JPH0558441B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for removing residual monomers in hydrophilic polymers used in paper strength agents, drainage improvers, polymer flocculants, absorbent resins, etc. Regarding methods of reducing

[Prior Art] Hydrophilic polymers containing hydrophilic monomers such as acrylamide, methacrylamide, acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, and vinylpyrrolidone have traditionally been used as paper strength agents. , drainage improver,
It is well known that it is used in a wide range of applications such as polymer flocculants and water absorbent resins. When using a hydrophilic high molecular weight polymer for the above-mentioned purposes, in order to satisfy the required performance, it is generally necessary to increase the molecular weight of the hydrophilic high molecular weight polymer considerably or to further partially crosslink it. It is also well known that the invention has been devised.

By the way, such hydrophilic polymers have a large molecular weight, so when aqueous solution polymerization is used, they have a very high viscosity, making them difficult to handle during production, and especially at the end of the polymerization reaction, unreacted monomers are released. It is often difficult to distill off, usually 1000
~50000 ppm of unreacted monomer remains.
The negative effect of residual monomers is that, for example, in applications such as paper strength agents, drainage improvers, and polymer flocculants, the monomers remaining in the chemicals can place an unnecessary load on white water for papermaking and treated water. Furthermore, when a water-absorbing resin is used for sanitary materials, it has a great influence on skin irritation, etc., so reducing the amount of residual monomer becomes an important issue.

Therefore, in this application, it is desired to develop a technology that can provide a hydrophilic polymer with a small amount of residual monomer.

[Problems to be Solved by the Invention] In view of the above-mentioned circumstances, the present inventors have developed a hydrophilic polymer that can be used in paper strength enhancers, drainage improvers, polymer flocculants, water absorbent resins, etc. We have developed a method for reducing residual monomers in polymers, and have conducted extensive research with the aim of providing excellent hydrophilic polymers that can be suitably used for this purpose. As a result, by specifying the form of the hydrophilic high molecular weight starting material and polymerizing it again in the presence of a specific dispersion medium, the above problems were solved and the objective was met. It has been discovered that an excellent hydrophilic high molecular weight polymer can be provided. The present invention was completed based on this new knowledge.

[Means for Solving the Problems] In order to reduce the residual monomer in a hydrophilic polymer, the present invention makes the polymer powder and inorganic powder exist under stirring and mixing, and adds a radical polymerization initiator to the polymer powder and inorganic powder. The present invention relates to a method for reducing residual monomers in a hydrophilic polymer, which comprises spraying an aqueous solution of and heating the inside of the reaction system.

[Example] The hydrophilic polymer used in the present invention is not particularly limited, but it should be considered to be applied to paper strength enhancers, drainage improvers, polymer flocculants, water absorbent resins, etc. For example, it is usually preferable to use the various high molecular weight polymers shown below. That is, the hydrophilic polymer contains acrylamide, methacrylamide, acrylic acid, methacrylic acid, dimethylaminoalkyl acrylate, dimethylaminoalkyl methacrylate, dimethylaminoalkylacrylamide, dimethylaminoalkylmethacrylamide, diethylaminoalkyl acrylate as the constituent components. , diethylaminoalkyl methacrylate, diethylaminoalkylacrylamide, diethylaminoalkylmethacrylamide, vinylpyrrolidone, acryloyloxyalkylsulfonic acid, methacryloyloxyalkylsulfonic acid, acrylamidealkylsulfonic acid, and methacrylamidealkylsulfonic acid. It contains a monomer and the content thereof is 30% by weight or more, preferably 40% by weight or more. Further, the acid monomer component contained therein may be neutralized with an alkali metal salt, ammonia, or an organic amine. If the hydrophilic monomer content in the polymer is less than 30% by weight, it is not very suitable as a raw material for the above uses. Among the monomers, specific examples of dimethylaminoalkyl acrylate, dimethylaminoalkyl methacrylate, dimethylaminoalkylacrylamide, dimethylaminoalkylmethacrylamide, diethylaminoalkyl acrylate, diethylaminoalkyl methacrylate, diethylaminoalkylacrylamide, and diethylaminoalkylmethacrylamide include These monomers also include monomers in which the alkyl group has 2 to 10 carbon atoms. The acryloyloxyalkylsulfonic acid, methacryloyloxyalkylsulfonic acid, acrylamidealkylsulfonic acid, and methacrylamidealkylsulfonic acid have the general formula (): (wherein R is a hydrogen atom or a methyl group, M is a hydrogen atom, an alkali metal atom or an ammonium group,
X is an oxygen atom or an imino group, Y is a carbon number of 2 to 10
A monomer represented by a linear or branched alkylene group. Specific examples of such monomers include 2-acrylamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-
Examples include methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 2-acryloyloxypropanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 2-methacryloyloxypropanesulfonic acid, and their alkali metal salts and ammonium salts. can.

