KR102317519B1 - Polypropylene particles and method for preparing the same - Google Patents

Abstract

The present invention provides polypropylene particles formed in a continuous phase from a polypropylene resin and having a particle diameter of 1 to 100 μm. The polypropylene particles have an average particle diameter (D ₅₀ ) of 20 to 50 μm, a cumulative volume 10% particle diameter (D ₁₀ ) of 5 to 15 μm, and a cumulative volume 90% particle diameter (D ₉₀ ) of 50 to 80 μm have The polypropylene particles have a D value representing a particle distribution of 10 to 20.

Description

Polypropylene particles and their manufacturing method

The present invention relates to polypropylene particles and a method for preparing the same.

Currently, research on secondary batteries is being actively conducted. In order for secondary batteries to be used for large-capacity power storage, energy storage density must be high. In contrast, a redox flow secondary battery is in the spotlight as the most suitable secondary battery with high capacity and high efficiency.

In a redox flow secondary battery, the bipolar plate provides a flow path through which positive and negative electrolytes flow, and serves to move electrons. Accordingly, it may be preferable to use a material having excellent corrosion resistance to an electrolyte and excellent electron mobility for the bipolar plate. In the case of commercially available graphite-based bipolar plates, their use is very limited because electron mobility is excellent, but corrosion resistance to electrolytes is low, which causes electrochemical corrosion by electrolyte when a redox flow secondary battery is operated for a long time. . Therefore, research is needed to improve the corrosion resistance of the bipolar plate.

When the corrosion resistance of the bipolar plate is improved, the corrosion resistance may be improved compared to a commercially available graphite-based bipolar plate, whereas a phenomenon in which the specific resistance increases may occur. In this case, there is a disadvantage in that energy efficiency is lowered when applied to a redox flow secondary battery. In consideration of this point, the conventional bipolar plate is a synthetic resin composition composed by adding a conductive material such as carbon black, graphite or metal powder to a vinyl ester resin, a phenol resin, a polypropylene resin, a polyethylene resin, a propylene-ethylene copolymer resin, and a fluororesin. It is manufactured by molding.

The polypropylene used for the bipolar plate is provided in the form of particles and processed, and may be mixed with a bipolar plate material such as graphite during processing. In order to prepare polypropylene particles, the following three methods have been mainly used in the prior art. Specifically, the method for producing the polypropylene particles includes a pulverization method represented by freeze pulverization; a solvent dissolution precipitation method of dissolving in a high temperature solvent and then cooling to precipitate, or dissolving in a solvent and then adding a poor solvent to precipitate; and a melt kneading method in which a thermoplastic resin is mixed with a thermoplastic resin and an incompatible resin in a mixer to form a composition having a thermoplastic resin and an incompatible resin in a continuous phase in a dispersed phase, and then the incompatible resin is removed to obtain thermoplastic resin particles.

When the particles are manufactured through the pulverization method, it is difficult to secure uniformity in the size and shape of the prepared polypropylene particles. In addition, since liquid nitrogen is used for cooling of the pulverization method, higher cost is required compared to the particle obtaining process, and when a compounding process of adding pigments, antioxidants, etc. is added to the polypropylene resin raw material, it proceeds in a batch manner. Therefore, the productivity is lowered compared to the continuous particle obtaining process. When the particles are prepared through the solvent dissolution precipitation method and the melt kneading method, there may be a problem that other components such as a solvent may be detected as impurities in addition to the thermoplastic resin particles. The problem may be more serious as the amount of impurities may be higher.

Due to the above-described problems, the functionality of the bipolar plate may be reduced depending on the polypropylene particles used as the raw material of the bipolar plate. Accordingly, in the art, there is a need for polypropylene particles having improved particle properties to be suitable for application to a bipolar plate or the like.

Japanese Laid-Open Patent Publication No. 2001-288273 Japanese Laid-Open Patent Publication No. 2000-007789 Japanese Laid-Open Patent Publication No. 2004-269865

An object of the present invention is to provide polypropylene particles having excellent physical properties when manufacturing a bipolar plate constituting a redox flow battery.

According to a first aspect of the present invention,

The present invention provides polypropylene particles formed in a continuous phase from a polypropylene resin and having a particle diameter of 1 to 100 μm.

In one embodiment of the present invention, the polypropylene particles have an average particle diameter (D ₅₀ ) of 20 to 50 μm.

In one embodiment of the present invention, the polypropylene particles have a cumulative volume of 10% particle diameter (D ₁₀ ) of 5 to 15㎛.

In one embodiment of the present invention, the polypropylene particles have a cumulative volume of 90% particle diameter (D ₉₀ ) of 50 to 80㎛.

In one embodiment of the present invention, the polypropylene particles have a D value of 10 to 20 calculated by Equation 1 below:

[Formula 1]

Here, D ₁₀ is a particle diameter of 10% of the cumulative volume, D ₅₀ is an average particle diameter, and D ₉₀ is a particle diameter of 90% of the cumulative volume.

In one embodiment of the present invention, the impurity content of the polypropylene particles is 50 ppm or less.

