Chemistry of inorganic compounds – With additive
Reexamination Certificate
2000-08-15
2003-07-15
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
With additive
C423S636000, C423S274000
Reexamination Certificate
active
06592834
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-purity calcium hydroxide having fine particles and a high dispersibility in a resin, a process for the production thereof and a calcium hydroxide-containing resin composition containing said calcium hydroxide as an active ingredient for an acid-capturing agent. More specifically, it relates to calcium hydroxide which can work as a heat stabilizer for a resin, prevent the occurrence of dioxin or the like, prevent the corrosion of a processing machine or impart antifungal properties owing to the capture of an acid substance such as hydrochloric acid, generated from a resin or garbage at a processing or burning time, at high yields by incorporating a high-purity calcium hydroxide having fine particles and a high dispersibility, as an active ingredient, into a resin such as polyvinyl chloride or polyethylene, a process for the production thereof and a calcium hydroxide-containing resin composition containing said calcium hydroxide as an active ingredient for an acid-capturing agent.
2. Description of the Prior Art
A conventional calcium hydroxide has large primary particles (crystal) as large as about 1 &mgr;m to several &mgr;m, and these particles agglomerate strongly to form large secondary particles (the average secondary particle diameter at a cumulative percentage of 50% is about 4 to 20 &mgr;m). Further, the above calcium hydroxide is very unstable, and it has the problem that the calcium hydroxide is easily reacted with a carbonic acid gas in the air to convert to calcium carbonate. When the conventional calcium hydroxide is added in a resin, therefore, the calcium hydroxide is remarkably poor in dispersibility in the resin. For example, when a resin composition containing the calcium hydroxide is molded to a film, the surface of the film is rough, and further, the film is colored to have a puce color due to large amounts of impurities such as Fe or Mn. Further, the reactivity of the calcium hydroxide with an acid such as hydrogen chloride generated from polyvinyl chloride is impaired since the primary particles and the secondary particles are large. Therefore, a corresponding amount of the calcium hydroxide should be further added to the resin. When the amount of the calcium hydroxide increases, inherent properties of a resin are impaired, which extremely decreases a value as a commodity product.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fine-particle, high-dispersibility and high-purity calcium hydroxide of which the primary particles and secondary particles are fine, and which is prevented from converting to calcium carbonate, and a process for the production thereof.
It is another object of the present invention to provide a calcium hydroxide (acid-capturing agent)-containing resin composition which has a high dispersibility, a high purity and high whiteness and which is excellent in the appearance of a molded article, mechanical strength, thermal stability, antifungal properties and acid-capturing properties.
According to the present invention, there is provided a calcium hydroxide in which the average secondary particle diameter at a cumulative percentage of 50% by number in a particle size distribution is 2.0 &mgr;m or less, preferably 0.1 to 1.5 &mgr;m, particularly preferably 0.5 to 1.1 &mgr;m, and the BET specific surface area is 7 to 20 m
2
/g, preferably 8 to 20 m
2
/g, more preferably 9 to 18 m
2
/g, particularly preferably 10 to 15 m
2
/g. According to the present invention, there is provided a calcium hydroxide which is surface-treated with 0.1 to 10% by weight, preferably 0.5 to 5% by weight, more preferably 1 to 5% by weight, of an anionic surfactant.
According to the present invention, further, there is provided a calcium hydroxide-containing resin composition obtained by incorporating 0.1 to 100 parts by weight, preferably 0.2 to 50 parts by weight, particularly preferably 0.5 to 20 parts by weight, of said calcium hydroxide as an active ingredient into 100 parts by weight of a synthetic resin.
According to the present invention, further, there is provided a process for the production of the calcium hydroxide as recited above, comprising adding a water-soluble calcium salt aqueous solution to an aqueous solution containing at least one equivalent of alkali metal hydroxide to calcium with stirring, allowing the mixture to react at 30 to 90° C., preferably 40 to 90° C., then aging the resultant mixture at 40 to 120° C., preferably 40 to 80° C., for preferably about 0.1 to 2 hours to synthesize calcium hydroxide, and then adding an aqueous solution of an anionic surfactant in an amount of 0.1 to 10% by weight based on the calcium hydroxide at a temperature where the anionic surfactant is soluble or at a higher temperature with stirring, to surface-treat the calcium hydroxide.
According to the present invention, further, there is provided a process for the production of the calcium hydroxide as recited above, comprising wet-pulverizing a slaked lime obtained by slaking a quicklime (calcium oxide) having small contents of impurities such as silicone dioxide, alumina and ferric oxide (Fe
2
O
3
), then adding an anionic surfactant to the wet-pulverized slaked lime in a water medium with stirring to surface-treat the slaked lime, or adding the anionic surfactant before the wet-pulverization and carrying out the wet-pulverization and the surface-treatment at the same time.
DETAILED DESCRIPTION OF THE INVENTION
In the calcium hydroxide used in the present invention, the secondary particles of the calcium hydroxide are required to be fine particles, and therefore, the primary particles of the calcium hydroxide are also required to be fine particles. These states of the primary and secondary particles make it possible to give a good appearance of a molded article and to improve various properties such as mechanical strength and high acid-capturing properties.
Concerning the primary particles, at least the average particle diameter thereof is 1 &mgr;m or less, preferably 0.5 &mgr;m or less. The average particle diameter of the primary particles is measured by a scanning electron microscope (SEM) method. The secondary particles are ultrasonically treated in an isopropyl alcohol solvent for five minutes to be dispersed, and then, the average particle diameter of the secondary particles is determined by a particle size distribution measured by a laser diffraction method. The average secondary particle diameter at a cumulative percentage of 50% by number in the particle size distribution is 2.0 &mgr;m or less, preferably 0.1 to 1.5 &mgr;m, particularly preferably 0.5 to 1.1 &mgr;m. Concerning the secondary particles, besides the above definition in case of the cumulative percentage of 50% by number, the average secondary particle diameter at a cumulative percentage of 90% by number is preferably 8 &mgr;m or less, more preferably 5 &mgr;m or less, furthermore preferably 4 &mgr;m or less, particularly preferably 2 &mgr;m or less.
The BET specific surface area almost corresponds to the size of the primary particles. The BET specific surface area of the calcium hydroxide of the present invention is 7 to 20 m
2
/g, preferably 8 to 20 m
2
/g, more preferably 9 to 18 m
2
/g, particularly preferably 10 to 15 m
2
/g. When the BET specific surface area is larger than 20 m
2
/g, the calcium hydroxide is likely to agglomerate and the viscosity of a resin becomes too high so that it is difficult to knead a resin composition containing the calcium hydroxide and the moldability of the resin composition is deteriorated. Conversely, when the BET specific surface area is smaller than 7 m
2
/g, the primary particles become too large so that activities such as acid-capturing properties are decreased.
The calcium hydroxide used in the present invention may be produced by the following two methods. In the first method, the calcium hydroxide can be produced by adding an aqueous solution of a water-soluble calcium salt such as calcium chloride or calcium nitrate int
Bos Steven
Kabushiki Kaisha Kaisui Kagaku Kenkyujo
Wenderoth , Lind & Ponack, L.L.P.
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