Method for producing polyetheretherketone polymer pellets

Abstract

The present invention relates to a process for producing pellets of a polyetheretherketone polymer (PEEK polymer), the process comprising: a) melt extruding a thermoplastic composition using an extruder to form an extrudate wherein the thermoplastic composition comprises a PEEK polymer; b) cooling the extrudate on a moving conveyor belt, where the cooling comprises: b1) subjecting the extrudate to a first air cooling stage, b2) after b1) subjecting the extrudate to a water cooling stage, b3) after b2) subjecting the extrudate to a second air cooling stage, wherein the water cooling stage comprises conveying the extrudate through a first jet stream provided by a first water outlet located about 30 cm to about 70 cm from the outlet of the extruder and a second jet stream provided by a second water outlet, where the first water outlet and the second water outlet are separated about 20 cm to about 90 cm in the direction of travel of the conveyor belt, and wherein the exposed surface of the extrudate is in contact with the water jetted from the first jet stream and the second jet stream for a contact time in the range of about 2 seconds to about 6 seconds; and c) after b) comminuting the extrudate to form a plurality of pellets wherein the temperature of the extrudate during the comminuting step is in the range of about 5 DEG C to about 35 DEG C below the glass transition temperature of the thermoplastic composition.

Description

Technical Field

[0001] The present invention relates to a method for producing polyetheretherketone polymer (PEEK polymer) pellets, in particular wherein the PEEK polymer is melt extruded and subsequently cooled using a combination of air and water cooling. Background Art

[0002] For many years, the process of producing thermoplastic compositions has included three major steps, namely: extrusion, cooling and pellet forming. The use and production of polymer pellets is ubiquitous because pellets represent a convenient material form that can be used to handle and distribute polymer products. In addition, pellets are a convenient starting material for many downstream uses, such as injection molding.

[0003] Advanced thermoplastic materials have many high-performance uses, for example, in the automotive and aerospace industries, where example products include mechanical gears. Further uses are found in the medical industry, where example products include medical implants and devices. Therefore, one of the main factors in designing a pellet production process is to provide high-quality pellets that are free or substantially free of surface defects, have a consistent and repeatable crystallinity, and where different batches have consistent properties. In addition, given that thermoplastics used in high-performance industries tend to be expensive, it is desirable that pellet production be substantially error-free, which can be achieved in part by ensuring that pellet production can run continuously (e.g., 3 to 6 hours or more) without pausing production or performing maintenance.

[0004] By ensuring that the cooling step is performed in an efficient and repeatable manner, consistency and a high level of productivity in the pellet production process can be achieved. In addition, it is desirable that the cooling process produce pellets having a consistent and narrow size distribution and being completely free of significant surface defects and being substantially or completely free of small surface defects. Therefore, precise and repeatable control of extrudate cooling is a desirable quality.

[0005] It is an object of the present invention to seek to alleviate the above identified problems. Summary of the invention

[0006] In a first aspect, there is provided a method for producing polyetheretherketone polymer (PEEK polymer) pellets, the method comprising:

[0007] a) melt extruding a thermoplastic composition using an extruder to form an extrudate, wherein the thermoplastic composition comprises a PEEK polymer;

[0008] b) cooling the extrudate on a moving conveyor, wherein the cooling comprises:

[0009] b1) subjecting the extrudate to a first air cooling stage,

[0010] b2) after b1), subjecting the extrudate to a water cooling phase,

[0011] b3) after b2), subjecting the extrudate to a second air cooling stage,

[0012] wherein the water cooling stage comprises conveying the extrudate through a first water jet provided by a first water outlet and a second water jet provided by a second water outlet, wherein the first water outlet is located about 30 cm to about 70 cm from an exit of the extruder, wherein the first water outlet and the second water outlet are separated by about 20 cm to about 90 cm in a direction of travel of the conveyor belt, and wherein the contact time of the exposed surface of the extrudate in contact with the water ejected from the first water jet and the second water jet is in the range of about 2 to about 6 seconds; and

[0013] c) after b), comminuting the extrudate to form a plurality of pellets, wherein the temperature of the extrudate during the comminuting step is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

[0014] In a second aspect, there is provided a pellet produced according to the method of the first aspect.

[0015] In a third aspect, a plurality of pellets are provided comprising a thermoplastic composition, wherein the thermoplastic composition comprises a polyetheretherketone polymer (PEEK polymer) and about 5 wt % to about 50 wt % carbon black,

[0016] wherein the pellets are substantially cylindrical,

[0017] wherein a D99 length of a pellet in the plurality of pellets is less than about 2 mm,

[0018] Wherein a D99 diameter of a pellet in the plurality of pellets is in a range from about 0.6 mm to about 2 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 An exemplary schematic diagram of a pellet production system for producing pellets according to aspects of the present disclosure is shown. DETAILED DESCRIPTION

[0020] In a first aspect, there is provided a method for producing polyetheretherketone polymer (PEEK polymer) pellets, the method comprising:

[0021] a) melt extruding a thermoplastic composition using an extruder to form an extrudate, wherein the thermoplastic composition comprises a PEEK polymer;

[0022] b) cooling the extrudate on a moving conveyor, wherein the cooling comprises:

[0023] b1) subjecting the extrudate to a first air cooling stage,

[0024] b2) after b1), subjecting the extrudate to a water cooling phase,

[0025] b3) after b2), subjecting the extrudate to a second air cooling stage,

[0026] wherein the water cooling stage comprises conveying the extrudate through a first water jet provided by a first water outlet and a second water jet provided by a second water outlet, wherein the first water outlet is located about 30 cm to about 70 cm from an exit of the extruder, wherein the first water outlet and the second water outlet are separated by about 20 cm to about 90 cm in a direction of travel of the conveyor belt, and wherein the contact time of the exposed surface of the extrudate in contact with the water ejected from the first water jet and the second water jet is in the range of about 2 seconds to about 6 seconds; and

[0027] c) after b), comminuting the extrudate to form a plurality of pellets, wherein the temperature of the extrudate during the comminuting step is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

