CA1176050A - Cellular insulation from naturally occurring minerals - Google Patents

Abstract

Abstract:
An insulating material of cellular structure is described which is made from naturally occurring minerals, such as talc. A mineral component having a foliated or platy structure is mixed in aqueous solution with sodium silicate a bonding agent and a small amount of foaming agent. This mixture is then heated in a microwave oven to transform the aqueous mixture into a rigid cellular structure. The product is an excellent insulating material, with a good R value and a high flame resistance.

Description

This invention relates to an insulating material of cellular structure, and particularly to such material made from naturally occurring minerals, such as talc.
With the worldwide energy crisis, there are now great demands for energy conservation in all areas. In the cold countries, an essential is energy for heating and one of the best ways of reducing demand on heating fuel is improved insulation.
Many different insulating materials are now on the market and some of these have fallen into considerable disrepute. Thus, it has been known for some time that asbestos fibres are a dangerous material unless they are properly enclosed and, more recently, the dangers of urea-formaldehyde have been discovered. Moreover, many insula-ting materials represent a fire hazard either by beingflammable or by giving off a heavy black smoke and/or toxic gases when heated to high temperatures.
There is, therefore, a great demand for an insulating material which would be highly flame resistant and would not give off toxic gases or produce smoke at elevated temperatures, while being cheap and easy to produce.
According to the present invention there is provided a novel insulating material of cellular structure which meets the above requirements. This novel insulating material is formed of (a) a mineral component having a foliated or platy structure and (b) as a bonding agent for the mineral, sodium silicate. The novel material is produced by preparing an aqueous mixture of the mineral component and the sodium silicate bonding agent and heating this mixture by microwave heating, causing the mixture to expand and form into a cellular insulating structure. It may also be desirable to include in the mixture a water repellant, such as a silicone.
The mineral component is a naturally occurring mineral having a foliated or platy structure, e.g. minerals in the form of crystals belonging to the monoclinic system with excellent basal cleavage and flexible laminae. Generally, the minerals are silicates of varying compositions, preferably magnesium silicates, aluminu,n silicates, etc.
Talc is a preferred mineral, but many other minerals of a foliated or platy structure may be usedO Among these may be mentioned the mica group, such as muscovite, phlogo-pite, biotite, lepidolite, vermiculite, the chlorites, kaolin, serpentine, etc.
Materials of the above type have the great additional advantage of being geographically widespread. Thus, the mineral component can be obtained near large centers of population, thereby avoiding heavy transportation costs.
For example, naturally occurring minerals of this type are available widely across North America, as well as in the United Kingdom, Switzerland, Italy, France, Germany and many other countries.
Sodium silicate as the binding material also has the great advantage of low cost and ready availability through-out the world. It has the further important advantage of needing only low energy input during manufacture because the processing temperature need be no greater than that required to evaporate the water.
It has also been found that a reaction takes place between the mineral component and the sodium silicate which results in the converted product having low solubility in water. It is believed that this is the result of the composition complexity of the naturally occurring talc, and its reaction with the sodium silicate.
To obtain a cellular structure with the mineral compon-ent, some form of foaming agent is normally required. Many different chemical foaming systems are available, among which there may be mentioned freon gas and a variety of protein foamers. The foaming agents are used in very small amounts, typically less than 1~ by weight.
In the process of the invention, the mineral component, bonding agent and foaming agent are thoroughly mixed, with the mineral component preferably being present in an amount of 15 to 60 wt. ~ and the sodium silicate preferably being present in an amount of 85 to 40 wt. ~. This mixture is then subjected to microwave heating, causing the water to evaporate and internal steam pockets to form, resulting in the formation of voids within the mass. The result is the conversion of this mass into a rigid cellular form.
The microwave heating may be done in a microwave oven, with the mixture being held in containers or moulds. This results in rigid, cellular blocks of insulating material.
Alternatively, the mixture may be fed onto a continuous belt conveyor with the belt passing through a microwave heating zone to form an irregular mass of insulating material. It is also possible for the mixture to be fed into forms carried on a continuous conveyor whereby shaped pieces of rigid cellular insulating material are formed on the conveyor.
The product obtained in this manner typically has a density of less than 30 lbs/cu. ft. Its compressive strength has been found to vary widely depending upon the amounts of binder, mineral, foam, water and rate of conversion. The compressive strength is typically up to about 200 psi at a density of not more than about 30 lbs/cu.ft.
The product is not flammable even at high temperatures and resisted damage when a propane torch flame was held _ 4 _ ~17~

