DURABLE GROUND PATH SIGNALING FOR AIRCRAFT

Abstract

DURABLE GROUND PATH SIGNALING FOR AIRCRAFT A method 400 of manufacturing an emergency guidance assembly for aircraft comprises forming 401 a photoluminescent layer on a substrate by printing an ink onto the substrate, the ink comprising: a water-based resin, wherein the water-based resin forms at least 20% by mass of the ink; and a photoluminescent material, wherein the photoluminescent material forms at least 20% by mass of the ink. Figure to be published with the abstract: Figure 4

Description

Title of the invention: DURABLE GROUND PATH SIGNALING FOR AIRCRAFT TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to emergency guidance assemblies for aircraft, methods of manufacturing such emergency guidance assemblies for aircraft, and improvements to such assemblies. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] It is known to provide photoluminescent (PL) floor path signaling assemblies for aircraft cabins. These assemblies are typically installed on the floor of the aircraft cabin. In many cases, an assembly in the form of a track is provided along at least one side of an aisle. In most examples, a track is provided along both sides of the aisle to guide and direct passengers in the event of an emergency from their seat to an emergency exit. Aircraft emergency guidance assemblies may also include tracks or other signaling on or along other surfaces, for example, cabin walls or even seats.

[0003] Known aircraft emergency guidance designs, including products manufactured by the applicant, often have a photoluminescent insert enclosed within a polymeric housing such as an extruded polycarbonate sleeve or casing. Virgin (i.e., newly manufactured / non-recycled) polymers are used to ensure compliance with stringent aerospace standards, and although these polymers are recyclable, it has been found that in reality they are often not recycled. This is due in part to the additives and coatings (e.g., flame retardants) often required to comply with aerospace requirements, making the products potentially quite difficult to recycle, even where such a desire exists. A tough, highly transparent polycarbonate (PC) plastic is often used, which is particularly harmful to the environment and may end up in landfill for an indefinite period.The carbon footprint associated with the production of 1 kg of polycarbonate is approximately 6 kg. Standard virgin polycarbonate also uses 100% fossil fuel derivatives in its production and does not include any recycled material. It will be appreciated that other polymers may also be used, for example polymethyl methacrylate (PMMA), and similar environmental considerations apply. The insert typically comprises a photoluminescent material embedded within a resin. An organic solvent-based resin is typically used, with the resin then cured. and / or cured for use. The generation and use of organic solvents, as well as their release during the curing process, can have adverse effects on the environment. The resin itself can be deposited on a polymeric substrate, for example by screen printing. A virgin polymer meeting aerospace requirements is generally used, which presents the same environmental issues as for polymeric housing. Summary of the invention

[0004] The object of the invention is to provide a more durable emergency guidance assembly for aircraft.

[0005] According to a first aspect of the invention, there is provided a method of manufacturing an emergency guidance assembly for aircraft, the method comprising forming a photoluminescent layer on a substrate by printing an ink onto the substrate. The ink comprises: • a water-based resin, wherein the water-based resin forms at least 20% by mass of the ink; and • a photoluminescent material, wherein the photoluminescent material forms at least 20% by mass of the ink.

[0006] The substrate may be polymeric.

[0007] The water-based resin may form at least 25% by mass of the ink, and optionally at least 30% or 35% by mass of the ink.

[0008] The water-based resin and the photoluminescent material may together form at least 80% by mass of the ink, and optionally at least 85% or 90% of the ink. The water-based resin and the photoluminescent material may together form 90 to 100% by mass of the ink, and optionally 91 to 95% by mass of the ink, with the remainder being a retarder and / or one or more other additives such as a wetting agent and / or an emulsifier.

[0009] There has previously been a prejudice in the art against the use of water-based resins, as these often have a milky appearance once cured compared to organic solvent-based resins, which reduces light transmission. However, the inventors have appreciated that careful control of the ink properties (including the loading of photoluminescent material) and the thickness of the ink layer (which can be adjusted by controlling properties of the ink itself, as well as by controlling the printing process) can be used to mitigate this problem and form a product that still meets aerospace requirements, while providing better environmental credentials.

[0010] Due to the chemical compositions of the materials used and the surface interaction required for bonding, water-based resins have not previously been used alongside polymeric substrates for an aircraft emergency guidance assembly - poor bonding between a water-based resin and a polymeric substrate was expected. The approach described herein has overcome this bias in the art to form a robust photoluminescent layer suitable for use in aircraft emergency guidance assemblies.

[0011] As a result of using a water-based resin to make the ink, there is a reduction in the amount of Volatile Organic Compounds (VOCs) released during production, making the process more environmentally friendly than previous approaches.

[0012] As used herein, "resin" means a solid or liquid organic polymeric product such as that used as the base of various plastics, adhesives, varnishes, inks, paints and the like. While many resins rely on organic solvents, a water-based resin uses water as the primary, or even sole, solvent. It will be appreciated that the consistency of the ink can therefore be adjusted by adding water, thinning the resin (e.g., to make the consistency thin enough for the chosen printing technique, e.g., screen printing), or actually removing water (e.g., to thicken the ink sufficiently to achieve a desired layer thickness in a single print).

[0013] The ink may comprise at least 50% by mass of photoluminescent material, and optionally may comprise 60% by mass of photoluminescent material.

[0014] The ink may comprise 20 to 75% by mass of photoluminescent material, and optionally 25 to 75%, 30 to 75%, 40 to 75% or 50 to 75% by mass of photoluminescent material.

[0015] The ink may comprise at least 3%, and optionally at least 4%, 5%, 8%, 10%, or 12%, of water by mass, the mass of water being part of the mass of the water-based resin. The ink may comprise between 4% and 25% water by mass, and optionally between 15% and 20% water by mass. A higher percentage of water may be used to lower the viscosity of the ink, which may facilitate printing. Improved ink consistency may be achieved by thinning a resin for use with additional water.

[0016] It will be appreciated that the water-based resin generally loses water (and possibly one or more other relatively volatile components or additives, if any) before the photoluminescent layer is completed, for example during the drying and / or baking steps of the process, and even during the printing process, for example when the ink is on the screen of a screen printer. The photoluminescent material loading by mass of the final photoluminescent layer is therefore generally greater than the photoluminescent material loading by mass of the ink. The listed percentages by mass of the ink therefore concern “fresh” ink, for example when first opening a container of ink.

[0017] The substrate may be a polymeric substrate and may optionally comprise at least 20%, 30%, 40% or 50% by mass of recycled polymer. The substrate may be a polymeric substrate comprising 80% by mass of recycled polymer.

[0018] The method may include printing a plurality of layers of the same ink onto the substrate. The method may include printing a plurality of layers of different inks onto the substrate, each ink comprising a water-based resin that forms at least 20% (and optionally at least 25%) of the ink by mass; and a photoluminescent material that forms at least 30% by mass of the ink.

[0019] The method may include printing at least two layers of ink (optionally of the same ink) onto the substrate to form the photoluminescent layer. The method may include printing two, three, four, five, six, seven, eight, or nine layers of ink (optionally of the same ink) onto the substrate to form the photoluminescent layer. The method may include printing three to eight layers of ink to form the photoluminescent layer.

[0020] The printing process chosen may be screen printing. Alternatively, any suitable printing technique known in the art may be used, for example a roll-to-roll printing process, such as reverse gravure coating, or a pad printing process.

