Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-09-27
2003-10-07
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S062000, C521S063000
Reexamination Certificate
active
06630519
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for producing a porous polymer having continuous cells (hereinafter referred to occasionally as “open cells”) having through holes formed in both the surface and the interior thereof by polymerizing a water-in-oil type high internal phase emulsion (hereinafter referred to occasionally as “HIPE”), and more particularly to a method for producing the porous polymer by polymerizing (curing) the HIPE in a very short period.
The porous polymer of this invention can be extensively utilized as (1) liquid absorbents; such as {circle around (1)} cores of disposable diapers, i.e. absorbents for such body fluids as urine and blood and {circle around (2)} treating agents for waste water and spent oil and treating agents for waste solvents, i.e. absorbents for water, aqueous liquids, oils, and organic solvents, (2) energy absorbents, such as sound insulators and heat insulators for automobiles and buildings, i.e. absorbents for sound and heat and (3) carrier for chemicals, such as household goods impregnated with aromatics, detergents, polishing agents, surface protecting agents, and flameproofing agents.
BACKGROUND ART
The term “HIPE” refers to such an emulsion as has a water phase, namely the dispersed phase (internal phase), and an oil phase, namely the external phase, at a ratio (W/O ratio) of not less than about 3/1. The fact that a porous polymer is produced by the method of polymerizing this HIPE has been known to the art. The porous polymer produced from the HIPE is excellent because it tends to grow into a porous polymer of low density possessed of open cells of a fine diameter, whereas the porous polymer produced by using a foaming agent without being converted into the HIPE tends to grow into a porous polymer possessed of closed cells of a comparatively large diameter.
Methods for producing a porous polymer from the HIPE are disclosed in JP-A-57-98713, JP-A-62-50002, U.S. Pat. No. 5,210,104, U.S. Pat. No. 5,252,619, U.S. Pat. No. 5,189,070, and U.S. Pat. No. 5,358,974, for example.
JP-A-57-98713 and JP-A-62-50002 disclose a method which comprises preparing the HIPE containing a water-soluble and/or oil-soluble polymerization initiator and thermally polymerizing this HIPE at a temperature in the range of 50° C. to 60° C. for a period in the range of 8 hours to 72 hours. U.S. Pat. No. 5,210,104 discloses a method which comprises preparing an HIPE and subsequently adding a polymerization initiator thereto, U.S. Pat. No. 5,252,619 discloses a method which comprises preparing an HIPE containing a polymerization initiator and then polymerizing the HIPE at a temperature of not lower than 90° C., and U.S. Pat. No. 5,189,070 discloses a method which comprises forming a gel possessing a prescribed dynamic shear modulus from an emulsion at a temperature of 20—not higher than 65° C. and subsequently polymerizing the gel at a temperature of not lower than 70° C. Then, U.S. Pat. No. 5,358,974 discloses a method which comprises polymerizing an HIPE by the use of an alkyl peroxy dicarbonate branched from the carbon atom at the 1 position, namely an oil-soluble polymerization initiator.
The methods which are disclosed in JP-A-57-98713, JP-A-62-50002, and U.S. Pat. No. 5,358,974, however, are not good in production efficiency because they require long period for polymerization. Though the polymerization carried out at such high temperatures as described in U.S. Pat. No. 5,252,619 and U.S. Pat. No. 5,189,070 can be completed in comparatively short period, it still requires about several hours. The stability of the HIPE decreases under certain condition, and liberation of a large quantity of water tends to occur. As a result, a porous polymer having a prescribed pore diameter cannot be obtained. Further, U.S. Pat. No. 5,210,104 contains a statement to the effect that since the polymerization initiator is added after the preparation of the HIPE, the stability of the emulsification of the HIPE is indeed improved, but the polymerization requires several hours.
The present inventors have pursued a diligent study emphatically on the polymerization time of the HIPE with a view to developing a method for producing by the HIPE method a porous polymer in a very short period and have consequently found a method for shortening the polymerization time to a very short period such as, for example, not more than 30 minutes and preferably not more than 10 minutes by elevating the temperature of an emulsified HIPE at a specific rate of temperature increase (refer to International Publication of Unexamined Patent Application WO 01/27164).
It has been made clear, however, that when a specific HIPE such as, for example, an HIPE possessing such a low viscosity as not more than 500 mPa second is polymerized by following this method and/or when a porous polymer having such a large number-average pore diameter as not less than 80 &mgr;m, the use of this method will not greatly shorten the polymerization time and, on the contrary, will have the possibility of decreasing the stability of the HIPE, making it impossible to obtain a porous polymer having a prescribed pore diameter, and suffering the HIPE to undergo phase separation till collapse.
An object of this invention, therefore, is to solve the technical problem described above and provide a method for the production of a porous polymer by the polymerization of an HIPE, and more particularly to provide a method for producing the porous polymer within such a very short period as, for example, not more than 30 minutes and preferably not more than 10 minutes even in the production of a porous polymer of a large pore diameter from an HIPE possessing such a low viscosity as not more than 500 mPa second
DISCLOSURE OF THE INVENTION
When a water-soluble polymerization initiator is singly used in the polymerization of an HIPE, since the polymerization initiator is decomposed to generate a radical in the water phase of the HIPE, the polymerization reaction proceeds from the interface between the water phase and the oil phase and gradually advances toward the interior of the oil phase. Thus, the rate of polymerization increases in proportion as the distance to the interface between the oil phase and the water phase decreases and the strength of the pores in the porous polymer is high at the surface parts of the pores. The porous polymer, therefore, is characterized by having improved texture.
As a means to shorten the polymerization time, the method of heightening the radical concentration in the polymer system is conceivable. In the case of producing a porous polymer having such a small number-average pore diameter as falling short of 80 &mgr;m by polymerizing an HIPE with a higher viscosity than 500 mPa·second, since the emulsion of an HIPE with a high viscosity generally has a small particle diameter, this method can shorten the polymerization time with no conspicuous variation when a water-soluble polymerization initiator is singly used, when an oil-soluble polymerization initiator is singly used, or when a water-soluble polymerization initiator and an oil-soluble polymerization initiator are used in combination.
In the case of producing a porous polymer having such a large number-average pore diameter as exceeding 80 &mgr;m by polymerizing an HIPE with a lower viscosity than 500 mPa·second, however, since the emulsion generally has a large particle diameter, the area of the interface between the water phase and the oil phase is decreased. When the HIPE is polymerized by using a water-soluble polymerization initiator singly as mentioned above, therefore, since the rate of transfer of a radical from the water phase to the oil phase is restrained, the efficiency of the polymerization initiator, namely the quantity of radical generated that is consumed in the reaction of polymerization, is markedly degraded. It has been made clear that the rate of polymerization of the HIPE is consequently lowered markedly.
It is in consideration of the fact mentioned above that this invention has been perfected. To be specific, this invention co
Fujimaru Hirotama
Kadonaga Kenji
Minami Kenji
Nagasuna Kinya
Fish & Richardson P.C.
Foelak Morton
Nippon Shokubai Co. , Ltd.
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