CN115537096A - Mixed production method of metal powder coating - Google Patents
Mixed production method of metal powder coating Download PDFInfo
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- CN115537096A CN115537096A CN202211172978.7A CN202211172978A CN115537096A CN 115537096 A CN115537096 A CN 115537096A CN 202211172978 A CN202211172978 A CN 202211172978A CN 115537096 A CN115537096 A CN 115537096A
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- 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
- C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
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- 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
- C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
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- 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
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/03—Powdery paints
- C09D5/033—Powdery paints characterised by the additives
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Abstract
The invention discloses a mixing production method of a metal powder coating, and particularly relates to the technical field of coating production, wherein raw materials are put into a mixing auxiliary agent barrel with controllable flow rate and strictly put according to the proportion, then the mixing auxiliary agent barrel is subjected to dry mixing treatment through high-speed rotation to obtain bottom powder, the internal temperature of the mixing auxiliary agent barrel is adjusted to be 10-20 ℃, so that the mixing production method can effectively prevent the particle size of the metal powder from being damaged in the material mixing process to influence the appearance of a coating film, prevent the powder coating from being aggregated in the material mixing process, ensure the processing effect of the metal powder, avoid the influence of the change of the metal effect, and simultaneously add silicon oxide in the raw materials for coating treatment, so that the metal powder coating processed by the method has excellent weather resistance and chemical resistance, particularly good electrification property and bright flashing effect, and further meets the requirements of processing and use of the metal powder coating.
Description
Technical Field
The invention relates to the technical field of paint production, in particular to a mixing production method of a metal powder paint.
Background
The VOC discharge amount of the sprayed metal paint is large, the pollution control difficulty is high, the metal powder is adopted to replace the VOC discharge amount in the existing metal electroplating factories, the coating effect is relatively ideal, and most of the domestic metal powder coatings are imported. Currently, INTEPONEPANOWLOW with higher technical level abroad is used for manufacturing metal powder coating by adopting a bonding method, at present, the metal powder coating is mainly manufactured by adopting the bonding method abroad, the metal powder and base powder are not easy to separate, the construction performance is good, the metal powder coating is easy to recover, but the metal powder coating has high investment and expensive equipment, few domestic manufacturers adopt the method, and the electrification property and the metal flashing property of the metal powder coating are poor after the metal powder coating is prepared by adopting a conventional processing mode, so that the metal powder coating cannot meet the requirements in use.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a mixing production method of a metal powder coating, and the technical problems to be solved by the invention are as follows: the conventional processing mode has poor charging property and metal flashing property after the metal powder coating is prepared, so that the problem that the metal powder coating is difficult to meet the requirement in use is caused.
In order to achieve the purpose, the invention provides the following technical scheme: a mixing production method of metal powder coating comprises the following raw materials:
50 parts of epoxy resin, 50 parts of polyester resin, 4 parts of curing agent, 0.8 part of flatting agent, 1 part of benzoin, 0.5 part of ultraviolet assistant, 1 part of silicon oxide and metal powder.
As a further scheme of the invention: the epoxy resin, the polyester resin, the curing agent, the flatting agent, the benzoin, the silicon oxide and the ultraviolet auxiliary agent are prepared into the adhesive, and the raw material ratio of the adhesive to the metal powder is 100.
As a further scheme of the invention: comprises the following production steps:
s1, preparing materials: removing the ingredients with the fixed proportion of the adhesive, and mixing to prepare the adhesive.
S2, premixing: the preparation method comprises the steps of putting ingredients of the adhesive into a mixing aid barrel with controllable flow rate, putting the ingredients strictly according to the above proportion, then carrying out dry mixing treatment on the ingredients through high-speed rotation of the mixing aid barrel to obtain bottom powder, adjusting the internal temperature of the mixing aid barrel to be 10-20 ℃, and adding metal powder into the bottom powder according to the above mass proportion in the mixing process.
S3, melt extrusion: adding metal powder into the raw materials, pre-dispersing, melting, extruding, tabletting and crushing by a high-speed dispersion machine, and cooling to obtain primary processing fragments.
S4, crushing treatment: and (3) grinding the primary processing fragments by using a grinder, and stopping processing when the primary processing fragments are ground to have a granularity of-300 meshes to 500 meshes to obtain the crude metal powder coating.
S5, sieving treatment: and (3) primarily screening the rough metal powder coating through a 360-mesh sieve, and secondarily screening the primarily screened metal powder coating through a 120-mesh sieve, so as to obtain the metal powder coating.
S6, bonding metal powder: and (4) putting the screened metal powder coating into a bonding machine, operating the bonding machine for 20min, and cooling and screening to obtain a finished product.
