WO2024023125A1

WO2024023125A1 - Mineral fibre panel and process of manufacture

Info

Publication number: WO2024023125A1
Application number: PCT/EP2023/070652
Authority: WO
Inventors: Cornelus Johannes Maria GHIJZEN; Martinus Adriana Baets
Original assignee: Rockwool A/S
Priority date: 2022-07-25
Filing date: 2023-07-25
Publication date: 2024-02-01

Abstract

The invention relates to a process for manufacturing mineral fibre panels. The invention relates in particular to a process of manufacturing mineral fibre panels having high strength despite reduced binder content, thereby providing improved fire safety. The panels are produced by compressing a mixture of mineral fibres and a binder. The mat is wetted with 0.01 to 3 wt.% water before compression and curing.

Description

MINERAL FIBRE PANEL AND PROCESS OF MANUFACTURE

The invention relates to a process for manufacturing mineral fibre panels. The invention relates in particular to a process of manufacturing mineral fibre panels having high strength despite reduced binder content. The panels therefore provide improved fire safety in construction materials without compromising their suitability as structural materials. The mineral fibre panels of the invention can be used, for example, as protective and/or decorative cladding on the outside of buildings or as acoustically insulating/absorbing ceiling or wall panels.

Mineral fibre containing panels are conventionally obtained by subjecting mineral fibres and binder to a mixing and forming process and subsequently pressing and curing the formed mixture to obtain a cured panel having the required density.

There is growing interest in the use of mineral fibre panels as architectural cladding materials due to the high fire resistance of mineral fibre composites when compared to plastic-containing composites.

Mineral fibre-based materials are inherently fire resistant materials. Mineral fibres are noncombustible and can withstand extremely high temperatures without melting, well over 1000 °C in the case of stone wool. However, these materials are not entirely non-flammable due to the use of organic binders to ensure mechanical stability of the products. It is desirable to reduce the content of organic binders in mineral fibre-based materials in order to address the issue of fire safety. However, a reduction in binder content comes at the cost of impaired mechanical properties in terms of strength and cohesion. Architectural cladding must withstand weathering, and in particular high wind loads. Repeated bending and flexing of low strength panels by wind results in mechanical degradation and ultimately failure of the panel. This can be mitigated by reducing the span of the panels between fixing points, but this is undesirable for economical and design/aesthetic reasons. A better solution is to use panels that have sufficient bend strength to withstand high winds, even with greater spans between fixing points.

WO 2011/012712 A1 discloses a method for manufacturing a mineral fibre-containing element, said method comprising the steps of: providing mineral fibres in an amount of 90 to 99 wt % of the total weight of starting materials in the form of a collected web; providing a binder in an amount of 1 to 10 wt % of the total weight of starting materials; subjecting the collected web of fibres to a disentanglement process; suspending the fibres in a primary air flow; mixing the binder with the mineral fibres before, during or after the disentanglement process to form a mixture of mineral fibres and binder; collecting the mixture of mineral fibres and binder and pressing and curing the mixture to provide a consolidated composite with a density of from 120 kg/m³ to 1000 kg/m³, such as 170 kg/m³ to 1000 kg/m³.

There is therefore a need in the art for mineral fibre-based panels having a high degree of strength and cohesion while reducing the content of organic binders to improve the fire safety of the mineral fibre-based panels.

The composition of the mineral fibre panels of the invention is selected so as to maintain appropriate strength and thermal/acoustic insulation properties while also improving the fire safety of the mineral fibre panels.

Ordinarily, a high content of mineral fibres increases the fire resistance of the panels as well as its acoustic and thermal insulation properties and also reduces cost, however, strength and cohesion are reduced. Similarly, a high content of binder increases the strength and cohesion of the panels, but at the cost of reduced fire resistance and insulation properties. It is therefore an object of the invention to reduce the binder content of mineral fibre panels without compromising the mechanical properties that are essential for viable construction materials.

It is also an object of the present invention to provide a composite panel with an improved surface finish.

In a first aspect, the present invention provides a process for manufacturing a composite panel, comprising the steps of:

(a) providing mineral fibres in an amount of 85 to 99 wt% of the total weight of starting materials;

(b) providing a binder in an amount of 1 to 15 wt% of the total weight of starting materials;

(c) mixing the binder with the mineral fibres;

(d) collecting the mixture of mineral fibres and binder onto a surface to form a fibre mat having an upper surface, a lower surface and an initial thickness;

(e) wetting the fibre mat with 0.01 to 3 wt% water based on the total weight of the starting materials; and

(f) compressing and curing the fibre mat to provide a consolidated composite panel having a final thickness. As used herein, the term “composite panel” is used to refer to a structural element comprising a bonded and compressed fibre web comprising mineral fibres and a binder. The term “panel” is used herein to refer to a substantially planar structure having length and width dimensions substantially larger than the thickness dimension, such that the panel has a substantially planar structure having first and second major surfaces and a peripheral sidewall.

The term “fibre mat” refers to a collected mass of mineral fibres and binder prior to pressing and curing. Preferably, the fibre mat has uniform thickness in both lateral and longitudinal directions such that composite panels of uniform thickness as defined above are obtained.

The process of the invention comprises a step of wetting the fibre mat with 0.01 to 3 wt% water based on the total weight of the starting materials (i.e. 0.01 to 3 parts by weight of water per 100 parts by weight in total of mineral fibres, binder and any ancillary components of the composite panel). It has been found that spraying the fibre mat with water prior to pressing and curing results in a composite panel that has a higher strength in comparison to composite panels comprising the same level of binder but made by prior art processes that do not include step (e).

Without being bound by theory, it is believed that step (e) results in a different mode of curing when compared to prior art processes. In prior methods of preparing mineral fibre panels, a mineral fibre web is conventionally passed through a continuous heated press that progressively compresses the fibre mat from its initial thickness to the final thickness of the composite panel. Concurrently, thermal curing of the binder results in bonding of the mineral fibres, resulting in a consolidated panel of high strength. Curing of the binder is initiated as soon as the surfaces of the fibre mat reach the onset temperature of the curing reaction. However, unconsolidated mineral fibres are highly effective thermal insulators, therefore curing is initiated rapidly in the surface regions of the fibre mat, but the onset of curing in the interior of the fibre mat does not start until a later stage of compression. Curing of the binder is therefore progressive from the surfaces of the fibre mat to the interior as the level of compression increases. Furthermore, the rapid onset of curing means that the curing reaction can occur at least in part before the region of the panel has attained its final compressed configuration. Consequently, regions of cured binder that form in the initial stages of the curing process may be mechanically disrupted as compression continues to the final thickness of the panel. Accordingly, binder that is cured at the start of the compression process may not contribute fully to the strength of the final cured panel.