In one embodiment of the present invention, the polypropylene particles have a glass transition temperature (T _g ) and a melting point ( The peak of the cold crystallization temperature (T _cc ) appears at a temperature between T _{m ).}

In one embodiment of the present invention, the polypropylene particles have an aspect ratio of 1.00 or more and less than 1.05 calculated by Equation 2 below,

The degree of sphericity calculated by Equation 3 below is 0.95 to 1.00:

[Formula 2]

Aspect ratio = major axis/minor axis

[Formula 3]

Roundness=4×area/(π×long axis^2).

In one embodiment of the present invention, the polypropylene particles have a compressibility of 10 to 20% calculated by Equation 4 below:

[Formula 4]

Compression degree = (compressed bulk density - relaxed bulk density) / compressed bulk density x 100.

In one embodiment of the present invention, the polypropylene particles have a compressed bulk density ^{of 0.45 to 0.6 g/cm 3 .}

In one embodiment of the present invention, the polypropylene particles have a flow time of 20 to 30 seconds.

According to a second aspect of the present invention, there is provided a method for producing the above-described polypropylene particles,

The manufacturing method is

(1) extruding the polypropylene resin by supplying it to an extruder;

(2) supplying the extruded polypropylene resin and air to the nozzle, contacting the polypropylene resin with air to make the polypropylene resin particles, and then discharging the granulated polypropylene resin; and

(3) supplying the discharged polypropylene particles to a cooler to cool the polypropylene particles, and then obtaining cooled polypropylene particles.

In one embodiment of the present invention, the extruded polypropylene resin supplied to the nozzle in step (2) has a melt viscosity of 0.5 to 20 Pa·s.

In one embodiment of the present invention, air is supplied to the center and the outer portion based on the cross section of the nozzle in step (2), and the extruded polypropylene resin is supplied between the center and the outer portion.

In one embodiment of the present invention, the cross-sectional area ratio of the air supplied to the outer part and the extruded polypropylene resin supplied between the central part and the outer part based on the cross section of the nozzle in step (2) is 4:1 to 6 It is :1.

In one embodiment of the present invention, the inside of the nozzle in step (2) is maintained at 250 to 350 ℃.

In one embodiment of the present invention, in the step (2), the discharge portion of the nozzle is maintained at a temperature calculated by Equation 5 below:

[Formula 5]

Discharge part temperature = glass transition temperature (T _g ) + (decomposition temperature (T _d ) - glass transition temperature (T _g ))×B

In Equation 5, the glass transition temperature and the decomposition temperature are values for polypropylene, and B is 0.5 to 1.5.

The polypropylene particles according to the present invention have physical properties suitable for manufacturing a bipolar plate, and thus, the bipolar plate manufactured through this can improve the performance of a redox flow battery.

1 is an image schematically showing the shape of the polypropylene particles of the present invention.
Figure 2 is a process flow diagram schematically showing a method for producing polypropylene particles according to the present invention.
3 is a cross-sectional view of a nozzle discharge unit showing a supply position of a polypropylene resin and air to the nozzle according to an embodiment of the present invention.

The embodiments provided according to the present invention can all be achieved by the following description. It is to be understood that the following description is to be understood as describing preferred embodiments of the present invention, and the present invention is not necessarily limited thereto.

In the following specification, with respect to the numerical range, the expression "to" is used to include both the upper and lower limits of the range, and when it does not include the upper or lower limits, "less than", " The expressions "more than", "less than" or "more than" are used.

The present invention provides polypropylene particles having properties suitable for use in the production of a bipolar plate of a redox flow battery, which could not be obtained by a conventional particle production method. Hereinafter, the polypropylene particles according to the present invention will be described in detail.

polypropylene particles

The present invention provides polypropylene particles prepared by atomizing a polypropylene resin by contacting it with air after extrusion. The method for producing polypropylene particles according to the present invention is an improved method compared to the conventional pulverization method, solvent dissolution precipitation method, and melt kneading method. .

The polypropylene particles according to the present invention have a particle diameter of 1 to 100 μm, more specifically 5 to 80 μm. When the particles have a particle diameter of less than 1 μm, it is difficult to effectively mix with a bipolar plate material such as graphite due to agglomeration of the particles, and there is a problem in that the mechanical strength of the bipolar plate to which the particles are applied is reduced. When the particles have a particle diameter of more than 100 μm, it is difficult to efficiently disperse a bipolar plate material such as graphite because the particles are too large, and there is a problem in that the electrical resistance of the bipolar plate to which the particles are applied is lowered. _{The polypropylene particles have an average particle diameter (D 50} ) (or 50% cumulative volume particle diameter) of 20 to 50 μm, more specifically, 25 to 40 μm. When the particles satisfy the average particle diameter of the above-mentioned range, a bipolar plate material such as graphite may be uniformly dispersed while maintaining an appropriate distance between the materials. _{The polypropylene particles have a particle diameter (D 10} ) of 10% of the cumulative volume of 5 to 15 μm, more specifically 7 to 12 μm. The polypropylene particles have a 90% cumulative volume particle diameter (D ₉₀ ) of 50 to 80 μm, more specifically 60 to 70 μm. In the present specification, the particle size distribution of the polypropylene particles was measured by a wet method using a particle size analyzer (Microtrac, S3500), and the specific method will be described in Examples below. Here, D ₁₀ , D ₅₀ , and D ₉₀ mean particle diameters corresponding to 10%, 50%, and 90% of the cumulative volume percentage in the cumulative volume distribution of the particles, respectively. Regarding the particle size distribution of the polypropylene particles, the polypropylene particles according to the present invention have a D value of 10 to 20, more specifically 13 to 18, and the D value is calculated by the following formula (1).

