DK143659B - INSULATIVE COATING FOR ROADS, AIRCRAFT COATINGS AND SIMILAR SURFACES, AND PROCEDURE FOR PREPARING THE COATING - Google Patents

Description

(19) DENMARK (^) in lp <12, PUBLICATION WRITING (, ι, 143659 Β

DIRECTORATE OF THE PATENT-00 TRADE MARKET

(21) Application No. 6Ο57 / 72 (51) IntCI.3 E 01 C 3/06 (22) Filing date 5 · Dec. 1972 (24) Race day Dec 5 1972 (41) Aim. available June 7. 1973 (44) Posted Sep 21 1981 (86) International Application No. - (86) International Filing Day - (85) Continuation Day ..

(62) Stock Application No _

(30) Priority Dec 6 1971, 205381, US

(71) Applicant ATLANTIC RICHFIELD COMPANY, New York, US.

(72) Inventor Albert Carman Condo, US: George Richard Knight, US:

Glenn Ray · Burt, US: Alfred Edward Borchert, US.

(74) Associate Engineer Hofman-Bang & Boutard.

(54) Insulating coating for roadways, aerodrome coatings and similar surfaces as well as the method of making the coating.

The present invention relates to an insulating coating for roadways, aerodrome coatings and similar surfaces on frozen substrates, such as permafrost in arctic and sub-arctic areas, which comprises layers of foamed polyurethane disposed between upper and lower layers of hydrophobic water solids.

) Areas in the Arctic and Sub-Arctic zones where the still frozen earth begins half to a meter below the surface and stretches! settle down to great depths, usually called permafrost areas.

This permafrost is permanently frozen soil or soil and * consists of mixtures with different contents of water, salt, sand and rock.

In many cases, the ice content of the upper portions can exceed 90¾ of the total volume. This may thaw as soon as the ambient temperature exceeds the freezing point of the water.

At the surface of the soil there is an active growth layer called tundra, which covers the permafrost. During the winter months the soil is frozen firmly to the surface of the tundra, but in the spring and summer a thaw will occur to different depths, e.g. from 5 cm to 1 m in an area between the tundra layer and the permafrost zone, called the "active layer". Failure to take action will cause the thaw fracture in the spring and summer to transform the tundra and active layer into a soft marsh, and thus the frozen ground, which can carry a considerable weight in the winter months, will not be passed by wheeled vehicles in the summer months at all. If vehicles pass through a tundra area in the winter to such an extent that the surface is driven up even to a slight extent, such driveways or wheel tracks will sink or erode and may be furrowed, thereby releasing tearing water streams so that a permanent damage or alteration of the underlying permafrost and tundra structure.

The most common method of constructing roads, airports, and similar permafrost sign structures consists of laying stones or slabs on top of the tundra in such a thick layer that it insulates the underlying layer so that the active layer remains frozen even in the summertime and protects it. underlying permafrost layer so that a firm basis for a road or similar structure is obtained. This layer should be of such a thickness that the frozen state will continuously penetrate the lower part of the layer of road. In order to obtain such an insulating and protective structure, the slab layer must usually have a thickness of at least 90 cm in the northernmost regions of the Arctic, where the summer temperature is relatively low and the moisture content of the permafrost is relatively high, up to 2.5 m or more in the southern parts of the Arctic or sub-Arctic, where a higher temperature occurs in the spring and summer for a longer period. It is often necessary to transport gravel or ral to such structures over considerable distances when there is a shortage of such materials in said areas. This can be very costly and therefore proposals have been made to provide other materials for the isolation and protection of frozen Arctic and sub-Arctic substrates.

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Such a proposal is set forth in the description of U.S.A. Patent No. 3,279,334. Here, it is proposed to apply a layer of fiberglass or polyurethane plastic over the frozen soil during the winter months, pressing along the edges of this layer a railing to prevent drainage and prevent thawed soil from penetrating the frozen ground the isolation and thus weakening the ground. A layer of gravel is placed over the layer of fiberglass or polyurethane, and finally a roadway of concrete is placed on top of the gravel layer. The average temperature and duration of the summer months of the year are determined, and then the required thickness of the insulation layer is selected from known insulation material tables that will prevent a rise in temperature to the surface at the summer-prevailing temperature.

The insulating coating according to the invention is characterized by that of the characterizing part of claim 1.

The present invention makes it possible to avoid using a thick layer of gravel, as it has been commonly used in Arctic and sub-Arctic regions, and overcomes various disadvantages and gains certain advantages over the prior art.