Further: due to the adoption of low-temperature dry mixing, the method can effectively prevent the particle size of the metal powder from being damaged in the mixing process to influence the appearance of a coating film, and simultaneously prevent the powder coating from aggregating in the mixing process, thereby ensuring the processing effect of the metal powder.
The base powder and the metal powder are treated by a dry mixing method, so that the metal powder and the base powder are not very fierce in mixing, the deformation of the flaky metal powder is prevented, and the change of the metal effect caused by the influence is avoided.
As a further scheme of the invention: the internal rotation speed of the mixing aid bucket proposed in S2 is set to 900rmp for dry mixing treatment, and the grinding mill proposed in S4 is set to a ball mill.
As a further scheme of the invention: the epoxy resin is regarded as a curing agent with two functionalities, so that the functionality of the main resin must be more than 2, and deviation from the stoichiometric ratio can cause significant deterioration of coating film characteristics such as solvent resistance, boiling water resistance and impact resistance, and the polyester resin used for powder coating can be generally characterized by a determined acid value, and under the condition of known epoxy equivalent weight, the acid value can be used for calculating the amount of epoxy component required in the coating formula, and if the epoxy group in the epoxy resin reacts with the carboxyl group in the polyester resin in an equivalent manner, the theoretical value of the ratio of the two resins can be calculated by the following formula:
G＝56100E/A
in the formula: g is the amount of polyester resin required for 100G of epoxy resin, which is measured in G.
A is the acidity value of the polyester resin, and the measurement unit is mgKDH/g.
E is the epoxy value of the epoxy resin and is measured in eq/100g.
56100 is the factor to KDH mg.
Further: the key point of the technology is the covering problem of metal powder on the surface of a coating, the smaller the particle size of the metal powder is, the larger the covering rate is, and conversely, the poorer the covering rate is, so that the metal powder which is not only suitable for the powder coating but also has certain fineness in particle size must be screened, and the influence of the metal powder with different particle sizes on the appearance of the coating is shown in the following table:
effect of different particle size metal powders on coating outer tube
Further: the key point of the technology is that metal powder has strong flashing degree and strong dispersion, heat resistance and weather resistance, so that the powder coating is suitable for preparing the powder coating, a large number of tests prove that the non-floating aluminum powder and the bronze powder which are subjected to silicon oxide coating treatment on the surfaces have excellent weather resistance and chemical resistance, particularly good electric charge property and gorgeous flashing effect, and the coating effects and the performances prepared by the treated metal powder and the untreated metal powder are compared as shown in the following table:
coating Effect and Performance comparison
| Performance of | Treated metal powder | Untreated metal powder |
| Appearance of the coating | Flash intensity | Dark gray |
| Salt fog resistance | Good taste | Difference (D) |
| Resistance to reagents | Is very good | Difference (D) |
| Weather resistance | Good taste | Difference (D) |
| Sprayability | Good taste | Difference (D) |
| Recyclability | Good taste | Difference (D) |
| Thermal stability | Good taste | Difference between |
The invention has the beneficial effects that: according to the invention, the raw materials are put into the mixing aid barrel with controllable flow rate and are strictly put according to the proportion, then the mixing aid barrel is rotated at a high speed to carry out dry mixing treatment on the raw materials to obtain the base powder, the temperature inside the mixing aid barrel is adjusted to be 10-20 ℃, so that the mixing production method can effectively prevent the particle size of the metal powder from being damaged in the mixing process to influence the appearance of a coating film, and meanwhile, the powder coating is prevented from being aggregated in the mixing process, the processing effect of the metal powder is ensured, and the metal effect is prevented from being influenced and changed.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1:
a mixing production method of metal powder coating comprises the following raw materials:
50 parts of epoxy resin, 50 parts of polyester resin, 4 parts of curing agent, 0.8 part of flatting agent, 1 part of benzoin, 0.5 part of ultraviolet assistant, 1 part of silicon oxide and metal powder.
The adhesive is prepared from epoxy resin, polyester resin, a curing agent, a flatting agent, benzoin, silicon oxide and an ultraviolet auxiliary agent, and the raw material ratio of the adhesive to the metal powder is 100.
The method comprises the following production steps:
s1, preparing materials: removing the ingredients with the definite specific gravity of the adhesive, and mixing to prepare the adhesive.
S2, premixing: the preparation method comprises the steps of putting ingredients of the adhesive into a mixing aid barrel with controllable flow rate, putting the ingredients strictly according to the above proportion, then carrying out dry mixing treatment on the ingredients through high-speed rotation of the mixing aid barrel to obtain bottom powder, adjusting the internal temperature of the mixing aid barrel to be 10-20 ℃, and adding metal powder into the bottom powder according to the above mass proportion in the mixing process.
