[0001 ] The present invention relates to a mineral wool insulation panel for thermal and/or acoustic insulation, notably of household appliances or electrical appliances, particularly ovens, with or without a pyrolytic cleaning function.

[0002] Heat generating household appliances, for example ovens, commonly comprise double walls defining a space filled with insulation material. The insulation material is intended to: reduce loss of energy to the surroundings, thus reducing energy consumption of the appliance; and/or shield elements of the relevant appliances, for example wiring and electrical motors, and/or adjacent spaces or furniture from high temperature exposure; and/or reduce noise emission. Mineral wool is often a preferred insulation material for such applications thanks to its thermal insulation properties, its resistance to relatively high temperature exposure, its acoustic attenuation and its good fire resistance. Any organic binders used in the mineral wool product tends to decompose when first subjected to high temperatures and to generate unpleasant or undesired gas emissions; consequently, the insulation mineral fibre material for such applications preferably contains only low levels of organic binders. Alternatively, inorganic binders may be used but these tend to result in an insulation material which releases an undesirable level of dust during assembly and/or loses strength or becomes sticky if exposed to humid conditions, for example during the transport or storage.

[0003] Needled mineral wool panels have also been proposed for thermal insulation in household appliances, for instance in ovens or industrial muffle-type furnaces. Needling of mineral wool generally requires use of a needling aid applied to the fibres, for example a mineral oil, notably to prevent undesirable levels of fibre breakage during needling and facilitate the desired action of the needles. For example, US 5,057,173 discloses a mineral oil based needling aid.

[0004] Known needling aids have a number of drawbacks. The needling aids themselves and/or emulsifiers required to maintain the needling aid in an aqueous dispersion or emulsion for use often release undesired compounds, for example formaldehyde, acetone, methylisiocianate (MIC), aldehydes and/or fluorine compounds, for example hydrogen fluoride and/or carbonyl difluoride, upon decomposition when heated, for example during manufacture of an oven or first use of an oven or during a first pyrolytic cleaning cycle.

[0005] One aim of the present invention is to provide an improved needling aid for a mineral wool panel. A further aim is to provide an improved needled mineral wool panel, notably a panel which releases no or at least lower levels of one or more undesired compounds, for example fluorine compounds and/or formaldehyde, during manufacture and/or use of an appliance.

[0006] Thus, in accordance with one of its aspects, the present invention provides a method of manufacturing a mineral wool insulation panel in accordance with claim 1 . Other aspects are defined in other independent claims. The dependent claims define preferred or alternative embodiments. As used herein, the term "consists essentially of" is intended to limit the scope of a definition or claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the so defined or claimed invention.

[0007] The needling aid must satisfy a number of often competing criteria. For example, if applied by being sprayed on to the mineral fibres it must have a suitable rheology and/or viscosity i) when sprayed, notable to allow desirable distribution on the mineral fibres and to avoid clogging or blocking of any spray nozzles, and ii) to function well as a needling aid. The needling aid, notably in the form applied to the mineral wool fibres, may comprise an aqueous solution and/or an aqueous dispersion and/or an aqueous suspension; it may comprise a surfactant. For example, the graphite may be in dispersion in an aqueous solution, the aqueous solution comprising a further needling aid or it may be in dispersion in a liquid medium, notably water. Dispersion of the graphite in water may be facilitated by use of a dispersion system, for example comprising a surfactant. The needling aid may be modified between its application to the mineral wool fibres and needling; for example, a portion of any water present in the needling agent may evaporate between application and needling, for example due to air flow over the mineral wool fibres and/or exposure to storage or transport conditions.

[0008] The needling aid may consist or consist essentially of graphite. In addition to acting as a needling aid, the graphite may act as a darkening agent for the mineral wool insulating panel. It has surprising been found that graphite particles, even in when used in fairly small amounts, greatly facilitate needling of the mineral wool fibres, notably when applied in the form of a dispersion. Application of graphite in the form of a dispersion facilitates good distribution through the mineral wool; it also provides the graphite in a form which is convenient to apply and handle. In addition, notably when the needling aid consists or consists essentially of graphite particles, for example dispersed in water, the needling aid may comprise no or only very low quantities of organic compounds which would contribute to undesired emissions. In this case, the need to heat the needled insulation panel to decompose components of the needling aid may be avoided. The needled insulation panel may be dried by the application of heat subsequent to needling and prior to assembly in an appliance; such evaporation of water from a graphite needling aid applied as a dispersion in water requires less energy that decomposition of, for example mineral oil needling aids. In alternative embodiments, the needling aid may comprise graphite in combination with other needling aids, for example glycerol and/or a fatty acid ester.

