Patent Description:
Large numbers of emissions control devices comprising coated monolithic substrates are manufactured each year. One of the principal uses of such devices is for the treatment of exhaust gases, such as the exhaust gases produced by a power plant or by an internal combustion engine, particularly a vehicular internal combustion engine. The monolithic substrate contains a plurality of channels that bring the exhaust gas into contact with a coating on the channel walls within the substrate. This coating may trap, oxidise and/or reduce constituents of the exhaust gas that are hazardous to human health or that are environmentally unfriendly. The monolithic substrate may also be a filter substrate, which can remove soot (i.e. particulate matter), such as the soot produced by internal combustion engines.

A substrate for purification of exhaust gases may typically comprise a monolithic substrate that is provided with passages for the through-flow of exhaust gases. The substrate may be provided with a coating, which may be a catalytic coating. The coating may be applied to the substrate as a washcoat that is passed through the passages of the substrate. Various methods for applying the coating to a substrate are known. One such method involves applying washcoat to a first face of the substrate (e.g. an upper face) and subjecting an opposite, second face (e.g. a lower face) of the substrate to at least a partial vacuum to achieve movement of the washcoat through the passages. After coating the substrate may be dried and calcined.

The substrate may be configured as a flow-through substrate wherein each passage is open at both the first and second faces of the substrate and the passage extends through the whole length of the substrate. Consequently, exhaust gases entering through a first face of the substrate into a passage pass through the substrate within the same passage until the exhaust gases exit a second face of the substrate. Alternatively, the substrate may be configured as a filter substrate, in which some passages are plugged at a first face of the substrate and other passages are plugged at a second face of the substrate. In such a configuration, exhaust gases entering through a first face of the substrate into a first passage flow along that first passage part-way along the substrate and then pass through a filtering wall of the substrate into a second passage. The exhaust gases then pass along said second passage and out of a second face of the substrate. Such an arrangement has become known in the art as a wall-flow filter.

The coated filter substrate or product may, for example, be a filter substrate comprising an oxidation catalyst (e.g. a catalysed soot filter [CSF]), a selective catalytic reduction (SCR) catalyst (e.g. the product may then be called a selective catalytic reduction filter [SCRF] catalyst), a NOx adsorber composition (e.g. the product may then be called a lean NOx trap filter [LNTF]), a three-way catalyst composition (e.g. the product may then be called a gasoline particulate filter [GPF]), an ammonia slip catalyst [ASC] or a combination of two or more thereof (e.g. a filter substrate comprising a selective catalytic reduction (SCR) catalyst and an ammonia slip catalyst [ASC]).

The substrate may be coated in a single dose wherein washcoat may be applied to the substrate in a single step with the substrate remaining in a single orientation. Alternatively, the substrate may be coated in two doses. For example, in a first dose the substrate is in a first orientation with a first face uppermost and a second face is lowermost. A coating is applied to the first face and coats a portion of the length of the substrate. The substrate is then inverted so that the second face is uppermost. A coating is then applied to the second face in order to coat the portion of the substrate that was uncoated by the first dose. Beneficially, a two-dose process may allow different coatings to be applied to each end of the substrate.

To provide best performance of the substrate it may be beneficial to ensure that the substrate is fully coated so that the surface area of the coated substrate is maximised. However, it is also beneficial to ensure that portions of the substrate are not coated by more than one layer of washcoat (for example, in a two-dose process) as this can lead to increased pressure loss within the substrate. It is therefore desirable that the process of applying the washcoat to substrates achieves reliable and controllable coating profiles of the substrates.

One of the challenges in manufacturing coated filter substrates relates to the application of a uniform coating onto the walls of the channels of the filter substrate. This is because each channel of a filter substrate generally has only one open end (the other end being closed, usually by plugging), which is problematic for the application of a washcoat. It can be difficult to apply a washcoat to the channels of a filter substrate to obtain a desired coating depth, an even coating depth across all of the channels and a uniform washcoat distribution within each channel.

<CIT> describes a general method for coating a monolithic support. A method of coating a flow-through honeycomb substrate is exemplified in <CIT>. This method is typically used to apply a washcoat having a relatively high viscosity.