S3, melt extrusion: adding metal powder into the raw materials, pre-dispersing, melting, extruding, tabletting and crushing by a high-speed dispersion machine, and cooling to obtain primary processing fragments.
S4, crushing treatment: and (3) grinding the primary processing fragments by using a grinder, and stopping processing when the primary processing fragments are ground to have a particle size of-300 meshes to 500 meshes to obtain the crude metal powder coating.
S5, sieving treatment: and (3) primarily screening the crude metal powder coating through a 360-mesh sieve, and secondarily screening the primarily screened metal powder coating through a 120-mesh sieve, so as to obtain the metal powder coating.
S6, bonding metal powder: and (3) putting the screened metal powder coating into a bonding machine, operating the bonding machine for 20min, and then cooling and screening to obtain a finished product.
And further: due to the adoption of low-temperature dry mixing, the method can effectively prevent the particle size of the metal powder from being damaged in the mixing process to influence the appearance of a coating film, and simultaneously prevent the powder coating from aggregating in the mixing process, thereby ensuring the processing effect of the metal powder.
The base powder and the metal powder are treated by a dry mixing method, so that the metal powder and the base powder are not very fierce in mixing, the deformation of the flaky metal powder is prevented, and the change of the metal effect caused by the influence is avoided.
The dry mixing process was carried out with the internal rotation speed of the mixing aid tank set to 900rmp as set forth in S2, and the mill set to a ball mill as set forth in S4.
Epoxy resins are considered as curing agents of two functionalities, so that the functionality of the principal resin must be greater than 2, and deviations from the stoichiometric ratio can lead to significant deterioration of coating film properties such as solvent resistance, boiling water resistance and impact resistance, and powder coatings are generally characterized by a defined acid number which, given the known epoxy equivalent weight, can be used to calculate the amount of epoxy component required in the coating formulation, and if the epoxy groups in the epoxy resin react with the carboxyl groups in the polyester resin in an equivalent amount, the theoretical value of the ratio of the two resins can be calculated using the following formula:
G＝56100E/A
in the formula: g is the amount of polyester resin required for 100G of epoxy resin, which is measured in G.
A is the acidity value of the polyester resin, and the measurement unit is mgKDH/g.
E is the epoxy value of the epoxy resin and is measured in eq/100g.
56100 is the factor to KDH mg.
When the metal powder coating is used for coating, the metal powder coating is required to be filled into a friction spray gun, the friction spray gun is generally not suitable for spraying the metal powder coating, in most cases, an electrostatic spray gun is used for coating, because the product contains metal pigments, the grounding of a system is ensured to be good when the electrostatic spray gun is used for construction, and meanwhile, a lower electrostatic voltage and a lower powder discharge amount are set, so that the ignition phenomenon generated during spraying is prevented, the effect of forming a coating film is greatly related to the setting, quality or brand of the spray gun, a large amount of metal powder is possibly accumulated at a spray gun discharge needle after long-time spraying, a constructor is required to regularly clean the discharge needle, and in order to keep the appearance of the metal powder coating consistent, the following matters must be paid attention to:
1) For the same product, the same batch of metal powder coating is used as much as possible, so that the difference between batches of the powder coating is avoided, and the method specifically comprises the steps of using the same set of spraying equipment, using the same voltage, air pressure and the like.
2) And keeping the stability of the spraying condition, specifically keeping the distance between the spray gun and the workpiece unchanged and keeping the stability of the film thickness as much as possible.
3) And the workpiece with a complex shape or a deeper concave shape is prevented from being sprayed by using the metal powder coating.
4) For a plurality of workpieces assembled together, the workpieces should be sprayed simultaneously.
In the electrostatic powder spraying process, powder coating is conveyed to a spray gun through air flow after being fluidized, the spray gun generates corona discharge at an electrode needle of the spray head through a high-voltage electrostatic generator, dense negative charge is generated near an electrode, when the powder is sprayed out from a gun head, the charge is captured to form charged powder, the charged powder flies to a grounded workpiece and is adsorbed on the surface of a section bar under the action of air flow, an electric field and self gravity, the electrostatic spraying principle of the metal powder is consistent with that of the conventional electrostatic spraying of the powder, but due to the particularity of the metal powder, the spraying mechanism needs to be further explained,
if the spray gun is a pipeline in a horizontal state, powder particles are sprayed out of the spray gun in an initial stage and are acted by a compressed gas conveying force and an electrostatic force, the powder particles can be regarded as a pneumatic conveying state of a multi-particle system and a superposition of an electric field force, according to a Barth derivation formula, a power equation of the externally-applied electric field multi-particle conveying system is as follows:
where ρ is the transport gas density, ρ ρ Is the powder particle density, epsilon is the voidage,
is the coefficient of collision pressure loss, f L Is fanning coefficient of friction, c is the velocity of the particles in the pipe, v ε Is the actual velocity of the gas, E x Is the actual electric field strength.