It is believed that the wetting of the fibre mat in step (e) delays the onset of the curing. Due to its high heat capacity, water acts as a heat sink in the process, delaying the onset of curing until the fibre mat has reached a more advanced stage of compression. Simultaneously, the steam produced by the evaporation of the water facilitates the transfer of heat into the interior of the fibre mat. Accordingly, the onset of curing is both delayed until a later stage of compression and essentially simultaneous throughout the thickness of the fibre mat. It is found that wetting of the fibre mat prior to compression and curing results in significantly better binder utilisation, such that the binder content can be reduced while maintaining excellent strength and cohesion. Accordingly, the invention is able to meet specifications for the mechanical properties of mineral fibre panels which also achieving the demanding specifications for fire resistance.

Put a different way, and without wishing to be bound by theory, it is believed that the presence of water increases the heat capacity of the fibre mat for a period of time. This in turn slows down the heating of the binder in the fibre mat during the curing/pressing phase. This causes the binder to be in a fluid, i.e. low-viscosity, phase for a longer period of time than if it were heated up more rapidly - it causes the binder to flow better within the fibre mat, especially near the surfaces. As a result, the surface finish on the product is improved. This is important for high-density products such as building cladding, which are typically to be painted or surface-treated in some way. A better surface on the substrate gives a better effect when painted. It is believed that this may even lead to a saving in surface treatment material.

The wetting of the fibre mat in step (e) is suitably carried out by spraying the fibre mat with water from one or more spray nozzles. The spray nozzles may be positioned above and/or below the fibre mat, such that water is sprayed onto the upper surface of the fibre mat, onto the lower surface of the fibre mat, or more preferably onto the upper surface and the lower surface of the fibre mat.

Wetting of the fibre mat in step (e) is preferably carried out such that there is a substantially uniform distribution of water across the entire mat.

Preferably, the amount of water used to wet the fibre mat in step (e) is from 0.02 to 2 wt%, more preferably 0.03 to 1.5 wt%, more preferably 0.04 to 1 wt%, more preferably 0.05 to 0.5 wt%, more preferably 0.06 to 0.2 wt%, more preferably 0.07 to 0.15 wt%, more preferably 0.08 to 0.13 wt%, more preferably 0.09 to 0.11 wt% water based on the total weight of the starting materials. If the amount of water is too low, the effect of delaying the onset of curing becomes small and the advantages of the invention are less. An excessive amount of water can exceed the absorbency of the fibre mat such that the fibre web becomes saturated and the excess water percolates out of the fibre web. Excess water may also delay curing excessively such that the curing time must be increased to achieve complete curing.

As the water is heated during step (f), the application temperature of the water in step (e) is not critical. For example, the water in step (e) may be supplied at a temperature in the range of 0 to 90 °C, or in the range of 10 to 50 °C, for example from 15 to 25 °C. The water may be tap water, the temperature of which may be dependent on, for example, the time of year.

The water may be supplied as pure water, or as part of a composition comprising water, for example a water-based solution.

It will be understood that the weight percentage of mineral fibres and binder provided in steps (a) and (b) determine the weight percentage of these components in the final composite panel. The percentages mentioned are therefore based on dry weight of starting materials. For the avoidance of doubt, water used to wet the fibre mat in step (e) is not included in the total weight of the starting materials. Any other volatile components, in particular solvents, are also not included in the total weight of the starting materials.

In order to obtain a suitable balance of properties, step (a) preferably comprises providing mineral fibres in an amount of from 85 to 99 wt%, preferably from 85 to 97 wt%, more preferably from 88 to 96 wt%, more preferably from 90 to 95 wt%, more preferably from 91 to 94 wt%, more preferably from 92 to 93 wt% based on the total weight of the starting materials. If the mineral fibre content of the panels is too high, the panels have excellent fire resistance but inadequate strength and cohesion. If the mineral fibre content of the panels is too low, then the panels have excellent strength and cohesion but inadequate fire resistance. The mineral fibre content is therefore selected so as to optimise the balance between these two objectives.

Similarly, step (b) preferably comprises providing binder in an amount of from 3 to 15 wt%, more preferably from 4 to 12 wt% more preferably from 5 to 10 wt%, more preferably from 6 to 9 wt%, more preferably from 7 to 8 wt% based on the total weight of the starting materials. If the binder content of the panels is too high, the panels have excellent strength and cohesion but inadequate fire resistance. If the mineral fibre content of the panels is too low, then the panels have excellent fire resistance but inadequate strength and cohesion. The binder content is therefore also selected so as to optimise the balance between these two objectives.

Preferably, the mineral fibres, and binder together form at least 96 wt%, more preferably at least 97 wt%, more preferably at least 98 wt%, more preferably at least 99 wt%, more preferably all of the total weight of the starting materials.

The mineral fibres (also known as man-made vitreous fibres or MMVF) used according to the present invention may be any mineral fibres, including glass fibres, ceramic fibres, stone fibres, slag fibres, or a mixture thereof. Preferably, the mineral fibres of the first surface layer and the base layer have the same chemical composition. However, it is not excluded that different types of mineral fibres are used in the first surface layer and the base layer.

Preferably, the mineral fibres are stone fibres. Stone fibres generally have a content of iron oxide at least 3% and alkaline earth metals (calcium oxide and magnesium oxide) from 10 to 40%, along with the other usual oxide constituents of mineral wool. These are silica; alumina; alkali metals (sodium oxide and potassium oxide) which are usually present in low amounts; and can also include titania and other minor oxides.

Preferably, the stone fibres have a composition comprising the following:

SiC>2 in an amount of from 33 to 45 wt%;

AI2O3 in an amount of from 16 to 24 wt%; an amount of K2O and/or Na2<D; an amount of CaO and/or MgO; wherein the ratio of the amount of AI2O3 to the amount of SiC>2 is in the range 0.34-0.73; wherein the ratio of the total amount of K2O and Na2<D, to the total amount of CaO and MgO, is less than 1.

More preferably, the stone fibres have a composition comprising the following:

SiO2 in an amount of from 33 to 45 wt%,

AI2O3 in an amount of from 16 to 24 wt%,

TiO2 in an amount of from 0 to 3 wt%,

Fe2Os in an amount of from 6 to 11 wt%, CaO and MgO in a total amount of from 23 to 33 wt%, and K2O and Na2<D in a total amount of 1 to 6 wt%.

