CA2009294A1 - Ceramic powders for electrostatic powder coating and processes for their preparation - Google Patents
Ceramic powders for electrostatic powder coating and processes for their preparationInfo
- Publication number
- CA2009294A1 CA2009294A1 CA002009294A CA2009294A CA2009294A1 CA 2009294 A1 CA2009294 A1 CA 2009294A1 CA 002009294 A CA002009294 A CA 002009294A CA 2009294 A CA2009294 A CA 2009294A CA 2009294 A1 CA2009294 A1 CA 2009294A1
- Authority
- CA
- Canada
- Prior art keywords
- ceramic
- powders
- milling
- powder
- frits
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000000919 ceramic Substances 0.000 title claims abstract description 68
- 239000000843 powder Substances 0.000 title claims abstract description 68
- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000011248 coating agent Substances 0.000 title claims abstract description 14
- 238000000576 coating method Methods 0.000 title claims abstract description 14
- 238000002360 preparation method Methods 0.000 title claims abstract description 7
- 238000003801 milling Methods 0.000 claims abstract description 17
- 239000002245 particle Substances 0.000 claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 10
- 239000000126 substance Substances 0.000 claims abstract description 10
- 210000003298 dental enamel Anatomy 0.000 claims description 6
- 238000009837 dry grinding Methods 0.000 claims description 4
- 230000005684 electric field Effects 0.000 claims description 2
- 229920001296 polysiloxane Polymers 0.000 abstract description 6
- -1 polysiloxanes Polymers 0.000 abstract description 5
- 238000009503 electrostatic coating Methods 0.000 description 8
- 238000009826 distribution Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000000875 corresponding effect Effects 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000007873 sieving Methods 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- 239000005046 Chlorosilane Substances 0.000 description 1
- 239000007900 aqueous suspension Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 150000001718 carbodiimides Chemical class 0.000 description 1
- KOPOQZFJUQMUML-UHFFFAOYSA-N chlorosilane Chemical class Cl[SiH3] KOPOQZFJUQMUML-UHFFFAOYSA-N 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000010410 dusting Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 239000012948 isocyanate Substances 0.000 description 1
- 150000002513 isocyanates Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 150000004819 silanols Chemical class 0.000 description 1
- 150000003377 silicon compounds Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000004528 spin coating Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000001238 wet grinding Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
- C04B41/4584—Coating or impregnating of particulate or fibrous ceramic material
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
- C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
- C04B41/5025—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials with ceramic materials
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
- C04B41/81—Coating or impregnation
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
- C04B41/81—Coating or impregnation
- C04B41/85—Coating or impregnation with inorganic materials
- C04B41/87—Ceramics
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
- C23D5/00—Coating with enamels or vitreous layers
- C23D5/04—Coating with enamels or vitreous layers by dry methods
Abstract
CERAMIC POWDERS FOR ELECTROSTATIC POWDER COATING AND
PROCESSES FOR THEIR PREPARATION
ABSTRACT OF THE DISCLOSURE
Surprisingly good adhesion is achieved between the surface of a ceramic article and ceramic powder applied to said surface by electrostatic techniques when the ceramic powder particles are surface treated with electrically insulating substances which comprise halogen-free polysiloxanes or mixtures thereof which react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amount of 0.05 to 0.1% by weight, relative to the ceramic powder, and the ceramic powder, which has been milled at a milling temperature of 70 to 100°C or has been cold-milled and then after-treated at temperatures of between 70°C and 300°C, has a fineness of 1 to 100 µm, a resistivity of 1012 to 1016 ohm.cm, a cubic coefficient of thermal expansion of (130 - 230) . 10-7K-1 and a fluidity of 50 - 90 g/30 sec.
