DESC:FIELD OF INVENTION

This invention is related to a painting process and method. This invention is particularly related to painting of components performed through a method known as ‘wet on wet over CED’ and especially related to wet on wet painting using water based paints.

PRIOR ART

Generally any painting process comprises following generic steps/stages for metal painting.
1. Pretreatment
2. Cathodic Electrodeposition using electrolytically depositing water based coat
3. Water rinsing of above using multiple spray rinsing
4. Baking in ED oven.
5. Painting in different line using solvent borne paint .
6. Baking in paint bake oven.

Known processes and methods of painting employ separate facilities for Cathodic Electrodeposition ( Known as ED Tank and rinsing system & ED baking oven ) and Spray painting (known as painting booth and paint baking oven).

These processes and method consumes lot of space, material handling from one facility to other facility limiting productivity aspect as well as consumption of energy as the processes are carried out in separate lines. Thus making overall process a very costly affair.

It can be understood that there is time lapse between Acrylic based Cathodic Electrodeposition (hereafter called as ACED ) and painting process using solvent borne paint as it is not possible to apply the paint directly over the waterbased Electrodeposition film i.e. baking is essential after ACED and could not follow wet on wet process.

Known wet on wet methods and processes of painting which apply painting components use solvent based paints when coated over baked film of CED. However, solvent borne or solvent based paints are hydrophobic in property and also environmentally hazardous, release VOC (Volatile Organic Compound) in atmosphere.

D1 US 5376457 discloses a process of applying a painting finish to a surface comprising passing through water based electrocoating bath to achieve a base coat, dehydrating the base coat to a state of sufficient dryness and spraying the primer coating and finally baking the coat and coating, which coatings are baked concurrently and wherein the dehydrating is done using an oven maintained at a set yield temperature of 122°F substrate. Even though this invention has achieved the ‘baking’ step it has introduced the use of an ‘oven at set temperature’ as intermediately step between the base coating and the finish coating.

D2 US 4943447 also discloses a process applying water based electro coating as a base coat, and using an infrared radiation source for generating heated air to cure the said base coat, and after which the primer coating is applied which too is exposed to infrared radiation source.

D3 US 4139672A This paragraph discloses applying an undercoat paint (A) by electro deposition, applying an intermediate coat (B) thereon without heating the undercoat, baking concurrently the undercoat (A) and intermediate coat (B), coating the surface thereafter with powdery top coat paint (C) on the baked surface of intermediate coat and finally baking the top coat paint (C). This patent also discloses use of resin which has a specific composition, specific particle size and having a number average molecular weight of most preferably 3000 and preferably in the range 2000-10000.

D4 US 3998716 This invention attempts to do the wet on wet coating method with a single baking step and avoiding the baking of primer, sealer and top coats independently. This patent disclose that primer coating can be dried at a temperature high enough for dehydration but below the curing temperature for a short duration of time or alternatively drying at low temperature for a long period of time. In this invention the top coat and the primer are baked simultaneously.

D5 US 3647509 This patent discloses a method of applying the ground coat electrostatically, drying the said coat and thereafter giving the final coating, the firing / baking of the said coatings being done singularly.

OBJECTIVE OF THE INVENTION

It is an objective of the invention to provide a painting process and method which reduces the cost of painting by painting both CED & paint in same facility employing wet on wet method. Another objective of the invention to provide a painting process and method which improves the productivity of the painting.

Another objective of the invention to provide a painting process and the method which is environment friendly and safe.

Another objective of the invention to provide a painting process and method which consumes less space and energy for painting activity.

In the Prior Art, there is no spray painting facility in ED line, rather a separate line at different location is required, i.e. a spray painting facility (painting booth) is installed and separate baking oven also has to be provided after the booth. In the said invention, spray painting facility is installed after air blowing and before ED baking stage to enable wet on wet spray painting over the ED. Many objectives of invention is to design a system:

? demanding less floor space required than prior art design
? demanding no facility for hazardous waste separation
? demanding no additional facility in booth design for solvent laden fume scavenging ( such as diffusion by water between venturi / entrainment chambers and baffles) as paint is water based and there are negligible VOC .
? demanding no handling of parts between two facilities
? demanding no possibilities for contamination over baked ED coat surface during the handling between ED line and Topcoat painting facility
? demanding less investment cost as the booth design is simplified
? posing no fire hazard as entire painting is water based for such kind of process.

