Method for removing ink printed on plastic films

Abstract

The present invention relates to a method for removing ink printed on a plastic film comprising various physical/chemical treatments. The main steps in the method are: conditioning the material, grinding, removing ink from the film, washing the film, recovering the cleaning solution, recovering the pigment and drying the film. As a result of the method, it is possible to obtain, on one hand, a plastic film free of ink and, on the other hand, the pigment. Said products may be reused in industry, thereby enhancing the value chain of the product.

Claims

1. A method for removing ink printed on a plastic film comprising the following steps; a) conditioning the input printed material in a plunger obtaining a film free of impurities; b) grinding the film free of impurities in a grinder; c) removing ink from the film in a cleaning system with a cleaning solution consisting of surfactants in water at basic pH, where a cleaning tank stirred with vanes generates a treated plastic film containing part of that cleaning solution and the dispersed ink residues, and in addition, the cleaning solution together with the ink removed from the film; d) washing the treated plastic film in the preceding cleaning system where at least two washing tanks obtain a clean film free of ink and cleaning solution residues; e) recovering the cleaning solution in a centrifuge; f) recovering the pigment in a thermal treatment reactor; and g) drying the film for obtaining a ground film free of ink and cleaning solution in a drying element.

2. The method for removing ink printed on a plastic film according to claim 1, where the input printed material can be polyethylene (PE), polypropylene (PP), film of polyester (PET) or polyamide (PA).

3. The method for removing ink printed on a plastic film according to claim 1, where the size of the film free of impurities after grinding is 6 to 14 mm in diameter.

4. The method for removing ink printed on a plastic film according to claim 1, where the cleaning solution contains a proportion of surfactants in water between 0.1 and 5% by weight.

5. The method for removing ink printed on a plastic film according to claim 4, where the cleaning solution contains hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide or dodecyl sulfate as surfactants.

6. The method for removing ink printed on a plastic film according to claim 4, where the cleaning solution has a pH between 11 and 13.

7. The method for removing ink printed on a plastic film according to claim 1, where the washing step is performed in two washing tanks, the first tank with recirculated water and the second tank with clean water.

8. The method for removing ink printed on a plastic film according to claim 1, where the centrifugation speed is 10,000 revolutions per minute.

9. The method for removing ink printed on a plastic film according to claim 1, where the thermal treatment reactor works by vigorous stirring at a temperature between 170 and 200 C. for 1 hour, where from a mixture of pigment and plant or mineral oil, the resin containing the pigment is thermally destroyed, and the mixture is filtered after the treatment to separate the pigment from the oil and the oil is reintroduced into the reactor to continue treating more pigment.

10. The method for removing ink printed on a plastic film according to claim 1, where the drying step is performed by means of a briquette machine.

11. The method for removing ink printed on a plastic film according to claim 1, where the drying step is performed by means of hot air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagram of the method object of this invention as well as the pieces of equipment involved in the invention.

(2) FIG. 2 shows a detailed diagram of the cleaning system of the method for removing ink from the printed film.

DETAILED DESCRIPTION OF EMBODIMENTS

(3) The preferred embodiment of the method described in the present invention is described below in view of the drawings.

(4) The method for removing ink printed on the plastic film comprises the following steps:

(5) Step 1: Conditioning the Material

(6) The input printed material 1 can be polyethylene (PE), polypropylene (PP), film of polyester (PET) or polyamide (PA). Once the input printed material 1 is collected, a conditioning step is performed in which the cores where the film as well as any object the composition of which is not of a plastic film in the form of a jumbo or dispersed material are removed. The equipment responsible for removing the core supporting the plastic 101 consists of a plunger that applies force on the cylindrical core and keeps the roll of plastic film fixed. The cylinder is separated from the plastic body by applying pressure. Once conditioning is performed, a film by-product free of impurities 2 containing the rolls of film without the cores and the input dispersed material is obtained.

(7) Step 2: Grinding

(8) The particle size of the film free of impurities 2 must be reduced to a diameter that can vary from 6 to 14 mm to favor the penetration of the cleaning solution. To that end, it is introduced in a blade grinder 102 comprising both fixed and moving blades. This grinder reduces the size of the film until obtaining a ground material 3.