[Formula 1]

The D value quantifies where the particles having a larger cumulative volume of 90% particle diameter (D ₉₀ ) and a particle having a smaller cumulative volume 10% particle diameter (D ₁₀ ) are located based on the particles having an average particle diameter (D _{50 ).} is one value. Here, particles having a relatively large particle diameter serve to support particles having an average particle diameter when applied together with particles having an average particle diameter, and particles having a relatively small particle diameter when applied together with particles having an average particle diameter It serves to fill the voids between particles with As the value of D is smaller, the particle diameters are distributed closer to the average particle diameter, and as the D value is larger, the particle diameters of the particles are distributed farther from the average particle diameter. If the D value is small, the ratio of particles close to the average particle diameter increases, so it is difficult to obtain the effect due to the diversity of particle sizes. On the other hand, if the D value is large, the ratio of particles far to the average particle diameter increases, difficult to apply Average particle size When the particle satisfies the D value in the above-mentioned range, large particles and small particles are distributed in an appropriate ratio around the average particle diameter, and excellent physical properties can be exhibited when applied to a bipolar plate for a redox flow battery. .

In the present invention, the shape of the particle is evaluated in the following aspect ratio (aspect ratio) and roundness (roundness), the closer the aspect ratio and sphericity (roundness) to 1, the shape of the particle is interpreted as closer to a spherical shape. The aspect ratio is calculated by Equation 2 below.

[Formula 2]

Aspect ratio = major axis/minor axis

In addition, the sphericity is calculated by Equation 3 below.

[Formula 3]

Roundness=4×area/(π×long axis^2)

In order to explain in detail the above calculation formula, Fig. 1 schematically shows polypropylene particles is provided. According to FIG. 1, in Equations 2 and 3, "long axis" means the longest distance among the vertical distances (d) between two parallel tangents of the 2D image (cross-section) of the polypropylene particle, and "short axis" means the It means the shortest distance among the vertical distances (d) between two parallel tangents of a 2D image (cross-section) of polypropylene particles. In addition, in Equation 3, “area” means a cross-sectional area including the long axis of the polypropylene particles. 1 is an example of the case where the vertical distance d between two parallel tangent planes of the polypropylene particle is the long axis, and shows the area A. As shown in FIG.

According to one embodiment of the present invention, the polypropylene particles according to the present invention may have an aspect ratio of 1.00 or more and less than 1.05, more specifically 1.02 or more and less than 1.05, and a spherical shape of 0.95 to 1.00, more specifically 0.98 to 1.00. You can have a flame. When the shape of the polypropylene particles satisfies the above-mentioned aspect ratio and sphericity range, the flowability and uniformity of the polypropylene particles are increased, so that handling of the particles is easy when applied to a bipolar plate, etc., and the particle is applied to a bipolar plate The quality can be improved by the good flowability and dispersibility of the particles.

Numerical values according to Equations 2 and 3 can be measured by image processing the image of polypropylene particles using ImageJ (National Institutes of Health (NIH)) - Converting to a binary image and quantifying the degree of spheroidization of individual particles - do.

The polypropylene particles according to the present invention are particles formed from a polypropylene resin into a continuous matrix phase. Formed from the polypropylene resin into a continuous matrix phase means that the polypropylene resin continuously forms a dense structure without additional components. By extruding the polypropylene resin, melting and then granulating the melt with air, polypropylene particles are continuously produced with a dense structure. On the other hand, according to the conventional manufacturing method, since particles are formed by adding additional ingredients or particles are formed through a discontinuous process of cooling and grinding, particles are not formed in a continuous matrix.

The particles formed as a continuous matrix from the polypropylene resin have a high purity because impurities are not incorporated in the production process of the particles. Here, “impurities” refers to components other than polypropylene that may be incorporated in the production of particles. Exemplary impurities include a solvent for dispersing the polypropylene resin, a heavy metal component included in the pulverization or grinding process, and an unreacted monomer included in the polymerization process. According to one embodiment of the present invention, the impurity content of the polypropylene particles of the present invention may be 50 ppm or less, preferably 20 ppm or less, more preferably 5 ppm or less.