[0028] The cooling conditions of the extrudate before being processed into pellets can have a significant impact on production efficiency and the quality of the resulting pellets. Embodiments of the method create a stable and reliable process in which the resulting pellets are completely or substantially free of defects. The method provides a more time-saving cooling than air cooling alone because contact with water spraying results in an increased cooling rate compared to air alone. This makes the conveyor belt shorter than the air cooling method. In addition, cooling using water spraying gives better control compared to using a water bath that quickly and indiscriminately cools the extrudate. Compared to a water bath, using sprayed water has other advantages: that is, designing and operating an unsubmerged conveyor belt is more logically straightforward, and it is easier to manually handle errors in production, such as conveyor belt breakage. The water bath is also prone to overcooling the extrudate, which can cause brittle extrudates to break on the conveyor belt and reduce production efficiency. In addition, hard and / or brittle extrudates cannot be consistently granulated and impose greater wear on the granulator / strip cutter blades.

[0029] Thus, the use of water sprays imparts advantageous control over the cooling of the extrudate, which helps prevent conveyor belt breakage (which would block the pelletizer and cause processing delays). The inventors have determined that the use of two water sprays provides the extrudate with a degree of structural integrity without imposing a drastic cooling rate that could render the extrudate brittle and susceptible to fracture.

[0030] It is advantageous to position the first water outlet at about 30 cm to about 70 cm from the extruder outlet. This gap defines the distance over which the first air cooling stage is performed and provides gentler cooling, followed by faster cooling provided by the first water jet. Since the extrudate is still hot, the first water jet provides a high cooling rate achieved with relatively little water. In addition, the water jet is not too close to the extruder outlet to prevent the extrudate from being impacted by the water and becoming too brittle. The position of 30 cm to 70 cm provides a good balance between cooling rate (increasing production efficiency and reducing water consumption) and extrudate stability (because the extrudate does not cool too quickly and become brittle).

[0031] Furthermore, because the extrudate comprises PEEK polymer, water cooling can be performed later than is typically performed in known systems (i.e., sometimes immediately to prevent thermal degradation) because PEEK has high thermal stability even at temperatures significantly above the glass transition temperature.

[0032] It should be understood that the surface of the extrudate in contact with water is preferably the entire upper surface of the extrudate, as well as the side and partial bottom surface of the extrudate. In other words, the exposed surface preferably represents all surface areas of the extrudate except the part in direct contact with the conveyor belt. The conveyor belt is preferably perforated, preferably a solid grid or mesh. This provides sufficient space for the water (under gravity) to be sprayed. Therefore, contact with water preferably represents contact between the water sprayed by the water outlet, because substantially no water is gathered or gathered on the surface of the conveyor belt. It should also be understood that, since the conveyor belt has a large amount of air gaps on its surface, during the air cooling stage, air can reach the lower side of the extrudate through the holes in the conveyor belt, thereby providing uniform and consistent air cooling.

[0033] The combination of water and air provides further cooling efficiency because three independent cooling mechanisms are established: i) rapid cooling by contact with water, ii) cooling provided by water evaporation, and iii) cooling by contact with air alone. Surprisingly, the contact time between the exposed surface of the extrudate and the water (including mechanisms i) and ii)) is between about 2 seconds and about 6 seconds, providing a favorable cooling rate that prevents the extrudate from bending and breaking during conveyance. In addition, the combination of cooling mechanisms provides a precisely controllable cooling rate that allows the temperature of the extrudate to be consistently controlled (and for a long period of time, for example, within about 3 hours to about 6 hours) below the glass transition temperature of the thermoplastic composition.

[0034] Preferably, the contact time of the exposed surface of the extrudate with the water sprayed from the first and second water jets is in the range of about 3 seconds to about 6 seconds, preferably in the range of about 3 seconds to about 5 seconds. This contact time allows for a particularly preferred cooling rate.

[0035] Preferably, the water cooling stage comprises only two water outlets, namely a first water outlet and a second water outlet. Preferably, the water cooling stage does not comprise a third water outlet. It is particularly preferred to have only two water outlets, as this is sufficient to achieve the required cooling and reduce water usage.

[0036] Preferably, the glass transition temperature of the thermoplastic composition is in the range of about 138° C. to about 165° C. More preferably, the glass transition temperature of the thermoplastic composition is in the range of about 140° C. to about 150° C., and still more preferably, the glass transition temperature of the thermoplastic composition is in the range of about 141° C. to about 145° C.

[0037] Preferably, the temperature of the extrudate immediately after extrusion is about 80°C to about 120°C higher than the glass transition temperature of the thermoplastic composition. It should be understood that "immediately" includes the moment the extrudate leaves the extruder, such as the moment it leaves the die, preferably less than one tenth of a second before leaving the extruder. This is an appropriate temperature for the extrudate to allow substantially uniform extrusion.

[0038] Preferably, the temperature of the extrudate before water cooling immediately before step b2) is in the range of about 40°C to 80°C above the glass transition temperature of the thermoplastic composition. It should be understood that "immediately" includes the moment before the water spray contacts the extrudate, preferably less than one tenth of a second before the water contacts the exposed surface of the extrudate. Advantageously, after extrusion, the initial cooling in the air helps to prevent the extreme cooling level from the first jet of water. Therefore, the initial air cooling allows a stable structure to be formed throughout the extrudate. Therefore, when the water contacts the extrudate, the water flow can form an amorphous surface layer on the surface of the extrudate, which provides further structural integrity to the extrudate and prevents rupture during transportation. If the temperature of the extrudate is too high, an amorphous surface layer may be formed prematurely, which can produce internal stresses in the extrudate structure, resulting in warping or fracture. In addition, higher temperature extrudates are prone to deformation, so water cooling at this early stage can harden the extrudate surface and make it more stable.

[0039] This cooling method is contrary to typical procedures, which tend to rapidly cool the hot extrudate as early as possible in an attempt to inhibit thermal degradation. However, PEEK polymer is thermally stable and can therefore tolerate higher temperatures for longer periods of time after extrusion. It is advantageous to allow gentler air cooling of the PEEK as a first cooling stage, which produces a stable extrudate with a more uniform crystal structure prior to the more rapid water cooling stage.

