HK1068366B - Thermal protective compositions - Google Patents

Description

Thermal protective composition

The invention is a divisional application of an invention patent application with the title of "thermal protective composition" and the application number of 96196082.5 filed from 5.2.1998 to the Chinese patent office.

Technical Field

The present invention relates to thermal protective compositions that form char when exposed to fire or other high heat environments. The invention is particularly suitable for solvent-based film-intumescent coatings on substrates, but the use of the invention is not limited thereto.

Background

Various compositions that are capable of protecting against fire and other high heat environments (e.g., temperatures above about 300 c) are known in the art. Some of these compositions are inorganic components that are inherently insulating to the foam, and they are protected from heat only by their low thermal conductivity and thick coatings. Examples of such compositions include foamed cement or expanded silicates. The present invention is not directed to such systems, but rather to polymeric binder systems that are capable of forming char when exposed to fire or high temperature conditions. The char-forming composition may act through various morphologies. The compositions may be used in a variety of forms including thick film (masticated) coatings, thin film coatings, paints, cast films, extruded films, and others. The composition may contain an organic or inorganic binder and various additives. When exposed to heat, the composition slowly loses the weight of its volatile portion and forms a char that prevents the transfer of thermal energy. Finally, the carbon is consumed by physical ablation and chemical processes (mainly oxidation by oxygen in the air) and loses its protective function. The time required for a given temperature increase within a predetermined thickness of the composition under specific heat flow, ambient conditions, and temperature conditions is a measure of the effectiveness of the composition in providing thermal protection.

The effect of the different coatings is different when subjected to heat and other high temperature conditions.

The ablative coating expands to less than twice its original thickness. They provide limited inherent thermal protection, but they tend to produce dense carbons with good physical and chemical resistance.

The intumescent coating expands to produce a char that is higher than the original thickness of the coating. This carbon produces a very thermally efficient insulating layer, but loses some of the physical and chemical properties of the ablative coating. The intumescent carbon tends to form coarse, irregular cell structures, cracks and fissures when expanded, the carbon cannot expand uniformly at the corners of the substrate, and the thermal protection of the carbon in the remaining areas is much less than the average thermal protection of the underlying structure. Examples of such swelling systems include silicate solution or ammonium phosphate coatings or mastic coating compositions as disclosed in U.S. patent 2680077 to Nielsen et al, U.S. patent 3284216 to Kaplan, and U.S. patent 4529467 to Ward et al.

A third type of char-forming coating is disclosed in U.S. patent 3849178 to Feldman. These compositions, when subjected to extreme heat, undergo an endothermic phase change and expand their original volume two to five times to form a continuous porous matrix. These coatings tend to be tougher than intumescent coatings. They have a much greater thermal protection than ablative coatings, and often greater than that of intumescent coatings, due in part to rapid cooling due to the gas formed by the endothermic phase change escaping through the open pore matrix. These coatings are also susceptible to cracking, forming voids and cracks.

Disclosure of Invention

The present invention relates generally to intumescent systems, and in particular to film intumescent coating systems, i.e. they are applied at a thickness of less than 5 mm. However, aspects of the invention may also employ thick film intumescent and Feldman type compositions that undergo an endothermic phase change that expands their original volume two to five times. Certain aspects of the present invention are also applicable to ablative char-forming coatings.

It is an object of the present invention to provide char-forming compositions having better thermal efficiency than previously known compositions.

It is another object of the present invention to provide such compositions which can be applied as a film to a substrate to significantly increase the time that the underlying substrate is protected.

It is another object of the present invention to provide such a composition which expands to a thickness more than ten times greater than its original thickness when exposed to a fire or other high temperature condition.

It is another object of the present invention to provide compositions which form cells having a highly uniform cell structure.

It is another object of the present invention to provide such compositions, or coatings thereof, or carbons formed therefrom, which have a high degree of physical toughness and chemical integrity, including adhesion and cohesion.

It is another object of the present invention to provide such a composition, or a coating thereof or a formed carbon, which has oxidation and chemical resistance.

