JP3621552B2 - Method for producing water-soluble polymer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention produces a water-soluble polymer having a high molecular weight suitable for a flocculant, a papermaking adhesive, a papermaking yield improver, etc., good solubility, and a small amount of residual monomer by light irradiation. On how to do.
[0002]
[Prior art]
Many of high molecular weight water-soluble vinyl polymers used for flocculant applications, such as polyacrylamide polymers and acrylamide copolymers, have molecular weights exceeding 10 million. As a means for obtaining such a high molecular weight polymer, it is common to polymerize monomers in an aqueous solution, crush the resulting aqueous gel into granules, and dry them with hot air.
[0003]
As a method for polymerizing monomers in an aqueous solution, there is a continuous polymerization method by light irradiation on a moving substrate. This is, for example, a method in which a monomer aqueous solution is supplied from one end on a continuous belt, polymerized by irradiation with light, and the resulting aqueous gel is continuously taken out from the other end.
[0004]
It is said that a polymer having a high molecular weight can be obtained in a shorter time by using a photoinitiator that generates an initiating radical by light irradiation than in the case of using a redox or a thermal initiator.
[0005]
When these polymers are used for an aggregating agent or the like, it is required that the polymer has a high dissolution rate in water, does not contain water insolubles, and has good solubility.
[0006]
However, it is generally known that the higher the molecular weight of a polymer, the lower the solubility of the polymer in water. The decrease in solubility can be solved to some extent by increasing the dissolution time during use.However, if the decrease in solubility is severe, it becomes a water-insoluble highly crosslinked polymer that does not dissolve but only remains in the form of particles. When used as a flocculant, it exhibits only a low agglomeration performance.When used as a thickener for oil recovery, the penetrating power decreases, and in the case of a papermaking thickener, fish eyes are generated on the paper. Problems arise.
[0007]
On the other hand, from the viewpoint of toxicity, a polymer containing only a very small amount of residual monomer is simultaneously demanded. For example, when acrylamide is the main component, the polymer obtained is not toxic, but since the acrylamide monomer is toxic, it is necessary to reduce the residual monomer concentration as much as possible. The level of residual acrylamide monomer concentration in the Japanese industry is 0.2% by weight or less for general wastewater treatment applications and 0.05% by weight or less for water supply applications.
[0008]
As a conventionally proposed method for reducing residual monomer,
(1) Reduction method by extending polymerization time (2) Reduction method by increasing initiator addition amount (3) Reduction method by extraction washing using solvent such as methanol (4) Reduction method by harmless adduct formation (5 ) A reduction method using a combination of a redox initiator and a photoinitiator can be mentioned, but none of them is a sufficient method.
[0009]
That is, the method (1) causes a significant decrease in productivity. In the method (2), a photoinitiator is added at a high concentration, and the light intensity is increased in the late stage of polymerization. However, a photoinitiator with low water solubility has a low solubility in an aqueous monomer solution, and therefore a high concentration addition is required. Although it is difficult to add a high concentration of water-soluble photoinitiator, the residual monomer concentration is reduced. However, in the case of a high molecular weight polymer, the water solubility is lowered, which is not preferable.
[0010]
The method (3) requires the use and recovery of a large amount of flammable solvent, which is not preferable from the viewpoint of safety and economy. As for the method (4), as shown in Japanese Examined Patent Publication No. 61-23926, in continuous polymerization by UV irradiation on a substrate to be moved, alkali sulfite and / or at least one kind on the surface of the aqueous gel sheet after polymerization. Although a method of reducing residual monomer by applying alkali metabisulfite, pulverizing and drying is disclosed, equipment such as a coating apparatus is required, which is not preferable.
[0011]
About the method of (5), as seen in JP-A-57-121009, a redox initiator and a photoinitiator are used in combination, and polymerization is carried out using a redox initiator at a polymerization rate of 80% or less up to 80%. Thereafter, a method of reducing the residual monomer by irradiating with ultraviolet rays has been disclosed, but since it is difficult to control the reaction up to a polymerization rate of 80%, it is difficult to obtain a polymer having a high molecular weight and good solubility. Further, since the polymerization time is remarkably long as several hours or more, it is not preferable from the viewpoint of productivity.
[0012]
[Problems to be solved by the invention]
In the production method in which the present invention performs polymerization by irradiating a monomer aqueous solution containing a photoinitiator with light, and heat-drys the obtained aqueous gel to obtain a water-soluble polymer such as an acrylamide polymer. To obtain a water-soluble polymer with good productivity that contains only a small amount of residual monomer and does not contain water-insoluble matter even if it has a high molecular weight and has good solubility. Is an issue.
