JPH0645652B2 - Continuous manufacturing method of modified water absorbent resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous production method of a modified water absorbent resin.

[Problems to be solved by conventional techniques and inventions]

Water-absorbent resins are used for sanitary items, diapers, disposable rags and other sanitary items, as well as agricultural and horticultural items such as water retention agents, as well as coagulating sludge, preventing dew condensation on building materials, and dehydrating oils. There is.

As this type of water-absorbent resin, carboxymethyl cellulose crosslinked product, polyethylene oxide partially crosslinked product, starch-hydrolyzate of acrylonitrile graft copolymer,
Partially crosslinked polyacrylates, vinyl alcohol-acrylic acid salt copolymers and the like are known, but in either case, the water absorption capacity is low, or even if the water absorption capacity is high, the gel strength after water absorption is high. It has weaknesses such as weakness and a sticky gel after absorbing water.

As a method of increasing the gel strength of the water absorbent resin after absorbing water,
Although there is a method of increasing the crosslink density of the water-absorbent resin, this method is not preferable because the water-absorbing ability which is the original performance of the water-absorbent resin is reduced.

As another method for increasing the gel strength of the water-absorbent resin after absorbing water, water is added to the water-absorbent resin in the presence of a hydrophilic organic solvent such as a lower monohydric alcohol to substantially add water to the water-absorbent resin. There is a method of crosslinking in a state of being uniformly absorbed and then drying. In this method, it is preferable to crosslink in the state of absorbing a large amount of water from the viewpoint of the water absorption capacity of the water-absorbent resin, but when the method is adopted, the resin in a water-swelling state even when the water absorption amount is small It is difficult to say that it is suitable for industrial use because the particles tend to agglomerate with each other to form lumps and the workability becomes poor. Therefore, the method generally has problems such as high manufacturing cost and low productivity.

[Means for Solving the Problems]

In view of the circumstances as described above, the present inventors maintain a water-absorbing ability and a water-absorbing rate of the water-absorbent resin, have a large gel strength after absorbing water, and have a modified water-absorbent resin that does not give a sticky feeling to the gel. As a result of intensive studies for the purpose of efficiently, easily and inexpensively and continuously producing, a water-absorbent resin powder having a carboxylate was dispersed in the air and a modifier ( By absorbing and cross-linking a solution containing a (cross-linking agent), it is possible to achieve the above-mentioned objects without using any solid powder such as hydrophilic organic solvent and silica, which were essential components in the prior art. The present invention has been completed and the present invention has been completed.

That is, the present invention is continuously supplied, a water-absorbent resin powder having a carboxylate dispersed in the air, and a solution containing a modifier, the diameter of which is 500μm or less fine droplets Mix
The present invention relates to a continuous process for producing a modified water-absorbent resin, wherein the water-absorbent resin powder is allowed to absorb the solution and heat-treated.

〔Example〕

The water-absorbent resin modified by the method of the present invention is a water-absorbent resin having a carboxylate and is not particularly limited as long as it is such a resin. The carboxylate is a concept including a carboxyl group and a salt of a carboxyl group.

Specific examples of the water-absorbent resin having a carboxylate include, for example, crosslinked products of (meth) acrylic acid polymers (meaning acrylic acid polymers or methacrylic acid polymers, and the same descriptions below have the same meaning). A crosslinked product of a polysaccharide- (meth) acrylic acid graft copolymer, a crosslinked product of a (meth) acrylic acid-acrylamide-sulfonated acrylamide terpolymer or an alkali metal salt or alkaline earth metal salt thereof, for example, Acrylic acid (salt)
Crosslinked products such as polymers, acrylic acid (salt) -methacrylic acid (salt) copolymers, starch-acrylic acid (salt) graft copolymers; polysaccharide- (meth) acrylic acid alkyl ester graft copolymer Ken Cross-linked product, saponified product of polysaccharide-acrylonitrile graft copolymer, cross-linked product of saponified product of polysaccharide-acrylamide copolymer, for example, starch-saponified product of ethyl acrylate graft copolymer, starch- Crosslinked products such as saponified product of methyl methacrylate graft copolymer, saponified product of starch-acrylonitrile graft copolymer, saponified product of starch-acrylamide graft copolymer; (meth) acrylic acid alkyl ester-vinyl acetate copolymer A crosslinked product of a saponified product of, for example, a saponified product of an ethyl methacrylate-vinyl acetate copolymer, Crosslinked products of saponified products of methyl acrylate-vinyl acetate copolymer; crosslinked products of saponified products of starch-acrylonitrile-acrylamido-2-methylpropanesulfonic acid graft copolymer; starch-acrylonitrile-vinylsulfonic acid graft copolymer Examples include, but are not limited to, water-absorbent resins containing a monomer unit having a carboxylate in the constituent components of a polymer or copolymer such as a crosslinked product of a saponified product of a coalescence; a crosslinked product of sodium carboxymethyl cellulose. Not something. These may be used alone or in combination of two or more. Among these water-absorbent resins having carboxylates, the main component is a cross-linked product of a (meth) acrylic acid polymer or a unit derived from (meth) acrylic acid and / or (meth) acrylic acid alkali metal salt. , Ie
A cross-linked polymer containing 50% (wt%, the same applies hereinafter) or more is particularly preferable from the viewpoint of water absorption capacity.

