CN110938206A

CN110938206A - Reduced gel formation in polyamide manufacturing processes

Info

Publication number: CN110938206A
Application number: CN201911254295.4A
Authority: CN
Inventors: 查尔斯·R·克尔曼; 托马斯·A·米茨卡; 加里·R·韦斯特
Original assignee: Invista North America LLC
Current assignee: Invista North America LLC
Priority date: 2013-05-01
Filing date: 2014-04-10
Publication date: 2020-03-31
Anticipated expiration: 2034-04-10
Also published as: WO2014179037A1; CN110938206B; TW201500403A; CN104130397A

Abstract

The present invention relates to reducing gel formation in polyamide manufacturing processes. In particular, described herein are methods of making high molecular weight polyamides that reduce or eliminate the production of undesirable gels during the manufacturing process. These methods reduce the undesirable formation of polyamide gels by polishing the interior surfaces of manufacturing equipment to provide surfaces having smaller surface roughness values.

Description

Reduced gel formation in polyamide manufacturing processes

This application is a divisional application of the application having a filing date of 2014, 10/4, application number 201410142781.8 and entitled "reducing gel formation in a polyamide manufacturing process".

This application claims priority to U.S. provisional patent application No. 61/817,963 filed on 5/1/2013, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to reducing gel formation in polyamide manufacturing processes. In particular, described herein are methods of making high molecular weight polyamides that reduce or eliminate the production of undesirable gels during the manufacturing process.

Background

Nylons are linear aliphatic polyamides having at least 85% aliphatic bonds between repeating amide units. The term "polyamide" is used widely today to refer to polymers containing multiple amide linkages. The term "linear" means that the polyamide may be derived from difunctional reactants in which the structural units are linked end-to-end and in a chain-like manner. As such, the term is intended to exclude three-dimensional polymer structures that may be present in the triamine derived or the triacid derived polymer.

Aliphatic polyamides can be derived from dicarboxylic acids and other amide forming derivatives of dicarboxylic acids when reacted with primary or secondary amines (e.g., anhydrides, amides, acid halides, half-esters, and diesters). The formation of essentially all aliphatic polyamide polymers from monomers consisting of dicarboxylic acids and diamines is accomplished by reacting a primary or secondary diamine (a diamine having at least one hydrogen attached to each nitrogen) with an amide-forming derivative of a dicarboxylic acid or dicarboxylic acid.

HOOC-R-COOH+H₂N-R’-NH₂→-[NH-R’-NH-CO-R-CO]_m-+nH₂O

The indicated formula, in which R and R' represent divalent hydrocarbon radicals, represents the product as a long chain built up from a series of identical units consisting of some of the following structures:

-NH-R’-NH-CO-R-CO-

wherein water is a by-product of polymer formation.

Polyamides can be prepared by continuously passing an aqueous solution of a diamine-dicarboxylic acid salt through successive reaction zones at superatmospheric pressure. A concentrated aqueous solution of an amide-forming reactant (e.g., a diamine-dicarboxylate salt) is continuously provided to a reaction zone where temperature-pressure conditions that cause vapor formation are prevented and a major portion of the salt is converted to polymer. The polymerization is complete when the desired degree of polymerization is obtained. The degree of polymerization is expressed indirectly in terms of polymer viscosity. The degree of polymerization, usually measured as relative viscosity or RV, is an alternative measure for viscosity and thus molecular weight.

At elevated temperatures, the degree of polymerization is a function of and defined by the amount of water present, including the manner in which the polymer is in dynamic equilibrium with, on the one hand, water, and, on the other hand, depolymerized polymer or even reactants. Polyamides with significantly higher RV than obtainable by equilibration with steam at atmospheric pressure are generally suitable. A disadvantage of this approach is that the increased time required to produce a high viscosity polymer often results in gelled or otherwise degraded polymer.

Undesirable side reactions, such as thermal degradation and discoloration of the polymer in the polymerization apparatus, can occur in the preparation of polyamides. Such side reactions are well known in the polymer processing art. Prior device tools to prevent side reactions are known from U.S. patent No. 3,361,537 to Ferrante and U.S. patent No. 4,134,736 to Hammond; see also U.S. patent No. 3,717,330 to Pinney.

Gel refers to a very high molecular weight, branched or cross-linked polymer formed in a nylon polymer melt. The gel is substantially insoluble and accumulates in the product and on the walls of the equipment in contact with the molten polymer. The presence of gelled polymers in the process equipment potentially leads to many manufacturing defects in the post-condensed product. The gel particles detach from the inner surfaces of the process equipment and damage equipment further downstream. Furthermore, the gel particles may become incorporated into the final product, leading to reduced quality and staining problems. Typically, the gel can only be removed from the device using extreme methods, such as by burning the gel.

There is a need for improved methods, articles, and systems that reduce gel formation during polyamide manufacturing processes.

Disclosure of Invention

The subject of the invention relates to a process for the manufacture of polyamides. More specifically, the subject matter of the present invention relates to a process for mixing and end-capping a dicarboxylic acid with a diamine and producing a high molecular weight polyamide with a reduced tendency to undesired gel formation. These methods reduce the undesirable formation of polyamide gels during the manufacturing process. The polyamide polymers are suitable for use in fibers, molded articles, films and articles containing the polymers.