The power state of powder ejection, air transport density rho (flow velocity), and powder particle density rho can be obtained by the above formula ρ (particle diameter) and porosity ε (powder amount) electric field intensity E x And the powder charge quantity q is closely related, the resistance forces such as collision force, friction force, eddy drag force and the like can be ignored, and the air transportation density, the void degree and the electric field intensity belong to external factors in the powder spraying process, so that the metal powderThe difference from the conventional powder lies in the powder particle density (. Rho.) ρ ) And the difference in charge amount (q).
After the common powder is crushed and sieved, the particles of the common powder are close to spherical shapes, but the metal powder is not all spherical particles, in order to obtain the surface flashing effect of the coating, part of the aluminum silver powder, the copper gold powder and the pearl mica powder are flaky particles, the influence of the gravity and the vortex interference force of the particles is very obvious in the motion process between the spray gun and the sectional material, and the flow resistance formula is as follows:
in the formula A P Showing the projected area of the particles in the direction of fluid flow, zeta the drag coefficient, related to the Reynolds number of the particle motion, the flaky metal powder fluctuating between the spray gun and the profile, A P The value is always in the change process, when the particle size of the metal powder is smaller, the resistance is relatively weakened, secondly, the densities of the aluminum silver powder, the copper gold powder and the mica powder are inconsistent, wherein the density of the aluminum silver powder is smaller, the density of the copper gold powder is larger, due to the action of gravity, if the aluminum silver powder, the copper gold powder and the mica powder are added into the coating in a dry mixing mode, the powder spraying process is easy to separate, the metal powder in a binding state can keep consistent with the base powder, in addition, the conductivity difference of the aluminum silver powder, the copper gold powder and the mica powder is very obvious, most of the untreated mica powder is almost in an insulating state, and the conductivity of the aluminum silver powder and the copper gold powder is very good, so the difference in the spraying process is very obvious.
Example 2:
a mixing production method of metal powder coating comprises the following raw materials:
50 parts of epoxy resin, 50 parts of polyester resin, 4 parts of curing agent, 0.8 part of flatting agent, 1 part of benzoin, 0.5 part of ultraviolet assistant, 1 part of silicon oxide and metal powder.
The adhesive is prepared from epoxy resin, polyester resin, a curing agent, a flatting agent, benzoin, silicon oxide and an ultraviolet assistant, and the raw material ratio of the adhesive to the metal powder is 100.
The method comprises the following production steps:
s1, preparing materials: removing the ingredients with the definite specific gravity of the adhesive, and mixing to prepare the adhesive.
S2, premixing: the preparation method comprises the steps of putting ingredients of the adhesive into a mixing aid barrel with controllable flow rate, putting the ingredients strictly according to the above proportion, then carrying out dry mixing treatment on the ingredients through high-speed rotation of the mixing aid barrel to obtain bottom powder, adjusting the internal temperature of the mixing aid barrel to be 10-20 ℃, and adding metal powder into the bottom powder according to the above mass proportion in the mixing process.
S3, melt extrusion: adding metal powder into the raw materials, pre-dispersing, melting, extruding, tabletting and crushing by a high-speed dispersion machine, and cooling to obtain primary processing fragments.
S4, crushing treatment: and (3) grinding the primary processing fragments by using a grinder, and stopping processing when the primary processing fragments are ground to have a granularity of-300 meshes to 500 meshes to obtain the crude metal powder coating.
S5, sieving treatment: and (3) primarily screening the rough metal powder coating through a 360-mesh sieve, and secondarily screening the primarily screened metal powder coating through a 120-mesh sieve, so as to obtain the metal powder coating.
S6, binding metal powder: and (4) putting the screened metal powder coating into a bonding machine, operating the bonding machine for 20min, and cooling and screening to obtain a finished product.
Further: due to the adoption of low-temperature dry mixing, the method can effectively prevent the particle size of the metal powder from being damaged in the mixing process to influence the appearance of a coating film, and simultaneously prevent the powder coating from aggregating in the mixing process, thereby ensuring the processing effect of the metal powder.
The base powder and the metal powder are treated by a dry mixing method, so that the metal powder and the base powder are not fiercely mixed, the deformation of the sheet metal powder is prevented, and the change of the metal effect caused by the influence is avoided.
