GB2572796A

GB2572796A - Composition for darkening the colour of polymers

Info

Publication number: GB2572796A
Application number: GB1805979.0A
Authority: GB
Inventors: Wilson Gerry
Original assignee: Performance Masterbatches Ltd
Current assignee: Performance Masterbatches Ltd
Priority date: 2018-04-11
Filing date: 2018-04-11
Publication date: 2019-10-16
Also published as: GB201805979D0

Abstract

A composition that does not substantially absorb infrared radiation contains (a) black pigment comprising mixed iron and manganese oxide and (b) carrier medium. The black pigment may have the formula (Fe,Mn)2O3 and may be Pigment Black 26. The composition may comprise 20-75 wt.% black pigment and 10-80 wt.% carrier medium. The carrier medium may include a pigment dispersant and/or carrier polymer, e.g. polyethylene, HDPE, LDPE, polypropylene, polystyrene, polyamide, polyethylene terephthalate, EVA, ABS, or SAN. The use of the composition or the black pigment as a black colorant in a recyclable polymer, such as polyethylene terephthalate or polypropylene, is disclosed, wherein the black pigment does not substantially absorb infrared radiation. A method of darkening the colour of a polymer comprises adding the composition to the polymer and mixing with heat to form a mixture, wherein the mixture is black and does not substantially absorb infrared radiation.

Description

COMPOSITION FOR DARKENING THE COLOUR OF POLYMERS

The present invention relates to a composition for darkening the colour of polymers, and in particular plastics.

The recycling of polymers, particularly plastics, allows used polymer items to be made into new items without the financial and environmental cost of making new polymers. Plastic sorting can be performed manually at recycling centres using the recycling codes imprinted on the item. However, this is labour intensive and costly.

The efficiency of plastic recycling has greatly increased with the use of near infrared (NIR) optical sorting technology. By analysing the reflected NIR in the 600-2800 nm waveband, different plastics can be identified extremely accurately and sorted for recycling. NIR optical sorting technology is now widely used in plastics recycling.

As described in WO 2011/098842, black plastic is normally coloured with the pigment carbon black. Convenience food plastic packaging is often black as this beneficially provides a contrasting background allowing the colours in the food to stand out. Black plastic is also extensively used in the automobile industry. Carbon black is low in cost, food safe, has high tint strength and has good masking properties. Masking is an important property in circumstances where mixed coloured plastic is to be recycled into black plastic.

However, carbon black effectively absorbs all NIR radiation, which is problematic as polymers containing carbon black cannot be detected and sorted using the NIR optical sorting technology. Therefore, this black plastic has to be manually sorted for recycling or is not recycled and is deposited in landfill.

GB2534594 describes the use of a mixture of two pigments, green iron chrome oxide and brown iron chrome oxide, for use in colouring polymers. It is disclosed that the correct mixture of the two pigments gives a black colourant and that the combination of pigments does not absorb all NIR so resultant polymers containing the pigments can be sorted using the NIR optical sorting technology. However, when mixing two pigments it can be difficult to achieve colour reproducibility and colour uniformity in the target polymer. Further, the need to measure exact ratios of the pigments and the need for extensive mixing of the pigments to try and achieve colour reproducibility and colour uniformity with the target polymer leads to high manufacturing costs and waste. Further, the green and brown iron chrome oxide are costly.

The present invention, in at least some of its embodiments, addresses the above mentioned problems.

According to a first aspect of the invention there is provided a composition for darkening the colour of a target polymer comprising a black pigment comprising mixed iron and manganese oxide, and a carrier medium, wherein the composition does not substantially absorb infrared radiation.

The present inventors have found that by using a single pigment of mixed iron and manganese oxide having the formula (Fe,Mn)₂O3 (with the CAS-No. 68186-94-7) a black colour tone is imparted to a target polymer and the coloured target polymer does not substantially absorb NIR radiation. Therefore, the resulting coloured polymer can advantageously be identified and sorted using

NIR optical sorting technology and go on to be effectively recycled. Beneficially, the pigment is also low in cost, which is an important consideration if the pigment is to be used on a large scale, such as in the automobile industry or in food packaging. The pigment is also beneficially of food grade and so may be used in packaging which comes into contact with food, and in particular may be used in convenience food packaging.

As the black colour tone can be achieved using a single pigment there is the advantage of ease of use, consistent colour tone and colour uniformity in the resulting coloured polymer. Therefore, there is a saving on cost and waste.