In addition, the particles may additionally have other properties as well as purity. _{As one of these characteristics, the polypropylene particles are the glass transition temperature (T g} ) and the melting point (T _m ) in the DSC curve derived from the analysis of the temperature increase of 10 ° C / min by Differential Scanning Calorimetry (DSC). At the temperature, a peak of the cold crystallization temperature (T _cc ) appears. Polypropylene particles are spherical solid particles at room temperature. When the temperature rise analysis of these particles using a differential scanning calorimeter, the fluidity gradually increases as the temperature rises. At this time, the polypropylene particles show a peak of the cold crystallization temperature (T _{cc ) at a temperature between the glass transition temperature (T g} ) and the melting point (T _m ), which is immediately exothermic before the polypropylene particles are melted. It means having characteristics. According to one embodiment of the present invention, the cold crystallization temperature (T _cc ) appears in the 30% to 70% section between the glass transition temperature (T _g ) and the melting point (T _{m ).} In the above section, 0% is the glass transition temperature (T _g ), and 100% is the melting point (T _m ). In addition, according to the DSC curve, the polypropylene particles may have a difference (ΔH1-ΔH2) value of an endothermic value (ΔH1) and a calorific value (ΔH2) of 3 to 100J/g. Due to these characteristics, when the polypropylene particles are used in a heating process, it is possible to obtain the advantage that processing is possible at a low temperature compared to the processing temperature of the same type of polypropylene particles.

The polypropylene particles of the present invention have a degree of compression comparable to that of conventional polypropylene particles. The degree of compressibility may be calculated by Equation 4 below. According to one embodiment of the present invention, the polypropylene particles have a degree of compression of 10 to 20%.

[Formula 4]

Compressibility = (P-R)/P×100

In Equation 4, P denotes compressed bulk density, and R denotes relaxed bulk density.

As described above, since the polypropylene particles according to the present invention have good flowability, the voids between the particles can be well filled, and accordingly, a degree of compression of a certain level or higher is maintained. The degree of compressibility of the polypropylene particles can affect the quality of the product in the manufacture of the product through the particles. In the case of using polypropylene particles having a degree of compression of a certain degree or more as in the present invention, in the case of a molded article, it may have an effect of minimizing voids that may occur in the product. According to one embodiment of the present invention, the polypropylene particles have a compressed bulk density ^{of 0.45 to 0.6 g/cm 3 .}

The polypropylene particles according to the present invention have a flow time of 20 to 30 seconds. The flow time is a numerical value indicating the fluidity of the powder. The short flow time means that the frictional resistance between the particles is small, and when the frictional resistance between the particles is small, it is easy to handle the particles. Since the polypropylene particles according to the present invention have a shorter flow time compared to the conventional polypropylene particles, they have good fluidity and are easy to handle.

The polypropylene particles according to the invention have a crystallinity of 5 to 10%. The crystallinity of the polypropylene particles is a value lower than that of the large-diameter particles in the form of pellets, and the polypropylene particles according to the present invention are easy to process due to the low crystallinity.

Polypropylene particles having the above-described characteristics are prepared by the following manufacturing method. Hereinafter, a method for producing polypropylene particles according to the present invention will be described in detail.

Method for producing polypropylene particles

2 schematically shows a process flow chart for the manufacturing method. The manufacturing method comprises the steps of supplying a polypropylene resin to an extruder and extruding (S100); supplying the extruded polypropylene resin and air to the nozzle, contacting the polypropylene resin with air to make the polypropylene resin particles, and then discharging the granulated polypropylene resin (S200); and supplying the discharged polypropylene particles to a cooler to cool the polypropylene particles, and then obtaining the cooled polypropylene particles (S300). Hereinafter, each step of the manufacturing method will be described in detail.

In order to manufacture polypropylene particles according to the present invention, first, a polypropylene resin as a raw material is supplied to an extruder and extruded. By extruding the polypropylene resin, the polypropylene resin has properties suitable for particle processing in the nozzle. The polypropylene resin used as a raw material may preferably have a weight average molecular weight (Mw) of 10,000 to 200,000 g/mol in consideration of appropriate physical properties of the prepared particles.

The extruder to which the polypropylene resin is supplied controls physical properties such as viscosity of the polypropylene resin by heating and pressurizing the polypropylene resin. The type of the extruder is not particularly limited as long as it is possible to adjust the physical properties suitable for granulation in the nozzle. According to one embodiment of the present invention, the extruder may be a twin screw extruder for efficient extrusion. The inside of the extruder may be preferably maintained at 150 to 300 ℃, specifically 170 to 270 ℃, more specifically 200 to 250 ℃. When the internal temperature of the extruder is less than 150° C., the viscosity of the polypropylene resin is high, which is not suitable for granulation in the nozzle, and the flowability of the polypropylene resin in the extruder is low, which is not efficient for extrusion. In addition, when the internal temperature of the extruder is more than 300 ° C., the flowability of the polypropylene resin is high, so that efficient extrusion is possible, but it is difficult to control fine physical properties when the polypropylene resin is granulated in the nozzle.

The extrusion amount of the polypropylene resin can be easily set in consideration of the size of the extruder to control the physical properties of the polypropylene resin. According to one embodiment of the present invention, the polypropylene resin is extruded at a rate of 1 to 10 kg/hr. The viscosity of the extruded polypropylene resin may be 0.5 to 20 Pa·s, specifically 1 to 15 Pa·s, and more specifically 2 to 10 Pa·s. If the viscosity of the polypropylene resin is less than 0.5 Pa·s, it is difficult to process the particles in the nozzle, and if the viscosity of the polypropylene resin is more than 20 Pa·s, the flowability of the polypropylene resin in the nozzle is low and processing efficiency is lowered. The temperature of the extruded polypropylene resin may be 150 to 250 ℃.