Thus, the present insulating coating comprises a hydrophobic screen or a water impervious layer of the material directly applied to the substrate which may be permafrost or tundra. This layer is extremely important as it forms a substrate on which the first polyurethane foam can be foamed on the spot. If the chemicals forming the rigid polyurethane foam are applied directly to a cold wet surface, they will not react or foam, as the required high temperatures during foaming will cause a melting of the frozen substrate to form water, and preferably if a reaction occurs between the isocyanate and the water, no polyurethane polymer will be formed, ie the reaction is interrupted. The substrate therefore permits the formation of the first layer of polyurethane foam without harmful effect from the outside. As one usually intends to build a road that will last for many years, it is reasonable to ensure that for a single year a higher average temperature in the summer will occur for a longer period of time. With the same probability will

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there must be at least one year in which there is a higher average temperature in winter. Furthermore, there may be periods when relatively hot summers and winters occur consecutively. Due to this probability, excess heat can be collected in the intermediate layer between the insulation material and the permafrost. Thus, although a reasonable safety factor has been used in determining the thickness of the insulating material, it is quite likely that at some point during the life of the road, a thaw will occur in the substrate. In the absence of a hydrophobic substrate over the aqueous substrate. the water will penetrate the polyurethane foam thus destroying its insulating properties and cause a breakdown of the road during the thawing period of the underlying substrate.

Due to the annual shift between frost and thaw, the insulation will become increasingly susceptible to water uptake. The hydrophobic backing material protects the foam against it. As the polyurethane foam is foamed on site to form a rigid foam insulation that will be further described, the polyurethane foam will follow and adapt to the surface irregularities of the tundra or permafrost. Thus, it is unnecessary to adjust the tundra or permafrost by leveling or leveling, which may otherwise damage the surface. By applying successive layers of foam on top of the substrate, several benefits are achieved. As each foam layer is applied on site, a certain degree of foaming occurs, and on top of each layer is formed a layer of non-foamed material, usually referred to as "the skin". The foam has closed cells and therefore has good insulating properties, while the skin which does not have insulating properties is resistant to penetration of vapors and therefore prevents the penetration of vapors into the foamed layer.

Said skin further contributes to a good strength in both compression and bending, as a bundle of sticks has a much greater strength than a single stick of the same diameter.

It will be appreciated that polyurethane foam has so far been sprayed onto surfaces to form insulating layers. The reason for this is that one has wanted to build a desired thickness of the foam layer, and in such a case it is preferable to have the foam layer as thick as possible, and only if such a layer becomes insufficiently thick, several layers are applied.

In carrying out the present invention, the thickness of each foamed layer is of paramount importance and this thickness is controlled to obtain a desired number of layers per layer. thickness unit in the total foam layer, as will be described below.

In the absence of the lower and upper hydrophobic barrier of the insulation described in the literature, the layers will act as a wick for the moisture and the insulating properties will be rapidly destroyed. Thus, fiberglass is undesirable as it does not have closed cells, and at the least moisture penetration, a wall effect will occur, thereby destroying the insulating properties.

The use of foamed polyurethane instead of rigid plate placement provides a high structural strength as the foam follows the contours of the underlying surface and thus avoids forming bridges which can cause fractures at rigid plates. By applying a hydrophobic or water impervious screen layer over the top skin of the foam, water penetration can be avoided from above, so that the insulating properties and strength of the material are maintained. None of these advantages are achieved by the prior art designs.

The present invention also relates to a process for the preparation of the coating according to the invention, which is characterized by the method of claim 2.

In accordance with the invention, the substrate is first applied to a hydrophobic water resistant barrier layer. This layer consists of a mixture of bituminous material and low molecular weight polyethylene, styrene / butadiene rubber or a blend of said plastic materials. Polyurethane foam layers are then applied, preferably by spraying. These are applied in such a way that they foam up on the spot and thus a vapor-permeable layer or skin will also be formed on the upper surface of each foam layer.

When the desired number of foam layers is applied, usually 3-8 layers per 2.5 cm, the upper foam layer, i.e. its skin layer, covered with another hydrophobic water impervious layer of the type indicated.

According to the present invention, there is provided an insulating coating which forms a protective structure with a low thermal conductivity and which protects the frozen substrate from surface damage when passing vehicles. Such a structure is particularly suitable for roads and airports.

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The invention can be used in connection with a large number of frozen substrates, e.g. ice, snow, frozen tundra or permafrost. It is also suitable in conjunction with thawed substrates, e.g. tundra during summer periods, or even in connection with permafrost, which is released and then thawed. When the coating is applied to a thawed surface, it will be necessary to avoid traffic until the substrate is frozen again by cold weather from below or in cold weather. After this freezing, the substrate will be maintained in the frozen state and the coating can then withstand the traffic load, even in the summertime.

