LAMINATED THERMAL INSULATING MATERIAL COMPRISING A SILICONE

BASED ADHESIVE

FIELD OF THE INVENTION

The present invention concerns a laminated flexible and malleable thermal insulating material comprising an insulating layer, an adhesive layer and an external layer, the adhesive layer having qualities of temperature resistance while retaining a flexibility suitable for the use of the insulating material.

BACKGROUND OF THE INVENTION

The terms "complex" and "laminated material" are used interchangeably below to designate a material comprising at least two layers of the same or different nature, joined by means of an adhesive layer.

Complexes formed by a film and a fibrous support joined by adhesion are frequently used in the field of technical textiles. The continuous joining process of the fibrous support and film is generally described as laminating or lamination by persons skilled in the art.

Examples can be cited of glass wool / aluminium sheet complex products used as thermal insulation. In the naval or aeronautical fields, glass fibre / aluminium sheet complexes are regularly used as thermal screens.

In the latter example, the two materials are assembled by adhesion, the adhesive being most often based on polyurethane resin. The weight of adhesive necessary for good joining is generally between a few g/m ² and a few hundred g/m ² depending on the surface state of the fibrous material.

This type of complex offers good mechanical properties, in particular with regard to the film / fibrous support adhesion force, puncture resistance and flexibility.

One major drawback of the current products based on polyurethane or polyolefin adhesives lies in their low thermal resistance which rarely exceeds 180 ⁰ C.

In certain applications, complexes are subject to high temperatures. One example is the thermal and acoustic insulation of exhaust pipes. In fact the temperature radiated by the catalytic converter can reach 700 ⁰ C, such that a complex used as a cold or external face of a thermo-acoustic catalyst screen must tolerate a temperature up to 300 ⁰ C.

The use of thermostable adhesives such as ceramics, epoxy or poiyimides in particular, leads to complexes that are temperature-resistant but have lost all flexibility and therefore can no longer follow the contour of a part to be protected, for example. Also, excessive rigidity of the adhesive layer reduces the delamination resistance of the complex. Furthermore, production is lengthy (several tens of minutes to several hours depending on adhesive used) and restricting as it requires pressurisation of the complex and heating. It is thus evident that these adhesives do not allow continuous assembly nor optimisation of industrial costs.

Silicone-based adhesives are known for their good temperature resistance, but such adhesives available commercially are designed for very different applications from the technical field of the invention, and in particular for joining materials which are not fibrous, for example glass on an aluminium frame. Furthermore according to the manufacturers' recommendations, it is necessary, in order to ensure all their properties, to perform a thermal post-baking treatment of several hours where the materials are held pressed against each other. Such treatment is thus incompatible with the industrial constraints and use of a continuous laminating process.

With regard to the adhesion of fibrous supports, document FR 2 854 637 teaches the use of a silicone adhesive but the fibrous supports concerned are already coated or impregnated with silicone such that their surface state and surface composition are favourable to such adhesion. Furthermore as stated above, it is necessary to perform a thermal post-baking treatment while maintaining the supports pressed

together, which makes the adhesion process economically incompatible with the use of a laminating line conventionally used in the industry.

BRIEF DESCRIPTION OF THE INVENTION

One of the objects of the invention is therefore to remedy these drawbacks by proposing a thermostable and flexible adhesive which retains the delamination resistance of the film / fibrous support complex even after being exposed to high temperature and avoid lost of flexibility of the complexes.

Another object of the invention is to propose a laminating process which can be implemented continuously in a conventional industrial installation.

In accordance with the invention, a laminated flexible and malleable thermal insulating material is proposed comprising:

- an insulating layer comprising a fibrous material intended to face a heat source,

- an adhesive layer, and

- an external layer comprising a film, wherein the adhesive layer comprises a silicone-based adhesive, which hardness is comprised between 10 and 80 Shore A (measured to standard DIN 53505).

In a preferred embodiment the hardness is preferably comprised between 20 and 40 Shore A.

The elongation at break is advantageously between 250 and 850%, preferably between 550 and 700%.

Finally, the tear strength is advantageously between 10 and 35 N/mm, preferably between 10 and 27 N/mm.