LeA 26 534
PROCESSES FOR THEIR PREPARATION
ABSTRACT OF THE DISCLOSURE
Surprisingly good adhesion is achieved between the surface of a ceramic article and ceramic powder applied to said surface by electrostatic techniques when the ceramic powder particles are surface treated with electrically insulating substances which comprise halogen-free polysiloxanes or mixtures thereof which react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amount of 0.05 to 0.1% by weight, relative to the ceramic powder, and the ceramic powder, which has been milled at a milling temperature of 70 to 100°C or has been cold-milled and then after-treated at temperatures of between 70°C and 300°C, has a fineness of 1 to 100 µm, a resistivity of 1012 to 1016 ohm.cm, a cubic coefficient of thermal expansion of (130 - 230) . 10-7K-1 and a fluidity of 50 - 90 g/30 sec.
LeA 26 534
Description
Z(~29~
Bayer Italia S.p.A. I-20156 Milan Viale Certosa, 126 Le/jo-c CERAMIC POWDERS FOR ELECTROSTATIC POWDER COATING AND
PROCESSES FOR THEIR PREPARATION
The present invention relates to ceramic powders for electrostatic powder coating of ceramic parts and a process for their preparation.
BAC~GROUND OF THE INVENTION
It is known that enamel powders can be electrically charged and can be applied to metallic substrates in an electric field with a potential difference of about 60000 to about 100000 volt. For this purpose, the particle surfaces of the enamel powders are -oated with insulating substances, which are added to the enamel frits in an amount of 0.1 to 2.0~ by weight before or during dry milling, in order to achieve a resistivity of 10l2 to 1016 ohm.cm. The insulating substances used are silanols, isocyanates, silicon/nitrogen compounds, carbodiimides, chlorosilanes and organopolysiloxanes (German Offenlegungsschrift 2,015,072).
Ceramic surfaces are coated either by wet coating by means of pouring, spraying, sprinkling and spin coating or by modifications of these techniques, or by the dry method, where ceramic granules or ceramic powders are applied to a preheated substrate by sieving, dusting or Le A 26 534 Z(~294 pouring, so that the ceramic part-cle partially melts during application itself, and thus adheres to the substrate and flows to ~i~e a smooth surface in the subsequent heat treatment.
Ceramic powders can also be applied electrostatically to ceramic surfaces, but adhesion of the powder is so small that it is virtually impossible to handle the parts bef~re the sintering and firing ~rocess since the powder falls off the parts.
It was therefore the object to provide ceramic powders which can be applied electrostatically to ceramic surfaces and have good adhesion to the ceramic surfaces.
This object could be achieved ~ith the ceramic powders according to the invention.
BRIEF DESCRIPTION OF THE INVENTION
It has now been discovered that surprisingly good adhesion is achieved between the surface of a ceramic article and ceramic powder applied to said surface by electrostatic techniques when the ceramic powder particles are surface treated with electrically insulating substances which comprises halogen-free polysiloxanes or mixtures thereof which react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amount of 0.05 to 0.1% by weight, relative to the ceramic powder, and the ceramic powder, which has been milled at a milling temperature of 70 to 100~C, has a fineness of 1 to 100 ~m, a resistivity of 1012 to 1016 ohm.cm, a cubic coefficient of thermal expansion of (130 - 230) . 10 7K 1 and a fluidity of 50 - 90 g/30 sec.
Le A 26 534 - 2 -20~3294 The invention also involves a process for preparing the ceramic powders and an improved method of electrostatic coating by use of the powders.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to ceramic powders for electrostatic powder coating of ceramic parts having a surface treated with electrically insulating substances. The electrically insulating substances are halogen-free polysiloxanes or mixtures thereof and react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amouri~ of 0.05 - 0.1% by weight, relative to the ceramic powder, The ceramic powder which has been milled a~ a milling temperature of 70 to 100C or has bsen cold-milled and then after-treated st tomperatures of between 70C and 300C, has a fineness of 1 to 100 ~m, a re-sistivity of 1012 to 1016 ohm.cm and a cubic coefficient.
of thermal expansiDn of (130 - 230) . 10-7K-1.
Le A 26 534 - 3 -:
.
