JP5256127B2 - Biodegradable clay and method for producing the same - Google Patents

Description

  The present invention relates mainly to clay for handicrafts, and more particularly to biodegradable clay having biodegradability and excellent quality as clay, and a method for producing the same.

Traditionally, clay for handicrafts is required to have excellent workability, texture, and ease of coloring.
In other words, clay that is soft and easy to handle, can be thinned, and does not lose its shape and has excellent workability such as being hard to touch, makes it possible to create more flexible works and is easy to handle even for beginners It becomes. In addition, clay that has an excellent texture, such as a material that gives a positive impression to the eye and a material that has a good tactile sensation, expands the range of application to the creation of works and stimulates the desire to create. In addition, since a workpiece manufactured using clay for handicrafts is often painted, the color of the clay is preferably white or transparent, which can be colored flexibly.

In order to ensure the quality required for such clay for handicrafts, the ingredients of clay for handicrafts include various synthetic resin pastes with low degradability typically represented by polyvinyl acetate, methylcellulose, carboxy Cellulosic synthetic pastes such as methylcellulose are frequently used as binders. Moreover, water-soluble cellulose ether and other chemical substances with little degradability are used as a thickener. Petroleum-related products such as liquid paraffin are also used for fats and oils for preventing hand-holding.
Thus, since the conventional clay for handicrafts is manufactured using a synthetic resin or the like as a base in order to improve its quality, it has hardly been biodegraded.

On the other hand, from the viewpoint of environmental protection, it is desirable that clay for handicrafts is produced only from biodegradable materials without using synthetic resins, synthetic glues, petroleum-related products, and the like.
However, without using any of these synthetic resins, producing clay using only biodegradable materials is an excellent workability, texture and ease of coloring required for handicraft clay. It was extremely difficult to realize such as.

For example, if the main component of clay is replaced with a synthetic resin and a biodegradable material such as wheat or corn is used as the main component, the protein component is oxidized and yellowish, which hinders coloring. . For this reason, in order to produce white clay, it is preferable to remove the protein component and use only the starch component.
However, when starch is the main component, the viscosity and strength necessary for handicraft clay cannot be obtained as it is. For this reason, when producing clay with starch as a main component, for example, a synthetic resin such as polyvinyl acetate is added like the clay for handicraft described in Patent Document 1, and the viscosity and strength of the clay are increased. There was a need to grant.

In this way, the viscosity and strength necessary for clay are achieved using synthetic resin, etc., for paper clay and other clays that seem to be most biodegradable. It has been extremely difficult to produce a high-quality white clay with excellent workability and texture without adding a synthetic resin or the like based on a possible material.
Therefore, conventionally, even a clay mainly composed of a biodegradable material is generally produced by adding a synthetic resin or the like, and is not highly biodegradable.

  On the other hand, Patent Document 2 describes that a highly biodegradable clay is produced using sawdust generated during the production of a pencil as a main component. The clay described in Patent Document 2 is environmentally friendly as recycled wood clay, is light and strong, and has excellent features such as being carved in the same way as wood when dried. He has received numerous awards including technology and new product awards.

JP 2001-31829 A Japanese Patent No. 4204208

However, the clay described in Patent Document 2 was not provided with excellent workability and texture suitable for clay for handicrafts.
That is, the clay described in Patent Document 2 is hard and poor in smoothness, and has a problem that it is quickly dried and cracked during production of a craft.
Moreover, since the color of the clay is the color of wood, there is a problem that it cannot be colored freely and cannot be used depending on the craft to be manufactured. In this regard, there has also been devised to make colored clay by containing titanium oxide. However, when titanium oxide is contained in this way, there is a problem that workability and texture of the clay are further deteriorated.

  In addition, since this clay has sawdust as a main component, it has a problem that it smells like a damp tree, and it is difficult to remove the smell even after creating a craft. Since there are many consumers of handicraft clay among housewives, such a problem of odor is inconvenient for meal preparation and is difficult to use.

  In this way, clay for handicrafts is required to have excellent workability, texture, ease of coloring, etc., but the properties of these clays have been conventionally realized with synthetic resins, etc. When an environmentally friendly biodegradable material was used as the main component, the properties of these clays could not be realized.

