Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-04-12
2003-11-04
Metzmaier, Daniel S. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C526S247000, C516S075000
Reexamination Certificate
active
06642307
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel process for preparing a fluorine-containing polymer, particularly a process for preparation characterized in that an emulsion prepared by applying a high shearing force is used when preparing the fluorine-containing polymer by emulsion polymerization.
BACKGROUND ART
For preparing a fluorine-containing polymer, various polymerization methods such as emulsion polymerization, suspension polymerization, solution polymerization and bulk polymerization have been employed. Among them, the emulsion polymerization method is widely used for preparing various fluorine-containing polymers from the points that a polymer having a fine particle size can be obtained as a product of polymerization reaction, a polymerization rate is high and a polymer having a high molecular weight can be obtained. Particularly in preparing a fluorine-containing elastomer by using perfluoro(alkyl vinyl ether), the emulsion polymerization method is used from the viewpoint of enabling a polymerization rate and molecular weight to become high.
For example, JP-A-61-223007 and JP-A-1-158002 describe processes for preparing a fluorine-containing elastomer by emulsion-polymerizing tetrafluoroethylene (TFE) and perfluoro(vinyl ether) having a perfluoro polyether group.
However perfluoro(vinyl ether) has a high molecular weight and a long chain and is inferior in polymerization reactivity and water solubility, and therefore is difficult to be introduced into an aimed polymer in a large amount.
In the preparation process described in the above-mentioned JP-A-61-223007, an aimed fluorine-containing elastomer is prepared by using an emulsifying agent having a perfluoro polyether group. Also in the preparation process of the above-mentioned JP-A-1-158002, an inorganic salt is added as an emulsification stabilizer.
Also in JP-A-62-288617, a process of preparing a sulfonic acid type perfluoro carbon by using an emulsifying equipment. In that publication, a perfluoro carbon monomer having sulfonic acid is emulsified in an amount up to ⅕ based on water by using an emulsifying agent in nearly the same amount as in conventional process to give monomer particles having a relatively large average particle size (460 nm at minimum) and then emulsion-polymerized.
However the emulsifying agent and inorganic salt described in the above publications remain in the prepared polymers, and have various influences on post-treatment steps and product quality. For example, in a field of production of semi-conductor, there is a problem with a contamination due to elution of an inorganic salt remaining in a fluorine-containing polymer used on an equipment and vessel, and also in a field of fluorine-containing elastomer, there is a problem with a vulcanization failure attributable to an emulsifying agent.
An object of the present invention is to provide a process for preparing a fluorine-containing polymer which makes it possible to carry out emulsion polymerization effectively by making an amount of emulsifying agent as small as possible and keeping a stable emulsified state without using an emulsification stabilizer.
DISCLOSURE OF INVENTION
Namely the preparation process of a fluorine-containing polymer of the present invention comprises a step for preparing an emulsion in which particles comprising a substance being substantially insoluble in water and being in the form of liquid at ordinary temperature at atmospheric pressure are dispersed and a step for polymerizing at least one of fluorine-containing ethylenic unsaturated monomers in the emulsion. The preparation process is characterized in that the liquid particles in the emulsion which are insoluble in water substantially comprise a polymerizable monomer or a mixture of a polymerizable monomer and a chain transfer agent, a weight of the liquid particles in the emulsion which are insoluble in water substantially is ¼ or more based on a weight of an aqueous medium in the emulsion and at least one of fluorine-containing ethylenic unsaturated monomers is in the form of gas at ordinary temperature at atmospheric pressure. A volume average particle size of the liquid particles being insoluble in water substantially is, for example, not more than 450 nm, preferably 30 to 350 nm, more preferably 80 to 250 nm.
In the present invention, in order to reduce an amount of emulsifying agent and obtain a stable emulsified state even if an emulsification stabilizer is not added, it is preferable to forcedly emulsify in the above-mentioned step for preparing the emulsion by applying a high shearing force on a mixture of the water insoluble liquid and water.
In the present invention, it is preferable that the step for preparing the emulsion comprises a pre-emulsifying step for preparing an emulsion containing the water insoluble liquid having a volume average particle size larger than 450 nm by pre-stirring in the presence of an emulsifying agent and a step for forcedly emulsifying the obtained pre-emulsified solution as it is with an emulsifying equipment to reduce the volume average particle size of the water insoluble liquid particles to not more than 450 nm, preferably 30 to 350 nm, more preferably 80 to 250 nm.
The emulsion obtained by the preparation step of the present invention is characterized in that the emulsion contains 10
13
to 10
17
particles of water insoluble liquid per 1 ml of water and an amount of the emulsifying agent is as small as 1×10
−6
mg or less per 10
5
particles of water insoluble liquid. By using the emulsifying agent in the amount mentioned above, the number of liquid particles (particles of monomer or a mixture of monomer and prepared polymer) does not change substantially throughout the polymerization step.
In the preparation process of the present invention, it is preferable that the fluorine-containing ethylenic unsaturated monomer in the form of gas at ordinary temperature at atmospheric pressure is at least one of tetrafluoroethylene, vinylidene fluoride, vinyl fluoride, hexafluoropropylene and perfluoro(alkyl vinyl ether) and that the above-mentioned water insoluble polymerizable liquid monomer is at least one of perfluoro(vinyl ethers) in the form of liquid at ordinary temperature at atmospheric pressure which are represented by the formula (I):
CF
2
═CFOR
f
(I)
wherein R
f
is a perfluoroalkyl group having 1 to 5 carbon atoms or a perfluoroalkyl (poly)vinyl ether group having 1 to 3 oxygen atoms and 3 to 12 carbon atoms.
Also it is preferable that the polymerization is carried out while decreasing a polymerization pressure so that a proportion of recurring units in polymer becomes constant.
The preparation process of the present invention is suitable particularly for preparation of a fluorine-containing elastomer having a glass transition temperature of not more than 25° C.
BEST MODE FOR CARRYING OUT THE INVENTION
At first the fluorine-containing polymer to be prepared by the preparation process of the present invention and a starting monomer are explained below.
The preparation process of the present invention is suitable for polymerization of a fluorine-containing ethylenic unsaturated monomer or a mixture of the fluorine-containing ethylenic unsaturated monomers, wherein at least one is in the form of gas at ordinary temperature (about 20° C.) at atmospheric pressure (about 1 atm). Examples of the fluorine-containing ethylenic unsaturated monomer in the form of gas at ordinary temperature at atmospheric pressure are, for instance, TFE, vinylidene fluoride (VdF), trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, hexafluoropropylene (HFP), pentafluoropropylene, perfluoro(methyl vinyl ether), and the like. Those monomers may be used solely, in a mixture of two or more thereof or in combination with other copolymerizable monomer mentioned below. Examples of the other copolymerizable monomer are, for instance, ethylene, propylene, and the like. Those copolymerizable monomers are introduced in the emulsion under pressure.
On the other hand, when the poly
Kishine Mitsuru
Kitaichi Masanori
Morikawa Tatsuya
Sogabe Toshio
Tanaka Yoshiyuki
Daikin Industries Ltd.
Metzmaier Daniel S.
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