JPH0416360B2 - - Google Patents

Description

Claim 1: A method for stripping an organic coating from a surface of an object to be coated, comprising: a stripping composition containing a halogenated hydrocarbon or a hydrocarbon as a main component is present in liquid form; contacting a phase atmosphere, and during said contact, said surface and said release composition gas phase are at a temperature and pressure not substantially greater than ambient temperature and pressure, and said contact is terminated with said release composition present in liquid form. A method characterized in that it is carried out under conditions below the boiling point. 2. The method of claim 1, wherein said contacting is carried out substantially in the absence of liquid condensate at the surface of said object to be coated. 3. The method of claim 1, wherein said contacting is performed while either said surface or said vapor phase of said release composition is cooled to below ambient temperature. 4. The method of claim 1, wherein the stripping composition contains a chlorocarbon or hydrocarbon as a major component. 5. The coating release composition has a chlorocarbon as a major component and at ambient temperature at least about 2
Water, ammonia, aliphatic hydrocarbon alkylamines, carboxylic acids, alkanols, alkyl ethers, alkyl esters, alkyl nitriles, carboxylic acid amides, alkyl ketones, benzene, lower alkyl and halogen-substituted benzenes, up to 8 with a vapor pressure of mmHg 2. A method according to claim 1, consisting essentially of a heteroaromatic compound containing carbon atoms in a mixture with at least one additional component selected from volatile inorganic acids. 6. The stripping composition is normally liquid at ambient temperature, and the vapor phase flow of the stripping composition causes air to be blown over the stripping composition without heating the liquid stripping composition to a boiling point. A method according to claim 1, wherein the method is formed by: 7. A method according to any one of claims 1 to 6, wherein the organic coating comprises paint, asphalt or oil. 8 further comprising: sealing said surface from the atmosphere in a stripping region; circulating said vapor phase stripping composition within said stripping region; and said coating until the adhesion between said coating and said surface is substantially destroyed. 7. A method according to any of claims 1 to 6, comprising: maintaining a vapor phase of a stripping composition in contact with the surface. 9. The organic coating is stripped from the internal coating surface of a large building, including in particular the interior of a storage tank on land or the hold or ballast tank of a ship or barge, and furthermore, said internal surface is sealed from the atmosphere to form a stripped area. forming a vapor phase stream of a stripping composition comprising a halogenated hydrocarbon or hydrocarbon as a major component at a temperature and pressure not substantially greater than about ambient temperature and pressure; dispensing a vapor phase of the release composition into the stripping region, circulating the vapor phase of the stripping composition within the stripping region, such that the adhesion between the coating and the surface is substantially continuing to contact the vapor phase of the stripping composition with the coating surface at a temperature and pressure not greater than substantially ambient temperature and pressure until breakdown. 6. The method according to any one of items 6 to 6. TECHNICAL FIELD The present invention relates to a method for stripping an organic coating from an object to be coated. More particularly, the invention relates to coatings and/or paints obtained from compositions based on organic resins, those prepared with organic vehicles such as paints, varnishes, lacquers, etc., as well as various oils, asphalts, etc. This relates to a method of peeling. The method of the invention is particularly suitable for objects with irregular surfaces and for vertical surfaces, such as objects with irregular surfaces, and inside large structures such as storage rooms and tanks on land, holds and ballast tanks of ships.
It is useful for removing such coatings from large sloped surfaces. BACKGROUND ART In general, paint can be removed from a painted object by using an organic or inorganic solvent, or a mixture thereof, if the painted surface is only slightly coated. (References - Kirk
−Othmer's, Encyclopedia of Chemical
Technology, Vol.14, PP485-493, 2nd
Edition John Wiley and sons, 1967). Among the chlorinated hydrocarbon solvents in which many formulations have been used, methylene chloride (dichloromethane) has been found to be particularly effective. The components of liquid strippers typically include additives such as thickeners and retarder detergents. Formulations for stripping paints and other coatings with organic solvents are of the "scrub-off" or "wash-off" type. Typically, the stripping composition is applied to the coated object by any of the methods described above and left there for a period of time, after which the swollen and/or softened coating is rubbed off, in the case of "scraping off". Sometimes, "washing off"
In this case, it is removed from the surface by rinsing with water and/or wiping with a wet cloth. Said method is relatively expensive since the organic solvent cannot be recovered except in the case of immersion applications.
