WO2011141936A1 - A novel dustless chalk and process of making the same - Google Patents
A novel dustless chalk and process of making the same Download PDFInfo
- Publication number
- WO2011141936A1 WO2011141936A1 PCT/IN2011/000334 IN2011000334W WO2011141936A1 WO 2011141936 A1 WO2011141936 A1 WO 2011141936A1 IN 2011000334 W IN2011000334 W IN 2011000334W WO 2011141936 A1 WO2011141936 A1 WO 2011141936A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- chalk
- hydrate
- chalks
- calcium sulphate
- dustless
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 17
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 claims abstract description 14
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims abstract description 12
- PASHVRUKOFIRIK-UHFFFAOYSA-L calcium sulfate dihydrate Chemical compound O.O.[Ca+2].[O-]S([O-])(=O)=O PASHVRUKOFIRIK-UHFFFAOYSA-L 0.000 claims abstract description 10
- -1 poly hydro compound Chemical class 0.000 claims abstract description 10
- 238000002156 mixing Methods 0.000 claims abstract description 6
- 229910052602 gypsum Inorganic materials 0.000 claims description 14
- 239000010440 gypsum Substances 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 239000002002 slurry Substances 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 8
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 6
- 239000011707 mineral Substances 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 4
- 230000002209 hydrophobic effect Effects 0.000 claims description 3
- 238000003825 pressing Methods 0.000 claims description 3
- 238000001035 drying Methods 0.000 claims description 2
- 238000012856 packing Methods 0.000 claims description 2
- 238000000465 moulding Methods 0.000 claims 1
- 239000002245 particle Substances 0.000 abstract description 13
- 239000000428 dust Substances 0.000 abstract description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 8
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 6
- 235000019738 Limestone Nutrition 0.000 description 5
- 239000006028 limestone Substances 0.000 description 5
- 235000011132 calcium sulphate Nutrition 0.000 description 4
- 230000018044 dehydration Effects 0.000 description 4
- 238000006297 dehydration reaction Methods 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 3
- 229910000019 calcium carbonate Inorganic materials 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 229910052925 anhydrite Inorganic materials 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- ZZUFCTLCJUWOSV-UHFFFAOYSA-N furosemide Chemical class C1=C(Cl)C(S(=O)(=O)N)=CC(C(O)=O)=C1NCC1=CC=CO1 ZZUFCTLCJUWOSV-UHFFFAOYSA-N 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 230000000241 respiratory effect Effects 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 238000001238 wet grinding Methods 0.000 description 2
- 208000010392 Bone Fractures Diseases 0.000 description 1
- 208000006670 Multiple fractures Diseases 0.000 description 1
- 235000010627 Phaseolus vulgaris Nutrition 0.000 description 1
- 244000046052 Phaseolus vulgaris Species 0.000 description 1
- 210000000988 bone and bone Anatomy 0.000 description 1
- 239000004359 castor oil Substances 0.000 description 1
- 235000019438 castor oil Nutrition 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 239000003240 coconut oil Substances 0.000 description 1
- 235000019864 coconut oil Nutrition 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000013270 controlled release Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 150000004683 dihydrates Chemical group 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- ZEMPKEQAKRGZGQ-XOQCFJPHSA-N glycerol triricinoleate Natural products CCCCCC[C@@H](O)CC=CCCCCCCCC(=O)OC[C@@H](COC(=O)CCCCCCCC=CC[C@@H](O)CCCCCC)OC(=O)CCCCCCCC=CC[C@H](O)CCCCCC ZEMPKEQAKRGZGQ-XOQCFJPHSA-N 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 description 1
- 239000001095 magnesium carbonate Substances 0.000 description 1
- 229910000021 magnesium carbonate Inorganic materials 0.000 description 1
- 238000005058 metal casting Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 235000019198 oils Nutrition 0.000 description 1
- 239000012188 paraffin wax Substances 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000001038 titanium pigment Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D13/00—Pencil-leads; Crayon compositions; Chalk compositions
Definitions
- Present invention relates to dustless chalk and process for the preparation of same. More particularly present invention relates to dustless chalk and process for the preparation of same by using the poly-hydro compounds alongwith the other chemically active compounds.