One method that shows good results for uniformly applying washcoat onto the walls of a filter substrate is described in <CIT>. <CIT> describes a method of coating a honeycomb monolith substrate comprising a plurality of channels with a liquid comprising a catalyst component, which method comprising the steps of: (i) holding a honeycomb monolith substrate substantially vertically; (ii) introducing a pre-determined volume of the liquid into the substrate via open ends of the channels at a lower end of the substrate; (iii) sealingly retaining the introduced liquid within the substrate; (iv) inverting the substrate containing the retained liquid; and (v) applying a vacuum to open ends of the channels of the substrate at the inverted, lower end of the substrate to draw the liquid along the channels of the substrate.

Another method for the application of a washcoat onto the walls of a filter substrate is described in <CIT>. The method utilises a "showerhead" comprising a plurality of apertures arranged to deposit the liquid evenly onto the upper end face of the filter substrate.

For some products there may be a desire to use washcoats for filter substrates which have a relatively low viscosity and minimal rheology properties. The present applicant has found that this can cause problems with achieving reliable and controllable coating profiles of the substrates because the rheology of the washcoat means that it is difficult to apply the washcoat uniformly to the upper face of the substrate. In particular, application of the washcoat to the upper face of the substrate may be by use of a washcoat showerhead which comprises a showerhead plate provided with an array of nozzle apertures. With low viscosity washcoats it has been found to be difficult to ensure a uniform discharge of the washcoat from the showerhead plate. This can lead to problems of uncoated portions of the substrate after coating, where too little washcoat is applied to a region of the substrate, or alternatively 'pull-through', where excess substrate is drawn out of the lower face of the substrate, where too much washcoat is applied to a region of the substrate.

<CIT> teaches a nozzle configured to discharge a fluid containing a raw material of a catalytic layer to a substrate, the nozzle being provided with discharge ports for discharging the fluid towards a first end face of the substrate. The nozzle may be provided with a deflector in the form of a mesh or perforated plate which causes a change in the flow of the fluid within the nozzle.

In a first aspect the present disclosure provides a washcoat showerhead for depositing a liquid washcoat onto a face of a substrate located below the washcoat showerhead, the washcoat showerhead comprising:.

Advantageously, the washcoat showerhead of the present disclosure comprising such a baffle may result in more even coating of the substrate and, in particular, may produce more reliable and controllable coating profiles. Use of the washcoat showerhead may thus allow for a maximisation of the surface area of the substrate that is coated while minimising the degree of overlapping of coatings and/or pull-through of the washcoat.

The baffle may comprise a plurality of arms, e.g. four arms, extending from the impermeable central body, the plurality of (e.g. four) arms defining a plurality (e.g. four) flow apertures circumferentially arranged around the impermeable central body; and optionally the plurality of (e.g. four) arms may be equispaced circumferentially around the impermeable central body. The plurality of arms may extend radially from the impermeable central body; and optionally wherein a width of each of the plurality of arms may increase from a location proximate to the impermeable central body to a location distal the impermeable central body. Four arms may preferably be provided.

The impermeable central body may be circular in shape in plan view. The impermeable central body may have a diameter greater than a diameter of the inlet to the housing; and optionally wherein a central longitudinal axis of the inlet and a central axis of the impermeable central body may be coincident. The impermeable central body may have a diameter of <NUM> to <NUM>; preferably <NUM> to <NUM>; more preferably selected to be <NUM>, <NUM> or <NUM>.

The inlet of the housing may have an internal diameter of up to <NUM> (<NUM> inch).

An upper face of the impermeable central body facing the inlet may comprise a protrusion; preferably wherein the protrusion is a conical, or part-conical surface.

Advantageously, the provision of a protrusion on the upper face has been found to minimise turbulence within the washcoat showerhead as the washcoat is directed to the periphery of the showerhead plate.

The baffle may be mounted to at least one of the housing and the showerhead plate; preferably wherein the baffle is mounted to only the housing. The baffle may be mounted to mounting points of the housing which surround, but do not impinge on, the inlet of the housing. The baffle may be mounted by fixatives extending between the plurality of arms and at least one of the housing and the showerhead plate. The fixatives may extend from a distal end of each of the plurality of arms. The fixatives may be located on a pitch circle diameter of <NUM> to <NUM>; preferably <NUM>, and may be centred on a central axis of the impermeable central body. Preferably the fixatives are located outside the diameter of the impermeable central body.

Advantageously, it has been found that positioning the fixatives outside the diameter of the impermeable central body may minimise interference of the fixatives with the incoming washcoat resulting in a more even distribution of washcoat onto the upper face of the substrate.