- , ' . ,~ ~ ' .. ' Z(~ 29~
Preferred ceramic powders are those which are treated with polymethylhydrogensiloxanes of the formula / H
I
~CH3)3 Si ~ - 7i-o - Si-~C~3)3 \CH~ / n in which n = 5 - 50, or mixtures thereof The invention also relates to a process for the preparation of the ceramic powders according to the invention, which is characterised in that the ceramic frits corresponding to the powders are trested with 0 05 to 0 1% by weight, relative to the frit, of halogen-free polysiloxanes reacting with their reactive groups at the surfaces of the frit particles, or mixtures of the said polysiloxanes, before or during the dry milling to be carried out at 70 ~o 100C or before or during ~he cold milling followed by heat treatment between 70C and 300C said ceramic frits being milled to powders having a particle BiZe of 1 to 100 ~m, a resi~tivity of 1012 to 1016 ohm cm and a cubic coefficient of therm31 ex-pansion of (130 - 120) 10-7K-l In a praferr-d procedur-, the ceramic frits correspond-ing to the powders ere treated with polymethylhydrogen-siloxanes of the formula Le A 26 534 - 4 -2C~ 9~
~I ~
~CH3)3 Si- tIi 7si ~CH 3)3 ~CH3 n in which n = 5 - 50, or mixtures thereof.
The ceramic powders according to the invention are used for the electrostatic powder coating of ceramic parts.
The electrostatic dry powder coating according to the invention has considerable advantages over other techniques:
For example, it is not necessary to carry out wet milling of the ceramic frits, for example for the technique of wet coating, in which aqueous suspensions are formed which achieve the required consistency of the slip only through the addition of clay and electrolytes. The dry process for removing water from the applied slip layers prior to firing is likewise dispensed with. This means that the procedure is simplified and a considerable amount of energy is saved in the electrostatic coating process according ~o the invention.
In addition, there is substantially less material consumed, since the ceramic powder treated by the process according to the invention is deposited in electrostatic coatin~ booths with an efficiency of > 99~.
Le A 26 534 ~ 5 ~
~. :
Z(~09~9(~
In electrostatic coating, the powders furthermore remain in a closed system, and the air emerging from the booth is purified via filters. A closed system of this type is present neither in wet coating nor in the dry process by means of sieving or pouring of ceramic granules or powders. Since the ceramic frits are, as a rule, lead-containing, the conventional application systems require stringent safety precautions.
For electrostatic powder coating on ceramic surfaces, it is, however, essential to have ceramic powders which permit electrostatic coating and adhere well to the ceramic substrate. These conditions are fulfilled by the ceramic powders according to the invention.
The Examples which follow are intended to illustrate the invention in more detail without imposing any restriction.
Exam~le 1 A 1000 kg mill is charged as follows:
1850 kg of Alubit spheres having a diameter of 32 to 45 mm, 1000 kg of a commercial frit in flake or granular form, consisting of 64% by weight of PbO, 33% by weight of SiO2 and 3% by weight of A12O3, Le A 26 534 - 6 -20~ 9~
0.5 kg of a mixture of polymethylhydrogensiloxanes (~
0.05% by weight) of the formula CH3-si- ~ fi- ~ si-(CH3~3 CH3 n in which n = 5 - 25.
Before the ball mill is closed, the interior is flushed with nitrogen gas in order to eliminate the oxygen.
The ceramic frit is milled for about 6 to 7 hours in order to achieve the desired fineness, that is to say a particle size distribution of lO0 percent by weight less than lO0 micron about 80 percent by weight less than 40 micron about 60 percent by weight less than 25 micron about 40 percent by weight less than 15 micron.
During milling, the temperature in the interior of the mill increases to about 80C.
