WO2024127011A1

WO2024127011A1 - Plastic substrate & method of removing a mark or image therefrom

Info

Publication number: WO2024127011A1
Application number: PCT/GB2023/053224
Authority: WO
Inventors: Richard Cook; Jonathan SNODGRASS; Jason TWEEDIE
Original assignee: Datalase Ltd.
Priority date: 2022-12-15
Filing date: 2023-12-14
Publication date: 2024-06-20

Abstract

The present invention relates to a method of removing a mark or image from a plastic substrate, as well as to plastic substrates and the compositions applied thereto that are suitable for use in such a method.

Description

PLASTIC SUBSTRATE & METHOD OF REMOVING A MARK OR IMAGE THEREFROM

FIELD OF THE INVENTION

The present invention is directed towards a method of removing a mark or image from a plastic substrate, as well as to plastic substrates and the compositions applied directly thereto that are suitable for use in said method.

BACKGROUND

In recent years, the drive to recycle plastic substrates has significantly increased. However, problems with the recycling of plastic substrates having compositions comprising colour-forming compounds displaying a mark or image applied thereto are extensive. In particular, following normal use of the plastic substrate, prior to, or during, recycling processes, it is difficult to separate the colour-forming compounds and other components of the compositions used to display the mark or image from the plastic substrate, resulting in contaminated and/or stained plastic material that cannot be appropriately recycled. The colour-forming compounds and other components of the compositions used to display the mark or image also contaminate waste streams during processing. Both issues result in additional expense and environmental issues.

There is therefore a desire to provide plastic substrates that are able to effectively display a mark or image but can also be recycled without any contamination from the materials used to form the mark or image thereon.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a use of a first composition comprising a protein to remove a mark or image from a plastic substrate, preferably through exposure of the plastic substrate to an aqueous alkaline solution.

According to a second aspect of the present invention, there is provided a use of a first composition for the manufacture of a plastic substrate having applied to at least a portion thereof or incorporated in at least a portion thereof, the first composition and a second composition applied over the first composition, wherein the first composition comprises a protein and the second composition comprises a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and the second composition displays a mark or image formed by application of radiation to localised positions of the second composition using a laser, such that the plastic substrate displays a mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the mark or image can be removed from the plastic substrate to provide plastic material that is not contaminated by the second composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution.

According to a third aspect of the present invention, there is provided a plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colourforming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and capable of forming a mark or image upon application of radiation to localised positions of the second composition using a laser, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent.

According to a fourth aspect of the present invention, there is provided a use of a first and second composition in the removal of a mark or image from a plastic substrate to provide a plastic material that is not contaminated by the second composition, the plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and the second composition displaying a mark or image formed by application of radiation to localised positions of the second composition using a laser, such that the plastic substrate displays the mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid- generating agent, and wherein the removal of the mark or image from the plastic substrate is preferably through exposure of the plastic substrate to an aqueous alkaline solution.

According to a fifth aspect of the present invention, there is provided a method of removing a mark or image from a plastic substrate to provide a plastic material that is not contaminated with a second composition, said plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and the second composition displaying a mark or image formed by application of radiation to localised positions of the second composition using a laser such that the plastic substrate displays the mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the method comprises: exposing the plastic substrate to an aqueous alkaline solution.

According to a sixth aspect of the present invention, there is provided a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12.

According to a seventh aspect of the present invention, there is provided a use of a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12 in a method of removing a mark or image from a plastic substrate to provide plastic material that is not contaminated by the composition, the plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and the composition applied over the first composition, wherein the leuco dye of the composition displays a mark or image, said mark or image having been formed application of radiation to localised positions of the composition using a laser, such that the plastic substrate displays a mark or image, and wherein the mark or image can be removed from the plastic substitute to provide plastic material that is not contaminated by the composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution.

According to a eighth aspect of the present invention, there is provided a use of a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12, for the manufacture of a plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein and the composition applied thereover, wherein the leuco dye displays a mark or image, said mark or image having been formed by application of radiation to localised position of the composition using a laser, such that the plastic substrate displays a mark or image, wherein the mark or image can be removed from the plastic substrate to provide plastic material that is not contaminated by the composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution.

According to a ninth aspect of the present invention, there is provided a plastic substrate having a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12, applied to at least a portion thereof, or incorporated in at least a portion thereof.

According to a tenth aspect of the present invention, there is provided a method of forming or displaying a mark or image on a plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the method comprises applying radiation to localised positions on the second composition using a laser. According to an eleventh aspect of the present invention, there is provided a method of forming or displaying a mark or image on a plastic substrate comprising a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12 applied on at least a portion thereof or in at least a portion thereof, wherein the method comprises applying radiation to localised positions on the composition using a laser.

According to a twelfth aspect of the present invention, there is provided a method of forming a plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and capable of forming a mark or image upon application of radiation to localised positions of the second composition using a laser, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the method comprises applying the first and second composition onto the plastic substrate or a plastic material component thereof, preferably printing the first and second composition onto the plastic substrate, and more preferably by pad printing, screen printing, flexographic printing or gravure printing.

According to a thirteenth aspect of the present invention, there is provided a method of forming a plastic substrate comprising a composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12 applied on at least a portion thereof or incorporated in at least a portion thereof, the method comprising applying the composition onto the plastic substrate or a plastic material component thereof, preferably by printing the composition onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing. DETAILED DESCRIPTION

The present inventors have surprisingly and advantageously identified plastic substrates capable of displaying a mark or image from which the mark or image can be removed, allowing for recycling of the plastic substrate without contamination from any of the materials used to form the mark or image. The present inventors have identified compositions for direct application to plastic substrates that enable the plastic substrates to effectively display a distinct and discernible mark or image under normal conditions of use, but that the mark or image may then be removed therefrom to provide uncontaminated plastic material, as well as uncontaminated waste streams.

With the present invention, the present inventors have found a way in which laser- reactive compositions can be applied to or incorporated within plastic substrates and then radiation from a laser source(s) utilised to cause the compositions to display a mark or image and form plastic substrates displaying a distinct and discernible mark or image thereon. These marks or images can then be subsequently removed from the plastic substrates through removal of the compositions to provide uncontaminated plastic material and waste streams and allow for effective recycling of the plastic material. This methodology is suitable for all plastic substrates, including multi-layer plastic constructions (‘laminate constructions’), especially those having layers formed of differing plastic materials that need to be separated and each undergo a different recycling process. The present invention not only enables these multi-layer plastic constructions to display a distinct and discernible mark or image, but advantageously enables the mark or image to be subsequently removed and for effective recycling of the different plastic materials from which the multi-layer plastic construction was formed. There is currently no established procedure that overcomes these issues for multi-layer plastic construction recycling.

Accordingly, the present invention enables the production of plastic substrates that are not only able to effectively display a mark or image but can also have the mark or image removed therefrom to provide plastic material and waste streams that are uncontaminated by any of the materials used to form the mark or image to allow recycling of the plastic material.

By ‘uncontaminated’ or ‘not contaminated’, and like terms as used herein in relation to the plastic substrate or plastic material, is meant the plastic substrate or plastic material comprises no second composition or composition comprising a colour-forming compound, and thus no mark or image. This is a result of the second composition or composition comprising a colour-forming compound being separated from the plastic substrate or plastic material. No second composition or composition comprising a colour-forming compound is retained on the plastic substrate or plastic material. This separation of the second composition or composition comprising a colour-forming compound occurs through use of the first composition as described herein, and preferably through exposure of the plastic substrate to an aqueous alkaline solution as described herein. By ‘removed’, ‘remove’, or ‘removal’, and like terms used herein with reference to the mark or image, is meant that the plastic substrate or plastic material no longer displays said mark or image. The mark or image is separated from the plastic substrate or plastic material. This is a result of the second composition or composition comprising a colour-forming compound being separated from the plastic substrate or plastic material. The plastic substrate or plastic material is not contaminated by the second composition or composition comprising a colour-forming compound, and thus does not display a mark or image. The mark or image can no longer be visually detected on the plastic substrate or plastic material by the human eye.

The removal of the mark or image may be assessed by a AE measurement between an uncoated (and thus unimaged) plastic substrate or plastic material (control), and the plastic substrate or plastic material following exposure to aqueous alkaline solution in the process of the present invention, e.g. a plastic substrate or plastic material to which the first composition, and second composition or composition comprising a colour-forming compound, have been applied, a mark or image formed according to the invention, and the mark or image then removed from the plastic substrate in accordance with the process described herein, preferably through exposure of the plastic substate to an aqueous alkaline solution as described herein. Suitable AE measurements may be less than 5, such as less than 3.5, such as less than 3, or less than 2. Such a AE measurement provides a good indication that there is no visual perception of a difference between the control and the plastic substrate or plastic material resulting from exposure to aqueous alkaline solution in the process of the present invention. This demonstrates how the plastic substrate or plastic material resulting from exposure to aqueous alkaline solution in the process of the present invention does not display the mark or image, i.e. the mark or image has been removed. The second composition or composition comprising a colour-forming compound has been separated from the plastic substrate or plastic material. AE may be measured using the standard mathematical calculation detailed herein, on an X- rite eXact spectrophotometer. AE measurements may be made on a white background.

For the use according to the first aspect of the present invention, the removal of the mark or image provides a plastic substrate on which said mark or image is no longer displayed.

For the use according to the first aspect of the present invention, the plastic substrate may be as defined herein in relation to the third aspect of the present invention, wherein the plastic substrate displays a mark or image, said mark or image being formed by the application of radiation to localised positions of the second composition using a laser.

The aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may be an aqueous solution of 0.1 to 5 wt.%, such as 0.5 to 3 wt.%, preferably 1 to 3 wt.%, of a base, preferably an alkali or earth alkali hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide, preferably sodium hydroxide.

The aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may further comprise a surfactant, such as a non-ionic surfactant. The surfactant may provide detergent properties. The surfactant may be present in the aqueous alkaline solution in an amount of from 0.1 to 4 wt.%, preferably 0.1 to 1 wt.%, such as 0.1 to 0.6 wt.%.

The aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may have a pH of from 7 to 15, such as from 9 to 14, or from 12 to 14.

The exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may be carried out at a temperature of from 50 to 95 °C, such as from 60 to 95 °C, or from 80 to 95 °C, such as from 80 to 90 °C. The aqueous alkaline solution is at a temperature of from 50 to 95 °C, such as from 60 to 95 °C, or from 80 to 95 °C, such as from 80 to 90 °C.

Preferably, the exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention is carried out in an aqueous solution of sodium hydroxide, and more preferably an aqueous solution of 0.1 to 5 wt.%, preferably 0.5 to 3 wt.%, more preferably 1 to 3 wt.% sodium hydroxide, preferably at a temperature of from 50 to 95 °C, such as from 60 to 95 °C, or from 80 to 95 °C, such as from 80 to 90 °C.

The exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may be known as a ‘hot caustic wash’ or washing in a ‘hot caustic solution’.

It will be appreciated that the exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention may be through immersion or washing in the aqueous alkaline solution.

During the exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention, the second composition or composition comprising the leuco dye is separated from the plastic substrate, and the mark or image thus removed therefrom, by at least partial solubilisation of the first composition. The first composition at least partially solubilises in the aqueous alkaline solution and separates from the plastic substrate (and the second composition or composition comprising the leuco dye). The first composition will be washed away in the wash stream. It will therefore be appreciated that, as well as the second composition or composition comprising the leuco dye, the first composition is also separated from the plastic substrate. The second composition or composition comprising the leuco dye remains as a solid or precipitate following exposure to the aqueous alkaline solution. The second composition or composition comprising the leuco dye will therefore be separated from the plastic substrate. It will typically float to the surface of the aqueous alkaline solution. The second composition or composition comprising the leuco dye may be removed by filtration.

It will be appreciated that the plastic substrate may be exposed to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention for the time taken for the first composition to at least partially solubilise in the aqueous alkaline solution, and the second composition or composition comprising the leuco dye to thus be separated, from the plastic substrate. The exposure to the aqueous alkaline solution may take from 1 to 45 minutes, such as from 1 to 30 minutes, or from 1 to 20 minutes, such as from 1 to 15 minutes, preferably from 1 to 5 minutes.

It will be appreciated that the plastic substrate may be exposed to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention to separate the second composition or composition comprising the leuco dye prior to reducing the plastic substrate to granules or flakes, as part of a recycling process. Alternatively, and preferably, the plastic substrate may be first reduced to granules or flakes thereof, for example by crushing, grinding or other suitable methods known in the art, and the granules or flakes of the plastic substrate then exposed to the aqueous alkaline solution to separate the second composition or composition comprising the leuco dye therefrom. Accordingly, in the context of exposure to the aqueous alkaline solution utilised in the first, second, fourth, fifth, seventh and eighth aspects of the present invention, reference to the plastic substrate may refer to either the plastic substrate as a whole (or at least the portion thereof to which the first, and/or second compositions or composition comprising the leuco dye are applied), or granules or flakes of the plastic substrate. Similarly, the plastic material resulting from exposure to the aqueous alkaline solution as described herein may be a plastic substrate as a whole from which the mark or image has been removed, or granules or flakes of a plastic substrate from which the mark or image has been removed.

It will be appreciated that where the plastic substrate is a multi-layer plastic construction, and different plastic materials are utilised in the differing layers thereof, the different plastic materials will typically be separated prior to recycling. Different plastic materials typically required different recycling processes. This separation preferably uses the aqueous alkaline solution described herein. The separation may be facilitated, for example, by making use of the differing physical properties of the materials, such as density difference between materials, for example between polyolefin and polyester materials.

To demonstrate that uncontaminated plastic material is produced, various industry standards may be utilised, for example, EPBP (European PET Bottle Platform) Quick Test QT 507 (March 2017) or Natural HDPE Flake Washing Test (HDPE-S- 01), the Association of Plastic Recyclers, 23 August 2021 , may be utilised. Different tests may be used depending on the types of plastic utilised for the plastic material, the construction of the plastic substrate, e.g. a multi-layer plastic construction (laminate construction), as well as the standards or requirements for recycling processes in different territories. This will be well known to a skilled person.