[0040] Preferably, the PEEK polymer has repeating units of formula I:

[0041] -O-Ph-O-Ph-CO-Ph-

[0042] wherein Ph represents a phenylene moiety. In this embodiment, all phenylene groups are 1,3- and / or 1,4-substituted to adjacent ether groups and / or carbonyl groups.

[0043] Preferably, the first water outlet is located at about 50 cm to about 65 cm from the extruder outlet, preferably about 55 cm to about 65 cm. It should be understood that the outlet of the extruder will be the point where the extrudate leaves the extruder. Preferably, the outlet is a die outlet. Providing water cooling no more than about 65 cm from the extruder outlet is beneficial because it helps to provide the most effective cooling effect; that is, because the closer to the extruder outlet, the hotter the extrudate, which means that water has a better cooling effect. In addition, using water flow to balance the cooling of the extrudate as quickly as possible without overcooling (which can cause internal stress and / or brittleness and / or rupture of the extrudate), it is advantageous to allow the pellets to be evenly cut and minimize defects.

[0044] Preferably, the post-water cooling temperature of the extrudate immediately after the first water jet is about 40°C to about 70°C lower than the pre-water cooling temperature of the extrudate immediately before the first water jet. It should be understood that the "post-water cooling temperature" refers to the surface temperature of the extrudate immediately after the cooling imparted by the water stream of the first outlet. Advantageously, the increase in cooling rate compared to using only air allows the conveying step to be shorter than the cooling time required when using only air cooling. In addition, the water stream allows for more precise control of cooling, especially compared to the amount of control that can be obtained using a water bath / immersion cooling method. In other words, the post-water cooling temperature can be precisely adjusted using the first water stream to provide a temperature reduction that is not so large as to cause the extrudate to rupture.

[0045] Preferably, the post-water-cooling temperature of the extrudate immediately after the second water jet is about 20°C to about 40°C lower than the post-water-cooling temperature of the extrudate after the first water jet. Advantageously, the increase in cooling rate compared to using air alone allows the conveying step to be shorter than the cooling time required when using air cooling alone. In addition, the water stream allows for more precise control of cooling, particularly compared to the amount of control that can be obtained using a water bath / immersion cooling method. In other words, the post-water-cooling temperature can be precisely adjusted using the first and second water streams to provide a temperature reduction that is not so great as to cause the extrudate to rupture.

[0046] Furthermore, the inventors have determined that cooling the extrudate to a temperature within this temperature range also reduces undesirable movement of the extrudate on the conveyor belt surface and further reduces the chance of the extrudate strands fusing together.

[0047] Preferably, the first water jet causes a greater reduction in the extrudate temperature than the second water jet. This is because the temperature of the extrudate is higher when the first water jet is used than when the second water jet is used.

[0048] Preferably, the first water outlet and the second water outlet are separated by about 30 cm to about 80 cm in the direction of travel of the conveyor belt. More preferably, the separation is about 30 cm to about 60 cm. Still more preferably, the separation distance between the first and second water outlets is about 35 cm to about 50 cm. This distance also generally applies to the separation between i) the point at which the first water stream from the first outlet contacts the extrudate surface and ii) the point at which the second water stream from the second outlet contacts the extrudate surface.

[0049] The inventors have determined that intervals within this range allow time for the extrudate to dry after being sprayed by the first cooling outlet (where the drying mechanism between water sprays is primarily through evaporation and / or boiling of water contacting the extrudate because the surface of the extrudate is above the boiling point of water). In addition, providing water cooling close to the extruder outlet while leaving sufficient drying time between the first and second water streams provides more efficient cooling and advantageously produces pellets of good size and quality, e.g., pellets of consistent size and shape and without surface defects.

[0050] Preferably, the water cooling stage comprises a first intermediate air cooling stage between the first water jet and the second water jet. This allows for better control of the cooling and enhanced cooling by evaporation.

[0051] Preferably, the extrudate has the following temperature:

[0052] T1: The temperature of the extrudate immediately after extrusion is about 80°C to about 120°C higher than the glass transition temperature of the thermoplastic composition;

[0053] T2: the temperature of the extrudate before water cooling immediately before step b2) is in the range of about 40°C to 80°C above the glass transition temperature of the thermoplastic composition;

[0054] T3: the temperature of the extrudate after water cooling immediately after the first water jet is about 40° C. to about 70° C. lower than the temperature of the extrudate before water cooling immediately before the first water jet;

[0055] T4: the water-cooled temperature of the extrudate immediately after the second water jet is about 20° C. to about 40° C. lower than the water-cooled temperature of the extrudate after the first water jet;

[0056] T5: Optionally, when the third water jet outlet is used, the water-cooled temperature of the extrudate immediately after the third water jet is about 10°C to about 30°C lower than the water-cooled temperature of the extrudate after the second water jet; and

[0057] T6: The temperature of the extrudate during the pulverization in step c) is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

[0058] An advantage of the present invention is that cooling is performed in a controlled manner to obtain an extrudate above the glass transition temperature of the thermoplastic composition, providing cooling and producing an extrudate that can be reliably pelletized. The disclosed method advantageously reduces production losses due to off-specification pellets, increases production reliability and produces a preferred product.

[0059] It will be appreciated that preferably there are only first and second water sprays and preferably the extrudate has a temperature of:

[0060] T1: The temperature of the extrudate immediately after extrusion is about 80°C to about 120°C higher than the glass transition temperature of the thermoplastic composition;

[0061] T2: the temperature of the extrudate before water cooling immediately before step b2) is in the range of about 40°C to 80°C above the glass transition temperature of the thermoplastic composition;

[0062] T3: the temperature of the extrudate after water cooling immediately after the first water jet is about 40° C. to about 70° C. lower than the temperature of the extrudate before water cooling immediately before the first water jet;

[0063] T4: the water-cooled temperature of the extrudate immediately after the second water jet is about 20°C to about 40°C lower than the water-cooled temperature of the extrudate after the first water jet; and

[0064] T6: The temperature of the extrudate during the pulverization in step c) is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

[0065] Preferably, the extrudate is substantially dry during the first intermediate air cooling step. The first intermediate air cooling stage preferably comprises conveying the dried extrudate by undisturbed, non-turbulent air. "Dry" will be understood to mean that there is no water mist or water droplets on the surface of the extrudate, however the composition of the extrudate itself may contain trace amounts (less than 1% by weight) of moisture.