[0009] The quantity of graphite particles in the mineral wool insulation panel may be (in % weight with respect of the total weight of the insulation panel)≥ 0.02%wt, ≥ 0.05%wt, ≥ 0.1 %wt,≥ 0.25 %wt,≥ 0.5%wt or≥ 1 %wt and/or < 5%wt, < 3%wt or < 1 .5%wt . The graphite may be synthetic or natural graphite; it may have a carbon content of about 90 % to about 100 %. Such quantities of graphite have been found effective to facilitate needling. The use of a needling aid which avoids generation of undesirable decomposition products allows the quantity of needling aid to be optimised without concerns about potential emissions. This may allow needling speed and conveyer speed to be increased, thus reducing the manufacturing time of the mineral wool panel. The amount of needling aids in the mineral wool insulation panel, notably immediately prior to needling, or immediately following needling and before being subjected to a temperature greater than 50 °C may be≥ 0.01 wt%,≥ 0.02 wt% or≥ 0.04 wt% and/or < 2 wt%, < 1 wt%, < 0.5 wt% or < 0.1 wt% based on the total weight of the mineral wool insulation panel.

[0010] The graphite particles may be in the form of powder or flakes. The powdered graphite may have a particle size of about 1 micron to about 50 microns, preferably of about 1 micron to about 20μη"ΐ, more preferably of about 1 micron to about 10 microns. In preferred embodiments, the median particle size of the graphite particles, even more preferably the particle size of at least 80%, at least 90% or at least 95% of the graphite particles, is within the range of about 1 micron to about 50 microns, preferably of about 1 micron to about 20μη"ΐ, more preferably of about 1 micron to about 10 microns, even more preferably about 1 micron to about 5 microns. Use of such particle sizes, particularly the lower values of particle sizes, facilitates spraying of the graphite particles through a nozzle, allows for dispersion within a liquid medium, notably water, and provides suitable needling properties. [001 1 ] Upon being heated to a temperature of≥ 100°C or≥ 200°C, notably about 350°C, for example subsequent to needling and prior to assembly in an appliance, the mineral wool insulating panel preferably releases no more that the following levels of one or more of the following compounds (expressed in mg of compound per kg of mineral wool insulation panel):

- Formaldehyde (mg/kg): < 15, < 10 or < 5; and/or

- Ethanal (mg/kg): < 20, < 15 or < 10; and/or

- Combination of propanal, butanal and pentanal (mg/kg): < 20, < 15 or < 10; and/or

- Methylisocianate (MIC) (mg/kg): < 0.02; and/or

- Acetone (mg/kg): < 20, < 15 or < 10; and/or

- Fluorine compounds, particularly hydrogen fluoride and/or carbonyl difluoride (mg/kg): < 20, < 15, < 10 or < 5; and/or

- Total volatile organic compounds (VOCs) (mg/kg): < 20, < 15 or < 10.

The use of a needling aid comprising graphite, particularly a needling aid consisting essentially of graphite facilitates such low levels of emissions, notably during manufacture and/or use of the mineral wool insulating panel.

The said heating to a temperature≥ 100°C or≥ 200°C, notably about 350°C, may be the first heating of the mineral wool insulating panel to such temperatures. The mineral wool insulating panel may be so heated subsequent to needling and prior to i) packaging for transport and/or ii) assembly in an appliance, notably to force decomposition of any organic compounds present. Such heating may comprise passing heated air having a temperature≥ 100°C or≥ 200°C or≥ 300°C and/or < 500°C or < 400°C through the mineral wool insulating panel. Alternatively, or additionally, the mineral wool panel may satisfy the aforementioned level of emissions when first raised to such temperatures once assembled in an appliance, for example, during first use of an oven or a first pyrolytic cleaning cycle of an oven.

[0012] An absence of fluorine compounds and/or mineral oil in the needling aid may be used to help avoid undesirable emissions.

[0013] The needling aid may be applied to the mineral wool fibres by spraying. A preferred arrangement comprises spraying the needling aid on the mineral wool fibres whilst the fibres are being carried in an air stream; this facilitates good distribution of the needling aid. The needling aid may be sprayed onto the fibres whilst the fibres are being carried in an air stream between formation of the fibres and laying down of the fibres to form a blanket of fibres which will be further processed, for example to form the mineral wool panel; this facilitates retrofitting of a needling aid spraying system to existing manufacturing facilities and/or allows good distribution of the needling aid without requiring an additional air carrying stage or equipment. The needling aid may be sprayed in to the fibres in a collecting hood or collecting chamber of a fiberiser. The sprayed needling aid may be an atomised spray, notable an air atomised spray; spraying of the needling aid may comprise spraying through a nozzle, notably an atomising nozzle, more particularly an air atomising nozzle.

