The invention relates to a composition serving as a coating or adhesive in a product and at the same time protecting the product from fire as a layer which inhibits the trans¬ fer of fire and ignition and above all remains cohesive in a fire situation, as specified in greater detail in the preamble of accompanying Claim 1. Such a fireproofed prod¬ uct is most commonly a board such as a building board, insulation board or cladding board, or a sandwich building panel. The composition may, however, be used together with any material or structure, for example on mineral, con¬ crete, metal, wood, plastic, mineral-wool and paper sur¬ faces and on plastic-based insulation surfaces.

The insulative capacity of known fire-resistant boards or panels is based primarily on the resistance of the material to ignition and secondarily on its heat insulating power. Such materials function rather well in terms of fire, but their structure is brittle so that the protective power is effective for a rather short time only, and thereafter the material can no longer withstand shock, compression or bending.

For example, paint-like coatings are used which are applied with a brush or sprayed onto the desired surface. Often some non-combustible filler, such as fine crushed stone, slag, asbestos, fiber, or the like, is added to the coat¬ ing. Such coatings do increase the so-called protection time of the coated products, but they are not capable of heat insulation, and thermal damage is caused in the pro¬ tected surface relatively rapidly as the protective struc¬ ture collapses. By protection time is meant the time in minutes that it takes for heat to be transferred through the test specimen in a burning test before the opposite surface has reached a certain temperature.

There are also known coatings the purpose of which is to prevent fire damage due to high temperatures. Such coatings have, in addition to fire damping properties, also insulat¬ ing properties. As the insulating component it is known to use as a filler in the coating for example waterglass, vermiculite, clay, etc. , which is pre-expanded and owing to its porous structure will retard the transfer of heat through the coating.

Such a coating does increase the protection time of the product to be protected, but the structure of this coating, also, is broken and brittle in a fire situation, and thus it cannot serve effectively as a heat-insulating layer for a long time, because it collapses rapidly.

The object of the present invention is to provide a fire- proofing which increases the resistance to ignition and the heat-insulating power of a product and, above all, at the same time provides a high strength for the burned struc¬ ture, activating these properties only upon the occurrence of a fire situation.

According to the invention this is achieved by giving for the composition serving as a coating or an adhesive the characteristics set forth in the characterizing clause of Claim 1. By proportioning the amounts of waterglass and blast-furnace slag or corresponding slag in the composition serving as a coating or an adhesive so that the proportion of waterglass in the composition is 65 - 99 % by weight and the proportion of blast-furnace slag 0.5 - 30 % by weight, pores which are completely closed and regulatable in size are produced in a fire situation in the coating of a prod¬ uct or in the adhesive layer or layers of a product. With the use of this component ratio in the composition, an active fireproofing has surprisingly been achieved; in a fire situation the fireproofing expands considerably, form-

ing a protective structure which does not collapse and thus provides a rather long travel path for and at the same time a good convection and radiation barrier to heat transfer, while the protective structure retains a dense and strong structure for a rather long time. When used between dif¬ ferent layers, the composition serves as an adhesive by means of which a sandwich structure can be produced. In a fire situation the adhesive layers of such a sandwich structure expand in the same manner as when used as a coat¬ ing, and owing to their unbroken homogeneous structure they enhance the strength of the sandwich structure for a con¬ siderable time.

Corresponding properties are not found in any known fire- proofing material. Above all, emphasis should be laid on the property of the composition according to the invention that, when spread on the surface of a product or between its different layers, in a fire situation it strengthens the cohesion of the burnt structure owing to a controlled reaction between the slag and the waterglass at an elevated temperature.

The invention is thus based on adding a controlled amount of blast-furnace slag or corresponding slag to a water- glass, either a potassium-containing or a sodium-containing waterglass, the slag being at room temperature inert with the said waterglass. When the temperature rises in a fire situation, the waterglass foams in this composition and, because of the presence of the slag, the composition strengthens the structure consisting of the product and the composition spread as a coating or as intermediate layers. The insulating and strength effects are regulated by means of the amount of slag used so that the pores formed in a fire situation will not explode and break the protective layer.

A board coated or a sandwich structure bound using the composition according to the invention thus expands con¬ siderably in a fire situation but, nevertheless, retains its dense and strong structure for a rather long time. The size of the pores in the expanded layer is optimized with respect to expansion and strength, and are in their size and distribution homogeneous throughout the entire insulat¬ ing layer. The pores are closed and the walls between them can withstand even high stresses. The structure expanded in a controlled manner at the same time provides a rather long travel path for and a good convection and radiation barrier to the transfer of heat.

The expanded insulating structure will not generate any toxic gases during a fire, as known protective coatings commonly do.

Under normal conditions, i.e. at a normal temperature, a coated board or a sandwich structure does not differ from a board coated with a conventional composition or from a sandwich structure bound using a conventional adhesive layer.

According to a preferred embodiment of the invention, the proportion of blast-furnace slag in the composition is 0.5 - 15 % by weight, specifically 4 - 8 % by weight. As the content of blast-furnace slag increases, the expanding ca¬ pacity of the composition decreases while its adhesive effect increases; this requires controlled proportioning in order to achieve the optimum effect.