  In order to produce highly biodegradable clay without impairing the properties required for such handicraft clay, the present inventors have experimented with a huge combination of materials over many years, Finally, we succeeded in producing high-quality handicraft clay with excellent biodegradability and workability and texture comparable to those of conventional synthetic resins.

Specifically, the present inventors searched for biodegradable materials that can be substituted for each component of clay mainly composed of conventional synthetic resins, and provided excellent workability, texture, ease of coloring, etc. The experiment was repeated to produce the prepared clay, and finally the clay with excellent workability and texture was produced by using the modified starch as the main component and using sodium alginate and calcium carbonate and / or calcium phosphate together. The present invention was completed successfully.
The present invention is a biodegradability for white handicrafts with high biodegradability and excellent workability and texture by blending sodium alginate and calcium carbonate and / or calcium phosphate into the modified starch. An object of the present invention is to provide clay and a method for producing the same.

The biodegradable clay of the present invention is a clay containing starch as a main raw material, and is characterized in that a modified starch contains sodium alginate and calcium carbonate and / or calcium phosphate.
The method for producing biodegradable clay of the present invention is a method for producing clay using starch as a main raw material, and mixing alginate with sodium alginate and calcium carbonate and / or calcium phosphate is stirred. Features.

  According to the present invention, when the modified starch is a main component of clay, the viscosity is adjusted by mixing sodium alginate and calcium carbonate and / or calcium phosphate, so that the biodegradability is high and the work is excellent. This makes it possible to produce white handicraft clay with properties and texture.

It is a figure which shows the correspondence of the compounding component of the clay which has the biodegradable clay of this invention and the conventional synthetic resin as a main component. FIG. 3 is a diagram showing blended components of clay of Example 1. It is a figure which shows the mixing | blending component of the clay of Example 2. FIG. It is a diagram illustrating a control material (biodegradation calculated from the amount of produced CO ₂₎ biodegradability test results (cellulose). It is a diagram showing a (biodegradation calculated from the amount of produced CO ₂₎ biodegradability test results of clay of Example 1. Is a diagram showing the amount of CO ₂ produced in the blank test (blank). Is a diagram showing the amount of CO ₂ produced reference material (cellulose). FIG. 3 is a diagram showing the amount of CO ₂ generated in the clay of Example 1. It is a figure which shows the biodegradation degree of a control material (cellulose). It is a figure which shows the biodegradation degree of the clay of Example 1. FIG. It is a figure which shows the free-form evaluation result with respect to the clay of Example 1 and Comparative Example 1. It is a figure which shows the summary of the evaluation content of workability | operativity, a texture, a color, an odor, and storage stability of the clay of Example 1 and Comparative Example 1.

Hereinafter, embodiments of the present invention will be specifically described.
Clay is generally produced by mixing and stirring a composition such as a binder, a thickener, an additive, an anti-handing agent, a surfactant, and a filler.
The present invention, as a result of searching for the properties imparted to the clay by these compositions, using a highly biodegradable material, to the clay, as a result of the combination of the biodegradable materials found, This makes it possible to produce biodegradable clay with excellent quality as handicraft clay.
First, with reference to FIG. 1, the compounding component of the biodegradable clay of this invention is demonstrated. The same figure is a figure which shows the correspondence of the biodegradable clay of this invention, and the compounding component of the conventional clay.

(binder)
The binder is a main component of clay, and realizes the mechanical strength, solidification, and tackiness of clay. In order to impart such properties to clay, conventionally, synthetic resins such as polyvinyl acetate have been used as binders.
In contrast, in the present embodiment, modified starch is used as the binder. When the modified starch is used as a binder, the mechanical strength, solidification, and tackiness of the clay are all greatly inferior to those using a synthetic resin.
Therefore, in this embodiment, as will be described later, by devising thickeners and fillers, anti-handing agents, etc., by compensating for these deteriorating properties, quality comparable to clay using synthetic resin It is possible to manufacture clay.

As the modified starch used for the binder, for example, pregelatinized starch, modified starch and the like can be used.
Further, when producing a clay base by gelatinizing the binder, it is also preferable to add trehalose in order to increase its activity and prevent the stickiness from dropping. Thus, by adding trehalose when gelatinizing the binder, it is possible to produce a base with further excellent viscosity.

