JPH059447B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sulfonic acid group-containing acrylamide crosslinked resin having the ability to absorb a large amount of water, and a method for producing the same. Conventionally, materials that physically absorb water, such as nonwoven fabrics, paper, pulp, and sponge-like substances, have been used in sanitary products, diapers, disposable wipes, etc. However, these water-absorbing materials have a low water-absorbing capacity and are not necessarily satisfactory for the above applications. It wasn't something. In recent years, in addition to the above-mentioned applications, materials with chemical water-absorbing ability have been increasingly used for applications in the medical industry, food industry, and agricultural fields. In particular, water-insoluble, hydrophilic, or water-absorbing polymeric materials have been used in various materials. It has found use in separation and purification materials such as planks and liquid chromatography carriers, microbial and plant culture media, medical materials such as contact lenses and suture coatings, and a variety of other uses that require water absorption or water retention. Many water-absorbing materials have been proposed for such uses. For example, crosslinked polyethylene oxide, polyvinylpyrrolidone, sulfonated polystyrene, etc., polyacrylamide crosslinked with a divinyl compound such as methylenebisacrylamide, saponified products of cellulose derivatives and starch grafted with acrylic acid or acrylonitrile, etc. Water-absorbing materials using natural or synthetic polymeric substances have been proposed. However, among these materials, except for saponified starch-acrylonitrile graft polymers, their water-absorbing capacity is small and they are not satisfactory as water-absorbing materials. In the case of saponified products, various improvements have been made to the manufacturing method, but the process is complicated, and if the starch components remain in a hydrated state for a long period of time, the starch components will rot and the gel structure will be destroyed. There remain problems with practicality. In addition, water-soluble monomers such as alkali metal salts of acrylic acid and methacrylic acid and acrylamide are added with a small amount of crosslinking agents such as methylene bisacrylamide and polyethylene oxydiacrylate to produce ceric salts, benzoyl peroxide, azobisisomer, etc. Suspension polymerization or emulsion polymerization using radical polymerization catalysts such as butyronitrile and ammonium persulfate, redox polymerization catalysts such as potassium persulfate and aniline, ammonium persulfate and monoethanolamine, and even solution polymerization is carried out to increase the A method of obtaining a super absorbent resin several hundred times as large has also been proposed. However, in such methods, radical initiators, suspending agents, emulsifiers, solvents, etc. inevitably remain in the superabsorbent resin, which may cause discoloration, depolymerization, corrosion resistance, chemical resistance, and weather resistance. Not only is it unfavorable in terms of
Depending on the application, the water absorption capacity may be insufficient. On the other hand, the present inventors have obtained a linear water-soluble linear polymer with a much larger molecular weight than conventional polymers by polymerizing various vinyl monomers using a plasma-initiated polymerization method. A similar polymer was obtained using 2-acrylamido-2-methylpropanesulfonic acid as a polymer, and this was published in the Journal of the Japan Institute of Fiber Science and Technology (Textiles and Industry), Vol. 37, No. 7, but a resin with even higher water absorption The present invention has been completed as a result of intensive research aimed at achieving this goal. An object of the present invention is to provide a sulfonic acid group-containing crosslinked acrylamide resin that is water-insoluble, has high water absorption of several hundred to several thousand times, and is substantially free of impurities, and a method for producing the same. The present invention comprises at least one monomer selected from 2-acrylamido-2-methylpropanesulfonic acid, its ammonium salt, its alkali metal salt, its alkaline earth metal salt, and its transition metal salt, and a vinyl monomer. Polymerization of a monomer consisting of 0 to 59% by weight of a polymer and a crosslinking component of 1% or less by weight is initiated in an aqueous medium in the presence of ionized gas plasma, and then postpolymerization is carried out in the absence of the plasma. This is a method for producing a sulfonic acid group-containing acrylamide crosslinked resin that is water-insoluble and has a high water absorption capacity of more than 500 times its own weight. The sulfonic acid group-containing acrylamide crosslinked resin produced by the method of the present invention has excellent water absorption, with a water absorption capacity of at least 500 times, preferably 800 times or more, and most preferably 1000 times or more relative to the resin's own weight. has. 2-acrylamide-2- applied to the present invention
Methylpropanesulfonic acid, or its ammonium salt, or its alkali metal salt, or its alkaline earth metal salt, or its transition metal salt (hereinafter referred to as these)
The amount of sulfonic acid group-containing acrylamide crosslinked resin (abbreviated as AMPS) is 40% by weight or more, preferably 60% by weight or more, and more preferably 80% by weight or more.