An appropriate test to demonstrate that uncontaminated plastic material is produced may be summarised as comprising the following steps. It will be appreciated that the steps or conditions may alter depending on, for example, the types of plastic utilised for the plastic material, the construction of the plastic substrate, e.g. a multi-layer plastic construction (laminate construction), as well as the standards or requirements for recycling processes in different territories: 1. Obtain plastic substrate having the desired composition(s) applied thereon or incorporated therein and displaying a mark or image in 1 cm² flakes.

2. Place flakes in an aqueous solution of 2 wt.% sodium hydroxide at 80 °C, 500 rpm for 15 minutes. Reserve supernatant.

3. Repeat another 2 times. Rinse flakes to remove aqueous solution.

4. Dry flakes in oven at 105 °C.

5. Evaluate colour measurements (L*, a* and b* values) of the flakes, and optionally the supernatant, compared to sample flakes not coated with the composition(s) (control). Obtain a AE measurement between the control and the flakes.

An appropriate test to demonstrate that uncontaminated plastic material is produced, when the plastic substrate is formed of PET, may be the EPBP (European PET Bottle Platform) Quick Test QT 507 (March 2017). The EPBP test may be summarised as comprising the following steps:

1. Obtain plastic substrate (PET) having the desired composition(s) applied thereon or incorporated therein and displaying a mark or image in 1 cm² flakes.

3. Repeat another 2 times. Rinse flakes to remove aqueous solution.

4. Dry flakes in oven at 105 °C.

5. Evaluate colour measurements (L*, a* and b* values) of the PET flakes, and optionally the supernatant, compared to PET sample flakes not coated with the composition(s) (control). Obtain a AE measurement between the control and the flakes. An appropriate test to demonstrate that uncontaminated plastic material is produced, when the plastic substrate is formed of HDPE, may be the Natural HDPE Flake Washing Test (HDPE-S-01), the Association of Plastic Recyclers, 23 August 2021. This HDPE-S-01 test may be summarised as comprising the following steps:

1. Obtain plastic substrate (HDPE) having the desired composition(s) applied thereon or incorporated therein and displaying a mark or image in 1 cm² flakes.

3. Repeat another 2 times. Rinse flakes to remove aqueous solution.

4. Dry flakes in oven at 105 °C.

5. Evaluate colour measurements (L*, a* and b* values) of the HDPE flakes, and optionally the supernatant, compared to HDPE sample flakes not coated with the composition(s) (control). Obtain a AE measurement between the control and the flakes.

Where the plastic substrate is a multi-layer plastic construction, it will be appreciated that where two different plastic materials may be utilised, these plastic materials are typically separated prior to drying and evaluation of the colour measurements (steps 4. and 5. as detailed above). This may be, for example, by making use of the differing physical properties of the materials, such as density difference between materials, for example polyolefin and polyester materials.

For all of the tests, whether general or specific, detailed above, a AE measurement can be used to assess the visual difference between a control (not coated with the composition(s) and thus, with no mark or image formed herein) and the plastic substrate or plastic material following exposure to aqueous alkaline solution in the process of the present invention (having had the mark or image removed therefrom). AE may be measured using the standard mathematical calculation detailed herein, on an X-rite eXact spectrophotometer. AE measurements may be made on a white background. AE allows for the quantification of the visual perception of the difference between two colours. The AE measurement may be less than 5, such as less than 3.5, such as less than 3, or less than 2. Such a AE measurement provides a good indication that there is no visual perception of a difference between the control and the plastic substrate or plastic material resulting from exposure to aqueous alkaline solution in the process of the present invention.

The first composition advantageously enables the second composition utilised in any of the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in any of the sixth, seventh, eighth, ninth, eleventh and thirteenth aspects of the present invention to be separated from the plastic substrate such that any mark or image displayed by the second composition or composition comprising the leuco dye is removed from the plastic substrate.

For the second to fifth, tenth and twelfth aspects of the present invention, the colour-forming compound may be selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof, or a leuco dye.

When the colour-forming compound is an oxyanion of a multivalent metal or hydrate of an oxyanion of a multivalent meta, it is preferably an ammonium salt of an oxyanion of a multivalent metal, and more preferably an ammonium salt of an oxyanion of molybdenum. Most preferably, the oxyanion of a multivalent metal or oxyacid or hydrate thereof is ammonium octamolybdate (AOM).

For the second to fifth, tenth and twelfth aspects of the present invention, the colour-forming compound is preferably a leuco dye. Leuco dyes can facilitate the display of coloured marks or images, specifically coloured marks or images displaying a colour other than black. Accordingly, the use of a leuco dye as the colour-forming compound advantageously enables the formation of a mark or image other than black to be achieved on, and then subsequently effectively removed from, the plastic substrates having marks or images formed thereon by laser-reactive compositions. The leuco dye may be selected from spiroxazines, naphthopyrans, phthalides, fluorans, triarylmethanes, benzoxazines, quinazolines, spiropyrans, quinones, tetrazolium salts, thiazines, phenazines and oxazines, some of which are disclosed in WO 2006/108745, the content of which is incorporated herein by reference. Examples of suitable leuco dyes are also contained in WO 2015/015200 and WO 2013/068729, the content of each being incorporated herein by reference.

For the second to thirteenth aspects of the present invention, the leuco dye may be selected from 2’-Anilino-6’-(dibutylamino)-3’-methyl-3H-spiro[2-benzofuran- 1 ,9’-xanthen]-3-one (CAS No. 89331-94-2), 6’-(Diethylamino)-3’-methyl-2’- (phenylamino)spiro[2-benzofuran-3,9’-xanthene]-1-one (CAS No. 29512-49-0), 2- Anilino-6’-[ethyl(p-toyl)amino]-3’-methylspiro[isobenzofuran-1 (3H),9’-

[9H]xanthene]-3-one (CAS No. 59129-79-2), Blue3-CVL 6-(dimethylamino)-3,3- bis-[4-(dimethylamino) phenyl) phthalide (CAS No 1522-42-7), Blue-4 4,4'-[(9- butyl-9H-carbazol-3-yl)methylene]bis[N-methyl-N-phenylaniline] (CAS No 67707- 04-4), Red-5 3,3'-Bis(1-n-octyl-2-methylindol-3-yl)phthalide (CAS No 50292-95- 0), Orange-6 6'-(Diethylamino)-3-oxo-spiro [isobenzofuran-1(3H),9'-[9H] xanthene]-2'-carboxylic acid ethyl ester (CAS No 154306-60-2), Blue-8 7-[4- (diethylamino)-2-ethoxyphenyl]-7-(2-methyl-1 -octyl-1 H-indol-3-y I) Furo[3,4- b]pyridin-5(7H)-one (CAS No 87563-89-1), Green-9 2’-(Dibenzylamino)-6'- (diethylamino)fluoran (CAS No 34372-72-0), Yellow-10 N,N-dimethyl-4-[2-[2- (octyloxy)phenyl]-6-phenyl-4-pyridinyl]- Benzenamine (CAS No 144190-25-0), Black-15 6'-(diethylamino)-2'-[(dimethylphenyl) amino]-3'-methylspiro [isobenzofuran-1(3H),9'-[9H]xanthene]-3-one (CAS No 36431-22-8), KetoAcid-1 4-(N,N-diethylamino)-2-hydroxy-2'-carboxybenzophenone (CAS No 5809-23-4), KetoAcid-2 4-(N,N-dibutylamino)-2-hydroxy-2'-carboxybenzophenone (CAS No 54574-82-2).

Suitable suppliers of leuco dyes include, but are not limited to: Yamada Chemical Company Limited, Chameleon Speciality Chemicals Limited, and Connect Chemicals. The leuco dye may be present in the second composition utilised in the second, third, fourth, fifth, tenth or twelfth aspects of the present invention, or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention in any suitable amount. Preferably, the leuco dye is present in the second composition or the composition comprising the leuco dye in an amount of from 4 to 30 wt.% of the second composition or composition, such as from 5 to 30 wt.%, or from 5 to 20 wt.%, or from 6 to 20 wt.% of the second composition or composition comprising the leuco dye.

For the second to fifth, tenth and twelfth aspects of the present invention, the thermal acid-generating agent may be selected from suitable thermal acidgenerating agents including, but are not limited to the following: 4-Hydroxyphenyl- 4'-isopropoxyphenyl sulfone (Chameleon Developer-1); N-(p-toluenesulfonyl)-N'- (3-(p-toluenesulfonyloxy)phenyl)urea (Pergafast 201); 1 , 1 , 1 -Tris(4-

Hydroxyphenyl)Ethane (THPE) and amine salts of an organic metal compound.

Preferably, for the second to fifth, tenth and twelfth aspects of the present invention, the thermal acid-generating agent is an amine salt of an organic metal compound.

For the second to thirteenth aspects of the present invention, the amine salt of an organic metal compound may be of the formula (I):

in which X is silicon or boron, and E and F are the same or different and are selected from the group consisting of:

in which R⁶ and R⁷ are the same or different, and are hydrogen, Ci-4-alkyl, Cialkoxy, halogen, amino or carboxy, and for X = silicon, o = 1 and p = 0, and R¹ is aryl, aralkyl or Ci -4-alky I , or o = 1 and p = 1 , and R¹ and R² together form a one residue selected from the group consisting of:

and for X = boron, o = 0 and p = 0, and

R³, R⁴ and R⁵ are the same or different and are hydrogen, Ci-12-alkyl, C1-6- hydroxyalkyl, allyl, aralkyl or arylsulfonyl, in which aralkyl or arylsulfonyl can be substituted with Ci-4-alkyl, or R³ and R⁴ together with the nitrogen to which they are attached form a morpholino or piperidino ring.

Examples for Ci-4-alkyl are methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl and tert-butyl. Examples for Ci-₄-alkoxy are methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butyoxy, isobutoxy and tert-butoxy. Examples of halogen are chlorine, bromine, fluorine and iodine. Examples of aryl are phenyl, 1 -naphthyl, 2-naphthyl and pyridyl. Examples of aralkyl are benzyl and 2-phenylethyl. Examples of Ci-12-alkyl are methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl and tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl and dodecyl. Examples of Ci-6-hydroxyalkyl are hydroxymethyl, 2- hydroxyethyl, 2-hydroxypropyl, 3-hydroxy propyl, 4-hydroxybutyl, 5-hydroxypentyl and 6-hydroxy hexyl. Examples of arylsulfonyl are phenylsulfonyl and tosyl.

When X is silicon, preferably E and F are the same or different and are selected from a, b, c, d and e, in which R⁶ and R⁷ are the same or different, and are hydrogen, Ci-4-alkyl, Ci-4-alkoxy, halogen, amino or carboxy, and o = 1 and p = 0, and R¹ is aryl, aralkyl or Ci-4-alkyl, or o = and p = 1 , and R¹ and R² together form one residue selected from a¹, b¹, c¹, d¹, and e¹, and

R³, R⁴ and R⁵ are the same or different and are hydrogen, CI-12-alkyl, C1-6- hydroxyalkyl, allyl, aralkyl or arylsulfonyl, in which aralkyl or arylsulfonyl can be substituted with Ci-4-alkyl, or R³ and R⁴ together with the nitrogen to which they are attached form a morpholino or piperidino ring, and optionally when E and F are both residue a, o =1 and p = 1 , and R¹ and R² together form residue a¹, then R³, R⁴ and R⁵ are not all ethyl.

When X is silicon, more preferably, E and F are the same of different and are selected from a, b, c, d and e, in which R⁶ and R⁷ are the same or different and are hydrogen or Ci-₄-alkyl, o = 1 and p = 0, and R¹ is aryl, o = 1 and p = 1 , and R¹ and R² together form a one residue selected from a¹, b¹, c¹, d¹, and e¹, and R³, R⁴ and R⁵ are the same or different and are hydrogen, Ci- -alkyl, C1-6- hydroxyalkyl, allyl, or arylsulfonyl, in which arylsulfonyl can be substituted with Ci- 4-alkyl, or R³ and R⁴ can together with the nitrogen to which they are attached form a morpholino or piperidino ring.

Examples of Ci- -alkyl are methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl and tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl and decyl.

When X is silicon, more preferably, E and F are the same and are selected from a, b, c, in which R⁶ and R⁷ are hydrogen, o = 1 and p = O, and R¹ is phenyl, o = 1 and p = 1 , and R¹ and R² together form a one residue selected from a¹ b¹, and c¹, and R³, R⁴ and R⁵ are the same or different and are hydrogen, Ci-s-alkyl or allyl, or R³ and R⁴ together with the nitrogen to which they are attached form a morpholino ring. Examples of Ci-s-alkyl are methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl and tert-butyl, pentyl, hexyl, heptyl, octyl and 2-ethylhexyl.

When X is silicon, the amine salts of the organic metal compound of formula (I) may be selected from the group consisting of:

When X is boron, and E and F are the same or different and are selected from a, b, f, g, and h, in which R⁶ and R⁷ are the same or different, and are hydrogen, Ci- 4-alkyl, Ci-4-alkoxy, halogen, amino or carboxy, and o = 0 and p = 0, and R³, R⁴ and R⁵ are the same or different and are hydrogen, Ci-12-alkyl, C1-6- hydroxyalkyl, allyl, aralkyl or arylsulfonyl, in which aralkyl or arylsulfonyl can be substituted with Ci-₄-alkyl, or R³ and R⁴ together with the nitrogen to which they are attached form a morpholino or piperidi no ring, and optionally, when E and F are both residue a, and o = 0 and p = 0, then R³, R⁴ and R⁵ are not all butyl.

When X is boron, preferably E and F are the same or different and are selected from a, b, and f, in which R⁶ and R⁷ are hydrogen, and o = 0 and p = 0, and

R³, R⁴, and R⁵ are the same or different and are hydrogen, C1 -Salkyl or allyl. When X is boron, the amine salts of the organic metal compound of formula (I) is selected from the group consisting of:

For the second to thirteenth aspects of the present invention, the thermal acidgenerating agents may be an amine salt of borobenzylate and tri-n- butylammonium borodisalicylate such as tri-n-butylammonium-4,4’-dioxo-4H,4’H- 2,2’-spirobi[benzo[d][1 ,3,2]dioxaborinin]-2-uide, N,N-dibutylbutan-1-aminium bis [2-(hydroxy-kO)benzoato(2-)-kO] borate(l-) or hydrogen bis [2-(hydroxyl-kappa O) benzoate (2-)-kappa O]-(T-4)-borate(1-) compound with N, N-dibutyl-1 - butanamine (1 :1 :1).