[0066] Preferably, the method does not include the use of air blowing. An advantage of the present invention is that it is not necessary to use air blowing as part of the cooling step. Air blowing would interfere with any water spraying and is preferably not used.

[0067] Preferably, the water cooling stage further comprises additional water outlets. Preferably, the additional water outlets are located between the first and second water outlets. Preferably, the water cooling stage further comprises an intermediate air cooling stage between each water outlet. Although it is an advantage of the present invention that only first and second water outlets are required, it will be appreciated that additional water outlets may be used to further control cooling. Any additional water outlets preferably include any of the features of the first and / or second water outlets.

[0068] Preferably, the temperature of the water sprayed from the first water outlet and / or the second water outlet is in the range of about 10° C. to about 40° C., preferably in the range of about 15° C. to about 30° C., more preferably about 18° C. to about 25° C. Such a temperature allows effective cooling of the extrudate.

[0069] Preferably, the process is carried out at a temperature of about 10° C. to about 50° C., preferably about 15° C. to about 30° C., more preferably about 18° C. to about 25° C. Such temperatures allow for efficient cooling of the extrudate.

[0070] Preferably, the total length of the conveyor belt is in the range of about 10m to about 14m, more preferably in the range of about 11m to about 13m. With the water cooling stage, the overall space occupied by the conveyor belt can be reduced, thereby taking up less space. In addition, the shorter conveyor belt reduces the possibility of the extrudate breaking on the way to the granulator, which may cause production delays and stoppages (for example, because the broken extrudate strands cannot be effectively cut by the granulator and / or block the granulator, which means that production may have to be stopped manually and the damage and / or granulator may have to be removed and cleaned). Due to the reduced possibility of breakage caused by the water cooling stage, the productivity of the pellet production process can be improved.

[0071] Preferably, the exposed surface of the extrudate is in contact with the first water jet for a contact time in the range of about 1 second to about 4 seconds, preferably about 1.5 seconds to about 3 seconds; and / or preferably, the exposed surface of the extrudate is in contact with the second water jet for a contact time in the range of about 1 second to about 4 seconds, preferably about 1.5 seconds to about 3 seconds. It should be understood that the contact times of the first and second water jets may be different.

[0072] Preferably, the first water outlet is positioned at an inclined angle so that the first jet of water immediately after leaving the first water outlet forms an angle in the range of about 40 degrees to about 80 degrees relative to the direction of travel of the conveyor belt, and the angle is preferably in the range of about 50 degrees to about 70 degrees relative to the direction of travel of the conveyor belt, and more preferably, the angle is about 55 degrees to about 65 degrees.

[0073] Preferably, the second water outlet is positioned at an inclined angle so that the second jet of water immediately after leaving the second water outlet forms an angle in the range of about 40 degrees to about 80 degrees relative to the direction of travel of the conveyor belt, and the angle is preferably in the range of about 50 degrees to about 70 degrees relative to the direction of travel of the conveyor belt, and more preferably, the angle is about 55 degrees to about 65 degrees.

[0074] The angle of the water stream is defined as the acute angle between i) the direction of the water jet from the outlet and ii) the plane of the conveyor surface (or in other words, the direction of travel of the conveyor). The direction of the inclined water jet is the same as the direction of travel of the conveyor.

[0075] The strands of extrudate cannot be easily rotated nor sprayed from below the conveyor. Advantageously, however, by spraying the extrudate strands at an angle (measured between the plane of the conveyor surface and the direction of the water stream), water from the sprayed water stream can be transported along at least some of the exposed surfaces of the extrudate. Thus, the water from the sprayed water stream contacts a larger surface area of ​​the extrudate (than would be achieved if the water stream intersected the extrudate at a perpendicular angle) and thus achieves more uniform water coverage. Furthermore, the oblique spraying of the water stream results in an increased contact time between the water and the extrudate: this not only provides a greater cooling effect, but also represents a more efficient use of water.

[0076] Preferably, the second air cooling stage comprises passing the extrudate through air in the absence of water from the first and second jets of water, wherein the extrudate is substantially dry for the duration of the second air cooling step. Advantageously, the cooling method avoids the need to cool the extrudate using actively blown air or gas after the water cooling stage. Thus, immediately after the water cooling stage, water evaporates from the surface of the extrudate (due to the high temperature of the extrudate still being above the boiling point of water). Therefore, the second air cooling stage preferably comprises passing the dry extrudate through undisturbed, non-turbulent air. The meaning of "dry" will be understood to mean that there is no water mist or water droplets on the surface of the extrudate, although the composition of the extrudate itself may contain trace amounts (less than 1% by weight) of moisture.

[0077] Preferably, the temperature of the extrudate during the comminuting step is in the range of about 10°C to about 33°C below the glass transition temperature of the thermoplastic composition.

[0078] Therefore, preferably, in terms of absolute value, the temperature of the thermoplastic composition during pulverization is in the range of about 105° C. to about 135° C. More preferably, the temperature of the thermoplastic composition during pulverization is in the range of about 110° C. to about 130° C. Further preferably, the temperature of the thermoplastic composition during pulverization is in the range of about 115° C. to about 130° C., and more preferably, the temperature of the thermoplastic composition during pulverization is in the range of about 122° C. to about 128° C.