The presence of organic fibres in a mineral fibre-containing panel would reduce the resistance of the element to fire and reduce the insulation properties of the element. Therefore, preferably, the composite panel comprises less than 5% organic fibres. More preferably, the composite panel comprises substantially no organic fibres, e.g. less than 0.5 wt% organic fibres, more preferably less than 0.1 wt% organic fibres.

The mass-weighted median fibre diameter of the mineral fibres is preferably in the range from 1 to 20 pm, preferably from 2 to 10 pm, more, preferably from 3 to 5 pm. Preferably the range of variation of the fibre diameter (defined as the 84% quantile minus the 16% quantile) is less than 5 pm, preferably less than 4 pm, preferably less than 3 pm, preferably less than 2.5 pm.

The mass-weighted median fibre length of the mineral fibres is preferably in the range from 20 to 800 pm, or from 50 to 500 pm, or from 60 to 400 pm, or from 80 to 300 pm, or from 100 to 250 pm.

The mineral fibres and binder may be arranged in step (d) to form a base layer and a first surface layer, wherein the first surface layer forms the upper surface of the fibre mat. As a result, the composite panel may have a laminar structure wherein the layers have a different composition of fibres and/or binder. In particular, step (d) may comprise arranging the mineral fibres and the binder such that the surface layer is formed of finer fraction of fibres than the base layer.

The relative fineness of the mineral fibres in the surface layer may be quantified by a difference in the mass-weighted median fibre length of fibres at the first surface as compared to the mass-weighted median fibre length of the mineral fibre mat as a whole. Specifically, the mass-weighted median fibre length of the first surface layer is designated herein as L1 , wherein the first surface layer is defined as a lamina comprising 20 wt% of the fibre mat adjacent the first surface of the panel. The mass-weighted median fibre length of the mineral fibre panel as a whole is designated herein as L2, and therefore where L1 <L2, the fibres in the first surface layer of the fibre mat will comprise a finer fraction of fibres than the remainder of the fibre mat. L1 is preferably in the range from 20 to 150 pm, more preferably from 30 to 120 pm, more preferably from 40 to 100 pm.

L2 is preferably in the range from 50 to 800 pm, more preferably from 60 to 500 pm, more preferably from 80 to 400 pm, more preferably from 100 to 300 pm, more preferably from 150 to 250 pm.

The ratio L1/L2 is preferably in the range from 0.1 to 0.95, more preferably from 0.5 to 0.9, more preferably from 0.55 to 0.85, and more preferably from 0.6 to 0.8.

The mass-weighted median fibre diameter and mass-weighted median fibre length are defined herein as the mass-based median average of the fibre diameters and fibre lengths in the respective layer(s) of the fibre mat. The mass-weighted median fibre diameter and median fibre length can be determined using sieving and weighing techniques and optical microscopy to measure a plurality of fibres and identify the midpoint value. In order to obtain accurate median values, preferably at least 200 fibres are measured, more preferably at least 250 fibres are measured. Rapid automated analysis allows for the measurement of several thousand fibres in a short period of time so as to obtain accurate fibre diameter and fibre length distributions. A suitable instrument is the DIAMLENGTH fibre analyser from OFDA.

Optionally, the mineral fibres and binder may be arranged in step (d) to further form a second surface layer, wherein the second surface layer forms the lower surface of the fibre mat. In particular, step (d) may further comprise arranging the mineral fibres and the binder such that the second surface layer is formed of finer fraction of fibres than the base layer. Preferably, step (d) comprises arranging the mineral fibres and the binder such that both the first surface layer and the second surface layer are formed of finer fraction of fibres than the base layer.

Optionally, the mineral fibre mat further comprises a second surface layer, wherein the second surface layer forms the lower portion of the thickness of the mineral fibre mat, and wherein the second surface layer comprises a finer fraction of mineral fibres than the base layer. In this embodiment, the panel has a substantially laminar structure, with the first and second surface layers disposed on either side of the base layer. Preferably, the mass-weighted median fibre length of the second surface layer is designated herein as L3, wherein the second surface layer is defined as a lamina comprising the 20 wt% of the fibre mat adjacent the second surface of the panel, and wherein L3<L2.

L3 is preferably in the range from 20 to 150 pm, more preferably from 30 to 120 pm, more preferably from 40 to 100 pm.

The ratio L3/L2 is preferably in the range from 0.2 to 0.95, more preferably from 0.5 to 0.9, more preferably from 0.55 to 0.85, and more preferably from 0.6 to 0.8.

Optionally, the binder content by weight may vary between the first surface layer, the base layer and the optional second surface layer. However, it is preferred that the first surface layer, the base layer and the optional second surface layer each contain the same percentage by weight of binder. Preferably, the binder is the same in each layer.

The mineral fibres preferably comprise no more than 40 wt% shot having a diameter of greater than 63 pm, more preferably no more than 35 wt% shot having a diameter of greater than 63 pm, more preferably no more than 30 wt% shot having a diameter of greater than 63 pm, more preferably no more than 25 wt% shot having a diameter of greater than 63 pm, more preferably no more than 20 wt% shot having a diameter of greater than 63 pm, more preferably no more than 15 wt% shot having a diameter of greater than 63 pm, more preferably no more than 10 wt% shot having a diameter of greater than 63 pm, based on the total weight of mineral fibres.

The mineral fibres preferably comprise no more than 3 wt% shot having a diameter of greater than 250 pm, more preferably no more than 2 wt% shot having a diameter of greater than 250 pm, based on the total weight of mineral fibres.

The shot percentages are determined by taking a sample of the mineral fibres and sieving the material through a first sieve having apertures of diameter 250 pm, and through a second sieve having apertures of diameter 63 pm. The material in the two sieves and the material that has passed through both sieves are weighed and the percentages calculated. Prior to the sieving process the mineral fibre sample may be subjected to a heat treatment to burn off organic material, such as binder, oil and other additives, e.g. by heating the mineral fibres to 590°C for at least 20 minutes.

Preferably, all of the mineral fibres (i.e. in the first surface layer, the base layer and the optional second surface layer) have the same chemical composition. However, it is not excluded that different types of mineral fibres may be used in the first surface layer, second surface layer and the base layer. Preferably, the mineral fibres in at least one of, preferably all of the first surface layer, the second surface layer and the base layer are stone fibres as described above.

