GR1010421B - Recycling of polyester thermosetting powder (fines) derived drom electrostatic paint industries - Google Patents

Abstract

There is disclosed a method of recycling waste colored thermosetting polyester powder of electrostatic painting for the manufacture of durable, colored, three-dimensional objects in which method the powder is mixed with low-granularity granular or fibrous fillers. According to said method the dry mixture is placed in molds and heated until the temperature in its entire mass exceeds 190 degrees Celsius for at least 5 min; then -after cooling and extraction of the mixture from the molds- the finished objects are ready. By applying said method, three-dimensional new- technology products colored throughout their mass, highly resistant, absolutely hydrophobic, electrically insulating and of low thermal conductivity are produced in a process characterized in that it does not produce residues, it has a negative carbon dioxide footprint by recycling thermosetting resins and it is able to produce any simple three-dimensional shape. Said method is susceptible to easy industrial application with the aim of manufacturing a multitude of objects with utility value.

Description

RECYCLING OF POLYESTER THERMOCURING POWDER (FINES) FROM ELECTROSTATIC PAINT INDUSTRIES

DESCRIPTION

INTRODUCTION:

Industries carrying out electrostatic painting produce as waste large quantities of residual polyester or other polymer thermosetting powders which they are obliged to dispose of. The quantities of discarded powder are significant and their proper disposal or recycling is imperative.

The characteristics of this "fines" powder are:

1. It is a thermosetting polyester or other type of polymer

2. It is in a finely divided form (fine powder)

3. It has different shades with the white color dominating. When found in mixtures of different color lots, the color mixture is usually gray.

4. Factories usually package the waste in 15-25 kg polyethylene bags and often place these inside the cartons of its original packaging.

The most common disposal methods currently followed are:

1. Disposal in landfill for sanitary landfill. Although this involves a lower cost, it creates problems of flammable waste in landfills, extremely difficult to biodegrade and is certainly not an ecological way of disposal, since it does not apply recycling-recovery of the discarded percentage of the powder.

2. Promotion to smaller companies that conduct electrostatic painting of various metal objects, fails to legally channel sufficient quantities of powder.

3. Potentially there is also the method of burning it to exploit its energy content. But this method is dangerous (burning plastic), does not recycle, has a high Carbon Dioxide footprint and produces dangerous gaseous waste for which special and expensive methods of cleaning the combustion gases are required.

Hazard characteristics of the by-product:

The by-product is polyester resin in fine powder form. Therefore:

1. It is flammable. It can keep burning for a long time producing large amounts of toxic combustion gases, because it is a polymer-macromolecular.

2. Easily dispersed into the environment by air currents and/or misuse without proper methods, procedures and control.

3. When mixed with air, it could potentially create an explosive mixture.

DISCLOSURE OF THE INVENTION:

The thermosetting resin can be placed in molds and heated to 190 - 200 deg C, for a sufficient time (about 5-10 minutes from the moment the whole mass is at the required temperature) to melt taking the form of the molds in which it was placed and after cooling to create three-dimensional objects of the hardened material for various, suitable uses. The same result can be achieved using simultaneous heating and compression of the material through an extruder to create suitable linear, three-dimensional, useful elements of the material.

In both cases of molding mentioned, unfortunately a brittle final product with a density of about 1.1 gr/ml is obtained, although glossy on the surface and solid pieces can be created for various applications. Also due to the excellent adhesion of the thermosetting polyester to the molds, expensive silicone molds or disposable molds are required which require refining of the final product.

When the powder is melted with a homogeneous filler material dispersed within its mass, a change in the final properties of the resulting objects occurs. Based on the powder and with the addition of suitable fillers within the molding and/or extrusion mass, elements with improved properties result. E.g.: with higher breaking strength - bending, tensile and compressive, greater or lesser density, with the possibility of not maintaining their combustion when exposed to flame, etc.

Overall achievable properties of the final objects - products resulting from the proposed method are:

1. Resistance to bending, compression, tension and especially the breaking of objects.

2. Reduction of the powder usage rate in relation to the simultaneous use and incorporation of cheap fillers

3. The use, if possible, of filler materials to be recycled so that the process includes only recyclable materials

4. The change in the density of the final products (eg: objects lighter or heavier than water) depending on the requested density of the objects to be produced

5. Change in combustion condition, e.g. with the addition of "flame retarder" and/or non-combustible filler material.

The following new features also arise in these innovative products:

1. All types of polyester electrostatic powders are fully recycled

2. The process can also take advantage of filler materials to be recycled, because it stabilizes/inerts them within the thermosetting polyester. E.G. could stabilize and potentially inactivate, slag or ash with high concentrations of heavy metals.

3. It can integrate thermoplastic materials together with thermosets and thus achieve recycling of a large category of plastics that cannot be recycled in any other way (at the end of their life cycle)

4. It produces useful products - three-dimensional objects, colored by the color of the powder or by adding another pigment to the powder, unbreakable with high added value. This is achieved with a variety of fillers by adding them in the appropriate proportion.