[0021] In some embodiments, one or more layers of ink, or other coating, without a PL component may be applied to the substrate prior to application of the ink with the PL component; for example, to provide an opaque (optionally white) and reflective layer behind the photoluminescent layer. This may improve the appearance and / or luminance of the finished product. For example, two layers of an opaque white ink with a reflective finish when dry may be applied, followed by seven layers of the ink as described above to provide a PL layer on top of the white backing of the substrate. The number of layers and / or the color of the backing ink may vary in other embodiments.

[0022] The photoluminescent layer (optionally formed by multiple individual layers of the ink or inks) may have a thickness in a range of 200 to 450 qm, and optionally 250 to 450 qm, and further optionally 250 to 400 qm, or 200 to 360 qm. The photoluminescent layer may have a thickness in a range of 300 to 360 qm, or 350 to 400 qm. It will be appreciated that the layer thickness is usually measured after the layer has dried / set / cured.

[0023] The photoluminescent material may have a carefully selected particle size and particle size distribution - the selections may be made based on a trade-off between brightness of the photoluminescent glow and duration of the photoluminescent glow (e.g. in terms of the period before the glow falls below a specified level, the specified level generally being based on aircraft safety regulations). The average (median) particle size, d50, may range from 10 pm to 100 pm, optionally from 15 pm to 50 pm, and still optionally from 20 pm to 45 pm. The average (median, d50) particle size may be 25 pm or 40 pm. For example, the material may have a d50 of 25 ± 5 pm or 40 ± 5 pm. Narrower limits can also be defined, for example 25 ±4 pm.

[0024] The particle size distribution may be relatively narrow, for example such that at least 90% of the particles are within a certain deviation of the average (median) particle size. Bounds may therefore be set for the d90 of the photoluminescent material. For example, the material may have d90< 115 pm or d90< 60 pm, such that at least 90% of the particles are smaller than 115 pm or 60 pm, respectively. The d90 of the material may be controlled to not exceed three times, and optionally not more than 2.5 times, the average particle size (d50).

[0025] The photoluminescent material may have a median particle size, d50, of X+5 pm or narrower, or a d50 of X±(X / 5) pm, X±(X / 6) pm, or X±(X / 8) pm, where X is any of the values ​​mentioned above for d50, or a value in one of the ranges listed for d50. The photoluminescent material may also have a d90 of less than or equal to 3X or 2.5X pm.

[0026] In some cases, a photoluminescent powder may be coated with a protective coating, for example, a hydrophobic coating to protect it from hydrolysis or other reactions, for example, when exposed to water. The coating may be thin relative to the particle size, and may be included in the particle size measurements described herein (if applicable).

[0027] The method may be arranged such that the formation of the photoluminescent layer is completed within 36 hours, and optionally within 24 hours, or within 12 hours, following a first printing of the ink on the substrate.

[0028] The ink may comprise at least 5% by mass of a retarder, for example a glycerin-based retarder. The retarder may be removed from the layer upon drying / baking.

[0029] The method may further comprise, after the printing (e.g. after the printing of the last layer in a multi-layer printing process) of the ink has been completed, baking the substrate and the printed material at a temperature of at least 100°C, and optionally 145°C or 160°C. The baking may include a residence time at the selected (maximum) temperature of between two minutes and two hours, optionally between 10 minutes and one hour or between 15 and 30 minutes, and still optionally 20 minutes.

[0030] Multiple layers of ink with a loading of at least 20% or 30% by mass of photoluminescent material may be deposited on the substrate. The method may include drying each layer before applying the next layer. The drying may be carried out for a period of less than 20 minutes, and optionally less than ten minutes, per layer. In embodiments in which both baking and drying are carried out, the drying may be carried out at a temperature lower than that of the baking.

[0031] The method may further comprise inserting the photoluminescent layer into a housing. Such a housing may protect the photoluminescent layer during use. The housing may comprise a polymeric cover arranged to cover the layer of photoluminescent material.

[0032] In some implementations, the method may further comprise attaching a polymeric cover to the substrate, the cover being arranged to protect the photoluminescent layer during use. The substrate and the cover may together form a housing for the photoluminescent layer.

[0033] In any scenario, whether the substrate is placed within a housing or is part of a housing, the polymeric cover may comprise: • at least 20% by mass of recycled polymer; and • a biodegradable additive.

[0034] In such embodiments, the lid therefore both includes recycled materials and is itself biodegradable, thereby reducing end-of-life landfill periods. Such a lid may comprise 50 ± 10% or 50 ± 5% by mass of virgin polymer and 50 ± 10% or 50 ± 5% by mass of recycled polymer, the virgin and recycled polymers optionally being of the same type, for example polycarbonates. The loading of the biodegradable additive may be between 0.01% and 0.2% of the mass of the lid, optionally between 0.01% and 0.10% of the mass of the lid, and still optionally may be 0.05% by mass of the lid. The loading of the biodegradable additive may be 0.05 ± 0.0025% by mass of the lid.

[0035] The ink may have a viscosity ranging from 200 Pa.s to 400 Pa.s, and optionally between 300 Pa.s and 350 Pa.s. This viscosity may be the dynamic viscosity of the ink, measured using a vertical falling ball viscometer.

[0036] The resin used to make the ink may be transparent or translucent. Before its combination with the photoluminescent material, the resin of the thickness intended to be used in the PL layer may have a total light transmittance of at least 85% or 90%, and optionally at least 95%, of incident light. This transmittance may apply to the entire visible light spectrum or, in other embodiments, at least in the wavelength ranges of (i) the light desired to charge the PL material and (ii) the light emitted by the PL material.

[0037] The resin may comprise at least 5%, 7% or 10% of an acrylic copolymer by weight of the resin, and may optionally comprise between 5% and 60% of acrylic copolymer by weight of the resin, and further optionally between 5% and 30%.

[0038] The ink may comprise a flow-forming agent. The flow-forming agent may be used to reduce the viscosity of the resin, facilitating flow. The flow-forming agent may also act as an emulsifier, for example, by stabilizing a suspension of acrylic in water. The flow-forming agent may be selected to have a flash point of at least 40°C, and optionally at least 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C. The flow-forming agent may be or comprise one or more of glycerin, or a glycol ether such as diethylene glycol and / or propylene glycol.It will be appreciated that, for some substances, the same substance may act as both a flow agent (reducing viscosity) and a retarder (slowing down the drying / hardening of the ink in the screen (for screen printing), or on the pad or reel or other printing tool as appropriate in other printing processes), or could act as both a flow agent and a wetting agent, for example. However, other substances may only play one role or the other.

[0039] The ink may comprise at least 1.2%, 1.5% or 2% of the resin fluidizing agent by mass, and optionally at least 2.5% of the resin fluidizing agent by mass.

[0040] According to a second aspect of the invention, there is provided an emergency guidance assembly for aircraft arranged to be mounted in an aircraft cabin, the assembly comprising: • a photoluminescent layer extending longitudinally; • a substrate supporting the photoluminescent layer; and • a housing designed to protect the photoluminescent layer, and wherein the photoluminescent layer is comprised of a water-based resin having embedded therein a photoluminescent material optionally having an average particle size, d50, in the range of 10 pm to 100 pm, and optionally 15 pm to 50 pm.

[0041] The photoluminescent layer may comprise at least 20% or 25% by mass of photoluminescent material, the photoluminescent material being embedded within the cured resin. The photoluminescent layer may comprise at least 30%, 35%, 40%, 45%, 50% or 55% by mass of photoluminescent material, and may comprise 55 to 75% or 65 to 70% by mass of photoluminescent material.

