FR2488154A1 - METHOD AND DEVICE FOR APPLYING POWDER COATING REAGENTS - Google Patents

Abstract

A METHOD AND A DEVICE FOR DISPERSING POWDER COATING REAGENTS IN A FLOW OF CARRIER GAS ON THE SURFACE OF A SUPPORT. A POWDER COATING REAGENT IS MIXED WITH A FLOW OF CARRIER GAS. MIXTURE TURBULENCE IS PRODUCED IN ORDER TO MAINTAIN A UNIFORM DISTRIBUTION OF THE REAGENT IN THE CARRIER GAS. THE POWDER COATING REAGENT IS DELIVERED TO THE SURFACE OF THE SUPPORT BY A NOZZLE PLACED A SHORT DISTANCE FROM THE SURFACE TO BE COVERED.

Description

2488 154

  The present invention relates generally to the technique of depositing a coating on a support, in particular a glass support, and it relates more precisely to the technique of depositing a coating from a coating composition in powder. Different methods are known in the art for

  cover the glass with metal films or metal oxides-

  liques. A technique for depositing films of different metal oxides on a hot glass surface, in the

  part of the manufacturing of a continuous ribbon of glass by float

  ge, is described in US Patent 3,660,061 (Donley et al.). A mixture of organometallic compounds in organic solution is sprayed onto a glass surface at a temperature high enough to produce a thermal reaction of the organometallic compounds, resulting in the formation of a metal oxide film. This technique produces films of long-lasting metal oxides, with desirable properties from the point of view of aesthetics and control of solar energy. The use of large volumes of solvent produces rapid cooling of the glass, but

  its effects on health, safety and the environment

  have more serious disadvantages.

  These drawbacks can be reduced or eliminated by eliminating the organic solvent. A process for the solvent-free chemical vapor deposition of coatings from vaporized powder coating reagents is described in

  U.S. Patent No. 3,852,098 (Bloss et al.). A reaction

  powder coating material is dispersed in a hot stream of gas, vaporized and directed towards the surface to be coated which is

  maintained at least at the temperature at which the coating reagent

  is pyrolized, so as to deposit a film. Certainly, the disadvantages of a system comprising a solvent are avoided,

  but spraying the coating reagent requires temperatures

  crossed out high, with the risk of premature thermal reaction

  certain coating reagents.

  Another method of vapor deposition is described in

  U.S. Patent No. 4,182,783 (Henery), consisting of fluidi-

  be a solid particulate coating reagent by introducing

  a volume of fluidizing gas through a mass of reagent.

  The fluidized mixture of coating reagent and gas is diluted with an additional volume of gas before being dispensed onto

  the surface of the. support to be coated. A device for the applica-

  tion of the fluidization technique of a partial reagent bed

  solid coating coating is described in US patent na 4,182,783 and is claimed in US patent application na 74,582, filed September 13, 1979

by the same inventor.

  The subject of the invention is a method which eliminates the health, safety and environmental problems of a coating technique based on the use of a solvent, the risks of high temperature vaporization of a deposition technique. in the vapor phase and the complication of a coating technique

  from a powder in a fluidized bed.

  The present invention provides a method and a device

  tif for dispersing powder coating reagents in a

  carrier gas stream and to distribute the compound evenly

  sition. of powder coating on the surface of a support to be coated. Powder coating reagent is obtained

  with a very fine particle size and mixed with a coating

  carrier gas rant. Turbulence of the mixture is produced by means of at least one baffle, in order to maintain a uniform distribution of the powder coating reagent in the carrier gas during its path to the support to be coated. The powder coating reagent is delivered to the surface of the support by a nozzle placed a short distance from the surface to be coated. Typically, the length of the nozzle is greater than

  its width, preferably being substantially equal to the dimension

  parallel sion of the support, and it is generally oriented perpendicular to the direction of the relative movement between

the slot and the support.

  The figure illustrates the spray coating system.

  tion of powder according to the present invention. A powder coating reagent is introduced into the system and mixed

  with air. At the entry of the mixture into the coating chamber

  a baffle shouts a turbulence which maintains a uniform distribution of the powder in the mixture, until it is delivered, through the nozzle in the form of a slit,

on the surface to be coated.

  A support to be coated, in particular a sheet of glass, is maintained in a position, preferably horizontal, in

  a coating station. According to a particular embodiment

  strongly preferred, the support is maintained in an atmosphere

  oxidizing at a temperature sufficient to pyrolyze a reaction

  coating and deposit a metal oxide film

on the surface of the support.

  A coating reagent is prepared in the form of a powder, preferably having a fairly uniform particle size distribution of the order of 500 to 600 microns or less. Among the coating reagents which are suitable in the context of the present invention, mention will be made of metal beta-ketonates

  and other organic metal salts, such as acetates, hexa-

  noates, formates or the like. It is also possible to use organometallic compounds, such as tin-alkyl halides

  and tin-aryl, in particular tin-alkyl fluorides.

  Preference is given to halogenated acetonates and acetylacetonates, preferably to mixtures of metal acetylacetonates.