[0079] Advantageously, the use of two streams of water and a gentler air cooling stage on both sides allows the temperature of the extrudate to be precisely controlled when it reaches the pelletizer. Therefore, the temperature during the comminution process is within the desired range. It is beneficial to ensure that the extrudate temperature is not less than 33°C, the glass transition temperature of the thermoplastic composition, because this ensures the life of the pelletizer blades, which wear faster when pelletizing thermoplastic compositions with temperatures below this temperature. Extrudates far below the glass transition temperature are tougher and therefore dull the pelletizer blades and reduce overall production efficiency. In addition, if the temperature of the extrudate is below this range, the proportion of defects in the pellets will increase because the extrudate will be more brittle and more likely to break than be cut. It is also advantageous to ensure that the extrudate temperature is not less than 10°C below the glass transition temperature, because this enables the pelletizer to effectively cut the extrudate and produce pellets of consistently correct size and shape. Extrudate temperatures above this range can be detrimental because the hot extrudate may be too soft to be continuously cut by the pelletizer.

[0080] Therefore, it is best to keep the extrudate below 135°C, otherwise the extrudate strands may be too soft to cut, resulting in "overlong" pellets that do not meet specifications and other surface defects in the pellets.

[0081] Preferably, for each pellet in the plurality of pellets, the maximum pellet dimension is less than about 3 mm and the minimum pellet dimension is greater than about 0.5 mm. In other words, the pellet width is greater than about 0.5 mm and the pellet length is less than about 3 mm, preferably, wherein the pellet is substantially cylindrical with the major axis of the pellet aligned with the major axis of the cylinder. When the extrudate has a temperature in the preferred range of about 105°C to about 135°C, the pellets produced have a highly consistent size and dimension. Pellet quality and pellet size / dimension consistency are further improved within a preferred sub-range, for example, when the temperature of the PEEK during comminution is about 115°C to about 130°C.

[0082] Preferably, the D99 length of the pellets in the plurality of pellets is less than about 2 mm. Preferably, the D99 length of the pellets is between about 1 mm and about 2 mm. For processing and injection molding purposes, it is beneficial for a high proportion of the pellets to have a consistent size. Advantageously, embodiments of the first aspect of the present disclosure are able to consistently produce pellets within this size range, which is beneficial to production efficiency, for example, because the pellets rarely or never need to be screened to remove pellets longer than 2 mm.

[0083] Preferably, the cooling rate of the extrudate in the first water stream is greater than the cooling rate of the extrudate in the second water stream. This provides for more effective and efficient cooling of the extrudate, i.e. because a greater cooling effect can be produced using the same volume of water. Thus, it is advantageous that the cooling rate provided by the water from the second water stream is not as great as the cooling rate provided by the first water stream, for example, because this enables fine control of the temperature reduction so that a desired temperature range of about 105°C to about 135°C can be consistently achieved in the comminution step.

[0084] Preferably, the thermoplastic composition further comprises from about 5% to about 50% by weight of a filler. Preferably, the filler is selected from carbon black, talc, calcium carbonate, glass fiber, carbon fiber, or a combination of two or more thereof, preferably wherein the filler comprises carbon black. It should be understood that PEEK extrudates containing fillers (i.e., less than 50% by weight) cannot be effectively cooled by air alone. Therefore, the inventors have determined that more effective cooling of extrudates with low levels of fillers or no fillers at all can be achieved using two jets of water.

[0085] According to a second aspect, there is provided a pellet produced as described herein. These pellets advantageously have a highly consistent size, shape and dimension and are substantially or completely free of surface defects caused by poor pelletization / comminution.

[0086] According to a third aspect, a plurality of pellets are provided comprising a thermoplastic composition, wherein the thermoplastic composition comprises a polyetheretherketone polymer (PEEK polymer) and about 5 wt % to about 50 wt % carbon black,

[0087] wherein the pellets are substantially cylindrical,

[0088] wherein a D99 length of a pellet in the plurality of pellets is less than about 2 mm,

[0089] Wherein a D99 diameter of a pellet in the plurality of pellets is in a range from about 0.6 mm to about 2 mm.

[0090] Preferably, the plurality of pellets further comprises any of the features of the pellets disclosed herein.

[0091] Example

[0092] An experiment was conducted to compare the characteristics of pellets produced using different water cooling conditions using a pellet production system including an extruder, a conveyor belt, three water outlets for providing three corresponding water flows, and a pelletizer for pulverizing the extrudate after cooling.

[0093] Figure 1 A schematic diagram of a pellet production system 100 is shown, the system 100 being configured to perform the method according to the first aspect of the present disclosure and to produce pellets according to the second and third aspects of the present disclosure.

[0094] The system 100 includes an extruder 102 that produces an extrudate 104 as shown, a moving conveyor belt 106 for conveying the extrudate 104, three water outlets 108a, 108b, 108c, and a pelletizer 110. The extrudate moves in a direction from the extruder 102 to the pelletizer 110. Preferably, the speed at which the extrudate exits the extruder matches or substantially matches the speed at which the conveyor belt conveys the extrudate. Figure 1 Six temperature zones are also indicated, indicated between the vertical dashed lines as T1 to T6, in which the temperature of the extrudate can be measured. Temperatures T1 to T5 have been measured by a portable infrared thermometer. Temperature T6 is measured using a portable infrared thermometer or with a thermometer integrated into the pelletizer.

[0095] The distance D1 to D4 represents the following:

[0096] - D1: horizontal distance between the extruder outlet and the position of the first water outlet 108a;

[0097] -D2: horizontal distance between the first and second water outlets;

[0098] -D3: horizontal distance between the second and third water outlets;

[0099] - D4: the horizontal distance between the third water outlet and the granulator inlet (or alternatively, the distance between the third water outlet and the end point of the upper surface of the conveyor belt).

[0100] - It should be understood that only two of the water outlets 108a, 108b and 108c are required in the present invention and the distances between the die outlet, the water outlet and the pelletizer can be measured accordingly.

[0101] D 传送带 represents the horizontal length of the conveyor belt, which is approximately equal to the sum of distances D1 to D4.

[0102] In some embodiments, D1 is from about 20 cm to about 90 cm, or from about 30 cm to about 80 cm, or from about 30 cm to about 60 cm, or from about 35 cm to about 50 cm. In the results illustrated in Table 1 below, D1 is 50 cm.