The showerhead cavity may have a depth of <NUM> to <NUM>; preferably <NUM> to <NUM>.

The impermeable central body may be spaced from the showerhead plate by a gap of <NUM> to <NUM>.

Advantageously, it has been found that locating the impermeable central body at a spacing of <NUM> to <NUM> from the showerhead plate may improve washcoat circulation within the showerhead cavity, and in particular enable enough washcoat to flow back to the centre of the upper face of the showerhead plate to achieve a more even distribution of washcoat onto the upper face of the substrate.

In a second aspect, the present disclosure provides a baffle for forming a part of a washcoat showerhead as described above, wherein the baffle comprises an impermeable central body and a plurality of arms extending from the impermeable central body, the plurality of arms defining a plurality of flow apertures circumferentially arranged around the impermeable central body.

The plurality of arms may extend radially from the impermeable central body; and/or a width of each of the plurality of arms may increase from a location proximate to the impermeable central body to a location distal the impermeable central body; and/or the impermeable central body may be circular in shape in plan view; and/or the impermeable central body may have a diameter of <NUM> to <NUM>; preferably <NUM> to <NUM>; more preferably selected to be <NUM>, <NUM> or <NUM>; and/or an upper face of the impermeable central body may comprise a protrusion; preferably wherein the protrusion is a conical, or part-conical surface; and/or the plurality of arms may be provided with mounting points for connecting fixatives; and/or the mounting points may be located at a distal end of each of the plurality of arms; and/or the mounting points may be located on a pitch circle diameter of <NUM> to <NUM>; preferably <NUM>, and may be centred on a central axis of the impermeable central body.

In a third aspect, the present disclosure provides a substrate coating apparatus comprising the washcoat showerhead as described above.

In a fourth aspect the present disclosure provides a method of coating a substrate with a liquid washcoat using a washcoat showerhead;.

Various substrates are known including flow-through substrates (e.g. monolithic flow-through substrates) and filter substrates (e.g. monolithic filter substrates), beads and ceramic foams. However, preferably the substrate is selected from a flow-through substrate or a filter substrate (for example, a wall-flow filter substrate).

A flow-through substrate generally comprises a plurality of channels, typically extending therethrough, wherein each channel is open at both ends (i.e. an open end at the inlet and an open end at the outlet). The channels are formed between a plurality of walls. The walls generally comprise a non-porous material. A flow-through monolithic substrate comprising an array of parallel channels extending therethrough is also referred to herein as a honeycomb monolithic substrate.

By contrast, a filter substrate comprises a plurality of channels, wherein each channel has an open end and a closed end (e.g. a blocked or plugged end). Each channel is typically separated from an adjacent or neighbouring channel by a wall. The wall comprises, or consists essentially of, a porous material. Such porous materials are well known in the art.

In general, a filter substrate comprises a plurality of inlet channels and a plurality of outlet channels. Each inlet channel has an open end at a first face of the substrate and a closed (e.g. blocked or plugged) end at an opposite second face of the substrate (i.e. the second end is the opposite end to the first end), and each outlet channel has a closed (e.g. blocked or plugged) end at the first face of the substrate and an open end at the opposite second face of the substrate.

In a filter substrate, each channel having an open end at a first face of the substrate and a closed end at a second (i.e. opposite) face of the substrate is typically adjacent to a channel having a closed end at the first face of the substrate and an open end at the second (i.e. opposite) face of the substrate. Fluid communication between the channels is via a wall (e.g. through the porous material) of the substrate.

The wall typically has a thickness of <NUM> to <NUM> inches (<NUM> to <NUM>), such as <NUM> to <NUM> inches (<NUM> to <NUM>), particularly <NUM> to <NUM> inches (<NUM> to <NUM>).

Typically, the channels of a filter substrate have alternately closed (e.g. blocked or plugged) and open ends. Thus, each inlet channel may be adjacent to an outlet channel, and each outlet channel may be adjacent to an inlet channel. When viewed from either end of the filter substrate, the channels may have the appearance of a chessboard.

However, the filter substrate may have an inlet channel (i.e. a "first" inlet channel) that is adjacent to another inlet channel (i.e. a "second" inlet channel) and optionally to an outlet channel, such as the "first" outlet channel and/or the "second" outlet channel. The filter substrate may have an outlet channel (i.e. a "first" outlet channel) that is adjacent to another outlet channel (i.e. a "second "outlet" channel) and optionally to an inlet channel, such as the "first" inlet channel and/or the "second" inlet channel.