  Preferably, acetyl coating reagents

  acetoriate are ground and / or sieved, so as to obtain

  a relatively uniform particle size distribution. A -

  powder formed of particles having an average diameter of the order of 500 to 600 microns is especially advantageous. Such a powder coating reagent has physical properties comparable to those of flour. the coating coating reagent is mixed with a carrier gas, preferably air

  and preferably at room temperature. The coating reagent

  Powder can be injected, blown or drawn into the carrier gas stream. It does not matter which means are used to mix the powder coating reagent and

  the carrier gas, but the drawing shows a supply screw

  tion. The preferred device is a vacuum cleaner comprising a vacuum ejector mounted in this screw. Preferably, the powder / gas mixture passes through a current spray mill

  gaseous which effectively reduces the average size of the particles

  particles of the powder coating reagent at a value of 1 to 2 microns, comparable to that of dust particles, by the impact of the particles and the centrifugal forces of the air

  created in the gas flow projection mill.

  The carrier gas can be maintained at a temperature

  Conch below the decomposition temperature of the coating reagent, preferably below its vaporization temperature, and in particular at room temperature, which minimizes the risks of decomposition of the coating reagent, which is detrimental to your results obtained with the processes

  vapor deposition. The distribution of the reagent

  - Much powder in the carrier gas is maintained practically uniform in its path to the support by the creation '. turbulence by means of a baffle, for example in the form of a cylindrical rod at the entrance to the coating chamber, or by means of a series of baffles, as shown in

the drawing.

  The uniform mixture of powder coating reagent and carrier gas is delivered to the surface to be coated through a nozzle of the slot type having, in the context of the present

  invention, a length much greater than its width.

  Preferably, the slit is no more than 3.17 mm in width and is preferably as long as the parallel dimension of the surface to be coated, which promotes uniformity of the coating. The slot is preferably oriented perpendicular to the direction of relative movement between the nozzle and the surface to be coated. A large immobilized support can be coated using one or more movable nozzles, or the support can pass opposite one or more fixed nozzles. Preferably, the nozzle is placed less than about 5.1 cm from the surface to be coated, preferably at a distance of 1.2 to 1.9 cm, which creates a back pressure which promotes

  uniform flow of carrier gas / reactant mixture

  in the longitudinal direction of the slot and improves

  again the uniformity of the coating.

  The carrier gas / coating reagent mixture enters into

  contact with the surface to be coated to deposit a film there.

  Preferably, the carrier gas / coating reagent mixture comes into contact with a glass surface at a temperature sufficient to pyrolyze the coating reagent and thus form a metal oxide film, this temperature typically being of the order of 510 to 56620. Under these conditions, the reactive coating / carrier gas mixture may resemble a mist or smoke when it comes into contact with the hot glass surface. Evacuation hoods

  attract unreacted dust away from the surface

  face. The powder is easily collected for reuse, which allows optimal yield conditions to be obtained

of the process.

  The thickness of the film can be adjusted by varying the speed of the relative movement between the nozzle and the support, by adjusting the flow rate of the carrier gas / coating reagent mixture, by increasing or decreasing the concentration of coating reagent in the gas. carrier or by raising or lowering the temperature of the support. The support can be

  coated in horizontal or vertical position.

  The present invention can be well understood using

  of the following description of particular examples.

  Examples - - A ribbon of glass, loosely formed by floating, passes at a linear speed of approximately 9.1 m / min opposite a

  fixed coating device as shown in the drawing.

  A powder coating reagent, having an average particle size of approximately 500 microns, is introduced at a rate of 200 g / min into a stream of air produced with a flow rate of 0.85 m3 / min. Turbulence is created in the powder / air mixture by a baffle at the entrance to the coating chamber. The powder / air mixture is delivered through a slotted nozzle about 1.6 mm wide, almost as long as the width of the glass ribbon. The nozzle is placed approximately 9.5 mm from the surface of the glass, so as to create a back pressure which contributes to maintaining the uniformity of distribution of the powder coating reagent. The surface of the glass is at a temperature of about 566.20. A uniform coating of oxide

  metal is deposited on the surface of the glass. Acetylaceous-

  following metal tonates can be used successfully

as coating reagents.

  Example Metal acetylacetonate I Cobalt II Chromium III Iron IV Nickel V Copper VI Copper / chromium VII Cobalt / iron / chromium VIII Manganese / copper II Iron / copper / chromium

Example X

  We proceed as in the previous examples to form

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  coating using tin dibutyl bifluoride as a powder coating reagent. A uniform film of tin oxide is formed, having a resistivity

  from 9.57 to 11.96 ohms per square meter.