[0042] The emergency guidance assembly for aircraft may be manufactured according to the method of the first aspect.

[0043] The substrate may be a polymeric substrate.

[0044] The substrate may comprise at least 50% recycled material.

[0045] The photoluminescent layer may have a thickness in a range of 200 to 450 pm, 200 to 360 pm or 300 pm to 400 pm, or 300 to 350 pm. The photoluminescent layer may have a thickness of about 350 pm or about 375 pm.

[0046] The photoluminescent material may have a d50 (median particle size) of X pm and a d90 less than or equal to 3X pm.

[0047] The photoluminescent layer may be formed from at least two layers deposited and dried individually. The plurality of layers may together constitute a total thickness of the photoluminescent layer. The photoluminescent layer may comprise five, six, seven or eight of these layers.

[0048] The longitudinally extending photoluminescent layer and the substrate may be slidably inserted into and / or removed from the housing.

[0049] The housing may be polymeric and may comprise at least 20%, 30% or 50% by mass of recycled polymer. The recycled polymer may be recycled polycarbonate. The recycled polymer may be colorless, and may optionally be a colorless polycarbonate.

[0050] The housing may be polymeric and may include a biodegradable additive arranged to enable or facilitate biodegradation of the polymer. The loading of the biodegradable additive may be 0.05% by weight of the housing. The biodegradable additive may cause some frosting or opalescence of the housing. In a portion of the housing covering the photoluminescent material, a minimum light transmission threshold may be set, and the loading may be controlled so as not to cause the light transmission to fall below this threshold. The biodegradable additive may be or include a carbohydrate or starch-based additive (in additional or alternative embodiments, pro-oxidation additives and / or bioaugmentation additives may also be used, as discussed in more detail in Applicant's UK patent application GB 2403007.4 entitled "SUSTAINABLE AIRCRAFT FLOORPATH MARKING", which is incorporated herein by reference). The biodegradable additive may be or include BioSphere 201 grade biodegradable additive, and may optionally be BioSphere 201J biodegradable additive.

[0051] In embodiments using both recycled polymers and a biodegradable additive, frosting may be beneficial in masking aesthetic defects caused by the use of the recycled material.

[0052] A roughness of the top surface (or display surface) of the photoluminescent layer may be greater than 35 pm, and optionally about 45 pm. The roughness may be similar to that of P320 grit sandpaper.

[0053] The upper surface (or display surface) of the photoluminescent layer may have a brightness of less than 1 GU for an 85° measurement, optionally less than 0.5 GU, and optionally about 0.1 GU.

[0054] The upper surface of the photoluminescent layer may therefore be rougher and / or less shiny than is typically the case for prior art photoluminescent layers.

[0055] According to a third aspect of the invention, there is provided an aircraft having an aircraft cabin comprising an aircraft emergency guidance assembly in accordance with the second aspect.

[0056] The aircraft cabin may comprise a plurality of such interconnected emergency guidance assemblies.

[0057] The plurality of such interconnected emergency guidance assemblies may be used to form a track arranged to guide a person from a seat to an emergency exit.

[0058] The aircraft emergency guidance assembly may be arranged to be mounted on the floor of the aircraft cabin.

[0059] The aircraft cabin may include at least one track extending along an aisle of the aircraft cabin, the track including a plurality of interconnected emergency guidance assemblies, as described in connection with the first aspect. BRIEF DESCRIPTION OF THE FIGURES

[0060] The invention will now be described by way of example only with reference to the following figures in which: • [Fig. 1] is a sectional view of a portion of a photoluminescent layer and a substrate in accordance with the invention; • [Fig.2] is a sectional view of a portion of a layer photoluminescent and an alternative substrate in accordance with the invention; • Figures 3A and 3B illustrate two different aircraft emergency guidance assemblies, each containing a photoluminescent layer; • [Fig.4] shows a method of manufacturing a photoluminescent layer in accordance with the invention; • [Fig.5] is a diagram of an aircraft in accordance with various aspects of the invention; and • [Fig. 6] is a sectional view of a portion of an alternative photoluminescent layer and substrate in accordance with the invention. DETAILED DESCRIPTION

[0061] [Fig.l] of the accompanying drawings illustrates a sectional view of a component 1 of an aircraft emergency guidance assembly 100 in accordance with various aspects of the invention. The component 1 comprises a photoluminescent layer 2 and a substrate 3 on which the photoluminescent (PL) layer 2 is provided. The component 1 is generally arranged to form an interior portion of the aircraft emergency guidance assembly 100 in use, and may therefore be referred to as an insert 1.

[0062] The resulting aircraft emergency guidance assembly 100, two examples of which are shown in cross-sectional view in Figures 3A and 3B, is adapted to be mounted in an aircraft cabin. The assembly 100 comprises a layer 2 of longitudinally extending photoluminescent material and a housing 4 surrounding and protecting the photoluminescent material 2. In some embodiments, the substrate 3 may be part of the housing 4 - the PL material 2 may be seen deposited directly on a portion of the housing 4. In other embodiments, the substrate 3 may be placed within the housing 4.

[0063] Returning to [Fig.l], the insert 1 comprises a substrate 3. The substrate 3 is designed to serve as a support for the PL material 2. In the described embodiment, the substrate 3 is made of a polymer, and more specifically polypropylene. Any suitable polymer - for example a polyurethane or polycarbonate compliant with aerospace regulations - can be used instead. In the described embodiment, the substrate 3 is made of recycled polypropylene, which reduces the need for virgin polymers and increases sustainability. A polypropylene sheet or strip including 20% ​​to 80%, and optionally 80%, recycled polypropylene is used for the substrate 3 in the described embodiment. In various embodiments with polymeric substrates 3, the substrate 3 may comprise at least 50% by mass of recycled polymer, and optionally also a biodegradable additive as described in more detail below.

[0064] In alternative embodiments, a paper-based substrate 3 may be used instead, the paper-based substrate 3 preferably having a weight of at least less than 250 g / m2. Such a substrate may comprise at least 50% by mass of recycled paper.

[0065] The insert 1 further comprises a layer 2 of PL material 2 mounted on the substrate 3. In the described embodiment, the PL layer 2 is formed by screen printing an ink onto the substrate 3. In the embodiments described below, screen printing is the selected printing process. It will be appreciated that other printing processes may be used in other embodiments, and that the properties and composition of the ink may be adjusted appropriately for the printing process.

[0066] In various embodiments, the PL layer 2 may be deposited directly on the material constituting the bulk of the substrate (e.g., a surface of the polypropylene), or on an interposing layer, for example, a coating provided on the substrate. Such a coating may be used to improve the adhesion of the PL material and / or to provide a uniform background of a desired color (e.g., white). In embodiments in which a raw material of the substrate 3 is at least partially transparent, such a layer may improve the aesthetics of the insert 1 from below (i.e., from the opposite side of the substrate 3 from the PL layer 2, which is the bottom surface in the orientation shown).