The filter substrate may have from <NUM> to <NUM> cells (or "channels") per square inch ("cpsi"), particularly <NUM> to <NUM> cpsi.

A washcoat comprises a liquid and typically a catalyst component. The liquid may be a solution or a suspension. The suspension may be a colloidal suspension, such as a sol, or a non-colloidal suspension. When the liquid is a solution or a suspension, then it may be an aqueous solution or an aqueous suspension. Typically, the liquid is a suspension, particularly an aqueous suspension.

Typically, the liquid comprises a catalyst component. The expression "catalyst component" encompasses any component that may be included in a washcoat formulation that contributes to the activity of the resulting emissions control device, such as a platinum group metal (PGM), a support material (e.g. refractory oxide) or a zeolite. It is to be understood that the term "catalyst component" does not require that the component itself has catalytic activity in the strict sense of the meaning of the term "catalyst" (e.g. increasing the rate of reaction). For example, the catalyst component can refer to a material that is able to store or absorb NOx or a hydrocarbon. Liquids (e.g. washcoats) comprising a catalyst component are known to those skilled in the art. The catalyst component(s) included in the liquid will depend on the product that is to be manufactured.

The coated filter substrate or product obtained by a method of the invention or using an apparatus of the invention may, for example, be a filter substrate comprising an oxidation catalyst (e.g. a catalysed soot filter [CSF]), a selective catalytic reduction (SCR) catalyst (e.g. the product may then be called a selective catalytic reduction filter [SCRF] catalyst), a NOx adsorber composition (e.g. the product may then be called a lean NOx trap filter [LNTF]), a three-way catalyst composition (e.g. the product may then be called a gasoline particulate filter [GPF]), an ammonia slip catalyst [ASC] or a combination of two or more thereof (e.g. a filter substrate comprising a selective catalytic reduction (SCR) catalyst and an ammonia slip catalyst [ASC]).

In addition to the "catalyst component", the liquid may further comprise a formulation aid. The term "formulation aid" refers to a component that is included in the liquid to modify its chemical or physical properties for coating onto a filter substrate. The formulation aid may, for example, aid the dispersion of a catalytic component in the liquid or change the viscosity of the liquid. The formulation aid may not be present in the final coated filter substrate product (e.g. it may decompose or degrade during calcination). The formulation aid may, for example, be an acid, a base, a thickener (e.g. organic compound thickener) or a binder.

The washcoat may have a viscosity of <NUM> - <NUM> cP at <NUM> rpm Brookfield, preferably <NUM> - <NUM> cP at <NUM> rpm Brookfield, more preferably less than <NUM> cP at <NUM> rpm Brookfield; in one embodiment the washcoat may have a viscosity of <NUM> to <NUM> cP at <NUM> rpm Brookfield, in another embodiment the washcoat may have a viscosity of <NUM> to <NUM> cP at <NUM> rpm Brookfield, more preferably <NUM> to <NUM> cP at <NUM> rpm Brookfield. In the present application all viscosity measurements refer to measurements carried out on a Brookfield DV-II+ Pro (LV) viscometer using a SC4-<NUM> spindle, available from Brookfield Engineering Laboratories, Inc. , Middleboro, MA, USA.

The washcoat may be supplied to the washcoat showerhead from a supply of washcoat using a piston which is movable within a bore, the bore having an internal diameter of <NUM> to <NUM> and the piston being moved at <NUM>-<NUM>/s.

The washcoat may be supplied to the washcoat showerhead at a rate of <NUM> - <NUM><NUM>s-<NUM>, preferably at a rate of <NUM> - <NUM><NUM>s-<NUM>.

Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:.

The present disclosure will now be described further. In the following passages different aspects/embodiments of the disclosure are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. It is intended that the features disclosed in relation to the products may be combined with those disclosed in relation to the method and vice versa.

<FIG> shows a cross-sectional view of a coating apparatus <NUM> that may be used for coating a substrate <NUM> with a washcoat.

The coating apparatus <NUM> may comprise a depositor <NUM> having a housing <NUM> containing apparatus for activating a dispensing mechanism. As shown, the dispensing mechanism may comprise a piston <NUM> which is axially moveable within a bore <NUM> to displace a fluid out of an outlet <NUM> towards a conduit <NUM> located downstream of the depositor <NUM>.

