Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-05-30
2004-04-20
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S335000, C524S081000, C524S115000, C524S157000, C524S200000, C524S504000, C524S571000, C524S573000, C524S706000, C524S714000, C524S742000
Reexamination Certificate
active
06723764
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for preparing an enlarged latex having a larger particle diameter by enlarging a latex by aggregation, and more particularly to a process for preparing an enlarged latex, which is economical and high in productivity and permits enlarging a latex while retaining the stability of the latex. The present invention relates to a process for preparing a graft copolymer making use of such an enlarged latex, a resin composition containing the graft copolymer and a thermoplastic resin, etc.
BACKGROUND ART
A latex is an emulsion in which a polymer such as rubber or a plastic is dispersed in the form of colloid in water by an emulsifying agent. As synthetic latices, are prepared, for example, rubber latices such as styrene-butadiene rubber latices, acrylonitrile-butadiene rubber latices and polychloroprene rubber latices; and resin latices such as vinyl acetate (co)polymer latices, styrene (co)polymer latices and acrylic ester (co)polymer latices by emulsion polymerization. The latices are used in a wide variety of fields such as a field of synthetic resins, a field of paints, a field of treating agents of paper and fabrics and a field of civil engineering such as concrete and asphalt.
A latex is generally an emulsion in which a polymer having a fine particle diameter is dispersed. However, a latex having a larger particle diameter is required in many application fields as necessary for the end application intended. A graft copolymer obtained by polymerizing a vinyl monomer in the presence of a rubber latex is used as an impact modifier or the like for thermoplastic resins. In such graft copolymers, those having various particle diameters are chosen for use as necessary for the end application intended. In order to obtain a graft copolymer having a large particle diameter, a latex having a large particle diameter is preferably used.
A latex is generally prepared by an emulsion polymerization process. However, it takes a long polymerization time to obtain a latex having a large particle diameter by a seed polymerization process, so that productivity is lowered. In particular, when a diene monomer or a monomer mixture containing a diene monomer and a vinyl monomer will be polymerized by the seed polymerization process to obtain a latex having a large particle diameter, it takes a very long polymerization time. As a process for obtaining a latex having a large particle diameter in a short period of time, there has heretofore been proposed a process in which an inorganic acid, an organic acid, a salt, a polymeric flocculant and/or a latex for enlargement is added to a latex having a small particle diameter to enlarge the latex by aggregation.
For example, Japanese Patent Application Laid-Open No. 71603/1997 has proposed a process in which so mild shear as to produce no rubber lump is applied to a diene polymer rubber latex obtained by emulsion polymerization to enlarge the latex by aggregation mainly by virtue of Brownian aggregation while facilitating mixing of a flocculant. The Brownian aggregation means that latex particles undergo Brownian movement, thereby colliding with one another to aggregate. More specifically, the process comprises lowering the number of revolutions upon stirring in enlargement of the latex by aggregation making use of the flocculent to conduct aggregation mainly by virtue of Brownian movement, thereby inhibiting the formation of aggregated lumps to enlarge the latex by aggregation. This process uses shear aggregation by a stirring blade and Brownian aggregation in combination. According to this process, particles of the latex can be enlarged to a certain extent. However, the particles cannot be enlarged to a sufficient extent judging from Examples thereof. In addition, in this process, an acid is used as a flocculant, and the flocculant is added so as to keep the pH of the system at 5 or lower. When it is intended to raise the pH of the system by adding a basic substance to the enlarged latex obtained by this process so as to stabilize the latex, however, the stability of the latex becomes insufficient due to a high salt concentration in the system. Therefore, when graft polymerization of a vinyl monomer has been attempted in the presence of said latex, a problem that deposit is easy to be formed has arisen.
Japanese Patent Publication No. 2229/1969 has proposed a process in which a formaldehydesulfoxylate and a peroxide are added to an aqueous dispersion containing fine particles of a butadiene polymer to enlarge the particles while causing graft polymerization to progress by adding a monomer to the dispersion. According to this process, however, it is difficult to enlarge the particles to a sufficient extent.
Japanese Patent Application Laid-Open No. 45921/1981 has proposed a process in which an acrylic ester-unsaturated acid copolymer latex obtained by polymerization in the presence of an anionic surfactant and having a pH of 4 or higher is added to a synthetic rubber latex the pH of which has been adjusted to 7 or higher, thereby enlarging the particle diameter of the synthetic rubber latex. According to this process, however, it is necessary to separately prepare the latex for enlargement. Therefore, this process is complicated in operation and not preferable from the economical point of view. In addition, when graft polymerization of a vinyl monomer has been attempted in the presence of the synthetic rubber latex enlarged by adding such an acrylic ester-unsaturated acid copolymer latex, a problem that the stability of the latex is impaired to form aggregated lumps has arisen.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a process for preparing an enlarged latex, which is economical and high in productivity and permits enlarging a latex while retaining the stability of the latex.
Another object of the present invention is to provide a process for preparing an enlarged latex the stability of which is not impaired even when a polymerizable monomer is graft polymerized in the presence of the enlarged latex.
A further object of the present invention is to provide an enlarged latex having such excellent various properties, a process for preparing a graft copolymer by polymerizing a polymerizable monomer in the presence of such an enlarged latex, a resin composition containing the graft copolymer and a thermoplastic resin, and a graft copolymer (latex, slurry or particles) having an even particle diameter distribution.
The present inventors have carried out an extensive investigation with a view toward achieving the above objects. As a result, it has been conceived to cause an anionic surfactant and a cationic surfactant and/or an amphoteric surfactant to exist in a latex and add an acid or a substance capable of forming an acid as an aggregating and enlarging agent thereto to cause the acid to act, thereby enlarging the particle diameter of the latex.
When the pH of a latex stabilized by an anionic surfactant is lowered by an acid, the primary particles of the latex are aggregated and enlarged. However, the stabilizing effect by the anionic surfactant becomes weak as the pH is lowered, so that the stability of the latex tends to be impaired. On the other hand, when an anionic surfactant and a cationic surfactant and/or an amphoteric surfactant are caused to exist in a latex, (1) the system is stable by virtue of the stabilizing effect by the anionic surfactant when the pH is high, (2) the stabilizing effect by the anionic surfactant is weakened when the pH is lowered by an acid, so that aggregation and enlargement of latex particles occur, and (3) the system is stabilized again by virtue of the stabilizing effect by the cationic surfactant and/or the amphoteric surfactant when the pH is more lowered. As a result, a stabilized enlarged latex can be obtained. Even when the stabilized enlarged latex is used in a graft polymerization reaction, the stability of the system is not impaired.
When the lowering of the pH in this process is conducted by using a combination of at lea
Rohm and Haas Company
Sanders Kriellion A.
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