1. Field of the Invention
The present invention relates to a lightweight clay and a manufacturing method thereof, and more particularly to a lightweight clay, which has proper lightweight characteristics and proper moldability, exhibits excellent coloring characteristics and reduces a manufacturing cost and a manufacturing method thereof.
2. Description of the Related Art
The conventional clay which has been used in fine art and as school teaching material or the like, in many cases, is configured such that the clay contains a granular material or a decomposed product of dead plant bodies as a main material and adds additives such as a binder for binding the granular materials, flavor, pigment, water, oil and the like to the main material. Accordingly, there has been observed a drawback that the conventional clay has large weight and exhibits poor availability.
In view of the above circumstance, JP51-893B discloses a lightweight clay, which is constituted by using pulverized foamed styrol as a main material and by adding pulpwood, water and the like to the foamed styrol.
However, the pulverized foamed styrol forms a large number of open pores on a surface thereof in view of the structure thereof and water or the like permeates these open pores and hence, the clay becomes rich in a water content or a liquid content. Accordingly, there still remains a drawback on lightweighting that the weight of the lightweight clay as a whole cannot be remarkably reduced. Further, there has been also observed a drawback on manufacturing that the micronization of the foamed styrol is not easy and hence, it is difficult to uniformly mix the foamed styrol with the blending materials.
Further, JP59-50615B discloses a polish-able molding clay in which 30 to 40 weight % of micro hollow powdery bodies made of a foamed inorganic material having a particle size of less than 150 xcexcm and a bulk density of not more than 0.6, 3 to 13 weight % of fiber powder having a fiber length of not more than 10 mm, 31 to 60 weight % of talc powder having a particle size of not more than 150 xcexcm, 3 to 8 weight % of a water-soluble synthetic paste material in a single or a plural form, and water are mixed and the penetration is adjusted to 100 to 350. Further, a plastic art material having the similar composition is disclosed in JP57-16356B.
However, such a molding clay or plastic art material contains a large amount of micro hollow powdery materials formed of the foamed inorganic material and rock powder and hence, it is not easy to mix or disperse these materials. Furthermore, the obtained molding clay or plastic art material exhibits poor handling characteristics and moldability. Further, there has been a drawback that these clays push up a manufacturing cost.
Still further, in JP2-123390A, there is proposed a lightweight clay which is lightweighted, exhibits high whiteness degree and enables easy incineration treatment by blending 3 to 20 weight % of organic hollow micro spheres having an outer shell made of copolymer containing acrylic nitrile or vinylidene chloride, 5 to 20 weight % of a synthetic binder (carboxymethylcellulose), 10 to 30 weight % of fiber powder and 50 to 60 weight % of water with respect to a total quantity of the clay.
That is, for example, when the blending ratio of the organic hollow micro spheres is less than 3 weight %, a given target weight cannot be achieved, while when the blending ratio of the organic hollow micro spheres exceeds 20 weight %, the nature of the lightweight clay is damaged.
Further, when the blending ratio of the fiber powder is less than 10 weight %, the working of the fiber powder as the binder becomes insufficient, while when the blending ratio of the fiber powder exceeds 30 weight %, the lightweight clay preserves a large quantity of water and hence, the lightweighting characteristics of the lightweight clay is damaged.
Further, when the blending ratio of water is less than 50 weight %, the molding operation becomes difficult, while when the blending ratio of water exceeds 60 weight %, the lightweight clay is softened so that the lightweight clay exhibits poor moldability. Furthermore, the lightweighting characteristics of the lightweight clay are damaged.
However, an addition quantity of the organic hollow micro spheres in such a lightweight clay is large, that is, 20 weight % at maximum and hence, it is not easy to mix or disperse the organic hollow micro spheres. Further, the obtained lightweight clay excessively has the lightweighting characteristics so that there has been a problem that the lightweight clay exhibits poor handling and moldability and a manufacturing cost is pushed up.
Further, since an addition quantity of the organic hollow micro spheres is large in such a lightweight clay, there has been also a drawback that the organic hollow micro spheres in a state that a foamed gas (foamed liquid) remains, that is, so-called un-expanding organic hollow micro spheres are present in a large quantity. Accordingly, assuming a case in which the lightweight clay is stored for a long period by covering the lightweight clay with a packaging material such as a polyethylene film, when an ambient temperature is elevated during a summer season or the like and the lightweight clay is held in high temperature state, there has been observed a drawback that the lightweight clay which is covered with the packaging material is swelled to a volume which is approximately 1.2 to 3 times as large as an initial volume due to the remaining foamed gas (hereinafter referred to as a swelling problem) has been observed.
Further, since an addition quantity of the organic hollow micro spheres is large in such a lightweight clay, when color elements are added, there has been also a drawback that the organic hollow micro spheres interrupt the dispersion of the color elements so that it is impossible to obtain the excellent coloring characteristics.