The powder removed after the milling procedure has a resistivity of 10l~ ohm.cm, flow characteristics of 50 to 80 g/30 sec, measured using an apparatus from Sames, and a cubic coefficient of thermal expansion of 180 - 200 1 o-7K- I
~e A 26 534 ~ 7 ~
: :' ; ~' :: . ;
Z~ 329~
The fluidity is determined using an apparatus fxom Sames, Grenoble. The method of measurement is described in detail in a publication by Dr. H.J. Schittenhelm in the Journal of the VDEFa, Volume 32 (1984), Part 10, pages 137 - 148. The optimum flow value for electrostatic coating is between 50 and 90 g/30 sec. Values below 50 ~/30 sec and especially below 40 g/30 sec are to be regarded as critical in that they give rise to coating difficulties owing to poor flow characteristics.
ExamDle Z
Milling is carried out in a 1 ~9 mill, which is charged with lO00 g of the frit described in Example 1 and 5 kg of grinding balls consisting of stea~ite and having a diameter of 15 Lo 25 mm, as well 85 0.8 g (0.08% by weight) of polymethylhydrogensiloxane mixture. Dry mil-ling to the prescribed par~icle size distribution as described under Example 1 is carried ou~ in the course of 5 hours, The temperature of the mill base during milling is approximately room temperaturH. The resis~i-vity i6 1015 ohm.cm and the flow characteristics are 0 gl30 sec. The material i6 unsuitsble for electrostatic coating. If this powder is thermally after-treated, for example at a temperaturo of 150C for 6 hours, the flow value rises to about 70 9~30 sec. and the material is suitable for electrostatic coating.
Le A 26 534 ~ 8 -'~
. :
ZC~C~9~94 Exam~le 3 Milling is carried ou~ analogously to Example 2, excep~
that the 1 kg mill is preheated and is heated from outside during the milling process, so that the mill base has a temperature of about 70C during milling. After the particle size distribution as described in Example 1 has been reached, the ceramic powder has a resistivity of 1016 ohm.cm and flow characteristics of 65 g/30 sec according to the Sames test. This material can be satisfactorily applied by the electrostatic method.
ExamDle 4 Milling is carried out analogously to Example 1, except that 1000 9 of a commercial ceramic frit are used, the said frit having the following composition:
SiO253% by weight Al2O38% by weight B2O39% by weight ZnO 10% by weight CaO 8% by weight Le A 26 534 - 9 -Z(~Q~94 MgO 3~ by weight K2O 4% by weight Zr2 5~ by weight After the particle size distribution as described in S Example 1 has been reached, the mill base has a resistivity of 10l5 ohm.cm and flow characteristics of g/30 sec. The ceramic powder is suitable for electrostatic coating and can be fused on unfired bodies.
Instead of the discontinuous ball mills, continuous milling units can bP used, such as, for example, vibratory mills or Hardinge mills. The former develop a milling temperature of about 100C while the latter have to be heated from outside in order to achieve the required reaction temperature of 70 - 100C. In both lS cases, a mixing mill which is charged with a few heavy grinding balls has to be located upstream in order to ensure that the ceramic frits to be milled are homogenised with the encapsulation oil.
Le A 26 ~34 - 10 -
Bayer Italia S.p.A. I-20156 Milan Viale Certosa, 126 Le/jo-c CERAMIC POWDERS FOR ELECTROSTATIC POWDER COATING AND
PROCESSES FOR THEIR PREPARATION
The present invention relates to ceramic powders for electrostatic powder coating of ceramic parts and a process for their preparation.
BAC~GROUND OF THE INVENTION
It is known that enamel powders can be electrically charged and can be applied to metallic substrates in an electric field with a potential difference of about 60000 to about 100000 volt. For this purpose, the particle surfaces of the enamel powders are -oated with insulating substances, which are added to the enamel frits in an amount of 0.1 to 2.0~ by weight before or during dry milling, in order to achieve a resistivity of 10l2 to 1016 ohm.cm. The insulating substances used are silanols, isocyanates, silicon/nitrogen compounds, carbodiimides, chlorosilanes and organopolysiloxanes (German Offenlegungsschrift 2,015,072).