The polypropylene resin extruded from the extruder is fed to the nozzle. Along with the polypropylene resin, air is also supplied to the nozzle. The air contacts the polypropylene resin in the nozzle to granulate the polypropylene resin. In order to properly maintain the physical properties of the polypropylene resin, high-temperature air is supplied to the nozzle. According to one embodiment of the present invention, the temperature of the air may be 250 to 450 ℃, preferably 260 to 400 ℃, more preferably 270 to 350 ℃. When the temperature of the air is less than 250 ° C. or more than 450 ° C., when the polypropylene particles are prepared from the polypropylene resin, the physical properties of the surface in contact with the air may be changed in an undesirable direction, which is a problem. In particular, when the temperature of the air exceeds 450 ℃, excessive heat is supplied to the contact surface with the air may cause the decomposition of polypropylene on the surface of the particles.

The polypropylene resin and air supplied to the nozzle are set so that the polypropylene particles can have an appropriate size and shape, and the formed particles can be evenly dispersed. 3 is a cross-sectional view of the nozzle discharge unit, and the supply position of the polypropylene resin and air according to an embodiment of the present invention will be described in detail with reference to FIG. For a detailed description herein, the position of the nozzle is expressed as “injection part”, “discharge part”, and “end part”. The “injection part” of the nozzle means the position where the nozzle starts, and the “discharge part” of the nozzle means the position where the nozzle ends. In addition, the "distal end" of the nozzle means the position from the two-thirds point of the nozzle to the discharge portion. Here, point 0 of the nozzle is the injection part of the nozzle, and point 1 of the nozzle is the discharge part of the nozzle.

As shown in FIG. 3 , a cross section perpendicular to the flow direction of the polypropylene resin and air is circular. The air is supplied through the first air stream 40 supplied to the center of the circle and the second air stream 20 supplied to the outer part of the circle, and the polypropylene resin is the first air stream 40 and It is supplied between the second air streams (20). Each supply stream (polypropylene resin stream 30, first air stream 40, and second air stream 20) from the time polypropylene resin and air are supplied to the inlet part of the nozzle to just before the outlet part of the nozzle is separated by the structure inside the nozzle. Immediately before the discharge portion of the nozzle, the polypropylene resin stream and the second air stream are combined to bring the polypropylene resin into contact with the air, whereby the polypropylene resin is granulated. In contrast, the first air stream is separated from the polypropylene resin stream and the second air stream by the nozzle internal structure until the polypropylene resin and air are discharged from the nozzle. The first air flow prevents the particles of the polypropylene resin granulated by the second air flow from sticking to the discharge part of the nozzle, and serves to evenly disperse the discharged particles after being discharged from the nozzle before being supplied to the cooler .

All of the polypropylene resin extruded from the extruder is supplied to the above-described position of the nozzle, and the flow rate of air supplied to the nozzle may be adjusted according to the flow rate of the extruded polypropylene resin. According to one embodiment of the present invention, the air is supplied to the nozzle at a flow rate of ^{1 to 300 m 3} /hr, specifically 30 to 240 m ³ /hr, more specifically 60 to 180 m ^{3 /hr.} Within the flow rate range of the air, air is supplied separately into a first air stream and a second air stream. As described above, the polypropylene resin is granulated by the second air stream, and the ratio of the polypropylene resin to the second air stream as well as the temperature of the second air stream may determine the physical properties of the particles. According to one embodiment of the present invention, the cross-sectional area ratio of the polypropylene resin and the second air flow based on the cross-section of the discharge part of the nozzle may be 4:1 to 6:1, specifically 4.3:1 to 5:1. . When the ratio of the polypropylene resin and the second air flow is adjusted within the above range, it is possible to manufacture polypropylene particles of an appropriate size and shape having high utility in a bipolar plate or the like.

Since the polypropylene resin is granulated in the nozzle, the inside of the nozzle is adjusted to a temperature suitable for the polypropylene resin to be granulated. Since the rapid increase in temperature may change the structure of polypropylene, the temperature from the extruder to the discharge portion of the nozzle may be increased in stages. Therefore, the internal temperature of the nozzle is set in a range higher than the internal temperature of the extruder on average. Since the temperature for the distal end of the nozzle is separately defined below, the internal temperature of the nozzle in this specification means the average temperature of the rest of the nozzle except for the distal end of the nozzle, unless otherwise specified. According to one embodiment of the present invention, the inside of the nozzle may be maintained at 250 to 350 ℃. If the internal temperature of the nozzle is less than 250℃, sufficient heat to satisfy the physical properties when granulating the polypropylene resin is not transmitted. If the internal temperature of the nozzle exceeds 350℃, excessive heat is supplied to the polypropylene resin and can change

The distal end of the nozzle may be maintained at a temperature higher than the average temperature inside the nozzle in order to improve the external and internal properties of the generated particles. The temperature of the distal end of the nozzle _{may be determined between the glass transition temperature (T g} ) and the thermal decomposition temperature (T _d ) of the polypropylene, and specifically, it may be determined according to Equation 5 below.