5. Depending on the choice of filler material, products with various desirable properties result, such as:

- Sawdust: light, wood imitations

- Sand: Heavy, imitations of concrete objects

- Light stone-peat: Light, imitation of foam concrete

- Alumina: They slow down the burning of the object ("flame retarder") - Marble dust: Heavy, marble imitation

- etc.

6. The items are, waterproof, do not absorb moisture. Well, they are not destroyed by ice. They are insulators with a high insulation coefficient, depending on the filler material. They do not conduct electricity.

7. They can combine complete recycling, with a zero carbon footprint, with some of the aforementioned properties in the final product.

8. Finally, the objects themselves can be recycled by breaking, grinding and re-incorporating in the same or a similar process or safely disposed of accordingly.

9. Capabilities to create 3D objects

- Pots

- Cubicles

- Decorative bricks

- Decorative pieces, stones, shields, etc.

- Pieces of imitation wood for construction, fences, pots, etc.

10. Different many different types of molds can be used:

- Metal sprayed with non-stick silicone

- Cardboard sprayed with silicone oil

- Silicone-based (e.g. heat-resistant silicone for temperatures up to 300 °C)

- Molds of sand, marble dust, or clay that take a temporary form before use and are reused by reshaping after the finished object is removed

POWDER - FILLERS RATIO

The optimum ratio is from 30:70 to 70:30 % V/V, but other ratios or combinations are not excluded. Also the fillers can be one or a mixture of more. Fibrous materials (e.g. wood chips) as well as light, porous materials (e.g. peat) give very good breaking strengths and lightweight objects. Granular heavy materials give heavy materials with high compressive strengths and satisfactory fracture strengths.

EXAMPLES

Example 1:

A gas-heated furnace (50,000 Kcal/hr, furnace dimensions 2 m * l m * 1.8 m) was used to heat the molds to 200 °C. The mixture used contained: 1) polyester powder to be recycled from profile extrusion and painting factories Aluminum in various colors, 2) Washed sea sand with an average particle size of 1 mm. Metal trays (2 m* l m * 0.16 m) were placed in the oven, in which molds were created from the same sand with the following procedure: Layering sand to a thickness of 15 mm. Placement of rectangular plates (20 cm * 10 cm * 6.3 cm) that form the perimeter of the cubes on the sand, leaving gaps of 25 mm between them. Filling the voids inside the plates with a sand/powder mixture homogenized in a blender with a ratio of powder/Sand = 1/1 by volume. Filling the gaps between the sheets was done with sand and vibration to fill the gaps completely. Vibration for 1 min and removal of the plates with continuous vibration. The pans were placed in the oven with a necessary gap between them at a height of 25 mm. The temperature in the oven was set at 200 °C for one hour. The exhaust gas duct from the oven ended in an active carbon filter with a cross-section of 1 m<Λ>2 and a length of 1 m. The pans were removed and allowed to bake at 40 °C. The separation and cleaning of the cobblestones from the sand used as a natural mold was easy and all the sand was sucked up and collected with the help of a small cyclone and bag filter for use in the next powder mix. 10 m<Λ>2 (approx. 1 m<Λ>3) colored cubes were obtained throughout their mass. The volume loss of the original powder/sand mixture was 5% and occurs at the height of the cube which must be factored in. Their specific gravity was = 1.9 gr/ml. Their compressive strength was measured at 70% of a standard concrete block. Moisture absorption in the cube mass after 4 hours immersion in water was zero.

Example 2:

An oven heated with natural gas (50,000 Kcal/hr, oven dimensions 2 m * 1 m * 1.8 m) was used to heat the molds to 200 oC. The mixture used contained: 1) polyester powder to be recycled from profile extrusion and painting factories Aluminum in various colors, 2) Marble dust of average grain size 0.7 mm. Metal trays were placed in the oven in which molds were created from the same marble powder with the following procedure: Laying marble powder to a thickness of 15 mm. Placement of rectangular plates (20 cm * 10 cm * 4.7 cm) that form the perimeter of decorative bricks on the marble dust leaving gaps of 25 mm between them. Filling the voids inside the plates with a mixture of marble dust/powder homogenized in a mixer with a ratio of Marble dust/powder = 1/1 by volume. The filling of the gaps between the plates was done with Marble Powder and vibration to completely fill the gaps. Vibration for 1 min and removal of the plates with continuous vibration. The pans were placed in the oven with a necessary gap between them at a height of 25 mm. The temperature in the oven was set at 200 oC for one hour. The exhaust gas duct from the oven ended in an active carbon filter with a cross-section of 1 m<Λ>2 and a length of 1 m. The pans were removed and allowed to bake at 40 °C. Separating and cleaning the decorative bricks from the marble dust used as a natural mold was easy and all the marble dust was sucked up and collected with the help of a small cyclone and bag filter for use in the next powder mix. 10 m<Λ>2 (approx. 1 m<Λ>3) colored decorative bricks were obtained throughout their mass. The volume loss of the original marble dust/sand mixture was 5% and occurs at the height of the brick to be accounted for. Their specific gravity was = 1.9 gr/ml. Their compressive strength was measured at 120 % of a standard decorative brick. Moisture absorption in the brick mass after 4 hours immersion in water was zero.