Preferably, for the second to thirteenth aspects of the present invention, the thermal acid-generating agent is hydrogen bis [2-(hydroxyl-kappa O) benzoate (2- )-kappa O]-(T-4)-borate(1-) compound with N,N-dibutyl-1-butanamine (1 :1 :1).

This may be known as SABoTBA. This compound has CAS number 22450-96-0.

The thermal acid-generating agent acts as a colour developer. Upon application of radiation using a laser to the composition containing such, it generates an acid that reacts with the leuco dye to form colour such that a mark or image can be displayed thereby.

For the second to thirteenth aspects of the present invention, the thermal acidgenerating agent may be present in the second composition or composition comprising the leuco dye detailed therein in any suitable amount. Preferably, the thermal acid-generating agent may be present in the second composition or composition comprising the leuco dye in an amount of from 5 to 40 wt.%, such as from 7 to 30 wt.%, or from 10 to 30 wt.%, and preferably from 15 to 25 w.%.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may be a water-based composition, and further comprise water. In the context of the present invention, a water-based composition comprises less than 5 wt% of an organic solvent, such as less than 3 wt%. Preferably, no organic solvent is utilised as a component in the formulation process of a water-based composition. When the second composition or composition comprising the leuco dye further comprises water, water may be present in the second composition or composition comprising the leuco dye in an amount of from 15 to 65 wt.%, such as from 20 to 55 wt.%.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising a leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may be an organic solvent-based composition, and further comprise an organic solvent. More than one organic solvent may be utilised. It will be appreciated that for such a composition, no water is utilised as a component in the formulation of the composition. Suitable organic solvents may be selected from alcohols and acetates including, but not limited to: ethanol, benzyl alcohol, butanol, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, 2-butoxyethanol acetate, 2-butoxyethyl acetate, 1-methoxy-1- methylethyl acetate, cyclohexanone, solvent naptha petroleum, xylene, 2-ethoxy-

1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate, 2- butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-ne, ammonium salt of carbonic acid esters, and combinations thereof, preferably alcohols and acetates including, but not limited to: ethanol, benzyl alcohol, butanol, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, 2-butoxyethanol acetate, 2- ethoxy-1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate,

2-butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, ammonium salt of carbonic acid esters, and combinations thereof, more preferably, alcohols and acetates selected from 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2- methoxy-1 -methylethyl acetate, 2-butoxyethyl acetate, 4-hydroxy-4- methylpentan-2-ne, or ammonium salt of carbonic acid esters, or combinations thereof, and more preferably, the combination of 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate, 2-butoxyethyl acetate, 4- hydroxy-4-methylpentan-2-one, and ammonium salt of carbonic acid esters. The organic solvents may be polar or non-polar. When the second composition or composition comprising a leuco dye is an organic solvent-based composition and further comprises organic solvent(s), the organic solvent(s) may be present in the second composition or composition comprising a leuco dye in an amount of from 20 to 75 wt.%.

When the second composition or composition comprising a leuco dye further comprises an organic solvent(s), the organic solvent(s) may be introduced into the second composition or composition comprising a leuco dye using commercially available formulations such as, but not limited to: those available under the tradename Tampoprint®, for example Tampoprint® ACP (Tampoprint® Transparent Lacquer ACP), Tampoprint® K-VDS Thinner, and Tampoprint® K- VDL Thinner, commercially available from TAMPOPRINT Gmbh and TAMPOTECH Ltd; those available under the tradename Tampa®, for example Tampa® Pol TPY, Tampa® Plus TPL, and Tampa® Star TPR, commercially available from Marabu-lnks; those available under the tradename Mara®, for example Mara® Prop PP, commercially available from Marabu-lnks; T120 commercially available from RUCOINX; Series 786 commercially available from Printcolor; and TPC 630 commercially available from Teca-Print.

It will be appreciated by a skilled person that upon application of the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, to the plastic substrate, some or all of the water or organic solvent may be lost by virtue of the application methods detailed herein such that no, or only residual, or low levels of water or organic solvent is left.

Alternatively, the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may not further comprise water or an organic solvent, i.e. may not be water-based nor organic solvent-based composition. The second composition or composition comprising the leuco dye may instead be curable with ultraviolet radiation.

Preferably, the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention is an organic solvent-based composition when the colour-forming compound is a leuco dye.

The composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention contains an organic solvent and is an organic solvent-based composition.

It is surprising and advantageous that a leuco dye can be utilised as the colourforming compound when formulated in organic solvent, i.e. in an organic solventbased composition.

The formation of colour by a leuco dye is facilitated through its interaction with the thermal acid-generating agent, the ‘colour developer’. In laser-reactive compositions, upon application of radiation using a laser, the thermal acidgenerating agent generates acidic conditions so that the two components interact and the leuco dye displays a colour. However, problems exist when such components are utilised in organic solvent-based compositions. In organic solvent-based laser-reactive compositions comprising a leuco dye and thermal acid-generating agent, the leuco dye and thermal acid-generating agent may interact prematurely on account of the organic solvent, and prematurely form colour during standard formulation of the composition (during stirring, mixing, blending, processing and storage thereof) prior to application to a substrate. A distinct and discernible mark or image cannot therefore be formed as significant background coloration has occurred. To avoid such negative interactions, previously utilised organic solvent-based compositions have needed to use low amounts of the leuco dye and thermal acid-generating agent (solid components) and high quantities of organic solvent to ensure the leuco dye and thermal acidgenerating agent are solubilised in the organic solvent. However, such compositions are then unsuitable for commercial purposes, requiring extremely high and unrealistic wet coat weights in order to generate a distinct and discernible mark or image suitable for purpose. Known organic solvent-based compositions are therefore not commercially viable for processes to effect a mark or image on a substrate in the formation of variable information on substrates. Furthermore, given the low amount of the solid components of leuco dye and thermal acidgenerating agent present, any mark or image formed by these known compositions fades over time.

However, the present inventors have been able to provide a composition comprising a leuco dye and thermal acid-generating agent in organic solvent that does not prematurely react during formulation of the composition, and a distinct and discernible mark or image can be formed only when desired when the composition has been applied to or incorporated within the plastic substrate. This advantageously enables organic solvent-based compositions comprising leuco dyes to be applied to or incorporated within plastic substrates and used to form marks or images thereon, as well as being compatible with the recycling process discussed herein. It is desirable to use a leuco dye as a colour-forming compound when applying compositions according to the present invention to plastic substrates. This is particularly advantageous as leuco dyes are able to form colours other than black, such that the present invention provides a novel way of achieving plastic substrates displaying colour other than black, the plastic substrates then also being able to be recycled to provide uncontaminated plastic material and waste streams as discussed above. Furthermore, it is typically desirable to use an organic-solvent based composition comprising a leuco dye versus a water-based composition comprising a leuco dye as the compositions provide a higher quality and smoother composition (visual assessment) on the plastic substrate following application due to their lower surface tension, are more robust (improved environmental resistance such as abrasion resistance and chemical resistance) and have a faster drying time following application to the plastic substrate.

Furthermore, the present inventors have advantageously found that by enabling leuco dyes to be introduced to onto plastic substrates, upon exposure of the mark or image formed by the leuco dye to aqueous alkaline solution during removal of the mark or image from the plastic substrate, the alkaline conditions of the aqueous alkaline solution cause the leuco dye to revert to back to its colourless form pre-interaction with the thermal acid-generating agent. This is very advantageous in the method of removing the mark or image from the plastic substrate as discussed herein, as the colour of the mark or image is lost and any staining of plastic material avoided.

The advantageous use of a leuco dye and thermal acid-generating agent in an organic solvent-based composition may be achieved through the selection of the thermal acid-generating agent to be a thermal acid-generating agent selected from an amine salt of an organic metal compound, and the presence of an alkaline stabiliser having a pKa of from 2 to 12 in the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention. Without being bound by theory, the present inventors consider that this selection of the alkaline stabiliser and thermal acid-generating agent prevent any acetate, alcohol or acidic groups that may be found in the organic solvents from initiating a reaction with the leuco dye that would cause premature colour formation.

The presence of an alkaline stabiliser having a pKa of from 2 to 12 in the second composition or composition comprising a leuco dye allows the leuco dye and thermal acid-generating agent (solid components) to be dispersed rather than solubilised in the organic solvent. Accordingly, higher concentrations of these two components (leuco dye and thermal acid-generating agent) can be utilised such that lower wet coat weights are required to achieve a distinct and discernible mark or image. Such production processes are commercially viable, and the increased concentration of the components means that the mark or image stability can be retained over time.

The second composition or composition comprising a leuco dye thus comprises a greater amount of leuco dye and thermal acid-generating agent (solid components) than previously known, unfavourable, organic-based solvent composition comprising leuco dyes and thermal acid-generating agents.

Preferably, in the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, the composition comprises 9 to 70 wt% of the leuco dye and thermal acid-generating agent, such as 12 to 60 wt%, or from 15 to 50 wt%, or from 21 to 45 wt%. The leuco dye and thermal acid-generating agent are solid components, i.e. in solid form.

Preferably, in the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, the composition comprises 25 to 70 wt% of components in solid form, such as 30 to 70 wt%, such as 35 to 70 wt%, or 40 to 65 wt%, or 45 to 60 wt% of components in solid form. The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention can be said to have a solids content of from 25 to 70 wt%, such as 30 to 70 wt%, such as 35 to 70 wt%, or 40 to 65 wt%, or 45 to 60 wt%.

Accordingly, preferably, the second composition, utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention of the present invention, comprises a leuco dye, thermal acid-generating selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12. Such a second composition advantageously enables the use of organic solvent-based compositions comprising leuco dyes in the present invention as discussed above.

It will be appreciated that for the use according to the seventh aspect of the present invention, the plastic substrate may be as defined herein in relation to the third aspect of the present invention (the composition comprising a leuco dye and second composition being used interchangeably), wherein the plastic substrate displays a mark or image, said mark or image being formed by the application of radiation to localised positions of the second composition or composition comprising the leuco dye using a laser.

Preferably, for the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, the alkaline stabiliser has a pKa of from 4 to 11 , such as from 6 to 11 , for example 6 to 10.5.

The pKa value is the negative base-10 logarithm of the acid dissociation constant (K_a) of an aqueous solution. The pKa value may be defined by:

where K_a is the acid dissociation constant, [A-] is the conjugate base, [H⁺] is the protons, and [HA] is the acid. For the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, the alkaline stabiliser having a pKa of from 2 to 12 may be selected from, but not limited to the following: sodium carbonate, sodium bicarbonate, potassium carbonate, mono ethanolamine, and triethanolamine, or combinations thereof. Preferably, the alkaline stabiliser having a pKa of from 2 to 12 is selected to be sodium bicarbonate.

The alkaline stabiliser having a pKa of from 2 to 12 may be present in the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention in any suitable amount. Preferably, the alkaline stabiliser having a pKa of from 2 to 12 may be present in the second composition or composition comprising the leuco dye in an amount of from 0.1 to 6 wt.%, such as from 0.5 to 3 wt.%.

When present in organic solution, the alkaline stabiliser having a pKa of from 2 to 12, the leuco dye and the thermal acid-generating agent utilised in the second composition of the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, prior to application on the plastic substrate and the application of radiation thereto, are dispersed in the organic solution. They are not dissolved. This prevents premature colour formation.

The advantageous use of a leuco dye and thermal acid-generating agent in an organic solvent-based composition, such as the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, may further be achieved through the selection of the organic solvent used. The organic solvent(s) selected also allows the leuco dye and thermal acid-generating agent (solid components) to be dispersed rather than solubilised in the organic solvent. Suitable organic solvents may be selected from alcohols and acetates including, but not limited to: ethanol, benzyl alcohol, butanol, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, 2-butoxyethanol acetate, 2-butoxyethyl acetate, 1-methoxy-1- methylethyl acetate, cyclohexanone, solvent naptha petroleum, xylene, 2-ethoxy- 1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate, 2- butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, ammonium salt of carbonic acid esters, and combinations thereof, preferably alcohols and acetates including, but not limited to: ethanol, benzyl alcohol, butanol, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, 2-butoxyethanol acetate, 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1- methylethyl acetate, 2-butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, ammonium salt of carbonic acid esters, and combinations thereof, more preferably, alcohols and acetates selected from 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate, 2-butoxyethyl acetate, 4- hydroxy-4-methylpentan-2-ne, or ammonium salt of carbonic acid esters, or combinations thereof, and more preferably, the combination of 2-ethoxy-1- methylethyl acetate, n-butyl acetate, 2-methoxy-1 -methylethyl acetate, 2- butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, and ammonium salt of carbonic acid esters. The organic solvents may be polar or non-polar. When the second composition or composition comprising a leuco dye is an organic solventbased composition and further comprises organic solvent(s), the organic solvent(s) may be present in the second composition or composition comprising a leuco dye in an amount of from 20 to 75 wt.%.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may further comprise a binder. Suitable binders include but are not limited to styrene acrylics, polyvinyl butyral, nitrocellulose, polyurethane, acrylics, polyvinylchloride, polyvinyl acetate, polyamides, alkyd, cellulose acetate butyrates, polyesters, melamine- based resins, and epoxy-based resins, or combinations thereof. Preferably the binder is a polyester. The binder may be present in the second composition or the composition in an amount of from 5 to 55 wt.%, such as from 10 to 50 wt.%.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention is insoluble in water. The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention is insoluble in the aqueous alkaline solution. It therefore does not dissolve in the aqueous alkaline solution utilised in the removal of the mark or image. It can therefore be removed therefrom in order to prevent contamination of the resulting plastic material orwaste streams. When the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention further comprises a binder, the binder is insoluble in water.