- the document CN 101831218 (A) the invention relates to an environment-friendly dustless biochemical chalk and a making method thereof.
- the environment-friendly dustless biochemical chalk is made of main materials and auxiliary materials, wherein the main materials comprise the following components in parts by weight: 10-20 parts of calcium carbonate, 9-13 parts of castor oil, 6.5-8.5 parts of bean oil, 5- 6 parts of coconut oil, 14-16 parts of surfactant, 4.5-5.5 parts of magnesium carbonate and 3.2-3.8 parts of paraffin; and the auxiliary materials comprise the following components in parts by weight: 10-20 parts of calcium carbonate, 9-13 parts of castor oil, 6.5-8.5 parts of bean oil, 5- 6 parts of coconut oil, 14-16 parts of surfactant, 4.5-5.5 parts of magnesium carbonate and 3.2-3.8 parts of paraffin; and the auxiliary materials comprise the following components in parts by weight: 10-20 parts of calcium carbonate, 9-13 parts of castor oil, 6.5-8.5 parts of bean oil, 5- 6 parts of coconut oil, 14-16 parts of surfactant,
- the obtained dustless biochemical chalk has fine and flexible quality, smooth writing and bright color and is not easily broken, furthermore, the product has clear characters and easy identification no matter the product is dry or wet and is written on a blackboard, a glass or the surface of any substance, and most important of all, no dust occurs in the writing and erasing processes. But these chalks writing on black board cannot be easily erased by dry duster as it contains oily based auxiliary components.
- the main component of known chalk is calcium carbonate (CaCCb), a form of limestone.
- the first step is primary crushing.
- the major difference in processing gypsum is that it must be dehydrated to form calcium sulfate, the major component of coloured chalk. This is done in a kettle, a large combustion chamber in which the gypsum is heated to between 244 and 253 degrees Fahrenheit (116-121 degrees Celsius). It is allowed to boil until it has been reduced by twelve to fifteen percent, at which point its water content will have been reduced from 20.9 percent to between 5 and 6 percent. To further reduce the water, the gypsum is reheated to about 402 degrees Fahrenheit (204 degrees Celsius), at which point it is removed from the kettle. By now, almost all of the water has evaporated, leaving calcium sulfate.
- the particles of chalk or calcium sulfate are now conveyed to vibrating screens that sift out the finer material.
- the ensuing fine chalk is then washed, dried, packed in bags, and shipped to the manufacturer.
- the chalk factory Upon receiving chalk or calcium sulfate, the chalk factory usually grinds the materials again to render them smooth and uniformly fine.
- the manufacturer adds water to form a thick slurry with the consistency of clay.
- the slurry is then placed into and extruded from a die— an orifice of the desired long, thin shape. Cut into lengths of approximately 24.43 inches (62 centimeters), the sticks are next placed on a sheet that contains places for five such sticks.
- the sheet is then placed in an oven, where the chalk cures for four days at 188 degrees Fahrenheit (85 degrees Celsius). After it has cured, the sticks are cut into specified lengths.
- the chalk so obtained are not dustless chalk and hazardous to health.
- Object of the present invention aims at developing dustless chalk and process for the preparation of same.
- Yet another object of the present invention is to eliminate the limitations and drawbacks of the existing chalks by eliminating the soiling of the chalks.
- the dustless chalk having cylindrical shape with specified length and diameter, made of compositions comprising: calcium sulphate di-hydrate 20% to 60% and Calcium sulphate hemi-hydrate 30% to 70% mixed with poly hydro ccrr.pound; the said composition is treated with air removing agent to maintain uniformity and strength of chalk.
- gypsum heated between 100 °C and 150 °C (302 °F) partially dehydrates the mineral by driving off approximately 75% of the water contained in its chemical structure to form calcium sulphate hemi hydrate; .