The present subject matter relates to a method, article, and system for reducing the formation of polymer gels during polyamide manufacturing processes. The inventive subject matter reduces the formation of polymer gels by reducing surface roughness on the interior surfaces of process equipment to reduce the generation and stagnation of gels during the manufacturing process.

The inventive subject matter can include a method of reducing the formation of polymer gel during a polyamide manufacturing process, the method comprising directing a molten polyamide compound through a portion of a polyamide manufacturing system and contacting an interior surface of the system with the molten polyamide compound, subjecting the interior surface to a surface treatment to produce a treated interior surface, and contacting the treated interior surface with the molten polyamide compound. The molten polyamide may have a gel time of greater than 15 hours in steam at one atmosphere of pressure when maintained at a temperature between 280 ℃ and 295 ℃. The treated inner surface may have an average surface roughness of no greater than 6.00 μm or an average surface roughness between 1.00 μm and 6.00 μm. The surface treatment may include an abrasive flow machining method.

Drawings

The drawings, which are not necessarily to scale, generally illustrate the invention by way of example, but not by way of limitation.

FIG. 1 is a schematic flow diagram of an example system for the manufacture of polyamides.

Figure 2 illustrates a method of reducing the formation of polymer gel during the manufacture of polyamide.

Detailed Description

Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the present invention. However, the subject matter of the present invention may be practiced without these specific details. In other instances, well-known elements have not been shown or described in detail to preserve brevity. These embodiments may be combined, other elements may be utilized, or structural or logical changes may be made without departing from the scope of the inventive subject matter. The description is thus to be regarded as illustrative instead of limiting.

As used herein, the terms "gelation time", "gel time", and the like refer to the time required to produce a polymer that is insoluble in 98-100% formic acid when heated to a particular temperature by a stream of steam at one atmosphere of pressure. Nylon 6, 6 (sometimes abbreviated as "N66"), for example, can be heated to a temperature of 280 ℃ to 295 ℃. The insolubility of the polymer in formic acid can be verified in the following manner: rolling the polymer to a powder of 10 to 20 mesh, charging the powder (0.1g) in a flask and adding 98-100% formic acid (20mL) thereto; the flask was allowed to stand for four hours, at which time the state of the polymer was observed. When the polymer did not contain any gel, it was completely dissolved in the solvent within four hours. On the other hand, when the polymer contained any gel, the particles were merely wetted and swelled by the solvent, and a uniform formic acid solution was not obtained after four hours. Gelation of the polymer was confirmed by the presence of such wetted and swollen polymer.

In one example, gelation time can be measured as the time required for a polymer sample to exhibit deformation on a viscosity versus heating time curve for a polymer sample held at a constant temperature and constant vapor pressure. This measurement typically takes substantially comparable time to the gelation time obtained by measuring insolubility as described above.

As used herein, the term "relative viscosity" (RV) refers to the ratio of solution and solvent viscosities measured in a capillary viscometer at 25 ℃. The RV measured by ASTM D789-06 is the basis of a test procedure and is the ratio of the viscosity in centipoise at 25 ℃ of an 8.4 weight percent solution of polyamide in 90% formic acid (e.g., a solution of nine parts by weight formic acid and one part by weight water) to the viscosity in centipoise at 25 ℃ of 90% formic acid itself.

As used herein, the term "surface texture" refers to a typical surface that includes geometric irregularities (e.g., roughness, waviness, and particulates). Surface texture is measured by the perpendicular measurement of the deviation of a real surface from an ideal surface. Large vertical deviations indicate a rough surface, while small deviations indicate a smooth or more highly polished surface. Roughness is a high frequency (short wavelength) component measured by the surface in a standard manner.

The term "roughness average" (R)_a) Are the measured average of the surface peaks and valleys of those irregularities, and are expressed in micrometers (μm) and in microinches (μ in). Surface texture measurements are known to those skilled in the art and employ surface profiling devices. Known surface profiler devices are available from TAYLOR-HOBSON, Inc. AMETEK, INC., 1100Cassatt Road, P.O.Box 1764, Berwyn, Pa., 19312 USA.

The specification for the roughness of the manufactured part is usually expressed as an upper limit and is related to the frictional properties of the surface. The roughness average of the surface can be improved by techniques such as sandblasting, spinning, or electropolishing. Polishing with grit to obtain R of 1.00 to 6.00 μm_aThis is also known as No. 3 finishing or "half-polishing". A similar polishing procedure can be used to obtain an R of 0.9 to 1.50 μm_aAlso known as No. 4 finish, or R of 0.60 to 1.00. mu.m_aAlso known as No. 4A finish. The 4 and 4A finishes were bright and still had visible fines, but were not specular in reflective properties. No. 4A finishing is typically used where feed contact is expected. The smooth polishing finish is also referred to as No. 5 finish and it has an R of not more than 0.5 μm_a. The brightly polished surface is non-three-dimensional, has high image transparency and an R of not more than 0.10 μm_a. Non-traditional polishing techniques, such as electropolishing, have the potential to achieve R of 0.10 to 0.80 μm_a. The grit polishing can achieve No. 7 with 600 grit powder (e.g., SiC powder) or No. 5 with 320 grit powder.