In the present invention, the water-absorbent resin having the carboxylate is dispersed in the air as a powder, and therefore it is preferable that the particle size is suitable for the dispersion.

The particle size varies depending on the dispersion method, the use of the modified water absorbent resin, and the like, and cannot be specified unconditionally, but it is usually preferably about 20 mesh pass.

The modifier used in the present invention is a polyfunctional compound used for improving the gel strength after water absorption of the water absorbent resin having the carboxylate, and specific examples thereof include diglycidyl ether compounds, Examples thereof include cross-linking agents such as polyvalent metal salts, haloepoxy compounds, aldehyde compounds, and isocyanate compounds, but are not limited thereto.

The cross-linking agent used as a modifier of the water absorbent resin having a carboxylate has two or more functional groups capable of reacting with a carboxylate group, a hydroxyl group, a sulfone group, an amino group or the like present in the water absorbent resin. A compound, the purpose of which is to impart a cross-linking structure to the water-absorbent resin to be modified again, and improve the gel strength after water-absorption of the water-absorbent resin while maintaining the water-absorption capacity and water-absorption rate. . In addition, the cross-linking improves gel strength and reduces stickiness on the surface of the water-absorbent resin.

Examples of the diglycidyl ether compound include diglycidyl ether compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether.

Examples of the polyvalent metal salt include compounds capable of forming crosslinks with the carboxylate of the water-absorbent resin by an ionic reaction, and specific examples thereof include divalent metals such as magnesium, calcium, barium and zinc, or aluminum and iron. And trivalent metal halides, sulfates, nitrates, and the like, more specifically, magnesium sulfate, aluminum sulfate, ferric chloride, calcium chloride, magnesium chloride, aluminum chloride, polyaluminum chloride, iron nitrate, Examples include calcium nitrate and aluminum nitrate.

Specific examples of the haloepoxy-based compound include epichlorohydrin, epibromohydrin, α-methylepochlorohydrin, and the like, and aldehyde compounds include glutaraldehyde and glyoxal.

The above modifiers may be used alone or in combination of two or more, but an appropriate one is selected depending on the kind of the water absorbent resin having a carboxylate modified according to the present invention. Of these modifiers, diglycidyl ether compounds are preferable from the viewpoints of reactivity and handleability.

The modifier is used as a solution containing the modifier (hereinafter referred to as a modifier solution), and water is suitable as the solvent used at this time, and if necessary, it is compatible with water or An organic solvent such as a miscible alcohol may be used together.

The role of water contained in the modifier solution is to swell the water absorbent resin having the carboxylate modified according to the present invention,
By allowing the modifier to penetrate into the swollen portion of the water absorbent resin, the water absorbent resin and the modifier can be efficiently crosslinked. Therefore, the more water is used, the more the crosslinking reaction occurs inside, so it becomes easier for the water-absorbent resin to maintain the network structure even after swelling by absorbing water, and the gel strength is stable over time. A water absorbent resin having

Further, in the conventional modification method, the swollen water-absorbent resin tends to aggregate to form a lump, and it is difficult to make the water-absorbent resin and water into a uniform state, but in the present invention, the carboxylate to be modified is contained. Since the modifier solution is absorbed while the water-absorbent resin is dispersed in the air, it is possible to achieve a uniform dispersion state without aggregation even if the amount of water absorbed increases. By heating in such a state to carry out a crosslinking reaction and distilling off water, a water absorbent resin having improved gel strength after absorbing water can be obtained.

