Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-04-12
2002-04-23
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C428S543000, C428S702000, C428S703000
Reexamination Certificate
active
06376580
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cement retarder (a cement-hardening retardant), a method for retarding the hardening or setting of a cement using the cement retarder, a cement retardative sheet as produced using the retarder, a decorative (dressing) kit sheet comprising the cement retardative sheet, and a method for producing a dressing-finished concrete product with using the cement retardative sheet or the decorative kit sheet.
BACKGROUND OF THE INVENTION
A cement retarder is a kind of a cement admixture (a cement additive) and used for retardation of a hydration reaction of a cement, thereby retarding the setting or hardening of a mortar or concrete.
As disclosed in Japanese Patent Application Laid-open No. 172250/1989 (JP-A-1-172250), conventional cement retarders can be roughly classified into two categories, organic cement retarders and inorganic cement retarders. The inorganic retarders include lead oxide, boron oxide, borax, zinc chloride, zinc oxide, magnasium silicofluoride and the like. The organic retarders include sugar, a salt of an oxycarboxylic acid, a salt of lignosulfonic acid, gluconic acid or its salt, pyruvic acid, &agr;-ketoglutaric acid and other keto acids and so on. These cement retarders are used mainly for longer hours of transportation of ready-mixed concrete in the summer season and for mitigation of stress in a large-sized concrete structure due to the retained heat.
The surfaces of concrete products and various buildings are frequently decorated by means of washing (washing finish) technology of plastering technologies. The washing finish technology comprises washing a surface of a concrete product with water just before the hardening of a cement, so that the mortar on the concrete surface can be washed out, thereby exposing a part of aggregates on the surface. The washing operation has to be carried out in a strictly limited time period, because the timing for the washing operation is closely linked to the rate of the concrete hardening.
Concrete products produced by the precast technology are prevailing these days, and a wall member (a wall material), a concrete slab for pavement decoration and the like decorated by washing-finishing are manufactured in the factories. Regrettably, it is difficult to conduct a timely washing operation, although the rationalisation of production steps is of significant importance for this industry. Therefore, it is advantageous if the moulding step of the concrete slab and the washing step of the cement can be separated, so that the washing step can be operated irrespective of the hardening or setting degree of the cement.
By applying a cement-hardening retarder, which is a kind of a cement admixture (a cement additive), on the surface of a concrete product for retardation of the hardening of the concrete surface layer, the concrete surface can be washed out for decoration, regardless of the hardening rate of the cement. By way of illustration, Japanese Patent Application Laid-open No. 47725/1994 (JP-A-6-47725) suggests a process which comprises the steps of coating the inner surface of a mould with an aqueous solution containing a conventional cement retarder and a thickener in advance, depositing (casting) a concrete in the mould, removing the hardened article therefrom and washing out the surface of the article. Japanese Patent Application Laid-open No. 71412/1973 (JP-A-48-71412) and Japanese Patent Application Laid-open No. 141020/1979 (JP-A-54-141020) disclose the use of a conventional cement retarder which is impregnated in a sheet or paper.
The above cement retarders serve for retardation of cement hardening, the effect of which is lost in a relatively short period. It is, therefore, difficult to improve the productivity of a concrete product by separating the washing step completely from the cement moulding step.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a cement retarder (a cement-hardening retardant) whose high hardening-retarding properties (hardening-retardancy) can last for a long period, and a method for retarding the hardening or setting of a cement using this cement retarder.
Another object of the present invention is to provide a cement retarder which insures precise formation of decorative patterns on the surface of a concrete product by means of the washing-finish technology, and a method for retarding the hardening or setting of a cement using this cement retarder.
It is a further object of the present invention to provide a cement retardative sheet (a cement-hardening retarding sheet) which can retain high hardening-retarding properties or hardening-retardancy for a prolonged period of time and be useful for formation of decorative patterns on a predetermined position.
Another object of the present invention to provide a decorative (dressing) kit sheet used for simple and precise formation of a decorative pattern at a predetermined position.
Yet another object of the present invention is to provide a method for producing a dressing-finished (faced) concrete product (a decorated concrete product), which method insures excellent productivity, and according to which a decorative pattern is formable with high precision on the surface of the concrete product.
The inventors of the present invention have been devoted to the realisation of the above objects, and found that a cement retarder comprising a copolymer (a macromolecule) of plural specific components not only exhibits improved hardening-retardancy for a cement for a long period, but also prevents fluidisation or washout of the cement retarder by water. The present invention is based on the above findings.
The cement retarder of the present invention comprises a polymer having an anionic group which can form a chelate with a divalent metal ion and a hydrophilic segment. The anionic group of the cement retarder may comprise at least one species selected from the group consisting of an acid anhydride group, a carboxyl group and a sulfonic acid group, e.g. a succinic acid residue. The hydrophilic segment includes a segment represented by the formula —O—(R
1
O)
n
—R
2
, for instance, a segment comprising a (poly)oxy-C
2-4
alkylene unit, wherein R
1
represents a C
2-4
alkylene group, and R
2
stands for a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or an acyl group, n being an integer of 0 to 100.
The polymer constituting the cement retarder may be a copolymer of a monomer mixture containing a polymerizable compound having the anionic group and a polymerizable compound having the hydrophilic segment. The polymerizable compound having the anionic group may not necessarily be a polymerizable monomer having the anionic group, but also be a polymerizable monomer which can generate the anionic group, a polymerizable macromolecule having the anionic group or a polymerizable macromolecule which can generate the anionic group. The copolymer may be either of a copolymer having a polymerizable monomer unit having an acid anhydride group or a carboxyl group and a polymerizable monomer unit having a (poly)oxyalkylene segment, or a copolymer having a unit of maleic acid, its ester or maleic anhydride and a polymerizable monomer unit having a (poly)oxyalkylene segment. The copolymer may further have another copolymerizable monomer unit.
The method of the present invention also includes a method for retarding (hindering) the hardening of a cement by using a polymer comprising an anionic group which can form a chelate with a divalent metal ion, and a hydrophilic segment.
The present invention further includes a cement retardative sheet, at least one surface of which is applied (coated or impregnated) with the cement retarder. This cement retardative sheet may comprise a sheet formed with the cement retarder, or a sheet comprising a base sheet containing (retaining or holding) the cement retarder. The surface of the cement retardative sheet may be imparted with tacky adhesive (pressure-sensitive adhesive) properties.
The decorative kit sheet of the pr
Arita Hiroaki
Ikuta Toru
Birch & Stewart Kolasch & Birch, LLP
Daicel-Huels Ltd.
Lipman Bernard
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