Moreover, all known methods are generally dangerous and very expensive when the surfaces are large. In addition, the waxes used as retarders in the above formulations are difficult to completely remove, and residual waxes can interfere with subsequent surface coatings. U.S. Patent No. 2689198 by Judd, Nogueira
U.S. Pat. No. 3,794,524 to Cooper et al. and U.S. Pat. No. 3,832,235 to Cooper et al. describe methods in which paint is stripped from relatively small objects by contact with vapors of boiling solvent components. Ru. In these methods, hot vapors are liquefied on the painted surface. A method for cleaning tanks is described in US Pat. No. 3,042,553 to Kearney et al., in which a solvent is heated to boiling point and vapor is delivered to the tank where it condenses on the surface and is washed away. However, such methods cannot be applied to the removal of organic coatings over large areas. This is because the expense of heating to reflux sufficient solvent for a significant amount of time becomes a hindrance, and as the scale increases, expensive solvent-resistant equipment becomes necessary. Additionally, even moderate local temperature differences can be harmful in structures such as large metal tanks and ships. It is a modern industrial reality that removing paint and other protective coatings from large tanks and other large structures is a tedious, unpleasant, expensive, and dangerous process with an abrasive spray finish. It is. Ship's ballast tanks are usually filled with water and are therefore protected against rust. Finally, it is coated with a paint film. If by chance this paint coating is damaged or chipped, the paint must be removed from the inside of the ballast tank and repainted to prevent rusting and eventually pitting. This problem is particularly important for ships carrying liquefied natural gas. Ship ballast tanks have capacities of a million gallons or more and often have complex "honeycomb" structures that are difficult and labor-intensive for blast finishers to work with. Also, the removal and formulation of large amounts of spray debris is expensive. To date, abrasive jetting finishes are the only practical method of removing paint from large surfaces, although they have severe drawbacks, and when hydraulically jetting, hammering is also used. Fixed storage tanks, railway and truck tank cars, and tar, pitch, asphalt, petroleum and vegetable oil residues may be used to change the type of cargo, make structural repairs, or in response to government inspections. The most effective and least labor intensive method of cleaning barge and ship holds is in great demand. Some of these tanks and holds have a capacity of over 20 million gallons. Today they are primarily cleaned by hand, using high-pressure jets of water, water-soluble solutions, or emulsions, although sometimes it is necessary to scrub them with a shovel or other tool. Caustic soda solutions have also been used, but they are expensive and the cleaning achieved is marginal or unacceptable. The residue is usually waste and its formulation is also problematic. DESCRIPTION OF THE INVENTION The main object of the present invention is to provide a method for stripping organic coatings from coated objects in an economical manner, which avoids the problems of known stripping methods. An important object of this invention is to have a wide surface;
This means that organic coatings can be obtained from the interior of large structures such as storage tanks, ship ballast tanks and holds, as well as from objects of various shapes and with complex or sloped surfaces, more economically than by known methods.
To provide a method of stripping that is safe for workers, causes less pollution problems, consumes less fuel, and does not use additives that would be a hindrance to subsequent recoating. A further object of the invention is to provide a method for removing organic coatings and residues remaining in a tank after discharging petroleum products or vegetable oils. Other objects of the invention will be revealed in part herein and set forth in part below. In accordance with the foregoing and other objects of the present invention, our invention provides a stripping composition or a vapor phase composition having the ability to destroy adhesion between a coating and a surface even if the surface to be stripped is not at substantially ambient temperature. A stripping composition is provided to the target surface to strip the organic coating from the coated surface. One of the preferred embodiments of the present invention is that the vapor phase stripping composition contacts the surface to be stripped at near ambient temperature, and that there is substantially no liquid stripping composition condensed on the stripping surface. . Another preferred embodiment of the present invention is that the vapor phase stripping composition or surface being stripped may be below ambient temperature. DETAILED DESCRIPTION OF THE INVENTION We have found that simply by the action of a vapor release composition, organic coatings are substantially loosened and, in many cases, completely removed from the surface. Organic coatings are organic resins or organic vehicles such as paints, paints, varnishes, etc. used on metal or wood surfaces.
Refers to any coaching based on Lutzker et al. This method is also used to remove protective organic coatings used to protect and/or strengthen surfaces. In addition, this method can also be used to remove residual coatings, which are not normally referred to as protective coatings, but are included within the meaning of coating in this description. Residue coatings include crude oil, Bunker C (No. 6) heavy oil, high paraffin crude oil, asphalt, air-blown asphalt, and vacuum tar residues, i.e. high vacuum distillation residues of certain crude oils, tars, vegetable oils, etc. and must be removed from the surfaces of holds and tanks when they need to be cleaned for cargo changes or for repairs, coast guard inspections, etc. In accordance with our invention, the surface to be stripped is contacted with a vapor phase stripping composition until the adhesion between the coating and the surface is broken or the coating goes into solution and flows to the bed. In one embodiment of our method, the vapor phase stripping composition is contacted at a concentration, pressure, and temperature such that virtually no condensation occurs on the coating surface. This process therefore takes place virtually without liquefaction and condensation; vapor adsorption and/or absorption takes place within the coating during the process. Steam is generally recovered in high yields. There is no theoretical minimum temperature limit for this method as long as the stripping chemical has a small vapor pressure. For economic reasons, it is preferable to use this method at around room temperature. Depending on the particular conditions, the time required to destroy or remove the deposit of the coating ranges from a few minutes to several days. We believe that organic coatings are typically contacted with vapor phase release compositions at ambient temperatures and at higher temperatures given the higher concentrations of vapor phase release compositions and the faster rate of chemical reaction expected at higher temperatures. We found that the peeling was much faster than expected for the time required. Even more surprising, we have found that petroleum products such as asphalt, oils, and certain paints are stripped more quickly when vapor-phase stripping compositions or the surfaces being stripped are cold than when they are hot. I found out. For example, asphalt is stripped faster at 22°C than at 32°C or 36°C at a given vapor phase stripping composition concentration, and No. 6 oil is removed faster when either the substrate or the vapor is cooled. be done. Heating the gaseous stripping composition because there is no need to heat the stripping composition to reflux, and in many cases, the methods of the invention are preferably carried out at substantially ambient or lower temperatures. It is a particular advantage of the method of the invention that this is completely unnecessary or undesirable. When operating the process near ambient temperature, it is generally desirable to reduce the ambient temperature to at least around 0°C, otherwise the process may be disadvantageously slow for some types of coatings. Even at temperatures below 0° C., the present method typically provides better results than other available methods. For example, it is preferred that neither the release composition nor the release surface be above ambient temperature, and that either the surface or the release composition be allowed to cool below ambient temperature before contacting the vapor phase release composition with the coating. When a painted surface treated according to our vapor stripping method is released from the vapor-phase stripping composition by air drying or other convenient means, the paint coating often flakes off completely or only a small amount of paint remains. It can be seen that it can be easily rubbed off, leaving only a spot. Surfaces that come into contact with vapor phase stripping compositions often have about 75-100% free visible paint residue. However, even when unwanted amounts of coating remain, the surface can be cleaned in substantially less time than would be required to obtain a 100% clean surface by abrasive jetting alone.
Can be given an abrasive jet finish to be 100% clean. For cleaning surfaces of oily or tarry substances
95-100% removal is usually achieved. It is believed that through the process of our invention, vapors are adsorbed and/or absorbed by the coating to cause it to undergo physical and sometimes chemical changes and to be released from the substrate.
Many epoxies, alkyds, polyurethanes, and polyester coatings can be easily and economically processed or sold to form dry flakes, which according to our invention release in the virtual absence of liquefaction condensation. This is an unexpected advantage of processing compositions. When the surface is treated with liquid or condensate from the refluxing vapor, the liquid release composition leaches out the dissolved components of the coating, resulting in sticky and cumbersome coatings that are difficult to clean and virtually dry. less economical than removing flakes. For oils, asphalts, and some paints, recovery of both the stripping composition and the coating material is possible by distillation of the resulting solution. Another preferred embodiment of our invention is that the surface to be treated is isolated from the atmosphere to effectively form an ablation zone. A stream of gaseous stripping composition near or in some cases below ambient temperature is introduced into the stripping region and contacts the coating surface. If the stripping composition is a liquid at ambient temperature, a gas stream is generated by blowing air over the surface of the liquid in an evaporator and directed to the stripping region in a conduit.
The stripping region preferably has a return line to the vacuum side of the gas blower where the air and gaseous stripping composition are recirculated. As the partial pressure of the vapor phase stripping composition increases in the stripping region, air will flow out of the stripping region. The density of the gaseous stripping composition is usually greater than that of air, and the air is usually forced out near the top of the stripping region. This is used to create a high concentration of vapor phase stripping composition and avoid creating a substantial increase in pressure. The evaporator must exchange heat of vaporization of the liquid stripping composition to avoid overcooling of the liquid stripping composition. However, it is generally desirable for the vapor phase stripping composition to be at or below ambient temperature in the conduit and stripping area. If coating stripping were to proceed faster at lower temperatures, the heat of vaporization would not have to be completely heat exchanged and the steam would be cooler and energy would be saved. It is also possible to evaporate the liquid stripping composition inside the paint stripping zone, in which case a special evaporation zone is not required. A preferred method for circulating the vapor phase stripping composition is a gas pump or blower. When the vapor phase stripping composition is thoroughly circulated throughout the stripping area, the efficiency of the current process can be increased and the time required to break the coating and surface adhesion can be reduced. In the stripping region, the coating adsorbs and/or absorbs the vapor phase stripping composition, thereby causing physical and/or
Or it causes a chemical change to loosen and unravel the base. The vapor phase stripping composition is then pumped out of the stripping area and desorbed from the coating. During removal of the vapor phase stripping composition, air is instead vented to the paint stripping area through a vacuum regulating valve. This avoids the potentially dangerous depressurization process and keeps the tank safe. The vapor phase stripping composition is continuously introduced into the stripping zone and it is desirable to continuously remove the high vapor pressure component from the top of the stripping zone along with the air, which is controlled by a pressure regulating valve at about 1-2 psi. Adjustments are continued until the air is substantially removed and the concentrated vapor of the denser stripping composition is vented. The vented chemical vapors can be easily recovered by concentration and/or charcoal adsorption for reuse and avoid air pollution. The vapor phase stripping composition can also be continuously withdrawn and recovered from the stripping area, or retained in a gaseous state and recycled to the paint stripping area, or if there are two or more areas to be stripped. In this method, the vapor phase stripping composition drawn from one stripping region is circulated to another region. In large scale operations, blowers can be used to distribute the steam throughout the structure in a reasonable amount of time. The ideal single or mixture of gaseous compounds suitable for organic coatings of the type used today has not yet been found. Usually, with a few simple experiments, one skilled in the art can determine effective compounds or mixtures. The partial pressure is at least 2 at ambient temperature
Organic and inorganic compounds known to be useful in stripping paints, paints, varnishes, etc. that are mmHg can be used in our method. In practice, we wish to use a mixture containing a relatively high percentage of lower chlorocarbons, especially chlorocarbons containing 1 to 3 carbon atoms and 1 to 4 chlorine atoms. Methylene chloride is a particularly effective stripping agent from the standpoint of performance as well as safety and economy. However, other chloroalkanes such as 1,2-dichloroalkane and chloroform also have advantages. Generally, these chlorocarbon mixtures are not only effective and economical, but also allow the risk of fire and explosion to be reduced or eliminated. Approximately 25 ~ methylene chloride in volume
For a stripping composition containing 100% methylene chloride, it is more desirable to use a formulation containing methylene chloride as a main component, and a formulation containing about 70, 80, or 85 to 100% methylene chloride is used, especially considering economic efficiency and safety. . Compounds that we have found to improve the effectiveness of methylene chloride and other lower chloroalkanes with various coatings include aliphatic hydrocarbons containing up to about 8 carbon atoms, water, and lower carboxylic acids such as formic acid. There are alenes and volatile inorganic acids such as acids, ammonia, lower alkyl amines, lower alkanols, and lower alkyl ethers, esters, ketones, nitriles, amides, benzenes, and lower alkyl and halogen substituted benzenes. "low grade"
The term refers to compounds having 1 to 4 carbon atoms. Generally, the gas phase components most effectively contain about 70-95% methylene chloride, about 1% water, and about 4-29% of other compounds such as those mentioned above. It was also found that low alkyl and dialkyl amines are strong activators of methyl chloride in the gas phase. Methylene chloride about 70~
Formulations containing 90% by volume and 10-30% 33-75% ethyleneamine aqueous solution are particularly effective. In general, small molecules with dipole moments and those of acidic or basic nature appear to be most effective in release coatings, alone or in combination with methylene chloride. When a vapor phase stripping composition is selected that includes two or more components that do not form a homogeneous solution in the liquid phase, it is desirable to have a separate evaporator for each such component. The specific amount of stripping composition used will vary depending on the nature and thickness of the coating, the ambient temperature and the particular stripping composition selected or the volume of the stripping area and the area of the coating surface being treated. . Generally speaking, the ratio of weight of stripping composition used to weight of coating removed will range from about 0.5:1 to about 4:1. There is no practical upper limit as to the size or complexity of coating structures that can be treated with vapor phase release compositions according to our invention, provided that the area to be removed can be practically sealed from the atmosphere. An important advantage of the method is the fact that it does not pose any risk or damage to the structure due to pressure or temperature changes. Additionally, no corrosion problems were observed when using appropriate stripping compositions as described above for metal surfaces. Our method is extremely economical because the chemicals used are cheap today and most of the chemicals are recovered and reused. The necessary equipment is commercially available at reasonable prices, and input requirements are low. An important advantage of our stripping method is that the operator does not have to be exposed to chemical strippers or coatings, which can be hazardous, such as certain petroleum products. The chemical is transferred from the transport container to the stripping system with little or no exposure to the atmosphere, and no operator is required to enter the stripping area until the vapor is replaced with air. The following examples further illustrate the invention, but are not to be construed as limiting it in any way. In the examples below and throughout this description, all proportions of the stripping composition are by volume, and the relative proportions of solvent and paint coating are by weight, unless otherwise indicated. Example 1 Paint removal A 16 cm ² steel plate with an abrasive blast finish and sprayed with two coats (0.3 mm) of No. 1 paint (see Table 1) was used with “stun blast sand” (blast furnace residue). Grid blasting was performed using a sandblasting gun (4.8 mm inner diameter nozzle) at a pressure of 5.6 Kg/cm ² to a nearly white metal state in 85 seconds. The other side of the paint surface was treated with methylene chloride (9 ml), 90% formic acid (1 ml), i.e. MC:
FA:H ₂ O was placed in a plastic beaker containing a solution ratio of 9:0.9:0.1. 14 hours,
After exposure to the vapor at 23°C, most of the exposed epoxy coating became delaminated pieces and fell into the beaker. The plate was left in air at 23°C for 4 hours. The treated 16 cm ² surface was then grid blasted to a white metallic appearance using the equipment and conditions previously described. In this case, the quick clean-up took less than 5 seconds, which was 6% of the required coaching time without treatment. Example 2-15 Stripping of various paints Test panels coated with different paints except for Example 15 were placed on top of a container of liquid stripping composition.
Alternatively, the coated test plate may be exposed to the vapor phase stripping composition by placing the coated test plate inside a sealed container, such as a stoppered jar, desiccator, or thin layer chromatography (TLC) chamber containing a reservoir of liquid stripping composition. did. In all cases, the test panels were not exposed to the liquid release composition, and coating removal was solely due to the action of the vapor phase release composition. In Example 15, the coated steel plate was placed in a 4 container with gas inlet and draw tubes and insulated from the atmosphere. The vapor phase stripping composition was continuously circulated from side to side. The test plates in Examples 8 and 9 are made of wood, while all others are made of metal. All examples were also carried out at their respective ambient temperatures, but in Examples 7a and 7b the TLC chamber with the pool of release composition was placed in crushed ice and cooled to 0°C. Blotting paper was used to speed up equilibrium between the gas and liquid phases in the container. The peeling conditions and results of Example 2-15 are shown in Table 2. The paint reference numbers in Table 2 are the paint numbers in Table 1, and all release paints in the example are considered the same. The measured paint thickness is
It is shown in parentheses below the paint reference number in Table 2. The following abbreviations were used for the components of the release formulation in all examples. MC: methylene chloride
PCE: Perchlorethylene FA: Formic acid DMF: Dimethylformamide MEK: Methyl ethyl ketone
CLF: Chloroform EA: Ethylamine HEX: Hexane

[Table]

【table】

[Table] Example 16 Peeling of paint inside a tank A steel tank measuring 1.85 x 1.85 x 1.85 m was sandblasted and the inside was spray-painted with No. 7 paint to a dry film thickness of 0.23 mm. A few months later, the paint was removed as shown below. Two steel evaporators, containers A and B, are connected in series on the outlet side of the GM3-53 gas pump.