When the second composition or composition comprising the leuco dye further comprises a binder, the binder may be introduced into the second composition or composition comprising the leuco dye through the use of commercially available formulations such as, but not limited to, those available under the tradename Tampoprint®, for example Tampoprint® ACP (Tampoprint® Transparent Lacquer ACP), commercially available from TAMPOPRINT Germany; those available under the tradename Tampa®, for example Tampa® Pol TPY, Tampa® Plus TPL, and Tampa® StarTPR, commercially available from Marabu-lnks; those available under the tradename Mara®, for example Mara® Prop PP, commercially available from Marabu-lnks; T120 commercially available from RUCOINX; Series 786 commercially available from Printcolor; and TPC 630 commercially available from Teca-Print.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may further comprise a near-infrared absorbing compound capable of enhancing absorption of near-infrared or infrared radiation. Suitable near-infrared absorbing compounds include but are not limited to the following: inorganic copper salts such as copper (II) hydroxyl phosphate; organic NIR dyes and pigments such as N,N,N’,N’-tetrakis(4-dibutylaminophenyl)-p-benzoquinone bis(iminium hexafluoro-antimonate); non-stoichiometric, reduced or doped inorganic compounds such as reduced indium tin oxide, reduced zinc oxide, reduced tungsten oxide (tungsten bronze), reduced doped tungsten oxide including an inorganic compound of the following formula M_xW_yO_z (where M is at least one element selected from the group consisting of H, He, alkali metal, alkaline earth metal, rare earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, satisfying 0.001 < x/y < 1 ; and 2.2 <z/y < 3.0), reduced antimony tin oxide, or doped metal oxides such as aluminium-doped zinc oxide (AZO) and fluorinedoped tin oxide (FTO); conductive polymers such as poly polystyrene sulfonate (PEDOT); and combinations thereof. Preferably, the near-infrared absorbing compound is selected from inorganic copper salts such as copper (II) hydroxyl phosphate; non-stoichiometric, reduced or doped inorganic compounds such as reduced indium tin oxide, reduced zinc oxide, reduced tungsten oxide (tungsten bronze), reduced doped tungsten oxide including an inorganic compound of the following formula M_xW_yO_z (where M is at least one element selected from the group consisting of H, He, alkali metal, alkaline earth metal, rare earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, satisfying 0.001 < x/y < 1 ; and 2.2 <z/y < 3.0), reduced antimony tin oxide, or doped metal oxides such as aluminium- doped zinc oxide (AZO) and fluorine-doped tin oxide (FTO). The near-infrared absorbing compound may be present in the second composition or composition comprising the leuco dye in an amount of from 0.1 to 10 wt.%, such as from 0.2 to 5 wt.%.

It will be appreciated by a skilled person that an intensely coloured (highly visibly coloured) near-infrared absorbing agent, such as carbon black, is not appropriate for the second composition or composition comprising the leuco dye utilised in the present invention. Such an intensely coloured near-infrared absorbing agent would create a highly-coloured background for such a composition. In contrast, the second composition or composition comprising the leuco dye utilised in the present invention may be transparent or translucent upon application to the substrate such that effective mark or image formation can take place upon application of radiation using a laser. Near-infrared absorbing agents of low visible colour are therefore required. An intensely coloured near-infrared absorbing agent would be detrimental to the present invention. ‘Visibility’ in this context is meant visibility to the human eye and/or machine readable. Preferably, the nearinfrared absorbing agent is not a highly visibly coloured near-infrared absorbing compound. Preferably, the near-infrared absorbing compound is not a highly visibly coloured pigment or dye. Preferably, the second composition or composition comprising the leuco dye does not comprise carbon black.

When the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention further comprises a near-infrared absorbing agent, the second composition or composition comprising the leuco dye may further comprise an agent operable to transfer heat from the near-infrared absorbing agent to the colour-forming compound or leuco dye, i.e. a heat transfer agent. The heat transfer agent may be a metal oxide, a metal pyrophosphate or a metal phosphate of the following metals: iron, aluminium, zirconium, titanium or combinations thereof. Preferably, the heat transfer agent is a metal oxide, a metal pyrophosphate ora metal phosphate of the following metals: iron, aluminium, zinc, zirconium, titanium, or combinations thereof. It will be appreciated by a skilled person that references to metal oxides, metal pyrophosphates or metal phosphate are to be interpreted as also covering the hydrates of any of the given metal oxides, metal pyrophosphates or metal phosphates. The heat transfer agent may be selected from: iron (III) pyrophosphate hydrate, aluminium zinc oxide, zirconium (IV) oxide, zirconium dioxide, aluminium oxide, iron phosphate dihydrate and titanium dioxide. More preferably, the heat transfer agent is selected from: iron (III) pyrophosphate hydrate, aluminium zinc oxide, zirconium dioxide, zirconium (IV) oxide, aluminium oxide, zinc oxide, iron phosphate dihydrate and titanium dioxide. Even more preferably, the heat transfer agent is a metal oxide. The heat transfer agent may be a metal oxide of: iron, aluminium, zirconium and titanium, or combinations thereof. Even more preferably, the heat transfer agent is a metal oxide of: iron, aluminium, zinc, zirconium and titanium, or combinations thereof. The heat transfer agent may be selected from zirconium (IV) oxide, zirconium dioxide, aluminium oxide, and titanium dioxide. Even more preferably, the heat transfer agent is selected from aluminium zinc oxide, zirconium dioxide, zirconium (IV) oxide, aluminium oxide, zinc oxide and titanium dioxide. Most preferably, the heat transfer agent is zirconium (IV) oxide.

The second composition utilised in the utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention may further comprise an additive or combination of additives.

Suitable additives will be well known to a person skilled in the art. Examples of suitable additives include, but are not limited to the following: polymers; light or energy absorbing agents; UV absorbers; surfactants; wetting agents; dispersant agent; antifoaming agents; flow and levelling agents; coefficient of friction surface modifiers; waxes; drying promoters; tinting agents; gloss or matt enhancers; scuff, mar and abrasion improvers; fluorescent agents; plasticisers; optical brighteners; oxidising or reducing agents; stabilisers; light stabilising agents such as hindered amines; rheology modifiers such as thickening or thinning agents; humectants; solvents; adhesion promoters; acid or base scavenging agents; retarders; defoamers; antifoaming agents; and combinations thereof. The additive or combination of additives may be present in the second composition or composition in an amount of from 0.1 to 15 wt.%, preferably from 0.5 to 5 wt.%.

Preferably, the second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising the leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, does not comprise a pigment.

The second composition utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or the composition comprising a leuco dye utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention is not soluble in the aqueous alkaline solution used in the removal of the mark or image as detailed herein. The second composition or composition comprising the leuco dye remains as a solid or precipitate following exposure to the aqueous alkaline solution.

The first composition at least partially solubilises in the aqueous alkaline solution used in the removal of the mark or image as detailed herein. This means that the first composition is separated from the plastic substrate upon exposure to the aqueous alkaline solution as described herein, also facilitating the separation of the second composition or composition comprising the leuco dye from the plastic substrate, and thus removal of the mark or image from the plastic substrate. It will also be appreciated that the first composition will be separated from the second composition or composition comprising the leuco dye given its at least partial solubilisation in the aqueous alkaline solution.

Upon exposure to the aqueous alkaline solution, the time taken for the first composition to at least partially solubilise may be from 1 to 45 minutes, such as from 1 to 30 minutes, or from 1 to 20 minutes, such as from 1 to 15 minutes, preferably from 1 to 5 minutes. Preferably, the first composition solubilises within 45 minutes of exposure to the aqueous alkaline solution, preferably within 20 minutes, preferably within 15 minutes, and more preferably within 5 minutes.

In the context of the present invention, the first composition solubilises in the aqueous alkaline solution such that the first composition separates (bonds broken with the plastic substrate) from the plastic substrate. The first composition thus separates the second composition or composition from the plastic substrate. It will be appreciated that the first composition may partially or fully solubilise, or have any degree of solubilisation therebetween, upon exposure to the aqueous alkaline solution.

The use of a protein in the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention is advantageous as proteins are biodegradable materials that are environmentally friendly. Accordingly, if washed into any waste stream during the removal of a mark or image from a plastic substrate as detailed herein, they pose no threat to the environment.

The protein acts as the binder for the first composition. It is the protein that enables the first composition to be at least partially solubilised in the aqueous alkaline solution and separated from the plastic substrate (and the second composition or composition). The protein of the first composition is at least partially soluble in the aqueous alkaline solution. Upon contact with the aqueous alkaline solution, the protein breaks down into its constituent amino acid monomers (building blocks). Accordingly, when exposed to the aqueous alkaline solution, the first composition at least partially solubilises in the aqueous alkaline solution and facilitates separation of the second composition or composition comprising the leuco dye from the plastic substrate to remove the mark(s) or image(s).

For the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention, the protein of the first composition may be any suitable protein. The protein is in its natural state. The protein is not denatured. It has not been altered from its natural state. The protein may be sourced from a range of natural resources, including animal, dairy and plant proteins. Preferably, the protein is selected from an animal or plant protein. More preferably, plant proteins are selected due to their biodegradable and environmentally-friendly nature. Examples of animal proteins include, but are not limited to: collagen (hydrolysed or non-hydrolysed) such as hydrolysed bovine collagen; and gelatine. Examples of dairy proteins include, but are not limited to: egg white; whey; and casein. Examples of plant proteins include, but are not limited to: prolamine proteins, such as gluten, zein, soy, pea and hemp.

Preferably, the protein is selected from a prolamine protein. More preferably, the protein is selected to be zein, or soy, preferably zein.

All references to particular proteins herein are to be interpreted as covering the proteins perse, and also, where appropriate, derivatives, for example peptides or functionalised proteins.

The protein may be present in the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention, in any suitable amount. Preferably, the protein may be present in the first composition in an amount of from 0.1 to 50 wt.%, such as from 0.1 to 40 wt.%, or even from 3 to 30 wt.%. More preferably, the protein may be present in the first composition in an amount of from 5 to 25 wt.%.

The protein is solubilised in the first composition upon formulation of the first composition and prior to application of the first composition to the plastic substrate. It will be appreciated that different proteins solubilise at different pHs. Accordingly, the pH of the first composition may vary as the solubility of different proteins varies. Some will be more soluble in higher or lower pHs. Preferably, the first composition will have a pH of from 2 to 12.5, preferably 3 to 11.5. The first composition may comprise a neutral medium, i.e. the composition consequently has a pH of about 7. The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may comprise an aqueous medium in which the protein is solubilised upon formulation of the first composition and prior to application of the first composition to the plastic substrate. The first composition may comprise an alkaline aqueous medium, such as water with ammonia, monoethanolamine or other amine-based materials and carbonates. This may be formed through the addition of an aqueous solution containing ammonia, monoethanolamine or other amine-based materials and carbonates to water. The first composition may comprise an acidic aqueous medium, such as acetic acid, hydrochloric acid and other acid-based chemicals. Preferably, the first composition comprises an alkaline aqueous medium, such as water with ammonia, monoethanolamine, or other amine-based materials and carbonates, preferably monoethanolamine.

Alternatively, the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may comprise a solvent in which the protein is solubilised upon formulation of the first composition and prior to application of the first composition to the plastic substrate. The first composition may comprise a single solvent or a mixture of solvents. The solvent may comprise water, an organic solvent, a mixture of water and an organic solvent, or a mixture of organic solvents. A base such as ammonia, monoethanolamine or other amine-based materials and carbonates may optionally be present in the solvent. Suitable organic solvents include, but are not limited to the following: alcohols such as ethanol, n-propanol, isopropanol and n- butanol; esters such as ethyl acetate, butyl acetate, and n-hexyl acetate; aromatic hydrocarbons such as benzene, toluene, xylene, and solvent naphtha 100, 150, 200; ketones such as acetone, cyclohexanone, methylisobutyl ketone, and methyl ethyl ketone; glycols such as butyl glycol; glycol ethers such as methoxypropanol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether; and combinations thereof. Preferably, the first composition comprises water and/or an organic solvent. More preferably, the first composition comprises water and/or an alcohol, acetate or ketone. More preferably, the first composition comprises water and/or an alcohol or ketone. More preferably, the first composition comprises water and/or an alcohol. More preferably, the first composition comprises water and/or ethanol.

Preferably, the aqueous medium or solvent is present in the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention in amounts of from 15 to 95 wt%, such as from 15 to 80 wt.%, or from 15 to 70 wt%, such as from 15 to 60 wt%, or even from 20 to 55 wt%.

It will be appreciated by a skilled person that the protein is solubilised in the aqueous medium or solvent of the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention upon formulation of the first composition and prior to application of the first composition to the plastic substrate. The aqueous medium or solvent, and any components thereof, are present at levels such that the protein remains solubilised in the solvent or aqueous medium upon formulation, and prior to application of the first composition to the plastic substrate. Upon application to the plastic substrate, it will be appreciated that the majority of the aqueous medium or solvent is lost by virtue of the application methods detailed herein.

The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may further comprise a biocide, such as isothiazolinones, cationic quaternary salts e.g. ammonium/phosphonium, amines, urea, benzoic acid/sorbate salts. More than one biocide may be present in the first composition. Biocides increase the stability, i.e. shelf life of the protein and includes surfactants that possess biocidal properties and protein stabilisation capabilities. Example surfactants include but are not limited to, alkyl sulfate salts e.g. Dioctyl Sodium Sulfosuccinate (DSS), sodium xylene sulphonate, Sodium Lauryl Sulfate (SLS), Sodium Dodecyl Sulfate (SDS); Carboxylate salts e.g. Sodium Stearate; Sorbates e.g. Sodium sorbate (SS), Polysorbates e.g. Polysorbate 20 (aka Tween 20); Amine Oxides e.g Lauryldimethylamine Oxide; Phosphate esters. Additionally, non-conventional biocides could be used, i.e. preservatives typically used for food stuffs, such as sodium nitrates/nitrites, Lauryldimethylamine oxide (LDAO) and ascorbic acid. The first composition may comprise from 0.001 to 5 wt% of a biocide, such as from 0.1 to 5 wt%, or even 0.1 to 1 wt%, and preferably 0.1 to 0.5 wt%.