As used herein, the “binder” refers to a material that is thermally curable so as to provide cohesiveness between the mineral fibres and pigment, such that the composite panels are substantially rigid, dimensionally stable and resistant to weathering and impacts.

Inorganic as well as organic binders can be employed. Organic binders are preferred. Further, dry binders as well as wet binders can be used. Specific examples of binder materials include but are not limited to phenol formaldehyde binder, urea formaldehyde binder, phenol urea formaldehyde binder, melamine formaldehyde binder, condensation resins, acrylates and other latex compositions, epoxy polymers, sodium silicate, hotmelts of polyurethane, polyethylene, polypropylene and polytetrafluoroethylene polymers.

Preferred binders are thermosetting binders derived from the reaction of phenolic compounds and/or amine compounds with aldehydes, including Novolak resins and resole resins. Examples of binders in this class include phenol-formaldehyde binder, ureaformaldehyde binder, melamine-formaldehyde binder, phenol-urea-formaldehyde binder, melamine-urea-formaldehyde binder, and phenol-melamine-formaldehyde. A hardener is preferably added to the resin, such as a amine-based hardener.

Conventional formaldehyde-based binders may contain a sugar component. For these binders, reference is made to WO 2012/076462.

Other binders include a cured thermoset binder, wherein the non-cured binder comprises:

(a) a sugar component, and one or both of

(b) a polycarboxylic acid component, and

(c) a component selected from the group of alkanolamine compounds, ammonia, ammonium salts of polycarboxylic acids.

Another group of binders that can be used are curable thermoset binders based on alkanolamine-polycarboxylic acid anhydride reaction products. The non-cured binder comprises (1) a water-soluble binder component obtainable by reacting at least one alkanolamine with at least one polycarboxylic acid or anhydride and, optionally, treating the reaction product with a base; (2) a sugar component; and optionally (3) urea. For these binders, reference is for example made to WO 2012/010694 and WO 2013/014076.

The binder is preferably provided in dry form, for example as a powder that can be dry- blended with the mineral fibres. However, it is not excluded that the binder may be provided in wet form (for instance as a solution/suspension in water or another solvent). If the binder is provided in wet form, particular as a solution in water, the amount of water used in step (e) may optionally be adjusted to account for the water supplied as part of the wet binder.

Step (f) preferably comprises applying pressure to the fibre mat using at least one pair of opposed heated compression elements.

Step (f) preferably comprises compressing the fibre mat for a predetermined compression residence time.

Step (f) preferably comprises compressing the fibre mat at a curing temperature that is effective to cause curing of the binder.

The compression residence time is suitably in the range from 0.5 minutes to 50 minutes, depending on the chemical identity of the binder and the curing temperature, for example from 0.5 to 20 minutes, preferably from 1 to 10 minutes, more preferably from 1.2 to 7 minutes, more preferably from 1 .5 to 6 minutes, more preferably from 1 .8 to 5 minutes, more preferably from 2 to 4.5 minutes, more preferably from 2 to 4 minutes.

The curing temperature is any temperature that is effective to cure the binder within the curing residence time. As used herein, the curing temperature is defined as the maximum temperature of the heated compression elements that are used to compress and cure the fibre mat. The temperature of the fibre mat will typically increase to substantially the same temperature as the curing temperature as curing progresses. Preferably the curing temperature is in the range from 100 to 300 °C, more preferably from 120 to 280 °C.

Whereas prior art methods of preparing mineral fibre based composite panels employ a progressive compression regime, such that the fibre mat is gradually compressed from its initial thickness until achieving its final thickness toward the end of the compression process, the process of the invention preferably comprises a modified compression regime where the reduction in the thickness of the fibre mat is accelerated, such that the fibre mat achieves a thickness close to the final thickness of the composite panel within the initial phase of the compression step. The initial compression phase is preferably followed by a final compression phase, wherein compression and curing continues to achieve a consolidated composite panel having the required final thickness.

In this embodiment, step (f) preferably comprises an initial compression phase wherein the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 20% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 15% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 14% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 13% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 12% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 11% of the compression residence time. More preferably, the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 10% of the compression residence time.

In other words, step (f) preferably comprises an initial compression phase wherein the fibre mat is compressed to an intermediate thickness within a first portion of the compression residence time, wherein the first portion of the compression residence time begins at the start of the compression residence time. Preferably, the duration of the first portion of the compression residence time is from 1 % to 25%, preferably from 4% to 20%, more preferably from 5% to 19%, more preferably from 6% to 18%, more preferably from 7% to 17%, more preferably from 8% to 16%, more preferably from 9% to 14%, more preferably from 10% to 14%, more preferably from 11% to 13% of the compression residence time. Preferably, the intermediate thickness of the fibre mat is no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel.

It has been found that a compression regime wherein the reduction in the thickness of the fibre mat is accelerated provides a further improvement in the strength and cohesiveness of the final consolidated composite panel. Without being bound by theory, it is believed that the accelerated compression combined with the delayed onset of curing substantially prevents curing of the binder before the panel has attained its compressed configuration. Accordingly, the problem of curing of the binder in uncompressed regions of the fibre mat, wherein the cured binder is subsequently mechanically disrupted as compression continues to the final thickness of the panel, is effectively avoided.

The process of the invention may be performed as a batch process. However, according to an embodiment, the process of the invention is carried out continuously on a production line. This provides a particularly cost efficient and versatile method to provide composite panels having favourable mechanical properties and thermal insulation properties in a wide range of densities.

In particular, step (d) comprises collecting the mixture of mineral fibres and binder on a moving belt to form a continuous fibre mat. The moving belt is optionally a foraminous conveyor belt having suction means positioned below it to assist the formation of the fibre mat. The moving belt preferably passes beneath a fibre deposition means for depositing the mixture onto the belt to form a continuous fibre mat.

Optionally, the fibre deposition means may comprise two or more fibre deposition zones for sequentially depositing a coarser fraction and a finer fraction of fibres, so as to form said fibre mat comprising at least a first surface layer and a base layer, wherein the first surface layer comprises a finer fraction of mineral fibres than the base layer. Optionally, the fibre deposition means may comprise three fibre deposition zones for sequentially forming said first surface layer, said base layer, and said second surface layers, wherein the first and second surface layers each comprises a finer fraction of mineral fibres than the base layer.

The continuous fibre mat may optionally be divided into sections of defined length and width prior to steps (e) and (f). Alternatively, the continuous fibre mat may be wetted in step (e) then divided into divided into sections of defined length prior to step (f). Alternatively, the continuous fibre mat may pass through steps (e) and (f) without being divided into sections and the compressed composite panel is cut into panels of defined length after step (f).