Example XI

  A mixture of cobalt acetylacetonate. iron and chromium, having an average particle size of 500 to 600 microns, is prepared by mixing the solid particulate coating reagents in a ball mill for about one hour. The coarse powder mixture is introduced into a gas flow projection mill which reduces the powder mixture to fine dust having an average particle size of the order of 1 micron or less. The fine dust is entrained towards a coating chamber by means of 18.14 kg of aspirated air (5.27 kg per square centimeter at the rate of 1.415 m3 / min). An ankle-shaped rod at the entrance to the coating chamber causes an immediate swirl of dust / gas smoke (if the rod is removed, admission

  of air should be almost doubled, which results in a tex-

  poor film size and requires the use of high speed exhaust hoods). The cooling reagent dust is delivered through a slit nozzle, 68.7 cm long and 0.32 cm wide, at a rate of approximately 670 mg / s and it comes into contact with a 66 cm glass sheet. in width at a speed of about 5.1 m / s. The nozzle is fixed approximately 1.9 cm above the surface of the glass, while the glass ribbon is driven at a speed of 6.35 m / min at a temperature of the order of 56620. It forms a coating of metal oxides whose durability and spectral properties are roughly identical to that of a coating

  formed from a solution of the same coating reagents.

  The spectral properties are compared in the following table. Transparency coefficient Reflection coefficient Reactive (%) - (%) of Solar energy Energy Surface Surface coated - Total solar luminous coated with total glass Powder 23 - 28 31 35.6 13 Solution 22 27 31 36.0 14 Protection efficiency U factor against light Night Summer winter day Powder 0.47 - 1.09 1.11l Solution 0.46 1.10 1.11

Example XII

  The composition of coating reagents, the device

  and the operating parameters of the previous example are used

  lises to deposit a film on a continuous ribbon of glass - R SOLARBRONZE of 6 mm, obtained by floating. The entire coated surface, 68.6 cm wide, appears uniform in color and texture, with a light transparency coefficient of 21% and a reflection coefficient from the coated side of 37%. Because the rod placed at the inlet of the coating chamber allows low air flow, it is not necessary to provide exhaust hoods at high speed;

  we simply use dust collectors to collect

  perate the uncoated coating reagent. This material can

  be reused without further treatment.

Example XIII

  The composition of coating reagents and the operating parameters of the above examples are used in conjunction with a similar powder coating device, enlarged in order to successfully coat a glass width of 1.7 m. The spectral properties of the coated glass are comparable to

  properties presented in Example XII.

Example XIV

  A tin-dibutyl bifluoride powder, having an average particle size of approximately 500 to 600 microns, is introduced, as coating reagent, at a rate of g / min, into a gas jet projection mill in which the particle size is reduced to about 1 or 2 microns. The tin-dibutyl bifluoride dust is entrained in the air (1.415 m3 / min at a rate of 5.27 kg per square centimeter) and delivered to a glass surface through double fixed nozzles of 30.5 cm length and 1.6 mm

  width. The glass is at a temperature of 593 to 6272C approx.

  ron and passes at a speed of 4.6 to 6.1 m / min. A clear and uniform film of tin oxide is formed, having a

  resistivity of 23.9 ohms per square meter.

  The above examples are given to illustrate the

  present invention the scope of which is defined by the claims

cations that follow.

REEINDICATI0I-NS

  1. A method of coating a support with a film, by bringing a coating reagent into contact with a surface, characterized in that it comprises the operations consisting in: preparing the coating reagent in the form of a powder; dispersing this powder coating reagent in a stream of carrier gas; create turbulence in this current; deliver the reactive powder coating / carrier gas mixture to the

surface to be coated.

  2. Method according to claim 1, characterized in that the coating reagent powder has an average size of

  particles of the order of 500 microns.

  Ad Method according to claim 2, characterized in that the average particle size of the reagent is reduced to

less than about 10 microns.

  4. Method according to claim 3, characterized in that the particle size is reduced by treatment with

  gas current projection mill.

  Method according to claim 1, characterized in that the powder coating reagent is dispersed in a gas

  carrier at room temperature.

  6. Method according to claim l, characterized en.ce that

the carrier gas is air.

  7. Method according to claim 1, characterized in that the turbulence is created in the stream of carrier / reactive gas

  coating with at least one baffle.

  8. Method according to claim 1, characterized in that the mixture of powder coating reagent / carrier gas is

  delivered to the surface to be coated through a slit nozzle.

  9. Method according to claim 8, characterized in that the

  slit nozzle is no more than 1.6 mm wide and has practical-

  the same length as the parallel dimension of the surface

to be coated ..

  10. Method according to claim 1, characterized in that

  the support is brought into contact with the reactive coating mixture

  Carrier gas at a temperature sufficient to pyrolyze

the coating reagent.

  11. The method of claim 10, characterized in that a turbulent stream of powdered metal acetylacetonate in air is delivered to the surface of a glass support for

  place a metal oxide film on it.

  12. Device for delivering a coating reagent for

  dre to a surface to be coated, characterized in that it comprises: means for introducing a powder coating reagent

  in a carrier gas stream; ways to create a tur-

  Bulence in the powder coating / carrier gas stream; and means for delivering this turbulent mixture to

the surface to be coated.

  13. Device according to claim 12, further characterized

  in that it includes means for reducing the average size

  ne particles of the powder coating reagent. -

  14. Device according to claim 13, characterized in that the means for reducing the particle size of the powder coating reagent consist of a grinder

with gas current projection.