It is at least 99% by weight, particularly preferably at least 99% by weight. If the amount of AMPS is less than 40% by weight, the water absorption capacity will be insufficient. In the present invention, a vinyl monomer may be copolymerized with a monomer such as 2-acrylamido-2-methylpropanesulfonic acid. These vinyl monomers are not particularly limited as long as they undergo radical polymerization. Generally, acrylonitrile, acrylic ester,
Methacrylic acid ester, styrene, vinyl chloride,
vinylidene chloride, vinyl acetate, acrylamide,
Methacrylamide, N-vinylpyrrolidone, acrylic acid, methacrylic acid, p-styrenesulfonic acid, vinylsulfonic acid, 2-methacryloyloxysulfonic acid, 3-methacryloyloxy-2
- Hydroxypropylsulfonic acid, allylsulfonic acid, methacrylsulfonic acid and ammonium salts and alkali metal salts of these acids; dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, 2
- hydrochloric acid of vinylpyridine and 4-vinylpyridine,
Examples include nitric acid, dimethyl sulfate, diethyl sulfate, and quaternized products of ethyl chloride. Preferred vinylic monomers are water-soluble, but
Particularly preferred are acrylamide, methacrylamide, N-vinylpyrrolidone; acrylic acid, methacrylic acid, P-styrenesulfonic acid, vinylsulfonic acid, 2-methacryloyloxyethylsulfonic acid, 3-methacryloyloxy-2-hydroxypropylsulfonic acid , allylsulfonic acid, methacrylsulfonic acid, and ammonium salts and alkali metal salts of these acids; dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate and diethylaminoethyl methacrylate, hydrochloric acid of 2-vinylpyridine and 4-vinylpyridine, It is a quaternized product of nitric acid, dimethyl sulfate, diethyl sulfate, or ethyl chloride. If the vinyl monomer is water-insoluble, such as acrylonitrile or methyl methacrylate, the water absorption capacity of the obtained sulfonic acid group-containing acrylamide crosslinked resin tends to decrease; The vinyl monomer content is at most 59% by weight, preferably 39% by weight or less, and more preferably 19% by weight, as it lowers the water absorption capacity compared to AMPS.
The range is below % by weight. The crosslinking component applied to the present invention is 1% by weight or less,
Preferably 0.1% by weight or less, more preferably 0.05%
The amount is not more than 0.0001% by weight, particularly preferably 0.0001 to 0.02% by weight, and most preferably not more than 0.01% by weight, and is an essential component for crosslinking. 1% by weight crosslinking component
If it exceeds this, the water absorption capacity will decrease. In general, the water absorption capacity tends to decrease as the amount of crosslinked components increases, and if you want to obtain a high water absorption capacity, you often reduce the amount of crosslinked components. In polymerization, suspension polymerization, solution polymerization, etc., the molecular weight of the resin obtained is low, so if the crosslinking component is less than 0.1% by weight, it may become solubilized, lose its shape when swollen with water, or cause stickiness. However, since the resin of the present invention has an ultra-high molecular weight, the crosslinking component is less than 0.1% by weight.