- step (a) the said calcium sulphate hemi hydrate 30% to 70% of step (a) is mixed with the calcium sulphate di -hydrate 20% to 60%
- step (b) adding the poly-hydro compound to the said mixer of step (b);
- step (c ) thoroughly mixing the said mixture of step (c ) in a mixing apparatus in the known way;
- step (e) adding air-removing agent to the said slurry of step (e);
- step (f) pouring the said slurry material of step (f) in a well prepared mould for partial setting;
- step (h) i. collection of chalks formed in step (h) in a tray
- step (j) the packing the said dried chalks of step (j) and ready for dispatch.
- the invented Dustless Chalk is cylindrical in shape unlike others, which are tapered from one end to another by 1.5 to 2.0 mm.
- the cylindrical shape has uniform strength through out the length, while in case of tapered shape strength changes across the length as diameter of chalk varies. It increases breakage frequency of chalk in tapered shape, while breaking of chalk gets minimized in cylindrical shape.
- the Chalk when used for writing on well-maintained School boards releases only desired quantity for marking the substrate and is erasable with dry piece of cloth.
- a novel Dustless chalk and process for the preparation of same uses Calcium sulphate di-hydrate, Calcium sulphate hemi-hydrate, air-removing agents, and Poly-hydro compound in the predefined proportion.
- Present invention contains Calcium sulphate di-hydrate not less than 20% and not more than 60%.
- Presenl invention contains Calcium sulphate hemi-hydrate not less than 30% and not more than 70%.
- ⁇ Present invention uses Poly-hydro compound to prevent release of dust particles which disperse in air.
- the dustless chalk is having cylindrical shape with specified length and diameter, made of compositions comprising: calcium sulphate di-hydrate 20% to 60% and Calcium sulphdie hemi-hydrate 30% to 70% mixed with poly hydro compound; the said composition is treated with air removing agent to maintain uniformity and strength of chalk.
- Air removing ayent is an additive which displaces entrapped air in powder particles and makes chalks more compact
- Air removing agent is an additive which displaces entrapped air in powder particles and makes chalks more compact
- the partially dehydrated mineral is called calcium sulfate hemihydrate or calcined gypsum
- the dehydration (specifically known as calcination) begins at approximately 80 °C (176 °F), although in dry air, some dehydration will take place already at 50 °C.
- the heat energy delivered to the gypsum at this time (the heat of hydration) tends to go into driving off water (as water vapor) rather than increasing the temperature of the mineral, which rises slowly until the water is gone, then increases more rapidly.
- calcined gypsum In contrast to most minerals, which when rehydrated simply form liquid or semi-liquid pastes, or remain powdery, calcined gypsum has an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice:
- FIG 1 is process flow diagram
- the said calcium sulphate hemi hydrate 30% to 70% is mixed with the calcium sulphate di -hydrate 20% to 60 %.
- the poly-hydro compound is added to the to the said mixer of step (b).
- the mixer of calcium sulphate hemi hydrate and calcium sulphate di hydrate and poly hydro compound thoroughly mixed in a mixing apparatus in the known way.
- the slurry is made by adding water to the said thoroughly mixed mixture.
- the air removing agent is added to the said slurry.
- the said slurry is poured in a well prepared mould for partial setting.
- the hydrophobic mould release agent is used in the mould.
- the chalks ejected from the mould by pressing the ejection rods.
- the chalks ejected from mould are collected in a tray and dried. When fully dried packed and kept ready for dispatch.
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Organic Chemistry (AREA)
- Inks, Pencil-Leads, Or Crayons (AREA)
Abstract
The invention relates to a dustless chalk, having cylindrical shape with specified length and diameter. A process of making dustless chalk comprises step of preparing calcium sulphate di-hydrate 20% to 60% and Calcium sulphate hemi- hydrate 30% to 70% mixing with poly hydro compound. The said composition is treated with air removing agent while chalk is made in the known way the said composition is treated with air removing agent maintain uniformity and strength of chalk. Also the said composition is treated with poly-hydro compound to prevent release of dust particle
Description
TITLE
A NOVEL DUSTLESS CHALK AND PROCESS OF MAKING THE SAME FIELD OF THE INVENTION:
Present invention relates to dustless chalk and process for the preparation of same. More particularly present invention relates to dustless chalk and process for the preparation of same by using the poly-hydro compounds alongwith the other chemically active compounds.