It is another object of the present invention to provide such compositions which expand in all directions when exposed to fire or other high temperature conditions to protect the corners they surround.

It is another object of the present invention to provide such compositions that resist cracking when exposed to fire or other heat flow.

Other objects of the present invention will become apparent to those skilled in the art from the following description and accompanying drawings.

According to the present invention there is provided a thermal protective composition comprising a binder which softens when exposed to high heat, a blowing agent which forms a gas when exposed to high heat and an unsaturated triacylglycerol present in the composition in an amount of from 0.33 to 3.3% by weight, preferably the unsaturated triacylglycerol comprises a fatty acid having conjugated double or triple bonds, further wherein the unsaturated triacylglycerol contains two to three conjugated double or triple bonds in each chain, each chain having twelve to twenty carbon atoms. Preferably, the unsaturated triacylglycerol is selected from the group consisting of octadecatrien-4-keto acids and cystine.

According to the invention, the composition also comprises an ingredient selected from the group consisting of: at least 0.5% by weight of said binder of elemental boron, a metal salt of a carboxylic acid containing from ten to thirty carbon atoms, preferably a stearate, and a metal oxide, preferably alumina. Wherein the metal salt and metal oxide are pre-reacted to form an adduct.

According to the invention, the composition also comprises a drying oil, present in an amount not exceeding 3.3% by weight.

According to the present invention there is also provided a thermal protective composition comprising a binder which softens when exposed to high heat, a blowing agent which forms a gas when exposed to high heat and a drying oil containing at least two conjugated double or triple bonds, said drying oil being present in an amount of no more than 0.33% to 3.3% by weight of the composition.

According to the present invention there is also provided a method of protecting a substrate against fire or high heat comprising applying to the substrate a film of a composition having a thickness of less than 5 mm which expands under high heat conditions to increase its original thickness by at least ten times, said composition comprising an organic polymer and a drying oil, said drying oil being present in an amount of not more than 0.33% to 3.3% by weight of the composition. The composition used in the method further comprises an adduct of a metal salt of a carboxylic acid having from ten to thirty carbon atoms with a metal oxide, at least 0.5% by weight elemental boron and carbon particles dispersed throughout the composition, and/or comprises a second drying oil, at least said first-mentioned drying oil being a triacylglycerol containing from two to three conjugated double or triple bonds per chain, each chain having from twelve to twenty carbon atoms.

According to one aspect of the invention, there is provided a char-forming thermal protective composition comprising a binder, a source of carbon, a blowing agent which forms a gas when exposed to a high thermal environment which expands the char, and elemental boron, the elemental boron being present in an amount of at least 0.5% by weight of the binder. Preferably, in the present invention, the carbon source contains a binder, that is, the binder can be used as the carbon source, and it is also preferable that the carbon source contains dispersed particles dispersed in the binder, and chopped fibers are contained in the particles, wherein the particles are made of one component selected from the group consisting of an organic acid and elemental carbon.

According to another aspect of the invention, there is provided, in general, a char-forming thermal protective composition comprising a binder, a carbon source, and 0.5-10% elemental boron. The preferred binder is a source of carbon, more preferably in the form of additional carbon sources such as chopped organic fibers like acrylonitrile, or graphite dispersed in the binder. The binder is preferably an organic polymer, most preferably a thermoplastic resin. In addition, the elemental boron preferably constitutes at least 2% by weight of the composition. Elemental boron imparts unexpectedly high oxidation resistance to the carbon and increases the weight and strength of the residual carbon. In certain formulations, it has been found that the composition unexpectedly increases in weight and forms a tough, uniform char when heated from 750 ℃ to 850 ℃ in the presence of oxygen. This aspect of the invention can be applied in a number of char-forming protection systems.