The composition preferably contains a hygrostatic agent, but, because of the moisture content of waterglass, it also works without a hygrostatic agent. The hygrostatic agent is added in order to accomplish an even drying process and to improve the thixotropy of the composition. The hygrostatic

agent used is preferably 0 - 5 % by weight cellulose or a cellulose derivative, or respectively 0 - 20 % by weight starch.

The molar ratio of waterglass, which means its SiC>2 content in proportion to its a2<0 or K2O content, is preferably between 2.0 and 4.5. Waterglass begins to expand when its molar ratio exceeds 0.5. The expansion can be made use of only after the molar ratio exceeds 1.5, and it is at its most advantageous at the value 2.5. When the molar ratio is greater than 3.0, the moisture resistance is good.

The slag to be added to the waterglass is preferably ground, granulated slag. It must be at least partly vitreous. The slag is ground preferably to a fineness of 250 - 400 m-Vkg. Granulated slag becomes activated when the temperature rises above approximately 50 °C, and when the temperature rises further, it reacts by becoming activated non-linearly. This reaction can be controlled so that the waterglass expands in a controlled manner and the matrix in its entirety is reinforced by the reaction products of the slag, forming a homogeneous, optimally porous structure.

With a crystalline slag it is more difficult to obtain an advantageous structure of this type, because it requires a lower molar ratio, approximately 1.5 - 2.5.

The dry matter content of the waterglass is to be such that it can be spread. Waterglass having a molar ratio of 3.2 - 3.4 usually has a dry matter content of 37 %. Approximately 1 - 3 months after coating the dry matter content of the waterglass layer will be approximately 70 %.

The composition is spread preferably by spraying, applying with a brush or with a spatula. The applicability of the composition with a brush can be affected by regulating the

dry matter content of the waterglass, which affects the viscosity of the composition, and by increasing or decreas¬ ing the amount of hygrostatic agent, which affects the thixotropy of the composition.

The composition may also be in a dry form, in which case the waterglass content is in a dry form, usually in a spray dried form. The dry form of the composition is a suitable commercial article. Water is added to the composition at the time of use.

Additives enhancing fireproofing and other properties can advantageously be added to the composition. The fireproof¬ ing properties can further be enhanced by means of, for example, vollanstonite, limestone, perlite, vermiculite and various fibrous substances and other fire-retardants. The elasticity and adhesive properties of the material and its resistance to water are also rather freely modifiable, as are its rheologic properties.

The composition is prepared by mixing the blast-furnace slag and possible other dry substances together and by adding the thus formed mixture to waterglass.

The composition according to the invention is described below in greater detail with reference to the accompanying figures, which depict the properties of the composition as various functions.

Figure 1 is a graphical illustration of the principle of the mean result of the tests, indicating the order of ex¬ pansion as a function of the slag: aterglass ratio for different quantities of waterglass per surface unit; Figure 2 is a graphical representation of the increase of the temperature of the surface to be protected, as a func¬ tion of time, when the surface is coated with the composi-

tion according to Embodiment Example 3; and Figure 3 (prior art) is a graphical representation of the increase of the temperature of the surface to be protected, as a function of time, when the surface has been coated with a known fireproofing paint with the composition ac¬ cording to Embodiment Example 4.

The curve in Figure 1 indicates the precise selection of the slag.waterglass ratio.

Within the range A, where the proportion of slag to water- glass is 0 - 0.5 % by weight, the invention does not work, i.e. a product coated with a composition such as this does not survive in a fire situation. Large non-homogeneous pores are formed in the surface, and the matrix is brittle.

Within the range C the invention works, but closer to a slag content of 30 % by weight its practical value is rather insignificant. Even with slag contents of over 15 % by weight, the expansion will decrease so much that the insulating properties decrease to an insignificant level. A high slag content provides a very strong matrix, since slag reacts drastically with waterglass in a fire situation. The slag content improves the adhesive properties of water- glass, i.e. improves adhesion and resistance to moisture.

Within the range B the invention works reliably. Homoge¬ neous pores and a rather strong matrix are formed in the coating or in the adhesive layers of a sandwich panel.

Range D, within which the slag content is between 4.0 and 8.0 % by weight, is the most advantageous range of the invention. With the smaller waterglass amount (1.5 kg/m ² board) and the lower value of the slag ratio, the order of magnitude of expansion is 9-fold, dropping to 6-fold when the slag content is 8 % by weight. Respectively the order

of expansion is with the higher waterglass amount (4 kg/m ² board) and with the lower value of the slag ratio 18-fold, dropping to the value 14 when the slag content is 8 ^" % by weight. This illustrates very clearly how, by varying the slag:waterglass ratio within a rather narrow range it is possible either to increase the expansion, i.e. to increase the pore size and to decrease the strength, or vice versa. The optimum composition for each product will most likely be found within the range D.