Ceramic surfaces are coated either by wet coating by means of pouring, spraying, sprinkling and spin coating or by modifications of these techniques, or by the dry method, where ceramic granules or ceramic powders are applied to a preheated substrate by sieving, dusting or Le A 26 534 Z(~294 pouring, so that the ceramic part-cle partially melts during application itself, and thus adheres to the substrate and flows to ~i~e a smooth surface in the subsequent heat treatment.
Ceramic powders can also be applied electrostatically to ceramic surfaces, but adhesion of the powder is so small that it is virtually impossible to handle the parts bef~re the sintering and firing ~rocess since the powder falls off the parts.
It was therefore the object to provide ceramic powders which can be applied electrostatically to ceramic surfaces and have good adhesion to the ceramic surfaces.
This object could be achieved ~ith the ceramic powders according to the invention.
BRIEF DESCRIPTION OF THE INVENTION
It has now been discovered that surprisingly good adhesion is achieved between the surface of a ceramic article and ceramic powder applied to said surface by electrostatic techniques when the ceramic powder particles are surface treated with electrically insulating substances which comprises halogen-free polysiloxanes or mixtures thereof which react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amount of 0.05 to 0.1% by weight, relative to the ceramic powder, and the ceramic powder, which has been milled at a milling temperature of 70 to 100~C, has a fineness of 1 to 100 ~m, a resistivity of 1012 to 1016 ohm.cm, a cubic coefficient of thermal expansion of (130 - 230) . 10 7K 1 and a fluidity of 50 - 90 g/30 sec.
Le A 26 534 - 2 -20~3294 The invention also involves a process for preparing the ceramic powders and an improved method of electrostatic coating by use of the powders.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to ceramic powders for electrostatic powder coating of ceramic parts having a surface treated with electrically insulating substances. The electrically insulating substances are halogen-free polysiloxanes or mixtures thereof and react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amouri~ of 0.05 - 0.1% by weight, relative to the ceramic powder, The ceramic powder which has been milled a~ a milling temperature of 70 to 100C or has bsen cold-milled and then after-treated st tomperatures of between 70C and 300C, has a fineness of 1 to 100 ~m, a re-sistivity of 1012 to 1016 ohm.cm and a cubic coefficient.
of thermal expansiDn of (130 - 230) . 10-7K-1.
Le A 26 534 - 3 -:
.
- , ' . ,~ ~ ' .. ' Z(~ 29~
Preferred ceramic powders are those which are treated with polymethylhydrogensiloxanes of the formula / H
I
~CH3)3 Si ~ - 7i-o - Si-~C~3)3 \CH~ / n in which n = 5 - 50, or mixtures thereof The invention also relates to a process for the preparation of the ceramic powders according to the invention, which is characterised in that the ceramic frits corresponding to the powders are trested with 0 05 to 0 1% by weight, relative to the frit, of halogen-free polysiloxanes reacting with their reactive groups at the surfaces of the frit particles, or mixtures of the said polysiloxanes, before or during the dry milling to be carried out at 70 ~o 100C or before or during ~he cold milling followed by heat treatment between 70C and 300C said ceramic frits being milled to powders having a particle BiZe of 1 to 100 ~m, a resi~tivity of 1012 to 1016 ohm cm and a cubic coefficient of therm31 ex-pansion of (130 - 120) 10-7K-l In a praferr-d procedur-, the ceramic frits correspond-ing to the powders ere treated with polymethylhydrogen-siloxanes of the formula Le A 26 534 - 4 -2C~ 9~
~I ~
~CH3)3 Si- tIi 7si ~CH 3)3 ~CH3 n in which n = 5 - 50, or mixtures thereof.
The ceramic powders according to the invention are used for the electrostatic powder coating of ceramic parts.