The concentration of the modifier solution is not particularly limited, but it must contain a considerable amount of water which is an essential component for reacting the modifier with the carboxylate in the water absorbent resin powder, and therefore Modifier is about 0.05-50%, and even 0.1
It is preferable that the content is about 20%. The amount of the modifier solution added varies depending on its concentration, but normally the modifier content is about 0.005 to 5% with respect to the water-absorbent resin powder, preferably
It may be appropriately adjusted so as to be about 0.01 to 1%. Generally, if the amount of the cross-linking agent used is less than 0.005%, the effect of improving the strength after water absorption tends to be insufficient, and if it exceeds 5%, the degree of cross-linking tends to be too high and the water absorption capacity tends to decrease. There is.

When the modifier solution is mixed with the water absorbent resin powder having a carboxylate, the diameter of fine droplets is 500 μm or less, preferably 100 μm or less. If the diameter of the liquid droplets exceeds 500 μm, the water-absorbent resin powder tends to aggregate during the addition of the liquid droplets, and the workability tends to deteriorate.

In the method of the present invention, the water-absorbent resin powder to be modified is continuously supplied, dispersed in the air, mixed with the fine droplets of the modifier solution as described above, and the fine particles of the modifier solution are mixed. The droplet is absorbed.

Of course, continuous supply means that the product is supplied without interruption.
Even if the supplied resin powder is intermittently supplied to the air, if the modified water-absorbent resin powder is produced substantially continuously, a concept including such a case is also included. Is.

The supply of the water-absorbent resin powder having a carboxylate is such a method that it is continuously and dispersed in the air, and as long as it is a method in which the fine droplets of the modifier solution are absorbed, that method, the supply The amount and the like are not particularly limited, but for the water-absorbent resin, for example, a method using a constant quantity feeder such as a vibration feeder, a screw feeder, a roll feeder or a rotary feeder can be adopted.

The modifier aqueous solution can be quantitatively supplied in the form of droplets by using a diaphragm pump, a gear pump and the like in combination with a disk atomizer, a spray nozzle and the like.

In the present invention, it is an essential requirement that the water absorbent resin powder be dispersed in the air. Here, the supply amount of the powder in a dispersed state naturally varies depending on the specifications of the apparatus, the residence time of the powder, etc., but normally 1 to 500 kg / min per 1 m ³ ,
It is preferably about 100 to 400 kg / min. The residence time of the powder under dispersion is determined by the absorption of the modifier solution in the powder.
It is appropriately determined in consideration of the degree of diffusion, the modification treatment capacity, etc., but is usually about 1 second to 10 minutes, preferably about 3 seconds to 1 minute.

Further, "in the air" refers to the air occupying the inside of the container in which the water-absorbent resin powder having a carboxylate is usually dispersed and mixed with the fine droplets of the modifier solution. Alternatively, nitrogen gas or the like may be used. As a method for dispersing, various mechanical dispersion methods such as a method using a stirrer such as a stirrer with a rotary blade and a method of suspending dispersion by blowing air can be adopted.

As a method for mixing fine droplets of the modifier solution and the water-absorbent resin powder having a carboxylate in the above-mentioned method, a predetermined amount of the modifier solution as fine droplets and carboxy dispersed in the air are used. The water-absorbent resin powder having a rate can be mixed substantially uniformly, and it is preferable to add and mix by a spraying method such as a showering method or a spraying method which is industrially preferable. Further, there is no particular limitation on how to mix the water-absorbent resin powder having a carboxylate to be modified and the modifier solution, and these components are substantially uniformly mixed and modified. Any method can be adopted as long as the agent solution is absorbed. For example, the water-absorbent resin powder may be dispersed in the fine droplets, or conversely, fine droplets may be added to the dispersed water-absorbent resin powder, or these may be added simultaneously.

The water-absorbent resin powder that has absorbed the modifier solution as described above is subjected to a heat treatment in order to smoothly carry out the crosslinking reaction and to dry it. The conditions at that time are the type of modifier used,
The temperature is usually 70 to 200 ° C, although it cannot be determined unconditionally because it depends on the application of the water-absorbent resin with improved gel strength.
Is the range.