BACKGROUND OF THE INVENTION:
Teachers, students and people giving presentations, commonly use school board chalks. These are tapered in design from one end to another end by 1.5-3.0 mm. On use these chalks soil the hand and leaving loose particles which are released in air during writing. These particles float in the air and enter in human body by inhalation resulting in various respiratory ailments. PRIOR ART:
In prior art there are no dustless chalks available in the market and the present invention is altogether a new product. The chalks available in the market have the tendency of more soiling of hands. It is typically seen that the existing chalks are not eco-friendly. It is also seen that the chalks available are polluting the environment thereby resulting in various respiratory ailments.
The document CN 101831218 (A) the invention relates to an environment-friendly dustless biochemical chalk and a making method thereof. The environment-friendly dustless biochemical chalk is made of main materials and auxiliary materials, wherein the main materials comprise the following components in parts by weight: 10-20 parts of calcium carbonate, 9-13 parts of castor oil, 6.5-8.5 parts of bean oil, 5- 6 parts of coconut oil, 14-16 parts of surfactant, 4.5-5.5 parts of magnesium carbonate and 3.2-3.8 parts of paraffin; and the auxiliary materials comprise the
l
following components in parts by weight: 25-45 parts of titanium pigment powder, 2-3 parts of glycerol and 0-3 parts of pigment. The obtained dustless biochemical chalk has fine and flexible quality, smooth writing and bright color and is not easily broken, furthermore, the product has clear characters and easy identification no matter the product is dry or wet and is written on a blackboard, a glass or the surface of any substance, and most important of all, no dust occurs in the writing and erasing processes. But these chalks writing on black board cannot be easily erased by dry duster as it contains oily based auxiliary components. The main component of known chalk is calcium carbonate (CaCCb), a form of limestone. Limestone deposits develop ascoccoliths (minute calcareous plates created by the decomposition of plankton skeletons) accumulate, forming sedimentary layers. Plankton, a tiny marine organism, concentrates the calcium found naturally in seawater from .04 percent to 40 percent, which is then precipitated when the plankton dies.
In the prior art chalk is generally manufactured as follows:-
Once comparatively large chunks of limestone have been quarried, and they are pulverized to meet the demands of the chalk industry. The first step is primary crushing. Various crushers exist, but the principle is the same: all compress the stone with jaws or a cone, or shatter it through impact. Secondary crushing is accomplished by smaller crushers that work at higher speeds, producing pebbles which are then ground and pulverized. The next phase, wet grinding, washes away impurities. It is used to make the fine grade of limestone necessary to make chalk suitable for writing purposes. Wet grinding is carried out in ball mills— rotating steel drums with steel balls inside that pulverize the chalk until it is very fine. Gypsum, like limestone, is also quarried and pulverized. The major difference in processing gypsum is that it must be dehydrated to form calcium sulfate, the major component of coloured chalk. This is done in a kettle, a large combustion chamber in which the gypsum is heated to between 244 and 253 degrees Fahrenheit (116-121 degrees Celsius). It is allowed to boil until it has been reduced by twelve to fifteen
percent, at which point its water content will have been reduced from 20.9 percent to between 5 and 6 percent. To further reduce the water, the gypsum is reheated to about 402 degrees Fahrenheit (204 degrees Celsius), at which point it is removed from the kettle. By now, almost all of the water has evaporated, leaving calcium sulfate.
The particles of chalk or calcium sulfate are now conveyed to vibrating screens that sift out the finer material. The ensuing fine chalk is then washed, dried, packed in bags, and shipped to the manufacturer. Upon receiving chalk or calcium sulfate, the chalk factory usually grinds the materials again to render them smooth and uniformly fine.