[Formula 5]

End temperature = glass transition temperature (T _g ) + (thermal decomposition temperature (T _d ) - glass transition temperature (T _g ))×B

Here, B may be 0.5 to 1.5, specifically 0.85 to 1.45, and more specifically 1.2 to 1.4. If B is less than 0.5, it is difficult to expect improvement of the external and internal physical properties of the particles as the temperature rises at the end of the nozzle. The structure of polypropylene can be modified. The glass transition temperature and thermal decomposition temperature may vary depending on the type of polymer, polymerization degree, structure, and the like. According to one embodiment of the present invention, the polypropylene of the present invention has a glass transition temperature of 0 to 50 ℃, polypropylene having a thermal decomposition temperature of 250 to 350 ℃ may be used. Since the distal end of the nozzle is maintained above the average temperature of the nozzle, the distal end of the nozzle may optionally be provided with additional heating means.

The polypropylene particles discharged from the nozzle are supplied to the cooler. The nozzle and the cooler may be spaced apart, and in this case, the discharged polypropylene particles are primarily cooled by ambient air before being supplied to the cooler. In the nozzle, not only polypropylene particles but also high-temperature air are discharged. By separating the nozzle and the cooler, the high-temperature air can be discharged to the outside instead of the cooler, so that the cooling efficiency in the cooler can be increased. According to one embodiment of the present invention, the cooler is positioned 100 to 500 mm apart from the nozzle, specifically 150 to 400 mm, more specifically 200 to 300 mm apart. When the separation distance is shorter than the distance, a large amount of high-temperature air is injected into the cooling chamber and the cooling efficiency is low. This cannot be done. In addition, when discharging the polypropylene particles from the nozzle, the injection angle may be 10 to 60°, and when discharging the polypropylene particles at the corresponding angle, the effect due to the separation between the nozzle and the cooler may be doubled.

The cooler may cool the polypropylene particles by supplying low-temperature air into the cooler and bringing the air into contact with the polypropylene particles. The low-temperature air forms a rotating airflow in the cooler, and the residence time of the polypropylene particles in the cooler can be sufficiently secured by the rotating airflow. The flow rate of air supplied to the cooler may be adjusted according to the amount of polypropylene particles supplied, and according to one embodiment of the present invention, the air may be supplied to the cooler at a flow rate of ^{1 to 10 m 3 /min.} The air may preferably have a temperature of -30 to -20 °C. By supplying cryogenic air into the cooler compared to the polypropylene particles supplied to the cooler, the polypropylene particles are rapidly cooled and the internal structure of the high-temperature polypropylene particles can be properly maintained when discharged. When the polypropylene particles are actually applied for the production of products, they are reheated again. At this time, the reheated polypropylene particles have advantageous properties for processing. Polypropylene particles cooled by low-temperature air are cooled to below 40°C and discharged, and the discharged particles are collected through a cyclone or a bag filter.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are only provided for easier understanding of the present invention, and the present invention is not limited thereto.

Example

Example One

100% by weight of polypropylene resin (PolyMirae, MF650Y, Mw: about 90,000 _g /mol, glass transition temperature (T g ): about 10°C, pyrolysis temperature (T _d ): about 300°C) was mixed with a twin-screw extruder (diameter (D) ) = 32 mm, length/diameter (L/D) = 40). The twin screw extruder was set at a temperature of about 220° C. and an extrusion amount of about 5 kg/hr to perform extrusion. The extruded polypropylene resin has a viscosity of about 10 Pa·s, and the extruded polypropylene resin has a nozzle set at an internal temperature of about 300° C. and an end temperature of about 400° C. (the B value according to Equation 5 is about 1.34) was supplied to In addition, air at about 350° C. was supplied to the nozzle at a flow rate of ^{about 1 m 3 /min.} The air was supplied to the center and the outer portion of the cross section of the nozzle, and the extruded polypropylene resin was supplied between the center and the outer portion of the nozzle to which air is supplied. The cross-sectional area ratio of the air supplied to the outer part and the extruded polypropylene supplied between the air-supplied central part and the outer part was about 4.3:1. The polypropylene resin supplied to the nozzle was atomized by contact with hot air, and the atomized particles were sprayed from the nozzle. The injection angle from the nozzle was about 45°, and the injected particles were supplied to a cooling chamber (diameter (D) = 1,100 mm, length (L) = 3,500 mm) spaced about 200 mm from the nozzle. In addition, the cooling chamber was adjusted to form a rotational airflow by injecting ^{air at -25°C at a flow rate of about 6m 3 /min before the injected particles were supplied.} Particles sufficiently cooled to 40° C. or less in the cooling chamber were collected through a cyclone or a bag filter.

comparative example One

Polypropylene particles were prepared in the same manner as in Example 1, except that the temperature of the distal end was adjusted to 140° C. (the B value according to Equation 5 was about 0.45).

