The present invention relates to the use of a sandwich panel the core material of which has a particular composition, as fire insulation or fire barrier, and a method for the continuous fabrication of sandwich panels.

U.S. Patent 4,286,013 describes a silicon based laminate

10 containing a fibrous filler and microspheres of glass. It is stated that the material has good properties with respect to burn-through and flame spreading. What distinguishes the subject matter of this patent from the present invention is:

!5 l. The laminate has a relatively high density, about 0.6 g/cn. . The insulating portion of the material used in the present invention has a density of 0.140—0.3 g/cm ³ .

2. The laminate per se does not have satisfactory insulating

20 properties. Accordingly, it is not suitable as fire insulation or thermal insulation by itself.

U.S. Patent 4,433,069 describes a silicon based foam and the production thereof. It is disclosed that the foam has good

25 properties for the sealing of fire walls/floors where pipeε/- cableε penetrate the fire barrier, the foam being very resistant to burn-through. The material according to this patent differs from the material used in the present invention, inter alia, by the following points:

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1. The foam is soft and cannot function, for example, in a self-supporting fire wall, or as insulation in a self- supporting sandwich element.

J5 2. Furthermore, it is assumed that the material is compara¬ tively heavy (based on the types of similar materials with which the applicant is acquainted).

U.S. Patent 4,820,576 describes a "flame retardant" resor- cinol based polymer which has certain features in common with parts of the material used in the present invention (the sandwich elements), but lacks the microspheres present in the material used according to the invention.

U.S. Patent 5,126,192 describes a "flame retardant" prepreg material containing glass spheres, where the essential features are the electrical properties (printed circuit boards), may easily be drilled and shows further that holes in a laminate prepared from the prepreg material. Again it must be concluded that the material per se has points of resemblance to the prepreg material included in the materials used according to the present invention. However, the resin types described are not suitable in connection with the types of fire exposure to which the present invention is directed.

EP 0,492,154 Al describes a thermoplastic film filled with hollow glass microspheres, specially designed for electrical application. Here the above comments on U.S. Patent 5,126,192 apply once more.

JP 4,178,440 A describes a light weight foam based on epoxy and glass spheres in combination with a foaming agent. It is not disclosed which of the material's fire resistance properties that are favourable, but the applicant's experien¬ ce is that epoxy based foams emit excessive smoke and thermal energy in relation to what is permitted within the sector where the present invention is to be used. The density is also high: 0.46 g/cm ³ in the example given. That which distinguishes this publication from the present invention is, inter alia:

ι. The publication describes only a foam having "fire resistant" properties.

2. The material according to this patent consists of a basic material which, because of its chemical nature, emits an appreciable amount of energy and smoke during combustion, and which therefore is unsuitable under present-day requirements as a fire barrier in vessels or buildings.

NO 157,854 C2 describes a product which is basically close to the core material used in connection with the present invention, a prepreg of glass fiber and phenol containing

10 thermoplastic, hollow microspheres. The patent describes both the product and the production process for the prepreg material. It also describes the preparation of what is termed "homogenous laminates" is produced, this being a material very close to the core material used in the present ' invention. The production of "heterogenous laminates" is also described, according to which the prepreg material is pressed together with plywood or other wood panels. What distinguishes the present invention from this patent is, inter alia, the following:

20

NO 157,854 C2 does not describe the use of the material as insulation in the build-up of a fire barrier. That is, although the surface layer is of importance, it is first and foremost the mechanical properties and thermal

25 insulation that are important during the strain imposed by a fire.

2. NO 157,854 C2 provides no description of materials suitable as laminates in connection with this prepreg foam 5° core, nor does it describe a structure which is suitable as a fire barrier.

An object of the present invention is the use of a sandwich panel, the core of which consists of a material prepared

35 from a varying number of layers of prepregs of a thermoset¬ ting resin containing thermoplastic microspheres and where the outer laminates are of a conventional type, as fire

insulation or fire barrier, the core constituting the whole insulation or a part thereof.

In what follows we shall attempt to elucidate certain concepts within fire technology, so that the invention can more easily be distinguished from prior art. In fire technology there are defined two main groups of properties for which separate requirements are set. The test ethod/- standards are likewise completely different:

10

Fire resistance is characterized by fire insulation and fire integrity (being sealed against smoke and having structural durability in a fire). This comprises, for example, fire doors and fire walls. The requirements to fire

!5 resistant structures are that they shall "keep the fire inside" for a certain period of time. This is generally implied in the requirement that the temperature on the unexposed side shall not exceed a given level during a given period of time. The structure must be able to support the

²⁰ loads for which it is dimensioned and no smoke or flames must penetrate the structure. Such a structure can be prepared from a number of materials, such as wood, steel, concrete, glass wool, rock wool, gypsum boards, each by itself or, pre¬ ferably, different materials in combination.

25

Fire reaction characterizes the reaction of materials to the impact of a fire (generally small, for example a cigarette glow, small burners simulating various fire sources, etc.), and what is tested is generally the properties of the 5° surface. Radiation of heat, smoke/gas production, flame spread, and ignition point are central magnitudes. These magnitudes do not indicate how the structure behaves as a fire barrier; cf. the point above on fire resistance.

5 More simply expressed, fire resistance is a description of how a fully developed fire influences the surroundings outside the fire cell, whereas fire reaction relates to

parameters which are important as to whether a fire will develop or how it does develop within the fire cell.