Preferably, the fibre mat passes a continuous wetting device in step (e). The continuous wetting device suitably comprises a spray device comprising one or more spray nozzles and adapted to wet the continuous fibre mat from the upper and/or lower surface thereof. Preferably, the continuous spray device comprises one or more fixed spray nozzles that evenly distribute water to the upper and/or lower surface of the continuous fibre mat as the continuous fibre mat passes the spray device.

The fibre mat may pass continuously into a continuous press comprising a plurality of pairs of opposed heated compression elements, wherein the heated compression elements suitably comprise heated rollers, heated belts, heated plates, or any suitable combination thereof.

The composite panels obtained by the process of the invention may have any suitable final thickness. Typically, the composite panels obtained by the process of the invention have a final thickness in the range from 4 to 50 mm, preferably from 4 to 30 mm, more preferably from 5 to 20 mm, more preferably from 5 to 15 mm, more preferably from 6 to 12 mm. In alternative embodiments, especially where the panel is used as an acoustic insulation panel for a wall or a ceiling, the final thickness of the composite panels is preferably from 12 to 25 mm, more preferably from 15 to 23 mm and most preferably from 18 to 21 mm.

Preferably, the final thickness of the composite panels is substantially uniform. Uniform thickness is defined herein as variation in thickness of no more than 10%, preferably no more than 5% across the entire surface of the panel. Preferably, any variation in thickness is less than 1 mm, more preferably less than 0.5 mm.

The length and width dimensions generally depend on the end use of the panels and handling requirements. However, suitable dimensions for manufacture and handling include a width dimension in the range from 500 to 2500 mm, preferably from 750 to 2000 mm, more preferably from 1000 to 1500 mm; and a length dimension in the range from 1000 to 5000 mm, preferably from 1500 to 4000 mm, more preferably from 2000 to 3500 mm, wherein the width is less than or equal to the length dimension.

Typically the aspect ratio of length to thickness (L:T) and width to thickness (W:T) of the composite panel obtained by the process of the invention are at both least 10, for example at least 20, or at least 50, or at least 100. The aspect ratio of width to length (W:T) may be in any suitable range, but is preferably in the range from 1 :10, more preferably from 1 :5, more preferably from 1 :3, wherein the width is taken as the shorter dimension.

Preferably, the composite panel obtained by the process of the invention has a density in the range from 600 to 1600 kg/m³, more preferably from 900 to 1550 kg/m³, more preferably from 1000 to 1500 kg/m³, more preferably from 1050 to 1450 kg/m³, more preferably from 1100 to 1400 kg/m³, more preferably from 1150 to 1350 kg/m³, more preferably from 1175 to 1325 kg/m³.

In a second aspect, the invention provides a composite panel obtainable by the process of the first aspect of the invention.

Preferably, the composite panel according to the second aspect of the invention has a loss- on-ignition (LOI) of from 3 to 15 wt%, more preferably from 5 to 12 wt%, more preferably from 6 to 10 wt%, more preferably from 7 to 9 wt%, more preferably from 7 to 8 wt%.

Loss-on-ignition (LOI) is defined herein as the percentage reduction in mass that is observed when a sample of the composite panel is ignited. The LOI of the composite panel is a measure of the amount of organic material such as binder and wetting agent in the composite panel. The LOI of a composite panel may be measured according to section 16 of BS2972, 1989 (Method 1).

Preferably, the composite panel according to the second aspect of the invention has an initial bending strength of more than 35 N/mm², preferably more than 36 N/mm², preferably more than 37 N/mm², preferably more than 38 N/mm². Preferably, the composite panel according to the second aspect of the invention has an initial bending strength in the range of 35 to 60 N/mm², preferably from 35 to 55 N/mm², preferably from 35 to 50 N/mm², preferably from 35 to 45 N/mm², preferably from 36 to 44 N/mm², preferably from 37 to 43 N/mm², preferably from 38 to 42 N/mm².

Preferably, the composite panel according to the second aspect of the invention has an aged bending strength of more than 25 N/mm², preferably more than 26 N/mm², preferably more than 27 N/mm², preferably more than 28 N/mm², preferably more than 29 N/mm², preferably more than 30 N/mm². Preferably, the composite panel according to the second aspect of the invention has an aged bending strength in the range of 25 to 60 N/mm², preferably from 25 to 55 N/mm², preferably from 25 to 50 N/mm², preferably from 25 to 45 N/mm², preferably from 27 to 40 N/mm², preferably from 28 to 38 N/mm², preferably from 30 to 35 N/mm².

Preferably, the composite panel according to the second aspect of the invention has an elastic modulus of more than 4500 N/mm², preferably more than 5000 N/mm², preferably more than 5500 N/mm², preferably more than 6000 N/mm². Preferably, the composite panel according to the second aspect of the invention has an elastic modulus in the range of 4500 to 15,000 N/mm², preferably from 5000 to 12,500 N/mm², preferably from 5500 to 10,000 N/mm², preferably from 6000 to 9000 N/mm².

The modulus of elasticity in bending (elastic modulus) and bending strength are determined by applying a load to the centre of a test piece supported at two points. The modulus of elasticity is calculated by using the slope of the linear region of the load-deflection curve; the value calculated is the apparent modulus, not the true modulus, because the test method includes shear as well as bending. The bending strength of each test piece is calculated by determining the ratio of the bending moment M, at the maximum load F_max, to the moment of its full cross section. The initial bending strength, the aged bending strength and the elastic modulus are each measured according to BS EN 310-1993. The initial bending strength of a panel is the bending strength of the panel when it is first produced. The aged bending strength of a panel is the bending strength of the panel after aging the panel.

Figure 1 shows an apparatus for use in a first embodiment of the method of the invention.

Figure 2 shows an apparatus for use in a second embodiment of the method of the invention.

Figure 3 shows an embodiment of the fibre deposition means 15.

Figure 4 shows schematically a compression regime used in prior art methods of making mineral fibre panels.

Figure 5 shows schematically a first compression regime according to the invention.

Figure 1 shows an apparatus for use in a first embodiment of the invention, wherein the spray nozzles 4a are positioned above the continuous fibre mat, such that water is sprayed onto the upper surface of the continuous fibre mat 2. The fibre deposition means 1 deposits fibres onto a moving belt 3 to form a continuous fibre mat 2. The fibre deposition means 1 may comprise one or more fibre deposition zones. The continuous fibre mat 2 then passes a continuous spray device 4 comprising one or more spray nozzles 4a that evenly distribute water to the upper surface of the continuous fibre mat 2 as the continuous fibre mat passes the spray device 4.