[0013]
[Means for Solving the Problems]
As a result of intensive studies on the production method of water-soluble vinyl polymers such as acrylamide polymers by light irradiation, the present inventors have used photoinitiators with different decomposition conditions and irradiated light in multiple stages. It has been found that a polymer having a low residual monomer concentration and a high molecular weight and good water solubility can be obtained by this method, and the present invention has been completed to solve all the above problems.
[0014]
That is, the gist of the present invention is “in the method for producing a polymer by photopolymerization in which a vinyl monomer aqueous solution to which a photoinitiator has been added is photoirradiated in the thickness direction, as a photoinitiator, at least during the first stage polymerization. Two or more types of initiator (A) which is an acyl phosphine oxide compound that decomposes under visible light irradiation conditions with a wavelength of 380 nm or more, and an initiator (B) in which 90% or more of the initiator does not decompose during the first stage polymerization. In combination with an initiator, after the light irradiation polymerization at a polymerization rate of 80% by weight or more in the first stage, the light after the second stage under irradiation conditions including light of less than 380 nm that decomposes the initiator (B) “Production method of water-soluble polymer characterized by performing irradiation polymerization”.
[0015]
The combination of the initiator (A) and the initiator (B) is an initiator having different decomposition wavelengths, and the decomposition of the initiator (B) with respect to the decomposition amount of the initiator (A) at the first stage irradiation. The combination is such that the amount is sufficiently small. As the initiators (A) and (B), one or more of each can be selected from benzoin, benzoin alkyl ether, benzyl, benzophenone, anthraquinone, acylphosphine oxide compound, azo-based initiator, and the like. . For reference, the maximum absorption wavelength of decomposition of various initiators is illustrated.
2-hydroxy-2-methyl-1-phenyl-propan-1-one: about 280 nm
1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one: about 280 nm
Benzoin ethyl ether: about 330 nm
Benzoin isopropyl ether: about 330 nm
2,2′-azobis (2-methylpropionamidine): about 360 nm
2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] hydrochloride: about 360 nm
2,4,6-trimethylbenzoyldiphenylphosphine oxide: about 380 nm
[0016]
As the light used in the present invention, various wavelengths of light can be used in combination with the initiator, but the wavelength in the region of 200 to 650 nm is seen from the viewpoint of absorption by the monomer itself and photon energy. desirable. There are various known light sources that give light of 200 to 650 nm, and typical examples thereof include a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, a fluorescent chemical lamp, and a fluorescent blue lamp.
[0017]
The light emitted at each stage may irradiate light of a specific wavelength, but considering the economy and simplicity, the first stage emits light that does not substantially contain light on the short wavelength side through filters. In the second and subsequent stages, it is preferable to irradiate light including the short wavelength side.
In this case, the initiator (A) is an initiator that is easily decomposed on the long wavelength side, and the initiator (B) is an initiator that is easily decomposed on the low wavelength side.
[0018]
The light intensity irradiated in the first stage may be constant or may be changed during the polymerization, and depends on the initiator species and the molecular weight of the target polymer.
[0019]
The light intensity irradiated in the second and subsequent stages depends on the irradiation time in the second and subsequent stages and the target residual monomer concentration, but is preferably approximately 50 to 2,000 W / m ² .
[0020]
As a specific example of the combination of the initiators (A) and (B), an acylphosphine oxide compound having a maximum absorption wavelength of 380 nm on the long wavelength side is preferable as the initiator (A) used in the first stage, and is water-insoluble. 2,4,6-trimethylbenzoyldiphenylphosphine oxide and its related compounds that are difficult to form a polymer are more preferred. The addition amount is determined from the balance between the molecular weight of the polymer and the solubility, but is generally 1 to 100 ppm.
[0021]
As the initiator (B), the maximum absorption wavelength of decomposition is different from that of the initiator (A), and most of them do not decompose under the light irradiation conditions in the first stage, preferably 90% does not decompose. It may be a mixture of two or more initiators, but a water-soluble azo-based initiator that does not easily form a water-insoluble polymer is preferable, and the amount added is preferably about 100 to 1,000 ppm. By adding such an amount, the residual monomer can be sufficiently reduced in a relatively short time.
[0022]
Azo-based initiators are known to decompose by heat, and if most of them are decomposed during the first stage irradiation, it becomes difficult to obtain a high molecular weight polymer. It is preferable to select a higher one, preferably one higher than 10 ° C. Examples of the azo initiator include 2,2′-azobis (2-methylpropionamidine) and its mineral salt, 2,2′-azobis (2-methylpropiononitrile), 4,4′-azobis (4-cyano). Valeric acid) and its alkali metal salts, ammonium salts, 2,2′-azobis [2-hydroxymethyl (propiononitrile)], 22′-azobis {2-methyl-N- [1,1′-bis (hydroxymethyl) ) -2-Hydroxyethyl] propionamide}, 2,2′-azobis [2-methyl-N- [1,1′-bis (hydroxymethyl) ethyl] propionamide}, 2,2′-azobis [2- Methyl-N- (2-hydroxyethyl) propionamide], 2,2′-azobis (2-methylpropionamide) and hydrates thereof.