[0103] D2 and D3 are preferably substantially equal, but may be different. D2 and D3 may vary between 20 cm, 40 cm or 60 cm. In the results illustrated in Table 1 below, D2 and D3 are both equal to about 40 cm.

[0104] D4 is preferably from about 9 m to about 13 m, preferably from about 10 m to about 12 m.

[0105] D 传送带It is preferably about 10 m to about 14 m, more preferably about 11 m to 13 m. In the results illustrated in Table 1 below, D conveyor belt is 12.5 m.

[0106] The term "horizontal" will be understood to mean horizontal in the reference frame of the Figure, and more generally, aligned with the plane of the upper surface of the conveyor belt, eg the direction of travel of the conveyor belt.

[0107] The speed of the conveyor belt 106 can be varied between about 10 m / min and about 40 m / min (consistent with the rate at which the extruder extrudes the extrudate). Preferably, the speed of the conveyor belt is about 20 m / min to 30 m / min. In the results illustrated in Table 1 below, the speed of the conveyor belt is about 24 m / min.

[0108] Extruder 102 can use the die with about 4 to about 10 holes.In certain embodiments, the extrudate output of extruder is about 50kg / hour to about 150kg / hour, or more preferably about 75kg / hour to about 125kg / hour.In the result illustrated in Table 1 below, 10 strands of extrudates were produced from the die with 10 holes.In this embodiment, the output of extrudate is about 110kg / hour.The die hole in the embodiment of Table 1 has a diameter of about 4mm, and produces the extrudate strand with about 4mm diameter immediately after extrusion.During the cooling process, in the following embodiments, it is observed that the extrudate shrinks, and the diameter of the extrudate reaches about 2mm immediately before the granulator is pulverized.The die of other diameters can also be used in the embodiment of the present method, for example, the diameter of the die hole can preferably be in the range of about 2mm to about 7mm.

[0109] The type of extruder used is not critical and different types of extruders may be used. However, it is preferred to use a screw extruder, more preferably a twin screw co-rotating intermeshing compounding extruder.

[0110] Each of the water outlets is preferably configured as an arm that extends across the width of the conveyor belt in a direction substantially perpendicular to the direction of travel of the conveyor belt. Each water outlet preferably includes 2 to 4 nozzles, wherein each nozzle produces its own water jet or stream. It should be understood that any reference to "first / second jet water stream" or "jet water stream" in this disclosure refers to the collective water output from each water outlet, and therefore, the first jet water stream represents all water output from two to four nozzles included on the water outlet arm.

[0111] The nozzle is preferably a hydraulic / pressure operated nozzle. Each nozzle of each water outlet is configured to output water of about 3L / hour to about 12L / hour, more preferably water of about 4L / hour to about 8L / hour. The nozzle is each configured to output a roughly fan-shaped water stream, wherein the fan-shaped plane extends across the width of the conveyor belt, so the water stream ejected from each nozzle is arranged to evenly cover all strands. Therefore, the fan-shaped water stream from the two nozzles of the combination evenly covers all 10 strands of extrudates on the conveyor belt width. The stream produced by the nozzle can be substantially continuous, i.e., has laminar flow, or can be a dense mist / spray formed by droplets.

[0112] The nozzle above the upper surface of the conveyor belt ( Figure 1 The height of the water outlet (not shown) can be in the range of about 10 cm to about 30 cm, preferably about 15 cm to about 25 cm, and more preferably between about 18 cm to about 22 cm. The angle of the water stream generated by the water outlet can vary between about 40 degrees and about 80 degrees, where the angle is defined as the acute angle formed between i) the direction of the water stream ejected from the water outlet and ii) the plane of the conveyor belt surface (or in other words, the line of the conveyor belt's travel direction).

[0113] Examples 1 to 7

[0114] Examples 1 to 7 provided in Table 1 below were prepared under the following parameters: the conveyor belt speed was 24 m / min, the three water outlets 108a, 108b and 108c were located 40 cm apart, which means D2 = D3 = 40 cm. The distance from the extruder outlet to the first water outlet was 50 cm, i.e. D1 = 50 cm. The conveyor belt length D 传送带 The diameter of the extruder die hole is 4 mm, and 10 die holes are used to produce 10 strands of extrudates. Each water outlet is equipped with two nozzles, each of which produces a water flow (roughly fan-shaped) at a rate of 6 L / hour (equivalent to 100 mL / minute). The height of the ejection port above the upper surface of the conveyor belt is 22 cm. The angle of the nozzle relative to the plane of the conveyor belt (as defined above) is about 60 degrees, wherein the ejected water flow is directed / inclined to the direction of travel of the conveyor belt (i.e., to the granulator).

[0115] The polymer type used in Examples 1 to 7 was PEEK 450G903, which contained a carbon black additive. The glass transition temperature of this PEEK was approximately 143° C. No other fillers or additives were used.

[0116] The extruder is a twin-screw co-rotating intermeshing mixing extruder.

[0117] The variable in the 7 examples of Table 1 is the use of three water outlets: all combinations using three water outlets were tested, excluding the option of no water outlets.

[0118] The conveyor belt comprises a solid metal grid with large gaps, providing ample space for the sprayed water to pass through the conveyor belt (under the force of gravity). In other words, the conveyor belt is a moving grid with coarse gaps. Therefore, contact with the water means contact with the water sprayed from the outlet, as substantially no water pools or collects on the surface of the conveyor belt.

[0119] Table 1

[0120]

[0121] The extrudate temperatures in the fifth column of Table 1 represent the temperature measured at T6, i.e., immediately before pelletization. The range represents the highest and lowest temperatures recorded during the entire experiment.

[0122] Examples 1, 2, 3, and 7 represent first samples of polymers used to form pellets, and Examples 4, 5, and 6 represent second samples of polymers used to form pellets.

[0123] Reference to an "off-spec" batch refers to any batch of pellets containing more than three "overlong" and / or "undersized" pellets. A batch of 250g pellets, one of which has a mass of approximately 0.03g. A single pellet may also be "off-spec", where the off-spec pellet is either "overlong" or "undersized". For each example, the number of "overlong" and "undersized" pellets is counted, so for any count greater than three, the batch is considered off-spec. "Overlong" can be obtained from the batch by screening. The size of an "overlong" off-spec pellet is defined as any pellet with a length greater than 2.0mm. The size of an "undersized" off-spec pellet is defined as any pellet with a width less than 1.0mm.