The electrostatic dry powder coating according to the invention has considerable advantages over other techniques:
For example, it is not necessary to carry out wet milling of the ceramic frits, for example for the technique of wet coating, in which aqueous suspensions are formed which achieve the required consistency of the slip only through the addition of clay and electrolytes. The dry process for removing water from the applied slip layers prior to firing is likewise dispensed with. This means that the procedure is simplified and a considerable amount of energy is saved in the electrostatic coating process according ~o the invention.
In addition, there is substantially less material consumed, since the ceramic powder treated by the process according to the invention is deposited in electrostatic coatin~ booths with an efficiency of > 99~.
Le A 26 534 ~ 5 ~
~. :
Z(~09~9(~
In electrostatic coating, the powders furthermore remain in a closed system, and the air emerging from the booth is purified via filters. A closed system of this type is present neither in wet coating nor in the dry process by means of sieving or pouring of ceramic granules or powders. Since the ceramic frits are, as a rule, lead-containing, the conventional application systems require stringent safety precautions.
For electrostatic powder coating on ceramic surfaces, it is, however, essential to have ceramic powders which permit electrostatic coating and adhere well to the ceramic substrate. These conditions are fulfilled by the ceramic powders according to the invention.
The Examples which follow are intended to illustrate the invention in more detail without imposing any restriction.
Exam~le 1 A 1000 kg mill is charged as follows:
1850 kg of Alubit spheres having a diameter of 32 to 45 mm, 1000 kg of a commercial frit in flake or granular form, consisting of 64% by weight of PbO, 33% by weight of SiO2 and 3% by weight of A12O3, Le A 26 534 - 6 -20~ 9~
0.5 kg of a mixture of polymethylhydrogensiloxanes (~
0.05% by weight) of the formula CH3-si- ~ fi- ~ si-(CH3~3 CH3 n in which n = 5 - 25.
Before the ball mill is closed, the interior is flushed with nitrogen gas in order to eliminate the oxygen.
The ceramic frit is milled for about 6 to 7 hours in order to achieve the desired fineness, that is to say a particle size distribution of lO0 percent by weight less than lO0 micron about 80 percent by weight less than 40 micron about 60 percent by weight less than 25 micron about 40 percent by weight less than 15 micron.
During milling, the temperature in the interior of the mill increases to about 80C.
The powder removed after the milling procedure has a resistivity of 10l~ ohm.cm, flow characteristics of 50 to 80 g/30 sec, measured using an apparatus from Sames, and a cubic coefficient of thermal expansion of 180 - 200 1 o-7K- I
~e A 26 534 ~ 7 ~
: :' ; ~' :: . ;
Z~ 329~
The fluidity is determined using an apparatus fxom Sames, Grenoble. The method of measurement is described in detail in a publication by Dr. H.J. Schittenhelm in the Journal of the VDEFa, Volume 32 (1984), Part 10, pages 137 - 148. The optimum flow value for electrostatic coating is between 50 and 90 g/30 sec. Values below 50 ~/30 sec and especially below 40 g/30 sec are to be regarded as critical in that they give rise to coating difficulties owing to poor flow characteristics.
ExamDle Z
Milling is carried out in a 1 ~9 mill, which is charged with lO00 g of the frit described in Example 1 and 5 kg of grinding balls consisting of stea~ite and having a diameter of 15 Lo 25 mm, as well 85 0.8 g (0.08% by weight) of polymethylhydrogensiloxane mixture. Dry mil-ling to the prescribed par~icle size distribution as described under Example 1 is carried ou~ in the course of 5 hours, The temperature of the mill base during milling is approximately room temperaturH. The resis~i-vity i6 1015 ohm.cm and the flow characteristics are 0 gl30 sec. The material i6 unsuitsble for electrostatic coating. If this powder is thermally after-treated, for example at a temperaturo of 150C for 6 hours, the flow value rises to about 70 9~30 sec. and the material is suitable for electrostatic coating.
