MICA BASED SANDWICH STRUCTURES

Abstract

The present disclosure is related to a composite sandwich panel having a first layer including mica paper, a folded core or honeycomb structure including mica paper and a second layer including mica paper. The first and second layers are glued onto the foldcore using mineral adhesive made of one or more alkali metal silicate(s).

Claims

1. A composite sandwich panel (1) comprising a first layer (2) comprising mica paper, a folded core or honeycomb structure (3) comprising mica paper and a second layer (5) comprising mica paper; wherein the first (2) and second (5) layers comprising mica paper are glued onto the folded core or honeycomb structure (3) by a mineral adhesive comprising one or more alkali metal silicate(s) and in that the alkali metal silicate adhesive has a foam (4) structure, partially filling an empty space left by the folded core or honeycomb (3) structure between the first and second layer.

2. The composite sandwich panel (1) according to claim 1 wherein the one or more alkali metal silicate(s) is (are) selected from the group consisting of lithium silicate, sodium silicate, and potassium silicate.

3. The composite sandwich panel (1) according to claim 1, wherein the panel (1) comprises additional layer(s) comprising fiber mat(s) between the foldcore or honeycomb (3) structure and the first and/or second layer(s) (2,5) comprising mica paper.

4. The composite sandwich panel (1) according to claim 1 wherein a molar ratio of silica to alkali metal oxide is comprised between 1.6 and 3.5.

5. The composite sandwich panel (1) according to claim 1, wherein a foam density is comprised between 0.01 and 0.25 g/cm.

6. A method for producing the composite sandwich panel (1) of a claim 1, said method comprising the steps of: i. coating a liquid mineral solution comprising said alkali metal silicate(s) onto a first layer (2) comprising mica paper, or disposing a fiber mat impregnated with said alkali metal silicate(s) onto said first layer (2), thereby forming a first hydrated alkali metal silicate(s) surface; ii. disposing a first face of a foldcore or honeycomb structure (3) comprising mica paper onto said first hydrated alkali metal silicate(s) surface; iii. coating a liquid mineral solution comprising said alkali metal silicate(s) onto a second layer (5) comprising mica paper, or disposing a fiber mat impregnated with said alkali metal silicate(s) onto said second layer (5), thereby forming a second hydrated alkali metal silicate(s) surface; iv. disposing said second hydrated alkali metal silicate(s) surface onto a second face of the foldcore or honeycomb structure; v. heating the obtained foldcore or honeycomb sandwich structure at a temperature comprised between 250 and 350° C., for a duration comprised between 1 and 20 minutes.

7. The method according to claim 6 wherein the first and second hydrated alkali metal silicate(s) surface are pre-dried before final heating step at a temperature between 60 and 100° C.

8. The method according to claim 6 wherein the mica paper in the foldcore or honeycomb structure is a silicone impregnated partially cured mica paper, which is fully cured during the heating step.

9. The method according to claim 6 wherein the liquid mineral solution is an aqueous solution comprising between 25 and 55% by weight of alkali metal silicate (s).

10. The method according to claim 6, wherein the obtained structure is pressed at a constrained thickness during the heating step during the final heating step.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 represents a side view of an example of fire resistant panel according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present disclosure aims at improving the fire resistance of mica based sandwich panels 1 comprising two mica paper skins 2,5 wrapping a folded or honeycomb mica paper structure 3 by reducing the use of organic matters in such panels. This is obtained by using alkali metal based silicates such as lithium silicate, sodium silicate and potassium silicate instead of the usual silicone based adhesives.

[0033] As the silicates described here above are moisture sensitive, additional metal silicates improving moisture sensitivity are preferably added to the adhesive formulation.

[0034] Those silicate based adhesives not only have the advantage of sustaining higher temperature than silicone based adhesives. As an additional advantage, depending on their residual moisture, they swell in the form of a foam when heated at temperatures comprised between 250 and 350° C.

[0035] Such foamed structures have the advantage of increasing the contact surface between the skin layers and the core, thereby improving the macroscopic mechanical strength of the structure. As a further advantage, the foam 4 structure improves the isolating power of the panel, further reducing fire propagation.

[0036] Therefore, the preferred panel structure of the present disclosure is the one represented in FIG. 1, wherein the core structure is completely embedded in the foam 4 formed by the alkali metal silicate.

[0037] Such a structure can be obtained by pressing two mica paper skin layers 2,5 coated with hydrated alkali metal silicates onto a mica paper core 3 and heating the obtained structure at foaming temperature of the hydrated alkali metal silicates. Adequate temperatures are comprised between 250 and 350° C., preferably between 270 and 330° C. for time duration comprised between 1 and 20 minutes, preferably between 5 and 15 minutes.

[0038] In order to ease the water outflow during swelling of the foam, a foldcore structure is preferred over honeycomb. In case of honeycomb, openings are preferably made in the honeycomb walls to let water vapor flowing out of the foam.

[0039] The coating of the mica paper can be performed by usual liquid coating method, such as spraying, curtain coating or by using a mat impregnated by a liquid mineral solution comprising the alkali metal silicate.

[0040] In a preferred embodiment, a layer of alkali metal silicate is deposited, on a mica plate that has an integrated non-woven glass fiber surface. The silicate layer deposited on the plate is solid at room temperature and its thickness is enough for, by heating, achieve the gluing of the sandwich core and swelling and expansion in the free space of the core, in a way that it improves the thermal insulation.

[0041] The final product comprises at least one layer of mica paper comprising a glass fiber finish (mica silicone pressed together with non-woven glass mat)

[0042] In case of both plates surfaces having the glass fiber finish, one of the faces is used for a better adhesion of paint or finish of the external skin, or is also covered with a silicate layer, which is used to form a multi core sandwich (two or more cores piled together)

[0043] Those plates can be cut at the dimensions necessary for the final panel structure, then a core intercalated in between, cogetherm edge reinforcements can also be introduced on the perimeter of the structure, and the whole piece heated under limited spacing at for example 280 C for obtaining the final adhesion of the pieces and swelling of the foam.

EXAMPLE

[0044] A non-woven fiberglass paper of around 25 g/m.sup.2 is impregnated with around 2 kg per square meter of aqueous sodium silicate solution 43% in dry matters.

[0045] This wet non-woven is disposed on top of a Cogemicanite® 505.3P mica layer and a folded mica core is disposed on this wet non-woven.

[0046] Another mica layer with an identically sodium silicate impregnated non-woven is used to close the sandwich.

[0047] Then the sandwich is placed with a restriction of height at the value of the thickness of the core +2×thickness of the skins inside an oven. There it is dried for 1-1.5 h at 100° C. and then treated at 280° C. for also 1-1.5 hour for expansion.