The coating apparatus <NUM> may further comprises a hopper <NUM> defining a hopper reservoir <NUM> having an outlet <NUM> connecting with the outlet <NUM> of the depositor <NUM> via a diaphragm valve <NUM>. The hopper <NUM> may be filled with a washcoat that has been formulated and pre-mixed at another location. The washcoat may be pumped into the hopper reservoir <NUM> or may be fed under gravity into the hopper reservoir <NUM> through suitable conduits.

The outlet <NUM> of the depositor <NUM> fluidly connects with the conduit <NUM> which in turn may extend into fluid communication with a dosing valve <NUM>. A washcoat showerhead <NUM> may be connected to a lower face of the dosing valve <NUM> with the washcoat showerhead <NUM> being positioned above the substrate <NUM>.

The substrate <NUM> may be located and positioned between a headset <NUM> and a pallet insert <NUM>. A vacuum apparatus including a vacuum cone <NUM> may be located beneath the substrate <NUM>.

<FIG> shows an enlarged portion of the coating apparatus <NUM> of <FIG> and shows in more detail how the substrate <NUM> may be positioned relative to the washcoat showerhead <NUM> and headset <NUM>.

The substrate <NUM> may be a monolithic block having a substrate body <NUM> which may have a uniform cross-sectional shape along its longitudinal length. The substrate body <NUM> may have a circular or near circular shape in cross-section. The substrate body <NUM> may have a diameter, d.

The substrate body <NUM> may be positioned to extend between the headset <NUM> and the pallet insert <NUM> such that an upper face <NUM> of the substrate body <NUM> is upper most and a lower face <NUM> of the substrate body <NUM> is lowermost. The washcoat showerhead <NUM> may be located above the headset <NUM> and may be preferably aligned with the headset <NUM> and substrate <NUM> such that a central longitudinal axis, x, of the washcoat showerhead <NUM> is coincident with the central longitudinal axis of both the headset <NUM> and substrate <NUM> as shown in <FIG>.

The washcoat showerhead <NUM> may comprise a showerhead housing <NUM> to which may be coupled, on a lower side, a showerhead plate <NUM> by means of bolts <NUM>. An adaptor plate <NUM> may be coupled to an upper side of the showerhead housing <NUM>, also by means of bolts.

The showerhead housing <NUM> may comprise a centrally located aperture defining an inlet <NUM> to a showerhead cavity <NUM> that is defined between the showerhead housing <NUM> and the showerhead plate <NUM>. The axis of the inlet <NUM> may be coincident with longitudinal axis x. The adaptor plate <NUM> may also comprise a centrally located aperture, which may be coincident with longitudinal axis x, and sized to receive a central portion <NUM> of the showerhead housing <NUM>. The dosing valve <NUM> may be brought into, and held in, fluid communication with the inlet <NUM> of the showerhead housing <NUM>.

The showerhead plate <NUM> may be provided with an array of nozzle apertures <NUM>.

In use, diaphragm valve <NUM> is opened and washcoat is drawn into the bore <NUM> from the hopper reservoir <NUM> by movement of the piston to the right (as viewed in <FIG>). The diaphragm valve <NUM> is then shut and the dose of washcoat is then displaced through conduit <NUM> by action of the piston <NUM> of the depositor <NUM> moving to the left (as viewed in <FIG>). The washcoat passes through the dosing valve <NUM> and inlet <NUM> into the showerhead cavity <NUM>. The washcoat then passes through the nozzle apertures <NUM> and drops down into contact with the upper face <NUM> of the substrate <NUM>. The washcoat is then drawn down through the passages of the substrate <NUM>. Drawing of the washcoat through the substrate <NUM> is driven, at least in part, by a suction force applied to the lower face <NUM> of the substrate <NUM> by the vacuum cone <NUM>.

<FIG> illustrate a first version of the baffle <NUM> according to the present disclosure. <FIG> illustrates a washcoat showerhead <NUM> according to the present disclosure wherein a baffle <NUM> is provided within the showerhead cavity <NUM>.

The showerhead cavity <NUM> may have a depth of <NUM> to <NUM>, preferably <NUM> to <NUM>. The showerhead cavity <NUM> may have a diameter of <NUM> to <NUM>, preferably <NUM> to <NUM>. The showerhead plate <NUM> may extend across the full diameter of the showerhead cavity <NUM>. Nozzle apertures <NUM> may be arrayed across the showerhead plate <NUM>. The nozzle apertures <NUM> may be arrayed in a regular or irregular array. The nozzle apertures <NUM> may be arranged in a plurality of concentric circular arrays.