The continuous fibre mat then passes continuously into a continuous press 6 comprising a plurality of pairs of opposed heated compression elements 5a, 5b, wherein the heated compression elements 5a, 5b suitably comprise heated rollers, heated belts, heated plates, or any suitable combination thereof. The continuous fibre mat 2 passes continuously through the continuous press 6 to form a consolidated composite panel 8.

Figure 2 shows an apparatus as in Figure 1 for use in a second embodiment of the invention, wherein a spray device 4 is positioned above the continuous fibre mat 2 and a further spray device 7 is positioned below the continuous fibre mat 2. The spray nozzles 4a, 7a are positioned above and below the continuous fibre mat 2, such that water is sprayed onto the upper surface and the lower surface of the continuous fibre mat 2.

Figure 3 shows an embodiment of the fibre deposition means 15, wherein the fibre deposition means 15 comprises three fibre deposition zones 9, 10, 11 for sequentially forming said first surface layer 14, said base layer 13, and said second surface layer 12, wherein the first and second surface layers 14, 12 each comprises a finer fraction of mineral fibres than the base layer 13.

Figure 4 shows schematically a compression regime used in prior art methods of making mineral fibre panels, wherein C represents the thickness of the continuous fibre mat as a percentage of the initial thickness of the continuous fibre mat. The continuous fibre mat reaches approximately 25% of the initial thickness after approximately 50% of the compression residence time, before reaching approximately 20% of the initial thickness after approximately 70% of the compression residence regime. In this non-limiting example, the final thickness of the fibre mat is equal to approximately 20% of the initial thickness of the fibre mat. Therefore, the thickness of the continuous fibre mat reaches approximately 125% of the final thickness of the continuous fibre mat after approximately 50% of the compression residence time.

Figure 5 shows schematically a compression regime of the present invention, wherein C again represents the thickness of the continuous fibre mat as a percentage of the initial thickness of the continuous fibre mat. The continuous fibre mat reaches approximately 25% of the initial thickness after approximately 12% of the compression residence time, before reaching approximately 20% of the initial thickness after approximately 60% of the compression residence regime. Like in Figure 4, in this non-limiting example, the final thickness of the fibre mat is equal to approximately 20% of the initial thickness of the fibre mat. Therefore, the thickness of the continuous fibre mat reaches approximately 125% of the final thickness of the continuous fibre mat after approximately 12% of the compression residence time. This is significantly quicker than in the compression regime of Figure 4.

Examples

Example 1 :

The composite panel of Example 1 was produced according to a prior art method. Specifically, the starting materials, comprising 88 wt% of mineral fibres and 12 wt% of binder, were deposited from the deposition means onto a moving belt to form a continuous fibre mat with a density of 1118 kg/m³. The continuous fibre mat then passed into a continuous press for a compression residence time, wherein during the initial compression phase the continuous fibre mat was compressed to 8 mm to form a consolidated composite panel. The binder used was Prefere 94 8182110, obtained from Prefere Resins. The compression residence time was 2.28 minutes, and the curing temperature of the press was 200 °C.

Example 2:

The composite panel of Example 2 was produced according to the present invention. Specifically, the starting materials, comprising 92.4 wt% of mineral fibres and 7.6 wt% of binder, were deposited from the deposition means onto a moving belt to form a continuous fibre mat with a density of 1263 kg/m³. The continuous fibre mat then passed a continuous spray device that evenly distributed 0.1 wt% water based on the total weight of the starting materials to the upper surface of the continuous fibre mat. The continuous fibre mat then passed into a continuous press for a compression residence time, wherein during the initial compression phase the continuous fibre mat was compressed to 10 mm within 0.6 minutes, followed by a final compression phase wherein the continuous fibre mat was compressed to 8 mm to form a consolidated composite panel. The binder used was Prefere 94 8182110, obtained from Prefere Resins. The compression residence time was 3.2 minutes, and the curing temperature of the press was 200 °C. Table 1 : Comparison of the properties of the composite panels of Examples 1 and 2.

The data in Table 1 show that the composite panel formed by the process of Example 2 has a lower loss on ignition (7.6%) when compared to the composite panel of Example 1 (11.7%). This corresponds to a lower binder content in the final product and therefore improved fire safety. However, Table 1 also demonstrates that the mechanical properties of the composite panel of Example 2 are not compromised by the reduction in binder content. Instead, the composite panel of Example 2 exhibits improved mechanical properties. The method of Example 2 produces a panel that exhibits improved fire safety without compromising on the panel’s mechanical properties.

EMBODIMENTS

The invention may further be described by the following embodiments:

1 . A process for manufacturing a composite panel, comprising the steps of:

(c) mixing the binder with the mineral fibres;

(f) compressing and curing the fibre mat to provide a consolidated composite panel having a final thickness.

2. A process according to embodiment 1 , wherein step (e) comprises spraying water onto the fibre mat from one or more spray nozzles.

3. A process according to embodiment 2, wherein the water is sprayed: i) onto the upper surface of the fibre mat; ii) onto the lower surface of the fibre mat; or iii) onto the upper surface and the lower surface of the fibre mat.

4. A process according to any preceding embodiment, wherein step (e) comprises wetting the fibre mat with 0.02 to 2 wt%, or 0.03 to 1.5 wt%, or 0.04 to 1 wt%, or 0.05 to 0.5 wt%, or 0.06 to 0.2 wt%, or 0.07 to 0.15 wt%, or 0.08 to 0.13 wt%, or 0.09 to 0.11 wt% water based on the total weight of the starting materials.

5. A process according to any preceding embodiment, wherein the mineral fibres are provided in an amount of from 85 to 97 wt%, or from 88 to 96 wt%, or from 90 to 95 wt%, or from 91 to 94 wt%, or from 92 to 93 wt% based on the total weight of the starting materials.

6. A process according to any preceding embodiment, wherein the binder is provided in an amount of from 3 to 15 wt%, or from 4 to 12 wt% or from 5 to 10 wt%, or from 6 to 9 wt%, or from 7 to 8 wt% of the total weight of starting materials. 7. A process according to any preceding embodiment, wherein the mineral fibres and binder together form at least 96 wt%, or at least 97 wt%, or at least 98 wt%, or at least 99 wt%, or substantially all of the total weight of the starting materials.