Further, JP10-268755A discloses a lightweight clay, which is lightweighted, requires small number of drying days and exhibits small shrinkage ratio. Such a lightweight clay is produced by blending 30 to 70 parts by weight of glass micro hollow spheres having a particle size of 1 to 200 xcexcm, 30 to 60 parts by weight of fiber powder, 10 to 50 parts by weight of carboxymethylcellulose and 200 to 400 parts by weight of water (using a total quantity of the glass micro hollow spheres, fiber powder and carboxymethylcellulose as the reference).
That is, for example, when the blending ratio of the glass micro hollow spheres is less than 30 parts by weight, it is difficult to achieve given lightweighting characteristics, while when the blending ratio of the glass micro hollow spheres exceeds 70 parts by weight, the shrinkage and cracks in the lightweight clay are increased in number.
Further, when the blending ratio of the fiber powder is below 30 parts by weight, the shrinkage and cracks in the lightweight clay are increased in number, while when the blending ratio of the fiber powder exceeds 60 parts by weight, the lightweight clay preserves a large quantity of water and hence, the lightweighting is damaged.
Further, when the blending ratio of water is below 200 parts by weight, the molding operation of the lightweight clay becomes difficult, while when the blending ratio of water exceeds 400 parts by weight, the lightweight clay is softened and exhibits poor moldability. Further, the lightweight clay is liable to be stuck to a hand.
However, with respect to such a lightweight clay, since the adding rates of the glass micro spheres and the fiber powder are large, there has been a drawback that the lightweight clay exhibits poor moldability and a manufacturing cost is pushed up.
Further, since an addition quantity of the glass organic hollow micro spheres is large in such a lightweight clay, when color elements are added, the glass organic hollow micro spheres interrupt the dispersion of the color elements so that there has been observed a drawback that the excellent coloring characteristics is not obtained.
In view of the above, inventors of the present invention have studied the average particle size, the whiteness degree (WL) or an addition quantity of the organic hollow micro spheres in the lightweight clay to an extent that they reach respective values which are considered to cause problems conventionally. As a result of the studies, the inventors have found that these factors interact with each other and affect the whiteness degree (WL), the coloring characteristics, and the moldability, lightweight characteristics of the lightweight clay or the swelling problem of the lightweight clay.
Accordingly, it is an object of the present invention to provide a lightweight clay and a manufacturing method thereof in which the lightweight clay exhibits excellent coloring characteristics, moldability and lightweight characteristics and can solve the swelling problem even when the lightweight clay is subjected to a high temperature state when the lightweight clay is stored for a long period in a state that the lightweight clay is covered with a packing material or when an ambient temperature is elevated during a summer season thus obtaining excellent storing characteristics by solving the swelling problem.
According to the present invention, there is provided a lightweight clay which contains organic hollow micro spheres and a binder resin, wherein an average particle size of the organic hollow micro spheres is set to a value which falls within a range of 15 to 150 xcexcm, an addition quantity of the organic hollow micro spheres is set to a value not more than 6 weight % with respect to a total quantity, and whiteness degree (WL) of the lightweight clay which is measured in accordance with JIS L 0803 is set to a value of not less than 50, whereby the above-mentioned drawbacks can be solved.
That is, by controlling the whiteness degree (WL) of the lightweight clay while controlling the average particle size of the organic hollow micro spheres in a fixed range in this manner, it is possible to enhance the aesthetic appearance and, at the same time, it is possible to obtain the excellent coloring characteristics when coloring elements or the like are added to the lightweight clay for coloring.
Further, since an addition quantity of the organic hollow micro spheres is relatively small, even when the color elements are added to the lightweight clay for coloring, the organic hollow micro spheres do not interrupt the dispersion of the color elements and hence, the lightweight clay can obtain more excellent coloring characteristics.
Further, by setting an addition quantity of the organic hollow micro spheres to a value which is considerably smaller than an upper limit (20 weight %) of an addition quantity of the organic hollow micro spheres of a conventional lightweight clay, it is possible to obtain the sufficient and proper lightweighting (reduction of weight) of the lightweight clay and, at the same time, it is possible to obtain the lightweight clay which exhibits the excellent moldability.
Further, since an addition quantity of the organic hollow micro spheres is relatively small, not only the mixing and dispersion of the organic hollow micro spheres into the lightweight clay is facilitated, but also a quantity of unexpanded organic hollow micro spheres present in the lightweight clay can be reduced and a use quantity of the expensive organic hollow micro spheres can be reduced so that it is possible to obtain the excellent storing characteristics (expansion characteristics) and it is also possible to reduce a manufacturing cost to a low level.
Further, according to another mode of the present invention, in a method for manufacturing a lightweight clay containing organic hollow micro spheres and a binder resin, an addition quantity of the organic hollow micro spheres having an average particle size which is set to a value which falls within a range of 15 to 150 xcexcm is set to a value of not more than 6 weight % with respect to a total quantity, the organic hollow micro spheres and the binder resin are mixed using a kneader so as to set whiteness degree (WL) of the lightweight clay which is measured in accordance with JIS L 0803 to a value of not less than 50.
By exercising such a manufacturing method, it is possible to efficiently obtain the lightweight clay which exhibits excellent moldability and lightweight characteristics, can exhibit extremely distinct whiteness, and exhibits further excellent coloring characteristics when color elements are added.