comparative example 2

Polypropylene particles were prepared in the same manner as in Example 1, except that the temperature at the end was adjusted to 460° C. (the B value according to Equation 5 was about 1.55).

comparative example 3

The same polypropylene resin as in Example 1 was fed into a screw feeder through a hopper. Moisture was removed while moving the raw material through the screw, and then the raw material was introduced into a pulverizer supplied with liquid nitrogen at -130°C. As the crusher, a pin crusher type crusher was used. The particle size was controlled through a grinding size pin. Particles atomized through the grinder were collected through a cyclone.

comparative example 4

Polypropylene particles were prepared in the same manner as in Example 1, except that the cross-sectional area ratio of the air supplied to the outer portion and the extruded polypropylene supplied between the air supplied center and the outer portion was 3.5:1.

comparative example 5

Polypropylene particles were prepared in the same manner as in Example 1, except that the cross-sectional area ratio of the air supplied to the outer part and the extruded polypropylene supplied between the central part and the outer part supplied with air was 6.5:1.

Experimental example One

The particle size distribution of the polypropylene particles prepared according to Example 1 and Comparative Examples 1 to 5 was measured and shown in Table 1 below. Specifically, the particle size distribution was measured by the following two steps.

1) Sample pretreatment: Put about 0.003wt% of a powder sample in ethanol, set it to 30% of the maximum amplitude using a 50Watt/30kHz ultrasonic disperser, and disperse the powder sample in the ethanol by excitation for about 120 seconds.

2) Measurement of particle size distribution: Measure particle size distribution according to ISO 13320 standard.

particle size distribution D ₁₀ (μm) D ₅₀ (μm) D ₉₀ (μm) D Example 1 9.0 25.0 67.5 15.01 Comparative Example 1 425 650 870 4.13 Comparative Example 2 2.0 9.7 20.0 29.77 Comparative Example 3 6.0 42.0 71.0 51.86 Comparative Example 4 130 225 415 6.40 Comparative Example 5 3.2 10.3 38.5 24.33

According to Table 1, the particle diameter of the particles prepared according to Example 1 is not biased in a larger or smaller direction based on the average particle diameter, unlike the particle diameters of the particles prepared according to Comparative Examples 2, 3 and 5, D ₅₀ It can be seen that the ratio of /D ₁₀ and D ₉₀ /D _{50 remains similar.} In addition, the particle diameter of the particles prepared according to Example 1 is not too large unlike the particle diameters of the particles prepared according to Comparative Examples 1 and 4, and the ratio of D ₅₀ /D ₁₀ and D ₉₀ /D ₅₀ is at least a certain level ( It can be confirmed that it is maintained at about 2 to 3).

When the particles have the same particle size distribution as the particles prepared according to Example 1, it is possible to effectively compensate for the disadvantages of having only an average particle size when applied to a product.

Experimental example 2

The physical properties of the particles prepared according to Example 1 and Comparative Example 3 were measured and shown in Table 2 below.

Average particle size ^{1 )} (㎛) aspect ratio ^{2 )} Sphericity ^{3 )} Relaxed bulk density ^{4 )} (g/cm ³ ) Compressed Bulk Density ^{5 )} (g/cm ³ ) Compression degree ^{6 )} (%) Falling time ^{7 )} (s) Example 1 25 1.03±0.01 0.97±0.02 0.425 0.485 12.4 27 Comparative Example 3 42 0.64±0.02 0.76±0.01 0.40 0.425 5.9 33

1) Average particle diameter: D ₅₀ value was measured by the method of Experimental Example 1.

2), 3) Aspect ratio and sphericity: The formation of particles was analyzed by image processing using the same device - quantifying the degree of sphericization of individual particles after conversion to a binary image - derived.

4) Relaxed Bulk Density: Calculate the mass per unit volume by measuring the mass when the particles are quietly filled in a 100ml cylinder (average of 5 repeated measurements).

5) Compressed bulk density: The cylinder filled with particles according to 1) is arbitrarily compressed by tapping 10 times with a constant force, and then the mass is measured to calculate the mass per unit volume (average value measured repeatedly 5 times).

6) Compressibility (%)=(P-R)/P×100, P: particle compressed bulk density, R: particle relaxed bulk density.

7) Flow time: After filling a 100ml cylinder with particles, pour it into the KS M 3002 apparent specific gravity measuring device funnel, open the outlet, and measure the time it takes for the sample to come out completely (average value measured 5 times).

According to Table 2, the particles of Example 1 have a smaller diameter and uniform particle distribution compared to the particles of Comparative Example 3. In addition, the particles of Example 1 have a high degree of sphericity compared to the particles of Comparative Example 3, thereby securing a certain space during compression, and thus have a low compressed bulk density. The particles of Example 1 have a low compressive bulk density and a high degree of compression, so that when used in a bipolar plate, etc., it can have the effect of minimizing voids that may occur in the product.