For example, even if the concentration is 0.0001% by weight, the shape does not collapse even in a water-swollen state and no stickiness is observed. The crosslinking component is divinylbenzene, NN′-
methylenebisacrylamide, diallylamine,
Divinyl compounds such as diacrymethacrylamide, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 2hydroxyethyl acrylate, 2hydroxyethyl methacrylate, 2hydroxypropyl acrylate, 2hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methylol acrylamide or methylol methacrylamide Examples include, but are not limited to, these. As a crosslinking component, NN′−
Preferred are methylene bisacrylamide, diacrylmethacrylamide, polyethylene glycol dimethacrylate, diethylene glycol dimethacrylate, methylol acrylamide, and the like. The polymerization method applied to the present invention is a so-called plasma-initiated polymerization in which polymerization is initiated in the presence of ionized gas plasma and then post-polymerized in the absence of the plasma, and it is essential that the polymerization be performed in an aqueous medium. It is. Examples of the aqueous medium include water or mixtures of water and alcohols such as methanol, ethanol, and butanol, and ketones such as acetone and methyl ethyl ketone, but water alone is preferred. When an aqueous medium is used, especially an aqueous medium, the polymerization rate is significantly increased. The monomer concentration in the aqueous medium is usually 0.1 to 90% by weight, preferably 1 to 65% by weight, and more preferably 10 to 60% by weight. In general, in the case of an aqueous medium, the polymerization rate reaches its maximum when the monomer concentration is 50 mol%, and tends to decrease below or above that level. Furthermore, the molecular weight also shows the same tendency as the polymerization rate. When an organic solvent is used as a medium, not only the polymerization rate is generally slow, but also, in the case of polymerizing a water-soluble polymer as in the present invention, it is necessary to remove the organic solvent, which is not economical. Plasma-initiated polymerization in the present invention is one in which polymerization is initiated using non-equilibrium ionized gas plasma and most of the polymerization is completed in the absence of plasma. Generally, a substantially linear polymer having a high molecular weight is produced, but in the case of the present invention, a crosslinked structure polymer is produced because a crosslinking component such as a divinyl monomer is used. The generation of the ionized gas plasma can be accomplished by any of the known methods for generating such plasmas. For example, J.R. Hollahan and AT Bell, “Applied Techniques of Plasma Chemistry”, Wiley, New York 1974 and M. Shen.
Edition “Plasma Chemistry of Polymers” Detzker New York. Listed in 1976. That is, the monomer can be placed under vacuum between parallel plate electrodes connected to a high frequency generator, and the plasma can be generated using the parallel plates either outside or inside the vacuum chamber.
Alternatively, an electric field may be created by an external induction coil to generate a plasma of ionized gas, or a plasma may be generated by placing oppositely charged electrodes spaced apart directly into a vacuum chamber. In the present invention, polymerization of non-vapor phase (liquid and/or solid) monomers is initiated in the presence of an ionized gas plasma and postpolymerization is carried out in the absence of plasma. This two-step polymerization method allows the production of a large amount of ultra-high molecular weight, water-insoluble, highly water-absorbing resin with energy savings. To explain the method of the present invention in more detail, a monomer aqueous medium solution is cooled and frozen using a refrigerant such as liquid nitrogen, and deaeration is performed at 10 ^-1 to 10 ^-4 Torr. When the frozen monomer aqueous medium solution is gradually warmed to a state where liquid droplets appear, the non-solution area (ie, the vacuum space area) is irradiated with plasma using the above method. Glow discharge is usually performed at 20 to 200 watts, preferably 40 to 100 watts, to turn water and/or monomer into plasma. The irradiation time is usually 1 to 3600 seconds, preferably 10 to 60 seconds. After plasma irradiation, the monomer aqueous medium solution is left at a constant temperature for several hours to carry out post-polymerization. The polymerization rate during the plasma initiation period is significantly lower than the post-polymerization and usually does not exceed 1-2%. The post-polymerization temperature and time vary depending on the type of monomer used and are not particularly limited, but the usual temperature is 1.0-60°C and the time is 1-60°C.
25 hours is sufficient. 60℃ depending on the type of monomer
Caution is required when exceeding this temperature, as thermal polymerization may occur and low-molecular polymers may also be produced. Another major feature of plasma-initiated polymerization, unlike other polymerization methods, is that the superabsorbent resin obtained does not contain anything other than a polymer made of monomer components. That is, in other polymerization methods, radical initiators, suspending agents,
Emulsifiers, solvents, etc. tend to remain and are difficult to completely remove, but plasma-initiated polymerization does not use these additives, so only polymers are present. The thus obtained sulfonic acid group-containing acrylamide crosslinked resin is water-insoluble and exhibits high water absorption. That is, this resin is, for example, 2-acrylamide-2-
The product obtained by the method of the present invention, which consists of 99.999% by weight of methylpropanesulfonic acid and 0.001% by weight of methylenebisacrylamide, exhibits a water absorption capacity of 1400 times its own weight, and the swollen gel is neither sticky nor loses its shape. Furthermore, it is a water-insoluble resin that retains its shape even in boiling water at 100°C and does not contain any impurities, making it an epoch-making resin that cannot be obtained using conventional methods. The resin of the present invention is water-insoluble, has high water absorption, and does not contain impurities, so it can be used as a sanitary material.