Connections were made with 2.5 cm steel pipe and chemical-resistant plastic hose. The evaporator is a cylindrical steel vessel with a glass viewing window.
It has an inlet and an outlet for a 2.5cm pipe at the top, and is placed in a hot water bath. The outlet pipe was connected to the bottom of the test tank. A pipe is connected from the top of the tank to the inlet side of the blower. Also, the outlet of the tank was connected to the vent pipe with a T-shaped pipe. Remover MC
(16) and FA (3) were injected into containers A and B, respectively, and the blower was turned on to blow air at about 280/min over the surface of the release agent and into the tank.
Room temperature varied from 1 to 21°C, but sufficient heating was provided to maintain vapor flow at about room temperature during the test. After running the pump for eight hours, most of the tank walls were exposed and flakes of paint fell from the ceiling. The tank was left exposed to the atmosphere for a day and a night.
Afterwards, only a few loose pieces of paint could be seen on the walls and ceiling. The vent was opened, containers A and B were cooled with a slush of ice and water, and the gas pump rotation was reversed. The stripping vapor was replaced at room temperature and most of the reagents used could be recovered. The hatch of the tank was opened and the dried paint flakes (11.5 kg) were quickly removed using a vacuum cleaner. Close inspection of the interior surface revealed only some small spots in the anchor pattern and remaining in corner holes and welds.
Over 99% of the paint was removed and the surface was clean enough to be repainted without an abrasive blast finish. Examples 17-24 and Comparative Examples 17c-21c Stripping of Asphalt and Oil Coatings at Various Support Temperatures 12.5 cm x 0.9 cm test tubes of known weight were coated with a subbing layer and the specific liquid stripping described above Suspended in the gas phase of the composition. The container was covered with metal foil and kept at room temperature. To illustrate the facts of this invention, one of the test tubes was kept at room temperature, 22°C, or cooled with tap water to approx.
It was kept at 21℃. For comparison purposes, a second test tube, coated in the same manner as the first and suspended in a container, was heated by passing a stream of warm water through the interior. The amount of primer layer removed from the outer surface of each test tube was determined after exposure to the gas phase in a glass container. That is, either by drying the test tube after a certain period of time and measuring its weight, or by measuring the amount of coating that fell from the test tube after evaporation of the adsorbed and/or absorbed gas. The blotting paper soaked in liquid helped to keep the gas phase saturated in that case, however in all these and comparative examples the concentration of the gas phase was lower than the highest possible concentration, and methylene fluoride In this case, it was about 50%. The coating, its amount, vapor phase stripping composition and percent removal of the coating at various temperatures are shown in Table 3, in which RG and AB refer to roofing and air-blown asphalt, respectively.

TABLE Examples 25 and 26: Oil Stripping with Vapor Phase Stripping Compositions at Various Temperatures In this example, the temperature of the coating was kept constant by circulating water inside the coated test tube. The temperature of the stripping steam was varied while the air concentration remained constant. The coated test tube was suspended inside a small tank lightly covered with aluminum foil. Tap water was poured into the test tube. The air flow containing 30% MC is kept at a constant level by introducing air into the liquid MC.
Generated by stirring at 13/min, 78
It was heated with a copper coil heater at ℃ and air was blown into the center of the tank. In Example 26 the tank was cooled to 12° C. in a water bath, while in Example 25 the tank was completely exposed to the atmosphere. When the coated tube was so thin that the red cross mark on the white background was visible, stripping was stopped and the amount of coating left on the almost transparent tube was determined. The results are shown in Table 4.

[Table] Examples 27-30 Stripping with a vapor phase stripping composition at and below ambient temperature Test tubes coated with one type of material are exposed to a vapor phase stripping composition in a container and one coated with a vapor phase stripping composition at ambient temperature. (A), one was cooled to a specific temperature. The conditions and results for each example are shown in Table 5. Thus, in one embodiment of the present method, the stripping composition or the surface to be stripped is heated from about 10° C. to about 70° C. above ambient temperature.
℃ lower temperature, more preferably about 20℃ below ambient temperature
It is particularly advantageous to cool to about 50°C lower. Accordingly, in a preferred embodiment of the invention, the process is preferably carried out at a temperature of about -40°C to about 8°C, more preferably -20°C to 0°C.

【table】