[0067] An embodiment using such a coating 5 is shown in [Fig. 6]. In this example, the substrate 3 is a 300 µm thick polypropylene layer, composed of 80% recycled polypropylene. This substrate 3 is not transparent, or at least not completely transparent, and appears white. A layer 5 of MagnaPrint® AquaFlex White is then applied to the substrate 3, in this embodiment, by screen printing - other inks and / or other ink application methods may be used in other embodiments to provide a coating 5, and in still other embodiments, no such coating may be used. This coating 5 may be opaque and reflective, reflecting the incident light from the PL luminescence forward and thus improving the optical performance of the apparatus 1.A PL layer 2 is then formed on top of the coating 5, in this embodiment by building up multiple layers of a water-based ink containing a PL material. The PL material may be, for example, Sr4A114O25:Eu, Dy if a blue glow product is desired (e.g., a PL material from the Luminova® BGL range) or SrA12O4:Eu, Dy if a green glow product is desired. It is understood that any PL material that meets the requirements for use in aircraft safety signage may be used, and that these products and formulations are mentioned only as a non-limiting example (e.g., PL materials from Honeywell or another supplier may be used in place of those from Luminova®). The overall height, H, of the product 1 is about 0.75 mm, and more. precisely may be 0.75 ±0.05 mm, including the substrate 3, the coating 5 and the PL layer 2. In other embodiments, the total height, H, of the product 1 may be in the range of 0.3 mm to 5 mm.

[0068] [Fig. 1] shows an embodiment with a PL layer 2 formed from two layers 2a, 2b of the ink. [Fig.2] shows an embodiment with a PL layer 2 formed from seven layers 2a, 2b, 2c, 2d, 2e, 2f, 2g of the ink. It will be appreciated that different numbers of ink layers may be used in other embodiments. In various embodiments, the PL layer 2 may be formed from a single-layer ink deposit or multiple ink layers, for example from one to ten layers, and optionally three, four, five, six, seven or eight layers.

[0069] In the embodiments of Figures 1 and 2, the same ink is used to make each layer 2a-2g. In other embodiments, different inks may be used for different layers.

[0070] In some embodiments, multiple ink layers 2a, 2b, 2c,..., 2n, and optionally all ink layers of the final PL layer 2, may be applied sequentially, without moving or cleaning the screen of the screen printer between layer applications. Applying multiple layers without cleaning the screen may improve time efficiency and reduce ink waste, but increases the likelihood of ink drying on the screen. If the screen is not moved and the substrate is held in the same position (e.g., dried in situ when the screen is raised or returned to the same position), small depressions in the applied layer (e.g., due to imperfections in the screen or dried ink) may be found in the same location in subsequent layers, resulting in greater unevenness in the finished PL layer.Rotation of the screen and / or substrate between layer applications may be implemented between applications to minimize this effect. Additionally or alternatively, cleaning of the screen between applications (e.g., between each layer application, or less frequently, e.g., by applying three layers of ink, then cleaning the screen, then applying four more layers) may be performed to avoid this potential propagation of defects. A balance may be struck between tolerances of surface properties and process efficiency. It will be appreciated that the same principles may be applied, for example, to pad printing or reel-to-reel printing: a pad or reel may be realigned and / or cleaned between ink applications, as required.

[0071] In the described embodiments, the height of the PL layer 2, H PL, including all the ink layers that form it, is in the range of 200 to 500 pm, and optionally 250 to 450 pm, and more specifically about 350 to 400 pm. The thickness of the PL layer is 375 pm in certain embodiments. The total height of the insert 1, including the substrate 3, ranges from 500 pm (0.5 mm) to 3 mm, and more precisely around 1.5 mm, in various embodiments.

[0072] In various embodiments, each ink layer forms a portion of the PL layer 2 with a thickness of about 50 µm. It will be appreciated that a thinner, more fluid ink generally forms thinner layers than a thicker, more viscous ink, assuming other conditions are equivalent. The ink used is a water-based resin in which a PL pigment (and optionally one or more additives) is suspended; the resin can be thinned to the desired consistency by adding more water, to improve its printing performance and / or adjust the layer thickness.

[0073] In the disclosed embodiments, the PL material used in the ink is in the form of a ceramic powder, with an average particle size, d50, of 40 ± 5 pm in some embodiments, and 25 + 4 pm in other embodiments. The PL material may be, for example, SrA12O4:Eu, Dy or Sr4A114O25:Eu, Dy, although it will be appreciated that any PL material having a luminance and glow color suitable for use in aircraft emergency guidance may be used.

[0074] The PL materials tested include those listed in Table 1 below, all supplied by Luminova®:

[0075] [Table 1] Table 1 - PL Materials Formula Glow color PL d 50 d 90 Hydrophobic coating ? SrAl2O4:Eu, Dy Yellow-green 25+4pm < 60 pm Yes SrAl2O4:Eu, Dy Green 40+5 pm <115 pm Yes Sr4Ali4O25:Eu, Dy Blue-green 25±4pm < 60 pm No Sr4Ali4O25:Eu, Dy Blue-green 40+5 pm <115 pm No

[0076] The d50 and d90 values ​​in Table 1 include the coating, if any (for green and yellow-green emitting pigments). Blue emitting pigments are not coated with a hydrophobic coating because the structure is different and is not attacked by water in the same way.

[0077] In some embodiments, a retarder (e.g., glycerin-based) is also added to the ink to slow the drying of the ink, which may help prevent the ink from drying while still on a screen for screen printing.

[0078] Various commercially available water-based resins were tested for use in the inks. The resins were mixed with the photoluminescent material to form an ink containing 35% by mass resin and 60% by mass of PL material, the remaining 5% being a glycerol retarder. Variations have been tested, the most successful being 30-40% resin by mass and 50-60% PL material by mass in the wet ink (it will be appreciated that the loss of water, and possibly volatile additives, during drying will increase the % mass loading of PL material in the final layer 2).

[0079] Even with the use of a retarder, some of the resins were found to dry on the screen within 5 to 10 minutes, making printing difficult. The commercially available resins selected for further testing were narrowed down to MagnaPrint ND Base, MagnaPrint Glass Beads Reflective Clear, MagnaPrint AquaFlex V2, and Art2SilkScreen Water Based Resin. It will be appreciated that these resins are mentioned by way of non-limiting example only and that any suitable water-based resin with similar properties may be used in place thereof in other applications.

[0080] Furthermore, it will be appreciated that resins which have been found to dry too quickly for the process used in the specific method described below may be suitable for applications with shorter on-screen periods for the ink and / or may be usable with an additional retarder. Water-based resins such as Permaprint Premium Clear, Apollo Ink S34036 and Colograf Water-Based Clear Vamish, which have been tested and found to dry "too quickly", may therefore still be used in other embodiments of the invention.

[0081] Samples prepared using these inks were charged for 20 minutes by exposure to light at 250 lux, then allowed to discharge for one hour, after which the PL luminescence performance was measured (Table 2). All resins tested produced similar results (within 10%), including the resin containing glass beads which were reported to enhance light scattering (this did not appear to be beneficial). The results are shown in Table 2 below.