DETAILED DESCRIPTION OF DRAWINGS:

The invention is explained in detail with the help of accompanied figures
Figure 1 A-D illustrates the various composition of adjustable air amplifier.
Figure 2 illustrates a generic process flow of painting process according to prior art.
Figure 3 illustrates positioning or locations of stages /facilities of painting process according to prior art.
Figure 4 illustrates a process flow of painting process according to invention.
Figure 5 illustrates positioning or locations of stages /facilities of painting process according to one of the embodiment of invention.

DETAILED DESCRIPTION OF THE INVENTION:

It is an objective of the invention to provide a painting process and method which reduces the cost of painting by painting both CED & paint in same facility employing wet on wet method. With reference to above objectives, the present painting process comprises a sequence of processes wherein the essential steps in the process of the invention are:

1. Metal parts/components are first cleaned, made free from greasy matter, chemically treated using tri-cation phosphate treatment in Pretreatment line adjoining Electrodeposition equipment.

2. Acrylic resin based Cathodic Electrodeposition (ACED) coat is applied over metal parts/ components using Electrodeposition equipment with rectified voltage.
3. After which the process of water rinsing of the deposited film of ACED is done and this is followed by water scavenging process including air blow drying for water removal method .

Here the ‘drying’ word implies removal of water from the surface and not implying the curing / baking of the paint film.

4. Preferably water scavenging process employs use of high velocity air followed by painting process wherein the said painting process employs Acrylic based thermosetting type water based paint which can be applied as wet on wet over ACED film formed over the parts/components;

5. The above mentioned spray painting process facility is installed after air blowing chamber and before ED baking stage. The baking is done in ED oven where both the coats are simultaneously baked.

6. Preferably the CED is of Acrylic based type which is water based and UV resistant.

As an another aspect of invention, the present painting method comprises a series of painting process stages/facilities in a single painting facility wherein the water scavenging facility/means is positioned in series to ACED facility/means and the painting facility/means is positioned in series to water scavenging facility and before ED oven for baking.(refer fig 4)

In the above said baking process paint film of ACED & paint film of water based topcoat get heated to achieve cross-linking of the thermosetting polymers which is in the aqueous dispersion in the paints viz ACED & water base topcoat.

Water based paint (in this case a topcoat) used in which constitution could be:-

Water insoluble pigments / metallic pigments dispersed in aqueous dispersion of polymers of thermosetting types such as Acrylic resins with cross linking agents which can give a film that cures at same temperature that of Acrylic CED coat ( for Ex 170°C effective metal temperature) and also forms an opaque film with appropriate thickness to give desired optical effect and decorative & protective properties. This paint is thinned by using de-mineralized water and can be sprayed over ED film and then baked.

This water based paint composition is particularly suitable for wet on wet spray application on unbaked Acrylic Cathodic Electrodeposition (ACED). ACED and water based paint are baked in the same oven. It gives better aesthetic appeal to black ACED. Hard, flexible, chemical resistant and durable coating was achieved.

The water based paint will give required opacity at desired dry film thickness, say for ex 10-20 microns dry film thickness. Addition of pearl mica or aluminum pigment gives typical optical properties with metallic finish used as a decorative topcoat. The adhesion between ACED and water based paint is very strong and baked film has good hardness with inbuilt flexibility, which gives required mechanical resistance properties.

It is well known fact that the water rinsing is followed after ACED and water based paint cannot be applied directly over the component/part, because of the reason the water based paint being soluble in water, paint film cannot be formed. Instead, the paint applied over the component gets washed away. Solvent based paint cannot form a film over water as it is hydrophobic in nature.