Moreover, as shown in FIG. 1, it is preferable to use polylactic acid or a polylactic acid emulsion as an auxiliary binder. As described above, by using polylactic acid or polylactic acid emulsion as an auxiliary binder, the biodegradable clay of this embodiment can be given strength suitable for clay for handicrafts, and the mold can be deformed. It is difficult, and it becomes possible to produce a high-quality clay having excellent workability and shape retention.
Polylactic acid is a biodegradable material produced from corn and the like, and no conventional examples have been used for clay. Polylactic acid has been found by the present inventors as a biodegradable material capable of imparting strength to clay instead of synthetic resin.

  A small amount of polyvinyl alcohol can also be used as a plasticizer for the polylactic acid emulsion. Polyvinyl alcohol is a material capable of improving clay viscosity. For example, by using a trace amount of partially saponified polyvinyl alcohol soluble in cold and hot water with a biodegradation rate of 65%, the viscosity of clay is improved. At the same time, it is possible to increase the strength of the clay.

(Thickener)
A thickener is a component that imparts viscosity to clay, and conventionally, cellulose derivatives having low biodegradability such as water-soluble cellulose ether and carboxymethyl cellulose have been used.
On the other hand, in this embodiment, sodium alginate that readily biodegrades is used as the thickener. As this sodium alginate, those extracted from seaweed are commercially available, and these can be suitably used.

When sodium alginate is contained in the modified starch, which is the main component of the clay of the present embodiment, the viscosity of the clay is greatly increased, resulting in a sticky state like natto that is well kneaded and pulled.
In this state, the viscosity is too high to be used as clay. Therefore, by adding calcium carbonate and / or calcium phosphate, the viscosity is adjusted to a value suitable for clay for handicrafts.
At this time, by adding calcium carbonate and / or calcium phosphate, the pH of the clay is adjusted to about 5, it is reacted with sodium alginate to form a little gel, and the viscosity is adjusted to be suitable for clay for handicrafts. At the same time, it is possible to impart an anti-handing effect to the clay.

As a result, the clay mainly composed of modified starch can be provided with a viscosity suitable for clay for handicrafts and an anti-handing effect, and excellent workability and texture can be realized.
Furthermore, it is also preferable to finely adjust the viscosity of the clay using enzyme-modified starch or pregelatinized starch as an auxiliary thickener. As a result, it is also possible to realize a clay with even better workability.
In addition, the kind of enzyme-modified starch or pregelatinized starch is not particularly limited. The pregelatinized starch can also be used as a surfactant or a filler.

(Hand prevention agent)
An anti-hand agent is a component that suppresses stickiness of clay and improves its workability and texture.
Conventionally, a material having low biodegradability such as liquid paraffin has been used as an anti-handing agent. However, in this embodiment, castor oil, which is a vegetable oil with high biodegradability, is used. Castor oil is a material suitable for blending white clay because it is hard to oxidize and hard to be yellowish.

  In this embodiment, calcium carbonate and / or calcium phosphate is reacted with sodium alginate to give a slight gel state, thereby imparting an anti-hand effect to clay, but by adding castor oil, an even better hand It is possible to impart a prevention effect.

(Additive)
An additive is a compounding component for strengthening and improving the properties of clay, and various additives can be used depending on the use of the clay. As shown in FIG. 1, conventionally, propylene glycol, polyethylene glycol, glycerin, and the like have been used as the additive, but in the present embodiment, highly biodegradable glycerin is used.
Glycerin is a component that imparts fluidity to clay and improves water retention.

(Surfactant)
The surfactant is a component that has the effect of reducing the surface tension of the liquid and also reducing the interfacial tension between the liquids and between the liquid and the solid, and increases the mixing effect of each component of the clay.
In this embodiment, it is preferable to use a highly biodegradable nonionic surfactant or pregelatinized starch as the surfactant. As nonionic surfactants having high biodegradability, for example, sorbitan monooleate can be preferably used.

(filler)
Conventionally, cellulose powder, regenerated pulp, natural starch and the like have been used as the filler.
In this embodiment, cellulose powder, corn starch, and pregelatinized starch are used. By using cellulose powder and corn starch as the filler, the hardness of the clay can be adjusted, and an anti-handing effect can be imparted. Moreover, the viscosity of clay can also be improved by using pregelatinized starch.

