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
1999-09-29
2003-06-03
Egwim, Kelechi (Department: 1713)
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...
C524S558000, C524S563000, C524S564000, C524S803000, C524S832000
Reexamination Certificate
active
06573327
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous solution of a partially hydrolyzed vinyl ester resin which does not cause phase separation, deposition, gelation and the like of the partially hydrolyzed vinyl ester resin in the aqueous solution and has an excellent stability.
BACKGROUND ART
Partially hydrolyzed vinyl ester resins having a degree of hydrolysis of at most 70% by mole have been widely utilized as primary dispersing agents or secondary dispersing agents for suspension polymerization of vinyl compounds (particularly vinyl chloride), binders, plasticizers or hot melt adhesives.
However, partially hydrolyzed vinyl ester resins having a degree of hydrolysis of at most 70% by mole, in particular alkalihydrolyzed vinyl ester resins having a degree of hydrolysis of at most 67% by mole, are completely insoluble in water. Therefore, when these resins are used for example as a secondary agent for suspension polymerization, in general they are added in the form of a powder or they are dissolved in a water-alcohol solvent or water-ketone solvent and then added. The former procedure is poor in charging workability and also the effects as the secondary agent are not sufficiently exhibited. The latter procedure may raise a problem of environmental pollution (increase of BOD and COD loads) owing to alcohol solvent.
In order to solve such problems, proposed is a method using an aqueous dispersion containing as a dispersoid a vinyl ester polymer having amino group, ammonium group, carboxyl group or sulfo group in the side chains (Japanese Patent Publication Kokai No. 4-154810). It is also proposed to use, as a dispersion stabilizer, one or more water-soluble polyvinyl alcohols prepared by partial solvolysis of polyvinyl acetate in an alcoholic solution containing an acid catalyst (Japanese Patent Publication Kokai No. 56-104912). The present applicant also proposed a dispersion stabilizer comprising a vinyl ester resin having an oxyalkylene group in the polymer side chains and a water-soluble high molecular compound (Japanese Patent Publication Kokoku No. 3-60321).
However, according to the technique disclosed in Japanese Patent Publication Kokai No. 4-154810, there is a case where its characteristics (improvement in porosity, uniformity of porosity distribution, monomer removability, plasticizer absorptivity and the like of obtained polymers of vinyl compounds) cannot be sufficiently exhibited, the reason of which is assumed to be that the pH range (3 to 8) of the polymerization system varies depending on the amount of a buffer used in the polymerization of vinyl compounds, the opportunity of charging the buffer, the oxygen concentration of the polymerization system and the like. Further, when used as a secondary agent for suspension polymerization of vinyl monomers, there arises a problem that the suspension polymerization becomes unstable to result in production of coarse particles of polymers, the cause of which is assumed to be that protective colloid characteristics of a primary agent are lowered by the secondary agent since the hydrophilic property becomes strong. The technique disclosed in Japanese Patent Publication Kokai No. 56-104912 has the disadvantages that if the degree of hydrolysis of the polyvinyl alcohol is less than 55% by mole, it is completely insoluble in water and is unsuitable, and if the degree of hydrolysis is from 55 to 60% by mole, the aqueous solution thereof is stable at a concentration as high as 30 to 40% by weight, but the polyvinyl alcohol is deposited when diluted to a concentration of less than 30% by weight. It has also the disadvantages that the aqueous solution is easy to cause phase separation into two layers when stored because of low cloud point and that it is poor in workability in handling. In case of the technique disclosed in Japanese Patent Publication Kokoku No. 3-60321, it is not possible to prepare an aqueous solution having a high resin concentration of not less than 30% by weight and, also, the storage stability is bad. Further, even in aqueous solutions having a low resin concentration, the resin may be deposited and, therefore, inconvenience is expected also when used as a secondary agent.
DISCLOSURE OF THE INVENTION
The present inventors have found, as a result of intensive study made in view of such circumstances, that an aqueous solution containing at most 50% by weight of a partially hydrolyzed vinyl ester resin which has a degree of hydrolysis of at most 70% by mole and which satisfies the equation (I):
1n
y
>0.042
x
+1.0 (I)
wherein y is a cloud point (° C.) of the 30% by weight aqueous solution thereof and x is the degree of hydrolysis (% by mole) thereof, is excellent in stability of aqueous solution even if diluted to a low concentration of not more than 30% by weight, to say nothing of under a high concentration, and is suitable for use as secondary agent for suspension polymerization, binders for various purposes, plasticizer and the like, and that particularly in case of using as a secondary agent for suspension polymerization, appearance of cloud point is suppressed (miscibility with water is good) when used at ordinary temperature and no deposition occurs even if the resin concentration of the aqueous solution is as low as not more than 30% by weight, thus the solution is particularly excellent in storage stability, and further that when such an aqueous solution is added as a secondary agent to a polymerization system for suspension polymerization of vinyl compounds, it is assumed that the secondary agent can immediately exhibit an oil solubility as a partially hydrolyzed vinyl ester resin since perhaps the secondary agent cannot sufficiently include water molecules at a concentration of less than 1% by weight, so it is adsorbed by or dissolved in the vinyl monomers and, therefore, polymerization products having excellent plasticizer absorptivity and monomer removability are obtained without being affected by the polymerization conditions such as amount of a buffer used in the polymerization of vinyl compounds and pH change in the polymerization system owing to oxygen concentration or the like of the polymerization system. Thus, the present inventors have accomplished the present invention.
In accordance with the present invention, there is provided an aqueous solution of a partially hydrolyzed vinyl ester resin having an excellent stability, characterized by containing a partially hydrolyzed vinyl ester resin having a degree of hydrolysis of at most 70% by mole in a concentration of at most 50% by weight, said partially hydrolyzed vinyl ester resin satisfying the equation (I):
1n
y
>0.042
x
+1.0 (I)
wherein y is the cloud point (° C.) of a 30% by weight aqueous solution of said partially hydrolyzed vinyl ester resin, and x is the degree of hydrolysis (% by mole) of said partially hydrolyzed vinyl ester resin.
BEST MODE FOR CARRYING OUT THE INVENTION
The partially hydrolyzed vinyl ester resins used in the present invention are not particularly limited so long as they have a degree of hydrolysis of at most 70% by mole, and the cloud point y (° C.) of a 30% by weight aqueous solution thereof and the degree of hydrolysis x (% by mole) thereof satisfies the equation (I):
1n
y
>0.042
x
+1.0 (I)
Preferably, the degree of hydrolysis of the partially hydrolyzed vinyl ester resins is from 0 to 60% by mole, especially from 20 to 60% by mole, more especially from 30 to 60% by mole. If the degree of hydrolysis exceeds 70% by mole, the monomer removability, uniformity of porosity distribution and improvement in plasticizer absorptivity of polymers of vinyl compounds obtained by suspension polymerization using the partially hydrolyzed vinyl ester resins as a secondary agent are insufficient. Also, the partially hydrolyzed vinyl ester resins are preferred to be those satisfying the equation (II):
1n
y
>0.042
x
+1.7 (II)
wherein y is the cloud point (° C.) of a 30% by weight aqueous solution thereof and x is the degree of hydrolysis (% by
Armstrong Westerman & Hattori, LLP
Egwim Kelechi
Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha
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