Applicant arrived at a process and method which could scavenge out the water from the surface of the components passed through the water rinsing process and this stage could be located in series to water rinsing stage .As an example, the scavenging means could be an air amplifier which amplifies the flow and velocity of ambient air over the components.

Problem faced in such known prior art was water drops clinging on the wet ED film surface due to surface tension. The solution has been attempted to use the surface energy to dislodge the water drop and thereby disperse the dislodged water drops and such that it does not relocate itself on surface again at another location over wet film.
The problem has been solved with high velocity blow to remove the water drop and disperse in smaller drops and use reciprocating air amplifier blow to cover entire area of component to make sure those water drops do not settle over paint film.

As an example, reciprocating of amplifier is approx. 900 mm stroke height and at distance of approx. 350 mm from component surface. The stroke frequency is 24 numbers per minute and covers area of entire jig. (1.74 Sq M.) Hence the speed is about 43.2 m/min.

As an example ,air pressure is kept 4 to 5 Kgf/sq cm and volume is 96 cfm for 4 amplifiers (2 each on LH and RH sides) & 80 cfm for 4 air nozzles ( 2 each on LH & RH sides) to cover above surface area.

The velocity and amount of air needs to be optimized with respect type, shape /size of component, volume of facility etc.

The invention discloses a novel painting process, a wet on wet painting process on a surface of a material comprising of at least four steps.

a. The first step involves electrolytically depositing an acrylic resin based cathodic electrode position base coat over the surface of the material.
b. Thereafter drying the coated surface using high velocity air.
c. Spraying a paint coating over the air dried Acrylic CED coat with a water based paint This step is novel in that it is an aqueous thermosetting polymer based topcoat paint is used.
d. Finally oven baking the unbaked Acrylic CED coat and the water based topcoat paint simultaneously.

In another aspect the process is explained below and detailed below wherein a wet on wet painting process on a surface of a material comprises various steps as given below :-
a. Pre-treating the surface of the material for removal of dust, dirt and forming the phosphate on steel.
b. electrolytically depositing an acrylic resin based cathodic electrode position base coat over the surface of the material,
c. water rinsing the coated material.
d. drying the coated surface using high velocity air.
e. scavenging the water off the coat,
f. spraying a water based topcoat paint based on a aqueous thermosetting polymer
g. Oven baking the unbaked Acrylic CED coat and the paint coating simultaneously.

In another aspect, the step of spraying the paint includes applying a paint coating for the desired range of coating thickness for achieving desired opacity.
In another aspect, the preferred range of quoting is in the range of 10-20 microns.
In another aspect wherein the paint polymer may include pearl mica pigment & / or aluminium pigment for achieving determined optical properties/color for decorative effect
In another aspect wherein the painting stroke frequency is at 24 numbers per minute at a speed of 43.2 m/min covering the entire surface area.
In another aspect the paint coating may be a topcoat.
In another aspect wherein the paint coating may be a topcoat pigmented with a color.

Furthermore the invention includes the step of water scavenging includes using a high velocity blower to remove the water drop and disperse in smaller drops and also a reciprocating air amplifier blowing the entire surface area thereby preventing water drops from setting over the paint film.

Furthermore the water scavenging step includes reciprocating air amplifier has a 900 mm stroke height and is disposed at a distance of 350 mm from the painting surface.
In the method as described the blow air pressure is generally at 4 to 5 Kgf/Sq.cm. and volume is 96 cfm for 4 amplifiers and 80 cfm for 4 nozzles, and that 2 amplifiers and 2 nozzles each disposed on Left Hand Side and Right Hand Side of the conveyor to cover entire painting surface area.