[0124] Surface defects are visual defects. Minor defects are minor scratches that have little effect on the quality of the pellets. Major defects are any defects that significantly change the cylindrical appearance of the pellets or represent gouges or large dents on the surface, and / or any defects that result in a significant (e.g., more than 2%) reduction in the average mass of the pellets.

[0125] Based on the above table, the inventors determined that it was advantageous to turn on at least two water sprays. The batches produced by all embodiments (2, 3, 4, and 6) using at least two water sprays were in compliance with the specifications (i.e., no substandard pellets were produced at all). Therefore, the cooling conditions imparted by having at least two water flow positions result in the extrudate being cut by a pelletizer at a very high level of consistency, and thus producing high quality (i.e., very few defects) and pellets of consistent size. Specifically, using two or more water sprays to keep the extrudate temperature below 130°C is advantageous because the extrudate is too close to the glass transition temperature (i.e., within about 5 to about 10 degrees of the glass transition temperature) to be soft, and therefore is prone to excessive length when cut by a pelletizer.

[0126] The results of Table 1 show that it is more advantageous for at least one of the two water streams to be in the first water stream position. The water spray device 1 is located 50 cm from the extruder die outlet. For example, compare Examples 4 and 6 (using the same polymer sample to form an extrudate): both use the same total volume of water, so both result in the same total contact time between the sprayed water and the extrudate. However, in Example 6, water cooling begins at a later point (90 cm from the die outlet), which results in the temperature range of the extrudate being 3 degrees higher (115°C to 130°C) than the temperature range in Example 4 (112°C to 127°C). Therefore, the inventors have determined that starting water cooling earlier (e.g., using a water spray device 1, such as Example 4) has a better cooling effect, which is not only more water-saving and energy-saving, but also results in fewer surface defects. As shown in Table 1, Example 4 (whose first water stream is 50 cm from the die outlet) results in 12 severe defects, while Example 6 has 17 severe defects.

[0127] The same conclusion can be drawn by comparing Example 7 with Example 1, both of which use 1 water spray device. In Example 1, which uses only the water outlet of "Water Spray Device 1", the maximum temperature (143°C) is much lower than the maximum extrudate temperature (158°C) of Example 7.

[0128] The best quality pellets were produced by Example 2, which used two water sprays (Water Spray 1 and Water Spray 2) at exactly 50 cm and 90 cm from the die exit. This example resulted in the fewest defects (zero severe defects and eight minor defects), and produced extrudates with a temperature (at temperature point T6, immediately prior to pelletization) in the range of 115°C to 125°C. As discussed above, this range is advantageous because it is sufficiently below the glass transition temperature that the extrudate hardens somewhat and can be effectively cut without scarring the pellets, but not so far below the glass transition temperature that the pelletizer blades become worn and the extrudate is so brittle that it breaks and produces undersized or overlong pellets.

[0129] Thus, surprisingly, when applying the water stream using two water outlets, the best pellet results were provided when the first two water outlets (water spray device 1 and water spray device 2 at 50 cm and 90 cm from the die outlet) were used. In other words, in the case of using the first water spray position, it is preferred that the second water spray is located within 40 cm from the first water spray outlet (water spray device 2) rather than 80 cm from the first water spray outlet. This can be seen by comparing Examples 2 and 4: the pellets produced in Example 2 have zero serious defects (only 8 minor defects), while the pellets in Example 4 contain 12 serious defects. The temperature range of Example 2 is advantageously narrower (115°C-125°C) compared to the wider range of Example 4 (112°C-127°C). Therefore, it is preferred to keep the temperature of the extrudate within a narrow range, for example 28 to 18 degrees below the glass transition temperature of the PEEK polymer, and even more preferably 21 to 25 degrees below the glass transition temperature of the PEEK polymer.

[0130] Therefore, the results indicate that the most favorable cooling conditions include controlling the water contact time (e.g., by using just two or three water outlets) and controlling the location of the water outlets (e.g., relatively close to the extruder to provide better cooling without overcooling the extrudate) to produce pellets with high quality and consistency.

[0131] Other PEEK varieties and compositions, i.e., in addition to the PEEK 450G903 containing carbon black used in Examples 1 to 7, can be easily applied to the above cooling conditions in a corresponding manner to produce high-quality pellets in the same manner. The temperature of the extrudate should generally be lower than the glass transition temperature of the PEEK used by a certain level (preferably 5 to 35 degrees, or a more preferred sub-range as described above). Typically, the glass transition temperature of PEEK polymers ranges from about 143°C to about 162°C (measured using ISO11357 test method).

[0132] In this specification, embodiments have been described in a manner that enables a clear and concise description to be written, but it is intended and will be understood that the embodiments may be combined or separated differently without departing from the present invention. For example, it should be understood that all preferred features described herein apply to all aspects of the present invention described herein, and vice versa. For example, all preferred features of the composite material apply to all aspects of the present invention.

[0133] The glass transition temperature referred to in this disclosure refers to the glass transition temperature measured according to the ISO 11357 test standard.

[0134] In this specification, unless otherwise expressly stated, the term "about" refers to plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, and most preferably plus or minus 2%. For example, a distance of "about 50 cm" should be understood to include distances between 45 cm and 55 cm.

[0135] In the present specification, the term "substantially" refers to a deviation of plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, and most preferably plus or minus 2%.

[0136] In the present specification, referring to "substantially" includes referring to "entirely" and / or "exactly." That is, in the case where the word "substantially" is included, it should be understood that this also includes a reference to a specific sentence not including the word "substantially".

[0137] In this specification, reference to an event "immediately before" or "immediately after" includes the meaning of "at the moment of beginning" or "at the moment of ending" of the event. Reference to "immediately" also includes the moment before or after the event, such as up to 1 second after or before the event. In terms of distance and position, reference to "immediately" includes reference to a distance within 5 cm or even within 1 cm from an object or position.