There are no particular limitations on the constituent components that can be used in the polymer other than the hydrophilic monomer, but examples include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate,
- Examples include nonionic monomers such as ethylhexyl methacrylate, acrylonitrile, vinyl acetate, and styrene, as well as starches.

The hydrophilic polymer can be easily obtained by conventionally known production methods such as aqueous solution polymerization, suspension polymerization, and reverse phase suspension polymerization. Hydrophilic polymers used as paper strength agents, drainage improvers, and polymer flocculants are often produced by an aqueous solution polymerization method. When used for water-absorbing resins, known methods such as JP-A-56-93716 and JP-A-Sho
In addition to JP 56-131608, JP 56-147806, JP 58-71907, JP 58-117222, JP 54-30710, JP 54-
It can be produced by employing various methods disclosed in Japanese Patent Publication No. 37994, Japanese Patent Publication No. 53-46200, US Pat. No. 4,041,228, and the like.

Since the purpose of the reduction method of the present invention is to reduce the residual monomer in the hydrophilic polymer obtained as described above, in order to achieve this purpose,
First of all, the form of the hydrophilic polymer used as the starting material is important. That is, the form of the hydrophilic polymer is determined by taking into consideration the penetration and diffusion of the radical polymerization initiator added in the next step,
Therefore, it is essential that the form be a powdery substance (which may be particulate, irregularly shaped, etc.) with a specific size. Therefore, in order to turn the hydrophilic polymer obtained by the aqueous solution polymerization method into a powder, it is preferable to employ various drying methods such as spray drying and drying with a drum dryer, and to pulverize it if necessary. In addition, when producing by suspension polymerization method, reverse phase suspension polymerization method, etc., a powdered material can be easily obtained by ordinary filtration operation. The particle size of the powder is usually 20 to 2000 μm, preferably 50 μm.
It is preferable to set the thickness to 1000 μm.

In order to achieve the object of the present invention, secondly, it is essential to use a specific inorganic powder as a dispersion medium in the hydrophilic polymer powder. Specific examples of such inorganic powders include hydrated silicon dioxide powder, hydrated aluminum oxide powder, hydrated titanium oxide powder, anhydrides of these, or powders containing these as main components. It is also possible to use a mixture of two or more kinds. The crystal system of the inorganic powder is not limited,
For example, aluminum oxide powder has α-type, β-type,
Any of the γ types can be similarly effectively used, and the titanium oxide powder may be any of TiO, Ti ₂ O ₃ and TiO ₂ . Furthermore, there is no particular limitation on the water content of these hydrated powders; for example, aluminum oxide powder may contain Al ₂ O ₃ .H ₂ O powder, Al ₂ O ₃ .
2H ₂ O powder, Al ₂ O ₃ .3H ₂ O powder, etc. are similarly used, and titanium oxide powder such as TiO ₂ .H ₂ O powder, TiO ₂ .2H ₂ O powder, etc. are similarly used.

Further, as the powder containing a hydrous or anhydrous inorganic substance as a main component, for example, the main component is hydrous silicon dioxide and/or anhydrous silicon dioxide (hereinafter referred to as fine particulate silica) such as colloidal silica, white carbon, ultrafine particulate silica, etc. Examples include those containing hydrated and anhydrous aluminum oxide as a main component, such as plate-like hydrated alumina and fibrous hydrated alumina. Among these inert inorganic powders, fine particulate silica, titanium dioxide powder, alumina powder, and the like are preferred. The particle size of the inorganic powder has an average particle size of 0.001 to 10 μm, preferably
The thickness is preferably 0.005 to 1 μm.