[0014] When dispersed in an aqueous solution or a liquid medium, notably water, the amount of graphite in the liquid medium, notably water, may be≥10%wt,≥ 20%wt,≥30%wt and/or <50%wt or <40%wt with respect to the total weight of the aqueous solution or liquid medium containing the graphite.

[0015] In an alternative embodiment, the graphite needling aid may be applied to the mineral wool fibres without being dispersed in a liquid medium, for example it may be applied in the form of a powder.

[0016] The mineral wool insulation panel may comprise a colouring agent. The colouring agent may be part of the needling aid; particularly in this case, the colouring agent may take on its desired colour upon heating, notably during a heating step as previously described, for example by a transformation of the needling agent. This may be the case, for example, for any glycerol and/or any a fatty acid ester(s) of the needling aid. The graphite preferably contributes both as a needling aid and as a colouring agent.

[0017] The term "colouring agent" as used herein means any compound which darkens the mineral wool so as to enhance the heat absorption of the coloured mineral wool when compared with equivalent non-coloured mineral wool; this enhances the thermal insulation provided. The colouring agent preferably increases the light and/or the infrared absorption of the resulting coloured mineral wool, notably by at least 1 % or at least 2%. With the colouring agent, the mineral wool panel may have a darkness, i.e. a light and/or infrared absorption of at least a colour corresponding to RAL 7004, preferably corresponding to RAL 701 1 , and more preferably corresponding to RAL 901 1. According to a specific example of the present invention, the colouring agent is a black colour, such as RAL 9005. The coloured mineral wool may have a colour, wherein L ^* is lower than 40, preferably lower than 39, lower than 38, or lower than 37, and more preferably lower than 36, lower than 35, or lower than 32, a ^* is in the range of -10 to +10, or -8 to +8, preferably in the range of -6 to +6, -5 to +5, or -4 to +4, and more preferably in the range of -3 to +3, or -2 to +2, and b ^* is in the range of -10 to +10, or -8 to +8, preferably in the range of -6 to +6, -5 to +5, or -4 to +4, and more preferably in the range of -3 to +3, or -2 to +2, wherein L ^* , a ^* and b ^* are colour or coordinates defined in the CIELAB 1976 colour space system. Preferably, the entire thickness of the mineral wool insulation panel has a substantially uniform colour. Nevertheless, if desired, colour may be present exclusively or in greater quantity at or towards the top layer or the bottom layer of the mineral wool insulation panel.

[0018] The colouring agent may be a combination of two or more colouring agents and may further comprise additives such as stabilizers, emulsifiers, pigments, and hydrophilic agents. The colouring agent may be selected from the group consisting of C.I. 31600, C.I. Direct Black 80, Diazophenyl Black BW and Phenazo Black OB, soots, iron oxides, graphite or any combination thereof.

[0019] The mineral wool insulation panel is preferably free of thermoset binder. It may comprise less than 4% by weight of a binder, notably an organic binder, preferably less than 2% by weight and more preferably less than 1 % by weight as determined by loss on ignition (LOI). In preferred embodiments the mineral wool insulation panel may comprises less than 0.5% by weight binder or more preferable is free of or at least substantially free of binder, notably free of organic binder. This reduces undesired off gassing of the mineral wool upon first heating. Preferably, the needling of the mineral wool fibres provides a level of interconnection between fibres which is sufficient and provides integrity to the mineral wool panel, notably the needling provides sufficient integrity by itself to allow the panel to be handled and/or transported and/or assembled in an appliance.

[0020] The needling may provide a number of stitches per square centimetre which is≥ 10, ≥ 15 and/or < 50 or < 40. This has been found to provide a combination of i) suitable tensile strength, notably in the range 4-10 kPa, to facilitate use or assembly of the mineral wool insulation panel, for example in an oven, notably a domestic oven and ii) thermal performance .