The baffle <NUM> comprises an impermeable central body <NUM> and a plurality of arms <NUM> which extend from the impermeable central body <NUM> to define a plurality of flow apertures <NUM> circumferentially arranged around the impermeable central body <NUM>.

The baffle <NUM> may be mounted to the showerhead housing <NUM> by means of bolts <NUM> that may extend through bolt apertures <NUM> towards the distal end of each of the arms <NUM>. The mounting points of baffle <NUM> may surround, but preferably do not impinge on, the inlet <NUM> of the showerhead housing <NUM>. The bolts <NUM> may be <NUM> bolts. Each of the bolt apertures <NUM> may be surrounded by a standoff ring <NUM> which may serve to define the spacing between an upper face <NUM> of the baffle <NUM> and an upper interior face of the showerhead housing <NUM> as well as defining a spacing <NUM> between a lower face <NUM> of the baffle <NUM> and an upper interior face of the showerhead plate <NUM>. Each standoff ring <NUM> may have a height of <NUM> to <NUM>, preferably <NUM>. The spacing <NUM> may be <NUM> to <NUM>, preferably approximately <NUM>.

The baffle <NUM> (of the version shown in <FIG> and the other versions described hereafter) may be provided with an upper face <NUM> which may be flat as shown in <FIG> or may be provided with a conical or part conical protrusion <NUM> centrally located on the upper face <NUM> as shown in <FIG>.

As most clearly seen in <FIG>, the baffle <NUM> (whether or not provided with a conical or part conical protrusion <NUM>) may have a cross-like shape wherein four arms 52a-d are provided. Preferably the four arms 52a-d are equi-spaced around the circumference of the impermeable central body <NUM> such at they are each <NUM>° spaced from its neighbouring arms. Similarly, the baffle <NUM> may comprise four flow apertures 53a-d that are equi-spaced around the circumference of the impermeable central body <NUM> such at they are each <NUM>° spaced from its neighbouring flow apertures.

The length of the arms 52a-d may be relatively short compared to the diameter of the impermeable central body <NUM>. The arms 52a-<NUM> may have a uniform width and depth. In the illustrated example of <FIG> the bolt apertures <NUM> may be arranged on a pitch circle diameter of <NUM> and the impermeable central body <NUM> may have a radius r<NUM> of <NUM> and a diameter of <NUM>.

The baffle <NUM> may be formed of stainless steel, for example type <NUM>.

The first version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> that has a circular cross-sectional shape and a diameter less than approximately <NUM>, more particularly less than <NUM>. The first version of baffle <NUM> may also find particular beneficial use when coating a substrate <NUM> that has a non-circular cross-sectional shape. Further, the first version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> for a selective catalytic reduction filter (SCRF), a light duty diesel catalytic soot filter (LDD CSF), or a gasoline particulate filter (GPF).

<FIG> illustrate a second version of the baffle <NUM> according to the present disclosure. As most clearly seen in <FIG>, the baffle <NUM> (whether or not provided with a conical or part conical protrusion <NUM>) may have a cross-like shape wherein four arms 52a-d are provided. As with the first version, the four arms 52a-d may be equi-spaced around the circumference of the impermeable central body <NUM> such that they are each <NUM>° spaced from its neighbouring arms. Similarly, the baffle <NUM> may comprise four flow apertures 53a-d that are equi-spaced around the circumference of the impermeable central body <NUM> such at they are each <NUM>° spaced from its neighbouring flow apertures.

The length of the arms 52a-d is longer than in the first version. In the illustrated example of <FIG> the bolt apertures <NUM> may be arranged on a pitch circle diameter of <NUM> and the impermeable central body <NUM> may have a radius r<NUM> of <NUM> and a diameter of <NUM>. Consequently, the area of the impermeable central body <NUM> is reduced and the open area of the flow apertures 53a-d is increased compared to the first version of baffle <NUM>.

The arms 52a-<NUM> may have a uniform depth. The width of the arms 52a-d may taper. The width of each of the plurality of arms 52a-d may increase from a location proximate to the impermeable central body <NUM> to a location distal the impermeable central body <NUM>.

The second version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> that has a diameter greater than approximately <NUM>, more particularly greater than <NUM>. Further, the second version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> for a heavy-duty diesel filter (HDD).