Furthermore, since the inorganic powder functions as a dispersion medium as described above, the amount used is important in order to exhibit this function and to allow the reaction to proceed smoothly in the subsequent post-polymerization process. This amount is usually 0.1 to 20% by weight, preferably 0.5 to 5% by weight, based on the powdered hydrophilic polymer. If it is less than 0.1% by weight, it will not substantially play the role of a dispersion medium, and the contents will aggregate during the reaction, making it impossible to proceed with the reaction. It is possible to add more than 20% by weight, but in this case, the amount of hydrophilic polymer powder itself in the product will be reduced accordingly, and the apparent performance, such as cohesive strength, paper strength, and water absorption power, will be reduced. There is a disadvantage that the value decreases.

The inorganic powder is added to the hydrophilic polymer powder by uniformly mixing a predetermined amount of the inorganic powder with the hydrophilic polymer powder. Mixing may be performed by various commonly used operations, such as mechanical mixing operations.

Next, a post-polymerization reaction is carried out using a radical polymerization initiator while stirring in the presence of the hydrophilic polymer powder and inorganic powder. There is no particular limitation on the method of addition, as long as uniform contact can be achieved. For example, various methods such as atomizing an aqueous initiator solution by a spray method or a shearing method may be employed as appropriate. As the radical polymerization initiator, any of the various ones used in the production of polyacrylates, polyacrylamides, etc. can be used. Specific examples thereof include redox-based polymerization initiators made of a combination of a reducing agent such as an alkali metal sulfite, ammonium sulfite, or ammonium bisulfite, and a polymerization initiator such as an alkali metal persulfate or ammonium persulfate; Azobisisobutyronitrile, 4-t-butylazo-4'-cyanovaleric acid,
4,4'-azobis(4-cyano)valeric acid, 2,
A so-called azo polymerization initiator such as 2'-azobis(2-amidinopropane) hydrochloride, or a combination of two or more thereof can be appropriately selected. Among these, redox polymerization initiators consisting of a combination of ammonium persulfate and sodium bisulfite, and azo polymerization initiators such as azobisisobutyronitrile or 2,2'-azobis(2-amidinopropane) hydrochloride are particularly useful. etc. are suitable. The amount of radical polymerization initiator used is usually based on the amount of the hydrophilic polymer powder used.
0.05-10% by weight, preferably 0.1-2% by weight. If the amount is less than 0.05% by weight, it is not possible to effectively reduce the residual monomer in the powdered hydrophilic polymer, which is the object of the present invention.
In addition, if more than 10% by weight is used, the amount of hydrophilic polymer powder itself in the product will decrease accordingly, resulting in a disadvantage that the apparent performance, such as cohesive force, paper strength, and water absorption capacity, will decrease. be.

In the post-polymerization reaction process, it is necessary to maintain conditions necessary to initiate polymerization of the remaining monomers, and usually the temperature is 50 to 120°C and the heat retention time is 10 minutes to 3 hours.

In the present invention, post-drying may be carried out as necessary depending on the intended use, and water may be distilled out of the system under normal pressure to reduced pressure while or after the post-polymerization reaction. good.

Examples will be given below to explain the reduction method of the present invention in more detail, but the present invention is not limited to these examples. Note that parts and % represent parts by weight and % by weight, respectively.

Example 1 Acrylamide polymer powder (weight average molecular weight
Add 2.5 parts of hydrated silicon dioxide (Nippon Aerosil 200) to 100 parts of residual monomer content (relative to polymer weight: 2850 ppm), of which 80% or more has particle diameters of 100 to 200 μm, and mix with stirring. Ta. Next, the temperature inside the system was raised to 80°C, and then 10 parts of an aqueous solution of ammonium persulfate having a concentration of 5% was sprayed and uniformly added to the system while stirring, and the system was maintained at the same temperature for 15 minutes. After the contents were taken out and cooled, the acrylamide monomer remaining in the contents was quantified based on a residual monomer measurement method (high performance liquid chromatography measurement method, the same applies hereinafter). The result is
It was 310ppm.