The pigment has excellent masking properties. This is an important consideration when non-virgin coloured plastics are to be used at least in part as the target polymer. Therefore, advantageously, the composition can be added to the mixed coloured plastics and achieve a uniform black colour tone to the final polymer product.

The pigment does not degrade at temperatures of up to at least 500°C and therefore the composition can be used to colour polymers with a high melting temperature, such as PET (melting temperature of 260°C) and PA (melting temperature of 190-350°C). This is particularly important in the automotive industry and in food tray production, where polymer products having a high melting temperature are often required.

The composition may comprise between 20 and 75 weight percent (wt%) of the black pigment, preferably between 40 and 65 wt%, more preferably between 55 and 65 wt%, and most preferably between 59 and 61 wt%.

The term “black” is understood to mean that substantially all visible light is absorbed by the pigment. For example, 90% or more of the visible light is absorbed. The phrase “does not substantially absorb NIR radiation” means that a small proportion of NIR radiation in the 600-2800 nm waveband may be absorbed by the product, but most NIR radiation will be reflected from the product sufficient that the product can be detected using NIR optical sorting technology.

The composition may comprise between 10 and 80 wt% of carrier medium, preferably between 30 and 60, more preferably between 35 and 45 wt%, most preferably between 38 and 42 wt%.

The carrier medium beneficially comprises a carrier polymer and/or a pigment dispersant.

The carrier polymer may be any polymer in which the pigment is able to evenly disperse and which is compatible with the chemical composition of the target polymer. Compatibility with the chemical composition of the target polymer means that the carrier polymer and the target polymer will readily mix and bond together, without any adverse reactions. Preferably, the carrier medium and the target polymer are the same polymer. The target polymer (or end-use polymer) is the polymer from which, for example, the recyclable plastic product is to be manufactured.

The composition may comprise between 20 and 60 wt% of the carrier polymer, preferably between 30 and 50 wt%, and more preferably between 35 and 39 wt%.

Preferably, the carrier polymer is a plastic, such as HDPE (high-density polyethylene), LDPE (low-density polyethylene), PET (polyethylene terephthalate), coloured HDPE, coloured PET, PE (polyethylene), PP (polypropylene), polystyrene, EVA (ethylene-vinyl acetate), ABS (acrylonitrile butadiene styrene), SAN (styrene acrylonitrile resin) or PA (Polyamide).

The pigment dispersant helps the pigment evenly disperse within the carrier polymer. The composition may comprise up to 10 wt% pigment dispersant, and preferably up to 2 wt%. Examples of pigment dispersants may include polyethylene wax, polypropylene wax, ethylene vinyl acetate wax (EVA wax), montan ester wax, calcium stearate, zinc stearate, stearic acid, and ethylene bis-stearamide (EBS).

The carrier medium may further comprise other additives including at least one of antistatic agents, diluents, binders, process antioxidants, long term heat stabilizers, anti-scratch agents, UV absorbers, UV stabilizers, and metal deactivators. The composition may comprise up to 15 wt% of these other additives, preferably up to 10 wt%, more preferably up to 5 wt%, more preferably up to 3 wt%, and most preferably up to 1 wt%.

Examples of antistatic agents may include glycerol monostearate, lauric diethanolamide and ethoxylated fatty acid amines; examples of diluents may include sorbitan esters, polyethoxylated esters, polyisobutylene; examples of binders may include barium sulphate, barytes, calcium carbonate and talc; examples of process antioxidants may include as organic phosphites; examples of long term heat stabilisers may include phenols; examples of anti-scratch agents may include erucamide; examples of UV absorbers may include benzotriazole; examples of UV stabilisers may include sterically hindered amines; and examples of metal deactivators may include ethylenediaminetetraacetic acid (EDTA).

At room temperature and pressure, the composition of the invention may be a solid or a liquid, preferably is a solid, and more preferably a solid in the form of pellets. The composition may be described as a masterbatch. A masterbatch is a concentrated mixture of pigments in a carrier medium. In a solid form, the pigment is often encapsulated during a heat process into a carrier medium which is then cooled and cut into a regular granular shaped pellets.

A masterbatch allows the processor to colour target polymer with high accuracy by dosing small, but measureable quantities of pigment. The pigment and additives are beneficially dispersed in the solid carrier medium, and may be supplied for addition to a target polymer or subsequent colourant composition in the form of pellets. The compact nature of the solid pellets reduces problems with dust contamination, which can be a problem with fine-grained solid additives. Solid masterbatches also have a longer shelf life than liquid masterbatches, which can change concentration over time due to evaporation of solvent and settlement of pigment.