The method of heating the water-absorbent resin powder having the carboxylate absorbed by the fine droplets of the modifier solution is not particularly limited, and any conventionally known heating means can be adopted. Specific examples thereof include, for example, a method using a continuous fluidized bed dryer heated by hot air, and a spray dryer (dispersed powder) modified so that mixing / absorption of a modifier solution and heating can be performed at the same time. The modifier solution is sprayed on the water-absorbent resin powder thus obtained).

In the present invention, since it is not necessary to use an organic solvent or the like at all, in this case, steps such as recovery and regeneration of the organic solvent are not necessary, which contributes to the cost reduction of the modified water absorbent resin. sell. In addition, the water absorbent resin modified by the method of the present invention maintains the water absorbing ability and the water absorbing speed, and after the water absorption, the gel has a high gel strength with a dry feel. Further, according to the method of the present invention, the modified water absorbent resin as described above can be easily and efficiently produced.

Next, an example of an apparatus used in the method of the present invention will be described.

To carry out the method of the invention, an apparatus such as that shown in FIG. 1 is used. In FIG. 1, (1) is a water-absorbent resin powder (hereinafter, also referred to as raw material resin powder) tank containing galboxylate, and (2) is a fixed amount feeder for feeding the raw material resin powder. Further, (4) is a modifier solution pump, (5) is a modifier solution tank, and (6) is a spray nozzle for supplying the modifier solution as fine droplets. Further, (7) is a droplet absorbing device that mixes the dispersed raw material resin powder with the supplied fine droplets and causes the powder to absorb the fine droplets, which is supplied to the device (7). With a rotor blade to disperse the raw material resin powder in the air and sufficiently mix it with the fine droplets of the supplied modifier solution to promote absorption of the modifier solution into the raw material resin powder. Stirrer
(3) is provided. (8) is a fluidized bed dryer for heat treatment, and (M) is a motor. The bottom of the droplet absorbing device (7) has a structure such that the raw material resin powder that has absorbed the fine droplets of the modifier solution is smoothly fed to the fluidized bed dryer (8).

Next, the method of the present invention will be described more specifically based on examples, but the present invention is not limited thereto.

Example 1 After cooling, 1365.5 g of sodium hydroxide was added to a liquid composed of 3280 g of acrylic acid and 5432 g of water to neutralize the solution.
N'-methylenebis (acrylamide) 0.81g, ammonium persulfate 12.1g and sodium bisulfite 4.0g
Was added and dissolved. This monomer aqueous solution was allowed to stand and polymerize at 55-80 ° C in a nitrogen atmosphere to obtain a gel polymer.

After drying the obtained gel polymer in a hot air dryer at 150 ° C,
Grind with a pin grinder and sieve with a 28 mesh wire mesh, 28
The raw material resin powder (A-1) of the mesh pass was obtained. The particle size of the obtained raw material resin powder (A-1) was such that 95% thereof passed through 32 mesh.

Separately, 8 g of ethylene glycol diglycidyl ether was dissolved in 400 g of water to prepare a modifier solution (A-2).

As the apparatus for producing the water absorbent resin, the apparatus shown in FIG. 1 was used, in which the droplet absorbing device (7) had an inner diameter of 30 cm, a height of 60 cm, a material of stainless steel, and an inner surface coated with polyethylene tetrafluoride. . Inside the droplet absorbing device (7), a stirrer with a rotating blade (3) having 12 rotating blades with an area of 25 cm ² attached to a rotating shaft is provided.

While rotating the agitator (3) with a rotary blade at a rotation speed of 300 rpm,
100 kg of raw material resin powder (A-1) from the top of the liquid drop absorber (7)
Supplied continuously at a rate of hr. At the same time modifier solution (A-2)
5 kg above the upper rotor using a two-fluid nozzle at 12 kg / hr
It was continuously fed from the position m. Modifier solution at this time
The droplet diameter of (A-2) was about 200 μm. Immediately after the supply, the modifier solution (A-2) was contacted with and absorbed by the surface of the raw material resin powder (A-1), and the raw material resin powder was dispersed in the droplet absorbing device (7) for 2 to 3 seconds. It was discharged later. After that, the resin powder was put into a fluidized bed dryer (8) and dried with hot air at 130 ° C. for 20 minutes to obtain a modified water absorbent resin (1).