Le A 26 534 ~ 8 -'~
. :
ZC~C~9~94 Exam~le 3 Milling is carried ou~ analogously to Example 2, excep~
that the 1 kg mill is preheated and is heated from outside during the milling process, so that the mill base has a temperature of about 70C during milling. After the particle size distribution as described in Example 1 has been reached, the ceramic powder has a resistivity of 1016 ohm.cm and flow characteristics of 65 g/30 sec according to the Sames test. This material can be satisfactorily applied by the electrostatic method.
ExamDle 4 Milling is carried out analogously to Example 1, except that 1000 9 of a commercial ceramic frit are used, the said frit having the following composition:
SiO253% by weight Al2O38% by weight B2O39% by weight ZnO 10% by weight CaO 8% by weight Le A 26 534 - 9 -Z(~Q~94 MgO 3~ by weight K2O 4% by weight Zr2 5~ by weight After the particle size distribution as described in S Example 1 has been reached, the mill base has a resistivity of 10l5 ohm.cm and flow characteristics of g/30 sec. The ceramic powder is suitable for electrostatic coating and can be fused on unfired bodies.
Instead of the discontinuous ball mills, continuous milling units can bP used, such as, for example, vibratory mills or Hardinge mills. The former develop a milling temperature of about 100C while the latter have to be heated from outside in order to achieve the required reaction temperature of 70 - 100C. In both lS cases, a mixing mill which is charged with a few heavy grinding balls has to be located upstream in order to ensure that the ceramic frits to be milled are homogenised with the encapsulation oil.
Le A 26 ~34 - 10 -
Claims (6)
1. In an improved ceramic powder for electro-static powder coating of ceramic parts with the powder particles having a surface treated with electrically insulating substances, wherein the improvement comprises said electrically insulating substances comprising halogen-free poly-siloxanes or mixtures thereof which react with their reactive groups at the particle surfaces of the ceramic powders and are present in an amount of 0.05 to 0.1% by weight, relative to the ceramic powder, and the ceramic powder, which has been milled at a milling temperature of 70 to 100°C or has been cold-milled and then after-treated at temperatures between 70°C and 300°C, has a fineness of 1 to 100 µm, a resistivity of 1012 to 1016 ohm.cm, a cubic coefficient of thermal expansion of (130 - 230) . 10-7K-1 and a fluidity of 50 to 90 g/30 sec.
2. Ceramic powders according to claim 1, wherein the insulating substance is one or more polymethyl-hydrogensiloxanes of the formula Le A 26 534 - 11-in which n is 5 - 50.
3. Process for the preparation of ceramic powders according to claim 1 having a surface treated with electrically insulating substances, which process com-prises dry milling ceramic frits at 70 to 100°C or cold milling ceramic frits and then heat treating them at temperatures of between 70°C and 300°C and treating the frits, before or during the milling, with 0.05 to 0.1%
by weight, relative to the frit, of halogen-free poly-siloxanes which react with their reactive groups at the surfaces of the frit particles, and milling the powders to a particle size of 1 to 100 µm, a resistivity of 1012 to 1016 ohm.cm and a cubic coefficient of thermal ex-pansion of (130 to 230) . 10-7K-1.
by weight, relative to the frit, of halogen-free poly-siloxanes which react with their reactive groups at the surfaces of the frit particles, and milling the powders to a particle size of 1 to 100 µm, a resistivity of 1012 to 1016 ohm.cm and a cubic coefficient of thermal ex-pansion of (130 to 230) . 10-7K-1.
4. Process for the preparation of ceramic powders according to claim 3 wherein the frits corresponding to the powders are treated with one or more polymethyl-hydrogensiloxanes of the formula in which n is 5 - 50.
5. In an improved method for electrostatic powder coating of ceramic articles wherein ceramic enamel powders are electrically charged and applied to a ceramic article surface in an electric field, the improvement comprises said ceramic enamel powders are powders as claimed in claim 1.