According to another aspect of the present invention, there is provided a thermal protection composition comprising a binder that softens when exposed to high heat, a blowing agent that forms a gas when exposed to high heat, and a drying oil. The drying oil is preferably an unsaturated triacylglycerol or a conjugated fatty acid, most preferably a conjugated triglyceride. In a preferred embodiment, the unsaturated triacylglycerols contain two to three conjugated double or triple bonds per chain of twelve to twenty carbon atoms, exemplified by oiticica oil, which contains octadecatrien-4-keto acids (4-keto-9, 11, 13-octadecanoic acid), and also coat oil, which contains cystine (17-octadecene-9, 11-diynoic acid). Conjugated drying oils reduce the surface tension of the coating and provide a blowing agent with a lower foaming temperature than the other, thereby rapidly stretching the boundary between the heat source and the substrate and creating a large temperature gradient to keep the substrate cool. It is preferred to use a triglyceride/fatty acid mixture to control these properties. Said mixture may comprise, for example, equal parts of oiticica oil and castor oil as aerating agents, and linseed oil as plasticizer and flow agents.

In accordance with another aspect of the present invention, a thermal protective composition is provided comprising a binder that softens when exposed to high heat, a blowing agent that forms a gas when exposed to high heat, and a mixture of a metal salt of a medium chain (ten to thirty carbon atoms) carboxylic acid and a metal oxide. The carboxylate metal salt is preferably a T-2 metal salt, most preferably zinc or copper stearate, and the metal oxide is preferably alumina. This additive produces a foam that fills the outer corners more effectively in all directions than coatings known in the prior art.

Various combinations of aspects of the invention provide thin film coatings that produce carbon layers ten to thirty times thicker than the original coating. These carbons provide unexpected thermal efficiency, uniform closed cell structure, greatly increased protection of corners and underlying substrate edges, resistance to cracking and cracking, physical toughness, and oxidation resistance. The preferred embodiment of the present invention is a solvent-based (as opposed to water-based or water-latex) coating that protects the cylinder for one hour at a thickness of 0.8 mm under the heating conditions of ASTM E-119.

These additives of the present invention have the same advantages as described above without producing thick, closed-cell carbon thin film coatings, when formed into a Feldman-type coating, being able to expand to two to five times its original thickness and undergo an endothermic phase change to form an open-celled cell structure.

Drawings

FIG. 1 shows the heating profile of a cylinder coated with a prior art film coating of 0.905 mm thickness under ASTM E-119 flame characteristics.

FIG. 2 shows a graph of the heating profile of a cylinder coated with a 0.802 mm thick film coating of the present invention under ASTM E-119 flame characteristics.

FIG. 3 is a cross-sectional view of a column showing a thermally protected intumescent film coating on the column.

Fig. 4 is a partial view of the post of fig. 3 after being coated with a prior art composition after exposure to high heat.

Fig. 5 is a partial view of the post of fig. 3 after being coated with a composition of the present invention after exposure to high heat.

Figure 6 is a graph of the effect of different weight percentages of elemental boron on graphite cloth as determined by thermogravimetric analysis.

Detailed Description

The following examples are provided to illustrate the compositions of the present invention and their use as intumescent or other char-forming coatings.

Example 1

Formula of melt-expandable coating

For comparative testing, the formulation of a standard intumescent coating is as follows:

parts by weight

Vinyl toluene acrylate 12. + -.4

Chlorinated plasticiser 8 + -2

Polyol 6 + -2

Ammonium polyphosphate 21. + -.5

Foaming agent 8 +/-2

Inert fiber filler 2 +/-1

Pigment (TiO)₂) 8±4

Solvent 27. + -.2

To 100 parts by weight of this composition, 1.3 parts of a drying oil, a mixture of equal volumes of oiticin, castor oil, and linseed oil, was added to form the material of the invention; 1.3 parts by weight of a metal stearate/metal oxide additive consisting of 5 parts zinc stearate and 3 parts alumina, with minor amounts of a rheological agent, a degassing agent and bentonite.