It is usefully used in the medical industry, food industry, agricultural fields, etc. The present invention will be explained in detail below with reference to Examples. In addition, the water absorption capacity in Examples was measured by the following method. 0.5 g of the sample was immersed in 1 water, allowed to stand at room temperature for 24 hours, and then suctioned through a glass filter to remove excess water, and the total weight of the glass filter and the water-containing sample was measured. Water absorption amount (g) = (Total weight) - (Glass filter weight) Water absorption capacity = Water absorption amount / 0.5 Example 1 0.4 g of 2-acrylamide-2-methylpropanesulfonic acid, 10 g of water, and N as a crosslinking component.
N'-methylenebisacrylamide was changed as shown in Table 1, placed in a 100 ml ampoule, degassed at 10 ^-3 Torr, and sealed. It was then frozen with liquid nitrogen and degassed three times. Next up is the International Plasma Corporation Model 3001, which outputs up to 150 watts.
This ampoule, which was inserted between a pair of external parallel electrodes connected to a high-frequency generator, was irradiated with glow discharge plasma for 50 seconds at a power of 100 watts. After that, the glow discharge was stopped, and after sealing the tube, it was placed in a constant temperature oven at 25℃ for 10 minutes.
I left it for a while. Thereafter, the package was opened and swollen in a large amount of water to remove unreacted monomers, washed with a large amount of ethanol, and vacuum dried, and the polymer and water absorption capacity of the resulting resin were measured. Also 0.4g of 2-acrylamido-2-methylpropanesulfonic acid, water
10g and N,N↓methylenebisacrylamide as a crosslinking component were changed as shown in Table 1, and 0.004g of potassium persulfate was placed in a 100ml ampoule, vacuum degassed at 10 ^-3 Torr, sealed, and polymerized at 60°C for 24 hours. The water absorbency of the resin is shown for comparison.

[Table] Example 2 The ratio (A/B) of 2-acrylamido-2-methylpropanesulfonic acid (A) and acrylic acid (B) was
Plasma-initiated polymerization was carried out in the same manner as in Example 1, except that 0.001% by weight of N,N'-methylenebisacrylamide was added, the total monomer amount was 4 g, and water was 10 g, as shown in the table. The obtained resin was washed in the same manner as in Example 1, and the polymerization rate and water absorption capacity were measured.

【table】

[Table] Example 3 0.4 g of sodium 2-acrylamido-2-methylpropanesulfonate and 0.00004 g of diethylene oxide dimethacrylate were added to 10 g as shown in Table 3.
The solution was dissolved in a solvent of 100 mL, placed in a 100 ml ampoule, frozen in liquid nitrogen, and degassed at 10 ^-4 Torr. Next, this ampoule was connected to the model 3001 high-frequency generator of Example 1 and inserted between a pair of external parallel electrodes, and a glow discharge was generated at an output of 80 watts, and the ampoule was irradiated for 30 seconds. After that, the glow discharge was stopped and the tube was sealed for 25 minutes.
It was left in a constant temperature bath at ℃ for 15 hours. After that, the package was opened and thoroughly washed with water to remove unreacted monomers, washed with a large amount of ethanol, dried, and used as a sample.
The polymerization rate and water absorption capacity were measured.

【table】

Claims (1)

[Claims] 1 At least one monomer selected from 2-acrylamido-2-methylpropanesulfonic acid, its ammonium salt, and its alkali metal salt, and acrylic acid, methacrylic acid, p-styrenesulfonic acid, vinylsulfonic acid, 2-methacryloyloxy A monomer consisting of at least one vinyl monomer selected from ethyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, ammonium salts and alkali metal salts of these acids, and a crosslinking component is ionized in an aqueous medium with an ionized gas. A sulfonic acid group-containing acrylamide crosslinked resin that is water-insoluble and has a high water absorption capacity of 500 times or more its own weight, which is characterized by starting polymerization in the presence of plasma and then post-polymerizing in the absence of said plasma. manufacturing method.