A large volume of surrounding air is induced into the Amplifier at point (A) by the action of a small amount of compressed air which enters the annular chamber at point (B) that is then throttled through a small ring Nozzle at high velocity and into the inside of the Amplifier over a coanda profile. The compressed air stream clings to the coanda profile as it enters the inside walls of the Amplifier and thereby creating a vacuum that induces the outside air converting the pressure into amplified airflow. The amplified airflow leaves at the exit at point (C). Airflow is further amplified downstream at point (D) by entraining additional air from the surroundings at the exit.
In one of the embodiments the specification of air amplifier is normally set to .002” (.05mm) gap if greater air force is required. The gap may be adjustable. The first two sizes of adjustable air amplifiers come in two versions – unmarked regular versions and marked to gauge the gap setting from 0 to 1.5 mm.
The invention also relates to identifying the novel arrangement of the various stages for a wet on wet painting system. The paint spraying means is disposed after the drying means but before baking means, which arrangement is unknown in prior art. This arrangement providing a number of benefits detailed in the objectives of the invention.

As per the invention the spray painting booth is characterized such that the spray painting both is side draft type booth or down draft booth having top air pressurization with downward air velocity of 0.4 to 0. 5 m/sec and with water screen in front to carry away overspray of paint. Air filter in plenum is with 95% removal of particulates greater than 10 micron.

A comparison table shows improvements in quality, cost and productivity aspects as compared to known 2 coat 2 bake system.
A. Quality :

Parameter Observed value w.r.t to known method/process Observed value w.r.t to invented method/process Inference / Remarks
Corrosion Resistance
Neutral salt spray test
ASTM B117 – 700 hrs. exposure 5.5 mm rust creepage from cross hatch 3 mm rust creepage from cross hatch Superior corrosion resistance.
Edge corrosion resistance Rust spot development after 350 hrs Rust spot development after 550 hrs Superior edge corrosion resistance.
Humidity resistance No rust, no blisters & no adhesion failure No rust, no blisters & no adhesion failure Comparable
Mechanical properties
Adhesion as per
ASTM D3359-83 5B
( None, 0% area removed ) 5B
( None, 0% area removed ) Comparable
Abrasion resistance as per ASTM D 4060
(weight loss after 200 cycles) 8.65 gm 5.35 gm Superior abrasion resistance
Scratch hardness Pass
2 Kg Pass
3 Kg High scratch resistance
Impact resistance Pass
0.5 kg / 40 cm height Pass
1.0 kg / 40 cm height High impact resistance
Weatherometer
Expose panel in Xenon arc weatherometer for 400 hrs. Gloss retention
67 % Gloss retention
78 % Superior weather resistance
Optical properties
Colour / Shade Matches with standard colour Matches with standard colour Comparable

B. Cost :

Parameter Observed value w.r.t to known method/process Observed value w.r.t to invented method/process Inference
Cost including Paint material, Power & fuel, labor & transportation 412 Rs./Motorcycle 278 Rs./Motorcycle 32 % Cost reduction
C. Productivity : For Motorcycle components

Parameter Observed value w.r.t to known method/process Observed value w.r.t to invented method/process Inference
Lead time (Component loading stage to paint finish stage) 6.5 hrs. 3.5 hrs. Lead time reduced by 3 hrs.
Inventory 1 shift < 0.5 shift Inventory reduced
D. Land & space requirement : - In addition to the above, space required of painting equipment is reduced by about 795 Square Meters.
SPECIFICATION TABLE OF AIR AMPLIFIER
Adjustable air amplifier ratio ( Approx.)
Outside diameter of outlet 11/4” – 15 : 1
Outside diameter of outlet 2” – 16 : 1
Outside diameter of outlet 4” – 17 : 1
Outside diameter of outlet A B C D E F G H* NPT
2” 3.0 2.0 1.06 1.64 1.5 2.25 3.25 3/8”
In another aspect this invention covers an article or all articles having paint finish, painted by the process disclosed herein using the polymer disclosed herein.

As seen above, the invention relates to a disclosure of a system and method of applying paint on a surface and articles painted with a system & a process as disclosed herein.