To make white classroom chalk, the manufacturer adds water to form a thick slurry with the consistency of clay. The slurry is then placed into and extruded from a die— an orifice of the desired long, thin shape. Cut into lengths of approximately 24.43 inches (62 centimeters), the sticks are next placed on a sheet that contains places for five such sticks. The sheet is then placed in an oven, where the chalk cures for four days at 188 degrees Fahrenheit (85 degrees Celsius). After it has cured, the sticks are cut into specified lengths. The chalk so obtained are not dustless chalk and hazardous to health.
In the prior art process there is no feature for making dustless chalk. OBJECT OF THE PRESENT INVENTION:
Object of the present invention aims at developing dustless chalk and process for the preparation of same.
Yet another object of the present invention is to provide chalks that are user friendly. Yet another object of the present invention is to provide chalks capable of releasing quantity required for writing/marking only.
Yet another object of the present invention is to eliminate the limitations and drawbacks of the existing chalks by eliminating the soiling of the chalks.
STATEMENT OF INVENTION:
Accordingly invention provides the dustless chalk, having cylindrical shape with specified length and diameter, made of compositions comprising: calcium sulphate di-hydrate 20% to 60% and Calcium sulphate hemi-hydrate 30% to 70% mixed with poly hydro ccrr.pound; the said composition is treated with air removing agent to maintain uniformity and strength of chalk.
Accordingly invention also provides a process of making dustless chalk comprises step of
a. gypsum heated between 100 °C and 150 °C (302 °F) partially dehydrates the mineral by driving off approximately 75% of the water contained in its chemical structure to form calcium sulphate hemi hydrate; .
b. the said calcium sulphate hemi hydrate 30% to 70% of step (a) is mixed with the calcium sulphate di -hydrate 20% to 60%
c. adding the poly-hydro compound to the said mixer of step (b);
d. thoroughly mixing the said mixture of step (c ) in a mixing apparatus in the known way;
e. preparing slurry of the said mixture of step (d );
f. adding air-removing agent to the said slurry of step (e);
g. pouring the said slurry material of step (f) in a well prepared mould for partial setting;
h. ejection of chalks by pressing the ejection rods;
i. collection of chalks formed in step (h) in a tray;
j. the drying the said chalks of step (i) in the tray;
k. the packing the said dried chalks of step (j) and ready for dispatch.
DRAWING
The invention is described with figure of the accompanying drawing wherein Figure 1 shows the flow sheet of process of making dustless chalk according to invention.
BRIEF DESCRIPTION OF THE INVENTION:
The invented Dustless Chalk is cylindrical in shape unlike others, which are tapered from one end to another by 1.5 to 2.0 mm. The cylindrical shape has uniform strength through out the length, while in case of tapered shape strength changes across the length as diameter of chalk varies. It increases breakage frequency of chalk in tapered shape, while breaking of chalk gets minimized in cylindrical shape. The Chalk, when used for writing on well-maintained School boards releases only desired quantity for marking the substrate and is erasable with dry piece of cloth. It is formulated in such a way that excess particles, if released due to extra force in writing, fall directly on the ground under gravitational force and do not disperse in the air due to which chalk particles do not enter human body through inhalation resulting in user friendly characteristics A novel Dustless chalk and process for the preparation of same according to the present invention, uses Calcium sulphate di-hydrate, Calcium sulphate hemi-hydrate, air-removing agents, and Poly-hydro compound in the predefined proportion.
The preferred embodiment of the dustless chalks comprises of the following:
• Present invention contains Calcium sulphate di-hydrate not less than 20% and not more than 60%.
• Presenl invention contains Calcium sulphate hemi-hydrate not less than 30% and not more than 70%.
• Present invention uses air-removing agent to maintain uniformity and strength of chalk.
· Present invention uses Poly-hydro compound to prevent release of dust particles which disperse in air.