The subject matter of the present invention relates to methods of reducing the formation of polymer gels during polyamide manufacturing processes, such as nylon manufacturing processes (e.g., manufacturing processes for nylon 6, nylon 7, nylon 11, nylon 12, nylon 6, nylon 6, 9; nylon 6, 10, nylon 6, 12, or copolymers thereof). The subject of the present invention can reduce the tendency of nylon 6, 6 polymer to gel by reducing the stagnation zone available for the polymer in the process equipment. The stagnation zone can include substantially any of those regions through which the molten nylon 6, 6 polymer passes at the temperature of treatment (e.g., 260 ℃ to 290 ℃) during any time period. This reduction in flow stagnation is obtained by polishing the surface in contact with the molten polymer, since the rough inner surface can promote stagnation. The surface in contact with the molten nylon 6, 6 polymer is substantially the inner surface and may comprise the surface of a mixing device (e.g., a continuous static mixer) placed within a conduit conducting the polymer; surfaces that are typically inaccessible with conventional polishing techniques.

Typically, a continuous polymerization process comprises, in sequence: a reactor stage, a flasher stage, a steam/polymer separator stage, and a finishing stage. Fig. 1 illustrates such a process in the form of an exemplary system 10 for manufacturing nylon 6, 6.

The system 10 includes a reservoir 12 containing a liquid or substantially liquid phase aqueous solution of a dicarboxylic acid, a diamine, and a solvent (e.g., water). Dicarboxylic acids and diamines may form ammonium carboxylate salts. In one example, where system 10 is configured for nylon 6, 6 manufacture, reservoir 12 may include hexamethylene diammonium adipate (nylon 6, 6 salt), which may be dissolved in water in reservoir 12. Reservoir 12 may be used to mix, store or heat an aqueous solution of an ammonium carboxylate salt.

In one example, the evaporator 14 is used to increase the concentration of the ammonium carboxylate salt solution to, for example, about 72 wt% salt in water. In doing so, the solution in reservoir 12 is transferred to evaporator 14 via conduit 16. The evaporator 14 is configured to convert a portion of the water in the aqueous solution from a substantially liquid phase to a substantially vapor phase in the form of a water vapor stream 18. The evaporator 14 may do so by heating the solution. In one example, the concentration of the ammonium carboxylate salt solution exiting the reservoir 12 and fed to the evaporator 14 is about 35 wt% to about 65 wt% salt in water or about 52 wt% to about 65 wt% salt in water.

The reaction mixture from evaporator 14 can be directed to reactor 20 via conduit 22. Within reactor 20, the unreacted dicarboxylic acid and diamine can react with each other, or with the polyamide prepolymer, or both, to form a first polyamide polymer. The temperature in the reactor 20 may be further increased beyond the temperature in the evaporator 14 to remove additional water. Reactor 20 may be equipped with a rectification column 24 in fluid communication with reactor 20, such as via conduit 26. The rectification column 24 may, in turn, be in fluid communication with a discharge line 28.

The polyamide polymer formed in reactor 20 can be transferred from reactor 20 to flasher 30 via conduit 32, along with unreacted dicarboxylic acid and diamine, by using pump 38. Within flasher 30, the temperature of the reaction mixture of polyamide polymer and unreacted dicarboxylic acid and diamine is increased. At the inlet to flasher 30, the pressure of the reaction mixture is relatively high, such as from about 1.9MPa to about 2.1 MPa. The pressure may be gradually reduced as the reaction mixture travels through flasher 30 such that at the outlet of flasher 30, the pressure is relatively low, in some cases approaching a vacuum of about 25KPa to about 50 KPa. At the temperature within flasher 30, progressively less pressure is exerted on the reaction mixture as it passes through flasher 30, resulting in further removal of water from the reaction mixture in the form of flashed-off steam. As the steam is flashed away from the reaction mixture, the polyamide polymer can undergo further polymerization. At the outlet end of the flash vessel 30, a two-phase mixture of the polyamide polymer and the gaseous vapor and liquid mixture of unreacted dicarboxylic acid and diamine may be formed. Steam may be released from flash vessel 30, such as through a vent hole (not shown) in flash vessel 30, or exit flash vessel 30 with the product stream via outlet conduit 34. The effluent from the flasher stage (also referred to as the "secondary reactor") comprises a polyamide prepolymer, typically having an RV of 9 to 20 or a water content of less than about 2-3 wt%, or about 1 wt% or less.

The flash vessel 30 may include at least one relatively long tube wrapped around the flash vessel 30, also referred to as a coil of the flash vessel 30. The tube may carry the reaction mixture from the inlet to the outlet of flasher 30. The tube may start with a small cross-sectional area, e.g., a small diameter, at the inlet and may expand along the length of the tube until it has a relatively larger cross-sectional area, e.g., a relatively larger diameter, at the outlet. As described above, an increase in cross-sectional area from inlet to outlet may provide a decrease in pressure from the inlet to the outlet of flash vessel 30.

A catalyst may be added to the reaction mixture to help promote the condensation reaction to form the polyamide described herein. In an example, the catalyst can be added to the reaction mixture at evaporator 14 (e.g., into an inlet of evaporator 14), at reactor 20 (e.g., into an inlet of reactor 20), or at flasher 30 (e.g., into an inlet of flasher 30). Although a catalyst may be added, polyamide polymerization need not occur. In one example, the catalyst may include at least one of sodium hypophosphite, manganese hypophosphite, or phenylphosphinic acid.