[0138] It should be understood that various changes and modifications to the currently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without weakening its incidental advantages. Therefore, it is intended that the appended claims cover these changes and modifications.

Claims

1. A method for producing polyetheretherketone polymer (PEEK polymer) pellets, the method comprising: a) melt extruding a thermoplastic composition using an extruder to form an extrudate, wherein the thermoplastic composition comprises a PEEK polymer; b) cooling the extrudate on a moving conveyor, wherein the cooling comprises: b1) subjecting the extrudate to a first air cooling stage, b2) after b1), subjecting the extrudate to a water cooling phase, b3) after b2), subjecting the extrudate to a second air cooling stage, wherein the water cooling stage comprises conveying the extrudate through a first water jet provided by a first water outlet and a second water jet provided by a second water outlet, wherein the first water outlet is located about 30 cm to about 70 cm from an exit of the extruder, wherein the first water outlet and the second water outlet are separated by about 20 cm to about 90 cm in the direction of travel of the conveyor belt, and wherein the contact time of the exposed surface of the extrudate in contact with the water ejected from the first water jet and the second water jet is in the range of about 2 seconds to about 6 seconds; as well as c) after b), comminuting the extrudate to form a plurality of pellets, wherein the temperature of the extrudate during the comminuting step is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

2. The method according to claim 1, wherein: The glass transition temperature of the thermoplastic composition is in the range of about 138°C to about 165°C, preferably in the range of about 140°C to about 150°C, and more preferably in the range of about 141°C to about 145°C.

3. The method according to claim 1 or 2, wherein: The pre-water cooling temperature of the extrudate immediately prior to step b2) is in the range of about 40°C to about 80°C above the glass transition temperature of the thermoplastic composition.

4. A method according to any one of the preceding claims, wherein: The first water outlet is located about 55 cm to about 65 cm from the outlet of the extruder.

5. The method according to claim 3, wherein: The post-water-cooling temperature of the extrudate immediately after the first water jet is about 40° C. to about 70° C. lower than the pre-water-cooling temperature of the extrudate immediately before the first water jet.

6. The method according to claim 3 or claim 5, wherein: The water-cooled temperature of the extrudate immediately after the second water jet is about 20° C. to about 40° C. lower than the water-cooled temperature of the extrudate after the first water jet.

7. A method according to any one of the preceding claims, wherein: The first water outlet and the second water outlet are separated by about 30 cm to about 80 cm in the traveling direction of the conveyor belt.

8. A method according to any one of the preceding claims, wherein: The total length of the conveyor belt is in the range of about 10 m to about 14 m.

9. A method according to any one of the preceding claims, wherein: The exposed surface of the extrudate is in contact with the first water jet for a time in a range from about 1 second to about 4 seconds; and / or The contact time between the exposed surface of the extrudate and the second water jet is in the range of about 1 second to about 4 seconds.

10. A method according to any one of the preceding claims, wherein: The first water outlet is positioned at an inclined angle so that the first water jet immediately after leaving the first water outlet is at an angle in the range of about 40 degrees to about 80 degrees relative to the direction of travel of the conveyor belt; and / or The second water outlet is positioned at an inclined angle so that the second water jet immediately after leaving the second water outlet forms an angle in the range of about 40 degrees to about 80 degrees relative to the traveling direction of the conveyor belt.

11. A method according to any one of the preceding claims, wherein: The second air cooling stage includes passing the extrudate through air in the absence of water from the first and second water jets, wherein the extrudate is substantially dry during the second air cooling stage.

12. A method according to any one of the preceding claims, wherein: The temperature of the extrudate during the comminuting step ranges from about 105°C to about 135°C.

13. A method according to any one of the preceding claims, wherein: For each pellet in the plurality of pellets, a maximum pellet size is less than about 3 mm and a minimum pellet size is greater than about 0.5 mm.

14. A method according to any one of the preceding claims, wherein: The cooling rate of the extrudate at the first water jet is greater than the cooling rate of the extrudate in the second water jet.

15. A method according to any one of the preceding claims, wherein: The thermoplastic composition further comprises about 5 wt % to about 50 wt % of a filler, preferably, wherein the filler is selected from carbon black, talc, calcium carbonate, glass fiber, carbon fiber, or a combination of two or more thereof, preferably wherein the filler comprises carbon black.

16. A method according to any one of the preceding claims, wherein: A pellet in the plurality of pellets has a D99 length of less than about 2 mm.

17. A method according to any one of the preceding claims, wherein: The water cooling stage includes a first intermediate air cooling stage between the first spray water flow and the second spray water flow.

18. A method according to any one of the preceding claims, wherein: The extrudate has the following temperature: T1: the temperature of the extrudate immediately after extrusion is about 80° C. to about 120° C. higher than the glass transition temperature of the thermoplastic composition; T2: the temperature of the extrudate before water cooling immediately before step b2) is in the range of about 40°C to 80°C above the glass transition temperature of the thermoplastic composition; T3: the post-water-cooling temperature of the extrudate immediately after the first water jet is about 40° C. to about 70° C. lower than the pre-water-cooling temperature of the extrudate immediately before the first water jet; T4: the water-cooled temperature of the extrudate immediately after the second water jet is about 20° C. to about 40° C. lower than the water-cooled temperature of the extrudate after the first water jet; and T6: The temperature of the extrudate during pulverization in step c) is in the range of about 5°C to about 35°C below the glass transition temperature of the thermoplastic composition.

19. Pellets produced according to the method of any one of claims 1 to 18.

20. A plurality of pellets comprising a thermoplastic composition, wherein the thermoplastic composition comprises a polyetheretherketone polymer (PEEK polymer) and about 5 wt % to about 50 wt % carbon black, wherein the pellets are substantially cylindrical, wherein a pellet in the plurality of pellets has a D99 length of less than about 2 mm, Wherein a D99 diameter of a pellet in the plurality of pellets is in a range from about 0.6 mm to about 2 mm.

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