According to a preferred embodiment of the invention, the hardness of the adhesive is between 20 and 40 Shore A ₁ the elongation at break between 550 and 700% and the tear strength between 10 and 27 N/mm.

In a particular embodiment of the invention, the silicone-based adhesive comprises an adhesion promotion agent and/or stabilising agents.

The fibrous material of the insulating layer is advantageously a woven or non-woven fabric, in particular selected from glass, silica, basalt, carbon, aramide, flame- retardant cellulose, polybenzimidazole and their mixtures.

The external layer film comprises advantageously a metallic or organic material, in particular selected from aluminium, polyimide, PVDF, PTFE, PEEK, PEI. In the case of use of organic films, these have a surface metallisation giving them the same reflective properties as an aluminium metal film.

According to a particular embodiment of the invention, the insulating material is arranged on a primary insulating layer such that the insulating layer faces said primary insulating layer.

The invention therefore also concerns a laminated flexible and malleable thermal insulating material comprising a primary insulating layer and an insulating material as defined above and below, said insulating material being linked permanently to the primary insulating layer such that the insulating layer is in contact with said primary insulating layer.

The invention also concerns a method for preparation of a laminated flexible and malleable insulating material according to the invention, comprising the following steps: a) application of the adhesive layer to the insulating layer or external layer b) application of the other external or insulating layer to the adhesive layer, and c) application of a thermal treatment at a temperature suitable for promoting adhesion of the two insulating and external layers, advantageously between 160 and 200 ⁰ C.

Steps a), b) and c) are advantageously performed continuously.

The invention finally concerns a method for thermal insulation of a heat source in which the insulating material according to the invention is applied to said heat source, the insulating layer or where applicable the primary insulating layer facing said heat source.

In a particular embodiment of the invention, the heat source is a solid material, in particular the external housing of an enclosure containing a hot fluid, liquid or gas, for example a combustion gas exhaust pipe.

DETAILED DESCRIPTION OF THE INVENTION

The laminated flexible and malleable insulating material according to the invention comprises an insulating layer intended to face the heat source, an adhesive layer and an external layer comprising a film.

The three layers mentioned will be described together with the characteristics of the thermal insulating material comprising said layers.

First, the values characteristic of the thermal insulating material according to the invention will be defined.

The material grammage or basis weight is its mass surface density expressed in g/m ² .

The heat or thermal resistance is the ability of a material to be exposed to a particular temperature without undergoing degradation of its appearance or its mechanical properties.

The thermal efficiency of an insulating material is its ability to prevent energy transmission between its two faces. It can be expressed as a temperature difference

between the two faces of a material. In particular in the case of thermal screens which are used to limit the transmission of heat produced by a heat source, the thermal efficiency of these screens is measured as follows: the insulating material is arranged at a given distance from the heat source. By means of thermocouples, the temperature is measured of the heat source, the so-called hot face of the material (i.e. that facing the heat source), the so-called cold face of the material (i.e. that facing away from the heat source) and points situated at different distances from the cold face.

The elongation at break corresponds to the extension (in %) of a material before it breaks. Standard DIN 53504 gives standard test conditions.

The tear strength of a material is measured on a standardised specimen by the force to be applied per unit of thickness in order to cause tearing in the direction perpendicular to the traction. This test is standardised in standard ASTM D 624.

Finally, the delamination or peeling resistance of a glued complex is characterised by the force necessary to separate the two layers of the complex. It can be measured on a specimen of given width, which here is of the order of 2.5 cm, by means of a test with traction applied to the opposite ends of each of the two layers at a speed of 100 mm/min. The force necessary to separate the two layers is measured in relation to the width of the specimen. This method is based on standard ASTM D903 for example.

The adhesive layer comprises a silicone-based adhesive.

The term "adhesive" refers to a substance with high molecular density which, given its ability to adhere to surfaces (adhesion) and its internal stability (cohesion), is used to join different bodies.

A silicone-based adhesive means an adhesive comprising mainly silicone, where applicable with additives intended to improve its temperature resistance and/or mechanical properties, or facilitate its use.

A silicone-based adhesive according to the invention also has characteristics allowing a rapid curing kinetic. To this end it is advantageously selected from the silicones of the RTV family (Room Temperature Vulcanizing), LSR (Liquid Silicone Rubber) and HCR (Heat Cured Rubber), and more particularly those in which the curing reaction is catalysed by platinum salts and accelerated by temperature.