The standard material was applied approximately uniformly to the W10 x 49 pillars of the first part, with an average thickness of 0.905 mm, and the inventive material was applied to the same pillars in a slightly thinner coating (average thickness of 0.802 mm). The coating was cured and each column was then exposed to a standard ASTM E-119 simulated flame. Such simulated flame conditions include the use of a flame whose temperature continuously increases to 927 ℃ (1700 ° F) over an hour; the test was terminated when the average temperature of the steel substrate reached 538 ℃ (1000 ° F). In fig. 1 and 2, numeral 1 represents the ASTM furnace temperature, numeral 3 (triangle) represents the measured furnace temperature, numeral 5 represents the flange edge temperature, numeral 7 represents the flange temperature, numeral 9 represents the column web temperature, numeral 11 (small point) represents the measured average column temperature, and numeral 13 represents the slope of the average column temperature. The column coated with the standard composition persisted for less than 30 minutes before reaching the end of the test, while the column coated with the material of the present invention persisted for up to one hour.

The superiority of the composition of the preferred embodiment of the present invention is most clearly shown by curve 13 in figures 1 and 2. Curve 13 represents the temperature rise rate of the column. At ten minutes into the test, the column temperature protected with the preferred composition of the present invention was slightly lower than the column temperature protected with the control composition (both between 200 ° and 250 ℃), but the heating rate was about half (about eight degrees per minute to about eighteen degrees per minute). This curve shows that the rate of thermal ramp up produced by the preferred composition of the present invention is continually suppressed from ten minutes up to more than sixty minutes.

The carbon formed from the composition of the present invention has a very uniform cell size, is free of large voids, is not prone to cracking and crazing, and expands uniformly around the outside corner of the column flange. In fig. 3-5, the thermal expansion of the thin coating 17 (fig. 3) of the thermal protective composition on the post 15 is shown in fig. 4 and 5. With the standard formulation, as shown in fig. 4, the outer edge of the column flange showed expansion of the carbon 19 in both the horizontal and vertical directions, leaving an area of poor protection indicated by numeral 21 in fig. 4, where the heat was much faster than at the flange face or web, reaching 538 ℃ in about twenty-three minutes. As shown in fig. 5, the carbon 23 of the illustrated embodiment of the invention expands to a greater extent than standard and substantially fills the web region of the column. It is very significant that the expanded carbon expands radially outwardly uniformly along the outer edge of the flange to form a protective layer 25 much thicker than the standard layer 21. And the coating begins to swell earlier in the heating process. Thus, the formulation shows advantages in terms of thermal efficiency, thermal insulation and integrity of the char.

Example 2

Formulation of sample composition

Two film intumescent compositions, formulation a and formulation B, were formulated from the base formulation comprising example 1. Formulation B, which is suitable for external application, uses a polyol with more terminal hydroxyl groups than formulation a. To these formulations were added various amounts of the additives of the present invention. The drying oil ("oil") additive and stearate/oxide ("st/o") additive were the same as used in example 1. The amounts of additives shown in table 1 below are expressed by weight.

A 5 gram sample of each formulation was placed in an aluminum weighing pan and allowed to cure, with each sample forming a thin layer (approximately one millimeter thick). After curing, the disks were placed under a quartz lamp that generated heating in a manner similar to the ASTM E-119 curve at 40% power at zero time, 60% power at thirty seconds, and 70% power at one minute. The test was ended at 5 minutes. Note the time required for the surface to initially foam, which is the time at which the formation of char begins. At the end of each test, the thickness of the carbon was measured and measurements of the volume, shrinkage, cell structure, and friability of the carbon were obtained. The results are shown in Table 1:

TABLE 1

Height in seconds (mm.) of char formation by foaming (second) and brittleness of cell structure of char volume shrinkage

Formulation A

Control 70-7580-9035-456767

1% oil 4471507887

2.5% oil 4269558988

5% oil 396565998.58

10% oil 709.5979

1％st/o 56 77 40 6 7 8 7

2.5％st/o 66 86 55 8 8 8 8

5％st/o 46 69 70 9 8 7 8

Formulation B

Control 66-7480-9335-4566-76

1% oil 1032406777

2.5% oil 926507787

5% oil 820658888

1％st/o 6 22 55 6 8 7 6

2.5％st/o 8 26 65 7 8 7 7

5％st/o 11 24 75 9 8 7 8

Example 3

Influence of addition of elemental boron

The effect of elemental boron on the formulations of the present invention is unexpectedly greater than the effect of boron compounds used in prior art formulations.

