Field of the invention
The present invention relates to a composition for the conversion of paint sludge
into reusable paint, to a process for the preparation of said composition and to a process for the conversion of waste paint sludge back to useful paint. The sludge conversion process of the invention consumes the environmentally hazardous sludge collected from paint application systems by converting this paint sludge into a reusable paint. Background of the invention
Most original equipment manufacturers (OEM's) use spray technique for painting their components. In this process the paint is mixed/thinned with appropriate thinner to get required application viscosity. Then it is applied by spray method on respective components in a paint booth. During spray method some paint adheres on the component being spray painted. Over-sprayed paint goes to water stream as a waste. This over sprayed waste paint gets mixed with water stream and gets coagulated by flocculent present in water stream. From this water stream the sludge is collected using the flotation method. Generally this sludge is either dumped or incinerated by industries, which is environmentally hazardous. Typically, the sludge obtained is either not biodegradable or degrades at a very slow rate. Therefore, dumping or earth filling of such sludge poses an environmental hazard. Burning of this sludge also produces toxic flames causing environment pollution. Therefore dumping, earth filling or burning of paint sludge is not an environmentally safe method for disposal. It is therefore important to devise a method by which paint sludge can be converted at least in part into reusable paint by separating the paint component of such sludge. This will assist in reducing the environmental hazards associated with the paint process.
To the best of the applicant's knowledge, no processes are known in the art for recovery of paint from paint sludge such that useful paint can be recycled and environmental concerns addressed at the same time.
Objects of the invention
The main object of the invention is to provide a composition useful for the recovery of reusable paint from paint sludge.
It is another object of the invention to provide a process for the recovery of reusable paint from paint sludge, which is environmentally friendly and inexpensive.
Summary of the invention
The above and other objects of the present invention are attained by the novel composition of this invention which comprises a mixture of solvents in specific amounts with or without resins and a process for the use thereof which enables conversion of paint sludge into reusable paint.
A process for the conversion of paint sludge into reusable paint, said process comprising drying the paint sludge by any conventional method, and soaking said dried sludge with a solvent mixture comprising essentially a mixture of toluene or benzene in an amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone in an amount of 10 to 25% and if desired a resin mixture comprising methyl formamide in an amount of 1.5 to 8%, along with one or more conventional resins, the balance if any comprising one or more conventional additives, and all percentages being expressed in terms of weight of the amount of the paint sludge to be treated, and stirring the resultant product so obtained at ambient temperature, said solvent mixture being present in an amount of 30 - 80% by weight of the sludge, milling the stirred mixture of paint sludge and solvent mixture and filtering to obtain reusable paint.
In one embodiment of the invention, the paint sludge is soaked in the solvent mixture over 1 to 36 hours.
In another embodiment of the invention, the solvent mixture comprises a mixture of toluene or benzene in an amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl in an amount of 10 to 25%, all percentages being expressed in terms of weight of the amount of the paint sludge to be treated.
In another embodiment of the invention, the solvent mixture includes additives selected from alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, alkyl acetate selected from ethyl acetate and butyl acetate and methyl isobutyl ketone.
In another embodiment of the invention, the paint sludge comprises sludge of amino alkyd based paints.
In yet another embodiment of the invention, the solvent mixture comprises toluene in an amount of 30 to 40 %, xylene in an amount of 25 to 35 %, n-butyl alcohol in an amount of 10 to 20 %, butyl cellulose in an amount of 5 to 10 % and cellosol acetate in an amount of 1 to 3 %.
In a further embodiment of the invention, the paint sludge comprises sludge of polyester melamine based paints.
In yet another embodiment of the invention the solvent mixture comprises toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38 %, n-butyl alcohol or methyl isobutyl ketone or methyl cellosol in an amount of 5 to 12 %, diacetone alcohol in an amount of 3 to 10 %, cellusol acetate or amyl acetate in an amount of 2 to 5 % by weight expressed in terms of the amount of the paint sludge to be treated.