Curve 2 in Figure 2 shows the rate at which the temperature of a board coated with a coating according to the invention rises in a fire situation. In approximately 3 minutes the temperature rises to 100 °C, but within the next 3 minutes the temperature does not rise significantly. After this stop in the rising of the temperature, the temperature rises rather sharply and reaches a level of 300 °C at 20 minutes, calculated from the beginning of the experiment. The said stop is due to the swelling of the composition, which at the same time increases the insulating power of the composition.

The three different curves depicted in the figure indicate temperature values measured at three different points on the "cold surface" of the test specimen.

The curves in Figure 3 depict the same as the curves in Figure 2. However, the measurements were obtained using a test specimen coated with a known fireproofing paint. In this test specimen the temperature of 100 °C is reached in approximately 2 minutes, and at 3 minutes the temperature is approximately 110 °C, whereafter it rises considerably more sharply than in the previous case and reaches a level of 300 °C at slightly less than 9 minutes.

The composition according to the invention is advantageous-

ly used as an adhesive between boards to produce a strong sandwich panel. Suitable boards include fiber cement, gyp¬ sum cement and other such boards and various substrates such as mineral, concrete, metal, wood, plastic, mineral wool, plastic-based insulation surfaces and paper surfaces. The range of application of the invention is very wide.

In a fire situation the adhesive will expand 2- to 40-fold, depending on its slag:waterglass ratio and its original layer thickness. The protection time thus increases up to five-fold. After the burning test according to the stan¬ dard, the board structure is still cohesive. The expanded layer consists of small, closed and evenly distributed pores. Their size and number is dependent on the slag to waterglass ratio. The pore structure is thus precisely controllable between the extreme slag content values shown in Figure 1.

When spread as a coating on the surface to be protected, the composition works in the same manner as when used as an adhesive. It binds well the filler added to it, which fil¬ ler may be, depending on the intended use, for example pigment, fine crushed stone, various pozzolanas, fibers. The filler reinforces the surface, provides the desired outer appearance and does not prevent the layer from ex¬ panding in a fire situation. When expanding, the thickness of the coating increases about 5- to 10-fold, and the pro¬ tection time increases about 3- to 4-fold. The burned sur¬ face layer has small pores and cannot be easily removed by scratching.

The invention is described below in greater detail with the help of a number of examples of preferred embodiments. In the examples the dry matter content of waterglass is 37 % by weight and its molar ratio is 3.2.

Example 1

A sandwich structure was prepared which consisted of two cellulose cement boards (LUJA board) 60x60x4 mm in size and of a mixture placed between these boards as an adhesive, having the following composition:

The thickness of the structure in the normal state was 9.3 mm, i.e. the thickness of the adhesive layer was 1.3 mm.

The structure was burned according to standards SFS 4193 and NT FIRE 003. As a result of the burning it was noted that the protection time was 33 min and the thickness of the structure varied within a range of 16 - 22 mm.

During the burning the thickness of the adhesive layer had thus increased on average to 20 - 8 = 12 mm, i.e. 10-fold. After the burning the sandwich structure was cohesive and had so high a strength that it was able to withstand the weight of one person.

Example 2

A similar experiment was performed in which the composition of the adhesive was:

Waterglass: 92.2 % by weight, corresponding to

1.5 kg/m--* x board Slag: 7.3 % by weight Cellulose: 0.5 % by weight Molar ratio: 3.3

Respective results: Protection time = 25 min

Increase in the thickness of the adhe¬ sive layer = 6 - 10 mm

In this case the increase in the thickness of the adhesive layer was approximately 6-fold. The strength of the struc¬ ture after the burning was the same as in Example 1.

Example 3

A fireproofing combination was prepared in which a mixture having the following composition was applied to one of the large sides of a cellulose cement board 60x60x4 mm in size:

The total thickness of the board to which the composition was applied was in normal state 4.5 mm, i.e. the thickness of the coating was 4.5 - 4 = 0.5 mm.

The board was burned according to the above standards, as a result of which it was noted that the protection time was approximately 19 min and the increase in the thickness of the coating was 8 - 4 = 4 mm, i.e. 8-fold. It was not pos¬ sible to remove the expanded layer by scratching without tools.

During the burning, the following visual observations were made:

9 min: swelling has started

12 min: the exterior surface is beginning to darken, start¬ ing from the edges 20 min: burning was discontinued

- no cracks

- coating small-pored and unbroken

- coating cannot be removed by scratching with fingers

Figure 2 shows, as a function of the burning time, the temperature rise of the surface of this board.

Example 4 (prior art)

For comparison, an experiment according to Example 3 was carried out in which the coating used was a commercially available fireproofing paint, the consumption being 0.72 kg m*-- . board

Thickness of the coating before the burning: 0.5 mm Thickness of the coating after the burning: not determin- able

Protection time: approximately 9 min (difficult to deter¬ mine)

During the burning, the following visual observations were made:

1.3 min: is beginning to smolder

5 min: the exterior surface is darkening

- the board has bent a great deal

- smoldering is rather strong

9 min: burning was discontinued

- no cracks

- interior surface (fireproofing paint) completely black¬ ened and brittle, removable with fingers.

Figure 3 shows, as a function of the burning time, the temperature rise of the surface of this test board.