To determine the cause of this effect, graphite cloth was blended with powdered elemental boron. One sample was free of elemental boron, the other was doped with 0.5 wt% elemental boron, and the third sample was doped with 2.8 wt% elemental boron. The curve reflected by the material when tested by thermogravimetric analysis is shown in figure 6. The weight loss of both samples of material represented by curve 31 (0.5% elemental boron) and curve 33 (2.8% elemental boron) is much slower than the similar formulation without elemental boron represented by curve 29. Also shown in fig. 6 are: upon further heating in the presence of oxygen, the material comprising more powdered elemental boron begins to gain weight; in one case, the weight of the char when the temperature reaches 850 ℃ is greater than the original weight of the coating.

It will be obvious to those skilled in the art from the foregoing description that various changes may be made within the scope of the appended claims, which changes are intended merely to further illustrate the invention and not to limit its scope. For example, while the film-form solvent-based refractory system of the preferred embodiment of the present invention is particularly effective, many of the advantages of the present invention are also realized when the additive of the present invention is present in a thick film intumescent formulation or in the formulation of U.S. Pat. No. 3849178 Feldman, both of which are capable of expanding to form an open-celled matrix and undergoing an endothermic phase transition, or are equally obtainable in a flame retardant composition that retards flame propagation without raising the temperature, or in a water-based latex. The additives may be incorporated into a wide variety of thermoplastics; in addition to acrylics, the thermoplastics are, for example, styrene, polypropylene, polyethylene, ABS, polyamide, polyurethane, vinylidene chloride, modified epoxy, and copolymers of these thermoplastics. These are merely examples.

Claims (17)

1. A thermal protective composition comprising a binder which softens when exposed to high heat, a blowing agent which forms a gas when exposed to high heat and an unsaturated triacylglycerol present in the composition in an amount of from 0.33 to 3.3% by weight.

2. The composition of claim 1 wherein said unsaturated triacylglycerol comprises a fatty acid having conjugated double or triple bonds.

3. The composition of claim 2 wherein said unsaturated triacylglycerol contains two to three conjugated double or triple bonds in each chain, each chain having twelve to twenty carbon atoms.

4. The composition of claim 3 wherein said unsaturated triacylglycerol comprises a fatty acid selected from the group consisting of octadecatriene-4-keto acids and cystine.

5. The composition of any of claims 1-4 further comprising at least 0.5% by weight of said binder of elemental boron.

6. The composition of any of claims 1-5, further comprising a metal salt of a carboxylic acid of ten to thirty carbon atoms.

7. The composition of any of claims 1-6, further comprising a metal oxide.

8. The composition of claim 7 wherein said metal oxide is alumina.

9. The composition of any of claims 6-8 wherein said metal salt is a stearate.

10. The composition of any of claims 7-9, wherein said metal salt and metal oxide are pre-reacted to form an adduct.

11. The composition of any of claims 1-10, further comprising a drying oil present in an amount of no more than 3.3% by weight.

12. The composition of claim 7, further comprising a drying oil.

13. A thermal protective composition comprising a binder which softens when exposed to high heat, a blowing agent which forms a gas when exposed to high heat and a drying oil containing at least two conjugated double or triple bonds, said drying oil being present in an amount of no more than 0.33% to 3.3% by weight of the composition.

14. A method of protecting a substrate against fire or high heat comprising applying to the substrate a film of a composition having a thickness of less than 5 mm which expands under high heat conditions to increase its original thickness by at least ten times, said composition comprising an organic polymer and a drying oil, said drying oil being present in an amount of not more than 0.33% to 3.3% by weight of the composition.

15. The method of claim 14 wherein said composition further comprises an adduct of a metal salt of a carboxylic acid having from ten to thirty carbon atoms and a metal oxide.

16. The method of claim 14 or 15 wherein said composition further comprises at least 0.5% by weight elemental boron and carbon particles dispersed throughout the composition.

17. The method of any of claims 14-16 wherein said composition further comprises a second drying oil, at least said first-mentioned drying oil being a triacylglycerol containing two to three conjugated double or triple bonds per chain, each chain having twelve to twenty carbon atoms.