Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-04
2003-09-30
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C106S728000, C525S384000
Reexamination Certificate
active
06627703
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to air content stabilizing agents for hydraulic cement compositions (herein referred to simply as “air content stabilizing agents”) and hydraulic cement compositions containing such agents. When a prepared hydraulic cement composition such as concrete or mortar is transported while being kneaded either continuously or intermittently or is being stored temporarily, the entrained air content tends to increase with time. This invention relates more particularly to air content stabilizing agents for inhibiting such an increase with time in the entrained air content and stabilizing it with time, as well as hydraulic cement compositions containing such agents.
When a hydraulic cement composition is prepared, a cement dispersant (such as polycarboxylic acid cement dispersant, in particular, recently), an antifoaming agent and an agent for controlling air content such as an air entraining agent are mixed together in addition to cement, aggregates and water to be kneaded together. When a hydraulic cement composition is transported while being kneaded continuously or intermittently or is stored temporarily, however, there is the problem that its entrained air content increases with time. If the entrained air content increases, the strength of hardened objects produced from such a hydraulic cement composition is lowered. Japanese Patent Publications Tokkai 7-157348 and 9-183642 and U.S. Pat. Nos. 4,808,641 and 4,948,429 have disclosed additives for stabilizing the entrained air content of hydraulic cement compositions but these additives are not capable of addressing this problem satisfactorily, and some of them even have an adverse effect on the fluidity of hydraulic cement compositions.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide air content stabilizing agents which are capable of inhibiting the increase in the entrained air content of a prepared hydraulic cement composition being transported while being kneaded continuously or intermittently or being temporarily stored and stabilizing its entrained air content without adversely affecting its fluidity.
It is another object of this invention to provide hydraulic cement compositions containing such an air content stabilizing agent.
This invention is based on the discovery by the present inventors as a result of their diligent researches in view of the objects described above that a graft copolymer of a certain kind should be used as an air content stabilizing agent.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to air content stabilizing agents characterized as comprising graft copolymers obtained by the following two steps which are herein referred to as the “first step” and the “second step”. The first step is a step of obtaining copolymers with average numerical molecular weight 5000-50000 by radical polymerization of a mixture of radical polymerizable monomers containing anhydrous maleic acid and monomers of the form given by Formula 1 below, together in an amount of 80 molar % or more and at molar ratio of 40/60-60/40; the second step is a step of obtaining the graft copolymers by a graft reaction of 100 weight parts of the copolymers obtained in the first step and 7-60 weight parts of polyoxyalkylene monoalkylether and/or polyoxyalkylene monoalkenylether with a block addition of a total of 23-70 moles of ethylene oxide and propylene oxide per 1 mole of aliphatic alcohol with 8-20 carbon atoms:
CH
2
═CH—CH
2
—O—A—O—R (Formula 1)
where R is hydrogen, methyl group or a residual group obtained by removing the hydroxyl group from aliphatic acid with 1-18 carbon atoms, and A is a residual group obtained by removing all hydroxyl groups from (poly)alkylene glycol with repetition number 1-80 of oxyalkylene units consisting either only of oxyethylene units or of both oxyethylene units and oxypropylene units.
The invention also relates to hydraulic cement compositions characterized not only as comprising cement, aggregates, water, a cement dispersant and an agent for controlling air content, but also wherein an air content stabilizing agent of this invention as described above is contained in an amount of 0.001-0.5 weight parts per 100 weight parts of cement.
Air content stabilizing agents of this invention will be explained first. The air content stabilizing agents of this invention are characterized as comprising graft copolymers obtained by the aforementioned first and second steps. The first step is for obtaining copolymers by radical polymerization of a mixture of radical polymerizable monomers. According to this invention, the first step uses a mixture containing anhydrous maleic acid and monomers of Formula 1, together in an amount of 80 molar % or more and at a molar ratio of 40/60-60/40, and preferably 55/45-45/55.
Examples of what A may be in Formula 1 include (1) residual groups obtained by removing all hydroxyl groups from (poly)ethylene glycol of which oxyalkylene units consist only of oxyethylene units, and (2) residual groups obtained by removing all hydroxyl groups from (poly)ethylene (poly)propylene glycol of which oxyalkylene units consist of both oxyethylene units and oxypropylene units. In the case of (2), the combination of oxyethylene units and oxypropylene units may be by random addition, block addition or by both, but examples of type (1) are preferred. The repetition number of the oxyalkylene units in A is 1-80, but it is preferably 10-50.
Examples of what R may be in Formula 1 include hydrogen, methyl group and residual groups obtained by removing the hydroxyl group from aliphatic acid with 1-18. Among these, methyl group and acetyl group are preferred.
Practical examples of monomers, shown by Formula 1 explained above, include (1) &agr;-allyl-&ohgr;-hydroxy-(poly)oxyethylene, (2) &agr;-allyl-&ohgr;-methyl-(poly)oxyethylene, (3) &agr;-allyl-&ohgr;-alkyloyl-(poly)oxyethylene, (4) &agr;-allyl-&ohgr;-hydroxy-(poly)oxyethylene (poly)oxypropylene, (5) &agr;-allyl-&ohgr;-methyl-(poly)oxyethylene (poly)oxypropylene, and (6) &agr;-allyl-&ohgr;-alkyloyl-(poly)oxyethylene (poly)oxypropylene.
The mixture of radical polymerizable monomers in the first step contains anhydrous maleic acid and monomers of Formula 1 together in an amount of 80 molar % or more. In other words, radical polymerizable monomers of other types may be contained in an amount of 20 molar % or less. Examples of radical polymerizable monomers of such other types include styrene, vinyl acetate, acrylic acid, acrylic acid alkyl esters, (meth)allyl sulfonic acid and (meth)allyl sulfonic acid salts. Among these, styrene is preferred.
In the first step, a radical initiator is added to the mixture described above to cause radical polymerization and to obtain copolymers with average numerical molecular weight (hereinafter Pullulan converted by GPC method) of 5000-50000, or preferably 10000-40000. Any of known radical polymerization methods may be used for this purpose, such as (1) methods of radical polymerization of a mixture of radical polymerizable monomers without the use of a solvent and (2) methods of radical polymerization by dissolving a mixture of radical polymerizable monomers in a solvent such as benzene, toluene, xylene, methyl isobutyl ketone and dioxyane. Of the above, methods according to (1) are preferred, and it is more preferred to obtain copolymers with average numerical molecular weight of 10000-40000 by a method of (1). A method of (1) may be carried out by placing a mixture of polymerizable monomers in a reactor can and adding a radical initiator in a nitrogen atmosphere to cause a radical polymerization reaction at 60-90° C. for 5-10 hours. Methods of (1) without the use of a solvent are advantageous in that cumbersome steps of collecting and refining the solvent which has been used can be dispensed with. In order to obtain desired copolymers by controlling the radical polymerization reaction either by a method of (1) without using a solvent or by a method of (2) by using a solvent, kinds and amounts of radical initiator and ra
Kinoshita Mitsuo
Tamaki Shinji
Beyer Weaver & Thomas LLP
Lipman Bernard
Takemoto Yushi Kabushiki Kaisha
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