When an azo-based initiator is combined as the initiator (B), high-molecular-weight and water-soluble is obtained by irradiating visible light substantially free of light having a wavelength of 380 nm or less as light to be irradiated to the first stage. A good polymer can be obtained. In this case, even a light source including a wavelength of 380 nm or less can be used if the transmitted light is adjusted so as not to substantially include a wavelength of 380 nm or less using an appropriate filter as described above. Visible light which does not substantially contain a wavelength of 380 nm or less as used in the present invention is a light intensity Qu of a wavelength of 380 nm or less measured with a light intensity meter UVR-36 (Topcon) and UVR-40 (Topcon). This means light having a ratio Qu / Qv of 0.5 or less with respect to the light intensity Qv of wavelength 380 nm or more measured using The light intensity ratio Qu / Qv needs to be 0.5 or less, preferably 0.2 or less. By setting such a light intensity ratio, a polymer having a high molecular weight and good solubility can be obtained.
[0024]
The polymerization rate at the end of the first stage is preferably about 80% or more, and more preferably 95% or more, from the viewpoint of preventing the molecular weight from being lowered or the solubility from being lowered in the second and subsequent stages.
[0025]
Examples of the water-soluble vinyl monomer used in the present invention include acrylamide, methacrylamide, acrylic acid, methacrylic acid, and alkali salts, ammonium salts of these acids, and acrylamide alkane sulfones such as acrylamide-2-methylpropanesulfonic acid. Examples include acids and alkali salts and ammonium salts thereof. Furthermore, various dialkylaminoalkyl esters of acrylic acid and methacrylic acid and their tertiary salts and quaternary salts, or N, N′-dialkylaminoalkyl acrylamide, N, N′-dialkylaminoalkyl methacrylamide and their tertiary Salts, quaternary salts, dialkyldiallylammonium salts, and the like.
[0026]
Depending on the application, acrylonitrile, N-substituted derivatives of acrylamide, styrene, and the like can be used as long as the water solubility of the resulting polymer is not impaired. These monomers may be copolymerized by one kind or two or more kinds.
[0027]
In particular, a polymer obtained from an acrylamide monomer can have a high molecular weight and exhibits high aggregation performance as a polymer flocculant used in wastewater treatment and the like. As the acrylamide polymer used for this purpose, acrylamide alone or a polymer polymerized from at least one of acrylamide 25 mol% or more and a monomer copolymerizable therewith is preferably used. As the water-soluble monomer copolymerizable with acrylamide, the above-mentioned water-soluble vinyl monomers, acrylonitrile, N-substituted derivatives of acrylamide, styrene and the like can be used in combination.
[0028]
The monomer concentration of the aqueous vinyl monomer solution is preferably as high as possible in terms of productivity and drying efficiency, and is in the range of 20 to 80% by weight. However, it is difficult to remove the polymerization heat as the layer thickness increases. Therefore, it is necessary to make it not to boil. For example, in the polymerization of acrylamide or acrylic acid, it is preferable to perform the polymerization at about 20 to 40% by weight in order to obtain a high molecular weight polymer with a layer thickness of 30 mm or more and high productivity.
[0029]
The layer thickness of the monomer aqueous solution is preferably thick in order to increase productivity. When irradiating from one direction, it is 5 mm or more, preferably 30 to 200 mm, and when irradiating from both directions, preferably 100 to 400 mm. .
[0030]
The polymerization can be carried out in a batch-like container in a batch operation, but in the case of industrial production, polymerization on a continuous belt is advantageous. In this method, a monomer solution is supplied from one end of an endless belt to form a sheet, and polymerized by passing under a fixed light source together with the belt. After the point at which it stops flowing, it is also possible to continuously move it onto the roller conveyor and continue the light irradiation. In this case, light irradiation can be performed from both above and below.
[0031]
【Example】
EXAMPLES Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples. Below, a part shows a weight part.
[0032]
Example 1
25 parts of acrylamide was dissolved in pure water, and the pH was adjusted to 9 with an aqueous sodium hydroxide solution. Next, a 2 wt% methanol solution of a photoinitiator manufactured by BASF, trade name Lucillin TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide; initiator (A), maximum absorption wavelength of decomposition of about 380 nm) under shading 2 parts by weight of an aqueous solution of 0.15 part of 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] (initiator (B), maximum absorption wavelength of decomposition about 360 nm) And pure water was added to make 100 parts. Next, the liquid temperature was adjusted to 10 ° C. while replacing the dissolved oxygen with nitrogen gas. Thereafter, the monomer aqueous solution is supplied to a polymerization apparatus having a box shape (250 mm long, 250 mm wide, 130 mm high) sealed with nitrogen gas and having a glass plate on the upper surface so that the monomer aqueous solution layer has a thickness of 100 mm. did.