6. The method according to claim 5 wherein the ceramic enamel powders are powders as claimed in claim 2.
Le A 26 534 - 12 -
Le A 26 534 - 12 -
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT8919329A IT1228296B (en) | 1989-02-07 | 1989-02-07 | CERAMIC POWDERS FOR THE ELECTROSTATIC APPLICATION OF POWDERS AND PROCESS TO PRODUCE THEM. |
| IT19329A/89 | 1989-02-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2009294A1 true CA2009294A1 (en) | 1990-08-07 |
Family
ID=11156784
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002009294A Abandoned CA2009294A1 (en) | 1989-02-07 | 1990-02-05 | Ceramic powders for electrostatic powder coating and processes for their preparation |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0382003A3 (en) |
| JP (1) | JPH02243580A (en) |
| CA (1) | CA2009294A1 (en) |
| IT (1) | IT1228296B (en) |
| MX (1) | MX171811B (en) |
| PT (1) | PT92993A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1241063B (en) * | 1990-02-15 | 1993-12-29 | Bayer Italia Spa | CERAMIC DIMENSIONS FOR THE ELECTROSTATIC APPLICATION OF POWDERS AND PROCEDURE FOR THEIR PRODUCTION |
| IT1245353B (en) * | 1991-03-19 | 1994-09-20 | Bayer Italia Spa | CERAMIC MICROGRANULATES FOR ELECTROSTATIC APPLICATION AND PROCESS FOR THEIR PREPARATION |
| IT1254974B (en) * | 1992-06-18 | 1995-10-11 | Bayer Italia Spa | COMPOSITE, SLIDING, HYDROPHOBIC GRANULATES, A PROCEDURE FOR THEIR PREPARATION AND THEIR USE |
| DE4239541C2 (en) * | 1992-11-25 | 1995-06-08 | Cerdec Ag | Process for glazing non-metallic substrates |
| DE19531170C1 (en) * | 1995-08-24 | 1996-11-21 | Cerdec Ag | Electrostatically applicable coating powder for ceramic coatings |
| DE19722273A1 (en) * | 1997-05-28 | 1998-12-03 | Cerdec Ag | Coating powder for the electrostatic coating of glass and ceramic and metallic substrates, its production and use |
| DE10104121C2 (en) | 2001-01-29 | 2003-03-06 | Bosch Gmbh Robert | Process for producing a starting element |
| DE102016107992B4 (en) | 2016-04-29 | 2018-05-17 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Process for dry coating of substrates |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3928668A (en) * | 1974-05-06 | 1975-12-23 | Ferro Corp | Electrostatic deposition of dry ceramic powders |
| CS203209B1 (en) * | 1978-10-20 | 1981-02-27 | Alfonz Moravcik | Method of coating the glazes on the ceramic materials in electric field |
| DE3700702C1 (en) * | 1987-01-13 | 1988-02-11 | Bayer Ag | Enamel powder coated with organopolysiloxanes for electrostatic powder application and process for their production |
| JPH01212250A (en) * | 1988-02-19 | 1989-08-25 | Hosokawa Micron Corp | Method for coloring frit composition for dry electrostatic coating |
-
1989
- 1989-02-07 IT IT8919329A patent/IT1228296B/en active
-
1990
- 1990-01-23 MX MX019213A patent/MX171811B/en unknown
- 1990-01-25 EP EP19900101432 patent/EP0382003A3/en not_active Withdrawn
- 1990-01-29 PT PT92993A patent/PT92993A/en not_active Application Discontinuation
- 1990-02-01 JP JP2020516A patent/JPH02243580A/en active Pending
- 1990-02-05 CA CA002009294A patent/CA2009294A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| IT1228296B (en) | 1991-06-07 |
| EP0382003A2 (en) | 1990-08-16 |
| MX171811B (en) | 1993-11-16 |
| PT92993A (en) | 1990-08-31 |
| JPH02243580A (en) | 1990-09-27 |
| IT8919329A0 (en) | 1989-02-07 |
| EP0382003A3 (en) | 1991-09-25 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued |