Patent Application
20140224406
The subject of the invention is a resin system suitable for the preparation of fibre reinforced prepreg. The prepreg obtainable with the use of the resin system, and its application is also the subject of the invention. Among the applications the use of the prepreg for lining chimneys is a special application of the invention.
Exhausting of flue gases has thousands of years of history. By exploiting the phenomenon of rising of the hot or warm natural flue gases predominantly chimneys are used for exhausting.
The smoke rising in the chimney is steadily cooling, in the conventional brickset chimney about 15-16° C. per meter. Any material is combusted, the smoke always contains significant amount of water vapour. When it cools, intensive condensation of the water starts at about 50-70° C. Because of the dissolved CO2 content the liquid thus formed is faintly acidic, which corrodes the conventional brickset chimneys without lining, ruins the mortar and the concrete, therefore holes and cracks occur in the wall of the chimney, and as a consequence of this carbon dioxide and carbon monoxide can enter the living space.
To avoid danger now many places the chimney of each gas-fired appliance must be provided with acid resistant lining. Chimney lining is determined by many factors: the principle of operation of the combustion plant, the fuel, type and thermal output of the stove or oven, the temperature of the exhausting flue gas, etc. With the development of the chimney technology the significance of the air-tight systems is increasing. (See: MSZ EN 845:2010 Planning, implementation, monitoring of flue gas systems). There is no standard yet for the composite liners. The EN 1865 standard refers to the steel tubes, the EN 1457 standard refers to the ceramic tubes, and the EN 14471 standard refers to the PP tubes.
In order to eliminate the chimney lining problems many solutions were elaborated. Metal tubes (for example U.S. Pat. No. 4,846,147: Donald M. Townsend, John R. Jaklich: Chimney liner systems, 1989), or solid ceramic tubes with thin wall (for example: Hungarian Patent No. 189890). In case of condensing boilers the use of polypropylene tubes has also become a common practice (for example: Hungarian Patent No. 189890), but the real novelty was the appearance of the composite prepreg.
The chimneys were mainly lined with rigid, stainless steel tubes, flexible stainless steel tubes, or flexible plastic tubes, or with ceramic tubes of constant diameter. The rigid, stainless steel tubes can be built into the non-rectilinear (the so-called declined) or high chimneys only with demolition of the wall. The corrosion guarantee is generally 10 years. The wall of the flexible, stainless steel tubes is thin, therefore they are corroding more easily, and are damaged more easily at pulling in. The flexible plastic tubes can only be used at flue gases of very low temperature. The ceramic tubes can only be used for building new, rectilinear chimneys. Although their heat resistance is excellent, they are brittle, and their tightness at the couplings is uncertain.
The lining tubes which can be prepared from the prepreg are materials, with which any form, any size, any length chimney can be lined without demolition of the wall, and provide a tight lining tube, with solidity approaching that of a steel corrugated pipe, corrosion resistant, heat resistant to some extent, without extension. Lining with the fibre reinforced, prepreg based composite tubes reached an increasingly important role in the European market. (Best known: FuranFlex®, FitFire, Flexfort).
The essence of the prepreg based chimney lining process is that the lining material (special, thermoset, synthetic resin based composite) is pulled into the chimney in plastic form. Following this it is inflated and cured with hot air. The technology allows for the lining to take the shape of the chimney, and can be installed within a short period of time. It has also a great advantage that the composite lining tube is a good thermal insulator (Composite: ˜0.4 W/mK, aluminium: 300 W/mK, stainless steel: 16 W/mK), and this way it reduces cooling of the flue gas, and this way reduces condensation.
The suitability of the thermoset matrix based composite lining tubes for the household chimney reconstruction was comprehensively investigated at the Budapest University of Technology and Economics in the years of 1970. The well storable, sufficiently heat resistant AMP-1 and AMP-2 prepreg tubes produced even in commercial amount as a result of the R+D work were successfully used in the practice. Numerous patent applications and publications were prepared from the results of the investigations.
Synthetic resin binding agent prepared with blocked isocyanate, prepared by Bayer was used (Desmodur AP stabile) for the AP-1 and AP-2 prepregs, which, close to the room temperature was storable with the Desmophen 550 type polyol (also a Bayer product) for unlimited period of time. In the meantime production of the Desmodur AP stabile was terminated by Bayer, but numerous blocked isocyanates, produced in commercial quantity, are still on the market. But Bayer produces numerous blocked amine compounds, for example for the preparation of latent epoxy resins, well storable at room temperature.
The blocked amines are ketamine or aldimine type compounds, and with isocyanate theoretically these are also suitable for the preparation of polycarbamides of good quality, more thermo resistant than the epoxy resins. But their great disadvantage is that they are expensive, therefore the solutions using them are far from being cost effective, and the deblocking compounds can cause air pollution.
More than 10 years later another development team elaborated the solution, which is widespread, and protected by the Hungarian Patent No. 218726 (HU218726B, Kecskeméthy Géza et al.: “Method for the enhancement of the corrosion resistance of a chimney, and lining element for its embodiment”). The main point of the method is that for the formation of the lining element a composite material comprising thermoset, partly polymerized synthetic resin and glass fibre reinforcement system, connecting to the outer wall of a polyolefine tube is used. The material of the matrix is furan or phenoplast resin, or a mixture thereof between 5-95% to 95-5%, with Al(OH)3, or AnO3 flame retardant extender, which is prepared by the use of para toluenesulfonic acid as catalyzer. The chimney lining systems prepared with the process mentioned above were successfully used in the conventional open combustion chamber (gravitational) and closed combustion chamber (turbo) boilers (FuranFlex products, see: www.furanflex.com).
It has been proven by now that the phenol, furfurol and the formaldehyde is toxic and carcinogenic, therefore the FuranFlex products are produced with a modified composition. The resin mixture consists of phenol-furan and epoxy resin components, and these together represent less than 35% of the amount of the matrix. The composite contains glass-cloth, graphite, mineral powders and glass powder as inorganic component. Additive containing halogen, or antimony-trioxide cannot be found among the flame retardants used in the composition (see: Material Safety Data Sheet FuranFlex, 2012).
Further products similar to FuranFlex® also exist. Such products are for example the prepreg lining tubes available with the name FlexFort (Wolenta Vegyipari Kft) with epoxide modified phenoplast matrix, and FitFire (Beca Engineering s.r.l) with aqueous base furan matrix.
Although the currently used prepreg based chimney lining composite systems provide a satisfactory solution to many problems, they have serious disadvantages in some characteristics.
Such a disadvantage is for example that some components of the resins may contain materials harmful to health. The resins mentioned are not sufficiently stable, which is characterized by the fact that their shelf life in summer heat (30° C.) is about 1 week, at room temperature (22° C.) is 3 weeks, but even at cellar temperature (8° C.) is only 25 weeks. A further problem is that they can be transported only at 8° C., in precooled condition, which significantly increases the costs of application. It is also a problem, that their thermo resistance that can be safely performed is 250° C., which significantly limits their applicability. Furthermore the resin mixture contains even water, therefore at the storage of the prepreg drying may also cause complications.
German patent application No. DE 1295189 is dealing with the preparation of polyurethane foams. The main point of the protected solution is that from different aromatic diisocyanates prepared in commercial quantity (starting mainly from TDI and MDI) and polyols, prepolimers are prepared in a known manner, whose softening point is between 30° C. and 70° C., therefore they can be pulverized at room temperature. Powdery inorganic compounds (for example borax) or organic compounds (piperazine-hexahydrate), whose water pressure in pure form at a temperature 20° C. lower than the softening temperature of the prepolimer is negligible, which are able to release water of hydration, are added to these powders. In order to regulate the reaction and the foam structure small amount of polyurethane catalyser (for example dibutyltin-di-2-ethilhexanoate) and silicon compounds are added to the powders mentioned above. When this powder mixture is heated to 100° C., and stored at this temperature for 20-25 minutes, hard or soft foams are obtained in good quality. The disadvantage of this solution is that the solidity of the foams produced in the course of the process is low, and their thermo resistance is low because of the polyurethane bonds. In contrast, in the solution of this invention aromatic polycarbamides are formed, which do not melt even at higher temperature, just slowly graphitize. According to the solution of the invention the hydroxide powders considered to be reactive, and the inactive powders (for example CaCO3) to be used are dried as far as possible, in order to avoid foam formation as much as possible. The polyisocyanate mixtures according to our invention, which are still liquid at room temperature, mixed with the borax powder mentioned in the German file referred, or with another powders containing crystal hydrate, within a few days provide a polymer matrix curing within a few days, therefore poorly be stored, fragile, and with low solidity.
German patent application No. DE2743884A1 describes the preparation of foamy and non-foamy pastes. Alkaline aqueous solutions, alkaline aqueous suspensions or alkaline metal/alkaline earth metal pulps are used in the presence of compounds containing at least two isocyanate groups per molecules. The volume weight of the foams is 160-390 kg/m3, or bigger, with the characterization: “foams with coarse pores”. It is also mentioned in the description, that for the preparation of the solid structural materials from Portland cement, from other cements or from anhydrous plaster 50-400% of the mass of the total mixture is used (Page 15, Paragraph 1). The method described in this patent is somehow similar to the method described by us for the preparation of the 3P resins, because alkali is used in excess, which quickly and totally absorbs the CO2 released. Although essentially compact materials are mentioned in the patent, specific examples are not mentioned for their preparation.
Follows from the above that the object of the present invention is the elaboration of a resin system, with which the disadvantages of the solutions mentioned above can be eliminated, doesn't include materials harmful for the health, sufficiently stable, can be stored at room temperature for an unlimited period of time and transportable, its thermo resistance is high, and doesn't include water, or just to a minimum extent, in order to avoid the problems possibly occurring in this connection at the application. Further requirement in relation to the resin system is to have strong self-extinguishing characteristics.
Surprisingly it has been found that the task of the invention can be solved, if a special composition used for the resin system. It has been found that the task of the invention can be solved with a resin system, which is a liquid polyisocyanate mixture, containing preferably more than 50% by weight MDI based di- and polyisocyanates, which consists of raw P-MDI, polymer P-MDI homologs and isomers, MDI based prepolymers, modified MDI-s, etc., and in addition to these contains one or more, originally powdery inorganic hydroxides in less than 50% by weight.
The essence of the invention is that the resin system of the invention is a system storable at room temperature for an indefinite period of time, but the cyclic process resulting in curing can be initiated with water vapour. In the course of heat treatment measurable amount of water vapour diffuses through the so called heat treatment tube, and these, reacting with the polyisocyanates allow the formation of a polycarbamide matrix, and as a result of this self-supporting processes start, and last until the isocyanate groups and/or the inorganic hydroxides run out. As a result of the process unmeltable resin matrix is formed, with strong self-extinguishing characteristics, and with high Tg (glass transition temperature). Heat treatment takes the same amount of time as in case of the prepreg materials suitable for chimney lining, known from the prior art. In the course of heat treatment curing is not complete in 100%, therefore final characteristics of the material do not form, but during the 1-2 hours regularly used for heat treatment the structure becomes self-supportive
In the course of the experiments performed for the preparation of the resin system of the invention a prepreg material was fixed around such a thin-walled, but perfectly gas and vapour tight aluminium tube, which is the polyethylene tube in inflated condition. The process of heat transfer essentially has not been changed, meanwhile the same steam generator, steam pressure and temperature was used as in case of the polyethylene heat treatment tube. But as a consequence of this, since the resin of the prepreg tube did not receive water from external sources from the flow through steam, even the self-supporting cyclic process did not start, and the prepreg substructure material remained soft, even after 6-8 hour's heat treatment. From this it has become apparent that the key for the process is the steam diffusing through the polyethylene tube, which initiates the cycle process, and as a result of this cycle process system matrix with the characteristics of the invention is forming. The cycle process mentioned above is demonstrated on
As it is mentioned above, the resin system of the invention is such a liquid polyisocyanate mixture, containing preferably more than 50% by weight MDI based di- and polyisocyanates, which consists of raw P-MDI, polymer P-MDI homologs and isomers, MDI based prepolymers, modified MDI-s, etc., and in addition to these contains one or more, originally powdery inorganic hydroxides in less than 50% by weight in suspended form.
The inorganic hydroxides mentioned above, and used in the resin system of the invention, are materials which do not release water at room temperature, but at 90-110° C., still during heat treatment provide water, by reacting with the CO2 released in the course of the water-isocyanate reaction. Such inorganic powder can be for example the Ca(OH)2, Mg(OH)2, Ba(OH)2, or any combination thereof. The inorganic hydroxide powders mentioned above preferably contain the hydroxides mentioned above in more than 80% by weight. In addition to the inorganic hydroxide powders Mg-hydroxide-carbonate 4 MgCO3Mg(OH)2·5H2O), CaO, MgO and similar materials may also occur as impurity, accompanying material and/or water binding material.
The MDI based di- and polyisocyanates used in the resin system of the invention can be for example the following: Ongronat 2100 (mixture of diphenyl-methane-diisocyanates, manufacturer: BC), Lupranat M200R (mixture of diphenyl-methane-diisocyanates, manufacturer: BASF) or the PI-PIR MDI (polyisocianurate-containing MDI, manufacturer: Polinvent), and other such materials, described in the examples. It is obvious for an expert that in the resin systems of the invention the material with structure and characteristics similar to that of the above can be used successfully.
The resin system of the invention may contain different inert fillers, in addition to the reactive components mentioned above, in order to improve solidity and/or reduce inflammability. Such filler can be for example the fine-grained (particle size <100 μm) calcium carbonate, magnesium-carbonate, dolomite, quartz, corundum, talc, etc. powders or any mixture thereof. The inert fillers mentioned may be present at most in 40% by weight in the resin system of the invention, relative to the total weight of the resin system.
The resin system of the invention may additionally contain different additives, generally used in the resin system, such as phosphoric-acid type and other flame retardant materials and/or plasticizers. Listing of the additives mentioned as examples can be found in the examples of this description. It is obvious for an expert that the materials with similar structure and characteristics can be used in the resin system without limitation.
The resin system of the invention can be prepared simply, by mixing and homogenizing the suitable components in the necessary amount. Execution of the process, and the means and equipment necessary for it, and their application is apparent for the expert.
The invention further provides the use of the resin system in preparing a prepreg.
In the process of the invention thermo resistant and low elongation at break substructure material is impregnated with the resin system of the invention with one of the known prepreg preparation methods. For example different glass-cloth, basalt cloth, etc. can be used as substructure material for the prepregs. In the course of impregnation siliconized paper layer is put on the impregnated substructure material, and the material thus obtained is wound up to core rolls of paper, and finally enclosed in a two- or multilayer, water vapour impermeable packaging material with an aluminium layer, or until further processing is stored in a water vapour impermeable sheath. The water vapour impermeable packaging material mentioned is very important because the water vapour molecules probably penetrating from the air can initiate undesired polymerization processes. But the packaging material mentioned allows the product to be stored as long as you like.
In a preferred embodiment of the invention impregnation of the substructure material is performed at 30-70° C. resin temperature.
In another preferred embodiment of the invention impregnation is performed with 0.5-50 m/min rate. In an especially preferred embodiment of the invention the rate of impregnation is 5-15 m/min.
In another especially preferred embodiment of the invention width of the prepreg produced is 650-2600 mm. 1300 mm is especially preferred.
The invention further provides a method for lining chimneys.
In the course of the method mentioned the resin system of the invention is used in the prepreg used at lining the chimneys. In the course of the method tubes with suitable size are formed from the prepreg prepared with the use of the resin system with one of the methods known, and an extruded, one- or more layered heat treatment tube is put beforehand inside the prepreg tube containing the resin system of the invention, which at the site of application, before or during the heat treatment allows inflation and isotherm hold time, and the tube rolled up along the longitudinal axis is pulled first into a polyester calibration tube, then protected with water-vapour impermeable packaging material, on the site of application, by taking out of the packaging material is let in or pulled in the chimney flue, clamping to the fittings necessary (for example water collecting vessel, flue gas feeding T-fitting, end piece), and the 90-110° C. temperature necessary for curing is provided with the tube with the heat treatment tube mentioned, in such a manner, that hot steam, mixture of steam and air, or mixture of flue gas and steam is blown through the tube, suitably for 1-2 hours. The permeability of the heat treatment tube mentioned is sufficient for diffusing through the H2O vapour and optionally CO2 necessary for curing. Following hardening of the prepreg tube, i.e. curing of the synthetic resin the inner heat treatment tube is pulled out. Instead of the polyolefin heat treatment tubes it is preferred to use one- or multi-layered polyamide tubes, with higher water vapour and CO2 permeability.
a shows the powder drying and tempering device.
Laboratory and Large Scale Laboratory Experiments
We should like to demonstrate or prove the novelty of the technical solution of the invention, and its practical feasibility, by the description of the laboratory, large scale laboratory (some of these is called pilot experiment) and plant experiments, detailed hereunder. Generally materials industrially produced or commercially available are used for the experiments. Abbreviation, name and manufacturer of the materials mentioned in the description are listed in Table 1.
Following the measurement of the components the impregnating resins of the invention were first homogenized with a laboratory dissolver. Following this the viscosity of the resin was measured with a Brookfield DV-II type viscometer at 20° C. after the preparation, and the measurement was repeated in 1 day and 1 week of age at the same temperature. Between the measurements the samples were stored in a closed space, in protecting gas atmosphere. The same was repeated at 30° C. too, in order to determine the stability and storability of the resin.
Following this a selected glass-cloth type was carefully impregnated with the resins, and short, about 1 meter's prepreg tubes were prepared, as described in Example 1, and these were heat-treated as described in Example 4, and presented at
The tubes prepared this way were visually characterized, and the tubes prepared with the most promising recipe were submitted to gas tightness test and mounting bevel solidity test. What was experienced in the course of the visual inspection, the viscosity data of the starting and stored resins, and the results of the combustion experiments is summarized in Table 2 in case of the most important resin systems.
1See in more details in the Experimental part II, 4, Quality control, FIG. 4
2Prepared by mixing in compressed air, with 0.2 bar steam pressure with 0.7 bar air pressure
3Prepared by mixing in compressed air, with 0.2 bar steam pressure with 0.7 bar air pressure
4Inflation was started with 0.2 bar initial pressure, and the steam pressure was raised to 0.7 bar. This was maintained until total curing.
Based on the data of Table 2 it can be concluded that although the different recipes gave very different results, but many of them performed well. In other words, the prepregs impregnated with these were sufficiently storable, while the solidity, gas tightness, optical appearance, strongly self-extinguishing character of the cured tubes proved to be good, and with some of them it was expedient to perform even the more expensive plant experiments. As it can be seen later from the large scale experiments the recipe or system No. K-48 was tried first on larger scale. But for the sufficiently safe production at that time already expensive drying unit and closed dissolver had to be purchased or had it produced.
Pilot Plant Production of Prepreg Impregnation Resin
Drying of 39.8 kg A-1 type filler (manufacturer: OMYA, type CaCO3 powder) was performed in the experimental powder-drying unit of about 100 litre useful volume, prepared from stainless steel, equipped with a mixer, double walled, custom made, at 200° C. The powder-drying unit is heated with the TOOL-TEMP TT-390 type, nominally 24 kW tool tempering device (the powder drying and tempering device is seen on
Following this, after the A-1 type filler the 23.2 kg A-2 type filler powder (manufacturer: BAU-MIT type: CALMIT bagged hydrated lime powder) was dried analogously with this, and its cooling and packaging was performed identically with those of the A-1 filler.
The binder was measured in a 200 litre metal drum, into which, during and after a dry air flushing (its dew point temperature is less than −60° C.) 72 kg Lupranat M200R and 7.2 kg DPO was put. The temperature of the binder was raised to 60° C. in a drum heater, and poured into the dissolver, prewarmed, flushed with warmed and dry air. From the binder about 2 kg resin remains on the wall of the drum in a thin layer.
For the first time charging of the A-1 type filler was started into the dissolver, while its agitator was slowly rotating (about 50 rotation/min). The dried powder was charged intermittently, in 4 portions. Following the addition of the total amount (39.6 kg) the speed of the agitator was doublet (the dissolver can be seen on
Following this, similarly to the A-1 filler, the altogether 23.2 kg A2 type dried powder was charged in 4 portions. Charging of the two powder types took 2×15 minutes. The total charge measured this way was homogenized for an additional 40 minutes with 100 rpm, and the agitator was stopped. The 6 m3 bottle, containing the clean, dry nitrogen was put to the pallet of the dissolver, and the equipment was put under N2 pressure, its temperature was set to 50° C., and incubation was continued until next morning.
The impregnation resin prepared this way with the pre-set temperature was directly used for the production of the prepreg.
Impregnation
The equipment seen on
The material application roller and the resin storage tray of the equipment is heated to 50° C. with water heating. The glass-cloth roll (2330 g/m2 and 1.3 m wide) is put to the substructure material storing shaft 1 of the machine, and the separating, silicon impregnated paper roll 6 is put to shaft 7. The expansion tube is put to winder shaft 5. The impregnation resin (its temperature is about 50° C.) is warmed to about 60° C. by starting the electric heating. In the autoclave, in the space over the resin 1 bar N2 atmosphere is maintained continuously. Charging of the resin storage tray 10 is performed by the pressure of the N2, through a rubber hose. The 60 kg K-48 resin (60° C.) is charged into the resin storage tray 10 of the preheated machine. The scraper blade 11 slit pitch is set to 0.6 mm, the impregnation speed of the machine is set to 5 m/min. We wait until the different temperature equalize in the resin storage tray 10, at that time the temperature of the resin is about 56° C. The temperature of the resin is checked with an immersion thermometer at the two ends of the resin storage tray 10. At this time impregnation is started with 5 m/min speed. Cross-impregnability of the glass-cloth is inspected visually on the impregnated fabric. Impregnation is suitable if the gaps between the filaments of the fabric are uniformly filled by the resin, the fabric becomes uniformly impregnated. This visual inspection is performed on the impregnated fabric, on the section after the drying roller 3. If this is found faultless then the impregnation speed is gradually increased to 10 m/min. Refilling of the resin storage tray 10 with the resin is performed in the time of the roll-changes. The prepreg rolls are carefully (airtight) packaged into gas- and vapour-tight foil, to exclude the water vapour during transportation or storage (the packaged prepreg rolls can be seen on
Hose Preparation from the Prepreg Roll
A working foil is laid out to a smooth, hard surface, the length of the foil is about 1-2 m longer than that the hose to be prepared, its width is at least 1.5 m. From the prepreg roll a portion 20 cm longer than the length of the hose is rolled down and cut, together with the separating foil. Thereafter the roll is carefully packaged back into its airtight, vapour-tight package.
The cut material is put to the working foil prepared in advance, in unfolded condition in such a way that the separation foil is at the bottom (the prepreg rolled down, laid to the working foil can be seen on
Quality Control
Large scale laboratory quality control is performed on an arbitrarily chosen 1 m piece of the hose prepared according to Example 3. In the course of the operation connection elements are fixed to the ends of the hose, serving steam inlet and outlet. The external cylindrical surface of the connection elements is put into the polyethylene hose located inside the hose, and with the pipe clip put to the outer surface of the calibrating hose the hose, already with three layers is pressed to the surface of the connecting element, providing with this its tight seal (the prepreg hose assembled for heat treatment can be seen on
Steam is introduced through the steam inlet valve put to connecting element 17. The pressure of the steam presses the prepreg tube 16 to the calibrating polyester hose, this is the way as the compact structure of the tube forms. Steam pressure is adjusted at steam outlet valve 14. Pressure is checked with manometer 13. About 100° C. steam is used for the heat treatment, for about 1-1.5 hours. During this time the prepreg hose 16 becomes round, and cures. Thereafter the connecting elements 15 and 17 are removed from the cured tube, and the polyethylene hose is also removed from the inside of the tube. Thereafter the gas tightness and mechanical characters of the tube are checked. Following the quality control mentioned above still long (about 12 meters) hoses are prepared from the industrially produced prepreg materials, and some 14×14 cm flues of the experimental chimney block built on the site of the Polinvent Kft. were duly equipped with the liner pipe, exactly the same way as the Furanflex® type liner materials (authorized by ÉMI) were built in. Some characteristic moments of building in the liner hoses prepared from the industrially produced prepregs are illustrated on
The suitability of the operationally built in and heat treated, already cured liner pipes with high strength was checked with the gas boiler connected to the experimental chimney block and with a measuring system (the gas boiler and the measuring system can be seen on
Another advantage of the invention that it has a significantly longer shelf life than the materials known from the prior art. The results of the shelf life investigations demonstrate that in case of water tight packaging the prepreg raw material retained its characteristics without deterioration in quality for more than 1 year at 18-22° C., and excellent, flexible house could be prepared from it, whose incorporation (pulling in, inflation, and heat treatment) proved to be trouble free.
The results of the laboratory, pilot plant and plant experiments mentioned above are clearly proving that the goal of the invention was entirely achievable with the solution of the invention. Storage for a long period of time is significantly more economical than in case of the compositions known from the prior art, needing continuous cooling below 8° C.
Further advantage of the solution of the invention, that the material developed is a sufficiently flame retarded, i.e. self-extinguishing material, and doesn't melt even by the effect of open flame. According to our measurements although it darkens and blacks out around 300° C. temperature, but this degradation is moving towards graphitization, and the resulting special composite remains latching even during long lasting thermal effects (40-50 hours, continuous thermal effects around 400° C.) (
| Number | Date | Country | Kind |
|---|---|---|---|
| P 12 00723 | Dec 2012 | HU | national |