In another embodiment of the invention, a resin mixture is added to the mixture of paint sludge and solvent mixture during milling.
In another embodiment of the invention, the resin mixture comprises M.F in an amount of 1.5 to 8 %, along with one or more conventional resins and other conventional additives.
In another embodiment of the invention, the said one or more conventional resins is selected from the group consisting of alkyd resin, acrylic resin, epoxy resin, polyester resin and any mixture thereof.
In yet another embodiment of the invention, the said conventional additives are selected from the group consisting of corrosion additives, dipentene, para toluene sulfonic acid, soya lecithin and epoxy lacquer.
In a further embodiment of the invention, the MF resin is present in an amount of 1.5 to 6 % by weight of the paint sludge to be treated and the paint sludge comprises sludge of epoxy modified or polyester paints.
In yet another embodiment of the invention, the MF resin is present in an amount of 3 to 7 % by weight of the paint sludge to be treated and the paint sludge comprises sludge of amino alkyd and TSA paints.
In yet another embodiment of the invention, the corrosion additive comprises a linear polymer with amine and triazole functional groups.
In yet another embodiment of the invention, the resin mixture comprises MF resin in an amount of 3 to 7 %, alkyd resin in an amount of 7 to 14 %, a corrosion inhibitor in an amount of 0.5 to 2 %, dipentene in an amount of 0.5 to 2 %, soya lecithin in an amount of 0.05 to 0.7 %, para toluene sulfonic acid in an amount of 0.05 to 0.5 %, and if desired epoxy lacquer in an amount of 4 to 10 % by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of amino alkyd resin based paint.
In yet another embodiment of the invention, the resin mixture comprises MF resin in an amount of 2 to 8 %, acrylic resin in an amount of 5 to 15 %, a corrosion inhibitor in an amount of 0.2 to 2.5 %, dipentene in an amount of 1 to 2.5 %, soya lecithin in an amount of 0.02 to 0.3 %, para toluene sulfonic acid in an amount of 0.05 to 0.5 %, and if desired epoxy lacquer in an amount of 3 to 8 % by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of TSA based paint.
In yet another embodiment of the invention, the resin mixture comprises MF resin in an amount of 1.5 to 6 %, epoxy resin in an amount of 6 to 14 %, a corrosion inhibitor in
an amount of 0.2 to 2 %, dipentene in an amount of 1 to 3.5 %, soya lecithin in an amount
of 0.05 to 0.3 %, para toluene sulfonic acid in an amount of 0.05 to 0.5 %, and if desired epoxy lacquer in an amount of 0 to 5 % by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of epoxy modified based paint.
In yet another embodiment of the invention, the resin mixture comprises MF resin in an amount of 4 to 7 %, polyester resin in an amount of 5 to 15 %, a corrosion inhibitor in an amount of 0.3 to 2.5 %, dipentene in an amount of 1 to 3 %, soya lecithin in an amount of 0.05 to 0.4 %, para toluene sulfonic acid in an amount of 0.05 to 0.5 %, and if desired epoxy lacquer in an amount of 3 to 10 % by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of polyester based paint.
The present invention also relates to a novel composition for the conversion of paint sludge into reusable paint, said composition comprising toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone in an amount of 10 to 25 %, all percentages being expressed in terms of weight of the amount of the paint sludge to be treated.
In another embodiment of the invention, the solvent mixture includes additives selected from alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, amyl acetate selected from ethyl acetate and butyl acetate and methyl isobutyl ketone.
In yet another embodiment of the invention, the solvent mixture comprises toluene in an amount of 30 to 40 %, xylene in an amount of 25 to 35 %, n-butyl alcohol in an amount of 10 to 20 %, butyl cellulose in an amount of 5 to 10 % and cellosol acetate in an amount of 1 to 3 %.