The polyamide polymer formed in flash vessel 30, as well as unreacted dicarboxylic acid and diamine, can be transferred from flash vessel 30 to finisher 36 via conduit 34 by use of pump 44.

The finisher 36 can provide further removal of water to subject the polyamide polymer to further polymerization. The control variables (e.g., temperature, pressure, and hold volume) in the finishing unit can be adjusted to produce a final polymer having a desired RV, typically in the range of 30 to 100. The temperature in the finishing unit is typically maintained in the range of 270 to 290 ℃ while the pressure is typically maintained at 250 to 640 mbar and the holding volume is typically about 20 to 40 minutes.

The post-condensed polymer is then passed from the post-condenser 36 to one or more polymer transfer lines 40 and further to several downstream processes shown in fig. 1 as a finishing system 42. Transfer line 40 may be fed via pump 46 to finishing system 42, wherein the finished polyamide polymer may be subjected to further mechanical processing, such as one or more of spinning, extrusion, and pelletizing. For example, the final polyamide polymer may be extruded through a die having a plurality of small capillaries to continuously produce a plurality of polyamide strands. The strands may be cut into polyamide pellets in a pelletizer.

The polymer gel accumulates on the interior surfaces of the system that contact the molten polymer (e.g., on the interior surfaces of the various components of the system 10). For example, the multiple conduits or transfer lines of system 10 are typically stainless steel tubes that will accumulate polymer gel on the interior surface, which must then be periodically removed from the process for maintenance. Maintaining may include undergoing moving the tube to an elevated temperature in order to burn off the polymer gel from the inner surface. After cleaning in this manner, the tubing may be returned to the system for servicing. However, such burnt tubes generally have a shorter gel time than new tubes. For example, a fired tube is typically expected to have a gel time of substantially less than 15 hours or less than 10 hours.

The new, unused tube may have a number 3 finished interior and, in some cases, an R of 0.90 to 1.50 μm_aNo. 4 finishing. During use, contact with molten polymer causes the inner surface to wear and become pitted. This abrasive texture, particularly pitting, was found to provide an area for flow stagnation and eventual gel formation. It has been recognized that it is desirable to restore the inner surface texture to the state of the just received tube and results in reduced gel formation.

The subject of the invention includes a method for reducing the formation of polymer gels during the manufacturing process of polyamides. Fig. 2 illustrates a method 100 of the present invention for reducing the formation of polymer gel during such a manufacturing process. At 102, the method 100 includes directing a molten polyamide mixture through a portion of a polyamide manufacturing system, wherein the molten polyamide mixture contacts an interior surface of the manufacturing system, and the molten polyamide has a gel time of greater than 15 hours in steam at one atmosphere of pressure while maintained at a temperature of 280 ℃ to 295 ℃. At 102, polymer gel may accumulate on the inner surfaces of the system.

At 104, the method 100 includes subjecting the inner surface of the system to a surface treatment to produce a treated inner surface, wherein the treated inner surface has an average surface roughness of no greater than 6.00 μ ι η, 1.00 μ ι η to 6.00 μ ι η, 0.90 μ ι η to 1.50 μ ι η, 0.60 μ ι η to 1.00 μ ι η, no greater than 0.5 μ ι η, no greater than 0.10 μ ι η, 0.10 μ ι η to 0.80 μ ι η, or 0.90 μ ι η to 1.50 μ ι η.

To surface treat the inner surface, the component may be removed from the system to undergo an Abrasive Flow Machining (AFM) process. AFM methods that may be used include those described in U.S. patent 3,521,412 to McCarty; 3,634,973 of McCarty; 3,819,343 to Rhoades; 4,936,057 to Rhoades; 5,070,652 to Rhoades et al; 5,367,833 to Rhoades et al; similar to those described by Klein's 5,788,558. A longer length of polymer transfer tube (which may include a tortuous path) may be treated with AFM to machine the inner surface of the tube to the same or better polishing finish as the new tube. The AFM method passes a viscous mixture containing abrasive through the lumen of a processing device. The inner surface is brought into frictional contact with the abrasive as the mixture passes through the apparatus. Multiple mixtures, each with finer abrasives, can be sequentially passed through the apparatus to further polish the interior surface.

The AFM method can include contacting the inner surface with a first mixture of a first silicon polymer (e.g., polyborosiloxane or siloxane putty SS-91) and a first abrasive. The first mixture may include a plasticizer (e.g., isopropyl stearate) or a lubricant (e.g., silicone grease). The first abrasive can include particles of silica, alumina, garnet, tungsten, carbide, silicon carbide (e.g., silicon carbide #120), diamond, or boron carbide. The first abrasive can comprise 2 to 15 parts by weight of the first mixture. The first abrasive can have an average particle size in a range of 0.005mm to 1.5mm, an average particle size in a range of less than 16.0 μm, or an average particle size of less than 36.0 μm.

The AFM method may include contacting the interior surface with a mixture of an additional polymer and an abrasive. For example, the AFM method can include contacting the inner surface with a second mixture of a second silicon polymer and a second abrasive after contacting the inner surface with the first mixture. The second silicon polymer may be the same as or different from the first silicon polymer. The second abrasive can be the same or different from the first abrasive. For example, the average particle size of the second abrasive can be smaller than the average particle size of the first abrasive in order to produce a more polished interior surface.

The surface treatment may further comprise heating the inner surface to burn off polymer gel residue. The heating may be applied before or after the AFM process.

