Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2003-05-23
2004-11-16
Berman, Susan (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S084000, C522S085000, C522S062000
Reexamination Certificate
active
06818677
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a water-soluble polymer. In more detail, the present invention is a process for producing a water-soluble polymer by irradiating an aqueous solution of vinyl monomer with light. The production process of this invention allows an efficient and smooth production of a water-soluble polymer that is high in molecular weight, good in water-solubility and reduced in unreacted monomer (residual monomer) content. The water-soluble polymer obtained according to this invention can effectively be used for polymeric flocculants and other various applications because of the above-mentioned properties.
BACKGROUND ART
It has been widely practiced to irradiate an aqueous solution of vinyl monomer with light, for production of a water-soluble polymer. Especially, since high molecular weight water-soluble polymers are excellent in coagulation capability, they are widely used as polymeric flocculants for coagulation of various kinds of wastewater, and are also used for such applications as thickeners, paper sizing agents, paper strength agents, drainage agents, fiber-modifying agents and dyeing assistants. However, the water-soluble polymer produced by photopolymerization is apt to be high in unreacted monomer content. If a water-soluble polymer contains a large amount of unreacted monomer, for example, in use as a polymeric flocculant for treatment of wastewater, the wastewater obtained after the coagulation also contains a large amount of unreacted monomer to pose a problem of environmental pollution or the like. Furthermore, even when the water-soluble polymer high in unreacted monomer content is used for other applications, undesirable results often occur in terms of safety and others. From this point of view, a water-soluble polymer low in unreacted monomer content is demanded.
As processes for decreasing the unreacted monomer content of water-soluble polymers derived from vinyl monomers (hereinafter such polymers are also simply called “water-soluble polymer(s)”), have been proposed (i) a process for producing a water-soluble polymer by light irradiation using a benzyl dimethyl ketal as a photopolymerization initiator (JP-A-57-115409), (ii) a process for producing a water-soluble polymer by carrying out a first light irradiation step in a vessel with a depth of 50 mm or less under cooling using a benzoin alkyl ether or the like as a photopolymerization initiator, terminating the cooling, and carrying out a second light irradiation step a certain period of time after the termination of the cooling (JP-A-63-295604), (iii) a process for effecting polymerization in a vessel with a depth of 50 mm or less under light irradiation using a benzoin alkyl ether or the like as a photopolymerization initiator to produce a gelled polymer, and again exposing the surface of the gelled polymer that has been in contact with the inner wall of the vessel to light so that the monomer remaining on the surface of the gelled polymer is polymerized (JP-A-63-309501), (iv) a polymerization process which comprises a plurality of stages of irradiating an aqueous solution of vinyl monomer with light, in which the intensity of light is gradually increased in stages of the second and subsequent irradiation (JP-A-11-35612), (v) a process of producing a water-soluble polymer comprising the first step of irradiating an aqueous solution of vinyl monomer with a ray of light excluding a specific wavelength of light, and the second and subsequent steps of irradiating it with a ray of light including the above specific wavelength of light (JP-A-10-279615 and JP-A-10-298215), etc.
However, the above process (i) is liable to cause crosslinking reaction, thereby rendering the obtained water-soluble polymer to be insufficient in water-solubility, and is not always satisfactory in the effect of lowering the unreacted monomer content. Further, the processes (ii) and (iii) have some effect on decrease in unreacted monomer but are still insufficient, and also have a problem in that water-soluble polymers high in polymerization degree are not readily produced. The process (iv) requires the intensity of light to increase gradually in the second and subsequent stages for polymerization, thereby making the equipment and operation complicated undesirably. Moreover, the process (v) requires a filter for removing the light of a specific wavelength in the first light irradiation step, thereby making the equipment complicated and wasting light energy, and thus is not an efficient process. In addition, the process (v) is not desirable since the filter is extremely heated due to absorption of light energy, and there might be a risk of a fire in some cases.
Further, processes for photopolymerization of vinyl monomer using azo compounds as photopolymerization initiators are conventionally known (JP-B-53-22544, JP-B-57-19121, etc.). In such conventional processes using azo compounds, however, high molecular weight water-soluble polymers cannot readily be obtained, and thus these water-soluble polymers do not satisfactorily serve for such applications as flocculants.
Furthermore, known is a process for producing a water-soluble polymer, in which an aqueous solution of a cationic (meth)acrylate monomer containing a photopolymerization initiator such as benzoin, benzoin alkyl ether, benzyl, benzophenone and anthraquinones and another photopolymerization initiator composed of an azo compound, or a mixture of said cationic (meth)acrylate monomer with another vinyl monomer, is fed as a layer with a thickness of 3 to 18 mm onto a moving belt and is irradiated with light in the first and second steps at selected wavelengths and intensities, and then the resulting rubbery polymer sheet is taken from the moving belt, further irradiated with light, cut into small pieces and dried (JP-B-4-57682 and JP-B-7-10895). However, this process is apt to cause crosslinking reaction, thereby rendering the obtained water-soluble polymer to be insufficient in water-solubility, and is not sufficiently satisfactory in terms of decrease in unreacted monomer content.
The object of the present invention is to provide a process in which a water-soluble polymer that is high in molecular weight, good in water-solubility and low in unreacted monomer content is efficiently and smoothly produced.
DISCLOSURE OF THE INVENTION
To solve the above-mentioned problems, the inventors have intensively studied and, as a result, have found that a water-soluble polymer which is high in molecular weight, excellent in water-solubility and low in unreacted monomer content can be obtained by a production process of a water-soluble polymer comprising steps for irradiation of an aqueous solution of vinyl monomer with light, in which the first light irradiation step is carried out at a specific irradiation intensity, and subsequently the second or subsequent light irradiation step is carried out under a specific condition, whilst an azo compound with a 10-hour half-life decomposition temperature of 90° C. or lower is especially used as a photopolymerization initiator. Also, the inventors have found that, according to the above-mentioned specific production process, even when the light irradiation is carried out with a depth of the aqueous solution of vinyl monomer being kept at 50 mm or more, polymerization of the vinyl monomer can be achieved in the entire aqueous solution so as to efficiently and smoothly yield a water-soluble polymer high in molecular weight, excellent in water-solubility and low in unreacted monomer content. Based on these findings, the present invention has been completed.
That is, the present invention relates to (1) a process for producing a water-soluble polymer, including steps of irradiating a photopolymerization initiator-containing aqueous solution of vinyl monomer with light using an azo compound having a 10-hour half-life decomposition temperature of 90° C. or lower as the photopolymerization initiator, which comprises a first step of carrying out the light irradiation at an irradiation intensity of 0.
Gotoh Juichi
Ito Kenji
Miho Susumu
Tsuzuki Tetsuya
Berman Susan
Fitch Even Tabin & Flannery
Toagosei Co. Ltd.
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