against one side of a one inch thick piece of insulating material of the invention until the face of the piece became red hot.
The product is obtained from the microwave oven in rigid cellular form and may be crushed to form a particu-late insulating material. This particulate material may be in granular, nodular, powder or similar form designed to be installed dry, by pouring, blowing or hand placement between retaining surfaces or as a covering layer~ Such material may also be incorporated into other products during manufacture, such as rigid boards also containing wood fiber.
The product of the invention may also be formed into the typical type of batt insulation, such as that made frora rock, slag or glass with or without binders, or it may be made in a rigid sheet form similar to styrofoam sheet, or it may be molded into rigid or semi-rigid cylindrical, semi-cylindrical or segmented sections for application on pipes, structural steel, etc. It may also be prepared in a granular or particulate form that can be sprayed onto structural steel.
Another use of the product of the invention is in ceiling tiles. Although ceiling tiles are not normally classed as thermal insulation, a ceiling tile which has excellent thermal insulating and acoustic characteristics and fire resistance is obviously highly desirable. Par-ticularly in multi-floored apartments or condominiums where each occupant pays for his own heat, it is increas-ingly important not to heat the unit above. In addition, if the ceiling tile also constitutes a fire barrier, greater safety advantages result.
Certain preferred embodiments of this invention will now be illustrated by the following non-limiting examples:
Example 1 A talc was obtained from Baker Talc Ltd. in Quebec, Canada and this was crushed to a particle size of approxi-mately -325 mesh. This was thoroughly mixed with sodium ~7~ P5V
~ 5 --silicate and water in the proportions of 2 parts by weight talc, 1 part by weight sodium silicate and 2 parts by weight water. To the mixture was added 0.1 ~ by weight of foaming agent. This mixture was then poured into a forming tray and placed in a microwave oven. It was heated at 100C for 10 minutes during which time the mixture expanded and formed into an expanded cellular product. This product had a density of 7 lbs/cu.ft., a compressive strength of 36 psi and an R value of 2.9.
A series of additional mixtures were prepared in different proportions using this same source of talc and the conditions and results were as follows:

Parts ¦Parts of¦Parts ¦Foaming Heating¦Product IcomPress-¦ R-of Talc Sodium of Agent Time Density ive Str. Value Silicate Water (~) (min) (psi)

2 1 2 0.1 10 7 36 2.1 2 1.2 2 0.15 10 6.7 24 2.2 ~ 1.4 2 0.2 10 6.3 31 2.4 2 1.8 2 0.1 ~0 5.9 28 2.9 2 0.8 2 _ 10 11.3 37 1.8 2 0.5 1.5 _ 10 14.1 36 1.3 ~7~

Example 2 A sample of the mineral tremmolite obtained from Ontario, Canada was crushed to a particle size of -325 mesh. Using this material with sodium silicate and a foaming agent, samples of insulating material were prepared in the same manner as in Example 1 above. The conditions and results are set out in the Table below.

._ Parts Parts of Parts Foaming Heating Product Compress- R-of Trem- Sodium of Agent Time Density ive Str. Value molite Silicate Water (~)(min) (psi) 2 0.5 2 0.1 10 25 98 0.7 2 0.8 2 0.1 10 ~7 56 1.2 2 2 2 0.1 10 20 71 0.9 2 ~ 1.5 1.5 0.1 10 18 62 1.1 o E~ample_ A series of tests were conducted to determine the degree to which the products of the invention absorbed moisture. Two types of materials were used in this test, one being a ceiling tile made from the mineral tremmolite and the other being a loose fill material made from talc.
For this test, the products were held in an atmosphere at 50% humidity until the moisture absorption had levelled out.
The properties of the products and the results obtained are set out below:

Product Type Parts of Parts of Product Level Out Moisture Mineral Sodium Density Time (days) Absorption Silicate (%) Tremmolite-Ceiling Tile A 2 0.9 18 54 4.6 B 2 1.4 19 86 8.1 Talc Loose Fill A 3 2 6.4 61 3.7 B 2 2 5.8 48 3.3 ~L7~

Example 4 A further series of tests were conducted to determine the effects of subjecting the products of the invention to high temperatures over prolonged periods.
For these tests three different products were formed all using Baker talc as the starting mineral to obtain products of three different densities. These products of different densities were then subjected to temperatures of 200F and 1600F for prolonged periods to determine whether shrinkage fell within acceptable limits. The results were as follows:

TAsLE 4 Temperature 200F : Time 96 Hours . _ TALC TALC TALC
A s C
.
Density ~lbs/cu.ft.) 11.8 7.6 16.2 Weight Loss (%) 1.8 1.7 2.1 Linear Shrinkage (~) ~.8 0.8 n.s Temperature :L600F - Time 24 Hours Density (lbs/cu.ft.) 11.8 7.6 16.2 Weight Loss (%) 12.9 12.5 13.1 2Q Linear Shrinkage (~) 7.7 8.4 3.8

Claims (6)

Claims:

1. A method of making a cellular insulating product which comprises preparing an aqueous mixture of (a) particles of talc and (b) a sodium silicate bonding agent, and heating said mixture by microwave heating, causing said mixture to expand and form into a cellular insulating structure.

2. A method according to claim 1, wherein the aqueous mix-ture also contains a foaming agent.

3. A method according to claim 2 wherein the foaming agent is present in an amount of up to 1%.

4. A method according to claim 2 wherein the mixture is cured into a rigid, cellular block under microwave heating.

5. A method according to claim 2 wherein the mixture is fed onto a continuous conveyor and subjected to microwave heating on the conveyor to expand and form into a cellular insulating product.

6. A method according to claim 4 wherein the rigid, cellular block is crushed to form particles of insulating material.