FR2475970A1 - Heat formable sheet mfr. by hot pressing dried paper paste - contg. mineral and thermoplastic fibres opt. other mineral and/or plastics components; then firing to burn out organics - Google Patents

Abstract

Method of mfr. of a sheet of dry heat formable material based on refractory or semi-refractory fibres and thermoplastic binders is claimed using the paper making technique in which a machine is used selected from the flat table, round form, and the double cloth machines and a combination of these. Alternatively the cardboard roller machine or a simple sieve may be used as the sheet making appts. The heat formable material may be selected from the different types of mineral fibres, i.e. glass alumino silicate, rockwool, asbestos, carbon aramid or their mixts., bonded with thermoplastics such as polyolefine fibres opt. contg. fillers, and also thermoplastic binders. Thermosetting resins may be included according to the end prod. The sheets may be used at temps. from 150-1600 deg.C such as thermal insulating in the foundry, furnace construction, in high temp. electrical insulation and antipollution systems for engines. Finished materials may contain little or no organic materials, according to the use invisaged.

Description

 The present invention relates to a method for manufacturing a thermoformable cardboard based on inorganic fibers, and it also relates to the products and parts produced by the implementation of said method.

 The invention relates more precisely to the manufacture of a thermoformable dry carton by compression, making it possible to obtain shaped parts which can withstand in service at teipératires of 150 C to 1600 C.

 We know how to make thermoformable cartons from organic fibrous materials, but we then obtain parts with limited temperature resistance. The originality of the present invention lies in particular in the fact that quton can obtain finished parts containing little or no organic matter, which greatly increases the possibilities of temperature resistance.

The invention is characterized by the use of a papermaking process in the aqueous phase to produce a thermoformable sheet comprising
- as main base, temperature-resistant inorganic fibers, that is to say of the refractory or semi-refractory type
- as binder, thermoplastic materials in the form of fibers, powders, or dispersions
- as active ancillary products, materials used to give bonds between inorganic fibers
- as various ancillary products, materials facilitating the printing on a cardboard machine and charges making it possible to lower the price of materials.

 The sheet obtained, heated to the point of softening of the thermoplastic binders, is compressed in a mold, which gives a part with the desired shape.

 According to an additional characteristic of the invention, the part thus formed is made thermostable by a subsequent treatment acting on crosslinkable products holding hot introduced either during the manufacture of the sheet, or by impregnation or spraying of the part.

According to an additional characteristic of the invention, this treatment consists in heating the part either to the crosslinking temperature of the heat-resistant binders, or to a temperature higher than 40,000 allowing it to be; combustion-do all organic matter. By temperature resistant fibers is meant fibers which can withstand at least 4000C permanently. These are for example the following fibers:
- ceramic fibers of silico aluminate;
- rock wool fibers
- glass fibers
- carbon fibers
- asbestos fibers
- aramid fibers
- mixture of these fibers.

 To be able to be processed in a normal papermaking circuit, these fibers must have a length of less than 10 millimeters, with widths of between 20 and 300 microns.

 However, the mineral fibers which can easily be cut in a papermaking circuit can have several centimeters.

By thermoplastic binder is meant, under fiber forae
- polyethylene fibers;
- polypropylene fibers;
- polyester fibers;
- acrylic fibers; and in powder or dispersion form
- polyolefins;
- hot meits;
- polystyrene
- acrylic styrenes;
- vinyl acetates;
- ethylene vinyl acetate.

By active ancillary products is meant
- thermosetting organic binders, such as formalin ireas, melanins formaldehyde, phenols formaldehyde, resorcins formaldehyde - ~ -
- mineral binders such as colloidal silica, bentonite, alumina, alumina phosphate.

 This list is not exhaustive.

By various ancillary products, we mean:
- products intended to facilitate drawing on a cardboard machine, such as cellulose in its various fibrous forms, starch and manno-galactan;
- fillers such as calcium carbonate, kaolins, barytes, talcs.

 The process according to the invention is characterized by the following stages - Sheet setting by a papermaking-type manufacturing circuit.

 The fibers and the various products are mixed in a pulper.