A light source in which an acrylic plate (# 999, manufactured by Asahi Kasei # 3mm thickness) is attached to the front of a 20W fluorescent lamp type blue lamp (Toshiba FL-20S-B) above the polymerization apparatus is placed under UVR on the upper surface of the polymerization apparatus. It installed so that the light intensity measured using -40 might be 25 W / m < ² >. The light intensity ratio Qu / Qv was 0.1. Polymerization was performed by irradiation with light for 20 minutes. The polymerization rate at this time was 97%, and the residual rate of the initiator (B) was 95%. Next, the light source was changed to a 1 kw metal halide lamp (CUVH01-MA / N manufactured by Cosmo Giken), and the light intensity measured using UVR-40 was set at 160 W / m ^{2 at the} lower part of the upper surface of the polymerization apparatus. Irradiated for 40 minutes. The light intensity ratio Qu / Qv at this time was 5.3. The obtained polymer was a transparent and elastic aqueous gel.
[0034]
This aqueous gel was pulverized into several mm squares, dried at 60 ° C. for 16 hours, and pulverized to a particle size of 2 mm or less with a Wiley pulverizer. The polymer powder obtained in 4% by weight saline was dissolved to a concentration of 1% by weight, and Brookfield viscosity at 25 ° C. (B-type viscometer, rotor rotation speed 6 rpm), rotor No. 3 ; Hereinafter abbreviated as 4 wt% saline in water).
[0035]
Further, the polymer powder was dissolved in 500 g of pure water at a concentration of 0.1% by weight, and then filtered through an 80 mesh wire net to observe the dissolved state and water insoluble matter. The residual monomer concentration was measured by liquid chromatography after extraction with methanol / water = 80/20 solvent for 16 hours. The resulting acrylamide polymer had a viscosity of 3,100 mPa · s in 4% by weight saline, contained no water-insoluble matter, and had a residual monomer concentration of 0.05%.
[0036]
Comparative Example 1
The same procedure as in Example 1 was conducted except that 2,2-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] was not added. The obtained acrylamide polymer had a viscosity of 3,200 mPa · s in 4% by weight saline solution and contained no water-insoluble matter, but the residual monomer concentration was 2.5% by weight.
[0037]
Comparative Example 2
In Example 1 above, 2.15 parts of a 2 wt% methanol solution of lucillin TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) was added, and 2,2′-azobis [2-methyl-N- (2-hydroxy Ethyl) propionamide] was added in the same manner except that it was not added. The aqueous gel at the end of the light irradiation was elastic but clouded. The obtained acrylamide polymer powder only swelled in water and became a large amount of granular water-insoluble matter, and the viscosity in 4% by weight saline was not measurable.
Comparative Example 3
2 weight of 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] without adding lucillin TP0 (2,4,6-trimethylbenzoyldiphenylphosphine oxide) in Example 1 above 2.15 parts of a% aqueous solution was added, and measurement was carried out using UVR-36 at the lower surface of the upper surface of the polymerization apparatus as a 20 W fluorescent lamp type chemical lamp (Toshiba FL-20S-BL) instead of a fluorescent lamp type blue lamp. The same procedure was performed except that the light intensity was set to 21 W / m ² . The light intensity ratio Qu / Qv during the first stage irradiation was 4.8. The polymerization rate at the end of the chemical lamp irradiation was 97%.
[0039]
The obtained acrylamide polymer powder had a viscosity of 2,950 mPa · s in 4% by weight saline solution and a residual monomer concentration of 0.05%, but remained undissolved even after stirring for 4 hours. It was.
[0040]
【The invention's effect】
According to the method of the present invention, it is possible to efficiently obtain a polymer having a high molecular weight and a small amount of residual monomer and having good water solubility.

Claims (2)

In the method for producing a polymer by photopolymerization in which a vinyl monomer aqueous solution to which a photoinitiator is added is irradiated in the thickness direction, as a photoinitiator , visible light irradiation having a wavelength of 380 nm or more at least in the first stage polymerization The initiator (A), which is an acylphosphine oxide compound that decomposes under conditions, and an initiator (B), in which 90% or more of the initiator remains without being decomposed during the first stage polymerization, are used in combination. It is characterized by performing light irradiation polymerization after the second stage under irradiation conditions including light of less than 380 nm after the polymerization rate in the stage is 80% by weight or more and the initiator (B) decomposes. A method for producing a water-soluble polymer. The water-soluble vinyl-based monomer is an acrylamide-based monomer which is a monomer mixture composed of acrylamide alone or 25 mol% or more of acrylamide and at least one monomer copolymerizable therewith. 1. The production method according to 1.