Furthermore, in this embodiment, calcium carbonate, especially calcium carbonate derived from eggshell (egg shell calcium) is used as the filler. Further, calcium phosphate can be used instead of or together with calcium carbonate.
By blending these with sodium alginate, it is possible to balance clay viscosity and prevention of handling, and to realize excellent workability and texture.
The eggshell powder contains not only calcium carbonate but also a small amount of calcium phosphate, and these partially react with sodium alginate to form a gel. Experience has shown that by using eggshell powder, the same effect can be obtained even if the amount of calcium carbonate and / or calcium phosphate is small with respect to sodium alginate than when calcium carbonate alone is used. .

(Anti-septic and fungicidal agent)
The antiseptic and antifungal agent is a component that imparts an antiseptic and antifungal effect to the clay of the present embodiment. As the antiseptic / fungal agent, for example, an organic NS halogen-based antiseptic / antifungal agent can be used.
Since the antiseptic / antifungal effect and the biodegradability are contradictory, it is preferable not to add an antiseptic / antifungal agent from the viewpoint of improving biodegradability.
On the other hand, since the biodegradable clay of the present embodiment is mainly composed of modified starch, if the antiseptic and fungicidal agent is not applied, the produced workpiece is prone to mold and is not suitable for practical use.
For this reason, in this embodiment, as shown in the Examples, the minimum addition amount that does not impair the biodegradability as much as possible and can suppress the generation of mold is found and blended.

In addition, although tap water is used for moisture, other water such as distilled water may be used.
Furthermore, as long as the biodegradable clay of this embodiment is a mixture obtained by mixing sodium alginate and calcium carbonate and / or calcium phosphate into the modified starch, various other highly biodegradable materials can be used as necessary. It is also possible to add ingredients.

(Production method)
Next, the manufacturing method of the biodegradable clay of this embodiment is demonstrated.
The method for producing the biodegradable clay of the present embodiment has high biodegradability and excellent workability and texture by mixing and stirring sodium alginate and calcium carbonate and / or calcium phosphate in the modified starch. Although it will not specifically limit if it is a method which can manufacture the white clay which has, It is preferable to set it as the method shown below.

  First, water (30.0-37.0% by weight) was added to the modified starch of the binder (5.0-7.0% by weight of the whole clay), and an antiseptic and fungicide (0.1% by weight). ~ 0.3 wt%) is added and heated at 60-80 ° C for 2-7 minutes to gelatinize. In order to enhance the activity of the obtained starch paste, it is also preferable to add trehalose to a maximum of about 30% by weight with respect to the modified starch of the binder, for example. Based on the paste thus obtained.

Next, the above-mentioned base is put into a kneader, and further, additives, thickeners, fillers, anti-handing agents, surfactants and other various components (raw materials) as necessary, while stirring, Add in order according to the capacity of the kneader.
At this time, in this embodiment, sodium alginate is added as a thickener, and calcium carbonate (or eggshell powder) is added as a filler. Further, it is preferable to add castor oil as an anti-sticking agent and polylactic acid emulsion as an auxiliary agent for the binder.

In stirring the mixture, it is preferable to reversely rotate the stirring blades in the kneader for a predetermined time. Thereby, clay can be mixed efficiently and uniformly.
Furthermore, it is preferable to stop the kneading machine once before rotating the stirring blade to wash the inner wall portion of the kneading machine to remove unmelted raw materials and the like. As a result, a sufficiently uniform and textured clay can be produced.
Then, confirm the physical properties such as the properties and hardness of the crushed clay and finish the production.

Example 1
Next, Embodiment 1 of the present invention will be described with reference to FIG. The figure is a figure which shows the mixing | blending component in the biodegradable clay of Example 1 of this invention.
In Example 1, the blending components in the figure were added in the order of the numbers in the figure to produce white clay having high biodegradability and excellent workability and texture according to the present invention.

  Specifically, modified starch 200.0 [g] (6.11 [wt%]), tap water 1160.00 [g] (35.43 [wt%]), antiseptic mold agent 4.0 [g ] (0.12 [wt%]), pregelatinized starch 75.0 [g] (2.29 [wt%]), cellulose powder 300.0 [g] (9.16 [wt%]), sodium alginate 20.0 [g] (0.61 [wt%]), eggshell powder 100.0 [g] (3.05 [wt%]), calcium carbonate 200.0 [g] (6.11 [wt%] ), Nonionic surfactant 40.0 [g] (1.22 [wt%]), enzyme-modified starch 540.0 [g] (16.49 [wt%]), castor oil 185.0 [g] (5.65 [wt%]), corn starch starch 100.0 [g] (3.05 [wt%]), poly milk Emulsion 350.0 [g] (10.69 [wt%]) was stirred successively added to the kneader. At this time, after stirring until each component is sufficiently mixed, the next component is added. The stirring time is about 5 to 15 minutes for each component. As a kneading machine, a Warner type kneader (capacity 3 L, Satake Chemical Machinery Co., Ltd.) was used.