8. A process according to any preceding embodiment, wherein the mineral fibres are selected from glass fibres, ceramic fibres, stone fibres, slag fibres, or a mixture thereof.

9. A process according to any preceding embodiment, wherein the mass-weighted median fibre diameter of the mineral fibres is in the range from 1 to 20 pm, or from 2 to 10 pm, or from 3 to 5 pm.

10. A process according to any preceding embodiment, wherein the mass-weighted median fibre length of the mineral fibres is in the range from 20 to 800 pm, or from 50 to 500 pm, or from 60 to 400 pm, or from 80 to 300 pm, or from 100 to 250 pm.

11. A process according to any preceding embodiment, wherein the fibre mat comprises at least a first surface layer and a base layer, wherein the first surface layer forms the upper surface of the fibre mat, and wherein the first surface layer comprises a finer fraction of mineral fibres than the base layer.

12. A process according to embodiment 11 , wherein the mass-weighted median fibre length of the first surface layer is designated as L1 , wherein the first surface layer is defined as a lamina comprising 20 wt% of the fibre mat adjacent a first surface of the panel, wherein the mass-weighted median fibre length of the composite panel as a whole is designated as L2, and wherein L1<L2.

13. A process according to embodiment 12, wherein L1 is in the range from 20 to 150 pm, or from 30 to 120 pm, or from 40 to 100 pm and wherein L2 is in the range from 50 to 800 pm, or from 60 to 500 pm, or from 80 to 400 pm, or from 100 to 300 pm, or from 150 to 250 pm.

14. A process according to embodiment 12 or embodiment 13, wherein the ratio L1/L2 is in the range from 0.1 to 0.95, or from 0.5 to 0.9, or from 0.55 to 0.85, or from 0.6 to 0.8.

15. A process according to any of embodiments 11 to 14, wherein the fibre mat further comprises a second surface layer, wherein the second surface layer forms the lower surface of the fibre mat, and wherein the second surface layer comprises a finer fraction of mineral fibres than the base layer. 16. A process according to embodiment 15, wherein the mass-weighted median fibre length of the second surface layer is designated as L3, wherein the second surface layer is defined as a lamina comprising the 20 wt% of the fibre mat adjacent a second major surface of the panel, and wherein L3<L2.

17. A process according to embodiment 16, wherein L3 is in the range from 20 to 150 pm, or from 30 to 120 pm, or from 40 to 100 pm.

18. A process according to embodiment 16 or embodiment 17, wherein the ratio L3/L2 is in the range from 0.2 to 0.95, or from 0.5 to 0.9, or from 0.55 to 0.85, or from 0.6 to 0.8.

19. A process according to any preceding embodiment, wherein the binder is an organic binder.

20. A process according to embodiment 19, wherein the binder is selected from phenolformaldehyde binder, urea-formaldehyde binder, melamine-formaldehyde binder, phenol- urea-formaldehyde binder, melamine-urea-formaldehyde binder, phenol-melamine- formaldehyde binder.

21 . A process according to any preceding embodiment, wherein the binder is provided in dry form.

22. A process according to any preceding embodiment, wherein step (f) comprises applying pressure to the fibre mat using at least one pair of opposed heated compression elements.

23. A process according to any preceding embodiment, wherein step (f) comprises compressing the fibre mat for a predetermined compression residence time and at a curing temperature that is effective to cause curing of the binder.

24. A process according to embodiment 23, wherein the compression residence time is in the range from 0.5 to 50 minutes, or from 1 to 10 minutes, or from 1.2 to 7 minutes, or from 1.5 to 6 minutes, or from 1.8 to 5 minutes, or from 2 to 4.5 minutes, or from 2 to 4 minutes, or from 2.2 to 3.8 minutes, or from 2.5 to 3.5 minutes.

25. A process according to embodiment 23 or embodiment 24, wherein the curing temperature is in the range from 100 to 300 °C, or from 120 to 280 °C, or from 150 to 250 °C. 26. A process according to any one of embodiments 23 to 25, wherein step (f) comprises an initial compression phase wherein the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 20% of the compression residence time, or wherein step (f) comprises an initial compression phase wherein the fibre mat is compressed to an intermediate thickness within a first portion of the compression residence time, wherein the first portion of the compression residence time begins at the start of the compression residence time, wherein the first portion of the compression residence time is from 1 % to 25%, or from 4% to 20%, or from 5% to 19%, or from 6% to 18%, or from 7% to 17%, or from 8% to 16%, or from 9% to 14%, or from 10% to 14%, or from 11% to 13% of the compression residence time, and the intermediate thickness of the fibre mat is no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel.

27. A process according to any one of embodiments 23 to 26, wherein the initial compression phase is followed by a final compression phase wherein the fibre mat is compressed to the final thickness of the composite panel.

28. A process according to any preceding embodiment, wherein steps (a) to (f) are carried out continuously on a production line.

29. A process according to any preceding embodiment, wherein the final thickness of the composite panel is between 4 and 50 mm, or between 4 and 30 mm, or between 5 and 20 mm, or between 5 and 15 mm, or between 6 and 12 mm.

30. A process according to any preceding embodiment, wherein the composite panel has a density in the range from 600 to 1600 kg/m³, or from 900 to 1550 kg/m³, or from 1000 to 1500 kg/m³, or from 1050 to 1450 kg/m³, or from 1100 to 1400 kg/m³, or from 1150 to 1350 kg/m³, or from 1175 to 1325 kg/m³.

31. A composite panel obtainable by the process of any one of the preceding embodiments.

32. A composite panel according to embodiment 31 having a loss-on-ignition (LOI) of from 3 to 15 wt%, or from 5 to 12 wt%, or from 6 to 10 wt%, or from 7 to 9 wt%, or from 7 to 8 wt%. 33. A composite panel according to embodiment 31 or embodiment 32, having initial bending strength of more than 35 N/mm², or more than 36 N/mm², or more than 37 N/mm², or more than 38 N/mm².

34. A composite panel according to any one of embodiments 31 to 33, having an initial bending strength in the range of 35 to 60 N/mm², or from 35 to 55 N/mm², or from 35 to 50 N/mm², or from 35 to 45 N/mm², or from 36 to 44 N/mm², or from 37 to 43 N/mm², or from 38 to 42 N/mm².

35. A composite panel according to any one of embodiments 31 to 34, having an aged bending strength of more than 25 N/mm², or more than 26 N/mm², or more than 27 N/mm², or more than 28 N/mm², or more than 29 N/mm², or more than 30 N/mm².