[0082] [Table 2] Table 2 - Luminance of test samples after charge and one hour discharge (mcd / m2) MagnaPrint ND Base Resin MagnaPrint Glass Beads Reflective Clear MagnaPrint A quaFlex V2 Art2SilkScreen Water-based Resin Luminance 32.560 33.172 33.056 33.541

[0083] Water-based resins typically comprise a suspension of one or more polymers in water - acrylic copolymers are often used. The ratio of water to the polymer component(s) affects the viscosity of the resin, with resins with higher water content being more fluid / less viscous. For example, the resin may contain from 20 to 75% polymeric components by mass of the resin, and optionally at least 50% by mass of polymeric components. The resin may contain from 8 to 60% water, optionally 10 to 18% or 15% water, and still optionally about 13% water, by mass of the resin (the commercial resin acquired may be diluted with additional water in the manufacture of the ink described herein, thereby increasing the water % of the resin - the water-based resin of the ink may therefore have a higher percentage of water than the commercial resin from which it is made. It will be appreciated that the minimum of 20% water-based resin by mass of the ink includes any water added to thin the commercial resin).In addition to water and the polymeric component(s), the resin may include one or more additives, such as one or more emulsifiers (used to make the suspension more stable), flow agents (to reduce viscosity), wetting agents (to improve surface coverage during printing, e.g., butyl acetate), and / or retarders (to slow drying / curing). A single additive may serve two or more of these roles in some embodiments—for example, a glycol may act as both an emulsifier, a flow agent, and a retarder. In general, each additive may comprise no more than 10% by mass of the ink, and optionally no more than 5% or 2.5% by mass of the ink.

[0084] Magnaprint Aquaflex V2 water-based resin was selected for the tests described below.

[0085] Paper-based substrates 3 were tested with the ink, coated papers being avoided due to the risk of the layers fusing together during the ink drying process (described below). It was found that (uncoated) papers of less than 250 g / m2 were too thin to prevent the water-based resin from seeping through and the substrate 3 warped. The 255 g / m2 paper was chosen as it was thick enough to withstand the printing process without warping, but thin enough to fit into the cavity of a standard track / slot 4 (as described in more detail below) - it will be appreciated that minimizing weight is generally preferred in aerospace applications.

[0086] Polymeric substrates 3, such as polypropylene sheets (some including 80% recycled polypropylene, with this polypropylene optionally being post-consumer recycled) and polybutylene terephthalate sheets have also been successfully tested.

[0087] For post-consumer recycled (PCR) polymer sheets, it is impossible to trace the original components of the polymer; the recycled material is known to be polypropylene (in this case), but the precise types and origins of the polypropylene are unknown. The sheet manufacturer assigns a lot number to each final sheet and traceability (to meet aerospace requirements) is ensured in the form of a certificate of conformity. This certificate must be provided for each batch and provides assurance that the delivered material matches the batch number, is manufactured to the correct dimensions, and contains the specified percentage of PCR material (e.g., 80%). Further conformance testing may be performed internally to ensure that the PCR sheets are suitable for the printing purpose, and final printed sets 1 may be subject to first article inspection against established internal standards. In this way, post-consumer recycled material can be used without violating strict aerospace traceability requirements.

[0088] The ink compositions shown below in Table 3, using Magnaprint Aquaflex V2 water-based resin as the commercial resin, were all tested, on various substrates and with between four and seven layers of ink printed to form the PL 2 layer.

[0089] The commercial resin itself was found to contain about 13% water by mass, such that an ink comprising 35% commercial resin by mass and no additional water would contain about 4.6% water by mass, and an ink comprising 26% commercial resin by mass and 13% added water would contain 16.4% water by mass. The resin was found to be fully miscible with the added water (if any), such that it was possible to uniformly dilute the commercial resin to form a less viscous water-based resin.

[0090] [Table 3] Table 3 - Ink composition Loading / Composition in % of ink mass Component Ink A Ink B Ink C Ink D Ink E Ink F PL material 60% 60% 60% 60% 52% 50% Commercial resin 35% 30% 30% 30% 26% 25% Retarder 5% 10% 3% 5% 9% 8% Added water 0% 0% 7% 5% 13% 17%

[0091] While Ink A was functional, it was thick and dried quickly on the printing screen, so the use of added water and / or more retarder was investigated. Ink B, in which a portion of the resin in Ink A's composition was replaced with retarder, was still too thick for uniform printing, as the screen was not completely flooded. Replacing most of the retarder with water (Ink C) resulted in an ink that flooded the screen well, but dried too quickly for use with the desired printing process. The amounts of water and retarder were adjusted to achieve equal masses for Ink D, but this was not enough to completely resolve this problem, as the ink still dried too quickly. Different proportions of retarder and water were therefore tested in Inks E and F, with the composition of Ink E proving superior in terms of properties after the curing process (both inks printed well on the selected substrate, a sheet of polybutylene terephthalate).

[0092] For the E-ink test, for example, sheets of polybutylene terephthalate were used to provide substrate 3. Six sheets were printed with four layers of E-ink, two sheets with five layers of E-ink, two sheets with six layers of E-ink, and ten sheets with seven layers of E-ink (each with two different PL materials in the ink).

[0093] Between layer depositions, each newly added layer is dried. Once all desired layers have been deposited, the completed PL 2 layer is baked and then fully dried. In other implementations, the resin may be UV curable, and the layer may be cured by UV light rather than baked and dried.

[0094] For the tests described, the ink remained spread on the screen printing screen for at least one hour, and typically several hours; whereas printing a single layer took about 15 to 20 seconds, the screen was kept wet with the ink until all the desired layers had been printed on all the substrates 3 to be printed. This reduces ink waste and cleaning requirements compared to cleaning the screen between each layer application, but it will be appreciated that the use of retarder could be reduced if the ink was kept on the screen for a shorter time - this can be done in other implementations. Ink E showed no breakdown of the screen emulsion even when the ink was left on the screen for several hours, which facilitated this printing process.

[0095] In the described tests, after each layer deposition, the resulting product was placed in a drying tunnel for about two minutes - the air around the deposited material, circulated within the tunnel by means of a fan or negative pressure extraction system, reaches temperatures of about 100°C. A conveyor was used to move the product through the tunnel for a period of about two minutes during these tests, although it will be appreciated that any suitable drying process could be used in other embodiments. Specifically, during the described tests, the temperature was 100°C at the heating elements, and closer to 90°C at the sheet (substrate and printed material). The drying temperature was kept low enough not to melt or distort the substrate 3. The drying process is used to make the deposited ink layer dry to the touch, and therefore suitable for printing an additional layer (and moving, e.g., tilting, without the ink running), but water and / or a retarder (and optionally other additives) may still be present. After the final ink layer had dried, the completed insert 1 was then baked, following the recommendations in the data sheet of the commercial resin used (in this case, a bake process with a residence time of 20 minutes at 160 °C, in air) and the resulting PL layer 2 was then allowed to cool and dry. This higher temperature bake may serve to remove some or all of the remaining liquid within PL layer 2.It will be appreciated that the linear temperature increase and decrease periods of the baking process can be significantly longer than the residence time at the maximum temperature, thus allowing a high temperature to be achieved over a longer period, thus promoting evaporation. In the tests described, the total time in the oven was one hour and fifteen minutes, including twenty minutes of residence time at the maximum temperature. The baking process in these tests is simply a longer, higher temperature drying process to remove more moisture from the layer.

[0096] Inserts 1 printed with four layers of ink had an average thickness of 200 qm, for five layers of ink the average thickness was 250 qm, for six layers of ink the average thickness was 300 qm, and for seven layers of ink the average thickness was 350 qm, demonstrating a typical single layer thickness of about 50 qm.

[0097] A thickness of approximately 375 qm ±50 qm may be preferred for the PL 2 layer.

[0098] [Fig.4] illustrates a method 400 for manufacturing an emergency guidance assembly 100 for aircraft in a more generalized form.

[0099] The method 400 comprises the formation 401 of a photoluminescent layer 2 on a substrate 3 by printing an ink onto the substrate 3. The method 400 may comprise the formation 401 of the photoluminescent layer 2 on the substrate 3 by screen printing the ink onto the substrate 3.