Moreover, the kneading machine was stopped once in the middle of this stirring, and the kneading machine was washed with a waste cloth or a scourer. And after removing the undissolved material remaining on the inner wall of the kneading machine, the stirring blade was reversely rotated and stirred for 5 minutes. Thereafter, the stirring blade was rotated again in the forward direction and kneaded. In addition, the reverse rotation stirring for 5 minutes may be performed at the end of the stirring time or in the middle.
Then, after confirming the physical properties such as the properties and hardness of the rolled up clay, the production was completed.

Here, the blending ratio of the components of the biodegradable clay of the present embodiment is not limited to the above values, and for example, the following ranges are preferable.
The modified starch is preferably blended in the biodegradable clay of this embodiment in an amount of 3.0 to 10.0% by weight. If the blending ratio of the modified starch is in such a range, the effect of other blending components can be more fully exhibited while keeping the mechanical strength of the clay high. From such a viewpoint, the blending ratio is more preferably 5.0 to 7.0% by weight, and further preferably 5.5 to 6.5% by weight.

  Sodium alginate is preferably blended in the biodegradable clay of this embodiment in an amount of 0.1 to 3.0% by weight. If the blending ratio of sodium alginate is in such a range, the biodegradable clay of this embodiment can be given high viscosity, and the workability of clay can be improved by blending calcium carbonate or calcium phosphate together. And the texture can be improved. From such a viewpoint, the blending ratio is more preferably 0.2 to 1.0% by weight, and further preferably 0.3 to 0.7% by weight.

  It is preferable to mix 3.0 to 17.0% by weight of calcium carbonate with the biodegradable clay of this embodiment. If the blending ratio of calcium carbonate is within this range, the pH of the mixture is adjusted to about 5, and part of the mixture reacts with sodium alginate to gel the clay, thereby eliminating the stickiness of the clay. It is possible to impart excellent texture and workability to clay. From this point of view. The blending ratio of calcium carbonate is more preferably 4.0 to 13.0% by weight, and further preferably 5.0 to 10.0% by weight. In addition, it is also preferable to use eggshell powder as all or part of this calcium carbonate. When eggshell powder is used, experience has shown that the above effect can be obtained even if the content of calcium carbonate is reduced.

  The polylactic acid emulsion is preferably blended in the biodegradable clay of this embodiment in an amount of 5.0 to 20.0% by weight. If the blending ratio of the polylactic acid emulsion is within this range, the viscosity and strength of the clay can be improved, and excellent moldability can be imparted to the clay. From such a viewpoint, the blending ratio of the polylactic acid emulsion is more preferably 8.0 to 17.0% by weight, and further preferably 10.0 to 15.0% by weight.

  In addition, glycerin is 0.0 to 5.0% by weight, pregelatinized starch is 0.0 to 5.0% by weight, cellulose powder is 1.0 to 15.0% by weight, nonionic surfactant Is 1.0 to 2.0 wt%, enzyme-modified starch is 10.0 to 20.0 wt%, castor oil is 3.0 to 7.0 wt%, cornstarch starch is 1.0 to 15.0 wt% It is preferable to blend each weight%.

  In addition, the above blending ratio is optimal when producing the biodegradable clay using each of the above components, and when the blending components are different, the above ratio is not optimal due to the synergistic effect of each component. Sometimes. That is, the blending ratio of each component in the clay of the present invention may vary depending on the type of component to be blended. For example, Example 2 shown below improves the moisture retention of clay as compared with Example 1, and the blending ratio has a part different from Example 1.

(Example 2)
A modification of the biodegradable clay of this embodiment will be described with reference to FIG. The figure is a figure which shows the mixing | blending component in the biodegradable clay of Example 2 of this embodiment.
In Example 2, it is possible to produce a clay that is hard to dry compared to Example 1.