The dry mixing process was performed with the internal rotation speed of the mixing aid tank set to 900rmp as set forth in S2, and the mill set to a ball mill as set forth in S4.
Epoxy resins are regarded as curing agents of two functionalities, so that the main resin must have a functionality of more than 2, and deviations from the stoichiometric ratio can lead to significant deterioration of the coating film properties, such as solvent resistance, boiling water resistance and impact resistance, and for powder coatings polyester resins can usually be characterized by a defined acid number, which, given the known epoxy equivalent weight, can be used to calculate the amount of epoxy component required in the coating formulation, and if the epoxy groups in the epoxy resin react with the carboxyl groups in the polyester resin in an equivalent amount, the theoretical value of the ratio of the two resins can be calculated using the following formula:
G＝56100E/A
in the formula: g is the amount of polyester resin required for 100G of epoxy resin, which is measured in G.
A is the acidity value of the polyester resin, and the measurement unit is mgKDH/g.
E is the epoxy value of the epoxy resin and is measured in eq/100g.
56100 is the factor to KDH mg.
In the electrostatic powder spraying process, powder coating is conveyed to a spray gun through air flow after being fluidized, the spray gun generates corona discharge at an electrode needle of the spray head through a high-voltage electrostatic generator, dense negative charge is generated near an electrode, when the powder is sprayed out from a gun head, the charge is captured to form charged powder, the charged powder flies to a grounded workpiece and is adsorbed on the surface of a section bar under the action of air flow, an electric field and self gravity, the electrostatic spraying principle of the metal powder is consistent with that of the conventional electrostatic spraying of the powder, but due to the particularity of the metal powder, the spraying mechanism needs to be further explained,
if the spray gun is a pipeline in a horizontal state, powder particles are sprayed out of the spray gun in an initial stage and are acted by a compressed gas conveying force and an electrostatic force, the powder particles can be regarded as a pneumatic conveying state of a multi-particle system and a superposition of an electric field force, according to a Barth derivation formula, a power equation of the externally-applied electric field multi-particle conveying system is as follows:
where ρ is the transport gas density, ρ ρ Is the powder particle density, epsilon is the voidage,
is the coefficient of collision pressure loss, f L Is fanning coefficient of friction, c is the velocity of the particles in the pipe, v ε Is the actual velocity of the gas, E x Is the actual electric field strength.
The power state of powder ejection, air transport density rho (flow velocity), and powder particle density rho can be obtained by the above formula ρ (particle diameter) and porosity ε (powder amount) electric field intensity E x And the powder charge quantity q is closely related, the resistance such as collision force, friction force, eddy drag force and the like can be ignored, the air transportation density, the void degree and the electric field intensity belong to external factors in the powder spraying process, and therefore, the metal powder is different from the common powder in the powder particle density (rho) ρ ) And the difference in charge amount (q).
After the common powder is crushed and sieved, the particles of the common powder are close to spherical shapes, but the metal powder is not all spherical particles, in order to obtain the surface flashing effect of the coating, part of the aluminum silver powder, the copper gold powder and the pearl mica powder are flaky particles, the influence of the gravity and the vortex interference force of the particles is very obvious in the motion process between the spray gun and the sectional material, and the flow resistance formula is as follows:
in the formula A P Showing the projected area of the particles in the direction of fluid flow, zeta the drag coefficient, related to the Reynolds number of the particle motion, the flaky metal powder drifts between the spray gun and the profile, A P The value is always in the changing process, when the particle size of the metal powder is smaller, the resistance is relatively weakened, secondly, the densities of the aluminum silver powder, the copper gold powder and the mica powder are inconsistent, wherein the density of the aluminum silver powder is smaller, the density of the copper gold powder is larger, and due to the action of gravity, if the aluminum silver powder, the copper gold powder and the mica powder are dry-mixedThe method is added into the paint, so that the paint is easy to separate in the powder spraying process, the metal powder in the binding state can keep consistent with the base powder, in addition, the conductivity difference of the aluminum silver powder, the copper gold powder and the mica powder is very obvious, most of the untreated mica powder is almost in an insulating state, and the conductivity of the aluminum silver powder and the copper gold powder is very good, so the difference in the spraying process is very obvious.