[0100] The process of forming 401 the PL 2 layer comprises acquiring an ink suitable for forming the PL 2 layer. As described above, such an ink comprises: • a water-based resin, wherein the water-based resin forms at least 20%, and optionally at least 25%, of the ink by mass; and • a photoluminescent material, wherein the photoluminescent material forms at least 20% by mass of the ink.

[0101] Generally, at least 30%, 40%, 45% or 50%, and optionally about 60%, of the ink by mass is the photoluminescent material.

[0102] Different loadings of PL material may be suitable for different aircraft emergency guidance assemblies 100. For example, in embodiments in which the top / presenting surface of the PL layer 2 is arranged so as not to be obstructed during use (generally covered only with a transparent or highly translucent colorless protective layer), a loading of only 25-35% of the PL material in the ink may provide sufficient luminance to meet aerospace safety regulations.In contrast, in embodiments in which the PL layer 2 itself is to be printed (e.g., to show a pattern or symbol, which may be opaque or translucent (e.g., partially transparent)), covered with a colored film or a film having a pattern or symbol printed thereon, or contained within a colored housing, or a housing having a pattern or symbol printed thereon, a higher loading of the PL material may be preferred to ensure sufficient luminance—for example, a loading of 45 to 75% by mass of the ink, and optionally 50 to 70%, may be used.

[0103] Generally, at least 30%, and preferably at least 35%, of the ink by mass is the water-based resin, which may be a commercial resin used as is, or with water added to make it more fluid.

[0104] The remaining mass may consist of a retarder and any other desired additive or pigment.

[0105] Due to the loss of water and / or retarder from the PL layer 2 during the drying and baking process (which may be referred to as resin curing), the mass of the ready-to-use layer 2 is less than that of the freshly printed layer 2. For example, an ink such as Ink E with a PL pigment loading of 52% by mass may form a cured layer with a PL pigment loading of 66% by mass, due to the loss of the more volatile components.

[0106] The method 400 (and, more specifically, the formation 401 of the PL layer 2) comprises the deposition 402 of an ink layer on a substrate 3, by screen printing in this embodiment, and then the drying 404 of the deposited layer. These two steps 402, 404 are repeated until a desired number of layers has been built up - for example, two, three, four, seven or eight times. The desired number of layers may depend on the thickness of each individual ink layer, and therefore on the viscosity of the ink. A total thickness of the PL layer 2 of about 375 μm may be desired.

[0107] The dynamic viscosity of the ink was measured using a vertical falling ball viscometer. In particular, the density of the ink, pink, was calculated and A 30 mm diameter graduated cylinder was filled with ink to a level of 2 cm from the top of the cylinder. Markers were applied to the cylinder 2 cm below the surface of the liquid and 2 cm from the bottom of the cylinder, and the distance between the two markers was measured.

[0108] A metal ball of radius r = 4.4 mm and density p ball = 7778 kg / m3 was then placed just above or in contact with the surface of the liquid and dropped. The time taken for the ball to fall from the first mark to the second was recorded, which allowed the average speed v of the ball in the liquid between the marks to be calculated.

[0109] The dynamic viscosity was then calculated using the following equation:

[0110] 2gr^p -p} Viscosity = ----—■—-

[0111] where g is the acceleration due to gravity.

[0112] The viscosity of the above-mentioned ink E was measured at 333 Pa.s by this method (averaged over three measurements). More generally, the inks may be made with viscosities between 300 Pa.s and 400 Pa.s, and more specifically between 310 Pa.s and 350 Pa.s. It will be appreciated that the viscosities may be adjusted at will in various embodiments depending on the desired overall layer thickness and / or the desired number of screen deposits (or otherwise individual printed ink layers) to form the layer.

[0113] In addition to measuring the viscosity of the ink, the light transmission of the resin was also tested before combining it with the PL material to form the ink. Since the typical number of ink layers for the products tested was seven, seven layers of resin alone were therefore deposited on a transparent polycarbonate substrate and exposed to 250 lux light. Each layer of resin alone was found to be about 10 µm thick, for a total thickness of about 70 µm. This thickness is of course less than that of the PL ink samples due to the absence of PL material, but it provides a measure of the light blockage due to the resin itself. This thickness is representative of the total summed thicknesses of the resin itself in the final PL layer 2, around the PL material. The substrate was previously tested and found to allow 232 lux of the 250 lux incident light to pass through.With the application of the wet resin, this transmission dropped to 194 Lux. However, after the drying and curing process described below, it increased to 226 Lux, a drop of only 6 Lux (2%) more than that caused by the substrate. The resin can therefore be described as having a transmittance of approximately 98%, for the resin thickness typically used in the PL 2 layer.

[0114] Once the final drying step 404 is complete, the PL layer 2 can then be baked 406, or otherwise hardened. The conditions used generally depend on the resin used, the substrate 3 generally being chosen to be able to undergo this treatment without modification.

[0115] After curing, the final PL 2 layer may comprise at least 60% by mass of PL material (and optionally at least 65% by mass of PL material), and at least 30% by mass of cured resin.

[0116] Surface measurements were carried out on the cured PL 2 layer.

[0117] A roughness of the upper surface (or presentation surface, i.e. the surface furthest from the substrate 3) of the photoluminescent layer 2 was found to be similar to that of P320 grit sandpaper (46.2 ±1.5 pm). In contrast, PL layers made with the same PL material but a traditional organic solvent-based resin were found to be smoother, with surface roughnesses closer to that of P500 grit sandpaper (30.2 ±1.5 pm). It will be appreciated that the precise roughness will depend at least in part on the particle size distribution of the PL material used to make the ink, but that, for the same PL material, the water-based ink as described herein was found to provide a rougher surface finish than previously used organic solvent-based inks.

[0118] Similarly, the top surface of photoluminescent layer 2 was measured to be less bright than that of a counterpart made with a traditional organic solvent-based resin. The brightness was measured at an 85° angle as about 0.1 brightness units (BU), compared to measurements of 1.4 BU for the organic solvent-based counterpart using the same PL material.

[0119] The inventors appreciated that the smooth texture (and therefore also the gloss) could be increased by slowing down the drying process, for example by drying each ink layer, or at least the topmost ink layer, at a lower temperature for a longer time, thus allowing better settling and sinking of the PL material within the ink. However, the higher roughness and lower gloss were not found to be a significant disadvantage in the tests, so the faster production speed of the faster drying was preferred.

[0120] The cured component 1 is then enclosed 408 within a protective housing 4, or a cover 4a may be connected 408 to the substrate 3, thereby covering the PL layer 2 (the substrate may be considered part of a protective housing in such embodiments).

[0121] To complete the aircraft emergency guidance assembly 100, the photoluminescent (PL) layer 2 and the substrate 3, which may be collectively referred to as an "insert", of certain embodiments may therefore be inserted into a housing 4. The housing 4 is arranged to surround and protect the PL layer 2. A portion of the housing 4 covers the PL layer 2 and may be referred to as the cover 4a. The housing 4 may be made of a polymeric material, such as polycarbonate, and at least the cover 4a is designed to be translucent, or even transparent, in order to allow the transmission of light.