36. A composite panel according to any one of embodiments 31 to 35, having an aged bending strength in the range of 25 to 60 N/mm², or from 25 to 55 N/mm², or from 25 to 50 N/mm², or from 25 to 45 N/mm², or from 27 to 40 N/mm², or from 28 to 38 N/mm², or from 30 to 35 N/mm².

37. A composite panel according to any one of embodiments 31 to 36, having an elastic modulus of more than 4500 N/mm², or more than 5000 N/mm², or more than 5500 N/mm², or more than 6000 N/mm².

38. A composite panel according to any one of embodiments 31 to 37, having an elastic modulus in the range of 4500 to 15,000 N/mm², or from 5000 to 12,500 N/mm², or from 5500 to 10,000 N/mm², or from 6000 to 9000 N/mm².

Claims

1 . A process for manufacturing a composite panel, comprising the steps of:

(c) mixing the binder with the mineral fibres;

2. A process according to claim 1 , wherein step (e) comprises spraying water onto the fibre mat from one or more spray nozzles.

3. A process according to claim 2, wherein the water is sprayed: i) onto the upper surface of the fibre mat; ii) onto the lower surface of the fibre mat; or iii) onto the upper surface and the lower surface of the fibre mat.

4. A process according to any preceding claim, wherein step (e) comprises wetting the fibre mat with 0.02 to 2 wt%, or 0.03 to 1.5 wt%, or 0.04 to 1 wt%, or 0.05 to 0.5 wt%, or 0.06 to 0.2 wt%, or 0.07 to 0.15 wt%, or 0.08 to 0.13 wt%, or 0.09 to 0.11 wt% water based on the total weight of the starting materials.

5. A process according to any preceding claim, wherein the mineral fibres are provided in an amount of from 85 to 97 wt%, or from 88 to 96 wt%, or from 90 to 95 wt%, or from 91 to 94 wt%, or from 92 to 93 wt% based on the total weight of the starting materials, and/or wherein the binder is provided in an amount of from 3 to 15 wt%, or from 4 to 12 wt% or from 5 to 10 wt%, or from 6 to 9 wt%, or from 7 to 8 wt% of the total weight of starting materials, and/or wherein the mineral fibres and binder together form at least 96 wt%, or at least 97 wt%, or at least 98 wt%, or at least 99 wt%, or substantially all of the total weight of the starting materials.

6. A process according to any preceding claim, wherein the mass-weighted median fibre diameter of the mineral fibres is in the range from 1 to 20 pm, or from 2 to 10 pm, or from 3 to 5 pm, and/or wherein the mass-weighted median fibre length of the mineral fibres is in the range from 20 to 800 pm, or from 50 to 500 pm, or from 60 to 400 pm, or from 80 to 300 pm, or from 100 to 250 pm.

7. A process according to any preceding claim, wherein the fibre mat comprises at least a first surface layer and a base layer, wherein the first surface layer forms the upper surface of the fibre mat, and wherein the first surface layer comprises a finer fraction of mineral fibres than the base layer.

8. A process according to embodiment 7, wherein the fibre mat further comprises a second surface layer, wherein the second surface layer forms the lower surface of the fibre mat, and wherein the second surface layer comprises a finer fraction of mineral fibres than the base layer.

9. A process according to any preceding claim, wherein step (f) comprises applying pressure to the fibre mat using at least one pair of opposed heated compression elements.

10. A process according to any preceding claim, wherein step (f) comprises compressing the fibre mat for a predetermined compression residence time and at a curing temperature that is effective to cause curing of the binder, optionally wherein the compression residence time is in the range from 0.5 to 50 minutes, or from 1 to 10 minutes, or from 1.2 to 7 minutes, or from 1.5 to 6 minutes, or from 1 .8 to 5 minutes, or from 2 to 4.5 minutes, or from 2 to 4 minutes, or from 2.2 to 3.8 minutes, or from 2.5 to 3.5 minutes, and/or optionally wherein the curing temperature is in the range from 100 to 300 °C, or from 120 to 280 °C, or from 150 to 250 °C.

11. A process according to claim 10, wherein step (f) comprises an initial compression phase wherein the fibre mat is compressed to no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel within the first 20% of the compression residence time, or wherein step (f) comprises an initial compression phase wherein the fibre mat is compressed to an intermediate thickness within a first portion of the compression residence time, wherein the first portion of the compression residence time begins at the start of the compression residence time, wherein the first portion of the compression residence time is from 1 % to 25%, or from 4% to 20%, or from 5% to 19%, or from 6% to 18%, or from 7% to 17%, or from 8% to 16%, or from 9% to 14%, or from 10% to 14%, or from 11% to 13% of the compression residence time, and the intermediate thickness of the fibre mat is no more than 125%, or no more than 120%, or no more than 115%, or no more than 110%, or no more than 105% of the final thickness of the composite panel.

12. A process according to claim 11 , wherein the initial compression phase is followed by a final compression phase wherein the fibre mat is compressed to the final thickness of the composite panel.

13. A process according to any preceding claim, wherein the final thickness of the composite panel is between 4 and 50 mm, or between 4 and 30 mm, or between 5 and 20 mm, or between 5 and 15 mm, or between 6 and 12 mm, and/or wherein the composite panel has a density in the range from 600 to 1600 kg/m³, or from 900 to 1550 kg/m³, or from 1000 to 1500 kg/m³, or from 1050 to 1450 kg/m³, or from 1100 to 1400 kg/m³, or from 1150 to 1350 kg/m³, or from 1175 to 1325 kg/m³.

14. A composite panel obtainable by the process of any one of the preceding claims.

15. A composite panel according to claim 14 having a loss-on-ignition (LOI) of from 3 to 15 wt%, or from 5 to 12 wt%, or from 6 to 10 wt%, or from 7 to 9 wt%, or from 7 to 8 wt%.

16. A composite panel according to claim 14 or claim 15, having an initial bending strength in the range of 35 to 60 N/mm², or from 35 to 55 N/mm², or from 35 to 50 N/mm², or from 35 to 45 N/mm², or from 36 to 44 N/mm², or from 37 to 43 N/mm², or from 38 to 42 N/mm².

17. A composite panel according to any one of claims 14 to 16, having an elastic modulus in the range of 4500 to 15,000 N/mm², or from 5000 to 12,500 N/mm², or from 5500 to 10,000 N/mm², or from 6000 to 9000 N/mm².