As noted above, the protein of the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention performs the function of a binder. Accordingly, the first composition typically contains no binder in addition to the protein. However, alternatively, in order to further increase the strength of the binding of the first composition to the substrate, the first composition may comprise a binder in addition to the protein. Suitable binders will be well known to a person skilled in the art. Examples of suitable binders include, but are not limited to the following: natural products and derivatives thereof including natural resins such as shellac; and combinations thereof. The binder may be present in the first composition in any suitable amount. Preferably, the first composition comprises from 1 to 40 wt%, such as from 3 to 30 wt% and most preferably, from 5 to 20 wt% of binder.

The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may further comprise a near-infrared absorbing compound capable of enhancing absorption of near-infrared or infrared radiation. Suitable near-infrared absorbing compounds include but are not limited to the following: inorganic copper salts such as copper (II) hydroxyl phosphate; organic NIR dyes and pigments such as N,N,N’,N’-tetrakis(4-dibutylaminophenyl)- p-benzoquinone bis(iminium hexafluoro-antimonate); non-stoichiometric, reduced or doped inorganic compounds such as reduced indium tin oxide, reduced zinc oxide, reduced tungsten oxide (tungsten bronze), reduced doped tungsten oxide including an inorganic compound of the following formula M_xW_yO_z (where M is at least one element selected from the group consisting of H, He, alkali metal, alkaline earth metal, rare earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, satisfying 0.001 < x/y < 1 ; and 2.2 <z/y < 3.0), reduced antimony tin oxide, or doped metal oxides such as aluminium-doped zinc oxide (AZO) and fluorine- doped tin oxide (FTO); conductive polymers such as poly polystyrene sulfonate (PEDOT); and combinations thereof. Preferably, the near-infrared absorbing compound is selected from inorganic copper salts such as copper (II) hydroxyl phosphate; non-stoichiometric, reduced or doped inorganic compounds such as reduced indium tin oxide, reduced zinc oxide, reduced tungsten oxide (tungsten bronze), reduced doped tungsten oxide including an inorganic compound of the following formula M_xW_yO_z (where M is at least one element selected from the group consisting of H, He, alkali metal, alkaline earth metal, rare earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, satisfying 0.001 < x/y < 1 ; and 2.2 <z/y < 3.0), reduced antimony tin oxide, or doped metal oxides such as aluminium- doped zinc oxide (AZO) and fluorine-doped tin oxide (FTO).

It will be appreciated by a skilled person that an intensely coloured (highly visibly coloured) near-infrared absorbing agent, such as carbon black, is not appropriate for the first composition of the present invention. Such an intensely coloured nearinfrared absorbing agent would create a highly-coloured background for a first composition. In contrast, the first composition of the present invention utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may be transparent or translucent upon application to the substrate. Near-infrared absorbing agents of low visible colour are therefore required such that effective mark or image formation can take place upon application of radiation using a laser. An intensely coloured near-infrared absorbing agent would be detrimental to the present invention. ‘Visibility’ in this context is meant visibility to the human eye and/or machine-readable. Preferably, the near-infrared absorbing agent is not a highly visibly coloured near-infrared absorbing compound. Preferably, the near-infrared absorbing compound is not a highly visibly coloured pigment or dye. Preferably, the first composition does not comprise carbon black.

The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may comprise from 0.05 to 25 wt%, such as from 0.05 to 20 wt% of a near-infrared absorbing agent. The near-infrared absorbing agent utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may have any suitable D50 particle size distribution value. Preferably, the D50 particle size distribution value of the near-infrared absorbing agent is 5 pm or less. More preferably, the D50 particle size distribution value of the near-infrared absorbing agent is from 0.5 to 3 pm, and most preferably from 1 to 2 pm. D50 particle size distribution is measured using a Malvern Mastersizer according to ISO standard 13320:2009.

The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may further comprise an additive or combination of additives. Suitable additives will be well known to a person skilled in the art. Examples of suitable additives include, but are not limited to the following: polymers; light or energy absorbing agents; UV absorbers; surfactants; wetting agents; drying promoters; colourants such as pigments; tinting agents; fluorescent agents; plasticisers; optical brighteners; oxidising or reducing agents; stabilisers; light stabilising agents such as hindered amines; rheology modifiers such as thickening or thinning agents; humectants; adhesion promotors; acid or base scavenging agents; retarders; defoamers; antifoaming agents; and combinations thereof. Preferably, the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention comprises 0.1 to 25 wt%, such as from 0.1 to 20 wt%, such as from 0.1 to 15 wt%, such as from 0.1 to 12 wt%, or even from 0.1 to 10 wt% of an additive or combination of additives.

Preferably, the first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention does not comprise a pigment or dye.

The first composition may be formulated with the protein in a dry powder form, such as in a dehydrated form e.g. freeze dried or spray dried. It has further been identified by the present inventors that, in the context of the present invention, the first composition may act as a barrier layer, for example to gas migration. This is particularly the case when the plastic substrate is a multilayer plastic construction.

The first composition utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention may be formed by any suitable method, which will be well known to a person skilled in the art. Preferably, if utilised, the near-infrared absorbing agent is milled prior to addition to the other components of the composition, using a mechanical bead mill, such as an Eiger Torrance M50 mechanical bead mill.

For the second to thirteenth aspects of the present invention, upon application of radiation to the second composition or composition comprising the leuco dye that is coated over the first composition on the plastic substrate, it will be appreciated that the colour-forming compound will form colour. In addition, the protein also forms colour upon application of radiation to the second composition, and thus the first composition thereunder. It will be appreciated that the protein is denatured upon application of the radiation, and undergoes a conformational change i.e. transitioning from its non-denatured state to the denatured state at the localised positions to which the radiation is applied using a laser. A white colour is formed by the protein at these localised positions. This serves to enhance the colour formed by the colour-forming compound of the second composition upon the application of radiation thereto.

For the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate preferably defines a volume. The volume is operable to hold or store contents, such as liquids or solids. The contents may be pharmaceuticals, food and drink, or non-consumable personal care and household products. The plastic substrates may be three-dimensional. The plastic substrates may have an outer wall(s), such as an outer wall defining an internal volume operable to hold contents. It will be appreciated that the outer wall(s) may define more than one internal volume (separate or connected) with the plastic substrate operable to hold contents.

The first composition, second composition and/or composition comprising the leuco dye may be applied to or incorporated within the plastic substrate. Preferably, the first composition, second composition and/or composition comprising the leuco dye are applied to the plastic substrate.

The present inventors have advantageously found that the first composition, second composition, and/or composition comprising the leuco dye described herein can be directly applied to or incorporated within the plastic substrates. This finds particular use when the plastic substrates define a volume, for example, plastic packaging such as plastic containers, for example, plastic boxes, plastic pouches, plastic bottles, plastic blister packaging, or plastic clamshell packaging. The ability to achieve a mark or image directly on a plastic substrate through the application of radiation thereto, and then remove the radiation-reactive, preferably laser-reactive, composition from the plastic substrate so as to remove the mark or image without contaminating the resulting plastic material or waste streams avoids any need for a separate label component. This is advantageous because routinely, upon disposal of such plastic substrates and labels, the disposal processes for the plastic substrate and label differ and are incompatible. Either two different recycling processes are required for the separate articles (substrate and label), one of the articles is not recyclable, or in some instances, the two articles have become bonded following application of the label to the substrate and cannot be separated or a difficult to separate such that suitable recycling processes cannot be achieved or are difficult to achieve. From a sustainability perspective, this is far from ideal.

Preferably, the first composition, second composition and/or composition comprising the leuco dye are directly applied to the plastic substrate.

Accordingly, for the first to fifth and seventh to thirteenth aspects of the present invention, preferably the plastic substrate is other than a label. Preferably, for the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate is plastic packaging. Plastic packaging includes plastic lids and plastic containers such as plastic food and/or beverage containers or containers of pharmaceuticals or non-consumable personal care and household products. Suitable examples of plastic containers include plastic boxes, plastic pouches, plastic bottles such as plastic beverage bottles, the plastic blister packaging typically used in the pharmaceutical and tobacco or vaping industries, and clamshell packaging typically used in the food industry.

It will be appreciated that the plastic substrate includes plastic substrates as described herein having additional plastic components associated therewith, such as plastic bottles may have plastic lids associated therewith. The plastic substrate also includes plastic substrates as described herein having additional non-plastic components associated therewith, such as for example a metal, aluminium foil or paper sealing layer (lidding) in blister packaging. The plastic substrates of the present invention thus include any plastic substrate as described herein, including any associated closure, pump, cap, spout, handle, lid or cover.

The plastic substrates may be used to store, transport and distribute goods such as pharmaceuticals, food and drink and non-consumable personal care and household products.

Preferably, for the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate is a plastic container. More preferably, the plastic substrate is a plastic box, plastic pouch, plastic bottle, plastic blister packaging, or plastic clamshell packaging. More preferably, the plastic substrate is a plastic box, plastic pouch, or plastic bottle. Most preferably, the plastic substrate is a plastic bottle.

For the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate may be formed of any suitable plastic material.

Preferably, for the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate is formed of polyethylene terephthalate (PET), high density polyethylene (HDPE), polypropylene (PP) including orientated polypropylene (OPP) and biaxially orientated polypropylene (BOPP), recycled polyethylene terephthalate (r-PET), low density polyethylene (LDPE), or combinations thereof. It will be appreciated by a skilled person that these plastic materials are recyclable, such that the plastic substrate may be formed of any suitable recyclable plastic material.

More preferably, for the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate is formed of polyethylene terephthalate (PET), or recycled polyethylene terephthalate (r-PET). Most preferably, the plastic substrate is formed of polyethylene terephthalate (PET).

For the first to fifth, and seventh to thirteenth aspects of the present invention, the plastic substrate may be in the form of a polymer film.

For the first to fifth, and seventh to thirteenth aspects of the present invention, the plastic substrate may be metallised. By metallised is meant that the plastic substrate is coated with a thin layer of metal, for example, aluminium. In these cases, the plastic substrate may be a polymer film such that the plastic substrate is a mentalised polymer film. Such films may be used as barrier layers in, for example, a multi-layer plastic construction.

For the first to fifth and seventh to thirteenth aspects of the present invention, the plastic substrate may be transparent, translucent or opaque. The plastic substrate may be coloured, white or be colourless.

For the first to fifth, and seventh to thirteenth aspects of the present invention, the plastic substrate may be a multi-layer plastic construction. This may be known in the art as a laminate construction.

Such a multi-layer plastic construction may comprise two or more layers of any suitable plastic material, the plastic material being those detailed above for the plastic substrate. The multi-layer plastic construction may comprise at least one layer of the first composition and at least one layer of the second composition or composition comprising the leuco dye described herein positioned between two of the plastic material layers. For example, the multi-layer plastic construction may comprise one layer of the second composition or composition comprising the leuco dye between two layers of the first composition, positioned between two of the plastic material layers. The at least one layer of the first composition and at least one layer of the second composition or composition comprising the leuco dye may cover all of the plastic material layers, or at least a portion thereof. The at least one layer of the first composition and at least one layer of the second composition or composition comprising the leuco dye described herein may also be applied to at least a portion of the exterior of the multi-layer plastic constructions. The multi-layer plastic construction can be considered to comprise a plurality of discrete layers.

For the multi-layer constructions described herein, preferably each of the two or more layers of plastic material is associated with at least one layer of the first composition as described herein, on one or both sides thereof. By ‘associated with’ means that the at least one layer of the first composition is in direct contact with, or positioned relative to, each plastic material layer so as to facilitate the removal of any second composition or composition comprising the leuco dye therefrom. It will be appreciated that this at least one layer may be on one or both side of the plastic layer depending on its position within the multi-layer plastic construction. For example, it will be appreciated that if the plastic layer is the outer layer of the multi-layer plastic construction, this plastic layer will typically be associated with at least one layer of the first composition on its internal side, i.e. within the multi-layer plastic construction. Similarly, if the plastic layer is an internal layer of the multi-layer plastic construction, i.e. within the multi-layer plastic construction, the plastic layer will typically have at least one layer of the first composition positioned each side thereof, i.e. at least one layer of the first composition applied to each side thereof.

It will be appreciated that for the multi-layer plastic construction, at least one of the two or more layers of plastic material may be transparent or translucent, such that the mark or image can be seen therethrough. Typically, in the context of the present invention, the multi-layer plastic constructions correspond to laminated film packaging. Typically, the multi-layer plastic constructions are plastic pouches, plastic boxes or plastic bottles, preferably plastic pouches. Preferably, the two or more layers of plastic material are in the form of polymeric film.

For the multi-layer plastic constructions described herein, each layer of plastic material is preferably in contact with a layer of the first composition as described herein, on one or both sides thereof. For example, an outer layer of plastic material (those on the outside of the multi-layer plastic construction) may be in contact with at least one layer of the first composition which is within the multilayer plastic construction, and any inner layer of plastic material (within the multilayer plastic construction) may be in contact with at least one layer of the first composition on each side of the plastic material.

For the multi-layer plastic constructions described herein, the two or more layers of plastic material may be the same or different. This may be in terms of material type, colour, thickness, and/or transparency etc. One of the two or more layers of plastic material may be metallised. For example, to act as a barrier layer. One or more of the two or more layers of plastic material may be a ‘heat-sealed’ plastic material. Such a material is typically formed through processing, e.g. melting, of the plastic material itself.

For the multi-layer plastic construction, the multi-layer plastic construction preferably comprises two or three layers of plastic material. It will be appreciated that when three layers of plastic material are used, the at least one layer of both of the first and second compositions described herein may be positioned between two of the plastic material layers, or between both the first and second plastic material layers as well as between the second and third plastic material layers. For example, one layer of the second composition between two layers of the first composition, positioned between two of the plastic material layers, or one layer of the second composition between two layers of the first composition between both the first and second plastic material layers as well as between the second and third plastic material layers. When the at least one layer of both of the first and second compositions describe herein are positioned between two of the plastic material layers (e.g. first and second, or second and third respectively), a layer of the first composition may also be positioned between the other two (e.g. second and third, or first and second respectively). For example, one layer of the second composition between two layers of the first composition, positioned between first and second plastic material layers, and one layer of the first composition between the second and third plastic material layers. It will be appreciated that this will be dependent upon the construction of the multi-layer plastic construction with regard to the different plastic materials in terms of material type and required delamination of the layers for recycling processes.