• Present invention uses hydrophobic mould release agent, which does not affects the properties of product. The dustless chalk is having cylindrical shape with specified length and diameter, made of compositions comprising: calcium sulphate di-hydrate 20% to 60% and Calcium sulphdie hemi-hydrate 30% to 70% mixed with poly hydro compound; the
said composition is treated with air removing agent to maintain uniformity and strength of chalk.
Air removing ayent is an additive which displaces entrapped air in powder particles and makes chalks more compact Air removing agent is an additive which displaces entrapped air in powder particles and makes chalks more compact
The process steps:- Heating gypsum to between 100 °C and 150 °C (302 °F) partially dehydrates the mineral by driving off approximately 75% of the water contained in its chemical structure. The temperature and time needed depend on ambient partial pressure of H20. Temperatures as high as 170 °C are used in industrial calcination, but at these temperatures γ-anhydrite begins to form. The reaction for the partial dehydration is:
CaS0 2H20 + heat→ CaS04 ½H20 + 1½H20 (steam)
The partially dehydrated mineral is called calcium sulfate hemihydrate or calcined gypsum The dehydration (specifically known as calcination) begins at approximately 80 °C (176 °F), although in dry air, some dehydration will take place already at 50 °C. The heat energy delivered to the gypsum at this time (the heat of hydration) tends to go into driving off water (as water vapor) rather than increasing the temperature of the mineral, which rises slowly until the water is gone, then increases more rapidly.
In contrast to most minerals, which when rehydrated simply form liquid or semi-liquid pastes, or remain powdery, calcined gypsum has an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice:
CaSCv ½H20 + 1 ½ H20→ CaS04- 2H20
This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with
polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an alternative to adobe (which loses its strength when wet). The conditions of dehydration can be changed to adjust the porosity of the hemihydrate, resulting in the so-called alpha and beta hemihydrates (which are more or less chemically identical).
Referring to figure 1 which is process flow diagram, The gypsum treated as described abc.e to form calcium sulphate hemi hydrate. The said calcium sulphate hemi hydrate 30% to 70% is mixed with the calcium sulphate di -hydrate 20% to 60 %. The poly-hydro compound is added to the to the said mixer of step (b).The mixer of calcium sulphate hemi hydrate and calcium sulphate di hydrate and poly hydro compound thoroughly mixed in a mixing apparatus in the known way. The slurry is made by adding water to the said thoroughly mixed mixture. The air removing agent is added to the said slurry. The said slurry is poured in a well prepared mould for partial setting. The hydrophobic mould release agent is used in the mould. The chalks ejected from the mould by pressing the ejection rods. The chalks ejected from mould are collected in a tray and dried. When fully dried packed and kept ready for dispatch.
ADVANTAGES OF THE PRESENT INVENTION:
• It is evident visually during writing test carried out that release of dust particles is less 'n invented chalks and floating particles are also negligible in comparison to prior art chalks.
• Less soiling of hands in comparison to existing moulded school board chalks
• Controlled release of chalk particles during writing.
• Released particles directly fall on the surface under gravitational force and do not float in the air.
Claims
1. A dustless chalk, having cylindrical shape with specified length and diameter, made of compositions comprising: calcium sulphate di-hydrate 20% to 60% and Calcium sulphate hemi-hydrate 30% to 70% mixed with poly hydro compound; the said composition is treated with air removing agent to maintain uniformity and strength of chalk.
2. A process of making dustless chalk comprises step of
I. gypsum heated between 100 °C and 150 °C (302 °F) partially dehydrates the mineral by driving off approximately 75% of the water contained in its chemical structure to form calcium sulphate hemi hydrate; .
m. the said calcium sulphate hemi hydrate 30% to 70% of step (a) is mixed with the calcium sulphate di -hydrate 20% to 60
n. adding the poly-hydro compound to the said mixer of step (b);
o. thoroughly mixing the said mixer of step (c ) in a mixing apparatus in the known way;
p. preparing slurry of the said mixer of step (d );
q. adding air-removing agent to the said slurry of step (e);
r. pouring the said slurry material of step (f) in a well prepared mould for part!a; setting;
s. ejection of chalks by pressing the ejection rods;
t. collection of chalks formed in step (h) in a tray;
u. the drying the said chalks of step (i) in the tray;
v. the packing the said dried chalks of step (j) and ready for dispatch.