Powder spraying process parameters
According to the practical operation experience of a production field, the metal powder spraying process is approximately the same as the conventional powder spraying process, but in order to achieve a relatively ideal metal effect, the process parameters such as gun distance, voltage, powder amount, atomization air pressure and the like are required to be adjusted according to the type and particle size of the metal powder, and the metal effect has a phenomenon of echelon fluctuation due to the recycling of the recycled powder; in order to research the influence of the factors, the consistency of the metal effect of the surface of the spraying sample plate and the standard color plate is compared through an orthogonal test according to 8 factors of the metal powder type, the particle size distribution, the gun distance, the voltage, the powder quantity, the atomization air pressure, the recycled powder addition and the curing process.
Example 3:
a mixing production method of metal powder coating comprises the following raw materials:
50 parts of epoxy resin, 50 parts of polyester resin, 4 parts of curing agent, 0.8 part of flatting agent, 1 part of benzoin, 0.5 part of ultraviolet assistant, 1 part of silicon oxide and metal powder.
The adhesive is prepared from epoxy resin, polyester resin, a curing agent, a flatting agent, benzoin, silicon oxide and an ultraviolet assistant, and the raw material ratio of the adhesive to the metal powder is 100.
Comprises the following production steps:
s1, preparing materials: removing the ingredients with the fixed proportion of the adhesive, and mixing to prepare the adhesive.
S2, premixing: the preparation method comprises the steps of putting ingredients of the adhesive into a mixing aid barrel with controllable flow rate, putting the ingredients strictly according to the above proportion, then carrying out dry mixing treatment on the ingredients through high-speed rotation of the mixing aid barrel to obtain bottom powder, adjusting the internal temperature of the mixing aid barrel to be 10-20 ℃, and adding metal powder into the bottom powder according to the above mass proportion in the mixing process.
S3, melt extrusion: adding metal powder into the raw materials, pre-dispersing, melting, extruding, tabletting and crushing by a high-speed dispersion machine, and cooling to obtain primary processing fragments.
S4, crushing treatment: and (3) grinding the primary processing fragments by using a grinder, and stopping processing when the primary processing fragments are ground to have a granularity of-300 meshes to 500 meshes to obtain the crude metal powder coating.
S5, sieving treatment: and (3) primarily screening the rough metal powder coating through a 360-mesh sieve, and secondarily screening the primarily screened metal powder coating through a 120-mesh sieve, so as to obtain the metal powder coating.
S6, binding metal powder: and (4) putting the screened metal powder coating into a bonding machine, operating the bonding machine for 20min, and cooling and screening to obtain a finished product.
Further: due to the adoption of low-temperature dry mixing, the method can effectively prevent the particle size of the metal powder from being damaged in the mixing process to influence the appearance of a coating film, and simultaneously prevent the powder coating from aggregating in the mixing process, thereby ensuring the processing effect of the metal powder.
The base powder and the metal powder are treated by a dry mixing method, so that the metal powder and the base powder are not very fierce in mixing, the deformation of the flaky metal powder is prevented, and the change of the metal effect caused by the influence is avoided.
The dry mixing process was performed with the internal rotation speed of the mixing aid tank set to 900rmp as set forth in S2, and the mill set to a ball mill as set forth in S4.
Epoxy resins are regarded as curing agents of two functionalities, so that the main resin must have a functionality of more than 2, and deviations from the stoichiometric ratio can lead to significant deterioration of the coating film properties, such as solvent resistance, boiling water resistance and impact resistance, and for powder coatings polyester resins can usually be characterized by a defined acid number, which, given the known epoxy equivalent weight, can be used to calculate the amount of epoxy component required in the coating formulation, and if the epoxy groups in the epoxy resin react with the carboxyl groups in the polyester resin in an equivalent amount, the theoretical value of the ratio of the two resins can be calculated using the following formula:
G＝56100E/A
in the formula: g is the amount of polyester resin required for 100G of epoxy resin, which is measured in G.
A is the acidity value of the polyester resin, and the measurement unit is mgKDH/g.
E is the epoxy value of the epoxy resin and is measured in eq/100g.
56100 is the factor to KDH mg.
In the electrostatic powder spraying process, powder coating is conveyed to a spray gun through air flow after being fluidized, the spray gun generates corona discharge at an electrode needle of the spray head through a high-voltage electrostatic generator, dense negative charge is generated near an electrode, when the powder is sprayed out from a gun head, the charge is captured to form charged powder, the charged powder flies to a grounded workpiece and is adsorbed on the surface of a section bar under the action of air flow, an electric field and self gravity, the electrostatic spraying principle of the metal powder is consistent with that of the conventional electrostatic spraying of the powder, but due to the particularity of the metal powder, the spraying mechanism needs to be further explained,
if the spray gun is a pipeline in a horizontal state, powder particles are sprayed out of the spray gun in an initial stage and are acted by a compressed gas conveying force and an electrostatic force, the powder particles can be regarded as a pneumatic conveying state of a multi-particle system and a superposition of an electric field force, according to a Barth derivation formula, a power equation of the externally-applied electric field multi-particle conveying system is as follows:
where ρ is the transport gas density, ρ ρ Is the powder particle density, epsilon is the voidage,
is the coefficient of collision pressure loss, f L Is fanning coefficient of friction, c is the velocity of the particles in the pipe, v ε Is the actual velocity of the gas, E x Is the actual electric field strength.