The invention differs significantly from the prior art which makes it necessary to apply the coating to completely frozen substrates.

Whether the substrate is frozen or thawed, it is essential that the hydrophobic or water impervious coatings are applied prior to application of the foam layer. This is required in order for no water to come into contact with the first polyurethane foam layer applied. If no such first coating is used, the polyurethane, which must be applied in hot state to foam on the spot, will cause a melting of some of the frozen substrate or otherwise come into contact with the water if the substrate is in thawed state, and since the water reacts more vigorously with isocyanate than the polyhydroxy alcohols or polyols in the polyurethane mixture, the foaming will be poor or only a slight reaction will occur.

If the foaming chemicals for the polyurethane were applied to the cold substrate, the low temperature would also prevent a reaction, which would further prevent the foaming reaction.

Therefore, it is preferred to apply the hydrophobic screen layer or first coating in a warm state and, as soon as possible, to apply the first layer of polyurethane foam by spraying the reagents and foaming agent directly thereon. Since this screen coating is applied in warm condition, ie. at a temperature above approx. 5 ° C, e.g. between 10 and 21 ° C, the surface of the substrate can naturally thaw to a lesser extent if it is frozen. However, since the material is hydrophobic, the small amount of moisture thus formed will not be able to penetrate the surface and inhibit the subsequent foaming reaction for the formation of the polyurethane. If the tinder layer is frozen, the hydrophobic screen layer should have a thickness of between 0.1 and 0.8 mm, with a thickness of 0.4 - 0.5 mm being perfectly satisfactory. Under these conditions, the first coating applied hot as described above will allow the first layer of polyurethane to foam satisfactorily and thus adhere to the first foam layer. The small amount of thawed material will quickly freeze again as a result of the underlying cold material, and therefore the solid structure of the substrate will reappear during the subsequent application of polyurethane foam layers and the last upper hydrophobic layer. If the substrate is thawed, a thicker coating may be required, e.g. of 2 - 3 mm or more as indicated above.

The hydrophobic or water impervious first layer is, as mentioned, a bituminous mixture. Although asphalt * pitch and various synthetic polymeric resins could be used because of their water impermeability, they have certain disadvantages. Hot asphalt applied to thawed surfaces could cause the development of steam which would burst the asphalt coating. If the coating is applied in the form of solutions, e.g. of solvent naphta, there will be a fire hazard when hot polyurethane reagents are applied. Aqueous emulsions are not advantageous as water, as mentioned above, is very detrimental to the polyurethane reaction. Furthermore, the first coating should be sufficiently hot so that polyurethane will foam satisfactorily.

It has now been found that a "long" crude oil residue can be used as bituminous screen material. Thus, if the crude oil from North Slope, Alaska, provides a stripping to remove the most volatile constituents, you can, for example, expel 10 volume percent which can be used as fuel or can be added to other oil products for shipment or transport.The next 20% by volume of the crude oil can be removed for use as diesel oil, which can be used as a power for tractors, machines or power stations. The remaining 70% by volume boiling above the boiling point for the diesel oil, has proved particularly suitable as hydrophobic or water-impermeable substrate This can be used without further treatment or can be blown with air to increase the viscosity using the oxidized material.

A small amount of polymeric material of the type mentioned is introduced into the residue to increase the viscosity and improve the formability and flexibility at low temperatures. A satisfactory material for forming the lower hydrophobic or water-impermeable layer may comprise 85% by weight of said 70% by volume of remamination, 10% by weight of low molecular weight polyethylene (average molecular weight by number of 19,000) and 5% by weight of a technically styrene butadiene elastomeric material having a Mooney viscosity ML4f at 100 ° C of 105 - 110. The polyethylene may suitably have an average molecular weight of between 18,000 and 30,000 and the styrene-butadiene material may have a Mooney viscosity ML4 'at 100 ° C of 45 - 110.

The polymeric material is incorporated into the residue at a sufficiently high temperature, e.g. at 60 ° C or above, leaving the residue slightly liquid, after which the mixture is applied to the substrate at a temperature of 10 to 21 ° C. The content of polymers in the mixture can be between 5 and 25% by weight of the mixture, with the content of polyethylene relative to styrene butadine elastomer being between 1: 1 and 3: 1. Although these proportions are not particularly critical, large deviations from these will yield less desired materials, both in terms of price and properties.

