extremely rapid, and for example, the Φ polymerization initiation temperature is low even at room temperature. As polymerization progresses, heat is generated rapidly. In particular, when industrial production of sea urchin is carried out in large quantities and at high concentrations, it is difficult to control unless special consideration is taken, and sometimes runaway reactions occur, which is extremely dangerous. It is. From this point of view, in order to prevent runaway reactions, the acrylic B salt is polymerized by lowering the monomer concentration and using a temperature control system, but lowering the monomer concentration prevents moisture evaporation. There are problems in that it requires a large amount of heat and is unsuitable for AI, and the equipment incorporating the temperature control system is also expensive.

Purpose This invention was made in view of the above problems, and by using a special polymerization initiator, the polymerization of acrylic acid metal salt proceeds under extremely mild conditions, resulting in a highly safe method. It is also an object of the present invention to provide a method for producing a water-absorbing I4 fat having a high water-absorbing capacity.

Means for Solving the Problems> The method for producing a water-absorbing resin of the present invention, which has been devised to achieve the above object, has a degree of neutralization by monovalent cations of 30%.
The above 100% acrylic acid is polymerized using a polymerization initiator consisting of a sulfur-containing reducing agent and an oxidizing agent, and then treated with an oxidizing agent.3! Jl! It is characterized by:

In this paper, the degree of neutralization refers to the ratio of acrylate to the total amount of acrylic acid and acrylic i1m in the seven-layer mixture, and can be defined by the following formula.

Ac IJ Le MJu (-E/Iz) X100 Neutralization degree (
%) = acrylic acid + acrylate (mol) In the above configuration, the neutralizing agent used to neutralize the acrylic acid is appropriately selected depending on the purpose of use of the final product, the water-absorbing resin. For example, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, alkali gold FA carbonates or hydrogen carbonates such as sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, water Any fiI group that can act as a -valent cation can be selected, such as ammonium oxide, triethylamine, ethanolamines, pyridine, organic amines such as picoline, etc., but it is economical, safe and 1!
Taking into account the water absorption performance of the water absorbent resin, hydroxylated soot and cum are suitable.

Further, the degree of neutralization of acrylic acid is 30% or more, preferably 50% or more, more preferably 70% or more and 95%.
The following are preferable in terms of the water absorption performance of the obtained water absorbent resin. Alternatively, the aqueous acrylate solution may be prepared by mixing a monovalent cation salt of acrylic acid and acrylic acid in an appropriate ratio. Considering the feature of this invention that the concentration of the heavy-base solution generates less heat, the higher the monomer concentration in the solution, the more remarkable the technical, equipment, and performance effects of this invention are. When neutralizing the solution, sodium acrylate will precipitate if the water concentration falls below 45% to 50%, so if you want to increase the water content even higher, it is necessary to homogenize the solution by mixing, stirring, etc. There is.

In addition, in order to modify the water absorption ability, gel strength, etc. of the water absorbent resin obtained by this invention, acrylamide, methylenebisacrylamide, N-vinyl biOlidone, etc. are added to the acrylic acid to form a copolymer. Good too.

In the production method of the present invention, a sulfur-containing reducing agent and an oxidizing agent are used together as a polymerization initiator. Examples of the sulfur-containing reducing agent used include sulfite Fi salts such as sodium sulfite and potassium sulfite, hydrogen sulfites such as sodium bisulfite and potassium hydrogen nitrite, sodium thiosulfate, sodium thiosulfate, etc. Examples include thiosulfates, dithionates such as sodium dithionite, and mixtures thereof, with sulfites and dithionites being particularly preferred. Although these sulfur-containing reducing agents can be used in powder form, they are usually used as an aqueous solution.

In addition, as the oxidizing agent, a conventional oxidizing agent such as Beloxoni VA1%! Examples include peroxonisulfates such as sodium, peroxoniRM potassium, and ammonium peroxonisulfate, which are used alone or as a mixture. Although it can be used in powder form, it is usually used as an aqueous solution.