The power state of powder ejection, the air transport density rho (flow velocity), and the powder particle density rho can be obtained by the above formula ρ (particle diameter) and porosity ε (powder amount) electric field intensity E x And the powder charge q is closely related, but the resistance such as collision force, friction force, eddy current drag force and the like can be ignored, and the air transportation density, the void degree and the electric field intensity belong to external factors in the powder spraying process, so the metal powder is different from the common powder in the powder particle density (rho) ρ ) And the amount of charge (q).
After the common powder is crushed and sieved, the particles of the common powder are close to spherical shapes, but the metal powder is not all spherical particles, in order to obtain the surface flashing effect of the coating, part of the aluminum silver powder, the copper gold powder and the pearl mica powder are flaky particles, the influence of the gravity and the vortex interference force of the particles is very obvious in the motion process between the spray gun and the sectional material, and the flow resistance formula is as follows:
in the formula A P Showing the projected area of the particles in the direction of fluid flow, zeta the drag coefficient, related to the Reynolds number of the particle motion, the flaky metal powder drifts between the spray gun and the profile, A P The value is always in the changing process, when the particle size of the metal powder is smaller, the resistance is relatively weakened, secondly, the densities of the aluminum silver powder, the copper gold powder and the mica powder are inconsistent, wherein the density of the aluminum silver powder is smaller, the density of the copper gold powder is larger, due to the action of gravity, if the aluminum silver powder, the copper gold powder and the mica powder are added into the coating in a dry mixing mode, the aluminum silver powder, the copper gold powder and the mica powder are easy to separate in the powder spraying process, the metal powder in a binding state can keep consistency with the base powder, in addition, the conductivity difference of the aluminum silver powder, the copper gold powder and the mica powder is very obvious, and most of the metal powder is not subjected to powder sprayingThe treated mica powder is almost in an insulating state, and the aluminum silver powder and the copper gold powder have very good conductivity, so the difference in the spraying process is very obvious.
The powder is divided into dry mixed powder and binding powder according to the types of the powder, the dry mixed powder and the binding powder are subdivided into three types of aluminum silver powder, copper gold powder and mica powder, 5 types of the powder are respectively sampled, after the particle size distribution is tested, 6 factors of gun distance, voltage, atomization air pressure, powder quantity, recycled powder adding and curing process are sequentially adjusted, and 3 test plates are tested for each type for comparing the test result with a standard plate.
And observing the metal flash number in the unit area of the sprayed surface by using a low-power lens, wherein the metal effect consistency is the ratio of the metal flash number of the test plate to the standard plate, and finally, visually comparing and verifying the accuracy of data to obtain a series of process factors influencing the metal effect.
And (3) taking dry-mixed aluminum powder, copper-gold powder and mica powder, respectively adjusting according to the gun distance of 250-400mm, setting the voltage to be 80kV, and fixing the powder amount, the atomization air pressure, the non-addition of the recovery powder and the curing process to obtain the relation between the gun distance and the metal powder effect.
The conclusion is drawn: in the metal powder construction process, the farther the metal powder effect is along with the gun distance, the worse the effect is, wherein the metal effect of the aluminum powder is very close to that of a standard plate when the gun distance is 250mm, and the best effect is achieved; under the action of better electrification effect and self gravity, when the gun distance is shorter, the metal effect is better than that of a standard plate, but the back ionization phenomenon appears on a test plate, so that the comprehensive effect of the surface with the gun distance too close is not ideal, and the flash effect is relatively poor because the mica powder is covered by a coating during spraying.
Taking dry-mixed aluminum powder, copper gold powder and mica powder, respectively adjusting according to the voltage of 40-100 kV, and obtaining the relation between the spraying voltage and the metal powder effect, wherein the gun distance, the powder amount, the atomization air pressure, the recycled powder are not added, and the curing process is fixed.