[0021 ] The mineral wool fibres may comprise or consist of glass wool fibres and/or stone wool fibres. The glass mineral wool fibres may comprise: > 55 wt-% silicon oxide (Si0 ₂ ) and/or < 10 wt-% aluminium oxide (Al ₂ 0 ₃ ); and/or an alkali/alkaline-earth ratio of their composition which is > 1 ; and/or a combined quantity of CaO and MgO < 20 wt-%; and/or a combined quantity of Na ₂ 0 and K ₂ 0 > 8%wt. The rock mineral fibres may comprise: between 30 and 55 wt-% Si0 ₂ and/or between 10 and 30 wt-% Al ₂ 0 ₃ ; and/or an alkali/alkaline-earth ratio of their composition which is < 1 ; and/or a combined quantity of CaO and MgO ranging from 20 to 35 wt-%; and/or a combined quantity of Na ₂ 0 and K ₂ 0 < 8 wt%; and/or a total iron content expresses as Fe ₂ 0 ₃ of between 4 and 10 wt-%. The amount of shots (or beads), notably in a glass mineral wool panel, may be less than 1 wt%, a shot being defined as a particle having a largest apparent diameter of less than ΘΟμηι.

[0022] The mineral wool fibres may have an average diameter of less than δμηη, preferably less than θμηι, more preferably less than 5 μηη. The mineral wool fibres, particularly when stone wool fibres, may have an average length of at least 10μηι or at least 12μηΊ and/or less than 40μηι or less than 20μη"ΐ.

[0023] Particularly where the mineral wool fibres comprise stone wool fibres, prior to needling, the mineral wool fibres may be arranged in the form or a secondary blanket notably by assembling a stack of layers of a primary blanket, for example using a transversal pendulum distribution system to deposit the primary blanket on a moving conveyor belt to form the secondary blanket.

[0024] The mineral wool insulation panel, particularly when the mineral fibres comprise or consist of glass wool fibres, may have a density of at least 20 kg/m ³ , at least 25 kg/m ³ or at least 30 kg/m ³ and/or less than 100 kg/m ³ , less than 90 kg/m ³ or less than 80 kg/m ³ . Particularly when the mineral fibres comprise or consist of stone wool fibres the mineral wool insulation panel may have a density of at least 30 kg/m ³ , at least 40 kg/m ³ or at least 50 kg/m ³ and/or less than 180 kg/m ³ , less than 170 kg/m ³ or less than 160 kg/m ³ . The mineral wool insulation panel may have a thickness of at least 5 mm or at least 10 mm and/or less than 50 mm, or less than 40 mm.

[0025] To facilitate assembly of the mineral wool insulation panel in an appliance, for example a domestic oven, the mineral wool insulation panel may be provided in the form of a pre-cut panel configured to be assembled around the appliance by folding it along an edge of the relevant appliance, around at least two sides of the appliance, preferably three or four or even five sides thereof or as a rectangular shaped panel to insulate one side of the oven, for example a rear side, with no folding around the edges. The insulation panel may comprise cut outs; these may be convenient for the arrangement of cable ducts or tubing, such as power or water connections, or for the arrangement of electrical fans or other equipment elements. Further cut outs or notches may be provided to facilitate connection of two adjacent insulation panels. Yet further cut outs or notches may be provided in order to adapt the insulation panel to the design requirements of the household appliance it is intended to insulate. The insulation panel may comprise a facing, notably comprising an aluminium foil and/or a glass veil on one or each of its major surfaces.

[0026] The needling may be carried out in-line, for example as a continuation of the process of forming the mineral wool fibres in to a continuous blanket of fibres and before cutting of the continuous blanket in to individual panels. Alternatively, the needling may be carried out off-line.

[0027] An embodiment of the invention will be described in more detail, by way of example only, with reference to the attached drawings of which:

Fig. 1 is a schematic side view of part of a production line.

[0028] A needling aid is prepared by dispersing graphite particles having a median particle size of about 3 microns in water so that the graphite makes up about 20%wt of the total weight. The dispersion of graphite particles is sprayed on glass wool fibres in the chute of a collecting chamber. The glass wool fibres lay down on a conveyor, thus forming a continuous blanket of mineral wool fibres 1 1 . [0029] As illustrated in Fig 1 , the continuous blanket of mineral wool fibres 1 1 comprising glass wool fibres 1 10 and a graphite needling aid passes through an in-line needling station 13 at which it is needled preferably from above and below to rearrange the orientation of some of the fibres 120 in the blanket 12 and provide integrity to the blanket. Needling generally results in an increase in density. The amount of graphite in the blanket is about 0.1 %wt with respect of the total weight of the blanket.

[0030] Upon heating in oven at 350°C, the mineral wool insulating panel releases (in mg of emissions per kg of mineral wool insulating panel):

Formaldehyde < 5

Ethanal < 10

Propanal

Butanal < 10 total

Pentanal

MIC < 0.02

Acetone < 10

Total fluorine < 10

compounds

Total VOCs < 10