The amounts of reducing agent and oxidizing agent used in the polymerization are:
Although it varies depending on the type of reducing agent and oxidizing agent to be combined, the polymerization temperature, the concentration of the monomer aqueous solution, the properties required of the water-absorbing resin, etc., it is usually 0.001 to 0.001 to 100% by weight, respectively, relative to the weight of the FF1100 heavy hanging section for seven months preparation. It is appropriately selected from a range of 0.5 parts by weight. If the amount of the reducing agent, J and oxidizing agent added is less than 0.001 and 1, the reaction will be slow and the polymerization time will be long.

In addition, the amount of the reducing agent and the oxidizing agent added was 0.5 each.
If the amount exceeds 1 part by weight, the polymerization solution will have a high viscosity, and stirring and mixing will become difficult unless the monomer concentration is lowered. The preferable addition amounts of the reducing agent and the oxidizing agent are 0.01 to 0.11 parts, respectively.

In this invention, the oxidizing agent used in the post-polymerization treatment includes the same oxidizing agents as exemplified above. This oxidizing agent is usually used for monomer preparation ff1100.
It is added in an amount of about 0.001 to 0.5 parts by weight. Further, this oxidizing agent may be added together with the oxidizing agent in the above-mentioned combination of a reducing agent and an oxidizing agent as a polymerization initiator, or may be added to the reaction system after the car chassis is completed.

The water-absorbing resin produced by the production method of the present invention has a water-absorbing capacity, gel strength after water absorption, etc. depending on the amount of the reducing agent and oxidizing agent used as a polymerization initiator and the oxidizing agent used for post-treatment. can be changed as appropriate. Generally, for example, when the total amount of oxidizing agent added is constant and the amount of reducing agent used is changed, as the amount of reducing agent used increases, the water absorption capacity increases. becomes larger. In addition, if the total amount of oxidizing agent used is increased while the amount of reducing agent used is constant, the amount of water absorption decreases,
The gel state tends to become hard after absorbing water, and becomes soft when reduced. However, when each is used in a proportionately increased or decreased amount within the above-mentioned addition range, no significant difference is observed in the performance of the resulting polymers.

In addition, in the production method of the present invention, aluminum compounds such as aluminum salts such as aluminum nitrate, aluminum acetate, aluminum chloride, and 114M aluminum, aluminate a salts such as aluminum alcoholade, and sodium aluminate can be added. Combined frame m
You can also adjust the degree. In particular, water-absorbent resins produced under conditions with low initiator concentration tend to contain soluble portions or become soft after water absorption, so adding the above aluminum compound in such cases will reduce the amount of water absorbed. and improve gel strength.

Note that among the above aluminum compounds, aluminum salts can be used by adding them to either the monomer aqueous solution or the initiator aqueous solution, but in the case of aluminate, when added to the initiator aqueous solution, the alkali decomposes the initiator. Therefore, it is best to add it to the monomer aqueous solution. These aluminum compounds are usually prepared by monomer charging ff1
5 parts by weight or less, preferably 0.1 parts by weight per 100 parts by weight
~0.51! A hanging part is added.

Next, an example of the manufacturing method of the present invention will be explained in detail.

First, acrylic acid is neutralized with the aqueous neutralizing agent solution to a desired degree of neutralization and a concentration suitable for polymerization. The aforementioned reducing agent aqueous solution and oxidizing agent aqueous solution are added to this solution to initiate polymerization. As the polymerization progresses, the viscosity of the solution increases, and when the polymerization progresses to a certain extent and the viscosity becomes high, the above-mentioned oxidizing agent aqueous solution is further added to the reaction system, heated as necessary, and after treatment, the reaction is started. The water absorbent resin of the present invention is obtained by dehydrating and drying the liquid.

In the above process, the reducing agent and the oxidizing agent are added to the reaction system at the same time, but in this case, a more favorable result can be obtained by increasing the amount of the oxidizing agent used. Also,
The polymerization reaction can also be started by adding a reducing agent to a solution in which an oxidizing agent is added to an aqueous monomer solution in advance.

Further, in the above step, polymerization using a polymerization initiator consisting of a reducing agent and an oxidizing agent normally proceeds sufficiently at room temperature, but heating or heating may be performed as necessary. When heated or heated, the polymerization reaction proceeds quickly and the viscosity rapidly increases, so the timing of addition of the oxidizing agent for post-treatment is important and greatly affects the water absorption ability of the resulting resin.