In yet another embodiment of the invention the solvent mixture comprises toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38 %, n-butyl alcohol or methyl isobutyl ketone or methyl cellosol in an amount of 5 to 12 %, diacetone
alcohol in an amount of 3 to 10 %, cellusol acetate or amyl acetate in an amount of 2 to 5 % by weight expressed in terms of the amount of the paint sludge to be treated.
The present invention also relates to a process for the preparation of a paint composition useful for the conversion of paint sludge into reusable paint, said composition comprising toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone in an amount of 10 to 25 %, all percentages being expressed in terms of weight of the amount of the paint sludge to be treated, said process comprising intimately mixing the above ingredients in any conventional manner.
In another embodiment of the invention, the solvent mixture includes additives selected from alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, amyl acetate selected from ethyl acetate and butyl acetate and methyl isobutyl ketone.
In another embodiment of the invention, the paint sludge comprises sludge of amino alkyd based paints.
In yet another embodiment of the invention, the solvent mixture comprises toluene in an amount of 30 to 40 %, xylene in an amount of 25 to 35 %, n-butyl alcohol in an amount of 10 to 20 %, butyl cellulose in an amount of 5 to 10 % and cellosol acetate in an amount of 1 to 3 %.
In a further embodiment of the invention, the paint sludge comprises sludge of polyester melamine based paints.
In yet another embodiment of the invention the solvent mixture comprises toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38 %, n-butyl alcohol or methyl isobutyl ketone or methyl cellosol in an amount of 5 to 12 %, diacetone alcohol in an amount of 3 to 10 %, cellusol acetate or amyl acetate in an amount of 2 to 5
% by weight expressed in terms of the amount of the paint sludge to be treated.
* 1
Detailed description of the invention
The generation and disposal of sludge is explained in Flow Chart-1. Paint generally comprises of the following materials:
1. Resin
2. Pigment and Extenders
3. Solvents
4. Additives
All the ingredients are present in a homogeneous dispersed state. All have their specific roles in paint properties. Over-sprayed paint material consists of all the ingredients but very small percentage of solvents. When it is mixed in water and flocculates, solvent content is reduced further and the paint residuals become small droplets. The coagulation of small droplets results in mass formation i.e. sludge.
The process for conversion of the sludge into a usable paint form according to the present invention comprises separation of contaminants and addition of solvents and resins in specific proportions. The collected sludge is a semisolid mass containing paint residuals, water, oil/greases along with flocculent (Booth Additive). Water, Oil/grease and Flocculent has detrimental effect on paint properties and its reusability. These contaminants are either have to be eliminated or prevented from coming into the process. Flocculent having acidic properties will damage the paint by creating problems. To avoid this problem, the additive to be used should have alkaline nature instead of acidic. Oil/Grease contamination into the sludge should be avoided during the sludge formation and collection process. Water also to be removed from the sludge, which will be discussed in the process itself. CONVERSION PROCESS:
The sludge to be converted contains residual paints, acidic flocculent additive and
water. The process consists of following steps as illustrated in Flow Chart-2.
1 / De-watering and Solvent Removal.
a) Pressing: Sludge is pressed to remove water and solvent from the mass.
b) Heating: The Sludge mass is heated for maximum removal of water and solvents
contents.
2. Soaking of dried sludge either in a mixture of resin and solvents or only solvents for few hours depending on the final properties of the paint duration of soaking depends on the aging of the sludge.
3. Dispersion: The dispersion of the soaked sludge (viscous mass) can be achieved using ball mills, attritors, high speed or low speed dispersers or bead mills etc.
4. Filtration, testing of final paint properties and packing for usage.
Example:
Sludge of alkyd-amino system was taken and processed using above-mentioned system. This is better explained in Flow Chart II.
While work is not complete in the invention as yet, it is believed that the process of the invention can be used in respect of almost all paint systems which are spray used. The choice of solvents and resins and specific proportions would depend on the paint system used.