Preferably, for the multi-layer plastic construction, at least two of the two or more layers of plastic material are formed of different types of plastic material. For example, one plastic material may be PET, and another may be OPP. As detailed above, the present invention advantageously enables the different types of plastic in such constructions to be separated and each recycled effectively, without any contamination from the second composition. The densities of the different plastic material may aid their separation once delamination of the multi-layer plastic construction has occurred in the alkaline aqueous solution.

The two or more layers of plastic material of the multi-layer plastic construction as described herein may have a thickness of from 8 to 100 pm.

The multi-layer plastic constructions as described herein typically have an overall thickness of 500 pm or less, such as 200 pm or less.

For the multi-layer plastic constructions described herein, one or more additional layers may also be present. The one or more additional layers may have a thickness of from 100 pm or less. Suitable additional layers may be selected from but are not limited to: thermal insulating layers; protective layers; adhesion promoting layers; adhesive layers; barrier layers including metal foils or coated plastic materials; quenching layers; and hinder amine light stabilisers; or combinations thereof. It will be appreciated that the positioning of the one or more additional layer in the ordering of the discrete layers of the multi-layer plastic construction may differ depending on the type of one or more additional layer utilised and its function with the multi-layer plastic construction. Preferably, the one or more layer is an adhesive layer, a barrier layer, an adhesion promoting layer or a protective layer.

The at least one layer of the first and second compositions for the multi-layer plastic constructions as described herein may be applied as single, or multiple layers, i.e. once or multiple times. This is also the case for the one or more additional layers. The at least one layer of the first and second composition and the one or more additional layers may be each applied to a coat weight as detailed herein for the first and second compositions.

Preferably, for the multi-layer plastic constructions described herein, the multilayer plastic construction is formed of, in order: a layer of plastic material; a layer of the first composition described herein; a layer of the second composition described herein; one or more additional layer; a layer of the first composition described herein; and a layer of a plastic material. As discussed above, the two layers of plastic material may be the same or different. For example, one may be PET and one may be OPP. Preferably, the two layers of plastic material are formed of different plastic materials. Preferably, the layers of plastic material are in the form of polymer film.

More preferably, for the multi-layer plastic construction described herein, the multilayer plastic construction is formed of, in order: a layer of plastic material; a layer of the first composition described herein; a layer of the second composition described herein; an adhesive layer; a layer of the first composition as described herein; and a layer of plastic material. As discussed above, the two layers of plastic material may be the same or different. For example, one may be PET and one may be OPP. Preferably, the two layers of plastic material are formed of different plastic materials. Preferably, the layers of plastic material are in the form of polymer film.

It will be appreciated that for the multi-layer plastic construction described herein, the mark or image is formed using the second composition and thus the mark or image is formed ‘within’ or ‘incorporated within’ the multi-layer plastic construction. In the context of the present invention, where the term ‘mark or image formed thereon’ is used, this also encompasses a mark or image being formed ‘within’ or ‘incorporated within’ a multi-layer plastic construction. The multi-layer plastic construction displays a mark or image.

When the plastic substrate is a multi-layer plastic construction, upon exposure of the plastic substrate to the aqueous alkaline solution, delamination of the multilayer plastic construction occurs, as well as de-inking of the second composition, and thus the mark or image.

The term ‘delaminate’, ‘delaminating’, ‘delamination’, or other like terms used herein with respect to a multi-layer plastic construction, refers to the separation of the layers of plastic material of the multi-layer plastic construction from each other.

The term ‘deink’, ‘deinking’, ‘deinked’ or other like terms used herein, specifically refers to the removal of the mark or image from the layers of plastic material of the multi-layer plastic construction. This is through the separation of the second composition which forms the mark or image from each of the layers of plastic material of the multi-layer plastic construction. ‘Delamination’ and ‘deinking’ of the multi-layer plastic construction typically occur simultaneously in the process described herein upon exposure to the aqueous alkaline solution. Complete ‘deinking’ occurs when each of the two or more layers of plastic material of the multi-layer plastic construction is associated with at least one layer of the first composition as described herein, on one or both sides thereof.

It will further be appreciated that the term ‘deink’, ‘deinking’, and ‘deinked’ or other like terms used herein also refer to removal of the mark or image from any plastic substrate, i.e. a plastic substrate defined herein other than a multi-layer plastic construction, through separation of the second composition or composition comprising the leuco dye from the plastic substrate upon exposure to the aqueous alkaline solution as described herein.

Upon formulation of the second composition used in the second, third, fourth, fifth, tenth or twelfth aspects of the present invention or composition comprising the leuco dye of the sixth, seventh, eighth, ninth, eleventh and thirteenth aspects of the present invention and application to the plastic substrate, there is no premature colour formation. The formation of a mark or image is achieved solely through the specific application of radiation to localised positions of the second composition or composition comprising the leuco dye using a laser. Accordingly, prior to application of this radiation, the plastic substrate does not display a mark or image formed by the second composition or composition comprising the leuco dye.

The colour-forming compound facilitates the formation of a mark or image on the plastic substrate.

By the term "colour" and like terms used herein is meant any of the colours and hues of the visible light colour spectrum, i.e. red, orange, yellow, blue, green and violet, in addition to black, brown, turquoise, purple, pink, cyan, and magenta, and mixtures thereof. Both primary and secondary colours are encompassed, i.e. it will be appreciated by a skilled person that the colour formed by a leuco dye upon exposure of the composition to radiation may be a primary or secondary colour. In the context of the present invention, the term may also be used to describe differing shades of each of the colours of the visible light colour spectrum, in addition to magenta, cyan, pink, purple, turquoise, brown and black.

It will be appreciated that the colour of the mark or image formed is dependent upon the selection of the colour-forming compound. Typically, when the colourforming compound is selected to be an oxyanion of a multivalent metal or oxyanion or hydrate thereof, the colour formed may be black. Typically, when a leuco dye is selected, the colour is a colour other than black.

The mark or image formed is clearly visible to the human eye and/or machine readable. Preferably, the mark or image formed is distinct, discernible.

By ‘distinct’ and discernible’ as used herein in relation to the mark or image, is meant that the image is clearly visible to the human eye and/or machine-readable. The mark or image contrasts with the background of the second composition or composition, and/or the colour of the plastic substrate, i.e. the mark or image is easily differentiable therefrom. The mark or image is thus a ‘contrasting’ mark or image.

The mark or image formed may be evaluated by measurement of an absolute density value. This may be: an absolute optical density black (ODB) value, typically used for evaluation of marks or images that are black in colour or a shade or tint thereof; an absolute optical density magenta (ODM) value, typically used for evaluation of marks or images that are red in colour or a shade or tint thereof; an absolute optical density cyan (ODC) value, typically used for evaluation of marks of images that are blue in colour, or a shade or tint thereof; or an absolute optical density yellow (ODY) value, typically used for evaluation of marks or images that a yellow in colour or a shade or tint thereof. In the context of ODB, ODM, ODC and ODY values, the higher the value, the darker the respective colour formed. The absolute ODB, ODM, ODC and ODY value quantifies the optical density on the respective black, magenta, cyan or yellow colour scale from low to high values, where ODB, ODM, ODC and ODY measurements can be made using a standard instrument densitometer and X-Rite eXact or SpectroEye or TechKon SpectroDens spectrophotometer. A distinct and discernible mark or image preferably has an absolute ODB, ODM, ODC or ODY value of 0.7 or more, such as 0.8 or more, or 0.9 or more, such as 1 .0 or more.

The mark or image may also be evaluated over time by measurement of the absolute density value discussed above over time. The mark or image can be said to be retained when an absolute ODB, ODM, ODC or ODY value of 0.7 or more, such as 1.0 or more, maintained over the stated time period. The mark or image may be retained from 1 week to 6 months, such as from 1 week to 5 months, or from 1 week to 3 months, such as from 1 week to 2 months, or from 1 week to 6 weeks, or from 1 week to 5 weeks, such as from 10 days to 6 months, or from 10 days to 5 months, or from 10 days to 3 months, such as from 10 days to 2 months, or from 10 days to 6 weeks, or from 10 days to 5 weeks.

Assessment of undue colouration of the ‘background’ of the second composition or composition comprising the leuco dye on which the mark or image is formed, i.e. the part of the composition on which the mark or image is not formed, may be evaluated by measurement of a AE value. This value represents any measurable difference in L*a*b* colour to determine if any colouration of the second composition or composition comprising the colour-forming compound has occurred, other than the desired formation of a mark or image. It will be appreciated that this measurement may also be used to determine if any premature colour by the second composition or composition comprising the colour-forming compound has occurred prior to application of the radiation to form the mark or image. A sample of a plastic substrate having the first composition applied thereto, with the second composition or composition comprising the colour-forming compound applied thereover, but unimaged (i.e. prior to radiation), or a sample of a plastic substrate having the first composition applied thereto, with the second composition or composition comprising the colour-forming compound applied thereover and imaged with radiation is compared with an uncoated sample of the plastic substrate. AE may be measured using the standard mathematical formula defined herein, on an X-rite eXact spectrophotometer. AE measurements may be made on a white background. A low AE measurement is preferred, indicating that there is little quantitative colour difference between the two samples being compared such that they can be considered qualitatively comparable and visually the same, i.e. no premature colouration has occurred, or the background of the composition has not significantly coloured, to prevent formation of a distinct and discernible mark or image. The AE measurement may be less than 5, such as less than 3.5, such as less than 3, or less than 2.

For the second to fifth, eighth and tenth to thirteenth aspects of the present invention the radiation may be applied to the plastic substrate to selectively facilitate colour formation at localised positions of the second composition or composition comprising the leuco dye in order to form the desired mark or image, i.e. the formation of variable information. The application of the radiation is controlled and specific. A human and/or machine-readable mark or image is formed. This is typically only in a portion or region of the plastic substrate.

It will be appreciated that the colour of the mark or image is selected so as to contrast with the colour of the background of the second composition or composition comprising the leuco dye, and/or the colour of the plastic substrate such that the mark or image is distinct and easily differentiable from the background of the second composition or composition comprising the leuco dye, i.e. the part(s) of the second composition or composition that have not been exposed to radiation, as well as any substrate visible through the part(s) of the second composition or composition comprising the leuco dye that has not been exposed to radiation.

The term ‘image’ or ‘mark’ incorporates, but is not limited to: logos, marks such as text and words, graphics, figures, pictures, symbols, codes such as linear barcodes, 2D Datamatrix, QR codes, Digimarc codes and text, such as that based on alphanumerics and symbols. It will be appreciated that in the context of the present invention, it is the colour-forming compound that facilitates the formation of a mark or image on the plastic substrate. The mark or image formed will be human and/or machine readable, and can be used for coding and marking, tagging, tracking and tracing and late-stage customisation or personalisation purposes. The mark or image formed is typically a mark or image used to display variable information.

In the context of the present invention, the radiation is applied following application of the second composition or composition comprising the colour-forming compound to the plastic substrate. This can occur immediately after application, or at a later time, such as after storage or transportation. It will be appreciated that when the plastic substrate is a multi-layer plastic construction, the radiation is applied following formation of the multi-layer plastic construction, either immediately after formation or at a later time, such as after storage or transportation.

It will be appreciated that the radiation selected will be that required to cause the colour-forming compound to form a mark or image.

"Radiation" and like terms used herein refers to energy in the form of waves or particles, and in particular, refers to electromagnetic radiation such as ultraviolet (UV), visible, near-infrared (NIR) and infrared (IR) particle radiation, e.g. alpha (a) radiation, beta (p) radiation, neutron radiation and plasma. The wavelength ranges of the different regions of the electromagnetic spectrum are known to a skilled person.

For the second to fifth, eighth and tenth to thirteenth aspects of the present invention, the radiation may be selected from ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, including near-infrared (NIR) radiation with a wavelength of from 700 to 1600 nm, such as 950 to 1100 nm. Preferably, the radiation is selected from infrared (IR) radiation with a wavelength of 9000 to 12000 nm, such as 9300, 9600, 10200 or 10600 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm. More preferably, the radiation is selected from infrared (IR) radiation with a wavelength of 9300, 9600, 10200 or 10600 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm. Most preferably, the radiation is infrared (IR) radiation with a wavelength of 10600 nm and near-infrared (NIR) radiation with a wavelength of from 950 to 1100 nm.

Preferably, the infrared radiation with a wavelength of from 9000 to 12000 nm, such as 9300, 9600, 10200 or 10600 nm, is applied using a CO₂ laser.

In the context of the present invention, the term ‘NIR or IR radiation’ refers to radiation selected from infrared (IR) radiation with a wavelength of 9000 to 12000 nm, such as 9300, 9600, 10200 or 10600 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm. Preferably, the radiation is infrared (IR) radiation with a wavelength of 10600 nm and near-infrared (NIR) radiation with a wavelength of from 950 to 1100 nm.

For the second to fifth, eighth and tenth to thirteenth aspects of the present invention, the radiation may be applied using a UV, CO₂ or fibre laser.

By the term ‘laser-reactive’ composition as used herein means a composition which forms colour upon the application of radiation from a laser thereto. It will be understood by a skilled person that the radiation may be applied to localised positions in a region or portion of the plastic substrate to selectively facilitate the formation of colour, and thus a mark or image, at these localised positions. These localised positions may overlap with each other.

It will also be understood by a skilled person that the radiation is applied for an appropriate amount of time required to facilitate the formation of the mark or image. Typically, the time required to deliver sufficient radiation will depend upon the means used to apply radiation and the method of application. For example, in one embodiment, the radiation may be applied for less than 30 seconds, such as less than 20 seconds or 15 seconds, or even less than 10 or 5 seconds.