Experimental example 3

DSC analysis of the particles prepared according to Example 1 and Comparative Example 3 is shown in Table 3 below. Specifically, using a differential scanning calorimeter (DSC, Perkin-Elmer, DSC8000), the temperature was raised from 0 °C to 200 °C under a temperature increase rate of 10 °C/min to obtain a DSC curve. Glass transition temperature (T _g ), melting point (T _m ), cold crystallization temperature (T _cc ), and the difference between endothermic value (ΔH1) and calorific value (ΔH2) were derived from each DSC curve.

T _g (℃) T _m (℃) T _cc (℃) ΔH1-ΔH2 (J/g) Example 1 10 151.4 96 65 Comparative Example 3 8.5 150.6 - -

It was confirmed that the polypropylene particles of Example 1 showed a cold crystallization temperature peak at 96° C., whereas the polypropylene particles of Comparative Example 3 did not exhibit such a cold crystallization temperature peak. Furthermore, in the case of Example 1, it was confirmed that the difference between the endothermic amount (ΔH1) and the calorific value (ΔH2) was about 65 J/g.

When the polypropylene particles have a cold crystallization temperature peak as in Example 1, when heat processing is performed using these particles, it may have an advantage that processing can be performed at a low temperature compared to the processing temperature of the polypropylene particles of Comparative Example 3.

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will become apparent from the appended claims.

d: perpendicular distance between two parallel tangent planes
A: area
10: nozzle
20: second air flow
30: polypropylene resin flow
40: first air flow

Claims (17)

A method for producing polypropylene particles, comprising:
The manufacturing method is
(1) extruding the polypropylene resin by supplying it to an extruder;
(2) supplying the extruded polypropylene resin and air to the nozzle, contacting the polypropylene resin with air to make the polypropylene resin particles, and then discharging the granulated polypropylene resin; and
(3) supplying the discharged polypropylene particles to a cooler to cool the polypropylene particles, and then obtaining cooled polypropylene particles,
Method for producing polypropylene particles, characterized in that the distal end of the nozzle in step (2) is maintained at a temperature calculated by the following formula 5:

[Formula 5]
End temperature = glass transition temperature (T _g ) + (decomposition temperature (T _d ) - glass transition temperature (T _g ))×B

In Equation 5, the glass transition temperature and the decomposition temperature are values for polypropylene, and B is 0.5 to 1.5.
The method according to claim 1,
The method for producing polypropylene particles, characterized in that the extruded polypropylene resin supplied to the nozzle in step (2) has a melt viscosity of 0.5 to 20 Pa·s.
The method according to claim 1,
In step (2), air is supplied to the center and the outer portion based on the cross section of the nozzle, and the extruded polypropylene resin is supplied between the center and the outer portion.
4. The method according to claim 3,
Polypropylene, characterized in that the cross-sectional area ratio of the air supplied to the outer part and the extruded polypropylene resin supplied between the central part and the outer part based on the cross section of the nozzle in step (2) is 4:1 to 6:1 A method for producing particles.
The method according to claim 1,
The method for producing polypropylene particles, characterized in that the inside of the nozzle in step (2) is maintained at 250 to 350 ℃.
As polypropylene particles prepared by the manufacturing method according to claim 1,
formed from a polypropylene resin into a continuous matrix phase,
Polypropylene particles having a particle diameter of 1 to 100㎛.
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that having _{an average particle diameter (D 50 ) of 20 to 50㎛.}
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that it has a particle _{diameter (D 10} ) of 10% of the cumulative volume of 5 to 15 μm.
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that it has a cumulative volume of 90% particle diameter (D ₉₀ ) of 50 to 80㎛.
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that the D value calculated by the following formula 1 is 10 to 20:

[Formula 1]

Here, D ₁₀ is a particle diameter of 10% of the cumulative volume, D ₅₀ is an average particle diameter, and D ₉₀ is a particle diameter of 90% of the cumulative volume.
7. The method of claim 6,
Polypropylene particles, characterized in that the impurity content of the polypropylene particles is 50ppm or less.
7. The method of claim 6,
The polypropylene particles are cold crystallized at a temperature between the _{glass transition temperature (T g} ) and the melting point (T _m ) in the DSC curve derived from the analysis of the temperature increase of 10 ° C / min by Differential Scanning Calorimetry (DSC) Polypropylene particles, characterized in that the peak of the temperature (T _{cc ) appears.}
7. The method of claim 6,
The polypropylene particles have an aspect ratio of 1.00 or more and less than 1.05 calculated by the following formula 2,
Polypropylene particles having a sphericity of 0.95 to 1.00 calculated by the following formula 3:

[Formula 2]
Aspect ratio = major axis/minor axis

[Formula 3]
Roundness=4×area/(π×long axis^2).
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that the degree of compression calculated by the following formula 4 is 10 to 20%:

[Formula 4]
Compression degree = (compressed bulk density - relaxed bulk density) / compressed bulk density x 100.
15. The method of claim 14,
The polypropylene particles are polypropylene particles, characterized in that having a compressed bulk density ^{of 0.45 to 0.6 g / cm 3 .}
7. The method of claim 6,
The polypropylene particles are polypropylene particles, characterized in that having a flow time of 20 to 30 seconds. delete

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