Preferably, said coating material is applied by spraying and since a relatively thin coating is desired, e.g. from 0.1 to 0.8 mm, preferably 0.4 to 0.5 mm, on the frozen substrates, the viscosity of the material should not be so high that no uniform coating can be obtained. If the coating is applied to thawed substrates, it may be somewhat more viscous, since a thicker coating is desired here, but even for these applications the uniformity is desirable. If desired, the residue can be air blown to increase the viscosity, allowing a smaller amount of polymer to be obtained to obtain the desired viscosity, however, any elastomeric polymer is desirable in all cases so that the coating can achieve good moldability and flexibility at low temperature. . This is also desirable for coating to thawed surfaces, because the coating upon re-freezing should have good flexibility at low temperature, so that the coating will not be damaged during freezing due to swelling.

The polyurethane foam is prepared in a manner known per se, as will be apparent from the examples. These foams are prepared by reaction of a polyol, e.g. a polyhydroxyl compound, and a diisocyanate in the presence of a catalyst and a propellant, and they are suitably applied by spraying in such a way that the foaming takes place after application, whereby the foam layer follows any unevenness of the surface of the substrate covered with a relatively thin layer of the first coating material. In foaming, a hydroxyl group in the polyol reacted with an isocyanate group in the diisocyanate or polyisocyanate, and preferably a ratio of 1: 1 is used as accurately as possible to obtain the best foam quality. Since it is often small amounts of impurities, such as moisture, that can react with isocyanate groups, it is sometimes appropriate that these be found in a small excess of the stoichiometric ratio of 1: 1.

It is well known that polyurethane foam is produced and a large number of recipes are known which are adapted to different uses, whereby foams having different physical properties can be obtained. These prescriptions are not included in the invention, but any person skilled in the art will be able to select precisely the prescriptions and reaction conditions that best suit the purpose of use.

For the purpose of the present invention, a material having a compressive strength of at least 2 kg / cm at the flow point and a

ISLAND

k factor (isolation value) of less than 0.0161 kcal / hour / m / deg / m 90 - 95% closed cells, 3 - 5% deflection at the flow limit and weights of 0.40-0.56 kg / drn · ^ .

In accordance with the invention, it has been found necessary to check the layer thickness of the foam to a thickness of between 3 and 8 mm, so that there can be 8-3 foam layers, preferably 4-5 foam layers, per layer. 2.5 cm. The foam layer must be applied in such a way as to obtain the desired thickness for each layer as uniformly as possible. Manual ironing can be used by a trained operator, but it is preferable to use an automatic spraying machine. If the layers are applied under particularly bad weather conditions, it may be necessary to use protective screens, tents or similar protective devices to ensure a satisfactory application of the foam layers.

It is important to apply successive layers of foam to obtain a suitable adhesion between the layers to ensure that sufficient time is left to form a uniform skin of uniform thickness and to avoid interruptions before the next layer is applied.

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In order to obtain a chemical bond and consequent greater adhesion and strength, it is preferable to apply the next layer of foam before the outermost layer of skin on the foam layer is completely cured. If the ambient temperature remains constant or increases, it may take longer for the next foam layer to be applied, under which circumstances a subsequent layer of foam will still adhere satisfactorily, although the curing of the process is almost complete. However, if the temperature is reduced both in the underlying foam layer and in the surrounding environment, it is preferable to apply the next foam layer as soon as possible to obtain good adhesion. Usually, the next foam layer should be applied within 0.5 to 30 minutes after the underlying layer has finished foaming. Thereby, on the surface of the underlying layer, a coherent skin will be formed without being completely cured, regardless of small temperature variations.

It will be appreciated that these indications are merely a guide and must be arranged according to special weather conditions, foam compositions and application methods. Crucially, the first layer must be foamed to form surface skin, but before it is permanently cured or before the temperature of the foam layer has dropped substantially, the next layer of foam must be applied to achieve the desired adhesion.

The total foam thickness needed to protect a given substrate is a function of a large number of variables. As a general rule, with a foam having the above physical properties, a thickness of between 30 and 60 cm can usually be used.

In addition to the polyol and polyisocyanate components of the urethane foam, propellants are usually used for low temperature applications such as fluorinated hydrocarbons. Examples of suitable fluorinated hydrocarbons are trichloromonofluoromethane, dichlorofluoromethane, monochlorotrifluoromethane, monobromo trifluoromethane, tetrafluoromethane. The volume percentage and the nature of the fluorinated hydrocarbon used depend on the state of the environment, such as the temperature at the time of application of the polyurethane. A low-boiling propellant is used if the temperature is below 15 ° C and amounts up to 5% by volume of propellant can be used, although the required amount is usually somewhat smaller, and e.g. at a temperature of approx. 10 ° C use 1-2% by volume of fluorinated hydrocarbon, while at temperatures of 21 ° C an amount of fluorinated hydrocarbon of 0.5% by volume can be used.