The radiation may be applied by any suitable means. Preferably, the radiation is applied to the plastic substrate, i.e. to the second composition or composition comprising the leuco dye, using non-contact means or source. By ‘non-contact’ means is meant a means or source that is not in contact with the plastic substrate and second composition or composition comprising the leuco dye when delivering radiation thereto. Suitable means include laser excitation through application of radiation by a laser source(s). Preferably, the radiation is applied using a laser source(s). By the term ‘laser source(s)’ and like terms used herein is meant any suitable commercial or non-commercial laser source(s). Suitable examples include but are not limited to a fibre laser, fibre-couped laser diode array, CO2 laser, laser diode array or direct diode laser for providing radiation, including nearinfrared or mid-infrared radiation.

It will be appreciated that when applied using a laser source(s), the radiation dosage applied can be controlled by alteration of the time for which the radiation is applied, the power of the means used to apply the radiation (wattage) and thus, the fluence (amount of energy delivered per unit area) delivered by a laser source(s), e.g. J/cm². It will be appreciated by a skilled person that this may affect the density/opacity i.e. ‘effectiveness’ of the mark or image formed. For example, where a laser source(s) is used to apply the radiation, the fluence (amount of energy delivered per unit area) may affect the density/opacity i.e. ‘effectiveness’ of the mark or image formed. In the context of the present invention, the fluence is dependent upon the power of the means used to apply the radiation (wattage), and the time for which the radiation is applied to a particular localised position on the portion of the plastic product, which may be controlled by the scanning speed of the laser or the speed of the moving stage. These two variables can be altered to change the fluence. Where the fluence is low (e.g. lower power and/or shorter irradiation times), the mark or image formed will have lower density/lower opacity, and where the fluence is high (e.g. higher power and/or longer irradiation times), the mark or image formed will have a higher density /higher opacity. In the context of the present invention, fluence values may range from 0.01 to 100 J/cm², such as from 0.1 to 50 J/cm², and even from 0.5 to 25 J/cm².

The composition comprising the leuco dye, first composition and second composition as defined herein for the first to thirteenth aspects of the present invention may be applied to the plastic substrate, or a plastic material component(s), i.e. a plastic material layer, when the plastic substrate is a multilayer plastic construction, by any suitable process. Suitable application methods include, but are not limited to the following: spray application, flexographic printing, gravure printing, screen printing and pad printing, preferably flexographic printing, gravure printing, screen printing and pad printing. Flexographic printing is in compliance with ISO 2834-2.

The composition comprising the leuco dye, first composition and second composition as defined herein for the first to thirteenth aspects of the present invention are preferably directly applied to the plastic substrate, or a plastic material component(s), i.e. a plastic material layer, when the plastic substrate is a multi-layer plastic construction.

By ‘directly applied’ as used herein is meant application of the first composition, second composition, or composition comprising the leuco dye onto the plastic substrate itself rather than any other substrate attached or connected to the plastic substrate. It will be appreciated that when the plastic substrate is a multi-layer substrate construction, ‘directly applied’ refers to the first composition and second composition or composition comprising the leuco dye being applied to a plastic material layer of the multi-layer plastic construction and positioned between two of the layers of plastic material of the multi-layer plastic construction, i.e. within the multi-layer substrate construction, with no other substrate being attached or connected to the multi-layer plastic construction. For example, when the plastic substrate is a plastic substrate defining a volume, this means that the first composition, second composition or composition are applied onto the plastic substrate itself rather than to a label or other substrate attached or connected to the plastic substrate.

The first composition, second composition or composition comprising the leuco dye of the first to thirteenth aspects of the present invention may be applied to at least a portion of the plastic substrate, or at least a portion of a plastic material component(s), i.e. a plastic material layer, when the plastic substrate is a multilayer plastic construction. They may be applied to more than one portion of the plastic substrate or a plastic material component(s) (e.g. a plastic material layer of a multi-layer plastic construction). It will be appreciated that if the first composition, second composition or composition comprising the leuco dye is applied to more than one portion of the plastic substrate or a plastic material component(s) (e.g. a plastic material layer of a multi-layer plastic construction), the colour-forming compound of the second composition or composition comprising the leuco dye may differ at each portion, such that different coloured marks or images can be provided on the same plastic substrate.

In some instances, the first composition, second composition or composition comprising the leuco dye of the first to thirteenth aspects of the present invention may be applied to all of the exterior surface of the plastic substrate.

An overvarnish may be applied over the second composition or composition comprising the colour-forming compound on the plastic substrate to increase the wear resistance of the first composition, second composition, or composition comprising the leuco dye. Suitable overvarnishes include but are not limited to those based on styrene-acrylic, polyvinyl butyral, nitrocellulose, polyurethane, acrylics, polyvinyl chloride, polyvinyl acetate, polyamides, alkyd, polyester and epoxy based resins. The first composition, second composition or composition comprising the leuco dye of the first to thirteenth aspects of the present invention may be applied to the plastic substrate or a plastic material component(s) (e.g. layer of plastic material layer of a multi-layer plastic construction) to any suitable dry coat weight (gsm) dependent upon both the substrate to which the composition is applied and the application method. It will be appreciated by a skilled person that the dry coat weight (gsm) of the composition on the substrate will affect the density of the mark or image formed.

For the first to thirteenth aspects of the present invention, the first composition may be applied to the plastic substrates or a plastic material component(s) (e.g. plastic material layer of a multi-layer plastic construction) at a dry coat weight of from 0.1 to 10 gsm (grams per square metre), such as from 0.2 to 5 gsm, or from 0.2 to 2 gsm, or from 0.5 to 2 gsm, such as from 0.5 to 1.5 gsm.

For the first to thirteenth aspects of the present invention, the first composition may be applied to the plastic substrate or a plastic material component(s) (e.g. plastic material layer of a multi-layer plastic construction) at a wet coat weight of from 0.2 to 20 gsm, such as from 0.4 to 10 gsm, or from 0.4 to 4 gsm, or from 1 to 4 gsm, such as from 1 to 3 gsm.

The second composition or composition of the second to thirteenth aspects of the present invention may be applied to the plastic substrates or a plastic material component(s) (e.g. plastic material layer of a multi-layer plastic construction) at a dry coat weight of from 0.5 to 15 gsm (grams per square metre), such as from 0.5 to 10 gsm, or 1 to 10 gsm, and most preferably from 1 to 8 gsm, or from 1 to 6 gsm, such as 1 to 4 gsm.

The dry coat weight may be measured by any suitable method. Suitable measuring methods will be well known to those skilled in the art. For the present invention, the dry coat weight is measured by weighing the same unit area of substrate (for example 100 cm²) with and without the composition applied thereto, and assessing the difference between two weights. The second composition or composition comprising the leuco dye of the second to thirteenth aspects of the present invention may be applied to the plastic substrates or a plastic material component(s) (e.g. plastic material layer of a multilayer plastic construction) at a wet coat weight of from 1 to 30 gsm, or 1 to 20 gsm, or 2 to 20 gsm, such as from 2 to 16 gsm, or from 2 to 12 gsm, or 2 to 8 gsm.

The wet coat weight may be measured by any suitable method. Suitable measuring methods will be well known to those skilled in the art. For the present invention, the wet coat weight is measured by calculating dry coat weight (weight of substrate with composition-weight of substrate) wt% of solids in composition

It will be appreciated that wet coat weight is the coat weight of the second composition or composition comprising the leuco dye that is applied to the plastic substrate or plastic material component(s) (e.g. plastic material layer of a multilayer plastic construction). Following application, the second composition or composition comprising the leuco dye dries, and all or some of the water or organic solvent lost.

The first composition, second composition or composition comprising the leuco dye according to any of the first to thirteenth aspects of the present invention may each be applied to the plastic substrate or a plastic material component(s) (e.g. plastic material layer of a multi-layer plastic construction) as a single, or multiple layers, i.e. once or multiple times.

All of the features contained herein may be combined with any of the above aspects in any combination.

All references to particular chemical compounds herein are to be interpreted as covering the compounds per se, and also, where appropriate, derivatives, hydrates, solvates, complexes, isomers and tautomers thereof.

For a better understanding of the present invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the following experimental data. Examples

Example 1

A second composition as utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention or a composition comprising a leuco dye as utilised in the sixth, seventh, eighth, ninth, eleventh or thirteenth aspects of the present invention, was prepared according to Table 1. All amounts are in weight percentage (wt%).

Table 1

* Tampoprint Transparent Lacquer ACP comprises 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2- methoxy-1 -methylethyl acetate, 2-butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, and ammonium salt of carbonic acid esters. Tampoprint K-VDS Thinner comprises n-butyl acetate. Tampoprint K-VDL Thinner comprises 2-ethoxy-1 -methylethyl acetate. Example 2

A second composition as utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention was prepared according to Table 1 . All amounts are in weight percentage (wt%). Table 2

* Tampoprint Transparent Lacquer ACP comprises 2-ethoxy-1 -methylethyl acetate, n-butyl acetate, 2- methoxy-1 -methylethyl acetate, 2-butoxyethyl acetate, 4-hydroxy-4-methylpentan-2-one, and ammonium salt of carbonic acid esters. Tampoprint K-VDS Thinner comprises n-butyl acetate. Tampoprint K-VDL Thinner comprises 2-ethoxy-1 -methylethyl acetate. Example 3

A first composition as utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention was prepared according to Table 3. All amounts are in weight percentage (wt%). Table 3

Example 4

A first composition as utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention was prepared according to Table 4. All amounts are in weight percentage (wt%).

Table 4

Example 5

In accordance with EPBP (European PET Bottle Platform) Quick Test QT 507 (March 2017):

A layer of the first composition prepared according to Example 3 was applied to a portion of a PET substrate at 1 gsm using a RK K control coater.

A layer of the second composition or composition comprising the leuco dye prepared according to Example 1 was applied over the first composition at 2 gsm using an RK K control coater.

Infrared radiation was applied to the second composition using a CO2 laser to form a QR code (mark or image) thereon on the plastic substrate.

The PET substrate was cut into 1 cm² flakes.

The PET flakes were placed in an aqueous solution of 2 wt.% sodium hydroxide at 80 °C, 500 rpm for 15 minutes. The supernatant was reserved. This was repeated another two times.

The PET flakes were rinsed to remove the aqueous sodium hydroxide solution.

The PET flakes were dried in an oven at 105 °C.

L*, a* and b* values of the PET flakes were measured with an X-rite eXact spectrophotometer (an average of 10 measurements were taken).

Example 6

In accordance with EPBP (European PET Bottle Platform) Quick Test QT 507 (March 2017): A layer of the first composition prepared according to Example 3 was applied to a portion of a PET substrate at 1 gsm using a RK K control coater.

A layer of the second composition prepared according to Example 2 was applied over the first composition at 2 gsm using an RK K control coater.

The PET substrate was cut into 1 cm² flakes.

The PET flakes were rinsed to remove the aqueous sodium hydroxide solution.

The PET flakes were dried in an oven at 105 °C.

Example 7

A layer of the first composition prepared according to Example 4 was applied to a portion of a PET substrate at 1 gsm using a RK K control coater.

Infrared radiation was applied to the second composition using a CO2 laser to form a QR code (mark or image) thereon on the plastic substrate. The PET substrate was cut into 1 cm² flakes.

The PET flakes were rinsed to remove the aqueous sodium hydroxide solution.

The PET flakes were dried in an oven at 105 °C.

Results

The L*, a* and b* values of the resulting PET flakes of Examples 5, 6 and 7 were compared to uncoated PET sample flakes (control). Results are shown in Table 5 below.

L* denotes lightness, a* denotes the red/green values and b* denotes the yellow/blue values in the Cl ELAB colour system (Cl ELAB colour space) - a colour space defined by the International Commission on Illumination (CIE) in 1976.

A AE measurement was then calculated using a white background. Results are shown in Table 5 below.

AE is a standard mathematical calculation which allows for the quantification of the visual perception of the difference between two colours (here, between the control and the PET flakes resulting from Examples 5, 6 and 7). AE is calculated using the below formula (L = L*, a = a* and b = b*).

ZIE = VC-f-i - i₂)² + («1 - a_z)² + (-bl - bz- )²

The AE measurements indicate that removal of the mark or image has occurred.

The second composition has been separated from the plastic substrate. There is no contamination of the plastic substrate by the second composition. Any colour change between the control and the PET flakes resulting from Examples 5, 6 and 7 is imperceptible to the human eye. There is no visual perception of a difference in colour between the control and the PET flakes resulting from Examples 5, 6 and 7. The PET flakes resulting from Examples 5, 6 and 7 are not contaminated with the second composition.

Table 5

Example 8 A second composition as utilised in the second, third, fourth, fifth, tenth and twelfth aspects of the present invention, was prepared according to Table 6. All amounts are in weight percentage (wt%).

Table 6

Example 9

A first composition as utilised in the first, second, third, fourth, fifth, eighth, tenth and twelfth aspects of the present invention was prepared according to Table 7. All amounts are in weight percentage (wt%).

Table 7

Example 10

A multi-layer plastic construction (laminate construction) was constructed having the following layers:

1. PET polymer film (23pm thickness);

2. First composition prepared according to Example 9;

3. Second composition prepared according to Example 8;

4. Adhesive (commercially known as Novacote SF716A +CA336 adhesive)

5. First composition prepared according to Example 9;

6. White OPP polymer film (40 pm thickness).

Comparative Example 10a

A multi-layer plastic construction not according to the present invention was constructed having the following layers:

1. PET polymer film (23pm thickness);

2. Second composition prepared according to Example 8;

3. Adhesive (commercially known as Novacote SF716A + CA336 adhesive);

4. White OPP polymer film (40 pm thickness).

Example 11

The first composition prepared according to Example 9 and the second composition prepared according to Example 8 were used to form the multi-layer plastic construction of Example 10. The second composition prepared according to Example 8 was used to form the multi-layer plastic construction of Comparative Example 10a.

For the multi-layer plastic construction of Example 10, a layer of the first composition prepared according to Example 9 was applied to the PET polymer film and OPP polymer film at a coat weight of 1 gsm using a RK K control coater.

A layer of the second composition prepared according to Example 8 was applied over the first composition on the PET polymer film at a coat weight of 2 gsm using an RK K control coater. A layer of the adhesive (commercially known as Novacote SF716A + CA336 adhesive) was applied over the second composition on the PET polymer film at a coat weight of 2 gsm using an RK K control coater.