Moreover, in Example 1, the viscosity of clay is used for handicrafts by adding 100.0 [g] eggshell powder and 200.0 [g] calcium carbonate to 20.0 [g] sodium alginate. It is adjusted to be suitable for clay. On the other hand, in Example 2, by adding 185.0 [g] eggshell powder to 20.0 [g] sodium alginate, the viscosity of the clay becomes suitable for clay for handicrafts. Yes.
As shown in Example 2, it is possible to adjust the viscosity of clay appropriately by using eggshell powder even if the blending amount with respect to sodium alginate is less than that in the case of using calcium carbonate. .

  Specifically, modified starch 200.0 [g] (5.80 [wt%]), tap water 1160.00 [g] (33.62 [wt%]), antiseptic mold agent 4.0 [g ] (0.12 [wt%]), glycerin 100.0 [g] (2.90 [wt%]), pregelatinized starch 1.0 [g] (0.03 [wt%]), cellulose powder 100 0.0 [g] (2.90 [wt%]), sodium alginate 20.0 [g] (0.58 [wt%]), eggshell powder 185.0 [g] (5.36 [wt%]) , Nonionic surfactant 40.0 [g] (1.16 [wt%]), enzyme-modified starch 540.0 [g] (15.65 [wt%]), castor oil 180.0 [g] ( 5.22 [wt%]), corn starch starch 420.0 [g] (12.17 [wt%]), polylactic acid Rujon 500.0 [g] (14.49 [wt%]) was stirred successively added to the kneader. At this time, after stirring until each component is sufficiently mixed, the next component is added. The stirring time is about 5 to 15 minutes for each component. As a kneading machine, a Warner type kneader (capacity 3 L, Satake Chemical Machinery Co., Ltd.) was used.

Further, the kneader was stopped once in the middle of the stirring, and the raw material remaining on the inner wall of the kneading machine was removed by waste or scrubbing. Then, the stirring blade was reversely rotated and stirred for 5 minutes.
Then, after confirming the physical properties such as the properties and hardness of the rolled up clay, the production was completed.

Here, also in this Example 2, it is preferable that the modified starch and sodium alginate have almost the same blending ratio as in Example 1, but in this Example 2, as a component of calcium carbonate and / or calcium phosphate, Since only eggshell powder is used, it is possible to make the blending ratio of the component small in comparison with the case where only calcium carbonate is used.
That is, when only eggshell powder is used as a component of calcium carbonate and / or calcium phosphate, the same effect can be obtained even if the blending ratio with respect to sodium alginate is less than eggshell powder and calcium carbonate in Example 1. It is possible to improve the workability and texture of the. From such a viewpoint, the blending ratio of the eggshell powder is more preferably 3.0 to 7.0% by weight, and further preferably 4.0 to 6.0% by weight.

In Example 2, the polylactic acid emulsion is preferably blended in an amount of 7.0 to 22.0% by weight. If the blending ratio of the polylactic acid emulsion is within this range, the viscosity and strength of the clay can be improved, and excellent moldability can be imparted to the clay. From such a viewpoint, the blending ratio is more preferably 10.0 to 19.0% by weight, and further preferably 12.0 to 17.0% by weight.
About the ratio of another compounding component, it is preferable to set it as the same range as Example 1.

(Evaluation of properties of biodegradable clay)
(1) Evaluation of biodegradability The biodegradability of the clay produced in Example 1 was evaluated by the following method. The results are shown in FIGS.

(Evaluation method)
The biodegradability test of the clay produced in Example 1 was requested to the Chemical Substance Evaluation Research Organization, and the compost embedding test was performed to evaluate the biodegradability. Specifically, based on JISK6953: 2000 "Plastics-Determination of aerobic ultimate biodegradation and disintegration under controlled compost conditions-Method by measurement of the amount of generated carbon dioxide-" under the following conditions: went.