At 106, the method 100 provides a complete surface treatment program and installs the treated interior surface in the polymer manufacturing system. The treated interior surface remains substantially free of gelation for greater than 15 hours or greater than 30 hours. Thus, the treated inner surface may not need to undergo additional surface treatment (e.g., a second surface treatment) for at least 15 hours or at least 30 hours after receiving the first surface treatment.

After receiving the first surface treatment, or after receiving additional supplemental surface treatments, the treated interior surface can have any suitable gel time, such as from about 15 hours to about 20 years, from about 30 hours to about 10 years, or about 15 hours or less, or about 20 hours, 36 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 1.5 weeks, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 8 months, 10 months, 1 year, 1.5 years, 2 years, 3 years, 5 years, 10 years, or about 20 years or more. Formation of the gel on the treated interior surface during use, after receiving the first surface treatment, or after receiving an additional supplemental surface treatment, can occur at any suitable rate such that an average thickness of about 1mm of gel is formed on the treated surface within about 15 hours to about 20 years, about 30 hours to about 10 years, or about 15 hours or less, or about 20 hours, 36 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 1.5 weeks, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 8 months, 10 months, 1 year, 1.5 years, 2 years, 3 years, 5 years, 10 years, or about 20 years or more. After receiving the first surface treatment, or after receiving an additional supplemental surface treatment, during use, the treated interior surface can remain substantially free of gel for any suitable period of time, such as from about 15 hours to about 20 years, from about 30 hours to about 10 years, or about 15 hours or less, or about 20 hours, 36 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 1.5 weeks, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 8 months, 10 months, 1 year, 1.5 years, 2 years, 3 years, 5 years, 10 years, or about 20 years or more.

At 106, the method 100 can include contacting the treated interior surface with a molten polyamide mixture. The molten polyamide may comprise nylon (e.g., nylon 6, 6). The molten polyamide mixture contacting the inner surface may be at a temperature in the range of 260 ℃ to 290 ℃.

The manufacturing process may be a continuous polyamide manufacturing process (e.g., a continuous nylon manufacturing process). The inner surface may comprise a portion of a continuous static mixer.

The molten polyamide mixture contacting the inner surface may include water in an amount of 0.1 wt% to 28 wt%, 0.1 wt% to 10 wt%, 0.1 wt% to 1 wt%, or 0.1 wt%.

The subject of the invention is also products comprising the polyamides produced by the process described above.

Examples

General system for the embodiments.In a continuous nylon 6, 6 manufacturing process, adipic acid and hexamethylenediamine are mixed in water in approximately equimolar ratios to form an aqueous mixture containing a nylon 6, 6 salt and having about 50% by weight water. The brine solution was delivered to the evaporator at about 105L/min. The evaporator heats the brine solution to about 125-. The evaporated salt mixture was transferred to the tubular reactor at about 75L/min. The reactor increased the temperature of the evaporated salt mixture to about 218 deg.C and 250 deg.C (235 deg.C), allowing the reactor to further remove water from the heated evaporated salt mixture such that the water concentration reached about 10 wt% and the salt was further polymerized. The reacted mixture was passed to a flash vessel at about 60L/min. The flasher heated the reacted mixture to about 270 ℃ and 290 ℃ (285 ℃) to further remove water from the reaction mixture, such that the water concentration reached about 0.5 wt%, and the reacted mixture was further polymerized. The flashed mixture, having a relative viscosity of about 13, was passed to a finisher at about 54L/min. In the flash evaporator and afterThe polymer mixture was maintained at a temperature of about 285 c in the transfer pipe between the polycondensers. The transfer pipe between the flash vessel and the finisher had a diameter of about 0.5 meters and a length of about 20 meters. The finisher subjects the polymerization mixture to a vacuum to further remove water such that the water concentration reaches about 0.1 weight percent and the relative viscosity reaches about 60 to achieve a suitable final range of degree of polymerization for the polyamide, after which the postcondensed polymerization mixture is passed to the extruder and pelletizer at about 54L/min.

In an embodiment, the gel time is determined by measuring the time the delivery tube is used in the system before exhibiting gel-forming properties when the gel-free nylon 6, 6 polymer contacts the inner surface of the delivery tube at 1atm and at about 285 ℃ with a flow of about 59L/min. The presence of gel was determined as follows: pressing the cooled sample of the polymer mixture emerging from the transfer tube to a powder of about 15 mesh; the powder (0.1g) was charged into a flask and 98-100% formic acid (20mL) was added thereto; the flask was allowed to stand for four hours, at which time the state of the polymer was observed. When the polymer did not contain any gel, it was completely dissolved in the solvent within four hours. On the other hand, when the polymer contains any visually detectable gel, the gel particles are merely wetted and swollen by the solvent, and a homogeneous formic acid solution is not obtained after four hours.

Abrasive flow machining processes are performed with one or more treatments using a mixture of siloxanes and abrasives.