(9) Step 3: Removing Ink from the Film

(10) The ink must be removed from the ground material 3, so it is introduced in the cleaning system 103 with the cleaning solution 6 consisting of a mixture of surfactants in water, at proportions between 0.1 and 5% by weight, and with a basic pH between 11 and 13, where the ink contained in the film is removed, the ink then becoming part of the cleaning solution in a non-dissolved form. In a preferred embodiment, the surfactants of the cleaning solution are hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide or dodecyl sulfate. The cleaning system 103 consists of the system formed by three tanks which is shown in FIG. 2. The cleaning tank 201 is a tank stirred with vanes where the plastic film is contacted with the cleaning solution 6. The other two tanks are washing tanks that start operating in the subsequent step. Three flows enter this cleaning system 103, i.e., the flow containing the ground material 3, the flow containing the cleaning solution 6 and the flow containing clean water; and another two flows that are described below exit said system. The flow containing the ground material 3 enters the cleaning system 103 feeding the cleaning tank 201. The cleaning solution 6 from the centrifuge 104 also enters this cleaning tank. It is very important for the vanes of the cleaning tank 201 to cause high turbulence inside the tank stirred with vanes in order to prevent the pieces of ground film from overlapping with one another, and to therefore increase method efficiency. Furthermore, the turbulence also favors the dispersion of the ink that detaches from the film in the cleaning solution 6. On one hand, the treated plastic film 21 containing cleaning solution and dispersed ink residues exits the cleaning tank 201, and, on the other hand, the cleaning solution together with the ink removed from the film 4 exits the cleaning tank 201 towards the centrifuge 104.

(11) Step 4: Washing the Film

(12) Two consecutive washing methods are performed in the same cleaning system 103 in two washing tanks with vanes. The cleaning tank 201 is washed with water in the first washing tank 202. The film from the first washing tank 202 is contacted with clean water in the second washing tank 203 to remove cleaning solution residues. The treated plastic film 21 is introduced in the first washing tank 202 to remove dispersed ink residues and cleaning solution residues. The washing liquid 25 that exits the first washing tank 202 is fed to the cleaning tank 201 in order to save water. The washed plastic film 22 containing cleaning solution residues exits the first washing tank 202 and is fed to the second washing tank 203. This second washing removes the last cleaning solution residues that may remain in the plastic. Two flows exit the second washing tank 203, i.e., one flow containing the clean film free of ink and cleaning solution residues 8 that is fed to the briquette machine 106; and another flow containing the washing water 24 that is fed to the first washing tank 202 to save water.

(13) Step 5: Recovering the Cleaning Solution

(14) The cleaning solution together with the ink removed from the film 4 must be continuously regenerated by means of using a centrifuge 104, at 10,000 revolutions per minute. This equipment consists of a centrifugal separator for separating the cleaning solution 6 from the ink 5. The cleaning solution 6 is reintroduced in the cleaning system 103 reducing the consumption of cleaning solution that the method would have, in case said solution was not reused.

(15) Step 6: Recovering the Pigment

(16) The flow containing the ink 5 is fed to an ink thermal treatment reactor 105 in order to destroy the structure of the resin and the pigment ready to be reused 7 exits said reactor. The thermal treatment reactor works at a temperature between 170 and 200 C. A mixture of pigment and oil is introduced in the reactor, where the resin containing the pigment is thermally destroyed. Both plant oil, such as, for example, sunflower seed oil or linseed oil, and mineral oil from petroleum can be used. The reactor operates with vigorous stirring and the mean residence time of the pigment is 1 hour. The mixture is filtered after the treatment to separate the pigment from the oil and the oil is reintroduced into the reactor to continue treating more pigment. The pigment is thereby free of resin and can be used in various applications.

(17) Step 7: Drying the Film

(18) The clean film free of ink and cleaning solution residues 8 is formed by the clean film after the ink 5 has been removed and washed with the cleaning solution 6. This plastic is introduced in the briquette machine 106 consisting of a drying element which removes the largest amount of water possible by means of pressing and compacting the material. A flow containing a ground film free of ink and cleaning solution 9 ready for use in other applications exits the briquette machine 106.

(19) As mentioned previously, two products, on one hand, the pigments and, on the other hand, the colorless recycled film in the form of pellets, are generated from this method.