(1) Test material Clay of Example 1 (freeze pulverization) TOC (total organic carbon content) 44.4%
(2) Control material MERCK made cellulose (microcrystal)
(3) Compost Gunma Prefecture Itakura Recycling Center 50% dry solids, 43% volatile solids, pH 9.0 suspension
(4) Sample preparation The sample was dried at room temperature, and the dried sample was subjected to the test.
(5) Test container volume: 500 mL Compost dry mass 60 g, Compost moisture content 50% Sample 10 g
(6) CO ₂ absorbing solution 2NKOH solution (100 mL in duplicate)
(7) CO ₂ measurement method Potentiometric titration method

(result)
The clay produced according to Example 1 showed an average biodegradation of 85.8% on the 88th day, indicating a tendency to further degrade. On the other hand, the biodegradation degree of the control material (cellulose) was 75.8% on the 66th day on average. It can be seen from the biodegradation degree of the control material (cellulose) that the test results are valid.
In addition, the clay produced according to Example 1 is shown to biodegrade faster after a certain period of time compared to the control material (cellulose). It still shows an almost constant upward trend.
Therefore, it can be seen that the clay produced in Example 1 has high biodegradability.

[Evaluation of quality as craft clay]
The clay of Example 1 and the clay manufactured by the method described in Patent Document 2 (commercial name: Mokuen-san, manufactured by Hokusei Pencil Co., Ltd., hereinafter referred to as the clay of Comparative Example 1) were used. The work was made by five people with 20-30 years of clay work making, and the quality of each clay was evaluated in a free form. A summary of the results is shown in FIG. 11, and a summary of the evaluation contents is shown in FIG.
As shown in these figures, although the clay of Comparative Example 1 is a biodegradable clay made of a biodegradable material, it is hard and smooth, is easy to dry and cracks during the production of the work, etc. Most of the evaluations were poor workability and difficult to handle. There was also an evaluation that works were limited because the color of clay was earthy. Furthermore, there was also an evaluation that it was not preferable because the wet smell of wood was in hand.

  In contrast, the clay of Example 1 was mostly a biodegradable clay, but it was evaluated that it had excellent workability and texture that was not different from conventional synthetic resin-based clay. In addition, there were many evaluations that it was possible to make free works because the color of the clay was white. Furthermore, since the odor was almost odorless, it was evaluated as preferable.

  As described above, it was confirmed that the clay of Example 1 not only has high biodegradability, but also has excellent quality as a clay for handicrafts and is satisfactory even for skilled workers. .

  The present invention can be suitably used in the production of clay for handicrafts and the like.

Claims (5)

It is a clay mainly composed of starch, which is a modified starch of 3.0 to 10.0% by weight , sodium alginate of 0.1 to 3.0% by weight , calcium carbonate and / or calcium phosphate of 3.0 to 17.0. A biodegradable clay comprising: wt% . The modified starch further contains at least one of polylactic acid 5.0 to 20.0% by weight , castor oil 3.0 to 7.0% by weight , or enzyme-modified starch 10.0 to 20.0 % by weight. The biodegradable clay according to claim 1. Modified starch 3.0 to 10.0 wt% , pregelatinized starch 0.0 to 5.0 wt% , cellulose powder 1.0 to 15.0 wt% , seaweed-derived sodium alginate 0.1 to 3 .0% by weight, and 3.0 to 17.0% by weight of calcium carbonate and / or calcium phosphate from egg shell, and a surfactant 1.0-2.0 wt%, enzyme modified starch 10.0 to 20.0 and weight, and castor oil 3.0 to 7.0 wt%, and wherein the 1.0 to 15.0 wt% corn starch starch, that formed by incorporating a polylactic acid emulsion 5.0 to 20.0 wt% The biodegradable clay according to claim 1 or 2. A method for producing clay using starch as a main raw material, which is a modified starch of 3.0 to 10.0% by weight , sodium alginate of 0.1 to 3.0% by weight , calcium carbonate and / or calcium phosphate of 3.0 to A method for producing a biodegradable clay, comprising mixing 17.0% by weight and stirring. After mixing and heating 5.0 to 7.0% by weight of modified starch, 30.0 to 37.0% by weight of water and 30% by weight of trehalose with respect to the modified starch , glycerin 0.0 to 5.0 And then stirred and then pregelatinized starch 0.0-5.0% by weight , cellulose powder 1.0-15.0% by weight , sodium alginate 0.1-3.0% by weight , carbonic acid Calcium and / or calcium phosphate 3.0-17.0 wt% , surfactant 1.0-2.0 wt% , enzyme-modified starch 10.0-20.0 wt % , castor oil 3.0-7. The biodegradation according to claim 4, wherein 0 wt% , corn starch starch 1.0 to 15.0 wt% , and polylactic acid emulsion 5.0 to 20.0 wt% are sequentially mixed and stirred. Method for producing clay.

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