General procedure for the determination of the gel fraction.Each gel fraction described in the examples was determined by taking the average of the gel fractions determined by the two methods. In the first method, while the reaction mixture is still hot, the liquid reaction mixture is drained from the system, the system is cooled, disassembled, and visually observed to estimate the volume of the gel therein. In the second method, while the reaction mixture is still hot, the liquid reaction mixture is drained from the system, the system is cooled, water is charged, and the water is drained. The volume of water drained from the system was subtracted from the volume of the system without gel to determine the volume of gel in the system. For determining one or more particular pieces or characteristics of equipmentGel fraction in the downstream of the other location, only the specific piece of equipment or the system downstream of the particular location is filled with water. In both methods, the density of the gel was estimated to be 0.9g/cm³。

Example 1a, comparative example. New pipe。

The transfer pipe between the flash evaporator and the finisher was a pipe with a number 4 finish and an R of 1 μm_aA new tube of the inner surface of (a). The delivery tube has a gel time of 5.4 months and remains substantially free of gel for about 5.4 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 10.8 months. The total gel accumulation downstream of the delivery tube was about 0.5 Kg/day before 5.4 months, which increased to about 0.6 Kg/day after 5.4 months.

Example 1b, comparative example. Untreated pitted tube.

The transfer pipe between the flash vessel and the finisher is a pipe used in the system for about 5 years. The inner surface of the tube is clean and has an R of about 0.5mm_a. The transfer tube had a gelation time of 5 hours and remained substantially free of gel for about 5 hours. A gel of about 1mm average thickness formed on the inner surface of the tube for about 1 month. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 1c, comparative example. Tubes with gel and burn treatments, 0.5mm roughness after treatment.

Subjecting the transfer tube between the flash evaporator and the finisher to a combustion treatment to remove the gel coat therefrom to give a coating having an R of about 0.5mm_aThe clean transfer tube of (1). The transfer tube had a gelation time of about 5 hours and remained substantially free of gel for about 5 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 1 month. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before reaching the gelation time, which increased to about 0.6 Kg/day after the gel time elapsed.

Example 1d comparative example. Tubes with gel and burn treatments, 100 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coat therefrom to give an R having about 100 μm_aThe clean transfer tube of (1). The transfer tube has a gelation time of about 10 hours and remains substantially free of gel for about 10 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 1 month. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 1e, comparative example. Tubes with gel and burn treatments, 10 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a burning treatment to remove the gel coat therefrom to give an R having about 10 μm_aThe clean transfer tube of (1). The transfer tube had a gelation time of about 13 hours and remained substantially free of gel for about 13 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 1 month. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 1f, comparative example. Tubes with gel and burn treatments, 6 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coat therefrom to give an R having about 6 μm_aThe clean transfer tube of (1). The transfer tube had a gelation time of about 14 hours and remained substantially free of gel for about 14 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 1 month. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 2. Tubes with gelation, combustion treatment and abrasive flow machining had a roughness of 5.9 μm after treatment.

Subjecting the transfer tube between the flash evaporator and the finisher to a combustion treatment to remove the gelcoat therefrom, before subjecting it toThe abrasive stream is machined to polish the inner surface of the tube so that it has an R of about 5.9 μm_a. The transfer tube had a gelation time of about 16 hours and remained substantially free of gel for about 16 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 1.5 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 3. Tubes with gelation, combustion treatment and abrasive flow machining had a roughness of 5.5 μm after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 5.5 μm_a. The transfer tube had a gelation time of about 72 hours and remained substantially free of gel for about 72 hours. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 2 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 4. Tubes with gelation, combustion treatment and abrasive flow machining, 4 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 4 μm_a. The delivery tube has a gelation time of about 2 weeks and remains substantially free of gel for about 2 weeks. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 3 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 5. Tubes with gelation, combustion treatment and abrasive flow machining had a roughness of 3 μm after treatment.

Transfer pipe between flash evaporator and post-condenserSubjected to a combustion treatment to remove the gel coat therein, and then subjected to an abrasive stream machining treatment to polish the inner surface of the tube so that it has an R of about 3 μm_a. The delivery tube has a gelation time of about 1 month and remains substantially free of gel for about 1 month. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 4 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 6. Tubes with gelation, combustion treatment and abrasive flow machining had a roughness of 2 μm after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 2 μm_a. The delivery tube has a gelation time of about 3 months and remains substantially free of gel for about 3 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 6 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before reaching the gel time, which increased to about 0.6 Kg/day after the passage of the gelation time.

Example 7. Tubes with gelation, combustion treatment and abrasive flow machining, 1 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 1 μm_a. The delivery tube has a gelation time of about 5.4 months and remains substantially free of gel for about 5.4 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 11 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 8. Tubes with gelation, combustion treatment and abrasive flow machining, 0.5 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 0.5 μm_a. The delivery tube has a gelation time of about 5.8 months and remains substantially free of gel for about 5.8 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 11.5 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 9. Tubes with gelation, combustion treatment and abrasive flow machining, 0.1 μm roughness after treatment.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 0.1 μm_a. The delivery tube has a gelation time of about 6 months and remains substantially free of gel for about 6 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 12 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 10. Tubes with gelation, combustion treatment and abrasive flow machining, 0.09 μm roughness after treatment And (4) degree.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 0.09 μm_a. The delivery tube has a gelation time of about 6 months and remains substantially free of gel for about 6 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 12 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 11. Tubes with gelation, combustion treatment and abrasive flow machining, 0.06 μm roughness after treatment And (4) degree.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 0.06 μm_a. The delivery tube has a gelation time of about 6 months and remains substantially free of gel for about 6 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 12 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

Example 12. Tubes with gelling, combustion treatment and abrasive flow machining, 0.02 μm roughness after treatment And (4) degree.