The layers were laminated together to form the laminate construction according to Example 10 using a Cheminstruments LL-100 laboratory laminator.

For the multi-layer plastic construction of Comparative Example 10a, a layer of the second composition prepared according to Example 8 was applied to the PET polymer film at a coat weight of 2 gsm using an RK K control coater.

A layer of the adhesive (commercially known as Novacote SF716A + CA336 adhesive) was applied over the second composition on the PET polymer film at a coat weight of 2 gsm using an RK K control coater.

The layers were laminated together to form the laminate construction according to Comparative Example 10a using a Cheminstruments LL-100 laboratory laminator.

Infrared radiation was applied to both multi-layer plastic constructions, and thus the second composition thereof, using a CO2 laser, such that a mark or image was displayed by the multi-layer plastic constructions.

Each multi-layer plastic constructions was cut into 20 x 1 cm² flakes.

The 20 flakes of each multi-layer plastic construction were placed into an aqueous solution of 2 wt.% sodium hydroxide at 80 °C, 500 rpm for 15 minutes. The supernatant was reserved. This was repeated another two times.

The flakes were then rinsed to remove the aqueous sodium hydroxide solution. The flakes were left to settle for 10 minutes, and where necessary, floating flakes separated from sunken flakes and the quantity of each recorded (flakes of OPP should float and flakes of PET should sink given their different densities). Results are shown in Table 8 below. If delamination has occurred, 40 flakes should be identified (20 of PET polymeric film and 20 of OPP polymeric film), i.e. the 20 flakes of the multi-layer plastic construction have been separated into 2x 20 flakes of the constituent plastic materials.

The flakes were dried in an oven at 105 °C.

If delaminated, L*, a* and b* values of the flakes were measured with an X-rite eXact spectrophotometer (an average of 10 measurements were taken). Results are shown in Table 9 below.

Results

Table 8

The multi-layer plastic construction of Example 10 is delaminated upon exposure to the aqueous alkaline solution. The induvial discrete layers of the PET polymeric film and OPP polymeric film of the multi-layer plastic construction are separated.

In contrast, delamination of the multi-layer plastic construction of Comparative Example 10a does not occur. The resulting number of flakes is only 20. The 20 flakes have sunk as the density of the combined PET and OPP polymeric films is greater than that of water.

The L*, a* and b* values of the resulting PET and OPP flakes obtained for the multi-layer plastic construction of Example 10 were compared to uncoated PET and OPP sample flakes respectively (control). L* denotes lightness, a* denotes the red/green values and b* denotes the yellow/blue values in the Cl ELAB colour system (Cl ELAB colour space) - a colour space defined by the International Commission on Illumination (CIE) in 1976.

A AE measurement was then calculated, using a white background. Results are shown in Table 9 below.

AE is a standard mathematical calculation which allows for the quantification of the visual perception of the difference between two colours (here, between the control and the PET or OPP flakes resulting from the multi-layer plastic construction of Example 10). AE is calculated using the below formula (L = L*, a = a* and b = b*).

The AE measurements indicate that de-inking has occurred for the multi-layer plastic construction of Example 10. The AE measurements indicate that removal of the mark or image has occurred. The second composition has been separated from the plastic materials of the multi-layer plastic construction. There is no contamination by the second composition for either of the plastic materials PET or OPP of the multi-layer plastic construction of Example 10. Any colour change between the control and the PET or OPP flakes resulting from Example 10 is imperceptible to the human eye. There is no visual perception of a difference in colour between the control and the PET or OPP flakes resulting from Example 10. The PET or OPP flakes resulting from Example 10 are not contaminated with the second composition. This is in contrast to the multi-layer plastic construction of Example 10a, which does not comprise a first composition as described herein according to the present invention.

Table 9

Claims

1. A use of a first composition comprising a protein to remove a mark or image from a plastic substrate, preferably through exposure of the plastic substrate to an aqueous alkaline solution, and optionally wherein the plastic substrate is a plastic substrate having applied directly thereto, on at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye and capable of forming a mark or image upon application of radiation to localised positions of the second composition using a laser, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent.

2. A use of a first composition for the manufacture of a plastic substrate having applied to at least a portion thereof or incorporated in at least a portion thereof, a first composition and a second composition applied over the first composition, wherein the first composition comprises a protein and the second composition comprises a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and the second composition displays a mark or image formed by application of radiation to localised positions of the second composition using a laser, such that the plastic substrate displays a mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the mark or image can be removed from the plastic substrate to provide plastic material that is not contaminated by the second composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution, and optionally wherein the manufacture of the plastic substrate comprises applying the first composition and second composition onto the plastic substrate or a plastic material component thereof, preferably by printing the first composition and second composition onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing. A plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and capable of forming a mark or image upon application of radiation to localised positions of the second composition using a laser, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent. A plastic substrate according to claim 3, formed by a method comprising applying the first composition and the second composition onto the plastic substrate or a plastic material component thereof, preferably by printing the first composition and the second composition onto the plastic substrate ora plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing. A use of a first composition and second composition in the removal of a mark or image from a plastic substrate to provide a plastic material that is not contaminated by the second composition, the plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye, and displaying a mark or image formed by application of radiation to localised positions of the second composition using a laser, such that the plastic substrate displays the mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the removal of the mark or image from the plastic substrate is preferably through exposure of the plastic substrate to an aqueous alkaline solution. A method of removing a mark or image from a plastic substrate to provide a plastic material that is not contaminated with the second composition, said plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein and a second composition applied over the first composition, the second composition comprising a colour-forming compound selected from an oxyanion of a multivalent metal or oxyacid or hydrate thereof and a leuco dye and displaying a mark or image formed by application of radiation to localised positions of the second composition using a laser such that the plastic substrate displays the mark or image, wherein when the colour-forming compound is a leuco dye, the second composition further comprises a thermal acid-generating agent, and wherein the method comprises: exposing the plastic substrate to an aqueous alkaline solution. The use, plastic substrate or method according to any of claims 1 to 6, wherein the colour-forming compound is a leuco dye, and the second composition further comprises a thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12. A composition comprising a leuco dye, thermal acid-generating agent selected from an amine salt of an organic metal compound, organic solvent, and an alkaline stabiliser having a pKa of from 2 to 12. A use of a composition according to claim 8 in a method of removing a mark or image from a plastic substrate to provide plastic material that is not contaminated by the composition, the plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein, and the composition applied over the first composition, wherein the leuco dye of the composition displays a mark or image, said mark or image having been formed application of radiation to localised positions of the composition using a laser, such that the plastic substrate displays a mark or image, and wherein the mark or image can be removed from the plastic substitute to provide plastic material that is not contaminated by the composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution. A use of a composition according to claim 8 for the manufacture of a plastic substrate having applied on at least a portion thereof or incorporated in at least a portion thereof, a first composition comprising a protein and the composition applied thereover, wherein the leuco dye displays a mark or image, said mark or image having been formed by application of radiation to localised position of the composition using a laser, such that the plastic substrate displays a mark or image, wherein the mark or image can be removed from the plastic substrate to provide plastic material that is not contaminated by the composition, preferably through exposure of the plastic substrate to an aqueous alkaline solution, and optionally wherein the manufacture of the plastic substrate comprises applying the first composition and composition onto the plastic substrate or a plastic material component thereof, preferably by printing the first composition and composition onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing. A plastic substrate comprising the composition according to claim 8 applied thereon. A plastic substrate comprising the composition according to claim 8 applied to at least a portion thereof, or incorporated in at least a portion thereof, the plastic substrate being formed by a method comprising applying the composition onto the plastic substrate or a plastic material component thereof, preferably by printing the composition onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing. The use, plastic substrate or method according to any of claims 1 , 2, 5, 6, 7, 9 or 10, wherein the aqueous alkaline solution is an aqueous solution of 0.1 to 5 wt.%, such as 0.5 to 3 wt.%, preferably 1 to 3 wt.%, of a base, preferably an alkali or earth alkali hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide, preferably sodium hydroxide, and optionally at a temperature of from 50 to 95 °C, such as from 60 to 95 °C, or from 80 to 95 °C, such as from 80 to 90 °C. The use, plastic substrate or method according to any of claims 1 , 2, 5, 6, 7, 9, 10 or 13, wherein following exposure to the alkaline solution, the second composition remains as a solid or precipitate and is preferably removed by filtration. The use, method, or plastic substrate according to any of claims 1 to 7 and 13 or 14, wherein the oxyanion of a multivalent metal or oxyacid or hydrate thereof is an oxyanion of a multivalent metal or hydrate of an oxyanion of a multivalent metal, preferably an ammonium salt of an oxyanion of a multivalent metal, preferably an ammonium salt of an oxyanion of molybdenum, preferably ammonium octamolybdate (AOM). The use, plastic substrate, composition or method according to any of claims 7 to 14, wherein the thermal generating agent is an amine salt of an organic metal compound of the formula (I):

in which R⁶ and R⁷ are the same or different, and are hydrogen, Ci -4-al ky I , Ci-4-alkoxy, halogen, amino or carboxy, and for X = silicon, o = 1 and p = 0, and R¹ is aryl, aralkyl or Ci -4-alkyl , or o = 1 and p = 1 , and R¹ and R² together form a one residue selected from the group consisting of:

and for X = boron, o = 0 and p = 0, and

R³, R⁴ and R⁵ are the same or different and are hydrogen, Ci-12-alkyl, Ci- 6-hydroxyalkyl, allyl, aralkyl or arylsulfonyl, in which aralkyl or arylsulfonyl can be substituted with Ci-4-alkyl, or R³ and R⁴ together with the nitrogen to which they are attached form a morpholino or piperidino ring. The use, plastic substrate, composition or method according to any of claims 7 to 14, or 16, wherein the alkaline stabiliser having a pKa of from 2 to 12 has a pKa of from 4 to 11 , preferably from 6 to 11 , and preferably wherein the alkaline stabiliser having a pKa of from 2 to 12 is selected from sodium carbonate, sodium bicarbonate, potassium carbonate, mono ethanolamine, and triethanolamine, or combinations thereof, and more preferably wherein the alkaline stabiliser having a pKa of from 2 to 12 is sodium bicarbonate. The use, plastic substrate or method according to any of claims 1 to 7, 10 or 13 to 17, wherein the protein of the first composition is selected from collagen (hydrolysed or non-hydrolysed) such as hydrolysed bovine collagen, gelatine, egg white, whey, casein, and prolamine proteins such as gluten, zein, soy, pea and hemp, preferably wherein the protein of the first composition is a prolamine protein selected from gluten, zein, soy, pea and hemp, more preferably zein or soy, and more preferably zein. The method, use or plastic substrate according to any of claims 1 to 7 and 9 to 18, wherein the plastic substrate is plastic packaging, preferably a plastic container, more preferably, a plastic box, plastic pouch, plastic bottle, plastic blister packaging, or plastic clamshell packaging, more preferably a plastic box, plastic pouch, or plastic bottle, and most preferably a plastic bottle. The method, use or plastic substrate according to any of claims 1 to 7, and claims 9 to 19, wherein the plastic substrate is formed of polyethylene terephthalate (PET), high density polyethylene (HDPE), polypropylene (PP), recycled polyethylene terephthalate (r-PET), low density polyethylene (LDPE), or combinations thereof, preferably polyethylene terephthalate (PET), or recycled polyethylene terephthalate (r-PET), and more preferably, polyethylene terephthalate (PET). The plastic substrate according to any of claims 3, 4, 5, 7, and 11 to 20, wherein the colour-forming compound of the second composition or composition comprising the leuco dye displays a mark or image, said mark or image having been formed by application of radiation to localised position of the second composition or the composition comprising the leuco dye using a laser. The plastic substrate according to any of claims 3, 4, 5, 7, and 11 to 21 , wherein the plastic substrate is a multi-layer plastic construction, preferably a multi-layer plastic construction comprising two or more layers of plastic material and comprising at least one layer of the first and second compositions positioned between two of the plastic material layers. A method of displaying a mark or image on a plastic substrate according to any of claims 3, 4, 5, 7 and 11 to 20, or 22, the method comprising applying radiation to localised positions on the second composition or composition comprising the leuco dye using a laser.

24. The method, use or plastic substrate according to any of claims 2 to 7, 10 and 13 to 23, wherein the radiation applied to the localised positions selected from ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, including near-infrared (NIR) radiation with a wavelength of from 700 to 1600 nm, preferably from infrared (IR) radiation with a wavelength of 9000 to 12000 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm, more preferably from infrared (IR) radiation with a wavelength of 9300, 9600, 10200 or 10600 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm, and most preferably from infrared (IR) radiation with a wavelength of 10600 nm and near-infrared (NIR) radiation with a wavelength of from 950 to 1100 nm.

25. A method of forming the plastic substrate according to any of claims 3, 4, 7, and 11 to 22, the method comprising applying the first composition, and second composition or composition comprising the leuco dye, onto the plastic substrate or a plastic material component thereof, preferably by printing the first composition, and second composition or composition comprising the leuco dye, onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing.

26. A method of forming the plastic substrate according to any of claims 3, 4, 7, and 11 to 22, and forming a mark or image thereon, the method comprising, applying the first composition, and second composition or composition comprising the leuco dye, onto the plastic substrate or a plastic material component thereof, preferably by printing the first composition, and second composition or composition comprising the leuco dye, onto the plastic substrate or a plastic material component thereof, and more preferably by pad printing, screen printing, flexographic printing or gravure printing, and applying radiation to localised positions on the second composition or composition comprising the leuco dye using a laser to form the mark or image thereon, preferably wherein the radiation applied is selected from ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, including near-infrared (NIR) radiation with a wavelength of from 700 to 1600 nm, preferably from infrared (IR) radiation with a wavelength of 9000 to 12000 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm, more preferably from infrared (IR) radiation with a wavelength of 9300, 9600, 10200 or 10600 nm, infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared

(NIR) radiation with a wavelength of 700 to 1600 nm, and most preferably from infrared (IR) radiation with a wavelength of 10600 nm and nearinfrared (NIR) radiation with a wavelength of from 950 to 1100 nm.