Some of the paint systems where the process of the invention can be used are Epoxy-amino/phenolic system (Single Pack - Stoving System), Alkyd-amino system, Thermosetting acrylic systems, Thermoplastic-acrylic system.
The physical performance of reusable paint obtained according to the process of the invention and fresh paint is given below in Table 1.

We claim:
1. A process for the conversion of paint sludge into reusable paint, said process comprising drying the paint sludge by any conventional method, and soaking said dried sludge with a solvent mixture comprising essentially a mixture of toluene or benzene in an amount of 28 to 40 %, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone in.an amount of 10 to 25 %, and if desired a resin mixture comprising methyl formamide in an amount of 1.5 to 8%, along with one or more conventional resins, the balance if any comprising one or more conventional additives, and all percentages being expressed in terms of weight of the amount of the paint sludge to be treated, and stirring the resultant product so obtained at ambient temperature, said solvent mixture being present in an amount of 30 - 80% by weight of the sludge, mining the stirred mixture of paint sludge and solvent mixture and filtering to obtain reusable paint.
2. A process as claimed in claim 1 wherein the paint sludge is soaked in the solvent mixture for 1 to 36 hours.
3. A process as claimed in claim 1 or 2 wherein the one or more conventional additives is selected from the group consisting of alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, amyl acetate selected from ethyl acetate and butyl acetate, methyl isobutyl ketone, and one or more resins.
4. A process as claimed in claim 1 wherein the paint sludge comprises sludge of amino alkyd based paints and the solvent mixture comprises toluene in an amount of 30 to 40%, xylene in an amount of 25 too 35%, n-butyl alcohol in an amount of 10 to 20%, butyl cellulose in an amount of 5 to 10% and cellosol acetate in an amount of 1 to 3%.
5. A process as claimed in claim 2 wherein the paint sludge comprises sludge of
polyester melamine based paints and the solvent mixture comprises toluene or
benzene in an amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl
alcohol or methyl isobutyl ketone or methyl cellulose in an amount of 5 to 12%,
diacetone alcohol in an amount of 3 to 10%, cellosol acetate amyl acetate in an
amount of 2 to 5% by weight expressed in terms of the amount of the paint sludge
to be treated.
6. A process as claimed in claim 1 wherein the said one or more conventional resins is selected from the group consisting of alkyd resin, acrylic resin, epoxy resin, polyester resin and any mixture thereof.
7. A process as claimed in claim 1 wherein the said conventional additives are selected from the group consisting of corrosion additives, dipentenes, para toluene sulfonic acid, soya lecithin and epoxy lacquer.
8. A process as claimed in claims 1 to 7 wherein the methyl formamide resin is present in an amount of 1.5 to 6% by weight of the paint sludge to be treated and the paint sludge comprises sludge of epoxy modified or polyester paints.
9. A process as claimed in claim 1 to 7 wherein the methyl formamide resin is present in an amount of 3 to 7% by weight of the paint sludge to be treated and the paint sludge comprises sludge of amino alkyd and toluene sulfonic acid paints.

10. A process as claimed in claim 1 to 9 wherein the corrosion additive comprises a linear polymer with amine and triazole functional groups.
11. A process as claimed in claim 1 wherein the resin mixture comprises methyl formamide resin in an amount of 3 to 7%, alkyd resin in an amount of 7 to 14%, a corrosion inhibitor in an amount of 0.5 to 2%, dipentene in an amount of 0.5 to 2%, soya lecithin in an amount of 0.05 to 0.7%, para toluene sulfonic acid in an amount of 0.05 to 0.5%, and if desired epoxy lacquer in an amount of 4 to 10% by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of amino alkyd resin based paint..
12. A process as claimed in claim 1 wherein the resin mixture comprise methyl formamide resin in an amount of 2 to 8%, acrylic resin in an amount of 5 to 15%, a corrosion inhibitor in an amount of 0.2 to 2.5%, dipentene in an amount of 1 to 2.5, soya lecithin in an amount of 0.02 to 0.3%, para toluene sulfonic acid in an amount of 0.05 to 0.5%, and if desired epoxy lacquer in an amount of 3 to 8% by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of toluene sulfonic acid based paint.