The transfer tube between the flash evaporator and the finisher was subjected to a combustion treatment to remove the gel coating therein, and then to an abrasive stream machining treatment to polish the inner surface of the tube so that it had an R of about 0.02 μm_a. The delivery tube has a gelation time of about 6 months and remains substantially free of gel for about 6 months. A gel of about 1mm average thickness was formed on the inner surface of the tube within about 12 months. The total gel accumulation downstream of the transfer tube was about 0.5 Kg/day before the gelation time was reached, which increased to about 0.6 Kg/day after the gelation time had elapsed.

The following are some statements regarding aspects of the present invention:

statement 1: the subject of the invention described comprises a method for reducing the formation of polymer gels during the manufacture of polyamides, said method comprising: producing a polyamide by directing a molten polyamide mixture through a portion of a polyamide production system, wherein the molten polyamide mixture contacts an interior surface of the production system and the molten polyamide mixture comprises a polymerized polyamide having a gel time of greater than 15 hours in steam at one atmosphere when maintained at a temperature of 280 ℃ to 295 ℃; subjecting the inner surface to a first surface treatment to produce a treated inner surface, wherein the treated inner surface has an average surface roughness of less than 6.00 μ ι η; and continuing the production of the polyamide by contacting the treated interior surface with the molten polyamide mixture.

Statement 2: the method of statement 1, wherein the treated interior surface has an average surface roughness of about 0.10 μ ι η to about 6.00 μ ι η.

Statement 3: the method of statement 1, wherein the treated interior surface has an average surface roughness of 0.90 μ ι η to 1.50 μ ι η.

Statement 4: the method of statement 1, wherein the treated interior surface has an average surface roughness of 0.60 μ ι η to 1.00 μ ι η.

Statement 5: the method of statement 1, wherein the treated inner surface has an average surface roughness of no greater than 0.5 μ ι η.

Statement 6: the method of statement 1, wherein the treated inner surface has an average surface roughness of no greater than 0.10 μ ι η.

Statement 7: the method of statement 1, wherein the treated interior surface has an average surface roughness of 0.10 μ ι η to 0.80 μ ι η.

Statement 8: the method of statement 1, wherein the treated interior surface has an average surface roughness of 0.90 μ ι η to 1.50 μ ι η.

Statement 9: the method of any of statements 1-8, wherein the surface treatment comprises an abrasive stream machining method.

Statement 10: the method of any of statements 1-9, wherein the surface treatment comprises contacting the inner surface with a first mixture of a first silicon polymer and a first abrasive.

Statement 11: the method of statement 10, wherein the silicon polymer is a polyborosiloxane.

Statement 12: the method of statement 10 or 11, wherein the first mixture comprises a plasticizer.

Statement 13: the method of statement 12, wherein the plasticizer is isopropyl stearate.

Statement 14: the method of any of statements 10-13, wherein the first mixture comprises a lubricant.

Statement 15: the method of statement 14, wherein the lubricant is a silicone grease.

Statement 16: the method of any of statements 10-15, wherein the first silicone polymer is silicone putty SS-91.

Statement 17: the method of any of statements 10-16, wherein the first abrasive comprises particles of silica, alumina, garnet, tungsten, carbide, silicon carbide, diamond, or boron carbide.

Statement 18: the method of statement 17, wherein the first abrasive comprises silicon carbide # 120.

Statement 19: the method of any of statements 10-18, wherein the first abrasive comprises 2 to 15 parts by weight of the first mixture.

Statement 20: the method of any of statements 10-19, wherein the first abrasive has an average particle size in the range of 0.005mm to 1.5 mm.

Statement 21: the method of statements 10-19, wherein the first abrasive has an average particle size range of less than 16.0 μ ι η.

Statement 22: the method of any of statements 1-21, wherein the surface treatment comprises contacting the inner surface with a second mixture of a second silicon polymer and a second abrasive after contacting with the first mixture.

Statement 23: the method of statement 22, wherein the second silicon polymer is the same as the first silicon polymer.

Statement 24: the method of statement 22 or 23, wherein the second abrasive has an average particle size that is less than the average particle size of the first abrasive.

Statement 25: the method of any of statements 10-24, wherein the abrasive flow machining method comprises using an abrasive having an average particle size of less than 36.0 μ ι η.

Statement 26: the method of any of statements 1-25, wherein the surface treatment comprises heating the inner surface to burn off polymer gel.

Statement 27: the method of statement 26, wherein the inner surface has an average surface roughness of 6.00 μ ι η to 0.5mm after heating to burn off polymer gel.

Statement 28: the method of any of statements 26 or 27, wherein the surface treatment comprises subjecting the inner surface to an abrasive flow machining method after heating the inner surface to burn off polymer gel.

Statement 29: the method of any of statements 1-28, wherein the molten polyamide comprises nylon.

Statement 30: the method of statement 29, wherein the nylon is nylon 6, 6.

Statement 31: the method of any of statements 1-30, wherein the molten polyamide mixture is at a temperature in a range of 260 ℃ to 290 ℃.

Statement 32: the method of any of statements 1-31, wherein the treated interior surface undergoes additional surface treatment no earlier than 15 hours after receiving the first surface treatment.

Statement 33: the method of statement 32, wherein the treated interior surface undergoes the additional surface treatment no earlier than 30 hours after receiving the first surface treatment.