Example 2 Acrylamide-dimethylaminoethyl methacrylate copolymer powder (weight ratio 90/10, weight average molecular weight 420000, particle size 100-200 μm)
% or more (residual monomer content (based on polymer weight) 3020 ppm) 100 parts of hydrated silicon dioxide (manufactured by Nippon Aerosil Co., Ltd., trade name Aerosil 200)
1.5 parts were added and mixed by stirring. After the temperature inside the system was raised to 80°C, 10 parts of a 3% potassium persulfate aqueous solution was sprayed and uniformly added to the system while stirring, and the system was maintained at the same temperature for 25 minutes. After the contents were taken out and cooled, both monomers remaining in the contents were quantified based on the residual monomer measuring method. The result was 480ppm.

Example 3 Acrylamide-acrylic acid copolymer powder (weight ratio 95/5, weight average molecular weight 350000, particle size
Residual monomer content (relative to polymer weight) 1970 ppm) 100, with 100 to 200 μm accounting for 80% or more
Part by weight is hydrated silicon dioxide (Nippon Aerosil Co., Ltd.)
3 parts of Aerosil 200 (trade name, manufactured by Manufacturer, Inc.) were added thereto, and the mixture was stirred and mixed. Then, after raising the temperature in the system until it reached 80°C, 10 parts of a 2% concentration 2,2'-azobis(2-amidinopropane) hydrochloride aqueous solution was sprayed and uniformly added under stirring, and the mixture was heated at the same temperature for 20 minutes. held. After the contents were taken out and cooled, both monomers remaining in the contents were quantified based on the residual monomer measurement method. The result was 330ppm.

Example 4 Commercially available water-absorbing resin powder (starch-acrylic acid graft copolymer, manufactured by Sanyo Chemical Co., Ltd., particle size 100 to 200μ)
Add 5 parts of hydrated silicon dioxide (manufactured by Nippon Aerosil Co., Ltd., trade name Aerosil 200) to 100 parts by weight (residual monomer content (relative to polymer weight) of 1,560 ppm), in which 80% or more of monomer m is present, and stir and mix. I did it. Then, after raising the temperature in the system until it reached 80℃,
Ammonium persulfate aqueous solution with a concentration of 5% under stirring10
was added uniformly by spraying and kept at the same temperature for 20 minutes. After the contents were taken out and cooled, the amount of acrylic acid monomer remaining in the contents was determined based on the following residual monomer measurement method. The result is 120ppm
It was hot.

Example 5 Polyacrylic acid-based water absorbent resin powder (particle size
Residual monomer content (relative to polymer weight) 1380 ppm) 100 with 100 to 200 μm accounting for 80% or more
Part by weight is hydrated silicon dioxide (Nippon Aerosil Co., Ltd.)
5 parts of Aerosil 200 (trade name, manufactured by Manufacturer, Inc.) were added thereto, and the mixture was stirred and mixed. Next, after raising the temperature in the system until it reached 80℃, 10 parts of ammonium persulfate aqueous solution with a concentration of 3% was sprayed and added uniformly under stirring, and the mixture was heated at the same temperature.
Hold for 20 minutes. After taking out the contents and cooling them,
The amount of acrylic acid monomer remaining in the contents was determined based on the residual monomer measurement method. The result is
It was 200ppm.

Example 6 Polyacrylic acid-based water absorbent resin powder (particle size
Residual monomer moisture content (relative to polymer weight) 1380 ppm) 100
Part by weight is hydrated silicon dioxide (Nippon Aerosil Co., Ltd.)
5 parts of Aerosil 200 (trade name, manufactured by Manufacturer, Inc.) were added thereto, and the mixture was stirred and mixed. Then, after raising the temperature in the system until it reaches 50°C, 5 parts of a 5% ammonium persulfate aqueous solution is sprayed and added uniformly while stirring, and then 3 parts of a 5% sodium bisulfite aqueous solution is sprayed and uniformly added. and held at the same temperature for 20 minutes.
After the contents were taken out and cooled, the amount of acrylic acid monomer remaining in the contents was determined based on the residual monomer measuring method. The result was 60ppm.