A silicone-based adhesive according to the invention also has the properties of thermal resistance, hardness and delamination resistance of the complex. Thus it has been found that silicone-based adhesives which give the best results for implementation of the invention have in combination a hardness, elongation at break and tear strength in specific value ranges which will be explained below.

The hardness of the adhesive is advantageously between 10 and 80 Shore A (measured to standard DIN 53505), preferably between 20 and 40 Shore A.

The elongation at break is advantageously between 250 and 850%, preferably between 550 and 700%.

Finally, the tear strength is advantageously between 10 and 35 N/mm, preferably between 10 and 27 N/mm.

According to a preferred embodiment of the invention, the hardness of the adhesive is between 20 and 40 Shore A, the elongation at break between 550 and 700% and the tear strength between 10 and 27 N/mm.

Silicone-based adhesives are well known to the person skilled in the art who may seek those commercially available products which combine properties of hardness, elongation at break and tear strength in the value ranges mentioned above.

In particular, the silicone elastomer sold under reference LR3003/30 by the company Wacker Silicones, which has a hardness of 30 Shore A, an elongation at break of 640% and a tear strength of 24 N/mm, gives good results.

Particularly advantageously, the silicone-based adhesive according to the invention may also comprise an adhesion promotion agent and/or stabilising agents. An adhesion promotion agent means any compound able to promote adhesion without compromising the properties of temperature resistance and hardness. An adhesion promotion agent comprising a monomer or polymer organo-functional silane used in a proportion of 0.1 to 2 parts per 100 parts silicone resin, preferably between 0.5 and 2 parts, allows an improvement in the properties of adhesion between film and fibrous support.

Such adhesion promotion agents are known to the person skilled in the art, for example under reference HF86 sold by Wacker Silicones.

A stabilising agent is any compound allowing an improvement in the thermal properties of the adhesive. In a non-limitative manner, reference can be made here to the red iron oxide-based pigments, aluminium pigments or carbon black particles. In the formulation, between 1 and 10 parts thermal stabiliser can be used per 100 parts resin, preferably between 3 and 6 parts.

Such stabilising agents are well known to the person skilled in the art, for example red iron oxide under reference FL3013 sold by Wacker Silicones.

A flame-retardant agent can also be provided, such as alumina trihydrate for example, in a proportion between 0 and 50 parts per 100 parts silicone resin, preferably 0 to 2 parts.

Finally, the use of a thinner such as toluene may be necessary to adapt the viscosity of the adhesive to the application method. This compound does not remain in the adhesive layer after drying.

Also the adhesive layer may be continuous, i.e. with an even substance over the entire interface between the two materials, or discontinuous, i.e. comprising a plurality of adhesive zones. Said zones can take the form of spots, lines or any other form which allows a temperature resistance and flexibility at least equivalent to those of a continuous adhesive layer.

The insulating layer comprises a fibrous material which can take the form of a woven or non-woven fabric.

The insulating layer is characterised by its composition, flexibility, thermal resistance, grammage or basis weight and thickness.

The substance is selected so as to allow satisfactory mechanical strength of the insulating material, thus allowing its handling. For a woven fabric, a grammage or basis weight of the order of 50 to 1000 g/m ² is generally adequate. In a preferred manner, fabrics with grammage or basis weight between 100 and 600 g/m ² are suitable for the application while retaining a satisfactory cost.

The person skilled in the art may prefer a non-woven fabric for a lower price, and select a non-woven fabric which retains a particular perforation and tear strength and an ability to be sewn. Non-woven fabrics with a grammage or basis weight between 100 and 5000 g/m ² and a thickness of 1 to 50 mm are suitable for this application. Preferably the grammage or basis weight is between 300 and 2400 g/m ² and the thickness between 3 and 25 mm. In a preferred embodiment, a non-woven fabric of 960 g/m ² and 10 mm thickness is used.

The threads and fibres used in the composition of the insulating layer are such that they have a high thermal resistance. Amongst these for example are glass, silica, basalt, carbon, aramide, flame-retardant cellulose and polybenzimidazole. Evidently the person skilled in the art can combine these materials or select other materials, the thermal resistance of which is suitable for implementation of the invention.