[0122] For use in the aerospace sector, all components must be fully traceable in terms of raw material. Due to the mixed nature of recycled materials, it is not usually possible to trace their composition. In order to meet the aerospace industry's requirements for material traceability, the recycled polycarbonate (or other polymer) in housing 4 is product manufacturing waste (industrial waste that would normally be discarded / sent to landfill) as opposed to post-consumer waste; batch numbering and recycled polymer recording can therefore be implemented, with each batch of re-shredded material being assigned its own part and batch numbers. Due to the nature of the re-shredded material, it is often not possible to determine its exact composition.However, all possible grades of polycarbonate (or other polymer, if applicable) that could be included can be noted for each batch, and the lowest-performing grade for a given aerospace requirement can be used as the limiting case for testing. For example, in a batch of recycled polycarbonate, Calibre 6303 / 3 may be the least flame-retardant polycarbonate that could be included in the reshredded material. Therefore, a sample composed of 50% Makrolon® 6717 and 50% Calibre 6303 / 3 reshredded polymer can be used as the test sample for flammability requirements. A different sample can be used for testing another characteristic for which Calibre 6303 / 3 is not the lowest.The approach described here therefore makes it possible to manufacture an emergency guidance assembly 100 for aircraft including recycled materials with complete traceability. In particular, recycled polymers may be used in the substrate 3 and / or the housing 4.

[0123] In the embodiment shown in [Fig.3A], the housing 4 is a single-piece housing 4, with the cover 4a being integral with the rest of the housing 4 - the housing 4 effectively forms a sleeve surrounding the insert 1. The entire housing 4 is generally made of the same material in such embodiments. In other embodiments, such as that shown in [Fig.3B], the housing 4 comprises multiple parts, for example two separable parts: • (i) the cover 4a arranged to be located above the layer PL 2; and • (ii) a base 4b arranged to be located below the PL layer 2 (in certain embodiments, this base 4b can be provided by the substrate 3).

[0124] It will be appreciated that the terms "above" and "below" are defined herein with respect to a typical orientation of a ground path sign in use, where the upper face of the guidance assembly 100 is the face intended to be seen by users. The cover 4a may therefore be described as providing a display surface, regardless of orientation, with the base 4b being on the side of the PL 2 layer remote from the cover 4a, and optionally joining the cover 4a at the edges of the PL 2 layer.

[0125] In the second embodiment, shown in [Fig.3B], the sides of the PL layer 2 are enclosed by portions of the base 4b. In other embodiments, the cover 4a may be curved downward to protect the sides, and / or separate side pieces of the housing 4 may be provided. In still other embodiments, the cover 4a itself may be split into several pieces. In still other embodiments, the substrate 3 itself may be part of the housing 4 for the PL layer 2. For example, the substrate 3 may extend beyond the PL layer 2 and may have a cover 4a connected thereto. The substrate may take the place of a base 4b of the housing 4.

[0126] In embodiments in which the housing 4 comprises multiple parts, one or more of the parts may be made of different materials. For example, in some embodiments, the percentage of recycled polymer and / or the loading of the biodegradable additive may be higher in the substrate 3 and / or the base 4b (and optionally in any side piece) than in the cover 4a. For example, one or more parts of the housing 4 other than the cover 4a may comprise at least 50%, 55%, 60%, 65%, 70% or 75% by mass of recycled polymer, and may optionally be made of 80% or even 100% recycled polymer (i.e., entirely recycled polymer, except for small percentages of possible additives).The optical property requirements are generally more stringent for the cover 4a than for the base 4b (and any side pieces of the housing 4), which allows the use of a less transparent material for the base.

[0127] A loading of a biodegradable additive in the base 4b and / or the substrate 3 (and optionally in any side piece of the housing 4) may be much higher than that in the cover 4a, for example by a factor of ten, twenty or fifty. For example, the loading of the biodegradable additive in the base 4b may be about 1%, 1.5%, 2%, or 2.5% by mass of the polymeric part 4b.

[0128] In the lid 4a, the loading of the biodegradable additive is generally kept lower to ensure sufficient light transmission / minimal light blockage of the lid material, thereby allowing the PL layer 2 to be charged by incident light without hindrance, and allowing the PL glow of the material 2 to pass through the coating 4a without hindrance. In particular, in various embodiments, the light transmission through the polymeric lid 4a is at least 80%, and optionally at least 85%, of incident light (which may be light in the daylight spectrum).

[0129] In the examples described above, the selected biodegradable additive is a BioSphere 201 grade biodegradable additive, and more specifically BioSphere 201 J biodegradable additive. In other implementations, a different biodegradable additive may be used, for example, one or more of the products available from EcoPure®. It will be appreciated that the choice of additive may depend on the particular polymer(s) of the housing 4, among other factors, and that any suitable additive may be used provided that compliance with applicable aerospace requirements is assured.

[0130] The loading of the biodegradable additive in the housing 4, or at least in the cover 4a, is 0.05% by mass in some embodiments, and may be 0.05 ± 0.0025% by mass of biodegradable additive. In other embodiments, a loading of at least 0.02% and at most 0.20%, and optionally at most 0.12%, may be used, the loading optionally being in the range of 0.03% to 0.10% or 0.04% to 0.09%. A trade-off between biodegradation rate and light transmission of the material may be considered when determining the loading. Higher loading of the biodegradable additive (or "bio-additive," for brevity) may be possible for the same light transmission when the percentage of virgin polymer is higher (because the polymeric material itself may be more transparent, thus allowing for greater opalescence due to the additive while still meeting optical performance targets).The partial light blocking due to the bio-additive also advantageously provides some frosting which can mask cosmetic imperfections due to the use of recycled materials.

[0131] It will be appreciated that the base of the assembly 100 - i.e., the underside of the housing 4 in the embodiment shown in Figures 3A and 3B - may be adapted to be lashed to the floor of an aircraft cabin 20 in use. The base of the assembly 100 may be lashed to or mounted on the floor by any suitable conventional means.

[0132] In embodiments in which the aircraft emergency guidance assembly 100 is used as ground path signaling, an underside of the housing 4 (e.g., the base 4b or the substrate 3) is thus arranged to be secured to the floor of an aircraft cabin 20. Light transmission through the base 4b or the substrate 3 may therefore be unimportant - an opalescent, or even opaque, material may therefore be used for the base 4b when the base 4b is a separate part of the cover 4a (although it is generally firmly attached thereto, either directly or via interposing lateral portions of the housing 4), and for the substrate 3. Even in embodiments in which the base and the cover are formed integrally to provide a one-piece housing, the composition of the materials may vary between the base and the cover, for example by careful coextrusion of two or more materials, or by any suitable technique known in the art.

[0133] In many embodiments, the assembly 100 is generally adapted to be connected to another assembly 100 to form an elongated track adapted to be installed on the floor of an aircraft cabin 20 and to extend along an aisle 21 of the aircraft cabin toward an emergency exit.

[0134] In various embodiments, a lower surface of the housing 4 (e.g., a side of the base 4b furthest from the lid 4a in multi-part housings, or an underside of the substrate 3) has a printed image or pattern, e.g., to indicate the product name, type, size, batch number, and / or other details. The base 4b / lower part of a one-piece housing 4 / substrate 3 may be made partially or entirely opaque by such printing in some of these embodiments. Particularly in embodiments in which the housing 4 is one-piece, the entire surface of the housing 4 may therefore be arranged to be suitable for use as a printing substrate.