 The mixture contains from 50 to 90% of inorganic fibers, from 10 to 50 of thermoplastic fibers or of powder or dispersion (counted as dry matter).

To this basic mixture, the additional products are added
- from 0 to 50% by weight of cellulosic fibers
- from 0 to 30% by weight of mineral binders;
- from 0 to 15% of starch or manno-galactan binders
- from 0 to 500 charges.

 The percentages are counted in relation to the treatment. inorganic fibers and thermoplastic binders.

 The mixture being well assured, a paste is obtained which is sent to a conventional paper or cardboard machine, of the Poudriier type, or with a round shape. You can also use a multiform, multitable, or mixed machine, with shapes and tables. One can use a machine with two fabrics or several of these machines in series.

 Finally, we can use a reel machine, whether table or form. In some cases the sheets can be obtained by suction under sieves.

 Some of the auxiliary products can be introduced at the machine head. We can thus obtain sheets of 100 to 8000 grams per square meter.

- Thermoforming.

 One or more are preheated (in the case where the thermoplastic binder allows the sheets to be welded together during compression) sheets obtained by the above process up to the point of softening of the thermoplastic binder and preferably a few tens of degrees centigrade at -of the.

 The preheated sheet or sheets are introduced into a mold and pressed. The pressure is variable depending on the density to be obtained, from 0.5 to 100 kg / cm2.

 The part cooled below the softening point of the binder can be handled: it is left to cool outside the mold.

- Post treatment.

The parts thus obtained are sensitive to temperature in two ways:
- by softening of the binder for temperatures above rea at their softening point
- by burning the binders for temperatures above their decomposition point. Depending on the case, we operate as follows:
a) for the temperatures between the point of rsmollial oath and the point of decomposition of thermoplastic binders, r is used
- the thermosetting urea formaldehyde resins, lelamines, formaldehyde, phenol formaldehyde or resorcinol formaldehyde introduced into the mass which we have designated under the name of active side products;
- the same resins or others which cannot be used in the manufacture of the polyester sheet or epoxies used by impregnation or spraying.

 In both cases, the resins are polymerized. by heat treatment unless catalysts allow cold polymerization.

b) For high temperatures, we use s
- mineral products, colloidal silica, bentonite, used in the mass that we have designated by active side products.

 - The same or other unusable by introduction into the mass and which are provided by impregnation or spraying of the part, such as aluminum phosphates, alkali silicates.

 Bang both cases, the parts can be treated in an oven to burn all organic matter.

 Parts are thus obtained without any organic matter.

 The following examples, given without limitation, will allow a better understanding of the characteristics of the invention.

Example 1
In a pulper containing 2 cubic meters of water, we add:
- silico aluminate fibers 85 kg
- polyethylene fibers 15 kg
We add as additional materials r
- Bentonite 5 kg
- colloSdale silica 5 kg
- Starch 8 kg
The dough thus obtained is sent to a winding machine making it possible to produce a sheet of 1000 g / m2 with a thickness of approximately 2 n.

 This sheet, heated to 200-C, is pressed to 10kg / R2 in a cold mold. This gives a piece of about 1.2so thick for. The part obtained is passed through an oven at 800 C, until the complete combustion of organic matter.

 The part retains its shape and the temperature resistance of the silico aluminate fi bre. The piece can be used as a protective element for foundry molds, or as insulation in household appliances that should not emit odors.

Example 2
In a pulper containing 2m3 of water, add s
- glass fiber 85 kg
- polypropylene fibers 15 kg
We add cons annex material
- phenolic powder 15 kg
- starch 5 kg
The dough is sent to a round-shape winding machine.

A polyacrylamide in solution is introduced at the machine head to improve the retention of the phenolic powder. A sheet of 2000 g / m2 is thus obtained. This sheet, heated to 200 C, is brought into a cold mold and pressed to 15 kg / cm2, which gives a piece of about 2 minutes thick. Preheating is sufficient to polymerize the phenolic powder. The part retains a resistance at over 1500C and is used without post-treatment, as an electrical insulator, for example.