The external layer comprises a film which can be metal or organic. Amongst organic films, without the scope of the invention being restricted to these materials, can be cited: polyimide, PVDF (polyfluoride vinylidene), PTFE (polytetrafluorethylene), PEEK (polyetheretherketone) or PEI (polyether imide). These films advantageously undergo a surface metallisation treatment giving them reflective properties compatible with their function as a thermal screen.

Films giving good results include aluminium films, or more precisely comprising over 99% aluminium alloy. The aluminium film has a thickness between 5 and 200 microns, which allows the complex to maintain its form, while being able to adapt to the desired contour.

Aluminium films with a thickness between 12 and 80 microns, in particular 40 microns, are satisfactory in relation to their tear and perforation strength. The surface state of the film is preferably polished on the outside so as to ensure maximum thermal reflectivity while it is preferably matt on the side facing the fibrous support so as to promote the adhesion strength.

The a laminated flexible and malleable insulating material according to the invention is characterised by its flexibility, its temperature resistance, its delamination resistance and its thermal efficiency.

The materials used in the invention, and the resulting complex, are fine and flexible so it is difficult to quantify flexibility by a standardised test used conventionally for the more rigid materials, such as for example a flexion test. A criterion which can be used to characterise the flexibility of the material is its ability to be shaped around a part to be protected or where applicable joined to another flexible material.

The temperature resistance of the complex according to the invention is preferably around 300 ⁰ C; also this can locally tolerate higher temperatures up to 45O ⁰ C.

With regard to the delamination resistance, this is advantageously, when new i.e. before first heating in contact with the heat source, greater than 2N / 2.5 cm, preferably greater than 3 or even 5 N / 2.5 cm. After ageing, it is considered that a delamination resistance greater than 2 N / 2.5 cm, preferably greater than 3 N / 2.5 cm, can ensure satisfactory cohesion of the complex.

Finally, the thermal attenuation achieved by the complex when the face comprising aluminium film is oriented towards a heat source at 32O ⁰ C, at a distance of 35 mm from this, is advantageously at least 100°C, preferably greater than 200 ⁰ C.

The person skilled in the art is able to select appropriate materials for the insulating and external layers constituting the material according to the invention to meet these technical constraints.

The insulating material according to the invention may be produced in the form of a sheet, the width of which is a function of the width of the starting materials and the laminating device. The material may also be made in the form of panels. Said sheets or panels can then be cut to the desired format.

In a preferred embodiment of the invention, the aluminium film and fibrous support take the form of rolls or coils. A laminating line of the known type is provided, comprising means of unwinding the coils of materials, means for depositing and distributing the adhesive, an oven and finally means for winding the resulting complex. The whole forms part of a continuous device and advances at a given speed.

A first step comprises unwinding the coil of aluminium film and depositing the silicone-based adhesive on its upper face, preferably in liquid form and with a suitable viscosity comprised between 500 and 200,000 mPa.s, preferably greater than 5000 mPa.s.

To this end, a doctor (blade) is used or a cylinder which spreads the adhesive over the entire surface of the aluminium film to form a continuous adhesive layer. The quantity of adhesive used is such that the grammage or basis weight of the dry adhesive layer is between 5 and 200 g/m ² , preferably between 20 and 150 g/m ² .

The coil of fibrous material is unwound and presented above the glued aluminium film, then a device comprising rollers brings the film and fibrous material into contact.

In a first embodiment, the contact is ensured by application of pressure to the rollers.

This pressure is typically between 0.5 and 8 bar. In a second embodiment, the contact is ensured by adjustment of the roller spacing. This spacing is typically between two values E _mjn and E _max such that:

E _m in = thickness of film + thickness of adhesive + 1/3 thickness of fibrous material, and

E _max = thickness of film + thickness of adhesive + 2/3 thickness of fibrous material.

This pressure need then not be maintained, as the viscosity of the adhesive is sufficient to ensure that the components remain in contact, in the case of a production line fitted with drying ovens, or it may be maintained in the case where the complex is produced on a production line fitted with endless drying belts (for example technology known as "Flat bed laminating system" by the company S-Line).