An attempt as disclosed herein the features of the invention, with preferred embodiments and with a degree of specifically, but these are not intended to limit the scope of invention but on the contrary it is intended to cover such modifications, alterations, equivalents, tally with the sport and scope of invention and defined in the appended claims. ,CLAIMS:1. A wet on wet painting process on a surface of a material comprising :-

a. electrolytically depositing an acrylic resin based cathodic electrodeposition paint base coat over the surface of the material,
b. scavenging the water film from the surface of the material and drying the coated surface using high velocity air,
c. spraying a water based topcoat paint based on an aqueous thermosetting polymer, and simultaneously oven baking the unbaked electrodeposition paint coat and the waterbased topcoat paint coating.
2. The process as claimed in claim 1 may further comprise of :-
a. pre-treating the surface of the material for removal of dust and dirt, prior to step (a) which is electrolytically depositing an acrylic resin based cathodic electrodeposition paint base coat over the surface of the material, and
b. water rinsing the coated material and scavenging the water off the coat, prior to step (c) which is spraying a water based top coat paint based on an aqueous thermosetting polymer.
3. The process as claimed in claim 1 and 2 wherein the step of spraying the waterbased paint includes applying a paint coating which is preferably in the range of 10-20 microns dry film thickness for achieving desired opacity.
4. The process as claimed in claim 1 and 2 wherein the paint may include pearl mica or Aluminium paste pigment for achieving determined optical properties.
5. The process as claimed in claim 1 and 2 wherein the paint coating may be a top coat.
6. The process as claimed in claim 1 and 2 wherein the paint coating may be a top coat pigmented with a color.
7. The process as claimed in claim 2 wherein the step of water scavenging includes using a high velocity air blower to remove the water drop and disperse in smaller drops and also a reciprocating air amplifier blowing the entire surface area by air thereby preventing water drops from setting over the paint film.
8. The process as claimed in claim 7 wherein the painting stroke frequency is at 24 numbers per minute at a speed of 43.2 m/min covering the entire surface area.
9. The process as claimed in claim 7 wherein the reciprocating air amplifier has a 900 mm stroke height and is disposed at a distance of 350 mm from the painting surface.
10. The process as claimed in claim 7 wherein the blow air pressure is at 4 to 5 Kgf/Sq.cm. and volume is 96 cfm for 4 amplifiers and 80 cfm for 4 nozzles, and that 2 amplifiers and 2 nozzles each disposed on Left Hand Side and Right Hand Side of the painting surface area.
11. The process as claimed in claim 2 wherein the step of pretreating comprises of degreasing solution and water rinsing followed by metal phosphating treatment.
12. A wet on wet painting system for painting a surface of a material comprising :
a. an electrolytic deposition means for electrolytically depositing an acrylic resin based cathodic electrodeposition paint base coat over the surface of the material,
b. a water scavenging cum drying means for drying the coated surface using high velocity air,
c. a paint spraying means for spraying a water based topcoat paint coating over the electrodeposition paint coat with a paint that it is an aqueous thermosetting polymer.
d. a baking means for oven baking the unbaked electrodeposition paint coat and the waterbased topcoat paint coating simultaneously characterized in the arrangement of depositing the said paint spraying means between the said drying means and said baking means.
13. The system as claimed in claim 12 further comprising a water scavenging means positioned in series to the electrodeposition means.
14. The system as claimed in claim 12 wherein paint spraying means positioned in series to the drying means and adjacent to baking means.
15. The system as claimed in claim 12 wherein the paint spraying means is positioned after drying means and before baking means.
16. The system as claimed in claim 12 further comprising a spray painting booth which is side draft type booth / downdraft booth with filter air flow from top.
17. The system as claimed in claim 12 and 16 further comprising the spray painting booth having top air pressurization means with downward air velocity of 0.4 to 0.5 m/sec.
18. The system as claimed in claim 12, 16 and 17, wherein the spray painting booth having a water screen to carry away overspray of paint.
19. The system as claimed in claim 12, further comprising an air filter in plenum in the spray painting booth, thereby removing 95% of particulates greater than 10 microns.
20. An article having a paint finish, painted by the process as claimed in claim 1-11.
21. An article having a paint finish painted by a painting system as claimed in claim 12-19.