As a general tendency, if the timing of adding the oxidizing agent is delayed,
The high viscosity prevents homogeneous dispersion of the added oxidizing agent, resulting in a non-homogeneous polymer, which may result in soluble portions. Therefore, when warming or heating,
It is preferable to use a system in which an oxidizing agent for post-treatment is added in advance, or to use a Φ-retarding agent such as allyl alcohol or propylene glycol in combination.

Shun's 51 with added oxidizing agent for post-processing! The temperature may be at or above the temperature at which the oxidizing agent used is decomposed or activated, or may be around room temperature when a reducing agent and an oxidizing agent are used simultaneously. After treatment with an oxidizing agent, water in the reaction system must be removed and dried, and even after treatment with an oxidizing agent at around 100°C, no changes in performance or other aspects were observed. 51 at the boiling point of the coexisting water! ! It is convenient to do so immediately.

Effects> The present invention has the above configuration, and unlike polymerization using a conventional redox initiator, the polymerization of acrylate using a polymerization initiator consisting of a sulfur-containing reducing agent and an oxidizing agent has extremely low exothermicity. The polymerization proceeds rapidly under mild conditions, and after the polymerization has progressed to some extent, it is treated with an oxidizing agent and further polymerization or crosslinking reactions are performed, making it easy to control the temperature during polymerization and preventing runaway reactions.

In addition, since the polymerization proceeds under mild conditions, there are few side reactions, etc., and a water-absorbing resin with a large water-absorbing capacity can be produced.

<Examples> The present invention will be described in more detail below with reference to Examples.

Example 1 110 g of acrylic was neutralized by adding 20 g of a 25% aqueous sodium hydroxide solution, and then a 1% aqueous solution of potassium belloxoniilQ acid 13 was added at room temperature.
When 3J of 1% potassium pyrosulfite aqueous solution is added,
When the solution temperature reaches 35°C to 40°C, it immediately polymerizes, becoming a rubbery polymer with almost no tackiness after about an hour, and after several hours it shows slow water absorption and some soluble parts are present. However, after addition of potassium pyrosulfite, 1
Those that were dehydrated and dried by heating to 60° C. or higher within an hour showed water absorption performance 800 to 1000 times higher than that of tap water, and there was no soluble portion. If the mixture is poured into a heating container at the initial stage when a viscosity due to polymerization after addition of potassium pyrosulfite is produced, it becomes rubbery after a few minutes, and no special light heat or bumping is observed during polymerization.

After dehydrating and drying this rubbery material, it can be immersed in tap water at 120%
It showed water absorption performance of 0 times or more and 12018 or more in 0.9% saline.

According to the method for producing a water-absorbing resin of the present invention, polymerization proceeds under mild conditions by using a special polymerization initiator, and temperature control becomes easy. Polymerization conditions can be set within a safe and wide range. In addition, it is technically and equipment-wise easy and simple, and has excellent safety and economical efficiency. The obtained water absorbent resin 6 has excellent water absorption performance, and its properties and performance can be changed by appropriately changing the sulfur-containing reducing agent and oxidizing agent used, and the desired properties can be achieved. The product can be changed and its scope of application can be expanded. Furthermore, a wide range of methods including well-known methods can be used for its production. For example, if a monomer solution is continuously and uniformly poured onto a rotating belt, a film or plate-like product can be obtained; It can be made into a powder by spraying it into a rotating heating plate, heated inert gas, or air. In addition, various methods are used, such as heating after coating and impregnating shaped objects and nonwoven fabrics, kneading and heating in rolls, screws, or mixers, and inverse emulsification methods that utilize the boiling point of the solvent to dehydrate and form powders. It has the advantage that the manufacturing method can be used.

Claims (1)

[Claims] 1. Degree of neutralization by monovalent cations is 30% or more Contains less than 100% acrylic acid and sulfur Polymerization initiator consisting of a system reducing agent and an oxidizing agent Polymerize using A method for producing a water-absorbing resin characterized by Law. 2. The sulfur-containing reducing agent is sulfite or sulfite. Hydrogen salt, thiosulfate or dithionite Said claim 1, which is a salt. A method for producing a water-absorbing resin.