The composition of the invention may be added to a target polymer, or owing to its excellent masking properties may be advantageously added to coloured plastics, which themselves have already been recycled.

The carrier medium is preferably selected to be compatible with the chemical composition of the target polymer. Compatibility with the chemical composition of the target polymer means that the carrier medium and the target polymer will readily mix and bond together, without any adverse reactions.

The composition of the invention may be added to the target polymer in an amount of less than 1 wt% to 8 wt% of the total mixture, or preferably less than 1 wt% to 5 wt%, depending on the target polymer and the required application. For example, some polymers are clear whereas others are opaque, and some polymers have a strong 'off-white' base colour whereas others have minimal tint.

The composition may further comprise tinting pigments and/or dyes, which may not substantially absorb infrared radiation. The composition may comprise between 1 and 15 wt% of the tinting pigments and/or dyes, preferably between 1 and 10 wt%, and more preferably between 1 and 5 wt%. The tinting pigments and/or dyes can beneficially alter the shade of the black colour tone and the aesthetic appearance of the final polymer, without substantially affecting the ability for detection by NIR.

The tinting pigment and/or dyes may be organic or inorganic. Examples of such other colourants (using the Colour Index numbering system) include Pigment Yellow 180 (benzimidazolone) suitable for, for example, polyolefins such as PE and PP, and the dye Solvent Yellow 114 (quinophthalone) suitable for, for example, higher temperature polymers such as PET; Pigment Orange 64 (benzimidazolone) suitable for, for example, PE and PP, and the dye Solvent Orange 60 (perinone) suitable for, for example, higher temperature polymers such as PET; Pigment Red 254 (diketo-pyrrolo-pyrrole) suitable for, for example, PE and PP, and the dye Solvent Red 135 (perinone) suitable for, for example, higher temperature polymers such as PET; Pigment Blue 15.3 (phthalocyanine) suitable for, for example, PE and PP, and the dye Solvent Blue 104 (anthraquinone) suitable for, for example, higher temperature polymers such as PET; and Pigment Green 7 (phthalocyanine) suitable for, for example, PE and PP, and the dye Solvent Green 3 (anthraquinone) suitable for, for example, higher temperature polymers such as PET. Preferably, the tinting pigment and/or dye which may be added to the composition of the present invention is blue, such as Pigment Blue 15.3 (phthalocyanine) and/or the dye Solvent Blue 104 (anthraquinone), which advantageously gives the appearance of a deep jet black colour.

According to a second aspect of the invention there is provided the use of a black pigment comprising mixed iron and manganese oxide as a black colourant in a recyclable polymer product, wherein the black pigment does not substantially absorb infrared radiation.

According to a third aspect of the invention there is provided the use of a composition according to the first aspect of the invention as a black colourant in a recyclable polymer product, wherein the black pigment does not substantially absorb infrared radiation.

According to a fourth aspect of the invention there is provided a recyclable black polymer product comprising a black pigment comprising mixed iron and manganese oxide, wherein the recyclable black polymer product does not substantially absorb infrared radiation.

According to a fifth aspect of the invention there is provided a method for manufacturing a composition according to the first aspect of the invention, wherein the method comprises the step of mixing the black pigment comprising mixed iron and manganese oxide with a carrier medium.

The manufacture of the composition requires the mixing of only one pigment (assuming no tinting pigments or dyes are added) with the carrier medium and so is advantageously a simpler and more cost effective process than mixing two or more pigments, for example, with the carrier medium.

According to a sixth aspect of the invention there is provided a method of darkening the colour of a target polymer, the method comprising the steps of adding the composition according to the first aspect of the invention to a target polymer, and mixing and applying heat to form a mixture, wherein the mixture is black and does not substantially absorb infrared radiation. For example, a high speed mixer may be used to blend the pigment and carrier medium and a twinscrew extruder heats and melts the carrier medium and disperses the pigment evenly throughout the molten matrix. The screws intermesh to provide the shear force required to break up the agglomerates in the pigment and to produce a homogeneous dispersion. The dispersion is passed through an extruder and die, and may be formed into a composite solid (a masterbatch). The solid masterbatch may be formed into continuous strands and cut into regular shaped pellets, which can be accurately added to virgin or waste polymers. These pellets may alternatively be added as part of a colourant mix for forming of another colourant.