<FIG> show a third version of baffle <NUM> according to the present disclosure. As most clearly seen in <FIG>, the baffle <NUM> (whether or not provided with a conical or part conical protrusion <NUM>) may have a cross-like shape wherein four arms 52a-d are provided. As with the first and second versions, the four arms 52a-d may be equispaced around the circumference of the impermeable central body <NUM> such that they are each <NUM>° spaced from its neighbouring arms. Similarly, the baffle <NUM> may comprise four flow apertures 53a-d that are equi-spaced around the circumference of the impermeable central body <NUM> such at they are each <NUM>° spaced from its neighbouring flow apertures.

The length of the arms 52a-d is longer than in the second version. In the illustrated example of <FIG> the bolt apertures <NUM> may be arranged on a pitch circle diameter of <NUM> and the impermeable central body <NUM> may have a radius r<NUM> of <NUM> and a diameter of <NUM>. Consequently, the area of the impermeable central body <NUM> is reduced and the open area of the flow apertures 53a-d is increased compared to the second version of baffle <NUM>.

The arms 52a-<NUM> may have a uniform depth. As with the second version, the width of the arms 52a-d may taper. The width of each of the plurality of arms 52a-d may increase from a location proximate to the impermeable central body <NUM> to a location distal the impermeable central body <NUM>.

The third version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> that has a diameter between <NUM> and <NUM>, more particularly between <NUM> and <NUM>. Further, the third version of baffle <NUM> may find particular beneficial use when coating a substrate <NUM> for a catalytic soot filter (CSF).

In use, washcoat may be supplied to the washcoat showerhead <NUM> from a supply of washcoat using the piston <NUM> of the depositor <NUM>. The piston <NUM> is movable within the bore <NUM>, and the bore <NUM> may have an internal diameter of <NUM> to <NUM> and the piston <NUM> may be moved at <NUM>-<NUM>/s. The washcoat is displaced along conduit <NUM> through dosing valve <NUM> and into the washcoat showerhead <NUM>. The washcoat may be supplied to the washcoat showerhead <NUM> at a rate of <NUM> - <NUM><NUM>s-<NUM>.

Washcoat may enter the showerhead cavity <NUM> through the inlet <NUM>. The washcoat comes into contact with the impermeable central body <NUM> of the baffle (including the conical or part-conical protrusion where present) before reaching the showerhead plate <NUM>. The washcoat is therefore deflected laterally towards the periphery of the showerhead cavity <NUM> so that the washcoat does not immediately reach the nozzle apertures <NUM> located at or near the centre of the showerhead plate <NUM>. The washcoat flows through the plurality of flow apertures 53a-d of the baffle and then circulates within the showerhead cavity <NUM> to pass through the nozzle apertures <NUM>. Due to the configuration of the size and shape of the arms 52a-d and flow apertures 53a-d it may be enabled that sufficient washcoat recirculates back to a centre of the showerhead plate <NUM> such that a uniform or near uniform discharge of washcoat through the nozzle apertures <NUM> is achieved.

The washcoat then is deposited onto the upper face <NUM> of the substrate <NUM> and is drawn through the passages of the substrate body <NUM> by the suction force applied by the vacuum cone <NUM>.

The washcoat comprises a liquid and typically a catalyst component. The liquid may be a solution or a suspension. The suspension may be a colloidal suspension, such as a sol, or a non-colloidal suspension. When the liquid is a solution or a suspension, then it may be an aqueous solution or an aqueous suspension. Typically, the liquid is a suspension, particularly an aqueous suspension.

The washcoat may have a viscosity of <NUM> - <NUM> cP at <NUM> rpm Brookfield, preferably <NUM> - <NUM> cP at <NUM> rpm Brookfield, more preferably less than <NUM> cP at <NUM> rpm Brookfield; in one embodiment the washcoat may have a viscosity of <NUM> to <NUM> cP at <NUM> rpm Brookfield, in another embodiment the washcoat may have a viscosity of <NUM> to <NUM> cP at <NUM> rpm Brookfield, more preferably <NUM> to <NUM> cP at <NUM> rpm Brookfield. (All measurements obtained on a Brookfield DV-II+ Pro (LV) viscometer using a SC4-<NUM> spindle.