3. the process as claimed in claim 2 wherein the temperature and time needed for forming calcium sulphate hemi hydrate depend on ambient partial pressure of H2O.
4. The process as claimed in claim 2 wherein the hydrophobic mould release agent is used in mould while molding chalks.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IN2628MU2009 | 2010-05-13 | ||
| IN2628/MUM/2009 | 2010-05-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2011141936A1 true WO2011141936A1 (en) | 2011-11-17 |
Family
ID=44914023
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/IN2011/000334 WO2011141936A1 (en) | 2010-05-13 | 2011-05-12 | A novel dustless chalk and process of making the same |
Country Status (1)
| Country | Link |
|---|---|
| WO (1) | WO2011141936A1 (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102673246A (en) * | 2012-05-16 | 2012-09-19 | 浙江创元文具制造有限公司 | Dust-free chalk machining device and use method thereof |
| CN103468062A (en) * | 2013-08-30 | 2013-12-25 | 龙启知 | Neodymium iron boron magnetic chalk |
| CN105440804A (en) * | 2015-12-30 | 2016-03-30 | 崇夕山 | Healthy and durable chalk |
| CN105482561A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Environment-friendly chalk |
| CN105482559A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Green and healthy chalk |
| CN105482560A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Chalk not easily subjected to dust fall |
| CN105505004A (en) * | 2015-12-30 | 2016-04-20 | 崇夕山 | Low-cost lightweight chalk |
| CN105505003A (en) * | 2015-12-30 | 2016-04-20 | 崇夕山 | Environment friendly durable chalk |
| CN109021714A (en) * | 2018-05-09 | 2018-12-18 | 董英杰 | A kind of dust-free chalk and preparation method thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01203484A (en) * | 1988-02-09 | 1989-08-16 | Hagoromo Bungu Kk | Chalk |
| CN1078686A (en) * | 1992-05-18 | 1993-11-24 | 李范桥 | Nontoxic dust-free chalk and manufacture craft thereof |
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2011
- 2011-05-12 WO PCT/IN2011/000334 patent/WO2011141936A1/en active Application Filing
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01203484A (en) * | 1988-02-09 | 1989-08-16 | Hagoromo Bungu Kk | Chalk |
| CN1078686A (en) * | 1992-05-18 | 1993-11-24 | 李范桥 | Nontoxic dust-free chalk and manufacture craft thereof |
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| DATABASE WPI Week 198939, 14 September 2011 Derwent World Patents Index; AN 1989-280949 * |
| DATABASE WPI Week 199711, 14 September 2011 Derwent World Patents Index; AN 1997-109536 * |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102673246A (en) * | 2012-05-16 | 2012-09-19 | 浙江创元文具制造有限公司 | Dust-free chalk machining device and use method thereof |
| CN103468062A (en) * | 2013-08-30 | 2013-12-25 | 龙启知 | Neodymium iron boron magnetic chalk |
| CN105440804A (en) * | 2015-12-30 | 2016-03-30 | 崇夕山 | Healthy and durable chalk |
| CN105482561A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Environment-friendly chalk |
| CN105482559A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Green and healthy chalk |
| CN105482560A (en) * | 2015-12-30 | 2016-04-13 | 崇夕山 | Chalk not easily subjected to dust fall |
| CN105505004A (en) * | 2015-12-30 | 2016-04-20 | 崇夕山 | Low-cost lightweight chalk |
| CN105505003A (en) * | 2015-12-30 | 2016-04-20 | 崇夕山 | Environment friendly durable chalk |
| CN109021714A (en) * | 2018-05-09 | 2018-12-18 | 董英杰 | A kind of dust-free chalk and preparation method thereof |
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