The performance of the obtained modified water absorbent resin was evaluated by the following method. The results are shown in Table 1.

(Water absorption capacity) 150g of physiological saline (0.9% saline) and 0.12g of modified water-absorbent resin were added to a 200ml beaker, left for 30 minutes, filtered with a 200-mesh wire net, and discharged. The amount of incoming water is measured and the water absorption capacity is calculated by the following formula.

(Gel strength) 60 g of physiological saline and 2.0 g of the modified water-absorbent resin were mixed and stirred to prepare a gel (hereinafter, referred to as 30 times gel), and a neocard meter manufactured by Iio Electric Co., Ltd. was used for 1 hour. After 3 days, the hardness of the gel is measured. Here, the hardness of the gel means an elastic force until the gel is broken.

(Water Absorption State of Water-Absorbent Resin) 1 g of the water-absorbent resin powder is placed in a beaker, and 30 ml of water is gradually dropped into the beaker, and the presence or absence of mamko is visually observed.

Example 2 Starch-acrylic acid-based graft polymer cross-linked product
51-125468 (described in Example 3) was used as a raw material water-absorbent resin, and this was pulverized in the same manner as in Example 1 to obtain a raw material resin powder (A-3). The particle size of the powder was such that 89% passed through 32 mesh.

Thereafter, the raw material resin powder (A-3) was subjected to surface modification in the same manner as in Example 1 to evaluate the modified water absorbent resin powder (2). The results are shown in Table 1.

Comparative Example 1 5000 g of the raw material resin powder (A-1) used in Example 1 was charged into a speed mixer (manufactured by Kawata Co., Ltd.), and 650 g of the modifier solution (A-2) was stirred with 500 rpm to form a two-fluid nozzle. Using 16
Sprayed at 0 g / min. At this time, the droplet size of the modifier solution (A-2) was about 200 μm.

Approximately 30 seconds after the modifier solution (A-2) was sprayed, the raw material resin powder (A-1) became an aggregate (Mamako), showed no fluidity, and sprayed the modifier.

Comparative Example 2 The performance of the raw material resin powder (A-1) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 The performance of the raw material resin powder (A-3) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 4 The same operation as in Example 1 was carried out except that the spraying conditions were changed and the average particle size of the droplets was changed to 700 μm. However, the raw material resin powder aggregated about 40 seconds after the start of spraying, and the droplet absorption. The operation was stopped because the inside of the device (7) was blocked.

[Effects of the Invention] According to the production method of the present invention, a modified water-absorbent resin having excellent water absorption performance, high gel strength after absorption of water, and a gel that does not give a sticky feeling can be produced efficiently, easily and inexpensively. Can be manufactured continuously.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of an apparatus used in the method of the present invention. (Symbols in the drawing) (1): Raw material resin powder tank (2): Fixed amount feeder (3): Rotating blade agitator (4): Modifier solution pump (5): Modifier solution tank (6): Spray nozzle (7): Droplet absorber (8): Fluidized bed dryer

Claims (5)

[Claims] 1. A solution containing a water-absorbent resin powder having a carboxylate, which is continuously supplied and dispersed in the air, and a modifier, and fine droplets having a diameter of 500 μm or less. Is mixed, the water-absorbent resin powder is allowed to absorb the solution, and heat treatment is performed, and a continuous process for producing a modified water-absorbent resin. 2. A water-absorbent resin powder having a carboxylate is a powder composed of a cross-linked polymer containing a unit derived from (meth) acrylic acid and / or an alkali metal salt of (meth) acrylic acid as a main component. Item 2. The production method according to Item 1. 3. A solution containing a modifying agent is a solution containing at least water and a diglycidyl ether compound, and the content of the modifying agent in the solution is 0.05 to 50% by weight, and the solution. The manufacturing method according to claim 1, wherein the mixing amount of the above is 0.005 to 5% by weight based on the water-absorbent resin powder when converted as a modifier content. 4. The method according to claim 1, wherein the temperature during the heat treatment is 70 to 200 ° C. 5. The method according to claim 1, wherein the water-absorbent resin powder having a carboxylate is dispersed in the air for 1 second to 10 minutes.