As noted, the invention relates to the use of a sandwich panel where the core, constituting the insulating part of the structure, is prepared from a varying number of layers of preimpregnated fiber reinforcement, so-called prepregs. This preimpregnation consists of a fire retardant resin and microspheres having low weight, so that the density of the

10 prepreg material is low. This prepreg can be used to produce the core in various thicknesses and densities, depending upon requirements set to fire insulation/fire protection. This production takes place in press tools, where heat is supplied to complete the curing of the prepreg ! material.

The type of core material used in the above mentioned panel has, to our knowledge, never been used before in structures serving as fire barriers/fire insulation. Other types of ²⁰ cores between laminates, which in principle are similar to the laminates used in the present case, have been used, however. Thus, polyimide foam and other suitable insulation material may be mentioned.

² In the core material used according to the invention, the fire retardant resin can advantageously consist of phenolic resin, which at room temperature is liquid and thus can easily be applied to the selected reinforcement material. Most types of phenolic resin can be used since all have good o properties in a fire. The reinforcement of the core can advantageously consist of glass fiber or other reinforcement material having good properties at high temperature. The microspheres used to impart low density to the core, can advantageously consist of thermoplastic. The main thing is

35 that they are light and on application are well distributed in the prepreg material. The laminates used in conjunction with the core can advantageously consist of glass fiber

reinforced phenolic resin, or another high-temperature resistant combination of resin and reinforcement. Metallic surfaces can also be used. Optionally, the sandwich panel may also be provided with a light weight backing insulation of polylmide foam or other material having low weight and good insulating properties at high temperature.

The fire protection panel that is obtained by the present invention has low weight compared to previously used panels allegedly fullfilling the same requirements. The panel has furthermore low heat conducting power, has good sound absorbing properties, is rigid and can support relatively heavy loads, is very easy to form/adapt in installation, does not corrode and has good resistance to moisture, rot and most chemicals.

An advantageous area of application for the sandwich panels obtained according to the invention is that of fire barrier and fire insulation in connection with aluminum structures.

As mentioned by way of introduction, the present invention also relates to a method for continuous fabrication of sandwich panels.

A continuous fabrication of sandwich panels is most often carried out by fabricating laminates and core material separately and thereafter joining them in a gluing process. Since the method thus comprises many steps, it becomes relatively expensive and elaborate.

In a single case one has succeeded in producing a machine where wet laminates are applied to the core in a continuous vertical process. This process is described in "Proceedings from the First International Conference on Sandwich Construc- tions" (1989), pp. 599-605, ISBN 0 947817 37 9. This is a process which demands very high accuracy with respect to the thickness of the core material (to avoid excessive waste of

liquid resin and to obtain a good surface), and which demands a production hall of great height (15-20 meter). This method is therefore encumbered with two serious defects, demanding both costly production premises and a costly production line.

Accordingly, there is a need for a method of fabricating sandwich panels which is simple and can be carried out at lower costs than those of previously known methods.

The present invention therefore provides a method for continuous fabrication of sandwich panels, which method is characterized in that it is carried out horizontally in such a manner that the reinforcement is drawn from rolls down to an upper and a lower conveyor belt, the reinforcement is wetted with the desired thermosetting resin, the reinfor¬ cement with the thermosetting resin is pressed against the conveyor belt by means of rollers in order to achieve distribution of the resin and thorough wetting of the reinforcement fibers, the core is positioned in the lower conveyor belt and pressed against the reinforcement/resin, whereafter the curing and cutting is carried out in a manner known per se.

The curing of the panels can advantageously be carried out in, for example, a tunnel oven having a pre-set temperature profile.

In the method according to the invention the laminates, while wet, are placed on the core in a continuous, horizontal process. This means that the laminates do not have to be prefabricated, and additional gluing processes are avoided.

Another advantage of the method according to the invention is that it does not depend upon a very accurately adjusted thickness of the core, since the core is pressed down upon the bottom laminate (independently of the thickness) and

thereafter the top laminate is placed on the core. Gravity will thus work to the advantage of the process.

The production line of the method according to the present invention is horizontal, thus requiring little height in the production premises, and it is simple and involves fewer steps than known processes, thus providing an economically advantageous overall solution.

Finally, the production line used in the method according to the invention can also be used to produce laminates only. In that case the core is omitted and only the lower laminating line is used.

According to a preferred embodiment of the invention, the wetting with the thermosetting resin is carried out by means of an oscillating dispenser which also mixes the components of the resin.

The method according to the invention can in be used in the manufacture of any type of sandwich panel. One type of such panels having successfully been manufactured by the method according to the invention is a panel to be used as fire barrier and fire insulation, such as the sandwich panel mentioned by way of introduction.

Embodiment example

The panels can be used as a protection for aluminum structu- res, the requirements for such protection being described in IMO Resolution A.373. For a fire barrier affording protec¬ tion for 60 minutes, the so-called "A-60" class, the requirement is that the rise in temperature on the side opposite to that of the fire exposure does not exceed an average of 139°C during the test period of minimum 60 minutes. At the same time it is not permitted that the

temperature anywhere in the aluminum structure increase by more than 200°C. The test is described in IMO Res. A. 517.

A panel produced with the core material according to the invention was tested pursuant to the above provisions.

The panel that was tested was a self-supporting sandwich panel having a thickness of 26 mm, consisting of laminates of glass fiber reinforced phenol and a core of glass fiber reinforced, expanded phenol having a light weight backing insulation of polyimide foam.

This panel fulfilled all requirements set in the above mentioned standards and is therefore well suited to the above indicated use.

The panels can also be used as self-supporting fire barriers, and in door constructions, where the same requirements to back-side temperature and surface are set.