Example 3:

An oven heated with natural gas (50,000 Kcal/hr, oven dimensions 2 m * l m * 1.8 m) was used to heat the molds to 200 oC. The mixture used contained: 1) polyester powder to be recycled from aluminum profile extrusion and painting factories in various colors, 2) Marble dust with an average grain size of 0.7 mm and a small amount of Alumina trihydrate as a fire retardant. Metal trays were placed in the oven in which molds were created from the same marble powder with the following procedure: Laying marble powder to a thickness of 15 mm. Placement of rectangular plates (20 cm * 10 cm * 4.7 cm) that form the perimeter of decorative bricks on the marble dust leaving gaps of 25 mm between them. Filling the voids inside the plates with a mixture of marble dust/powder/Alumina trihydrate homogenized in a blender with a ratio of Marble dust/Powder/Alumina = 1/1/0.05 by volume. The filling of the gaps between the plates was done with Marble Powder and vibration to completely fill the gaps. Vibration for 1 min and removal of the plates with continuous vibration. The pans were placed in the oven with a necessary gap between them at a height of 25 mm. The temperature in the oven was set at 200 °C for one hour. The exhaust gas duct from the oven ended in an active carbon filter with a cross-section of 1 m<Λ>2 and a length of 1 m. The pans were removed and allowed to bake at 40 °C. Separating and cleaning the decorative bricks from the marble dust used as a natural mold was easy and all the marble dust was sucked up and collected with the help of a small cyclone and bag filter for use in the next powder mix. 10 m<Λ>2 (approx. 1 m<Λ>3) were obtained, colored throughout their mass decorative bricks. The volume loss of the original marble dust/sand mixture was 5% and occurs at the height of the brick to be accounted for. Their specific gravity was = 1.9 gr/ml. Their compressive strength was measured at 120 % of a standard decorative brick. Moisture absorption in the brick mass after 4 hours immersion in water was zero. The resulting bricks did not sustain their combustion after being exposed to fire for a sufficient period of time to be considered practically incombustible.

Claims (8)

CLAIMS: 1. A method of recycling colored thermosetting polyester or other type of thermosetting polymer in the form of electrostatic paint powder for the manufacture of shatter-resistant, colored, hydrophobic, low thermal and electrical conductivity, three-dimensional objects in which such powder is mixed as is with filler materials granular or fibrous or a mixture thereof and with a maximum dimension of from 1 µm to 2 cm and preferably from 0.5-2 mm, in volume ratios of 10:90 - 90:10 and preferably from 40:60 to 60:40 in in which the mixture is placed in molds and heated until the temperature in its entire mass exceeds 190 °C for at least 5 min and then after cooling and exiting the molds the ready three-dimensional objects for various uses emerge. 2. The three-dimensional objects as new technology products from recycling resulting from the application of the method described in claim 1. 3. The recycling method of claim 1, producing products as described in claim 2, wherein the powder and filler mixture is filled into reusable silicone, or metal or wooden molds with or without silicone oil coating for easy release of the objects . 4. The recycling method of claim 1, producing products as described in claim 2, wherein the mixture of powder and filler materials is filled into disposable molds of pressed paper or paperboard with or without silicone oil coating which are removed from the three-dimensional objects by simple pulling or after first immersing them in hot or cold water. 5. The recycling method of claim 1, producing products as described in claim 2, in which the mixture of powder and fillers is filled into molds of non-permanent - temporary construction from compressed into the form of the mold - suitable shape of fine sand, marble dust, clay , of wood chips sprayed with or without water or oil or silicone oil, which are removed from the three-dimensional objects by simply pulling the finished object, after it has cooled and stabilized, from the mass of the temporary mold. The material of the temporary mold can be reused and/or incorporated as inert material in the powder/inert mix of the next production cycle achieving its complete recycling. 6. The recycling method of claim 1 when applied to thermosetting electrostatic paint resins, epoxy or other type of thermosetting polymer in powder form. 7. The recycling method as described in claim 1, in which the mixture of thermosetting resin and inert materials can contain a mixture of thermosetting resins of similar melting point and different shades or a mixture of various fillers with the aim of improving the properties of the final products, such as: pumice stone or peat for light objects, Alumina as a flame retardant, sawdust or chopped straw to increase the breaking strength and for light objects in imitation of wood, fine marble dust for heavy objects and imitation of marble, fine sand for heavy objects and imitation of concrete products. 8. The recycling method of claim 1, which produces products as described in claim 2, where low particle size (e.g. after grinding) solids resulting as waste or by-products of various processes and requiring their disposal can be used as fillers after their stabilization/solidification (e.g. fly ash, metallurgical slag, etc.), achieving a double recycling of by-products by stabilizing/solidifying them within the thermosetting resin.