The complex thus formed then passes into an oven where the adhesive undergoes a drying and curing treatment. The temperature of the oven is between 160 and 200 ⁰ C, the curing period is a function of the production speed of the complex and the length of the oven. The production speed is between 3 and 300 m/min. The duration of passage through the oven is between 1 and 5 minutes. Preferably, for a production speed of 10 m/min, satisfactory curing is obtained of a complex comprising 70 g/m ² adhesive after passage for one minute through an oven brought to 18O ⁰ C.

At the outlet from the oven, the complex may be wound into coils or cut into panels, depending on its subsequent use.

It is thus evident that this process allows adhesion of the two materials in a conventional manner in a continuous process.

Thus the desired thermal resistance and delamination resistance are achieved without post-treatment or pressurisation of the materials, in contrast to the usual recommendations of the manufacturers of silicone-based adhesives. In fact the first exposure of the complex to a high temperature environment is equivalent to post- baking treatment.

In a variant of the invention, the adhesive may be deposited on the aluminium film and spread over the surface of the film by means of a needle-point cylinder to form a discontinuous adhesive layer distributed regularly in spots.

This method of application of a discontinuous layer allows deposition of a silicone- based adhesive which has much higher temperature resistance but which is more rigid than the adhesive for which the formulation has been described above.

However this spot deposition allows compensation for the greater rigidity of the adhesive, and the final complex has the expected flexibility while being resistant up to a temperature of 600 ⁰ C. Such an adhesive generally has the form of a powder which can be placed in solution in a solvent, then applied in the process described above.

It is evident that these examples of presentation of the adhesive layer are not limitative, and the person skilled in the art will be able to establish a discontinuous adhesive layer which defines other patterns, for example lines, while maintaining a compromise between the quantity of adhesive and the mechanical strength of the complex.

The a laminated flexible and malleable insulating material according to the invention may be used alone or in combination with a so-called primary insulating layer. In the second case, it is placed on said primary insulating layer such that the insulating layer faces the primary insulating layer, and the primary insulating layer is interposed between the heat source and the laminated flexible and malleable insulating material according to the invention.

The primary insulating layer comprises a material with properties of thermal insulation and heat resistance. Particularly advantageously the primary insulating layer also has properties of acoustic absorption.

The primary insulating layer may also have a protective layer on its face directed towards the heat source. This protective layer is intended firstly to protect it from the high temperature of the heat source, and secondly to avoid wear of the primary insulating layer, in particular in the case where the primary insulating layer is a non- woven fabric, the fibres of which have a tendency to lose cohesion under the effect of vibration.

In the field of thermal screens for exhaust silencers or catalytic converters, we find a primary insulating layer comprising a non-woven fabric based on fibres of glass, basalt or rock wool, protected on the heat source side by a glass or silicone fabric. For example reference is made to document WO 03/054373 which describes a

thermal screen for an exhaust manifold comprising four layers of material, which are a protection layer able to be placed in contact with the exhaust manifold and comprising a metal braid, an insulating textile based on glass fibres, a fabric of glass fibres and an external layer comprising an aluminised textile.

The materials are selected as a function of the temperature which they must resist. For the protective material, glass fabrics are adapted for a temperature which can amount to 55O ⁰ C, whereas silica fabrics are adapted for a temperature up to 1200 ⁰ C. With regard to the primary insulating layer, glass fibre-based fabrics are resistant up to 550 ⁰ C whereas non-woven fabrics based on rock wool or basalt fibres are resistant up to 750 ⁰ C. Non-woven needled silica fibre based fabrics are resistant to a temperature up to 1200°C.

The laminated flexible and malleable insulating material according to the invention thus forms the external face of a thermal screen, for which it further improves the thermal insulation.

It may be linked to the primary insulating layer in a permanent manner by any means allowing retention of the expected flexibility. A permanent link according to the invention means a link of which breakage causes a substantial deterioration in all or part of the insulating material according to the invention. Such a permanent link can be achieved over the entire interface between the laminated flexible and malleable insulating material according to the invention and the primary insulating layer, or over just part of this interface in a defined zone.