The present invention provides a composition for addition to a target polymer, in which the resulting coloured polymer product does not substantially absorb infrared radiation (and in particular near infrared radiation). The resulting black polymer products can therefore be identified and appropriately sorted automatically using NIR sorting technology for recycling, without the need for hand sorting or transfer to landfill. Therefore, after the useful life of the polymer product, recyclability is enabled. Such applications can be anything from convenience food containers to automobile parts.

The present invention will now be described by way of example only.

The compositions of the invention vary depending upon which target polymer they are to be added. For example, a masterbatch for use in PET food trays may comprise approximately 55 wt% of the black pigment of the invention and 5 wt% of the dye Solvent Blue 104 (anthraquinone), so that the composition comprises approximately 60 wt% of colourant and approximately 40 wt% carrier medium. The carrier medium comprises the carrier polymer PET and the pigment dispersant montan ester wax, so that the composition comprises approximately 38 wt% of PET and approximately 2 wt% of montan ester wax. This composition when dispersed in the target polymer PET to make food trays provides a most attractive shade of black, which allows the colours in the food to stand out effectively.

The composition may further comprise process antioxidants such as organic phosphites.

As a further example, a masterbatch for use in polypropylene components for, in particular, the automobile industry may comprise approximately 55 wt% of the black pigment of the invention and 5 wt% of the tinting colourant ultramarine blue, so that the composition comprises approximately 60 wt% of colourant and approximately 40 wt% carrier medium.

The carrier medium comprises the carrier polymer polypropylene and the pigment dispersant polyethylene wax, so that the composition comprises approximately 38 wt% of polypropylene and approximately 2 wt% of polyethylene wax. This composition when dispersed in the target polymer 5 polypropylene to make automobile components provides a deep shade of black.

The composition may further include process antioxidants (such as organic phosphites), long term heat stabilisers (such as phenols), antistatic agents (such as glycerol monostearate), UV absorber/stabilisers (such as benzotriazole or stehcally hindered amines), anti-scratch agents (such as 10 erucamide), pigment dispersants (such as calcium/zinc stearate and/or polyethylene/polypropylene/EVA waxes) and/or binders (such as talc).

The present invention has been described by way of example only and it will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the 15 appended claims.

Claims

WHAT IS CLAIMED IS:

1. A composition for darkening the colour of a target polymer comprising:

a black pigment comprising mixed iron and manganese oxide; and a carrier medium, wherein the composition does not substantially absorb infrared radiation.

2. A composition according to claim 1, wherein the composition comprises between 20 and 75 wt% of the black pigment, and preferably between 55 and 65 wt%.

3. A composition according to claim 1 or 2, wherein the composition comprises between 10 and 80 wt% of the carrier medium, and preferably between 35 and 45 wt%.

4. A composition according to any preceding claim, wherein the carrier medium comprises a carrier polymer and/or a pigment dispersant.

5. A composition according to claim 4, wherein the carrier medium further comprises at least one of an antistatic agent, a diluent, a binder, a process antioxidant, a long term heat stabilizer, an anti-scratch agent, a UV absorber, a UV stabilizer and a metal deactivator.

6. A composition according to any preceding claim, wherein, at room temperature and pressure, the composition is a solid or is a liquid, and preferably is a solid and more preferably is a solid in the form of pellets.

7. A composition according to any preceding claim, wherein the carrier medium is selected to be compatible with the chemical composition of the target polymer.

8. A composition according to any preceding claim, wherein the composition further comprises tinting pigments and/or dyes, which do not substantially absorb infrared radiation.

9. A composition according to claim 8, wherein the composition comprises between 1 and 15 wt% of the tinting pigments and/or dyes.

10. The use of a black pigment comprising mixed iron and manganese oxide as a black colourant in a recyclable polymer product, wherein the black pigment does not substantially absorb infrared radiation.

11. The use of the composition according to any one of claims 1 to 9 as a black colourant in a recyclable polymer product, wherein the black pigment does not substantially absorb infrared radiation.

12. A recyclable black polymer product comprising a black pigment comprising mixed iron and manganese oxide, wherein the recyclable black polymer product does not substantially absorb infrared radiation.

5

13. A method for manufacturing a composition according to any one of claims

1 to 9, wherein the method comprises the step of mixing the black pigment comprising mixed iron and manganese oxide with a carrier medium.

14. A method of darkening the colour of a target polymer, the method

10 comprising the steps of adding the composition according to any one of claims 1 to 9 to a target polymer, and mixing and applying heat to form a mixture, wherein the mixture is black and does not substantially absorb infrared radiation.