Example 3
in a pulper containing 2x3 of water, add t
- rock wool 84 kg
- butadiene latex (B 40% dry)
styrene 80% styrene 40 kg
We add cons additional materials r
- cellulose 20 kg
- alumina sulfate 10 kg
The dough is sent to a Poudrinier machine. A polyethylenimine solution is added upstream of the machine head, in order to precipitate the latex well.

 The machine will output a sheet of 500 g / m2, about 1.2 n thick.

 This sheet heated to 125 C will be brought into a cold mold and pressed to 0.5 kg / cm2, which will give a piece of about 1 mm thick.

 The part is impregnated with a mixture of acid aluminum phosphate and flame retardant ammonium salts. A treatment bridge at 200 ° C. gives the part heat resistance and non-flammability.

Example 4
In a pulper containing 2m3 of water, we add
- silico aluminate fibers 30 kg
- rock wool fibers 30 kg
- polyethylene fibers 40 kg
We add as annex material t
- Cellulose fibers 40 kg
- starch 8 kg
The paste thus obtained is sent to a winding machine making it possible to produce a sheet of 1000 g / m2 with a thickness of 2 mm.

 This sheet heated to 170 C is pressed to 2 kg / cm2 in a cold mold.

 The part obtained without any other treatment can be used in the molding of metals for the protection of foundry cores and cores, in the shell casting processes.

E: willow 5
Without a pulper containing 2m3 of water, we add:
- silico aluminate fibers 85 kg
- 40% acrylic styrene emulsion 40 kg
The following products are added:
- bentonite 15 kg
- alumina sulfate at 16% Al2O3 10 kg
The pulp thus obtained is sent to a cardboard winding machine making it possible to produce a sheet of 1500 g / m2 of approximately 3 mm thick. This sheet heated to 150 ° C. is pressed in a cold mold at 10 kg / cm 2, which gives a piece of 1.5 mm thick.

 The part is impregnated with acidic aluminum phosphate, then brought to an oven at 800 C, where the organic matter is burned. A part is thus obtained which can serve as an insulator for industrial ovens.

Claims (12)

 1. Process characterized by the manufacture according to the papermaking technique in an aqueous medium of a dry thermoformable sheet based on refractory or semi-refractory fibers and on thermoplastic binders.  2. Method according to claim 1, characterized in that one uses to manufacture the sheet a continuous machine belonging to the group formed by flat table machines, round shape, double canvas, and combination of these systems.  3. Method according to claims 1 and 2, charac terized in that a cardboard rewinding machine is used to manufacture the sheet.  4. Method according to claim 1, characterized in that a simple sieve is used as a sheet manufacturing machine.  5. Method according to any one of the preceding claims, characterized by the use, as mineral fibers, of fibers belonging to the group formed by fibers of silico aluminate, glass, wool, rock, asbestos, carbon, aramids, or a mixture of the above.  6. Method according to any one of the preceding claims, characterized in that the thermoplastic binders are used in the form of polyolefin fibers, loaded or not.  7. Method according to any one of the preceding claims, characterized in that thermoplastic binders are used in the form of powder or aqueous dispersion, alone, mixed with one another, or with fibrous binders.  8. Method according to any one of the preceding claims, characterized in that thermosetting resins are added in the form of a solution, dispersion or powder in the paste used for the manufacture of the sheet.  9. Method according to any one of the preceding claims, characterized in that mineral binders such as bentonite and silica are added to the paste.  Xlloidale with the aim of ensuring - the bond of the general fibers after combustion of the organic compounds.  10. Sheets obtained by the implementation of the method according to any one of the preceding claims, and shaped parts obtained from said sheets, characterized in that they can be used as thermal insulation in foundries, for the construction of ovens , household appliances, engine anti-pollution systems, and as high temperature electrical insulation.  11. Method according to any one of claims 1 to 9, characterized in that, during thermoforming ,. a stack of unitary sheets is formed which are welded together under the effect of temperature and pressure.  12. A method according to any one of claims 1 to 9 and 11, characterized in that it allows the production of composite parts, that is to say composed of different materials, using the heat seal properties materials which are the subject of the implementation of the process.