The conclusion is drawn: because the conductivity of the aluminum powder is better than that of the copper-gold powder and the mica powder, when the voltage is very low, the metal effect of the aluminum powder is more obvious, and the voltage required for reaching the metal effect of the standard plate is also the lowest; along with the increase of voltage, the difference between the metal effect and the standard plate is smaller and smaller, when the voltage exceeds 80kV, the aluminum powder and the copper-gold powder test plate have a back ionization phenomenon, a powder coating is broken down, the surface metal effect is not ideal, the aluminum powder has better electrification property, the back ionization phenomenon is more obvious, and the metal effect is reduced more quickly; the electrical conductivity of the mica powder is very weak, and the influence of self gravity is added, so that the metal effect becomes more and more obvious as the voltage continues to increase, and the difference between the mica powder and a standard plate becomes smaller gradually.
Taking dry-mixed aluminum powder, copper-gold powder and mica powder, respectively adjusting according to the atomization air pressure of 0.05-0.20 MPa, and keeping the gun distance, voltage and powder amount, no addition of recovery powder and the curing process constant to obtain the relation between the atomization air pressure and the metal powder effect
And (5) drawing a conclusion that: under the condition of ensuring that other construction parameters are not changed, when the atomization air pressure is 0.05MPa, the metal effect is optimal, the metal effect is reduced along with the increase of the atomization air pressure, and the gravity is larger, the powder reduction speed is higher, and the metal effect is poorer due to the influence of the gravity (mica powder is larger than copper-gold powder and is larger than aluminum powder).
The points to be finally explained are: although the present invention has been described in detail with the general description and the specific embodiments, on the basis of the present invention, the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (5)
1. The mixed production method of the metal powder coating is characterized by comprising the following raw materials:
50 parts of epoxy resin, 50 parts of polyester resin, 4 parts of curing agent, 0.8 part of flatting agent, 1 part of benzoin, 0.5 part of ultraviolet assistant, 1 part of silicon oxide and metal powder.
2. The hybrid production method of metal powder coating according to claim 1, characterized in that: the epoxy resin, the polyester resin, the curing agent, the flatting agent, the benzoin, the silicon oxide and the ultraviolet auxiliary agent are prepared into the adhesive, and the raw material ratio of the adhesive to the metal powder is 100.
3. The hybrid production method of metal powder coating according to claim 1, comprising the following production steps:
s1, preparing materials: removing the ingredients with the quantitative specific gravity of the adhesive, and mixing to prepare;
s2, premixing: adding the ingredients of the adhesive into a mixed auxiliary agent barrel with controllable flow rate, strictly adding the ingredients according to the above ratio, then carrying out dry mixing treatment on the mixture through high-speed rotation of the mixed auxiliary agent barrel to obtain bottom powder, adjusting the internal temperature of the mixed auxiliary agent barrel to be 10-20 ℃, and adding metal powder into the bottom powder according to the above mass ratio in the mixing process;
s3, melt extrusion: adding metal powder into the raw materials, pre-dispersing, melting, extruding, tabletting and crushing by using a high-speed dispersion machine, and then cooling to obtain primary processing fragments;
s4, crushing treatment: grinding the primary processed fragments by using a grinder, and stopping processing when the primary processed fragments are ground to have a particle size of-300 meshes to 500 meshes to obtain a crude metal powder coating;
s5, sieving treatment: the rough metal powder coating is screened for the first time through a 360-mesh screen, and the metal powder coating after the screening for the first time is screened for the second time through a 120-mesh screen, so that the metal powder coating is obtained;
s6, bonding metal powder: and (4) putting the screened metal powder coating into a bonding machine, operating the bonding machine for 20min, and cooling and screening to obtain a finished product.
4. A hybrid production method of metallic powder coating according to claim 3, characterized in that: the internal rotation speed of the mixing aid bucket proposed in S2 is set to 900rmp for dry mixing treatment, and the grinding mill proposed in S4 is set to a ball mill.
5. The hybrid production method of metal powder coating according to claim 1, characterized in that: the epoxy resin is regarded as a curing agent with two functionalities, so that the functionality of the main resin must be more than 2, and deviation from the stoichiometric ratio can cause significant deterioration of coating film characteristics such as solvent resistance, boiling water resistance and impact resistance, and the polyester resin used for powder coating can be generally characterized by a determined acid value, and under the condition of known epoxy equivalent weight, the acid value can be used for calculating the amount of epoxy component required in the coating formula, and if the epoxy group in the epoxy resin reacts with the carboxyl group in the polyester resin in an equivalent manner, the theoretical value of the ratio of the two resins can be calculated by the following formula:
G＝56100E/A
in the formula: g is the amount of polyester resin required for 100G of epoxy resin, and the unit of measurement is G;
a is the acidity value of the polyester resin, and the measurement unit is mgKDH/g;
e is the epoxy value of the epoxy resin, and the unit of measurement is eq/100g;
56100 is the factor to KDH mg.
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Application publication date: 20221230 |