Although it is preferred to incorporate the propellant into the foam mixture, if possible taking into account the environment, e.g. gaseous propellants can also be used during the spraying and the absence of blown. However, in the areas where the material in question has the greatest application potential, such a technique is not possible.

The urethane foam is obtained by mixing the polyol and the isocyanate. These components are well known as indicated above. It is usually desirable to incorporate not only the propellant as described above, but also the known catalyst components together with other components such as surfactants used in the known manner in the manufacture of polyurethanes. As mentioned, it is desirable to mix the components so that a stoichiometric ratio of approx. a hydroxyl group to an isocyanate group and suitably selected polyol and polyisocyanate components having a molecular weight which allow the formation of equal parts or volume parts to obtain the urethane foam. Furthermore, it is desirable that the viscosity of the two components be approximately the same, so that normal oscillations of ambient temperature have only a minimal effect on the measured ratio.

The invention is explained in more detail below.

On a substrate located at Prudhoe Bay, Alaska, a protective coating for a roadway with a service life of 20 years was prepared as follows: On a substrate of permafrost, a substrate of a hydrophobic or water-impermeable substrate was manually applied in known manner by heat spraying. , the material being heated so that the substrate reached a temperature of 24 ° C after application. This layer consisted of a liquid bituminous mixture of a 70 volume spray distillation residue of crude oil from Prudhoe Bay of the above-described kind mixed with 10 weight-9e of low molecular weight polyethylene having an average molecular weight by number of approx. 19,000 and 5% by weight of a technically available styrene-butadiene elastomeric material with a Mooney viscosity, ML4 'at 100 ° C of 105-110.

12 U3 & 59 Depending on the condition of the substrate, the thickness of this substrate was adjusted between 0.4 and 2.5 mm or more if the substrate was thawed. After the bituminous layer was applied in a still hot state, the polyurethane foam material was applied in a manner known per se by means of a sprayer, e.g. a Gusmer pneumatic mixer with a container temperature of 60 ° C and a nozzle temperature of 45-49 ° C. The polyurethane was obtained from equal parts of a polyether polyol and a polyisocyanate in which the polyol had a Brookfield viscosity of 200 cP at 25 ° C and a density of 1.03 kg / dm 2, and the polyol contained an additional 2% by volume of trichlorofluoromethyl. as a propellant and a catalyst. The polyisocyanate was a black liquid with a Brookfield viscosity of approx. 250 cP at a temperature of 25 ° C and a density of approx. 0.98 kg / dm

The foam components were sprayed into successive layers, each layer being stiffened, without fully curing, to obtain a composite layered structure. A foam layer having a total thickness of 4 cm was obtained by applying 4-5 layers per square meter. 2.5 cm, so that each layer is separated by a skin of high density and a thickness of several hundred parts, etc., which skin was formed by affecting the upper surface of each layer with air, adjusting the time as indicated above. At a temperature of 21 ° C, the foam rose within 6 seconds and solidified within 12 seconds, while complete curing took 30 minutes or more.

The properties of the applied polyurethane foam are as follows:

Properties units area test method

Core Density kg / dm ^ 0.34-0.38 ASTM-D-1622-63

Total Density kg / dm ^ 0.43-0.45 ASTM-D-1622-63

Content of closed cells% 90 Pycnometer

Content of open cells% 6.8

Compression Strength 5% Deflection bp / no 3.5 ASTM-D-1621-64

k-factor 21 ° C kcal / hour / m 2 / deg / m 0.00136 ASTM-D-2326-64T

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After the top layer of polyurethane foam cured completely to the surface, this surface layer was coated with another hydrophobic or water-impervious layer of a similar composition to the substrate, but preferably containing a greater amount of diluent, e.g. up to 25% or more, as described above, preferably with a thickness of 2.3 mm or more to obtain protection of the top layer, not only from moisture penetration, but also for tearing. This coating is suitable as a protective structure when only slightly affected, but if it is to be used as a substrate for roadways to carry vehicles, especially heavy traffic, the substrate must be covered by gravel 45 to 60 cm thick to prevent, that the vehicles damage the ground and to achieve a better weight distribution.

Instead of applying 45-60 cm of gravel on top of a 4 cm foam layer, as recommended in areas near Prudhoe Bay, at Point Barrow, Alaska, due to the harsher climate, a thinner foam layer can be used here, Umiat needs a thickness of 54 mm due to the milder climate here.