[0135] In some embodiments, particularly in embodiments with sleeve-like housings 4, the longitudinally extending layer of photoluminescent material 2 (usually together with its substrate 3) may be slid out of the housing 4 - the combination of PL layer 2 and substrate 3 of these embodiments may also be slid in during manufacture of the assembly 100, and may be described as an "insert". The "insert" 1 and the "sleeve" 4 may therefore be easily separated for recycling or reuse.It will be appreciated that one or both ends of the assembly 100 may be hermetically sealed before use (optionally sealed or sealed to an adjacent assembly so as to form a longer track, optionally with an adhesive - which may be cured - or with localized melting of the polymeric housing 4), and that all such sealed ends may be cut off before sliding the insert 1 out.

[0136] In embodiments with other housing designs 4, assembly and disassembly approaches may vary - for example, a hood-like cover 4a may be lifted from a base 4b (optionally after dissolving or cutting an adhesive or other seal holding one part to the other) and the PL material 2 (optionally with its substrate 3) can be lifted or tilted once the housing 4 has been opened.

[0137] In various implementations, as noted above, the assembly 100 extends longitudinally (being elongated) and may be adapted to be connected to another assembly to form a track 26 which may be installed on the floor of an aircraft cabin 20 and extend along an aisle 21 of the cabin.

[0138] [Fig.5] is a schematic illustration of an aircraft 22 having an aircraft cabin 20 and a number of assemblies 1 connected together to form a track 26 extending along an aisle 21 of the cabin and arranged to guide a passenger from a seat to one or more emergency exits 28. The track 26 may guide passengers around or past one or more interior walls or partitions 24.

[0139] As illustrated in [Fig.5], the assembly 100 is intended to be used in a cabin 20 of an aircraft 22. The assembly 100 may be adapted to be secured to the floor of the cabin 20, for example along an aisle 22 and / or between rows of seats in exit rows.

[0140] An assembly 100 according to the invention has been found to be robust and durable. The rigorously tested assembly 100 has been found to meet each of the stringent performance requirements for an aircraft cabin emergency exit indicator, even though various features—particularly the use of a water-based resin rather than more traditional organic solvent-based resins, and, where appropriate, the use of a biodegradable additive, the use of recycled materials, and / or the use of mixed polymeric materials to form the substrate and / or housing—go against long-standing prejudices in the art.

[0141] It has been found that the use of materials as described herein reduces the use of organic solvents and makes it possible to considerably reduce the amount of virgin material required, and therefore to reduce the environmental impact of the assembly. In addition, the use of a biodegradable additive makes the polymer used for the substrate 3 and / or the housing 4 biodegradable, which reduces the environmental impact at the end of life of the assembly 100.

[0142] The upper surface 6 of the assembly 100 may be used to display one or more patterns or images, for aesthetic and / or safety reasons - for example, one or more arrows indicating an exit direction, and / or a pattern to match or complement an aircraft carpet or other floor covering may be provided. The housing 4 may therefore be used as a substrate onto which such patterns or images may be printed. Alternatively or in addition, an upper surface of the PL layer itself may be printed to form a desired pattern or symbol (optionally with opaque ink), and / or a film may be inserted between the PL layer and a bottom side of the cover 4a, and this film may be a colored or colorless film (provided that it is not opaque, at least not over its entire surface), and may be patterned or printed thereon.

[0143] The ink using a water-based resin as described herein has been found to be suitable for print deposition, and the resulting assembly 1 has been found to comply with flammability requirements, luminance requirements (in particular, CS25 and CS23 standards for brightness requirements), temperature range tolerances, and pressure range tolerances for aircraft cabin use, while reducing the use of organic solvents, and thereby improving performance relative to environmental requirement standards such as DO-160). Thus, embodiments of the invention provide improved durability of aircraft emergency guidance assemblies while maintaining each of the required and desirable properties.

[0144] It will be appreciated that the embodiments described in detail herein are given by way of illustrative example only and are not intended to be limiting.

Claims

Claims

1. A method of manufacturing an emergency guidance assembly for aircraft comprising forming a photoluminescent layer on a substrate by printing an ink onto the substrate, the ink comprising: - - a water-based resin, wherein the water-based resin forms at least 20% by mass of the ink; and - - a photoluminescent material having a median particle size, d50, in the range of 10 pm to 100 pm, wherein the photoluminescent material forms at least 20% by mass of the ink.

2. The method of claim 1, wherein the ink comprises at least 30% by mass of photoluminescent material, and optionally comprises 60% by mass of photoluminescent material.

3. A method according to claim 1 or claim 2, wherein the substrate is a polymeric substrate optionally comprising at least 40% by mass of recycled polymer.

4. A method according to any preceding claim, wherein the method is arranged to form a photoluminescent layer having a thickness in the range of 200 to 450 pm, and optionally in the range of 200 to 360 pm, or about 375 pm.

5. A method according to any preceding claim, wherein at least one of the following applies: - (i) the method comprises printing a plurality of layers of the same ink onto the substrate so as to constitute a resulting photoluminescent layer having a thickness in the range of 200 to 450 pm; and - (ii) the formation of the photoluminescent layer is completed within 36 hours, and optionally within 12 hours, following a first printing of the ink onto the substrate.

6. A method according to any preceding claim, wherein at least one of the following applies: - (i) the photoluminescent material has a d50 of between 15 pm and 50 pm; and - (ii) the photoluminescent material has a d90 less than or equal to three times the d50.

7. A method according to any preceding claim, wherein at least one of the following applies: - (i) the ink comprises at least 5% by mass of a glycerin-based drying retarder; and - (ii) the ink comprises at least 5% by mass of water, and optionally at least 10%.

8. A method according to any preceding claim, further comprising, after the printing of the ink is complete, baking the substrate and the printed material at a temperature of at least 100°C, and optionally 145°C, and wherein optionally the baking comprises a residence time of between two minutes and two hours, and optionally 20 minutes, at the selected temperature.

9. A method according to any preceding claim, wherein multiple layers of ink with a loading of at least 20% by mass of photoluminescent material are deposited on the substrate, the method further comprising drying each layer before applying the next layer, the drying optionally being carried out for a period of less than 20 minutes per layer.

10. An aircraft emergency guidance assembly arranged to be mounted in an aircraft cabin, wherein the assembly comprises: - a longitudinally extending photoluminescent layer; - a substrate supporting the photoluminescent layer; and - a housing arranged to protect the photoluminescent layer, and wherein the photoluminescent layer is comprised of a water-based resin having embedded therein a photoluminescent material having a median particle size, d50, ranging from 10 pm to 100 pm.

11. An aircraft emergency guidance assembly according to claim 10, wherein at least one of the following applies: - (i) the photoluminescent layer comprises at least 20% by mass of photoluminescent material, the photoluminescent material being embedded within the cured resin; - (ii) the photoluminescent layer comprises at least 30% by mass of photoluminescent material, and wherein, optionally, the photoluminescent layer comprises between 55% and 75% by mass of photoluminescent material; and - (iii) the longitudinally extending photoluminescent layer and the substrate are together removable by sliding the housing.

12. An aircraft emergency guidance assembly according to claim 10 or claim 11, wherein the photoluminescent layer is formed from at least two individually deposited and dried layers, the plurality of layers together constituting the total thickness of the photoluminescent layer, the photoluminescent layer optionally comprising six or seven such layers.

13. An aircraft emergency guidance assembly according to any one of claims 10 to 13, wherein the housing is polymeric and comprises at least 20% by mass of recycled polymer, and wherein optionally the housing comprises a biodegradable additive, and wherein optionally the loading of the biodegradable additive is 0.05% by mass.

14. An aircraft having an aircraft cabin comprising an aircraft emergency guidance assembly according to any one of claims 10 to 13.

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