In order to maximise utilisation of the substrate volume and to prevent applying multiple coats to portions of the substrate <NUM> and to prevent pull-through of the washcoat, it is desirable to achieve a consistent and predictable coating profile. For example, a flat coating profile is desirable as illustrated schematically in <FIG>. As shown the substrate <NUM> has a coated portion <NUM> which has been coated by the washcoat and an uncoated portion <NUM> where the washcoat has not reached. The interface between the coated portion <NUM> and the uncoated portion <NUM> is flat which is a desirable outcome.

<FIG> illustrates an undesirable "V-shaped" interface between the coated portion <NUM> and the uncoated portion <NUM>. This is believed to result where too much washcoat is applied to a central portion of the upper face <NUM> of the substrate <NUM> and may be a particular problem where the washcoat has a low viscosity.

<FIG> illustrates a coating profile that is similar to that of <FIG> but shows how pull-through may occur where washcoat is pulled out of a central portion of the lower face <NUM> of the substrate before a peripheral portion of the substrate is adequately coated.

Finally, <FIG> illustrates another undesirable coating profile which has an "M-shaped" interface between the coated portion <NUM> and the uncoated portion <NUM>. This is believed to result where the washcoat is unable to recirculate sufficiently back into a centre of the showerhead plate <NUM> before it passes through the nozzle apertures <NUM>.

A catalyst washcoat for a substrate was prepared having a solids content of <NUM>% and a Newtonian viscosity of 5cP over a spindle rotation speed <NUM>-<NUM> rpm using a Brookfield DV-II+ Pro (LV) and a SC4-<NUM> spindle.

When the washcoat was coated onto a silicon carbide filter substrate using the coating apparatus <NUM> of <FIG>, utilising a washcoat showerhead <NUM> without a baffle present, more washcoat is ejected out of the centre holes of the washcoat showerhead <NUM>, as shown in <FIG>.

This was found to result in a v-shaped, uneven, coating profile shown in <FIG>. This figure is an x-ray image of the substrate where the coating of washcoat is shown as darker against the light bare substrate due to the higher mass density of the coating of washcoat.

To ameliorate the effect seen in <FIG>, the first version of the baffle <NUM>, as shown in <FIG>, was added to the showerhead housing <NUM> as shown in <FIG>.

A silicon carbide filter substrate <NUM> of <NUM> diameter was then coated using this baffle plate <NUM> and the same catalyst washcoat as the above comparative example. A more even coating profile was obtained as shown by the x-ray image of <FIG> where the coating of washcoat is shown as darker against the light bare substrate due to the higher mass density of the coating of washcoat.

To ameliorate the effect seen in <FIG>, the second version of the baffle <NUM>, as shown in <FIG>, was added to the showerhead housing <NUM>.

To ameliorate the effect seen in <FIG>, the third version of the baffle <NUM>, as shown in <FIG>, was added to the showerhead housing <NUM>.

Claim 1:
A washcoat showerhead (<NUM>) for depositing a liquid washcoat onto a face (<NUM>) of a substrate (<NUM>) located below the washcoat showerhead (<NUM>), the washcoat showerhead (<NUM>) comprising:
a housing (<NUM>) having an inlet (<NUM>) for receiving the liquid washcoat;
a showerhead plate (<NUM>); and
a baffle (<NUM>);
the housing (<NUM>) and showerhead plate (<NUM>) defining a showerhead cavity (<NUM>) and the baffle (<NUM>) being located within the showerhead cavity (<NUM>);
the showerhead plate (<NUM>) comprising a plurality of nozzle apertures (<NUM>) for discharging the liquid washcoat towards the face (<NUM>) of the substrate (<NUM>);
characterised by
the baffle (<NUM>) comprising an impermeable central body (<NUM>) and a plurality of arms extending from the impermeable central body (<NUM>), the plurality of arms (<NUM>) defining a plurality of flow apertures (<NUM>) circumferentially arranged around the impermeable central body (<NUM>);
the baffle (<NUM>) being mounted in the showerhead cavity (<NUM>) such that the impermeable central body (<NUM>) is spaced from the showerhead plate (<NUM>);
the impermeable central body (<NUM>) being aligned below the inlet (<NUM>) of the housing (<NUM>) such that liquid washcoat entering the showerhead cavity (<NUM>) through the inlet (<NUM>) is diverted to flow around the impermeable central body (<NUM>) and through the plurality of flow apertures (<NUM>) before being discharged through the nozzle apertures (<NUM>) of the showerhead plate (<NUM>).