Example 7 Polyacrylic acid-based water absorbent resin powder (particle size
Content of 100-200 μm: 80% or more, residual monomer content (relative to polymer weight): 1380 ppm)
100 parts of hydrated silicon dioxide (manufactured by Nippon Aerosil Co., Ltd.,
17 parts of (trade name: Aerosil 200) were added and mixed by stirring. After the temperature of the system was raised to 80° C., 10 parts of an aqueous ammonium persulfate solution having a concentration of 4% was added to the system while stirring to make it uniform by spraying, and the system was maintained at the same temperature for 20 minutes. After the contents were taken out and cooled, the amount of acrylic acid monomer remaining in the contents was determined based on the residual monomer measuring method. The result was 210ppm.

Example 8 Polyacrylic acid-based water absorbent resin powder (particle size
Content of 100-200 μm: 80% or more, residual monomer content (relative to polymer weight): 1380 ppm)
100 parts of hydrated silicon dioxide (manufactured by Nippon Aerosil Co., Ltd.,
5 parts of Aerosil 200 (trade name) were added and mixed by stirring. Next, the temperature inside the system was raised to 80°C, and then 15 parts of ammonium persulfate with a concentration of 20% was added to the system while stirring to make it uniform by spraying, and the system was maintained at the same temperature for 20 minutes. After the contents were taken out and cooled, the amount of acrylic acid monomer remaining in the contents was determined based on the residual monomer measuring method. The result was 200ppm.

Example 9 Powder of acrylamide-acrylonitrile-dimethylaminoethyl methacrylate terpolymer (weight ratio: 50/40/10, weight average molecular weight: 400000,
Particle size: 100-200 μm content: 80% or more, residual monomer content (relative to polymer weight):
3.5 parts of hydrated silicon dioxide (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 200) was added to 100 parts (2900 ppm), and the mixture was stirred and mixed. Then, after raising the temperature inside the system until it reached 80°C, 10 parts of a potassium persulfate aqueous solution with a concentration of 5% was sprayed under stirring (it was added uniformly and kept at the same temperature for 25 minutes. The contents were taken out and cooled,
All monomers remaining in the contents were quantified based on the residual monomer measurement method. The result was 450ppm.

From the above results, the reduction method of the present invention can reduce the amount of residual monomer in the powdered hydrophilic polymer.
It can be seen that it is possible to significantly reduce the amount from about 1000 to 50000 ppm to about 50 to 500 ppm.

[Effects of the Invention] According to the reduction method of the present invention, more than 80% of the residual monomer in the hydrophilic polymer powder can be removed. It is possible to improve the performance of agents, water-absorbing resins, etc.

Claims (1)

[Scope of Claims] 1. When reducing the residual monomer in a hydrophilic polymer, a powder of the polymer and an inorganic powder are present under stirring and mixing, and an aqueous solution of a radical polymerization initiator is sprinkled thereon, A method for reducing residual monomers in a hydrophilic polymer, the method comprising heating the reaction system. 2 The hydrophilic polymer contains acrylic acid, methacrylic acid, acryloyloxyalkyl sulfonic acid, methacryloyloxyalkylsulfonic acid, acrylamide alkyl sulfonic acid, methacryamide alkyl sulfonic acid, alkali metal salts of these acids, and ammonia as the constituent components of the hydrophilic polymer. salts and organic amine salts, as well as acrylamide, methacrylamide, dimethylaminoalkyl acrylate, dimethylaminoalkyl methacrylate, dimethylaminoalkylacrylamide, dimethylaminoalkylmethacrylamide, diethylaminoalkyl acrylate, diethylaminoalkyl methacrylate, diethylaminoalkylacrylamide, diethylaminoalkylmethacrylamide and The reduction method according to claim 1, which contains 30% by weight or more of at least one monomer selected from the group consisting of vinylpyrrolidone. 3 The particle size of the hydrophilic polymer powder is
The reduction method according to claim 1 or 2, wherein the particle diameter is 20 to 2000 μm. 4. The reduction method according to claim 1, 2, or 3, wherein the inorganic powder is at least one selected from the group consisting of anhydrous silicon dioxide, hydrated silicon dioxide, aluminum oxide, and titanium oxide. 5. The reduction according to claim 1, 2, 3, or 4, wherein the amount of inorganic powder used is 0.1 to 20% by weight based on the amount of hydrophilic polymer powder used. Method.