Statement 34: the method of any of statements 1-33, wherein the manufacturing process is a continuous polyamide manufacturing process.

Statement 35: the method of statement 34, wherein the continuous polyamide manufacturing process is a continuous nylon manufacturing process.

Statement 36: the method of any of statements 1-35, wherein the inner surface is part of a continuous static mixer.

Statement 37: the method of any of statements 1-36, wherein the inner surface is part of a static mixer.

Statement 38: the method of any of statements 1-37, wherein the molten polyamide mixture comprises water in an amount of 0.1 to 28 wt.%.

Statement 39: the method of statement 38, wherein the molten polyamide mixture comprises water in an amount of 0.1 wt.% to 10 wt.%.

Statement 40: the method of statement 38, wherein the molten polyamide mixture comprises water in an amount of 0.1 wt.% to 1 wt.%.

Statement 41: the method of statement 40, wherein the molten polyamide mixture comprises water in an amount of 0.1 weight percent.

Statement 42: the method of any of statements 1-41, wherein the inner surface prior to the first surface treatment has an average surface roughness of greater than 1.50 μm.

Statement 43: a product comprising a polyamide produced by the method according to any one of statements 1-42.

The above description is intended to be exemplary, and not restrictive. Other embodiments may be used, as would be apparent to one of skill in the art upon reading the above description. For example, elements of one described embodiment may be used in combination with elements from other described embodiments. Also, in the above detailed description, various features may be combined together to simplify the present disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may be found in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. As used herein, the terms "including" and "in which" are used as equivalents of the terms "comprising" or "in which".

The terms "a" or "an" are used herein to include one or more than one, regardless of any other instances or uses of "at least one" or "one or more. Herein, unless otherwise indicated, the use of the term "or" means a non-exclusive or such that "A, B or C" includes "a only", "B only", "C only", "a and B", "B and C", "a and C", and "A, B and C". In the accompanying aspects or claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. It should be understood that any numerical range explicitly disclosed herein should include any subset of the explicitly disclosed range, as if such subset range were also explicitly disclosed; for example, a range of 1-100 should also include a range of 1-80, 2-76, or any other numerical range falling between 1 and 100. In another example, disclosure of a range of "below 1,000" should also include any range less than 1,000, such as 50-100, 25-29, or 200-1,000.

The abstract is provided to comply with 37c.f.r. § 1.72(b) to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. A method of reducing the formation of polymer gel during the manufacture of a polyamide, the method comprising:

producing a polyamide by directing a molten polyamide mixture through a transfer tube between a flash vessel and a finishing vessel of a polyamide production system, wherein the molten polyamide mixture contacts an interior surface of the production system and the molten polyamide mixture comprises a polymerized polyamide having a gel time greater than 15 hours in steam at one atmosphere when maintained at a temperature of 280 ℃ to 295 ℃;

subjecting the inner surface to a first surface treatment to produce a treated inner surface, wherein the treated inner surface has an average surface roughness of less than 6.00 μ ι η; and

continuing the production of the polyamide by contacting the treated inner surface with the molten polyamide mixture.

2. The method of claim 1, wherein the treated inner surface has an average surface roughness between 0.1 μ ι η and 6.00 μ ι η.

3. The method of claim 1, wherein the first surface treatment comprises an abrasive stream machining process.

4. The method of claim 3, wherein the first surface treatment comprises contacting the inner surface with a first mixture of a first silicon polymer and a first abrasive.

5. The method of claim 4, wherein the first mixture comprises a plasticizer.

6. The method of claim 4, wherein the first mixture comprises a lubricant.

7. The method of claim 4, wherein the first abrasive comprises particles of silica, alumina, garnet, tungsten, carbide, silicon carbide, diamond, or boron carbide.

8. The method of claim 7, wherein the first abrasive comprises silicon carbide # 120.

9. The method of claim 4, wherein the first abrasive has an average particle size range of 0.005mm to 1.5 mm.

10. The method of claim 4, wherein the first surface treatment comprises contacting the inner surface with a second mixture of a second silicon polymer and a second abrasive after contacting it with the first mixture, and wherein the second abrasive has an average particle size that is less than an average particle size of the first abrasive.

11. The method of claim 1, wherein the first surface treatment comprises subjecting the inner surface to an abrasive flow machining process after heating the inner surface to burn off polymer gel.

12. The method of claim 1, wherein the inner surface has an average surface roughness of between 6.00 μm and 0.5mm after heating to burn off the polymer gel.

13. The method of claim 1, wherein the molten polyamide comprises nylon.

14. The process of claim 1, wherein the molten polyamide mixture is at a temperature in a range between 260 ℃ and 290 ℃.

15. The method of claim 1, wherein the treated interior surface does not undergo any further surface treatment for a period of at least 15 hours after receiving the first surface treatment.

16. The method of claim 1, wherein the polyamide manufacturing system is a continuous nylon manufacturing system.

17. The method of claim 1, wherein the inner surface is part of a continuous static mixer.

18. The method of claim 1, wherein the molten polyamide mixture comprises water in an amount between 0.1 wt.% and 28 wt.%.

19. The method of claim 1, wherein the inner surface has an average surface roughness of greater than 1.50 μ ι η prior to the first surface treatment.

20. A product comprising a polyamide prepared by the process of claim 1.