The means for achieving such a link are well known to the person skilled in the art, comprising mechanical means such as staples, rivets, press-studs, stitching points or any other mechanical means known to the professional person. They can comprise means promoting adhesion between the two elements such as adhesive materials, also well known to the professional person, where applicable combined with mechanical means.

A method of insulation using the laminated flexible and malleable insulating material according to the invention will now be described.

Such a method comprises application to a heat source of an insulating material according to the invention, the insulating layer facing said heat source. According to an embodiment, the insulating material according to the invention forms the outer or cold face of the thermal screen and is arranged on a primary insulating layer such that the insulating layer faces the primary insulating layer. In such a case, the primary insulating layer is oriented towards the heat source.

In a particular embodiment of the invention, the heat source is a solid material, in particular the outer housing of an enclosure containing a hot fluid, liquid or gas, for example a combustion gas exhaust pipe, a catalytic converter, a turbocompressor or any other constituent element of an exhaust system from a combustion engine, but also ovens, blast nozzles, boilers etc.

Depending on the application, said insulating material may be arranged directly in contact with the heat source or a gap may be left between the heat source and the material. Since the insulating material according to the invention is flexible, it can be shaped around the heat source of whatever form and held in place by mechanical means such as auto-grippers, press-studs, staples, collars, zips etc.

Example

A complex according to the invention is produced from the following materials: the insulating layer is formed from a glass fibre fabric of grammage or basis weight 420 g/m ² ; the external layer comprises an aluminium film of 40 microns thickness.

A silicone-based adhesive with the following composition (in weight) is used:

- 500 parts resin (component A): Elastosil LR3003/30A by Wacker Silicones

- 500 parts resin (component B): Elastosil LR3003/30B

- 15 parts adhesion promotion agent: HF86 from Wacker Silicones

- 50 parts thermal stabiliser: red iron oxide FL3013 (Wacker Silicones)

- 100 parts flame-retardant agent: alumina SH 150 (Alcan)

- 500 parts thinner: toluene.

The viscosity of the adhesive is 130.000 mPa.s.

The quantity of adhesive used is such that the mass surface density of the adhesive layer is 100 g/m ² during deposition and 70 g/m ² after evaporation of solvent and curing of the silicone.

In order to compare the resulting complex with complexes using known adhesives, also specimens of complexes are prepared using the same materials for insulating layer and external layer.

In a first case, polyurethane adhesive is used, which is the adhesive normally used in this type of application, in a quantity of 37 g/m ² corresponding to a typical value for products which can be found on the market.

In a second case, ceramic adhesive is used, which is a very rigid thermostable adhesive, in a quantity of 143 g/m ² , a value lying in a normal range for this type of adhesive.

For these three types of adhesive, the delamination force was measured in new state, i.e. on specimens after drying of the adhesive, and in aged state, i.e. on specimens which have been placed in an air ventilation stove at a temperature of 300 ⁰ C for 24 hours.

The results are shown in the table below:

With regard to the polyurethane adhesive, it is found that the adhesion is very good in new state but is practically zero after ageing.

In the case of the ceramic adhesive, the adhesion is low both in new state and after ageing. Also, simple manipulation of the complex such as slight creasing is sufficient to separate the layers.

Finally, we see that with the silicone-based adhesive, the formulation of which is given above, we retain a satisfactory delamination resistance. Furthermore by manipulating the corresponding specimens we find that the complex has retained good flexibility.

Also the thermal efficiency of the complex was measured.

This measurement comprised placing the complex 35 mm from a heat source at 320 ⁰ C, the aluminium face being directed towards the heat source. The temperature of the surface of the insulating layer is measured. The thermal attenuation is at least 100 ⁰ C, preferably 200 ⁰ C.

Finally the thermal resistance of the complex was tested. For this, the complex is placed directly in contact with the heat source brought successively to 27O ⁰ C, 300°C and 320°C. In a first case, the external face is placed on the heat source; in a second case, it is the insulating layer. After the test, no spontaneous delamination was noted, nor rigidification nor embrittlement of the complex which could provoke delamination. Nor was there any destruction of the fibres which could cause environmental pollution.

Finally, it is evident that the examples just given are merely particular illustrations and in no case limitative in relation to the methods of implementation or areas of application of the invention.