13 A process as claimed in claim 1 wherein the resin mixture comprises methyl formamide resin in an amount of 1.5 to 6%, epoxy resin in an amount of 6 to 14%, a corrosion inhibitor in an amount of 0.2 to 2%, dipentene in an amount of 1 to 3.5%, soya lecithin in an amount of 0.05 to 0.3%, para toluene sulfonic acid in an amount of 0.05 to 0.5%, and if desired epoxy lacquer in an amount of 0 to 5% by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of epoxy modified based paint.
14. A process as claimed in claim 1 wherein the resin mixture comprises methyl formamide resin in an amount of 4 to 7%, polyester resin in an amount of 5 to 15%, a corrosion inhibitor in an amount of 0.3 to 2.5%, dipentene in an amount of 1 to 3%, soya lecithin in an amount of 0.05 to 0.4%, para toluene sulfonic acid in an amount of 0.05 to 0.5%, and if desired epoxy lacquer in an amount of 3 to 10% by weight of the amount of paint sludge to be treated, said paint sludge comprising sludge of polyester based paint..
15. A novel composition for the conversion of paint sludge into reusable paint, said composition comprising toluene or benzene in an amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone in an amount of 10 to 25%, and the balance if any, comprising one or more conventional additives of the kind such as hereinbefore described, all percentages being expressed in terms of weight of the amount of the paint sludge to be treated.
16. A composition as claimed in claim 15 wherein the one or more conventional additives comprises alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, amyl acetate selected from ethyl acetate and butyl acetate and methyl isobutyl ketone.
17. A composition as claimed in claim 15 wherein the solvent mixture comprises toluene in an amount of 30 to 40%, xylene in an amount of 25 to 35%, n-butyl alcohol in an amount of 10 to 20%, butyl cellulose in an amount of 5 to 10% and cellosol acetate in an amount of 1 to 3%.
18. A composition as claimed in claim 15 wherein the solvent mixture comprises toluene or benzene in an amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl isobutyl ketone or methyl cellosol in an amount of 5 to 12%, diacetone alcohol in an amount of 3 to 10%, cellusol acetate or amyl acetate in an amount of 2 to 5% by weight expressed in terms of the amount of the paint sludge to be treated.
19. A process for the preparation of a composition useful for the conversion of paint
sludge into reusable paint, said composition comprising toluene or benzene in an
amount of 28 to 40%, xylene in an amount of 22 to 38%, n-butyl alcohol or methyl
isobutyl ketone in an amount of 10 to 25%, and the balance if any comprising one
or more conventional additives of the kind such as herein described, all percentages
being expressed in terms of weight of the amount of the paint sludge to be treated,
said process comprising intimately mixing the above ingredients in any conventional
manner.
20. A process as claimed in claim 19 wherein the one or more conventional additives comprises alkyl cellulose selected from butyl cellulose and methyl cellulose, butyl sorbitol, diacetone alcohol, cellosol acetate, amyl acetate selected from ethyl acetate and butyl acetate and methyl isobutyl ketone.
21. A process as claimed in claim 19 and 20 wherein the solvent mixture comprises toluene in an amount of 30 to 40%, xylene in an amount of 25 to 25%, n-butyl alcohol in an amount of 10 to 20%, butyl cellulose in an amount of 5 to 10% and cellosol acetate in an amount of lto 3%.

22. A process for the conversion of paint sludge into reusable paint substantially as describes hereinbefore and with reference to the foregoing examples and accompanying drawings.
23. A novel composition for the conversion of paint sludge into reusable paint substantially as described hereinbefore and with reference to the foregoing examples and accompanying drawings.
24. A process for the preparation of a composition substantially as described hereinbefore and with reference to the foregoing examples and accompanying drawings.